Responses of submersed vascular plant communities to environmental change performed for Eastern Energy and Land Use Team, National Water Resources Analysis Group, Office of Biological Services, Fish and Wildlife Service, U.S. Department of the Interior

[From the U.S. Government Printing Office, www.gpo.gov]

Biological Services Program

FWS/OBS-79/33
August 1980

T
T
@A

Responses of
Submersed Vascular
Plant Communities, to
Environmental Change

i rr od,-' Wildlife Service

QK930
.D38 Department of the Interior
R47
1980

The Biological Services Program was established within the U.S. Fish and
Wildlife Service to supply scientific information and methodologies on key
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For sale by the Superintendent of Documents. U.S. Government Printing Office
Washington, D.C. 20402

FWS/OBS-79/33
August 1980

RESPONSES OF SUBMERSED VASCULAR PLANT COMMUNITIES
TO ENVIRONMENTAL CHANGE

Graham 0. Davis and Mark M. Brinson
Department of Biology
East Carolina University
Greenville, North Carolina 27834

Contract No. 14-16-0009-78-032

Project Officer

Charles Segelquist
Eastern Energy and Land Use Team
Route 3, Box 44
Kearneysville, West Virginia 25430

property of CSC Librar,'Y

Performed for:
Eastern Energy and Land Use Team
National Water Resources Analysis Group
Office of Biological Services
Fish and Wildlife Service
U.S. DEPARTMENT OF THE INTERIOR

<=> US Department of Commerce
NOAA Coastal Services Center Library
2234 South Hobson Avenue
<C Charleston, SC 29405-2413

Library of Congress Catalog Card Number: 80-607178

wc2d"I

PREFACE

Many construction activities in or near streams and lakes cause changes
in the aquatic environment that affect submersed vascular aquatic plants.
This report was prepared to give biologists, engineers, and planners an over-
view of how submersed plants respond to changing environmental conditions
including light transmission, fluctuating water levels, currents and waves,
and other physical and biotic factors.

A companion document, FWS/OBS-80/42, is a summary of this technical
report. Inquiries concerning the availability of either report should be
directed to:

Information Transfer Specialist
U. S. Fish and Wildlife Service
Eastern Energy and Land Use Team
Route 3, Box 44
Kearneysville, West Virginia 25430

EXECUTIVE SUMMARY

Submersed vascular plants are native to many aquatic ecosystems where
they influence a number of ecosystem processes and provide food and shelter
for fish and wildlife. This report examines factors that 3ffect the light
environment of submersed macrophytes and eval 'uates the responses of submersed
plant communities to changing light conditions. Other requirements and stres-
ses important to submersed macrophyte communities are discussed also.

The amount of light available for photosynthesis and growth of submersed
plants depends on the combination of the turbidity of the water and the depth
at which they grow. Turbidity due to suspended sediments may vary greatly
depending on the energy of currents and waves that keep them in suspension or
on human activities that may c-eate new sources of particulate matter. Depo-
sition of sediments directly on @i.eaif surfaces may reduce light available to
plants. Increases in plankton density, matting filamentous algae, and dense
epiphytic growth, all common consequences of eutrophication, can reduce the
amount of light available to submersed macrophytes. Other factors affecting
the survival and growth of aquatic macrophytes are grazing and feeding acti-
vities of fish and waterfowl, fluctuating water levels, hydrostatic pressure5
and sediment type. All of these factors are reviewed briefly and examples
given from pertinent studies.

Data were assembled on depth distribution records of submersed angio-
sperms and the Secchi transparencies of water for mostly North American lakes.
These were lakes in which the maximum depth of submersed macrophyte establish-
ment was limited by light availability rather than shallow depth. Although
the data base lacks rigorous precision, several patterns reveal that species
respond quite differently to reduced light levels with increasing depth. Lab-
oratory and field studies generally show that most shade tolerant species have
a rapid photosynthetic response to increasing light in the low range of inten-
sities. In clear shallow waters, the competitive advantage is shifted toward
species in which photosynthesis is saturated only by extremely high light in-
tensities.

Further analysis of depth distribution patterns of species and water
transparency allowed identification of turbidity tolerant and non-tolerant
species. This was expressed as a turbidity tolerance index, which in turbid
waters (Secchi transparency < 2.5 m), is the ratio of the depth maxima of
species to the Secchi transp-arency depth. The index ranked ten species
according to their resistance to adverse effects of turbid systems.

Submersed macrophyte communities may respond differently to short term
and long term perturbations. Short term changes may vary from a few weeks
to a few years and usually have no lasting detrimental effects on the aquatic
macrophytes. Long term changes associated with factors such as eutrophi-
cation result in elimination of species sensitive to light reduction and often
in the appearance of exotic species.

Based on long term studies of northern lakes, a survival index for sub-
mersed species was developed. This index and the turbidity tolerance index
were used, along with other informati6n,@, to identify five groups of species
that have varying degrees of resistance to ecosystem alteration.

Finally the possible effects of human activities on'alterations in
aquatic ecosystems and an array of impacts on submersed plant communities are
considered. Since a wide range of ecosystem changes can be associated with a
single type of perturbation and since responses of submersed macrophytes to
system changes cannot be predicted with confidence, these impact evaluations
are tentative.

TABLE OF CONTENTS

Page

PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
EXECUTIVE SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
LIST OF TABLES . . . . ... . .. . . . . . . . . . . . . . . . . . . . . ix
ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . .

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PHYSICAL, CHEMICAL, AND BIOLOGICAL FACTORS AFFECTING SUBMERSED
PLANT GROWTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Fluctuating Water Levels . . . . . . . . . . . . . . . . . . . . . . 3
Currents and Waves . . * I' * * ' * ' * * ' * . . . . . . . . 4
Suspended Sediments and Their Effects on Submer@ed* P*Iants . . . . . . 5
Growing Season and Dormancy . . . . . . . . . . . . . . . . . . . . . 9
Rutri 'ent Availability and Uptake . . . . . . . . . . . . . . . . . . 9
Biological Factors . . . . . . . . . . . . . . . . . . . . . . . . . 10
Hydrostatic Pressure . . . . . . . . . . . . . . . . . . . . . . . . 12
RESPONSES OF SUBMERSED PLANTS TO LIGHT AND TURBIDITY . . . . . . . . . 14
.Light Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Relationship of Actual Light Transmission and Secchi Disc
Transparency Estimates to the Euphotic Zone . . . . . . . . . . . . 15
-Depth Zonation and Turbidity Tolerance of Submersed Species 17
Relationship between Maximum Depth Distribution and Secchi
Transparency . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Turbidity Tolerance Index . . . . . . . . . . . . . . . . . . . . . 29
,,Photosynthesis and Growth in Response to Light . . . . . . . . . . . 30
Laboratory Experiments . . . . . . . . . . . . . . . . . . . . . . 31
Field Studies . . . . . . . . . . . . . . . . . . . . . . * . . . 34
-RESPONSES OF SUBMERSED PLANTS TO ECOSYSTEM CHANGE . . . . . . . . . . . 35
Community Responses to the Duration of Perturbations . . . . . . . . 35
Short Term Perturbations . . . . . . . . . . . . . . . . . . . . . 35
Long Term Perturbations . . . . . . . . . . . . . . . . . . . . . . 37
Categories of Species Based on Resistance to Ecosystem Alteration . . 42
Rosulate Species . . . . . . . . . . . . . . . . . . . . . . I. . . 43
Northern Potamogetons . . . . . . . . . . . . . . . . . . . . . . 43
Tolerant Species Normally -with Low Biomass in Disturbed Systems 44
Tolerant Species Nonnally Dominant or Subdominant in Disturbed
Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Adventive Species . . . . . . . . . . . . . . . . . . . . . . . . 45

EFFECTS OF ENVIRONMENTAL ALTERATIONS ON SUBMERSED AQUATIC PLANTS . . . 46

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
APPENDICES
A. Regions of North America that Correspond to the
Distribution Codes of Appendix B : * * ' ' * * ' I ' * ' * ' * * 62
B. Species, Family, Common Name, and Distribution
of North American Aquatic Macrophytes Mentioned
in Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

vii

LIST OF FIGURES

Figure Page

1 Comparison of settling velocities described by Stokes law
and.the impact law . . . . . . . . . . . . . . . . . . . . . . . 7

2 The relationship between current velocity and particle size
which determines whether particles will be eroded,
transported, or deposited . . . . . . . . . . . . . . . . . . . 7

3 Schematic diagram of factors that contribute towards a
tendency for nutrient absorption by roots or shoots . . . . . . 11

4 Hypothetical changes in relative primary productivity of submersed,
emergent, epiphytic, and planktonic communities with
increasing nutrient enrichment . . . . . . . . . . . . . . . . . 12

5 Depth maxima for aquatic vascular plants and Nitella spp.
as related to the 1 percent light transmission depth for
some British lakes . . . . . . . . . . . . . . . . . . . . . . . 13

6 Absorption spectra of water from Lake George, Wisconsin,
compared with pure water . . . . . . . . . . . . . . . . . . . . 16
7 Depth distributions for submersed macrophytes . . . . . . . . . 18

8 Maximum depth distribution of selected species from Figure
7 plotted against Secchi disc transparency of the waters
where the distributions were observed . . . . . . . . . . . . . 27

9 Conceptual model illustrating the effects of environmental
forces on submersed aquatic macrophyte communities . . . . . . . 47

viii

LIST OF TABLES

Table 'Page

1 Turbidity tolerance index for selected species of Figure 7
expressed as the ratio of depth maxima to Secchi depth where
Secchi depth is 2.5 m or less . . . . . . . . . . . . . . . . . . 30

2 Changes in submersed macrophyte populations in Reelfoot Lake,
Tennessee . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

3 Long term changes in macrophyte populations in lakes and bays
in northern United States . . . . . . . . . . . . . . . . . . . . 38

4 Evaluation of the effects of various types of environmental
alteration on submersed plant communities . . . . . . . . . . . . 49

328-607 0 - 80 - 2

ACKNOWLEDGMENTS

The following persons contributed to the preparation of this manuscript:
Randy Creech prepared the illustrations, Carol Lunney photographically repro-
duced the figures, Sue Williams and Margaret Schiller typed preliminary drafts,
and Cindy Stack of the Institute for Coastal and Marine Resources typed the
final copy.

The cover diagrams were drawn by Ray Moore. An attempt was made to
illustrate the effects of phytoplankton turbidity on submersed plant community
structure in two otherwise similar areas of eutrophic Little John Lake and
oligotrophic Silver Lake in Wisconsin (after Wilson, 1935).

INTRODUCTION

There are many examples of waters that at one time supported luxuriant
growths of macrophytes but are now largely devoid of these plants. The causes
for the reduced abundance vary, but most aye associated with increases in
water turbidity. However, the absence of submersed macrophytes does not al-
ways imply that adequate light is lacking. Submersed macrophytes generally
colonize high energy and rather unstable zones of lakes, reservoirs, rivers,
and estuaries and are subjected to a number of stresses that may exclude
them. Some of these stresses are discussed to put in proper perspective the
importance of light availability. However, the main subject area of this re-
view is the effects that reduced light availability and increased turbidity
have on submersed plants in inland waters.

The probable effects that increased water turbidity might have on sub-
mersed angiosperms; will be evaluated. A number of human activities such as
dredging, waste disposal, boat traffic, road construction, land use, etc. may
add suspended solids to lakes and rivers at levels above background. How-
ever, background or "natural" turbidity can vary greatly in rivers- depending
on current velocity following heavy rains or snow melt and in lakes depending
on mixing by wind, bank erosion, and inflows from turbid rivers and streams.
The changes in turbidity and thus the light environment of submersed macro-
phytes corresponding with these events need to be evaluated relative to other
factors that limit macrophyte distribution. The importance of these "resi-
duals" is often veyy difficult to quantify.

The importance of submersed macrophytes in aquatic ecosystems is widely
recognized by biologists, but public perception of their value focuses pri-
marily on their utilization by migratory waterfowl as food. Many aquatic
vertebrates and invertebrates utilize aquatic macrophytes for food and cover.
In fact, the metabolism of many flowing and limnetic ecosystems is dominated
by photosynthesis and respiration of aquatic macrophytes which are at the
base of the detritus -food web. Exchange of nutrients among the compartments
of the sediment-plant-water system and calcium carbonate precipitation in
plant beds can have striking effects on the water chemistry of aquatic eco-
systems.

Most of the data and examples reviewed are from North America. Examples
from north-central and northeastern United States and contiguous Canadian
areas dominate the review. This is due partly to the abundance of lakes in
those districts and partly to the large number of limnological studies con-
ducted there. Data are presented for areas other than North America, but a

serious review of the world literature was not made. Some of the most rele-
vant studies on turbidity-macrophyte relationships have been conducted in
shallow estuaries rather than lakes.

While the studies cited date back to the early decades of this century,,
many of the relevant data are of recent origin. Problems associated with
overabundance of certain macrophytes (e.g., Myriophyllum spicatum, Hydrilla
verticillata)have provided the impetus for some of these studies. A few
investigators in the field have recently focused much of their effort toward
resolving the relationship between distribution of aquatic macrophytes and
water transparency. We hope that this review will provide additional in-
sight, identify some critical gaps in our knowledge, and suggest important
areas of research.

North American species mentioned in this report are listed alphabeti-
cally in the table in the Appendices with additional information on the
family, common name, and distribution. Distribution is given according to
the regions developed in Shelter and Skog (1978).

PHYSICAL, CHEMICAL, AND BIOLOGICAL FACTORS
AFFECTING SUBMERSED PLANT GROWTH

Among the submersed vascular plants, there is great variation in life
cycle, morphology, physiology, and reproduction which somewhat reflects the
diversity of their terrestrial ancestors (Arber, 1920). This diversity is
illustrated by the wide range of physical and chemical conditions to which
various species are adapted. The species composition and abundance in a
submersed plant community will depend upon the totality of these factors to
which an area is subjected. The purpose of this section is to provide an
overview of the importance of factors other than light which may limit the
abundance, or even the occurrence, of aquatic vascular plants. While the
discussion focuses on the submersed life forms, many of the factors mentioned
also relate to emergent and floating leaved species.

FLUCTUATING 14ATER LEVELS

Fluctuating water levels are common features in many shallow aquatic
ecosystems. The distribution of wetland plants in response to a drop and
subsequent rise in water level in a prairie pothole marsh is illustrated in
a study by van der Valk and Davis (1976). The submerged zone was completely
exposed during a summer drought which almost eliminated Ceratophyllum demer-
sum when reflooding occurred the following year. Another submersed species,
Potamogeton sp. aff. pusillus, was little affected but moved 4 or 5 m closer
to shore after reflooTi@ngThere was a tendency during the drought for emer-
gent species to germinate and invade the submersed zone such that biomass and
species richness of the zone increased after reflooding. This illustrates
that although some submersed species are severely affected by extreme water
level fluctuation (e.g., Ceratophyllum, which is not rooted), others adapt by
a shift in zonation. However, considering the community as a whole, irres-
pective of life form, there was little overall change in community production
and diversity due to water level fluctuation.

Where drawdown can be artificially controlled it is commonly used in con-
trol procedures for aquatic macrophytes. Peltier and Welch (1970) suggested
that drawdown, along with low rainfall, res'ulted in greatly increased cove-
rage by Najas spp. in an Alabama reservoir. Similarly, Jackson and Starrett
(1959) n5-t-ed that Potamogeton pectinatus grew best when water levels remained
low in the shallow, floodplain of Lake Chlataqua, Illi'nois. In.the Chippewa
Flowage, Wisconsin, which has received repeated winter drawdowns for 50

years, Nichols (1975) identified five submersed species that either recover-
ed, or increased in coverage after repeated water fluctuation. On the other
h-and, if drawdowns are not properly conducted, problems resulting from exces-
sive macrophyte growth may result especially in areas with long growing seasons,
as predicted by Hestand et al. (.1971) for Lake Ocklawaha, F.lorida.

Where drawdowns persist for several years or are frequent during a sin-
gle growing season, as in some reservoirs, submersed vascular plants will
not survive. Reservoirs typically have highly turbid waters and few shallow
areas which further reduces chances for establishment of submersed vegetation.
Controlled drawdowns have been used in the TVA reservoir system for management
of Mriophyllum spicatum, a nuisance plant (Leon Bates, personal communica-
tion).

Submersed species may be limited in their length of growth by shallow
water, but it is uncertain whether this would affect rates of production.
For example, Lind and Cottam (1969) found that Myriophyllum exalbescens, in
Lake Mendota, Wisconsin, wasabout half as dense at Z.0 to Z.5 m depth as at
1 m., but the average weight per plant wasabout twice as great in the deeper
water. Whether Myriophyll6m would respond to increasing water depths during
a single growing season by elongation and reduction in density is uncertain.
Alternatively, reduced depths may result in greater fragmentation and uproot-
ing from turbulence as more of the plant floats near the surface.

Martin and Uhler (1939) stated that at least a few inches of water must
be retained for truly aquatic plants to remain established. Of the species
that they suggested for propogation in periodically exposed wetlands, none
are submersed aquatics. None of the seeds of aquatic plants mentioned by
Sculthorpe (1967) that require drying before germination were from submersed
species.

CURRENTS AND WAVES

In medium to large lakes the eroding forces of waves may prevent the
establishment or result in the fragmentation of submersed aquatic plants in
the shallowest zone. Their absence is probably more commonly due to the
abrasive action of waves rather than instability of the substrates. In ma-
ture basins, the amount of erodable inorganic material in this high energy
zone is usually small, having long since been removed (Hutchinson, 1975).
There is a tendency for submersed vascular plants that grow in these situa-
tions to be small and their occurrence probably depends on resistance to
fragmentation.

Fragmentation due to wave action was determined by Jupp and Spence
(1977b) for Potamogeton filiformis in Loch Leven, Scotland. By comparing
peak biomass--oT plots protected from wave action and waterfowl grazi
(243 g/m2) with plots protected only from waterfowl grazing (125 g/m2?, a
loss of 118 g/m2 was attributable to wave action. Since plant densities did
not differ significantly between treatments, all of this loss was due to wave
pruning of shoots. It is uncertain, however, to what extent fragmentation

calculated by this procedure actually occurred and to what degree wave action
may have merely inhibited potential growth.

In running waters only rooted growth forms become established and thus
they are restricted to areas of sediment deposition, with the notable excep-
tion of members of the mostly tropical Podostemaceae which are attached to
rocks in fast flowing water (Arber, 1920). Hynes (1970a) stated that no
rooted plants show any special adaptation to running water, and the species
that occur in streams and rivers have tough, flexible stems or leaves, a
creeping growth habit, frequent adventitious roots, and strictly vegetative
reproduction.

According to Westlake (personal communication) the relationship between
plant distribution, depth, light and compensation point are complex, parti-
cularly in the relatively shallow depths colonized in fairly turbid river
waters. In these conditions many plants are capable of growing from the
bottom and creating a leaf array containing most of their biomass near the
illuminated surface. Such stands are ultimately limited in biomass partly
by turbidity, but mainly by self-shading. Their depth limits, as defined by
the deepest water in which they are rooted, are probably fixed by their
capacity to grow from reserves, out of the dark bottom waters and into the
light before other plants shade them. Size of storage organs is therefore
important. These principles apply also to still water conditions.

In many flowing water situations, the occurrence of spates or freshlets
following heavy rains severely limits the abundance of submersed species due
to strong currents. For example, Bilby (1977) quantified the effects of
macrophyte distribution in a stream pool before and after a spate resulting
from a large rainstorm in New York. The two dominant species, Elodea canadensis
and Potamogeton crispus underwent a pattern of displacement toward lower
current speeds following the spate. Most of the reduction in macrophyte
cover was where current speeds were highest.

Where current movement is slow as in irrigation canals, submersed plants
may become exceedingly abundant, as in south Florida (Blackburn et al., 1968).
Likewise, the steady flow and transparent waters of Florida spring runs often
support high biomass of submersed species, whose year-round productivity is
limited by light (Odum, 1956). In these latter two examples water current
serves as an important auxiliary energy source by increasing nutrient availa-
bility and exporting waste products. Within a range of slow currents for
which flow is laminar (0.02 - 0.5 cm/sec), Westlake (1967) demonstrated that
photosynthesis of submersed plants in the laboratory increased with increasing
current velocity. However, the high velocities that occur during flooding
of most streams and rivers would represent stressful and often quite damaging
conditiens for macrophytes (Haslam, 1978).

SUSPENDED SEDIMENTS AND THEIR EFFECTS ON SUBMERSED PLANTS

Suspended sediments have effects on submersed macrophytes in addition to
those directly related to a reduction in available light. For example, the

composition of bottom materials in which plants are rooted depends on the
balance between the rate of sediment supply and the rate at which sediments
are carried away by currents. Current velocity, particle density, and par-
ticle size are mainly responsible for this balance. These variables will be
treated briefly prior to discussing the relationship between macrODhytes and
sediment types.

The settling velocity of particles is classically described by Stokes
law which is formalized as

v gr2
9 n

where v is the velocity of the particle (cm/sec), r is its radius (cm), g is
acceleration of gravity, n is the viscosity of the f Iuid (poises), and dl and
d2 are the densities of the particle and fluid (g/cm ), respectively. If all
other conditions are constant, then the settling velocity is directly propor-
tional to the square of the particle radius, and the equation simplifies to
v = Cjr2, where Cl represents the various constants. This law does not hold
for large particles because above about 0.1 mm in diameter the settling velo-
cities are proportional to the square root of the radius according to the
impact law. The simplified form of the impact law is v = C2\l-r1 where various
constants are included in C2. Viscous forces operable in Stokes law become
negligible. Thus the settling velocity will follow the experimental curve
shown in Figure 1.

In streams and lakes which have turbulent flow, particles are kept in
suspension by kinetic energy that overcomes the gravitational and cohesive
forces. The relationship between velocity, particle size and the fate of the
particles is shown by the HjDstrom scheme in Figure 2. This graph incorpor-
ates the critical erosion velocity in addition to the settling velocity which
brackets the regions in which particles will be eroded, transported, or de-
posited. This conceptual model is based on a number of assumptions, few of
which have much applicability to field situations where the flow velocity is
stochastic and particles are seldom spherical, of homogeneous size, or of
similar density.

Nevertheless, Figure 2 correctly conveys the concept of segregation of
particle size with respect to flow velocity. In considering dredging acti-
vities, fine particles with their slow settling velocities will remain in
suspension longer and will tend to be transported greater distances than
larger particles. Particles from sediments largely composed of organic mat-
ter have lower densities and will have an even greater tendency to remain in
suspension. It becomes obvious that the duration of shading and the extinc-
tion coefficient of the water will depend greatly on the composition of the
material brought into suspension, whether by natural (floods) or by human
activity (dredging or other disturbances).

Submersed macrophytes and other structural features may act as sediment
traps because of their effectiveness in reducing flow velocity. Growth of

20 1
Stokes Low
Z

E 15

0 Impact ow
10-

Experimental
Curve

0--
0 0.5 1.0 1.5
Diameter (mm)

Fi gure 1. Comparison of settling velocities described by Stoke's law and the
impact law. The experimental curve is also shown. From STRATIGRAPHY AND
SEDIMENTATION, Second Edition, by W.C. Krumbein and L.L. Sloss. W.H. Freeman
and Company. Copyright 1963.

1000

Erosion

100

CD
Transportation
> Deposition
1.0

0.1-
.001 .01 0.1 1.0 10 100
Diameter (mm)

Figure 2. The relationship between current velocity and particle size which
determines whether particles will be eroded, transported, or deposited (after
Hju'ilstrom, 1935).
L

328-607 0 - 80 - 3

rhizomes and roots in the sediment further stabilizes the substratum. The res -
triction of vascular plant beds to the relatively low energy sectors of
streams contributes to the extremely patchy distribution that is often ob-
served.

In highly organic bottoms, such as in open water areas of peat bogs, the
soft ooze severely restricts the establishment of aquatic macrophytes. Plant
beds are often restricted to species that produce dense and persistent net-
works of rhizomes, as in the case of members of the Nymphaeceae. Although
this family is characterized by floating leaves, some members have submersed
11water leaves" which may persist year round in the southeastern United States
(Brinson and Davis, 1976). The importance of these leaves to the carbon
balance of the plant has never been established.

Not only must sediments be stable for successful colonization of macro-
phytes, but the particle size distribution' also influences the species that
occur. Spence (1964) showed that in Scottish lochs submersed broad leaf forms
predominated in water greater than 150 cm deep only when the sediments were
composed of fine muds. However, other factors such as light and turbulence
all change with depth, so it is not possible to single out substrate type as
the most important variable except perhaps by controlled experiments (Pond,
1903; Brown, 1913; Bourn, 1932; Misra, 1938).

Pearsall's (1920) work on the English lakes during the early part of this
century singled out the physicochemical. nature of the sediment as the main
factor in determining composition of the vegetation, although the original
interpretation of these results is somewhat questionable (Spence, 1967).
Isoetes was restricted to stony areas with thin silt. This genus apparently
cannot colonize areas of sediment deposition because it cannot alter its root
level. Potamo2@@ perfoliatus grows in areas with a high clay fraction,
which ma@ -also be related to nutrient availability, rather than texture alone.
However, life forms with a stoloniferous habit are probably able to adjust to
changes in sediment depth except in the most extreme cases of accumulation.

Another aspect of siltation is the accumulation of material on leaf sur-
faces which reduces light transmission to photosynthetic surfaces and possi-
bly alters gas and nutrient exchange. Sculthorpe (1967) suggested that the
linear leaves of Potamogeton pectinatus remain free of settling particles and
thus the species may colonize areas unsuited for submersed plants with leaf
forms more amenable to silt accumulation. Schiemer and Prosser (1976) con-
finned that the sediment coating on Myriophyllum spicatum, which has finely
,divided, feathery leaves, is markedly greater than for F_ pectinatus in
sheltered bays of Neusiedlersee, Austria. In addition, they suggested that
silt deposition is enhanced by the presence of epiphytic algae on heavily
infested macrophytes. Increased plant weight due to silt deposition was also
noted as having an inhibitory effect on macrophyte growth. These factors in
addition to wave action appear to be largely responsible for the distribution
of M. spicatum in Neusiedlersee.

GROWING SEASON AND DORMANCY

Submersed macrophytes may resist the effects of freezing by colonizing
depths below the zone of surface ice formation as compared with emergent or
floating leaved species that are exposed to freezing temperatures. In spite
of this, many temperate submersed species undergo a period of dormancy during
the winter and a few species are anatomically and physiologically adapted to
overwintering. However, a number of submersed perennials merely subsist with
reduced or negligible growth rates and reduced biomass until more favorable
light and temperature conditions at the onset of the growing season. Except
in cases of a limited number of annuals where viable seed development and
favorable conditions for germination must occur, most submersed species are
perennial and overwinter by means of vegetative structures.

Weber and Nooden (1976a, b) described the role of turions in the over-
wintering of Myriophyllum verticillatum. In this species turions are special-
ized compact buds that develop from nodes late in the growing season as a
response to photoperiod and possibly temperature. These reproductive struc-
tures sink to the bottom after detachment from the parent plant. Dormancy is
broken by cold temperatures (0 40 C) which compares well with observed
turion germination before ice breakup.

Apart from highly modified organs such as turions, many other less spe-
cialized organs appear equally capable of overwintering. These include dor-
mant apices and offsets, root tubers, stolons, and rhizomes. Dormant apices
and offsets as well as turions can be important in plant dispersal. These
structures in submersed aquatic plants appear to substitute for seed disper-
sal more commonly found in emergent or floating leaved species.

In addition to lower water temperatures and reduced day length during
the nongrowing season, the presence of an ice and snow cover in northern lati-
tudes poses severe restrictions on light penetration. Species that may have
only reduced biomass and growth during the winter season if open water per-
sists will be much reduced in more northern waters that become completely iced
in. This may result in regional differences in standing crops of submersed
plants at the beginning of the growing season.

The presence of ice may also result in physical disruption of macrophyte
communities' Martin and Uhler (1939) described the scouring action of ice
masses during spring breakup in flowing waters and shallow lentic habitats
that may cause severe damage to beds of submersed plants.

NUTRIENT AVAILABILITY AND UPTAKE

There has been considerable controversy concerning the importance of
roots in nutrient uptake from sediments. It is clear from a number of studies
that roots do accumulate nutrients from the sediments and these may be trans-
located to the shoots. However, in many aquatic plants, significant ion
absorption occurs by leaves and there appears to be a great diversity in
the relative importance of roots and shoots in mineral nutrition.

Figure 3 illustrates the spectrum of all possible cases for aquatic
macrophytes in which the x-axis represents a gradient in life form, root-
shoot ratio, or anatomical complexity (Denny, 1972). Emergent species will
obtain most of their mineral nutrition from the sediments, while those that
have floating leaves are intermediate between emergent and submersed plants.

The actual amount of nutrient absorption in field situations may be re-
lated also to the relative supply in the water and the sediments. For exam-
ple, Bole and Allan (1978) demonstrated that Myriophyllum spicatum and
Hydrilla verticillata utilized phosphorus from the sedimenT @until concentra-
tions in the water reach a threshold value which differs for the two species.
Above these water concentrations uptake from the water column increases.
Nutrient availability is not based solely on concentration since flowing
waters of low concentration may actually be a better source of nutrients than
higher concentrations in quiescent waters. Dense gyniths of submersed commu-
nities often require nitrogen and phosphorus in excess of the amount present
in the water at any one time. Sediment texture and cation exchange capacity
may also be important in the nutrient supply to roots. Since it has been
demonstrated that some aquatic macrophytes translocate phosphorus (Twilley
et al., 1977) and nitrogen (Nichols and Keeney, 1976) both from roots to
shoots and from shoots to roots, it is unlikely that the sediments or the
water alone are the singular source of nutrients.

Although nitrogen and phosphorus are generally believed to be the most
important limiting nutrients in fresh waters, there are no clear cut cases
where submersed macrophytes are excluded by the paucity of either. Rather it
would seem that the rate of productivity may be limited by the supply of these
nutrients. However, in the case of soft and hard waters (low and high CaCOI
concentration, respectively) there appears to be an important dichot omy in
species distribution. This has been reviewed extensively by Hutchinson (1975)
who also noted that pH may play an important role in species distribution in
soft waters.

BIOLOGICAL FACTORS

The absence of submersed aquatic plants in fertile lakes and ponds has
often been attributed to shading by dense populations of phytoplankton. Jupp
and Spence (1977a) reported an inverse correlation between biomass of P6tamo-
geton filiformis, and open water chlorophyll a concentrations at certai6_tF`mes
during a three-year study of Loch Leven, Scotland. Scums of blue-green algae
accumulating near the shore during Anabaena fl'os-aguae blooms intensified
shading in macrophyte beds. Jupp and Spence suggested that these algal blooms,
apparently enhanced by high levels of phosphorus from cultural eutrophication,
retard macrophyte growth by shading and possibly by producing elevated pH con-
ditions.

100%,

Shoot

,Root

Z 01 life form -
Emergent root/shoot ratio 0 Submersed
High io Low
Complex anatomy o Simple

Figure 3. Schematic diagram of factors that contribute towards a tendency
for nutrient absorption by roots or shoots. Axes are arbitrary. Modified
from Denny (1972).

However, Phillips et al. (1978) set forth a convincing argument for the
role of epiphytes and filamentous algae in suppressing submersed macrophyte
growth due to shading. They suggest that dense phytoplankton develops sub-
sequently to the macrophyte decline rather than being its cause. Although
the effects of shading will be treated more fully in later sections, the
scheme of Wetzel and Hough (1973) in the succession of littoral communities
with increasing fertility (Figure 4) is of interest here. According to this,
nutrients are initially limiting to macrophyte productivity and growth is
proportional to nutrient availability. At high concentrations of nutrients,
submersed macrophytes will be excluded due to shading by phytoplankton, epi-
hytes, and filamentous algae. The model probably applies somewhat to flowing
water situations although phytoplankton is expected to be less important and
physical factors more important than in lakes.

The importance of grazing on submersed plants has never received a com.-
prehensive review. Repeated mowings during a single growing season may in
some ways simulate high grazing intensities (Davis, in preparation). However,
when one considers the total effect of consumer activity, the disruptive
activity of feeding, whether on macrophytes or other food sources, may be
quite substantial. For example, the feeding attivities of carp in Lake
Mattamuskeet, North Carolina, increased turbidity so greatly that submersed
waterfowl food plants did not become established until the fish were removed
(Cahoon, 1953).

Shading of Submersed Macrophytes
Nutrient by Epiphytes and
>.. Limited Phytoplankton
Filament us Algae Dominance

0
L_
CL Emergent
*,Macrophytes
E
0- .,.--Phytoplankton
(D Epiphytes and
>
Filamentous
7@ Algae
ir
Submersed
Macrophytes
Ofigotrophic meso-to Eutrophic Hypereutrop
Increasing Fertility

Figure 4. Hypothetical changes in relative primary productivity of submersed,
emergent, epiphytic, and planktonic communities withlincreasing nutrient en-
richment (after Hough and Wetzel, 1973, with modifications.according to
Phillins et al., 1978).

Many migratory waterfowl species are primary consumers and may have tem-
porarily devastating effects on wetlands, oarticularly marshes that receive
overgrazing by geese (Lynch, et al. , 1947) . Muskrat "eat outs" have also been
observed, but again it is the conspicuous emergent species studied that are
reported to have heavy damage. Anderson and Low (1976) studied grazing rates
on Potamogeton pectinatus by ducks in the open water region of a Mantioba
prairie marsh. By comparing biomass in enclosures and in areas not excluding
birds, they estimated that 40 percent of the peak standing crop of foliage and
18 percent of the peak standing crop of tubers were removed. Some of this re-
duced biomass was not consumed but was lost by activities associated with
feeding. By comparison, Jupp and Spence (1977b) calculated that 30 percent of
th.e peak standing crop of P. filiformis was removed by waterfowl grazing in
Loch Leven. In this case, only shoot biomass showed significant grazing los-
ses, perhaps due to difficulty of uprooting tubers in the fine clay substrate.

HYDROSTATIC PRESSURE

In exceptionally clear lakes of great depth, it would appear that there
is adequate light for macrophyte growth at depths beyond the observed plant

12-

10- ---&-Nitella spp.
--o-Nascular Plants

(D
8-

7-
0
h_
(D 6- __0__0 - - - - - - -0

5- 0
-2 /0
4- 0-
E 3- 0

0 5 10 15 20 25 30
I % Light Transmission Depth (m)

Figure 5. Depth maxima for aquatic vascular plants and Nitella spp. as re-
lated to the 1 percent light transmission depth for some-9-ri-ti-s-h lakes (data
from Spence, 1976).

distribution. At lower altitudes one atmosphere of excess pressure is equal
to the pressure in about 10 m of water. Hence, depth maxima of species.tole-
rant to low light levels suggest that hydrostatic pressure is a factor in
depth limitation of plant-presence. As reviewed by Hutchinson (1975), charo-
phytes, mosses, and the lower vascular plants tend to grow at greater depths
than submersed angiosperms. R. G. Wetzel (quoted in Hutchinson, 1975) found
that 0.5 atmosphere of excess pressure reduced photosynthesis in Najas flexi-
lis by 50 percent. Spence (1976) compared depth maxima of vascular plants
T-i"ncluding lower vascular plants ) with various nonvascular plants in 23
freshwater lakes. Depth maxima summarized by Spence for submersed vascular
plants and the non-vascular charophyte, Nitella spp., in some British lakes
are plotted against the depth of 1 percent light transmission for each lake
(Figure 5). Only the data collected by divers (as compared with from a boat)
are used. The depth maxima for the vascular plants plateau at around 5.5 to
6 m regardless of water transparency. This suggests that factors other than
available light limited the depth maxima for vascular plants and a case for
hydrostatic pressure effects is strongly suggested. Depth maxima for Nitella
spp., on the other hand, increased throughout the range with increasing light
penetration, suggesting light limitation as being of primary importance.

Adaptations which result in resistance to hydrostatic pressure are un-
clear. In laboratory experiments physiological and/or anatomical and growth
changes in submersed angiosperms become apparent when hydrostatic pressures
of 0.5 to 1 atmosphere excess are applied (Gessner, 1952; Ferling, 1957).
0

One response is a decrease in the size of intercellular air spaces. Of
course, environmentalfactors such as sediment characteristics, nutrient
distribution, dissolved oxygen, temperature, and the quality of light reach-
ing the bottom may play a part in restricting depth penetration by plants.

RESPONSES OF SUBMERSED PLANTS TO LIGHT AND TURBIDITY

LIGHT ATTENUATIOii

The depth to which submersed aquatic vascular plants are distributed
depends on the availability of light, if no other factors such as hydrostatic
pressure, nutrient supply, substrate composition, an-d turbulence limit growth.
Three factors affect light attenuation: absorption by water itsel.f, absorp-
tion by suspended particles, and absorption by dissolved substances.

Monochromatic light passing through chemically pure water is absorbed
exponentially and thus decreases at a constant rate with increasing incre-
ments of depth. This relationship can be expressed as the extinction coeffi-
cient, ri, which decreases from the red to the blue end of the visible spec-
trum. The extinction coefficient, q, is a function of the light intensity at
the surface (10) and the intensity at depth z in meters

in I0 - in Iz

T1=
z

The extinction coefficients of natural waters deviate greatly from those of
pure water due to the presence of dissolved and particulate substances which
absorb and scatter light. Th espectral quality of light is particularly af-
fected by dissolved substances, since light scattering by particulate matter
is relatively nonspecific in optical effects.

The extinction coefficient of natural waters is separated into three
components such that

nt = qw + np + nc

where nt is the total extinction coefficient, and the remaining terms are
due to water, suspended particulates, and dissolved color, respectively.
Thus the expression can be rearranged so that the intensity of light, Iz, at
a depth of one meter below I0 is

-nw _11p _11c
I z i0e x e x e

Figure 6, adapted from the data of James and Birge (1938) for Lake
George in Wisconsin, clearly shows the effects of absorption by each of these
components. (The data are graphed as percenti'le absorption, expressed by the
formula, 100 (1 - jz)I0, where I is at 1 m depth.) Short wavelengths (vio@
let and blue) aroe most strongly a6sorbed by the dissolved material which most-
ly consists of dissolved organic compounds, absorption of long wavelengths
(red and infrared) is due mostly to water, while the particulate matter is
quite nonspecific in its absorption properties, at least when in low concen-
tration. However, in using sediment concentrations between 50 and 5,000 ppm,
Otto and Enger (1960) found that the red wavelengths penetrated somewhat fur-
ther than blue. The spectral discrimination was greater for a commercial
sodium base montmorillonite type bentonite than for a sediment obtained from
a reservoir. This indicates that although suspended sediments may have a
negligible effect on spectral quality at low concentrations (< 50 ppm),
higher concentrations may cause significant shifts in the rel-itive penetra-
tion of various wavelengths. Selective absorption by algal pigments may
occur in the blue (400-500 nm) and red (640-680 nm) when phytoplankton are
dense, but the amount is minor when compared with the attenuation by particu-
late matter throughout the visible spectrum (Westlake, 1966).

Vertical extinction coefficients then represent a composite of all wave-
lengths and vary considerably among natural waters depending on the contribu-
tion by suspended particulate and dissolved components. Values of nt range
from about 0.2 for exceptionally clear lakes such as Lake Tahoe, California,
to values in excess of 10 where turbidity is extremely high such as for re-
servoirs receiving inputs from flooding rivers (Wetzel, 1975; Westlake, 1966).
Ice cover reduces light transmission to variable degrees depending on whether
the ice is clear, contains bubbles, or is stained. Theoretically, clear ice
transmits light better than natural water because the dissolved substances
have been reduced. However, snow cover reduces transmission considerably.
Self shading by submerged macrophytes may be large depending on biomass, and
as little as 0.1 percent of the surface light may reach the bottom of a river
weed bed, mostly in the green wavebands (Westlake, 1966).

RELATIONSHIP OF ACTUAL LIGHT TRANSMISSION AND
SECCHI DISC TRANSPARENCY ESTIMATES TO THE EUPHOTIC ZONE

The euphotic zone is the region from the surface to the depth at which
99 percent of the incident surface light has disappeared. Work based on
response of phytoplankton suggests that the 'intensity of light at this level,
i.e., 1 percent of the surface light, represents the compensation light in-
tensity at which photosynthesis and plant respiration are in balance. For
many of the studies we cite, only Secchi disc transparency depths are availa-
ble. It would be valuable to be able to relate the Secchi depth to the more

328-607 0 - 80 - 4

100
Lake George otal Absorption
Pure H20
80

60-
n

CL
U_ 40-
0

20-
a) Dissolved organic Color
C)
Suspended Particulates
400 500 600 700 800
Wavelength (nm)

Figure 6. Total absorption spectrum of water from Lake George, Wisconsin,
as compared with spectra for pure water, dissolved .'organic color, and sus-
pended particulates. Modified from James and Birge (1938).
theoretically sound measuremenis of extinction coefficient or percent light
penetration at which the Secchi disc disappears. Attempts have been made to
do this (Poole and Atkins, 1929; Verduin, 1956; Cole and Barry, 1973). As
Hutchinson (1957) pointed out, the Secchi depth measurement actually is based
on a comparison of the brightness of the disc and the water surrounding it.
Thus light reflected from the bottom in shallow water or scattered upward by
silt-laden waters can introduce considerable error. Nevertheless, factors
of 2.7 to 3.0 times the Secchi depth have been found to approximate the 1
percent level in many cases (Cole, 1975). Based on empirical evidence for
coastal waters, Holmes (1970) suggested that a factor of 3.5 might be most
appropriate in water with a Secchi depth of less than 5 m and a factor of
2.0 for water with a Secchi depth between 5 and 12 m. However, as will be
discussed later, lower factors appear to be more appropriate for relatively
clear waters.

Within a single lake, s eston would be expected to have a greater corre-
lation with Secchi depth transparency than dissolved colored compounds be-
cause of greater seasonal change in suspended material. However, between
lakes, the confounding effects of varying color would weaken the relationship
between Secchi depths and extinction coefficients.

DEPTH ZONATION AND TURBIDITY
TOLERANCE OF SUBMERSED SPECIES

Species that become established and grow in the deeperregi 'ons.of aqua-
tic ecosystems where only a small fraction of the surface irradiation remains
are'better adapted,to survival at low levels of light than those-restricted
to shallower and better illuminated zones. In shallow aquatic ecosystems
where light is rapidly attenuated by high concentrations of suspended sedi-
ments, the same species tolerant to low levels of light might be expected to
compete more effectively than those requiring high light intensities. To
test this hypothesis, the depth distributions for a number of species from
diverse systems are presented graphically with their Secchi depth estimates
,in Figure 7. Available North American depth distribution records of submers-
ed angiosperms have been tabulated for aquatic systems where water depths
were such that the maximum depth of submersed plants would likely be limited
by irradiance rather than the shallowness of the system. Some data are given
for areas other than North America but an extensive search of world litera-
ture was not made.

The variety of methods of collecting and reporting the data summarized
in Figure 7 and the complexity and variations within and between the ecosys-
tems put the comparative analyses to be made later within the realm of approx-
imations. Normally for each species the shallowest and greatest depths re-
ported are shown along the depth axis and the area of greatest frequency,
density, cover, or standing crop is indicated by cross-hatching. No absolute
values are given; only the relative occurrence of a species along the depth
gradient is graphed. These data were often given in the literature just as
reported here, but in some cases we have given our best estimate. For exam-
ple, depth distribution may have been reported within range classes such as
percent frequency at 0-1, 1-3 and 3-8 m (Rickett, 1922, 1924; Wilson, 1935,
1941). In this specific case the minimum depth would be graphed as 0.5 m if
the species occurred at 0-1 m while the maximum depth would be graphed as
5.5 m if the species occurred at 3-8 m.

Secchi disc depths as given in the literature or as estimated from sub-
marine photometer readings aregiven when available. There are many problems
associated with attempting to relate Secchi readings to the light environment
of the plant. These range from the visual acuity of the observer to the
necessity of using Secchi data taken at times other than the growing season
for the plants in question. One possible source of error in Secchi readings
which doesn't appear to be serious is the lack of s-tandardization in disc
size and contrast (white as compared with black and white) common in earlier
studies. Baker and Magnuson (1976) found no significant differences in trans-
parencies in Crystal Lake, Wisconsin, as measured with a 20 cm black and
white disc and a 10 cmwhite disc.

To convert occasional clear water light transmission data taken with a
submarine photometer to Secchi depth transparency estimates, the depth (m) at
the 1 percent light level was divided by 1.7. This factor is consistent with
observations by Wile (in preparation) for fresh waters in southern Canada and

Figure 7. Depth distributions for submersed macrophytes.

PLANT DEPTH RANGE SHALLO11 LIMIT KNOW, DEEP LIMIT
DEPTH RANGE OF HIGHEST ABUNDANCE (DENSITY, UNKNOWN
FREQUENCY, BIOMASS, OR COVER) DEEP LIMIT KNOWN SHALLOW LIMIT
- ------ I ABUNDANCE ALONG DEPTH GRADIENT UNKNOWN UNKNOWN
ESTIMATES BASED ON DEPTH INTERVALS OR I SECCHI DEPTH TRANSPARENCY
GENERAL STATEMENT
Depth 0W
Specles 0 1 2 3 4 5 6 7 8 9 10 Locality Source
ALsmA GRAMINEUM VAR. SEYERI SALINE LAKES, ND METCALF, 1931

APMORACIA AQUATICA GREEN LAKE, WI RICKETT, 1924
BIDENS BECKII LAKE GEORGE, NY SHELDON A BOYLER, 1977
TROUT LAKE, WI WILSON, 1941

SOUTHERN ONTARIO LAKES 1. FILE, IN PREPARATION

CERATOPHYLLUM DEMERSUM WAKULLA SPRINGS, FL MARTIN & UHLER, 1939
T4RO4M0MM/00704M0M GREEN LAKE, VI RICKETT, 1924

LAKE BUNYONYI, UGANDA PENNY, 1973

SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION

LAKE FURES6, DENMARK SEIDELIN RAUNKIAER 9 BOVE PETERSON, 1917

LAKE WEST OKOOJI, IA CRUM A RACHMANN, 1973

LAKE OPINICON, ONTARIO CROWDER ET AL,,1977
TROUT LAKE, WI WILSON, 1941

LAKE FURE & DENMARK CHRISTENSEN 9 ANDERSON, 1958

LAKE MENDOTA, WI DENNISTON, 1921
BIG SPIRIT LAKE, ]A CRUM & BACHMANN, 1973
LAWRENCE LAKE, MI RICH ET AL. 1971
ELATINE MINIMA WEBER LAKE, WI POTZGER It VAN ENGEL, 1942
MIRROR LAKE, NH MOELLER, 1975

LAKE GEORGE, NY SHELDON & BOYLEN, 1977

ELEOCHARIS ACICULAR IS MIRROR LAKE, RH MOELLER, 1975
SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION

SILVER LAKE, WI WILSON, 1935

TROUT LAKE, WI WILSON, 1941

LAKE MUSKELLUNGE, WI WILSON, 1935
PAR POND, SC GRACE & TILLY, 197F

LITTLE JOHN LAKE, WI WILSON, 1935
ELEOCHARIS PARVULA BACK BAY, VAJ CURRITUCK, NC SINCOCK, 1965
ELODEA CANADENSIS 711 Wr I 7m- LAKE GEORGE, My SHELDON & BOYLEN, 1977
SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION

LONG LAKE, MN SCHMID, 1965
LAKE FURES6, DENMARK SEIDELIN RAUNKIAER 9 BoYE PETERSON. 191@

LAKE WEST OKOBOJI, IA CRUM 9 BACHMANN, 1973
07/40747M04M, GREEN LAKE, WI RiCKETT, 1924
TROUT LAKE, WI WILSON, 1941
LAKE FURESO, DENMARK CHRISTENSEN & ANDERSON, 1958
LITTLE JOHN LAKE, WI WILSON, 1935

Continued

Figure 7 (Continued)
Depth (m)
Species 0 1 2 3 4 5 6 7 8 9 10 Locality Source
0 413 1 1 . , I , I -r--1
CANADENS (CONT.) - LAKE EAST OKOBOJI, IA CRUM BACHMANN, 1973
1 LAKE CHAUTAUQUA, NY NICHOLSON P, AROYO, 1975
1 q3 BACK BAY, VAi CURRITUCK, 11C SINCOCK, 1965
ED 1 LAKE MENDOTA, W1 DENNISTON, 192.1
I.-qJq] UPPER CAR LAKE, IA CRUM 9 PACHMANN, 1973
[::3 LAKE MINNEWASHTA, [A CRUM 9 PACHMANN, 1973
ERIOCAULON SEPTANGULARE SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION

MIRROR LAKE, NH MOELLER, 1975

LAKE GEORGE, NY SHELDON 9 BOYLEN, 1977
WEBER LAKE, Wl POTZGER & VAN ENGEL, 1942

GRATIOLA AURE MIRROR LAKE, NH MOELLER, 1975
SILVER LAKE, W1 WILSON, 1935

TROUT LAKE, Wl WILSON, 1941

GRATIOLA LUTEA F. PUSILLA WEBER LAKE, Wl POTZGER 9 VAN ENGEL, 1942

HE TERANTHERA DUBIA LONG LAKE, MN SCHMID, 1965

LAKE VEST OKOBOJI, [A CRUM 9 BACHMANN, 1973

SOUTHERN ONTARIO LAKES 1, WILE, IN PREPARATION
5 qMR/qm/qm/, GREEN LAKE, Wl RiCKETT, 1924

LAKE GEORGE, NY SHELDON 9BOYLEN, 1977
AE LAKE EAST OKOBOJI, IA CRUM 9 BACHMANN, 1973
qiqr_-_----c q:q3 BIG SPIRIT LAKE, IA CRum & BACHMANN, 1973
LAKE CHAUTAUQUA, NY NICHOLSON It ARoyo, 1975
HYDRILLA VERTICILLATA SOUTH FLORIDA CANALS BLACKBURN ET AL., 1969
CONWAY LAKE (SOUTH POOL), FL NALL 9 SCHARDT, 1278 & PERS, COMM.
: Z LAKE BuNyomys, UGANDA DENNY, 1973
CONWAY LAKE (WEST POOL), FL NALL 9 SCHARDT, 1978 P, PERS. COMM,
CONWAY LAKE (EAST POOL% FL NALL & SCHARDT, 1978 & PEns. Comm.
JUNCUS PELOCARPUS SOUTHERN ONTARIO LAKES 1, WILE, IN PREPARATION
I SILVER LAKE, Wl WILSON, 1935
MIRROR LAKE, NR MOELLER, 1975

LAKE MUSKELLUNGE, Wl WILSON, 1935
TROUT LAKE, W1 WILSON, 1941
JUNCUS PELOCARPUS F. SUBMERSUS WEBER LAKE, W POTZGER & VAN ENGEL, 1942
LITTORELLA AMERICANA LAKE FIOLEN, SWEDEN TmuNMARK, 1931
LAKE MUSKELLUNGE, Wl WILSON, 1935
TROUT LAKE, Wl WILSON, 1941
LoBELIA DORTMANNA WEBER LAKE, Wl POTZ61EA I VAN ENGEL, 1942
=3 LAKE FJOLEN, SWEDEN TWUNMARK, 1931

MIRROR LAKE, NH MOELLER, 1975
LAKE GEORGE, MY SHELDON & BoYLEN, 1977

SILVER LAKE, WI WILSON, 1935
MYRIqOPqHYLLUM ALTERNIFLORUM SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION
LAKE GEORGE, NY SHELDON 9 BoYLEN, 1977

LAKE MUSKELLUNGE, Wl WILSON, 1935
TROUT LAKE, Wl WILSON, 1941

Continued

Figure 7 (Continued)

Depth 0qW
Species 0 1 2.q3 4 5 6 7 8 9 10 Locality Source
MYRIOPHYLLUM EXALBESCENS LONG LAKE, PIN SCHMID, 1965
SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION

LAKE WEST OKOBOJI, 1A CRUM & BACHMANN, 1973
17--- 8qX --I BIG SPIRIT LAKE, JA CRUM & BACHMANN, 1973
MYRIOPHYLLUM HETEROPHYLLUM SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION
LAWRENCE LAKE, MI RICH ET AL., 1971
MYRIOPHYLLUM SPICATUM 1-11.5 LAKE TOWDA, JAPAN JIMBqA ET AL- 1955
1-14 LAKE VARANA, YUGOSLAVIA GOLUBIC, 1963
LAKE FURESO, DENMARK SEIDELIN RAUNKIAER & BOYE PETERSON, 1917

SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION
FA LAKE FUREs6, DENMARK CHRISTENSEN & ANDERSON, 1953
F/qmqm/qm/ PAR POND, SC GRACE & TILLY, 1976

CHESAPEAKE BAY OSYTER BEDS STEENIS ET AL- 1962

CURRITUCK SOUND, NC DAVIS, IN PREPARATION

MYRIOPHYLLUM TENELLUM SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION

TROUT LAKE, W1 WILSON, 1941

I WEBER LAKE, W1 POTZGER & VAN ENGEL, 1942

LAKE GEORGE,-NY SHELDON & BoYLEN, 1977

LAKE MUSKELLUNGE, W1 WILSON, 1935

MYRIOPHYLLUM VERTICILLATUM GREEN LAKE, W1 RiCKETT, 1924

LAKES, U.S. & CANADA MARTIN & UHLER, 1939
q3 qC LAKE MENDOTA, W1 DENNISTON, 1921
TROUT LAKE, W1 WILSON, 1941

NAJAS FLEXILUS LAKE GEORGE, NY SHELDON & BOYLEN, 1977
LAKE WEST OKOBOJI, 1A CRUM & BACHMANN, 1973

WAKULLA SPRINGS, FL MARTIN & UHLER, 1939
GREEN LAKE, W1 RiCKETT, 1624

SILVER LAKE, W1 WILSON, 1935

LAKE MUSKELLUNGE, W1 WILSON, 1935

LONG LAKE, MN SCHMID, 1965

TROUT LAKE, W1 WILSON, 1941

LAKE MENDOTA, W1 DENNISTON, 1921
SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION

LAWRENCE LAKE, MI RICH ET AL., 1971

LAKE OPINICON, ONTARIO CROWDER ET AL., 1977

BIG SPIRIT LAKE, 1A CRUM 9 BACHMANN, 1973

LITTLE JOHN LAKE, W1 WILSON, 1935
q3qE LAKE CHAUTAUQUA, NY NICHOLSON & AROYO, 1975
LAKE EAST OKOBOJI, 1A CRUM 9 BACHMANN, 1973

NAJAS GUADALUPENSIS WAKULLA SPRINGS, FL MARTIN & UHLER, 1939

LAKE OPINICON, ONTARIO CROWDER ET AL., 1977
BACK BAY, VA; CURRITUCK, NC SINCOCKq, 1965
PAR POND, SC GRACE & TILLY, 1976

Continued

8qz8qo

Figure 7 (Continued)

Depth (m)
Species 0 1 2 3 4 5 6 7 8 91o Locality Source
I I I I I I I I I 1 -1
MAJAS GUADALUPENSIS (CONT.) PICKWICK RESERVOIR, AL PEIIER & WELCH, 1969

PAMLICO RIVER, NC DAVIS & BRINSON, 1976
WE BACK BAY, VAj CURRITUCK, NC BOURN, 1932
0qn CONWAY LAKE (@OUTH POOL), FL NALL & SCHARDT, 1978
NAJAS MINOR PICKWICK RESERVOIR, AL PELTIER 9 WELCH, 1969
POTAMOGETON ALPINUS a= LAKE.MENDOTA, Wl DENNISTON, 1921
POTAMOGETON AMPLIFOLIUS SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION
LAKE GEORGE, NY SHELDON 9 POYLEN, 1977

GREEN LAKE, W1 RICKETT, 1924
LONG LAKE, MN SCHMID, 1965
LAKE WEST OKOBOJI, IA CRUM & BACHMANN, 1973
qm LAKE MUSKELLUNGE, W1 WILSON, 1935
TROUT LAKE, W1 WILSON, 1941

LAWRENCE LAKE, Ml RICH ET AL., 1971
LAKE MENDOTA, W1 DENNISTON, 1921
SILVER LAKE, WI WILSON, 1935
LITTLE JOHN LAKE, W1 WILSON, 1935

POTAMOGETON BERCHTOLDII I MIRROR LAKE, NH MDELLER,1975
BACK BAY, VAj CURRITUCK, NC SINCOCK, 1965

POTAMOGETON CRISPUS SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION
LAKE WEST DKOROJI, IA CRUM 9 BACHMANN, 1973
LAKE GEORGE, NY SHELDON 9 BOYLEN, 1977

LAKE CHAUTAUQUA, NY NICHOLSON 9 Am, 1975
POTAMOGETON EPIHYDRUS SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION
MIRROR LAKE, NH MOELLER, 1975
LAKE MUSKELLUNGE, W1 WILSON, 1935
TROUT LAKE, WI WILSON, 1941
POTAMOGETON FOIOSUS 49 GREEN LAKE, W1 RICKETT, 1924
LAWRENCE LAKE, MI WILSON, 1935
POTAMOGETON GRAMINEUS SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION
LAKE GEORGE, NY SHELDON & BOYLEN, 1977

mk SILVER LAKE, W1 POTZGER & VAN ENGEL, 1942

LAKE MUSKELLUNGE, W1 WILSON, 1935

TROUT LAKE, W1 WILSON, 1941
17-71 LAWRENCE LAKE, W1 RICH ET At., 1971
LITTLE JOHN LAKE, W1 WILSON, 1935
POTAMOGETON ILLINOENSIS MONTEZUMA WELL, AZ COLE It BATCHELDER, 1969
LAKE GEORGE, NY SHELDON & BOYLEN, 1977

SOUTHERN ONTARIO LAKES 1. WILE, IN PREPARATION
LAWRENCE LAKE, W1 RICH ET AL., 1971

CONWAY LAKE (WEST POOL), FL NALL & SCHARDT, PqERSq. COMM.
LAKE WEST qOqKOBOJqI, IA CRUM q& BACHMANN, 1973

CONWAY LAKE (MIDDLE PqOOL)q,FL NALL & SCHARqDT, PERqSq. COMM

Continued

Figure 7 (Continued)
Depth (m)
Species 0 1 2 3 4 5 6 7 8 9 10 Locality Source

Potamogeton Illinoensis (cont.) Conway Lake (South Pool), FL Mall & Schardt, Pers. Comm.
Conway Lake (East Pool) FL Mall & Schardt, Pers. Comm.
Potamogeton Lucens Lake Fureso, Denmark Seidelin Raunkiaer & boye Peterson, 1917
Lake Mendota, WI Denniston, 1921
Lake Fureso, Denmark Christensen & Anderson, 1958
Potamogeton Natans Green Lake, WI Rickett, 1924
Lake West Okoboji, IA Crum & Bachman, 1973
Trout Lake, WI Wilson, 1941
Lake Muskellunge, WI Wilson, 1935
Potamogeton Obtusifolius 11.5 Trout Lake, WI Wilson, 1941
Potamogeton Pectinatus Lake Towda, Japan Jimbo et al., 1955
Lake Fureso, Denmark Seidelin Raunkiaer & Boye Peterson, 1917
1-14 Lake Varana, Yugoslavia Golubic, 1963
Lake West Okoboji, IA Crum & Bachmann, 1973
Lake Sibayi, South Africa Boltt et al., 1969
Southern Ontario Lakes I. Wile, in preparation
Long Lake, MN Schmid, 1965
Green Lake, WI Rickett, 1924
Lake Bunyonyi, Uganda Denny, 1973
Lake Fureso, Denmark Christensen & Anderson, 1958
Lake Mendota, WI Denniston, 1921
Big Spirit Lake, IA Crum & Bachmann, 1973
Lake George, NY Sheldon & Boylen, 1977
Back Bay, VA; Currituck, NC Sincock, 1965
Trout Lake, WI Wilson, 1935
Back Bay, VA; Currituck, NC Bourn, 1932
Lake East Okoboji, IA Crum & Bachmann, 1973
Lake Chautaqua, IL Jackson & Starrett, 1959
Lawrence Lake, MI Rich et al., 1971
Upper Gar Lake, IA Crum & Bachmann, 1973
Lake Minnewashta, IA Crum & Bachmann, 1973
Lower Gar Lake, IA Crum & Bachmann, 1973
Potamogeton subsection Lake George, NY Sheldon & Boylen, 1977
Perfoliati (includes P. Lake Fureso, Denmark Seidelin Raunkiaer & Boye Peterson, 1971
Perfoliatus, P. Perfoliatus Southern Ontario Lakes I Wile, in preparation
var. Bupleuroides and P. Lake Windermere, England Pearsall, 1921
Richardson II) Green Lake, WI Rickett, 1924
Trout Lake, WI Wilson, 1941
Lake Ullswater, England Pearsall, 1921
Lake Fureso, Denmark Christensen & Anderson, 1953
Lake Mendota, WI Denniston, 1921
Back Bay, VA; Currituck, NC Sincock, 1965
Lake Derwentwater, England Pearsall, 1921

Continued

Figure 7 (Continued)

Depth (m)

Species 0 1 2 3 4 5 6 7 8 9 10 Locality Source

Potamogeton Subsection Little John Lake, WI Wilson, 1935
Perfoliato (includes P. Lake Chautauqua, NY Nicholson & Aroyo, 1975
Perfoliatus, P. Perfoliatus Lake East Okoboji, IA Crum & Bachmann, 1973
var. Bupleuroides and P.
RichardsonII) (cont.) Back Bay, VA; Currituck, NC Bourn, 1932
Pamlico River, NC Davis & Brinson, 1976
Upper Gar Lake, IA Crum & Bachmann, 1973
Lake Minnewashta, IA Crum & Bachmann, 1973
Lake George, NY Sheldon & Boylen, 1977
Southern Ontario Lakes I Wile, in preparation
Lake Windermere, England Pearsall, 1921
Lake Ullswater, England Pearsall, 1921
Long Lake, MN Schmid, 1965
Lake Derwentwater, England Pearsall, 1921
Lake West Okoboji, IA Crum & Bachmann, 1973
Trout Lake, WI Wilson, 1935
Big Spirit Lake, IA Crum & Bachmann, 1973
Lawrence Lake, MI Rich et al., 1971
Lake Muskellunge, WI Wilson, 1935
Potamogeton Pusillus Lake George, NY Sheldon & Boylen, 1977
Lake Ullswater, England Pearsall, 1921
Lake West Okoboji, IA Crum & Bachmann, 1973
Lake Windemere, England Pearsall, 1921
Trout Lake, WI Wilson, 1941
Lake Muskellunge, WI Wilson, 1935
Silver Lake, WI Wilson, 1935
Big Spirit Lake, IA Crum & Bachmann, 1973
Little John Lake, WI Wilson, 1935
Wakulla Springs, FL Martin & Umler, 1939
Lake East Okoboji, IA Crum & Bachmann, 1973
Upper Gar Lake, IA Crum & Bachmann, 1973
Lake Minnewashta, IA Crum & Bachmann, 1973
Potamogeton Robbinsii Lake George, NY Sheldon & Boylen, 1977
Little Sissabogama Lake, WI Steenis, Pers.-Comm.
Southern Ontairo Lakes I Mile, in preparation
Trout Lake, WI Wilson, 1941
Lake Muskellunge, WI Wilson, 1935
Mirror Lake, NH Moeller, 1975
Lake George, NY Sheldon & Boylen, 1977
Mirror Lake, NH Moeller, 1975
Lake Muskellunge, WI Wilson, 1935
Silver Lake, WI Wilson, 1935
Trout Lake, WI Wilson, 1941
Potamogeton Strictifloius Southern Ontario Lakes I Mile in preparation

Continued

Figure 7 (Continued)

Depth (m)
Species 0 1 2 3 4 5 6 7 8 9 10 Locality Source

Potamogeton zosteriformis Long Lake, MN Schmid, 1965
Southern Ontario Lakes I Mile, in preparation
Lake West Okoboji, IA Crum & Bachmann, 1973
Lake Mendota, WI Denniston, 1921
Green Lake, WI Rickett, 1924
Lake George, NY Sheldon & Boylen, 1977
Big Spirit Lake, IA Crum & Bachmann, 1973
Ranunculus Aquatilis Green Lake, WI Rickett, 1924
Southern Ontario Lakes I Wile, in preparation
Trout Lake, WI Wilson, 1941
Lake Bunyonyi, Uganda Denny, 1973
Lake George, NY Sheldon & Boylen, 1977
Ramunculus Longibostris Lake West Okoboji, IA Crum & Bachmann, 1973
Lake George, NY Sheldon & Boylen, 1977
Ruppia Maritima Big Spirit Lake, IA Crum & Bachmann, 1973
Back Bay, VA; Currituck, NC Sincock, 1965
Saline Lakes, ND Metcalf, 1931
Pamlico River, NC Davis & Brinson, 1976
Back Bay, VA; Currituck, NC Bourn, 1932
Sagittaria cuneata Trout Lake, WI Wilson, 1941
Sagittaria gramikea Trout Lake, WI Wilson, 1941
Lake George, NY Sheldon & Boylen, 1977
Mirror Lake, NH Moeller, 1975
Sagittaria subulata Back Bay, VA; Currituck, NC Sincock, 1965
Scirpus acutus Trout Lake, WI Wilson, 1941
Scirpus subterminalis Lawrence Lake, MI Rich et al., 1971
Sparganium Angustifolium Weber Lake, WI Potzger & Van Engel, 1942
Mirror Lake, NH Moeller, 1975
Trout Lake, WI Wilson, 1941
Subularia aquatica Lake George, NY Sheldon & Boylen, 1977
Lake Fiolen, Sweden Thunmark, 1931
Utricularia cornuta Lawrence Lake, MI Rich et at., 1971
Utricularia gibba Lawrence Lake, MI Rich et al., 1971
Utricularia intermedia Lake Opinicon, Ontario Craig, 1976
Utricularia minor Lake Opinicon, Ontario Craig, 1975
Utricularia purpurea Mirror Lake, NH Moeller, 1975
Utricularia resupinata Lake George, NY Sheldon & Boylen, 1977
Utricularia vulgaris Lake opinicon, Ontario Craig, 1976
Vallisneria americana Wakulla Springs, FL Martin & Uhler, 1939
Lake George, NY Sheldon & Boylen, 1977
Southern Ontario Lakes I Wile, in preparation
Lake West Okoboji, IA Crum & Bachmann, 1973
Silver Lake, WI Wilson, 1935

Continued

Figure 7 (Concluded)
Depth W
0 1 2 3 4 5 6 7 8 9 10 Locality Source
Species
VALLISNERIA AMERICANA (CONT.) LAKE OPINICON, ONTARIO CROWDER ET AL., 1977
CONWAY LAKE (WEST POOL), F1 flALL P SCHARDT, PERS. CGM.

DETROIT RIVER, M1 HUNT, 1963
BACK BAY, VA; CURRITUCK, ?K SINCOCK, 1%5
BIG SPIRIT LAKE, [A CRUM & BACHMANN, 1973
CONWAY LAKE (EAST POOL), FL NALL & SCHARDT, PERS. COMM.

GREEN LAKE, Wl PICKETT, 1924

LAKE MUSKELLUNGE, W1 WILSON, 1935

PAMLICO RIVER, K DAVIS & BRINSON, 1976

LAKE CHAUTAUOUA, NY NICHOLSON Z AROYO, 1975
LAKE EAST OKOBOJI, [A CRUM 9 BACHMANN, 1973

BACK BAY, VA; CURRITUCK, IC BOURN. 1932
C:1 UPPER GAR LAKE, IA CRUM & BACHMANN, 1973
ZANN[CHELLIA PALUSTRIS fOWA GREAT LAKES, Ift. CRUM & BACHMANN, 1973

Wetzel (1975; Figures 5-9 and 5-16) for Lawrence Lake, Michigan. Based on
studies of turbid waters in Back Bay, Virginia (Sincock, 1965), a conversion
factor of 2.5 was used for the data of Bourn (1932).

Perhaps the maximum depths of plant growth recorded in Figure 7 are mom
reliable than other information given. However, as discussed by Hutchinson
(1975) and Spence (1976), there can be problems in establishing the maximum
depth in a water body where a species is rooted and growing. Accuracy in-
cludes judgement as to whether a small number of plants (or the plant at a
depth are living and are truly rooted. Ceratophyllum demersum is a special
problem because it does not form roots although a portion of the shoot often
becomes embedded in the sediment and thus "rooted" (Arber, 1920). Othe r
species such as Myriophyllum spicatum at times produce rooted floating shoot
fragments which normally sink with time. Hence shoots of C. demersum and
other species may be carried to the deeper areas and sink -fo
where they may soon become moribund in the more stressful environment. Even
though some shoots were found as deep as 9.2 m, Spence (1976) set the macro-
phyte limit for Loch of Lowes at 3.9 m which was close to the 1 percent cover
line of 3.6 m. The increasing use of SCUBA divers in studies of submersed
macrophytes should lead to more accurate data.

Though the ecological importance of straggling plants surviving in the
lower depths is probably minimal , depth records suggest that there are
physiological limits due to hydrostatic pressure as discussed previously.
Hutchinson (1975), in summarizing depth records for a number of aquatic
macrophytes, rejected some of the published depths of colonization due to
problems mentioned above. He suggested that the record depth for submersed

freshwater angiosperms was for Potamogeton strictus Philippi, which is ap-
FT
parently not found in North Ameri'ca (Shetler and Skog, 1978). Tutin (1940)
found this species at slightly deeper than 11 m in the high mountain Lake
Titicaca, Peru-Bolivia. Recent data, especially those of Moel.ler (1975),
Sheldon and Boylen (1977), and Wile (in preparation), all from the same geo-
graphical area of northeastern United States and southeastern Canada, extend
the depth ranges for a number of species native to North America. Perhaps
the most notable depth record is for Elodea canadensis which was found at one
of the 12 m sampling stations in Lake George, New York (Sheldon and Boylen,
1977).

Relationship between Maximum Depth
Distribution and Secchi Transparency

Figure 8 is a summary of depth records for 10 species in Figure 7 plot-
ted as a function of Secchi depth. Some trends are discernable and factors
which may affect depth distribution will be discussed. However, conclusions
drawn from these graphs are necessarily tentative owing to the paucity of
data points as well as problems already mentioned in interpretation of the
original data. The resistance of these species to environmental changes will
be discussed further on page 44.

Since Eleocharis acicularis is a sedge, one might judge a priori that it
is a shallow water species. This is confirmed by depth records of 2 m or
less for five of the seven data points (Figure 8a). The scattering of the
points suggests that E. acicularis does not respond to water clarity in a
predictable manner as do some other species that have increasing maximum
depth distribution with increasing Secchi depth. In fact, Wilson (1935)
placed it in an ecological group of species (mainly rosulate) which becomes
totally submerged only in response to changing lake conditions. Other species
placed in this group were Lobelia dortmanna, Juncus peloca*rpus,, and'GPatiola
allrea. These relatively clear water species with generally shallow maximum
deptF records (Figure 7) are probably limited in depth maxima by factors
other than reduced irradiance. An affinity for sandy sediments which are
normally characteristic of shallow areas subjected to fetch and water turbu-
lence is one possible explanation for the depth distribution patterns. Lab-
oratory and field experiments have shown that certain species grow best when
rooted in specific types of aquasoils (Pond, 1903; Brown, 1913; Bourn, 1932;
Misra, 1938).

The relationship between depth maxima and Secchi depths for Potamo@eton
praelongus (Figure 8b) can be considered representative of several species
of this genus with a North American distribution, primarily in clear fresh
waters in Canada and northern United States. In addition to P. orciolongus
these species i ncl ude P. , robbi ns i i $- P. zos teri f ormi s , P. amp I i fo I i us , and
P
gramineus. Since dep maxima for this group are normally high, one might
.
expect that these species would tend to survive under reduced light penetra-
tion due to suspended particles. However, some studies of long term changes
in lakes where turbidity has increased show that these northern species tend
to disappear or decrease in biomass (Volker and Smith, 1965; Lind and Cottam,

15- 15- 15-
b C
10, 10- 10-

5 5-

1'5
5 0 15 5 10 15 0
15- 15 15-
d f
10- 10- 10-

5- 5-

CL
0 5 10 1'5 5 10 15 5 10 15
15- 15- 15-
E h
9
E
10- 10- 10-
5- 5 5@
5 10 15 5 10 15 5 10 15
15-

10-

5 10 15

Secchi Transparency (m)

Figure 8. Maximum depth distribution of selected.species from Figure 7 plot-
ted against Secchi disc transparencies of the waters where the distributions
were observed: (a) Eleodharis acicUlaris, (b) PotaMogeton pra6 on_gus, (c) Najas
flexilis, (d) Potamogeton pectinatus, (e) Myriophyllum spicatum, (f) *VaTlisne-
ri a'arh6ti can a, ) Na'J'as U-6d-Alupensi (h deme (i) Tota-
_Fg u S, ) 'Ceratoph,@' I um' Psum
mogeton subsection Perfoliati, (j) Elodea CanaFensis.

1969; Stuckey, 1971; Nichols and Mori, 1971; Crum and Bachmann, 1973; Baumann
et al., 1974; Bumby, 1977). Especially striking was the virtual elimination
of the group with increasing human activities over 70 years in the vicinity
of Put-In-Bay Harbor, Lake Erie, Ohio (Stuckey, 1971). Though these species
do well at the low light intensities of deeper waters, they appear to be re-
stricted to rather narrow conditions which do not include highly turbid waters.

A number of physical and biological changes are likely to be associated
with increasing turbidities from increasing suspended sediments. These in-
clude increasing inorganic nutrient levels and changes in biological compon-
ents of the ecosystem. Of 19 lakes and ponds of Southern Ontario studied by
McCombie and Wile (1971), Potamogeton amplifolius was present only in the
most oligotrophic impoundment. Disappearance or reduced importance of northern
species has also been associated with increased importance of other species,
especially Myriophyllum spicatum (Lind and Cottam, 1969; Nichols and Mori,
1971; Steenis, 1970) and perhaps P. crispus (Fassett, 1957; Stuckey, 1971;
McCombie and Wile, 1971; McIntosh-et-al., 1978). Both of these species have
been naturalized from Europe.

Najas flexilis (Figure 8c) is found under a wider range of Secchi depths
than the northern species. of Potamogeton. This species principally has a
northern distribution and does not range southward sufficiently to be consi-
dered cosmopolitan. There does not appear to be much tendency for an increase
in maximum depth with increasing water transparency for the data points avail-
able.

Compared with the three species just discussed, the remaining species all
show some degree of linearity between Secchi transparency and maximum depth
distribution (Figures 8d-8j). All except Najas guadalupensis, which tends
to have southern affinities, are strongly cosmopolitan. Potamogeton Vectina_
tus grows well under a wide variety of conditions. This is consistent with
the wide range of Secchi transparencies and depth records for the plant. In
their study of Canadian ponds and lakes, McCombie and Wile (1971) found P.
pectinatus growing in waters of wide specific conductance range and spanning
the complete range of Secchi transparencies from 0.9 to around 5.7 m. This
species may be found in waters high in suspended sediment and organic pollu-
tion and is often rooted in silty sediments (Butcher, 1933; Hynes, 1970;
Haslam, 1978; Ozimek, 1978). The essentially linear leaves have been obser-
ved to be relatively free of the silt blanket which tends to cover submersed
macrophytes in waters high in suspended sediments as discussed previously
(McCombie and Wile, 1971; Schiemer and Prosser, 1976).

The data points for Ceratophyllum demersum (Figure 8h) indicate a dis-
tribution at somewhat greater depths than other species for water bodies
with Secchi depths less than 5 m. This suggests a degree of shade tolerance
for this species which will be discussed in more detail in a later section.
For Elodea canadensis, the li-nearity between maximum depth and Secchi trans-
M
arency is remarkable. The depth record of 12 m in Lake George, New York
eldon and Boylen, 1977) is the greatest depth reported for submersed
angiosperms. Summer water temperature to 12 m ranged from 22-250C in Lake

George. Light transmission to 12 m during the summer was about 10 percent
of incident and the water column and sediments were aerobic at least to 12 m
water depth. Thus, these factors probably were not limiting the maximum
depth of growth. Rather, hydrostatic pressure is important in limiting the
depth of growth of deep water species in Lake George. Elodea canadensis was
somewhat more resistant to excess pressure than two other species studied by
Ferling (1957). A number of depth records in Figure 7 were for Lake George.

The linear pattern between maximum depth and Secchi transparency for
Elodea canadensis differs from a tendency for some of the other species,
such as riop y spicatum (Figure 8e), Vallisneria americana (Figure 8f),
Najas uadalupens.is. Figure TO, and the Potamogeton subsection Perfoliati
group Nigure 8i), to reach a plateau at 6 to 7 m depth. This plateau indi-
cates that hydrostatic pressure rather than light availability controls maxi-
mum depth distribution.

Turbidity Tolerance Index

When the maximum depths for submersed angiosperms of Figure 7 are plot-
ted against their Secchi depths, a linear relationship is apparent at shallow
depths for most species (Figure 8). This suggests that, in the range of
around 2.5 m Secchi depth or less, turbidity is an important factor affecting
maximum depths of growth. It follows that if a species is found in the deeper
areas in water bodies with 2.5 m Secchi depths or less, the species would have
a degree of turbidity tolerance. More specifically, the higher the depth
maxima to Secchi depth ratio in the turbidity-stressed systems, the higher
the turbidity tolerance of the species. This ratio, along with related infor-
mation, is given in Table 1 for species of Figure 8. Species with higher tur-
bidity tolerance indices are better adapted for survival under conditions of
low light transmission.

The absence of Potamogeton praelongus in the systems with turbidity stress
typifies potamogetons that are mainly restricted to northern areas as discuss-
ed previously. The low ratio for Eleocharis acicularis is not surprising; the
depth distribution of this species does not correlate with Secchi transparency.
Elodea canadensis is apparently sensitive to turbidity, even though it may
grow at great depths where turbidity is low. Perhaps the effects of suspended
particles on light quality reaching the plants is especially important for
this species. Of the remaining species Ceratophyllum demersum, Vallisneria
americana, Najas guadalupensis, and P. pectinatus 'have th@7h_ighest turbidity
tolerances. The mean depth of Ceratophyllum demersum is greater than that of
other species (Figure 8).

Thus, it appears that not all species tolerant to low levels of light
and growing at great depths in clear lakes will be successful in colonizing
aquatic ecosystems of high turbidity. These exceptions may be species that
are sensitive to factors such as eutrophication, substrate type, siltation
of leaves, or light quality, rather than just the quantity of light.* Never-
theless, the turbidity tolerance index provides an approximation of the re-
lative resilience of several species to turbidity stress and their rank is

Table 1. Turbidity Tolerance Index for Selected Species of Figure 7
Expressed as the Ratio of Depth Maxima to Secchi Depth
Where Secchi Depth is 2.5 m or Less

No. Systems: Total No. Turbidity
Species Secchi < 2.5 m Systems Tolerance Index

Potamogeton praelonqus 0 11 0

Eleocharis acicularis 2 7 0.5

Elodea canadensis 7 14 1.1

Potamogeton s.s. Perfoliati 9 17 1.5

Najas flexilis 3 11 1.7
Myriophyllum spicatuma 11 40 1.7

Potamogeton pectinatus 9 22 2-.0

Naias guadalupensis 5 6 2.2

Vallisneria americana 6 17 2.4

Ceratophyllum demersum 2 11 2.8

aFrom data for lakes of southern Ontario, Canada. Twe n ty - th re esampling
stations were in Georgian Bay of Lake Huron with the rest from various
other lakes (I. Wile, in preparation).

supported by observations on distribution in nature. Additional data are
needed to firmly establish the relationship between submersed species and
turbidity.

PHOTOSYNTHESIS AND GROWTH IN RESPONSE TO LIGHT

It is'apparent from the foregoing discussion that some macrophyte spe-
cies have an affini,ty for deeper or more turbid waters while others tend to
be restricted to conditions of higher light intensities. It would be impossi-
ble from the data given above to classify all species as being either shade
tolerant or high light requiring although the approach used in Table 1 is prom-
ising. Rather we will examine the experimental evidence available for a few
species to see if it provides further insight to the possible light control of
macrophyte zonation and turbidity tolerance.

Many of the experiments reported in the literature on apparent photosyn-
thetic rates of submersed macrophytes relate to the light intensity at which
the photosynthetic system is saturated. The lowest irradiance necessary to
achieve the maximum rate of photosynthesis (saturation) provides a valuable
point of reference for comparing species. Since the subject of this review
is concerned more with the response of macrophytes to reduced levels of light,
these experiments might appear irrelevant. However, where light is only oc-
casionally limiting due to shading by high turbidity waters, the competitive
advantage of species with a high photosynthetic efficiency may help to ex-
plain their occurrence. Such conditions might occur in shallow zones of lakes
or normally clear rivers with pulses in turbidity due to storms, dredging,
high runoff, etc. Moreover, it might be proposed that species with high light
saturation correspondingly have lower photosynthetic rates at low light levels
and higher compensation points than shade adapted species.

The compensation point of light, i.e., where photosynthesis and respira-
tion are in balance, should limit the lower depth distribution of a species.
In laboratory and field experiments where compensation points are measured,
they can only approximate depth distributions in nature. This is partly be-
cause experiments are normally of short duration, while under natural condi-
tions plants respond to a seasonal range of light conditions (turbidity, day
length, solar angle, etc.). Furthermore, experiments are normally with active
apical portions of plants and do not reflect respiratory utilization of photo-
synthate by older stem portions and underground parts. There is another pro-
blem with extrapolating low irradiance experiments in the laboratory to deep
water conditions. In deep clear lakes, selective light absorption by water
(red region) and by organic compounds (blue region) may be as great a factor
in photosynthesis -as reduction in total irradiance (Figure 6). Research ap-
pears to be lacking on this problem for aquatic macrophytes.
A further problem with interpretation of the experiments discussed below
is the lack of consistency among experiments. For example, some workers re-
port .light values as ill Iuminescence lux or foot candlesA while others more
appropriately use irradiance (cal/cXhr or lleinsteins/m6-sec). The two ex-
pressions are not interconvertable because illuminescence does not take into
account the variation in energy distribution of different spectral regions.
Moreover, there are problems with differences in temperature, 1-ight source,
enclosed biomass, and inorganic carbon availability both within and among
experiments. Finally problems are associated with accumulation and utiliza-
tion of oxygen in intercellular spaces (lacun@e) of submersed plants (Hartman
and Brown, 1967). However, to the extent possible, these experiments will be
discussed as they may relate to macrophyte depth zonation and turbidity toler-
ance.

Laboratory Experiments
In a series of laboratory experiments, Gessner (1938) determined light
saturation for photosynthesis in six submersed species. Four of the species,
Ceratophyllum demersum, Cabomba aquatica, Hottonia palustris, and Ranunculus
aquatilis, appeared to saturate at approxi@_ately 10,000 to 40,000 T`ux. This
low light saturation of C. demersum is in agreement with its high turbidity
tolerance index.(depth maximum to Secchi depth ratio) reported in Table 1.

The other two species, Elodea crispa, and Potamogeton 'p6rfoliatus, did not
saturate within the range oTlight i tensities used. It would appear that
particularly for P. perfoliatus light saturation was somewhat above 80,000
lux. This concurs somewhat with the low turbidity tolerance index of Potamo-
peton subsection Perfoliati of Table 1. The photosynthetic curves for-C-.-
demersum and C. aquatica appear to increase quite rapidly at the lower Tight
intensities relative to the other species.

Boyd (1975) reported changes in net photosynthesis of 1 g samples with
increasing light intensity. Photosynthesis in three of the species reached
light saturation at about 10,000 lux (Eleocharis acicularis, Elodea'dons-a,
Naias flexilis), while light saturation occurred at 15,OOU-Iux for*Potamogeton
sp. and 20,000 lux for Ceratophyllum demersum. None of the species required
more than-9,000 lux for@_5_0 percent of maximum photosynthesis. These results
are in general agreement with those of Gessner (1938) except for the two spe-
cies that he reported which did not reach maximal photsynthesis.

Comparative photosynthetic rates for four species of submersed plants
reported by Van et al. (1976) did n2t differ greatly in irradiance required
for saturation (600-700 peinstein/m -sec), but light compensation points dif-
fered substantiall,@. The compensation point for Hydrilla Vortidflla@a was
lowest, at 15 @E/m -sec, Cambomba caroliniana was highest at 55 jjE/ ec,
while Myriophyllum spicat-u-m--an-c-FC-eratophyllum demersum were intermediate at
35 pE/e*sec. Even though H. verticillata and C. demersum had high to medium
tolerances, respectively, @_o low light levels, _fheir maximal photosynthetic
rates were higher than the other two species per unit of chlorophyll content.
It would appear then that some species are adapted to a wide range of light
conditions, being able to tolerate quite low levels of light and have high
photosynthetic capacities at high light levels. Since H. y6ftitillata exhi-
bits th.is capability, this would explain its rapid biomass production under
favorable light conditions as well as its large standing crops where self
shading is high (Nall and Schardt, 1978). Carr (1969a, b) also characterized
C. demersum as a shade plant, being adapted to low levels and saturating at
'Ybout 40,000 lux in flasks and about 15,000 lux under artifical stream condi-
tions. She observed maximum photosynthesis in plants collected from 5 m
depth in Lake Ohakuri, New Zealand, where light intensity was about 2 percent
of surface. However, Meyer and Heritage (1941) found this species to have
maximum photosynthesis at the surface of Lake Erie. As Carr (1969b) pointed
out, this may have been a result of using only plants collected from the sur-
face rather than intub-ating them at light intensities at the depth from
which they were collected. Further evidence for shade adaptation of Cerato-
phyllum dermrsum relative to other species was reported by Guilizzon T_19_7_7T
for @ake Wingra, Wisconsin. Satration of photosynthesis occurred at 250
jjE/m -sec compared with 800 -pE/m -sec for Myribphyllum
It is uncertain to what extent these short term (usually :S I hour) lab-
oratory experiments, in which dissolved oxygen production rates are measured,
are comparable to longer term studies in which growth is measured by increases
in l.ength or biomass. For example, Blackburn et al. (1961) reported that
Elddea d6nsa (-Planch) Caspary has a low light requirement and that long-term

growth (12 weeks under fluorescent lamps) was optimum at about 100 foot can-
dles. Above 125 foot candles rapid ch.lorosis and death occurred. In com-
parison,, 'H6tetarithere! dubia had a high light requirement with optimum inten-
sity at 590 foot candles. Long-term studies would appear to take into account
differing abilities of species to adapt to light intensities.

A fundamental difference in response to light saturation by sun leaves
(acclimated under high light intensity) and shade leaves was reported by
Gessner (1938) for several species of submersed macrophytes. Proserpinaca
palustris Elodea crispa, and Potamooeton d6nsus all showed ligh.t saturation
at about 40,000 lux or less, while the sun leaves continued to show a near
linear photosynthetic response to increasing light abnve that -level.- Simi-
larly, the emergent leaf form of the heterophyllous Proserpinaca palustris
saturated at higher light levels than the submersed T-eaf form. Th-is suggests
that not only are there inherent differences in light saturation levels among
species, but that there is considerable plasticity within a species depending
on exposure to light conditions prior to experimentation.

This problem was addressed by Spence and Chrystal (1970a,b) who showed
th at s o meIPotamogeton species had a greater reduction in photosynthesis with
reduced irradiance than others. There was a tendency for these species to
be restricted to the more s4allow zones of lakes, and thus be less shade tole-
rant, than the ones that underwent less reduction in photosynthesis. The
mechanism for the adaptation of shade species appeared to be related to lower
leaf respiration and reduced thickness under low light conditions. These fea-
tures allow net photosynthesis to continue under low irradiance. In contrast,
the thicker leaves of sun species were more efficient at higher irradiances.
Otto and Enger (1960) maintained submersed plants (Potamogeton pectina7
tus, P. nodosus, Elodea canadensis) in tanks with varying concentrations of
suspended sediment. Growth reductions relative to controls were 20 to 40 per-
cent for sediment concentrations of 50 ppm. The amount of growth reduction
was approximately linear with increasing sediment concentrations up to about
1,250 ppm. Abnormalities in growth at higher concentrations over the 4-week
growth period included elongation of stem internodes and chlorosis of stems
and basal submersed leaves. Potamogeton pectinatus appeared to be less tole-
rant to suspended sediments than the other two species and the authors attri-
bute this to its lower leaf area. This does not agree with field observations
(Table 1, Figure 7) which show it to be reasonably turbidity tolerant.
This research is of interest because it is the only known study in which
suspended sediment concentrations have been manipulated to observe growth
responses of submersed vascular plants. However, the authors conclude that
"Sediment concentrations greater than 1,250 ppm would be necessary to cause
plant growth reductions that might be considered critical to the plants'
ability to survive." This statement should not be taken out of the context
of the experiments conducted and applied to field conditions. First, the
plants were growing in only about 60 cm of water and the results may apply
only to shallow water conditions. Secondly, and probably more importantly,
many natural stands of submersed vascular plants may be living near their

limit of tolerance owing to physical, chemical, and biological factors discus-
sed previously. Additional light reduction due to turbidity, even at the low-
est levels of suspended sediment used in these experiments (50 ppm), may ex-
ceed the threshold of tolerance for plant communities already subjected to
other stress factors.

Field Studies

Few field studies have been conducted to determine photosynthetic and
growth responses to light. Because of the problems discussed above as well
as changing light conditions with.in th-e course of a day or season, such experi-
ments are difficult to interpret and extrapolate to field observations of
plant distribution. However, they may have some value in a relative sense
when several species are compared. For example, Meyer et al. (.1943) determined
the compensation depth for shoot tips of several submersed species in Lake
E ri e. Compensation light intensity was approximately 1.percent of the inten-
sity measured at 5 cm depth for Elodea canadensis, 'POtamogeton ri.thaedtohii ,
he value for'N6jas fl'
Vallisneria aTfioricana and Het.6rahthera exi Tis
was somewhat higher at 2.6 percent.

Photosynthesis and respiration in submersed species were studied in de-
tail by Ikusima (1965, 1966, 1967). He showed that photosynthesis decreased
progressively from the upper part to the basal parts of community of'Potamo-
geton crispus and Vallisn6,@ia 6siatica Miki, but that respirati.on was fairly
constant throughout (Ikusima--l9--6-5T.-Pliotosynthesis in Val 1 ignetia 'deriseser-
rulata Makino beds varied considerably from day to day depending o-n w-Fe-t-Fe-r
tT-eweather was clear, cloudy, or rainy (.Ikusima, 1966). As expected, the
compensation depth may vary from hour to hour during the day even though the
light compensation point of the plants may remain constant. Monthly di ffe-
rences occurred as well (Ikusima, 1967). Interception of light by apical
portions of shoots, which reduces considerably the rate of photosynthesis of
lower portions, results in a large respiratory demand where biomass is general-
ly largest. Communities during overcast or-rainy days may even have a negative
net organic matter budget.

The results of the laboratory experiments and field studies cited above
demonstrate a number of problems in interpreting instantaneous measurements of
photosynthesis. Species can be ranked according to their capacity for photo-
synthesis at light saturation intensities, whicli-m& be indicative of their
success in competition if light saturation intensitie , rsist under field
conditions. However, distribution and abundance of aquati macrophytes in
nature reflects the totality of the forcing functions that affect macrophyte
growth, of which light is just one.

RESPONSES OF SUBMERSED PLANTS TO ECOSYSTEM CHANGE

COMMUNITY RESPONSES TO
THE DURATION OF PERTURBATION

Factors affecting the growth and distribution of submersed plants h.ave
been discussed. In this section one example of short term and one of long
term fluctuations in macrophyte community structure as related to natural and
anthropogenic stresses will be considered. Short term changes described in
the literature are often related to a single perturbation with observations
before and after the event. The observation period may vary from weeks as for
the study by Bilby (1977) of changes in cover and areal distribution of plants
fo-11-bwing a stream spate to several years as for changes in macrophyte commu-
nities in the Currituck Sound of North Carolina (Davis, in preparation). On
the other hand, some lakes in the northern U.S.A. have been studied sporadical-
ly for over a half century as for the Iowa Great Lakes (Crum and Bachmann,
1973)

Compared with responses of submersed plants to short term perturbations
which are usually associated with increased suspended sediment loads in the
water, long term changes in plant responses generally are harder to relate to
specific environmental changes. Although changes in parameters with time,
such as water transparencies, have been found during long term studies, short
term changes associated with meteorological conditions and human activities
such as dredging may be generally more important in effecting changes in sub-
mersed plant populations.

Short Term Perturbations

The observations of Steenis (1947) of the decimation of submersed macro-
phytes in Reelfoot Lake, Tennessee, following heavy rains in June 1945 repre-
sent changes which may occur following a single perturbation. The water level
rose and extensive siltation resulted from erosion of hills around the lake.
Steenis' observations are summarized in Table 2. Cer6toohyllum demersum was
the dominant submersed plant before the rains, but it appeared to succumb to
increased turbidity and wind action that resulted from increased fetch as the
water level rose. Lind and Cottam (1969) reported that C. demersum in Univer-
sity Bay of Lake Mendota, Wisco'nsin, "anchors poorly" in thi@ -sediment and was
restricted to areas of low turbulence. Potamogeton pectinatus remained fairly
abundant in places through 1945, but was limited in part by feeding activities
of carp and competition with filamentous algae. In 1946 growth of P. pectinatus

Tabl e 2. Changes in Submersed Macrophyte Populations in Reelfoot Lake, Tennessee (Steenis, 1947)

Species Before 1945 Summer 1945 1946

Ceratophyllum Dominant, many pure Fragmentary, but some exten- Showing definite signs
demersum stands sive beds in sheltered areas of again dominating

Najas Limited and suppressed' Scattered, sparce in much of Extensive cover in some
guadalupensis growth in C. demersum lake areas

Potamogeton Pyomirent in some areas Scattered, sparce in much of Extensive cover in some
pusillus but dominated by C. lake areas; more aggressive
demersum later in season than N. guadalupensis

Zannichellia Suppressed fragmentary Scattered, sparce in much of Extensive growth; expan-
palustris growth in limited areas lake sive and pioneer

Potamogeton Scattered small beds Scattered, sparce in much of Spots of existing growth
nodosus. lake; set back and slightly increased about 10-fold
redistributed

Potamogeton Scattered small beds; Scattered, sparce in much of Luxuriant beds in much
pectinatus greater range than P. lake; fairly abundant in one of the lake; largest
americanus area but set back by carp stands ever observed by
action and overcovering with Steenis for lake
algae

Heteranthera Limited; two areas Plants that had survived
dubia were slowly recovering

Cabomba Limited; one area Set back New growth in an addi-
carolinana tional area

Utricularia Mainly in shallow 'Nuphar Continued without change
vulgaris advena dominated areas

was more luxuriant and widespread than Steenis had ever observed before. Ac -
celerated growth of Najas guadalupensis and P. pusillus also occurred in some
regions of the lake Tn-1946. Pdtam6geton pusillus was described as the more
aggressive of the two. Corat6phyllum .derheMum came back strongly in the year
following the rains while there was a dramatic growth and spread of Zamnichel-
lia palustris. Here then, virtual elimination of the dominant species lgd to
cf5-nging niches with rapid recovery and increase in macrophyte diversity.

Other short term changes in species composition and/or biomass have been
reported for a shallow pond (Stuckey, 1971), a shallow flood plain (Jackson
and Starrett, 1959), a lake (Oglesby et al., 1976), and a resevoir (Peltier
and Welch, 1970). In all of these cases an increase in suspended sediment
turbidity resulted from changing environmental conditions.

Long Term Perturbations

Perhaps the most significant study of long term changes in submersed
macrophyte populations was that by Crum and Bachmann (1973) of lakes of the
Iowa Great Lakes region. They took advantage of an excellent opportunity to
compare the submersed macrophytes in six essentially contiguous lakes which
now have varying trophic states. The time element was added to their analy-
sis through reference to three other studies, the first of which was in 1894.
Depth distributions of submersed macrophytes given by Crum and Bachmann are
included in Figure 7. These data were especially valuable in establishing
relationships at the low end of,the Secchi depth scale for Several individual
species (Figure 8).

At the time of the study in 1972, some of the northern potamogetons re-
mained in Lake West Okoboji (4.2 m Secchi depth) and Big Spirit Lake (2.8 m
Secchi depth) while none were in the more turbid lakes (0.7 to 1.6 m Secchi
depth range) (Table 3). Generally, the species remaining in the more turbid
lakes were those which have been established as turbidity tolerant (Table 1);
however, these same species also were found in the clearer lakes. These
observations suggest that the northern potamogetons are sensitive to turbidity
and associated changes while plants that are turbidity tolerant may thrive
under a variety of conditions.

The initial invasion of the clearest lake by Potamogeton crispus is sur-
prising since it often grows in disturbed or eutrophic systems. Migration to
the other lakes might be expected in the future. The presence of Ruppia mari-
tima in only one lake is also of interest. Since this species is normal y
To-und in saline environments (cf. Metcalf, 1931), a comparison of salinities
of these lakes would be of interest. Indeed, further analyses of physical and
biological parameters that might affect the distribution of submersed macro-
phytes seems warranted.

Based on a study in which macrophytes of Lake East Okoboji were compared
with a 1915 survey, Volker and Smith (1965) suggested a number of factors res-
ponsible for the observed changes. These include nutrient enrichment from
agricultural runoff and from sewage leading to algal blooms, siltation from

Table 3. Long Term Changes in Macrophyte Populations in Lakes and Bays in Northern United States.
__________________________________________________________________________________________________
Iowa Great Lakes (1894-1972)
__________________________________________________________________________________________________
Lake West Okoboji Big Spirit Lake Lake East Okoboji Gar (three lakes)

Long term Ceratophyllum denersum Ceratophyllum Denersum Ceratopyllum denersum Ceratophyllum denersum
presence: Elodea canadensis Myriophyllum exalbescens Elodea canadensis Elodea canadensis
Heteranthera dubia Najas flexilis Heteranthera dubis Potamogeton pectinatus
Myriophyllum exalbescens Potamogeton amplifolus Najan flexilis P. richardsonii
Najas flexilis P. fflinoiensis Potamogeton pectinatus Vallisneria canadensis
Potamogeton amplilolfus P. nodosus potamogeton sub sec
P. natans P. pectinatus Pusilli
P. nodosus P. praelongus P. richardsonii
P. pectinatus Potanogeton sub. sec Vallisneria americana
P. praelongus Pusilli Aannichellia palustria
Potanageton sub. sec. P. richardsonii
Pusilli P. zosteriformis
P. richardsonii Ruppia Maritina
P. zosteriformis Vallisneria americana
Ranunculus longiristris Zannichellia palustris
Vallisneria Americana
Zannichellia palustris

Disappeared:Megalodonta (Bidens) beckii Elodea canadensis Potamogeton amplifolius Heteranthera dubia
Potamogeton diversifolius Megalodonta (Bidens) beckii P. diversifolius Hippuris vulgaris
P. epihydrus Potamogeton diversifolius P. epihydrus Megalodonta (bidens) beckii
P. gramineus P. epihydrus P. gramineus Myriophyllum exalbescens
P. natans P. natans Najas Flexilis
P. nodosus Potamogeton amplifolius
P. praelongus P. natans
P. zosteriformis P. nodosus
Megalodonta (Bidens) beckii P. praelongus
Myriophyllum exalbescens
Ranunculus longirostris
Recent Potamogeton crispus Heteranthera dubia Potamogeton sub. sec.
Adventive: P. illinoiensus Pusilli
Zannichellia palustria

Table 3 (Concluded)

Put-in-Bay Harbor, Ohio University Bay, Wisconsin Green Lake, Wisconsin Lake Wingra, Wisconsin
Condition (1898-1967) (1912-1965) (1921-1971, 74) (1929-1968, 69)

Long term Butomus umbellatus Ceratophyllum demersumb Ceratophyl Ium demersum a Certophyllum demersum
presence: f. vallisnerifolius Elodea canadensis Chara sp. Elodea canadensis
Ceratophyllum demersum Heteranthera dubia Elodea canadensis Heteranthera dubia
Heteranthera dubia a Najas flexilis Heteranthera dubia Myriophyllum spicatum
Myriophyllum exalbescens Myriophyllum exalbescens b Najas flexilis Najas flexilis
Potamogeto berchtoldii Potamogeton crispus Potamogeton amplifolius Potamogeton crispus
P. crispus P. pectinatus P. gramineus P. foliosus
P. pectinatus a P. richardsonii P. natans P. natans
P. pectinatus
P. richardsonii a P. zosteriformis P. pectinatus P. richardsonif
P. richardsonii P. zosteriformis
Vallisneria americana b Vallisneria americana ab
Zannichel1ia palustris Zannichellia palustris
P. zosteriformis Ranunculus longirostris
Ranunculus sp. Utricularia vulgaris
Zallisneria americana

Disappeared:: Elodea canadensis Potamogeton amplifolius a Myriophyllum verticillatum Potamogeton amplifolius
Megalodonta (Bidens) beckii P. illinoiensis var. pectinatum (perhaps) a P. friesii
Najas guadalupensis a P. natans Potamogeton foliosus P. illinoiensis
N. flexilis a P. nodosus P. parelongus
Potamogeton amplifolius P. praelongus Vallisneria americana a
P. filiformis
P. foliosus
P. friesii
P. gramineus
P. natans
P. nodosus
P. perfoliatus var.
bupleuroides
P. praelongus

P. pusillus
P. zosteriformis a
Recent Elodea nuttallii Potamogeton foliosus Myriophyllum spicatum b Myriophyllum spicatum
Adventive Potamogeton friesii (perhaps)
Potamogeton crispus
(perhaps)

a Dominant or subdominant in an earlier survey.
b Dominant or subdominant at last survey.

agriculture, the use of algicides, depletion of dissolved oxygen, and fluctua-
tions in water level. Crum and Bachmann (1973) suggested that stabilization
of water levels in some of the lakes may have led to the demise of certain
submersed macrophytes. The possible effects of herbicides in areas of intense
agriculture might also be considered (Correll et al., 1978).

Long term changes in submersed plants for other systems are summarized in
Table 3. Environmental degradation associated with shoreline development and
intense use of waterways in and around Put-in-Bay Harbor on an island in Lake
Erie, Ohio, led to a drastic decrease in macrophyte presence and density over
70 years (Stuckey, 1971). Changes in the s:ubmersed macrophyte community over
the period described by Stuckey did not begin with a pristine environment
which gradually deteriorated due to human activities. Poor agricultural prac-
tices on the island apparently contributed to a heavy suspended sediment load
in the study area from the beginning of the studies (Thorndale, 1898 as cited
in Stuckey, 1971). Stuckey cites Pieters (1901) as reporting that in 1898 it
was impossible to see plants in one area deeper than around 0.6-0.9 m due to
turbi di ty. Stuckey suggested that the demise of the plants over time was re-
lated to a combination of warming of the water, increased turbidity and de-
creased dissolved oxygen. Increased turbulence due to extensive bulkheading
along the shore could also have been a factor. In the Pamlico River, North
Carolina, submersed macrophytes were usually limited to a narrow band in the
deeper part of the littoral where bulkheading was extensive (Davis and
Brinson, 1976).

Lind and Cottam (1969) studied the submersed macrophytes of University
Bay of Lake Mendota, Wisconsin in 1966 and compared their results with those
of surveys made by Denniston (19Z1), Rickett (192-2), and others. Compared
with Rickett's data, they found that the biomass of"M ribohyllurn bxAlbescens
(or perhaps M. spicatum) had increased drastically that of Vallisneria
americana decreased and Ceratophyllum demersum increased (Table 3). Lind
and Cottam (1969) suggested that eutrophication caused the changes observed
in University Bay.

Bumby (1977) compared the submersed macrophyte biomass and distribution
in Green Lake, Wisconsin, in 1971-1974 with that in 1921 (Rickett, 1924). As
for University Bay (Lind and Cottam, 1969), Myrioehyllum (M. spicatum) had
become dominant, but relative biomass (46 percent) was not as great as for
M. exalbescens in University Bay. Secchi depths were not given, but Bumby
suggested thaf- there had been no change measured in light transmission since
1942. However, decreased light due to suspended sediments and seston in the
littoral and the abundance of the filamentous alga, Cladophora,sp., were sug-
gested as possible factors affecting the observed changes.

Lake Wingra is yet another Wisconsin lake in which Myriophyllum has be-
come dominant (Nichols and Mori, 1971). The relative frequency of M. Spica
tum was 68 percent and no other submersed species had a relative frequency
of over 10 percent. The authors suggested that the lake was once dominated
by potamogetons and Vallisneria americana. The species found in 1968-1969
were much the same as described for the other Wisconsin lakes (Table 3).

Vallisneria amoritana and northern potamogetons had disappeared by 1929, as
,determined-b7a -herbarium survey. Carp were introduced in the late 1800's
and practically eliminated submersed macrophytes from the lake from the 1920's
through 1955 (Baumann et al., 1974). The demise of V. arnOPicana was associated
with the carp infestation, apparently due to increas-ed turbidity.

All the long-terTned changes described thus far are for northern lakes
which apparently had no rosulate populations typical of sandy, shallow areas
of some northern oligotrophic lakes. Flora of such lakes has been reported
for northern Wisconsin (i.e. Steenis, 1932; Wilson, 1935; Potzger and Van
Engel, 1942), New Hampshire (Moeller, 1975), Scottish Lochs (Spence, 1967)
and Engl ish Lakes (i.e., Pearsall, 1920) as well as other northern European
c.ourttries (Hutchinson, 1975).

Hutchinson (1975) suggested that the oligotrophic Weber Lake in northern
Wisconsin had the simplest known macrophyte community for northern lakes of
moderate altitudes and latitudes. Potzger and Van Engel (1942) found that
all species growing in Weber Lake were basically rooted in sandy sediments
and suggested that growth of smaller plants (eight of nine species found) in
deeper waters was restricted by a cover of organic sediments. Even in the
observed depth ranges, Myriophyllum tenellum and Isoetes macrospora Dur. were
frequently etiolated up to near the tips du@_ to sediment cover. Other low
growing species included Elatine minima, Eriocaulon septangulare, Juncus pel.-
ocarpus f. submersus, Gratiol-a-Titea f. pusil.La a LoBeli dortmanna.

In comparing three northern Wisconsin lakes of varying trophic states,
Wilson (1935) found that most of the rosulate forms were not present in the
eutrophic lake. In the other lakes they were present in only trace amounts.
Sow of the northern potamogetons were present at very low relative biomasses
where Najas flexilis was dominant With Potamogeton richard8onii a weak sub-
domi n Of.

From 1821 through 1894, several rosulate forms disappeared from Loch
Leven, now eutrophic (Jupp et al., 1974). Several of the species described
here as northern potamogetons were present, but had disappeared by 1910. By
1966 Ceratophyllum demersum and perhaps M-riophyllum spicatum had disappeared.
Potamogeton pectinatus anU-Zannichellia palustris were adventive by 1959 and
P. crispus was first reported in 1966.

To summarize the long-term changes in submersed macrophyte communities
described above, a survival index has been developed for plants of the north-
ern lakes of Table 3 (Lake West Okoboji and Big Spirit Lake were omitted since
there was comparatively little change in submersed species). This is simply
a ratio of the number of lakes in which a species was reported in earlier
surveys to the number of lakes in which the species was present when last
studied. The survival index was calculated for species which were originally
found in three or more of the lakes. As for the turbidity tolerance index,
other factors in addition to an increase in turbidity surely played a -part
in changes in plant populations observed. Survival indices calculated and
turbidity tolerance indices from Table 2 are:

Turbid i ty
Survival Index Tblerance Index

Ceratophyllum demersum 1.0 2.8

Potamogeton pectinatus 1.0 2.0

P. richardsonii (s. s. Perfoliati) 1.0 1.5

Zannichellia palustris 1.0

Elodea canadensis 0.8 1.1

Heteranthera dubia 0.8

Vallisneria americana 0.8 2.4

Najas flexilis 0.7 1.7

Potamogeton zosteriformis 0.6

P. foliosus 0.3

P. gramineus 0.3

P. natans 0.3

?_. amplifolius 0.2

P. nodosus 0.0

praelongus 0.0 0.0

The tabulation of the survival indices merely emphasizes what is apparent
in Table 3. The more cosmopolitan species tend to remain with ecosystem
change while the northern potamogetons tend to disappear. As would be expect-
ed, there is a tendency toward a positive correlation between the survival
index and the turbidity tolerance index.

CATEGORIES OF SPECIES BASED
ON RESISTANCE TO ECOSYSTEM ALTERATION

An arbitrary grouping of submersed macrophytes based on their tendency
to decrease in biomass or disappear with increasing alteration of ecosystems
has been developed. Ecosystem alteration can be caused by a number of fac-
tors, but the net result is usually an increase in water turbidity. Five
categories ranked roughly in order of increasing resistance to change are sug-
gested as follows:

1. Rosulate species found mainly in northern lakes.

2. Northern potamogetons.

3. Tolerant species normally with low biomass in disturbed systems.
These species may have relatively high biomass in pristine systems.

4. Tolerant species normally dominant or subdominant in disturbed sys-
tems.

5. Adventive species that appear in disturbed systems and may be domi-
nant to rare.

Rosulate Species

Significant mixed rosulate populations appear to be restricted to oligo-
trophic northern lakes. Their absence elsewhem may be associated with fac-
tors related to increasing conductivity of the waters (Moyle, 1945) or, as
Potzger an.d Van Engel (1942) suggested, increasing accumulations of finer
sediments. Wilson (1935) said that several rosulate species should be con-
sidered terrestrial plants which "go aquatic" with submergence due to rising
water level. These are normally small plants found in shallow waters and
maximum depth distribution correlates poorly with Secchi depth (Figures 7 and
8). Myriophyllum tenellum, when present, is often included in rosulate popu-
lations since it is 6suall found with the rosulate species. Some of the
rosulate species are:

Elatine minima Isoetes macrocarpa

Eleocharis acicularis Littorella americana

E. palustris Lobolia dortmanna

Eriocaulon septangulare Myriophyllum tenellum

Gratiola aurea f. pusilla

Northern Potamogetons

There is a preponderance of evidence that the potamogetons which are re-
stricted to or are most widely distributed in northern areas do not survive
the long-term changes that lead to eutrophica'tion. Based primarily on the
studies of the northern lakes, the potamogetons most sensitive to increasing
eutrophication are:

Potamogeton amglifolius P. natans

P. foliosus P. nodosus

P. gramineus P. peaelonous

P. illinoiensis P. zostoriforMis

Of these species probably only P. foliosus can be considered truly cosmopoli-
tan in distribution.

Potamogeton gramineus is one of the most sensitive of the northern pota-
mogetons to ecosystem change. Stuckey (1971) cited Pieters (1901) as finding
this species in 1898 in Put-in-Bay only on a bar where presumably the sedi-
ments were sandy and the water was shallow. In comparing three northern
Wisconsin lakes, Wilson (1935) concluded that the comparatively low biomass
of P. gramineus found in the most eutrophic.lake was related to the greater
accumulation of organic soils there. Wilson suggested that this species is
a colonizer of primitive soils and disappears as the system develops. Bumby
(1977) found P. gramineus outside her transects, in Green Lake, Wisconsin in
1971, but was unable to find it again through 1973. Of the northern potamo-
getons, Potamogeton zosteriformis survives best. Just as the disappearance
of P. gramineus is an indicator of early ecosystem changes, the continued
presence of P. zosteriformis as other northern potamogetons disappear is an
indication oT further ecosystem change.

Tolerant Species Normally with
Low Biomass in Disturbed Systems

Any species may be dominant in a part of a system or throughout the sys-
tem depending on the conditions. However, for the systems reviewed here,
there are some species which are resistant to ecosystem changes relating to
decreased water transparency but which are commonly minor components of the
systems. The species are:

Elodea canadensis Pot6mogeton pusillus

Heteranthera dubia P. richardsonii

Najas flexilis ZanniChellia palUstris

Except for Najas flexilis which tends to have a northern distribution and Pota-
mogeton ricFa_rdson_i-i_`w`Fi__ch belongs to a subsection (Perfoliati) which extends
southward, the species in this group are widely distributed.

Tolerant Species Normally Dominant
or Subdominant in Disturbed Systems

A few native species tend to maintain relatively high biomass in dis-
turbe d sy stems. These include:

Ceratophyllum demersum Potamogeton. perfol 1 atus
var. bupleuroides

Naias guadalupensis Vallisnoria americana
Ceratophyllum demersum and Potamogeton pectinatus. are widespread, Vallisneria
americana exteTds from south to north with ratHer spotty distribution, P.

perfoliatus var. buple'uroldes. fo-m-s the southern extension of the subsection
PerfoM_tiand Na'jas'gUAdalUpensis is the southern counterpart of N. flekilis.

Potamogeton pectinatus is probably the most widespread and abundant of
all North American submersed species. In the 1930's this species was the
most important of the potamogetons as a food source of game ducks. Potamogetons
as a group were the most important waterfowl food in six of the eight North
American regions described by Martin and Uhler (1939). Only in two areas, the
lower Mississippi and Gulf Coast regions, were other species of greater impor-
tance. The most used species there were Cyperus esculentus L. and Ruppia
maritima, respectively. The resistance of P. pectinatus to suspended sediment
loads aFd short and long-term ecosystem cha-nges for the most part is consis-
tent with the widespread abundance and importance of this species.

Adventive Species

As is now. apparent, Myriophyllum spicatum has spread in the past quarter
century to many areas in the United States and Canada where infestations often
cause *problems in human uses of lakes, streams, and reservoirs. As reviewed
by Davis and Steenis (1973) intertwining mats of M. spicatum may adversely
affect swimming, boating and various types of fisfi-ing. Quiescent waters in
beds of M. spicatum may be conducive to breeding of mosquitos and decaying
plants in windrows along the shore often cause obnoxious odors. There is con-
fusion in distinguishing between M. spicatum and M. exalbescens but M. @.@ca-
tum is likely the species involveU in irruptions.

Observations in the Chesapeake Bay region (Steenis, 1970; Steenis et al.,
1971) and Currituck Sound-Back Bay (Davis, in preparation) indicate that
Myriophyllum spicatum is susceptible at least to short-term perturbations of
the ecosystem. Reestablishment of the species as the dominant is highly v.ar-
iable and may not occur for many years.

Potambgeton crispus is another widespread adventive, especially in the
northern region. This species is well established as an invader of eutrophic
or disturbed waters, but in the Chesapeake Bay area it fluctuates widely with
changing conditions (Steenis etal., 1971). Potamogeton crispus became a
strong dominant in an Indiana lake, and measures were taken to control it
(McIntosh et al., 1978).

EFFECTS OF ENVIRONMENTAL ALTERATIONS ON
SUBMERSED AQUATIC PLANTS

This section is intended to provide a better understanding of why reduc-
tions in submersed macrophytes occur and how specific environmental altera-
tions may affect submersed plants. It should be emphasized at the outset
that the capacity to predict changes in macrophyte communities due to natural
or human induced environmental alterations is quite low. However, the exam-
ples of long term and short term changes in macrophyte communities just des-
cribed show that some generalizations can be made that may allow some predic-
tive capacity. Where natural episodes are responsible for changes, efforts
toward conservation and management of submersed plant communities are not us-
ually applicable. Thus management efforts must be directed toward human in-
duced environmental changes. The condition of "overabundance" of aquatic
macrophytes that may result from environmental manipulation or from invasion
of adventive species will not be considered.

Since reduction in abundance of submersed plants can result from an
array of factors, it would be instructive to examine how the forcing functions
that cause these changes affect macrophyte communities. The diagram in Figure
9 is a conceptual model that separates these forces into three categories:
light attenuation, toxicity, and biomass removal. Some of these may result in
long term and others in short term changes of submersed plant communities.
Light attenuation due to suspended sediments and eutrophication acts by re -
ducing the energy available for photosynthesis. For suspended sediments, this
may be either short term, as in the case of storms or floods, or long term,
where the source of suspended sediments persists. Eutrophication is generally
a long term effect since nutrient levels in aquatic ecosystems can persist
long after the source of these nutrients are eliminated. Sediments of aquatic
ecosystems often have a high capacity for storing elemants critical to plank-
ton growth and may continue to supply these nutrients to the water column af-
te'r inputs to the system cease.

Toxicity due to herbicides, heavy metals, and other toxic substances acts
by altering the metabolism of plants (Figure 9). The affinity of herbicides
for small particles may result in the accumulation of these substances in the
sediments as previously discussed, and effects may persist for long periods
depending on the stability of the compounds in the environment and whether
degradation products are also toxic.

Sunlight LIGHT
Suspended ATTENUATION
Sediments

Reduced light
penetration
Eutroph! -
Shading by cation

phytoplankton
and periphyton

Reproduction

Submersed
Macrophyte
Community

Altered
Herbi- metabolism
ci des

TOXICITY Storm

Floods
Waves,
y
urrents

Waterfowl

Fish
Grazing

BIOMASS
REMOVAL Burial
edimen-
tation

Figure 9. Conceptual model illustrating the effects of environmental forces
on submersed aquatic macrophyte communities. These forces (circles) are se-
parated into three categories of stress: light attenuation, toxicity, and
biomass removal. Lines represent pathways of energy flow and bold arrows may
either reduce flow (indicated by "-" sign) or accelerate flow. Thus all bold
arrows represent stress on the macrophyte community, except for the one indi-
cating a positive feedback of macrophyte. reproduction. Symbols after Odum
(1971).

Environmental factors resulting in biomass removal (Figure 9) are gene-
rally short term so long as the reproduction of aquatic plants is not impair-.
ed. Of these, only burial by sedimentaiton would normally be induced by
human activities, such as dredging and instream mining, while the others are
not amenable to control. Damage to macrophyte communities by the simultan-
eous occurrence of more than one stress should also be considered as a possi-
bility.

With this model as a basis for understanding stresses on submersed plants,
the separation of factors due to human and natural forces is facilitated. The
management of submersed plants in relation to anthropogenic influences is con-
founded by a spectrum of problems associated with many variables such as the
soil types which are disturbed (including aquasoils), the nature of the aqua-
tic system (lotic vs. lentic, etc.) and the nature, time, and duration of the
activity generating the pollution. The resiliency of the submersed macrophyte
system under stress will be related to the ecological tolerance of the spec-
ies present. For example,, northern potamogetons are very sensitive to stress-
es associated with increased suspended sediments. As discussed in other sec-
tions, long term stresses may result in a greatly altered communities where
exotic species often dominate. Under extreme stress by one factor or a multi-
plicity of several stresses, macrophyte communities may cease to exist.

Examples of human activities which may adversely affect natural systems
and their possible effects on submersed plant populations are given in Table
4 along with possible plant community responses. These pertubations are a
function of the stress factors discussed for Figure 9. Literature reviews
relating to the effects of suspended sediments and sedimentation on aquatic
organisms include Cordone and Kelley (1961), Hynes (1970), Baxter (1977),--
Morton (1977), Sorensen et al . (1977), and Stern and Stickle (1978). Esti
mates of the magnitude of pollution of aquatic ecosystems given in Table 4
were compiled mainly from information in these reviews. However, little in-
formation on the impact of changes in aquatic systems affecting submersed
plants was presented. This paucity of research relating to clearcut examples
of the effects of human activities on submersed plant communities is evident
in this review as in others dealing with submersed plants (i.e., Spence, 1967;
Westlake, 1968; Westlake, 1973; Wetzel and Hough, 1973). Evidence that long
term environmental degradation associated with agricultural and urban pollu-
tion contributed to loss of many submersed species was given in a previous
section. Some other examples of community response to stress are cited in
Table 4.

Table 4. Evaluation of the Effects of Various Types of Environmental Alteration on Submersed Plant
Communities

Possible Effects
Environmental Suspended
Alteration Sediments Eutrophication Toxicity Sedimentation Community Resiliency

Instream mining Varies de- Varies depending Low Plants buried by Limited reestablishment
pending on on bed sediments coarse sediments after burial may be
bed sedi- in a downstream possible for forms like
Silviculture ments gradient Podostemum.ceratophyllum
Selective Low Low Low Low Low level continuous sil-
harvest tation may be conducive
to macrophyte establish-
ment
Clear High on Low on long term Low if Variable Impact ameliorated with
ko cutting short term herbicides reestablishment of ground
not used cover
Logging High Low Low High Erosion of ditches and
roads roadbed contributes
sediments

Urban
Construction High High if soils are Low High
nutrient rich
(i.3., phosphate) A few species such as
Potamogeton pectinatus
Waste waters Low High Low Low may survive high levels
(secondary to of urban pollution.a,b,c
treatment) High Recovery of diverse com-
munity possible unless
sediments are toxis
Storm waters High High (continued) High Medium

Table 4. (Continued)

Possible Effects
Envi ronmental T. ,-p e-n d _e T -
Alteration Sediments Eutrophication Toxicity Sedimentation Community Resiliency

Agriculture High High High High Adverse effects would be
minimized with best av-
ailable management tech-
niques; substantial rec-
overy of aquatic system
would be expected from
their application
Road construction High High if eroding Variable High Medium term pulse of pol-
soils are nutri- lution with community re-
ent rich covery expected except in
areas of extreme silta-
tion. Aquatic habitat
Ln
may change due to "dam"
effects of roadbed.
Stream High High Variable High Decreased shading condu-
channelization cive to increased plant
growth but spate stress
increased; gradual recov-
ery of nautral system
possible wit out channel
maintenance.
Dredging of High (short High Varies with Varies depending Subsequent growth of
navigation term and sediment on spoil dis- submersed plants not
channels localized) content posal techni- buried may be enhanced
ques by nutrient enrichment.e
Nearshore Variable Variable Variable Variable Effects vary according
mining to mining method and
control procedures.

(continued)

Table 4. (Concluded)

Possible Effects
Environmental Suspended
Alteration Sediments Eutrophication Toxicity Sedimentation Community Resiliency

Dams and
impoundments
Upstream (lake) High Variable Low High at mouth Establishment of submer-
of rivers sed plants depends on
width of littoral as well
as extent and periodicity
of drawdown.
Downstream High Varies; some Low Low Depends on discharge
nutrient deple- procedure. Extensive
tion in lake plant beds may develop- f
likely
Bulkhead, jetties, Low Low Low Variable Higher wave energy from
groins bukl heads may reduce re-
establishment;g lee
side of jetties and
groins conducive for
growth

aButcher (1933)
bHaslam (1978)
cOzimek (1978)
do'Rear (1975)
eOdum (1963)
fHynes (1970)
gDavis and Brinson (1976)

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CANADA
M Maritime
N North
W West
P Plains
E East CO
GREENLAND G

UNITED STATES
I Northeast
2 Southeast
3 North Central 8
4 North Plains
5 Central Plains 7
6 South Plains
7 Southwest
8 Intermountain
9 Northwest
0 California
A Alaska

Appendix A. Regions of North America that correspond to the distribution
codes of the Appendix B.

Appendix B. Species, Family, Common Name, and Distribution of North American Aquatic
Macrophytes Mentioned in Text. The Distribution Code Corresponds
with Regions in Appendix A Adapted from Shelter and Skog
(1978) Except as Indicated: (*) Fassett (1957)
and (**) Fernald (1950)

Species Family Common Name Distribution

Alisma gramineum var. geyeri J. A.1 ismataceae Narrowleaf Water 1,3,4,5,8,9,0
G. Gmel. Plantain

Armoracia aquatica (Eat.) Wieg. Brassi caceae Lake Cress 1,2,3,6,E

Bi dens. becki i J. Torrey Asteraceae Water Marigold 1,3,9,W,P,E,M

Butomus umbellatus f. vallisneri- Butomaceae Flowering Rush 1,3,9,P,E,M
foTTus L.

Cambomba caroliniana A. Gray Nymphaeceae Fanwort 1,2,3,6

Ceratophyllum demersum L. Ceratophyllaceae Coontai 1 , Hornwort 1,2,3,4,5,6,7,8,9
0,A,H,C,N,P,E,M

Cyperus esculentus L. Cyperaceae Nut Grass, Ground 1,2,3,4,5,6,7,8,9
Almond 0,A,E,M
Elatine minima (Nutt.) F. E. L. Elatinaceae Waterwort 1,3,E,M
Fischer and C. . Meyer

Eleocharis acicularis (L.) J. J. Cyperaceae Slender Spikerush 1,2,3,4,5,6,7,8,9
J. Roem. and Schu'lt. 0,A,N,W,P,E,M,G
Eleocha .s arv la (J. J. Roem. Cyperaceae Dwarf Spikerush 1,2,3,4,5,6,7,8,9,0
and Schult.)- Link W,E,M
Continued

Appendix B (Continued)

Species Family Common Name Distribution

Elodea canadensis Michx. Hydrocharitaceae, Waterweed 1,2,3,4,5,6,7,8,9
0,W,P,E,M

Elodea nuttallii (Planch.) H. Hydrocharitaceae Waterweed 1,3,4,5,8,9,0,E,m
St. John

Eriocau-lon septangulare With. Eriocaulaceae Pipewort 1,2,3,6,E,M
Gratiola aurea Pursch Scrophulariaceae Hedge Hyssop, 1,2,3,4,5,E,M
Goldenpert

Gratiola lutea f. pUsilla Scrophulariaceae Dwarf Hyssop 1,3,E,M*
( F as s e t7t 7-enn e 11 .

Heteranthera dubia (Jacq.) Pontederiaceae Water Stargrass 1,2,3,4,5,6,7,8,9
MacMill. O,E

Hydrilla verticillata Royle Hydrocharitaceae Hydrilla 2
Isoetes. macrospora Durieu Isoetaceae Quillwort 1,3,E,M
Juncus pelocarpus E. Meyer Juncaceae Bog Rush 1,2,3,E,M
Littorella americana Fern. Plantaginaceae 1,2,3,E,M
Lobelia dortmanna L. Campanulaceae Water Lobelia 1,3,4,9,W,P,E,M
Myriophyllum alterniflorum DC. Haloragaceae Li ttl e Watermi I - 1,A,N,P,E,M,G
foil

Continued

Appendix B (Continued)

Species Fami ly Common Name Distribution

Myriophyllum exalbescens Fern. Haloragaceae Northern Watermil- 1,2,3,4,5,6,8,9,0
foil A,N W,P,E,M,G*

Myriophyllum heterophyllum.Michx. Haloragaceae Variable Watermil- 1,2,3,4,5,6,E
foil

Myriophyllum spicatum L. Haloragaceae Eurasian Watermil- 1,2,3,4,5,6,8,9,0
foil A,N,W,P,E,M,G

Myriophyllum tenellum Bigel. Haloragaceae Leafless Watermil- 1,3,E,M
foil

Myriophyllum verticillatum L. Hal oragaceae Whorled Watermilfoil 1,2,3,4,5,8,9,0,A

Najas flexilis (Willd.) Rostk. Najadaceae Northern Naiad, 1,2,3,4,5,7,8,9,W
and ScF-midt Bushy Pondweed P,E,M

Najas guadalupensis (Spreng.) Najadaceae Southern Naiad, 1,2,3,4,5,6,7,8,9
Magnus Bushy Pondweed O,E

Najas minor All. Najadaceae Bushy Pondweed, 1,2,3
Naiad

Potamogeton amplifolius Tuckerm. Potamogetonaceae Largeleaf Pondweed 1,2j3q4y5p7s8s9,0
W,P,E,M

Potamogeton berchtoldii Fieber Potamoge.tonaceae Slender Pondweed 1,2,3,4,5,6,8,9,0
A,N,W,P,E,M,G**

Continued

Appendix B (Continued)

Species Fami ly Common Name Distribution

Potamogeton crispus L. Potamogetonaceae Muck Pondweed, 1,2,3,4,5,6,8,9
Curly Pondweed 0,E,M

Potamogeton diversifolius Raf. Potamogetonaceae Snai Iseed Pondweed 1,2,3,4,5,6,7,8,9,
0

Potamogeton epihydrus Raf. Potamogetonaceae Ribbonleaf Pondweed 1,2,3,4,5,8,9,0
A,W,P,E,M

Potamogeton filifonnis Pers. Potamogetonaceae Threadleaf Pondweed 1,3,4,5,8,9,0,A

Potamogeton foliosus Raf. Potamogetonaceae Leafy Pondweed 1,2,3,4,5,6,7,8,9,
0,A,N,W,P,E,M

Potamogeton friesii Rupr. Potamogetonaceae Fries Pondweed 1,3,4,8,9,A,N,W,P,
E,M

Potamogeton gramineus L. Potamogetonaceae Variableleaf Pond- 1,3,4,5,7,8,9,0
weed A,N,W,P,E,M,G

Potamogeton illinoensis Morong. Potamogetonaceae Variableleaf Pond- 1,2,3,4,5,6,7,8,9
weed 0,A,W,P,E,M

Potamogeton lucens L. Potamogetonaceae Variableleaf Pond- 1,2,3,4,5,6,7,8,9
weed 0,A,W,P,E,M

Potamogeton natans L. Potamogetonaceae Floatingleaf Pond- 1,2,3,4,5,6,7,8,9
weed 0,A,W,P,E,M,G

Continued

Appendex B (Continued)

Species Fami ly Common Name Distribution

Potamogeton nodosus Poir. Potamogetonaceae Longleaf Pondweed 1,2,3,4,5,6,7,8,9
0,W,E,M

Potamogeton obtusifolius F. C. Potamogetonaceae Bluntleaf Pondweed 1,3,4,5,W,P,E,M
Mert. and W. C. J. Koch
Potamogeton pectinatus L. Potamogetonaceae Sago Pondweed 1,2,3,4,5,6,7,8,9
0,A,N,W,P,E,M

Potamoqeton subsection Perfoliati Potamogetonaceae Redhead Grass, 1,2,3,4,5,A,N,E,M
(Includes P. perfoli tus L., P. Claspingleaf Pondweed G
perfoliatus var. bupleuroides
(Fern-T-Fayw., ana P. richardsonii
(Ar. Benn.) Rybd. - -
Potamogeton praelongus F. Wulf. Potamogetonaceae Whitestream Pond- 1,3,4,5,7,8,9,0
weed A,N W, P, E M, G

Potamogeton pusillus L. Potamogetonaceae Slender Pondweed 1,2,3,4,5,6,7,8,9
0,A,N,W,P,E,M,G

Potamogeton robbinsii Oakes Potamogetonaceae Fernleaf Pondweed 1,3,4,8,9,0,A,W,P
E,M

Potamogeton spirillus Tuckerm. Potamogetonaceae Snailseed Pondweed 1,3,4,E,M
Potamogeton strictifolius Benn. Potamogetonaceae Pondweed 1,3,4,5,8,9
Potamogeton zosteriformis Fern. Potamogetonaceae Flatstem Pondweed 1,3,4,5,8,9,0,A,M
W,P,E,M

Continued

Appendix B (Continuted)

Species Family Common Name Distribution

Proserpinaca palustris.L. Haloragaceae Mermaid Weed 1,2,3,6,0,E,M

Ranunculus aguatilis L. Ranunculaceae White Water Butter- 1,3,4,5,7,8,9,0qAs
cup, Growfoot N,W,P,E,M,G

Ranunculus longirostris Godron. Ranunculaceae White Water Butter- 1,3,5,6,7,E*
cup

Ruppia maritima L. Potamogentonaceae Widgeon Grass 1,2,3,4,5,6,8,9,)
A,W,P,E,M

Sagittaria cuneata Sheld. Alismataceae Northern Arrowhead, 1,3,4,5,7,8,9,0,A
CO Duckpotato N,W,P,E,M

Sagittaria graminea Michx. Alismataceae Slender Arrowhead 1,2,3,4,5,6,7,E,M

Sagittaria subulata (L.) Buckl. Alismataceae Water Arrowhead 1,2,9

Scirpgs acutus Muhl. Cuperaceae Hardstem Bulrush 1,2,3,4,5,6,7,8,9
0

Scirpus subterminalis J. Torr. Cyperaceae Water Bulrush 1,2,3,4,9,A,W,E,M

Sparganium anqustifolium Michx. Sparganiaceae Burreed 1,3,4,7,8,9,0,A,N,
W,P,E,M,G

Subularia aguatica L. Brassicaceae Awlwort 1,3,4,8,9,0,A,N,W
P,E,M,G

(conti.nued)

Appendix B (Concluded)

Species Family Common Name Distribution

Utricularia cornuta Michx. Lentibulariaceae Horned Bladderwort 1,2,3,6,0,P,E,M
Utricularia gibba L. Lentibulariaceae Eastern Bladderwort 1,2,3,5,6,0,C,E,M
Utricularia intermedia Hayne Lentibulariaceae Flatleaf Bladderwort 1,3,4,8,9,0,A,N,W
P,E,M,G

Utricularia minor L. Lentibulariaceae Purple Bladderwort 1,2,3,E,M

Utricularia resupinata B. D. Lentibulariaceae Lavender Bladderwort 1,2,3,E,M
Greene

Utricularia vulgaris L. Lentibulariaceae Common Bladderwort 1,2,3,4,5,6,7,8,9
0,A,N,W,P,E,M

Vallisneria americana Michx. Hydrocharitaceae Wildcelery 1,2,4
Zannichellia palustris L. Zannichelliaceae- Horned Pondweed 1,2,3,4,5,6,7,8,9
0,A,N,W,P,E,M

Zostera marina L. Potamogetonaceae Eelgrass 1,2,9,0,A,N,W,P,E
M,G

50272 -101
REPORT DOCUMENTATiO7. REPORT No. 2. 3. Recipient's Accession No.
PAGE FWS/OBS-79/33 1 1
4. Title ;nd Subtitle 5. Report Date
Re ponses of Submersed Vascular Plant Communities to Environ- August 1980
mental Change 6.

7. Author(s) & Performing Organization Rept. No.
Davis, Graham J., and Brinson, Mark M.
4. Performing Organization Name and Address 10. Project/Task/Work Unit No.
Department of Biology
East Carolina University 11. Contract(C) or Grant(G) No.
Greenville, NC 27834 (c)14-16-0009-78-032

(G)

12 Sponsoring Organization Name and Address 13. Type of Report & Period Covered
tastern Energy and Land Use Team, Office of Biological Services,
Fish and Wildlife Service, U. S. Department of the Interior Final report
Route 3 Box 44, Kearneysville, West Virginia 25430 14.

15. Supplementary Notes

16. Abstract (Limit: 200 words)

This report examines the response of submersed vascular plants to changing environmental
conditions, primarily those that affect light transmission. Among the physical factors
considered are fluctuating water levels, currents and waves, and suspended sediments.
Chemical and biological factors affecting plant responses to light conditions are
grwoing season and dormancy, nutrient availability, and plant-animal interactions. Depth
distribution data for many North American species of submersed vascular miacrophytes are
recorded as an indices of resistance to turbidity for some of the most tolerant of the
species. Survival indices were also calculated for several species typically found in
clearwater lakes. Turbidity tolerance and survival indices were then used to identify
groups of species with varying degrees of resistance to ecosystem alterations. The
report concludes with a brief discussion of the potential effects of human activities
on submersed plant communities.

There is a companion document which contains a summary of this literature review. It is
entitled Responses of Submersed Vascular Plant Communities to Environmental Changes:
Summary, FWS/OBS-80/42, August 1980.

17. Document Analysis a. Descriptors
Aquatic Plants, Aquatic Environments, Light Penetration, Light Intensity, Water Level
Fluctuations, Suspended Solids, Waves, Currents

b. 8d;ntr1fi -Endeq Terms
e ;e;60IVn
Su ascular palnts, Aquatic Macrophytes, Light Transmissivity, Turbidity,
Suspended Sediment

c. COSATI Field/Group 43F, 48G, 57H
18. Availability Statement 19. Security Class (This Report) 21. No. of Pages
Release unlimited -Unclassified 79
20. Security Class (This Page) 22. Price
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