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


                                                        /Lj,4 (t
                                         TASK 23







                 ZANNICHELLIA PALUSTRIS: A MODERN AND PALEOECOLOGICAL


                   INDICATOR OF HUMAN DISTURBANCE IN CHESAPEAKE BAY




                                William B. Hilgartner

                               Johns Hopkins University
                                 Baltimore, MD 21218

                                    November 1991




          This research was partially funded through a grant provided by the
          Coastal Zone Management Act of the of f ice  of Ocean and Coastal
          Resource Management, NOAA.



  00



























         QK
         122.8
         H55
         1991











                                              Abstract




                       Title:    Zannichellia    valustris:    A    Modern     and

                       Paleoecological Indicator of Human Disturbance in

                       Chesapeake Bay



                       An examination of Zannichellig palustris from disturbed

                       and undisturbed habitats in Chesapeake Bay reveals

                       differences   in size , and seed production of two

                      .populations, referred to as tall and short forms. The

                       tall form of Zannichellia produces a mean of 13 fruits

                       per plant and the short form 4 fruits per plant, while

                       surface sediments yield 150 Zannichellia seeds per 100 cc

                       where the tall form grows, and 13 seeds per 100 cc where

                       the short form occurs. Seeds of the two forms are

                       indistinguishable morphologically.



                       Robin Cove, a relatively undisturbed embayment, is the

                       habitat of five species of submerged aquatic vegetation

                       (SAV) including the tall and short forms of Zannichellia.

                       The tall form grows in predominantly clay sediment beyond

                       the intertidal zone, and is the dominant SAV where it

                       occurs during May and June. The short form Inhabits the

                       sandier substrates in shallower water and intertidal

                       zones. It is subdominant to Elodea nuttallii. In addition

                       to Zannichellia, surface sediments in Robin Cove







                        contained seeds of 16 species of plants, 71% occurring

                        within a 30 meter radius of the transect.



                        The short form of Zannichellia is the only SAV growing in

                        Brewer Creek, a tributary heavily used for recreation,

                        where it is found in a range of water depths and occurs

                        predominantly in sand. Surface sediments of Brewer Creek

                        contained 6 species of shoreline flora adjacent to the

                        transects.



                       .Distributions of Zannichellia populations indicate that
                        the 'different forms may be used to monitor human

                        disturbance around an estuary. Diversity of seeds in the

                        sediment along with abundance of Zannichellia seeds can

                        also be used as historical indicators of water quality

                        and disturbance in the past.




                              VS DePartment Of Commerce
                              YC'A coaotal services center Litrary
                              2234' South Hobson Avenue
                              Charleston, SC 29405-2413















                                          LISTS OF FIGURES




                       Figure                  Name                        Page

                         1        Mao of Chesapeake Bay                       8

                         2a       Location of Robin Cove                    10

                         3a       Location of Brewer Creek                  12

                         2b       Transects in Robin Cove                   14

                         3b       Transects in Brewer Creek                 15

                         4a       Cross-sections of Transects 1 & 2

                                    in Robin Cove                           17

                         4b       Cross-sections of Transects 3 & 4

                                    in Robin Cove                           is

                         5        Cross-sections of Transects in

                                   Brewer Creek                             19

                         6        Morpholoqy of Fruits of Zannichellia      20

                         7        Core SR3a from Brewer Creek               39

                         8        Distribution of Z.p. from Cores           44

                         9        Core CHR6c from Langford Creek            46

                         10       Core SRla from Severn River               47

















                                                iv












                                          LIST OF TABLES




                      Table                   Name                        Page



                      la         Percent Cover, SAV in Robin Cove          23

                      lb         Percent Cover, SAV in Brewer Creek        24

                      2          Mean Water Depth                          26

                      3          Number of Seeds in Sediment               27

                      4          Percent Cover   Percent Seed Number       29

                      5          Fruit Length   Rostrum/Fruit Ratio        32

                      6          Stem Length   Number of Fruits            33

                      7          Height of Zannichellia Plants             34

                      8          Sediment Descriptions                     35















                                                  TABLE OF CONTENTS


                                                                                        Page




                                  ABSTRACT                                              ii         

                                  ACKNOWLEDGEMENTS                                      iv 

                                  LIST OF FIGURES                                        v   

                                  LIST OF TABLES                                        vi

                                  TABLE OF CONTENTS                                    vii

                           INTRODUCTION..................................................1

                           GROWTH FORMS & ECOLOGY OF ZANNICHELLIA........................4

                           AREA OF STUDY.................................................6

                                Robin Cove...............................................9

                                Brewer Creek.............................................8

                            METHODS.....................................................13

                                Field Sampling..........................................13

                                Laboratory Analysis.....................................16

                                Statistical Analysis....................................22

                           RESULTS......................................................22

                           DISCUSSION...................................................36

                           CONCLUSION...................................................48

                           LITERATURE CITED.............................................50

                           VITA.........................................................57













                                                           vi









                      INTRODUCTION



                      Declines in populations of submerged aquatic vegetation

                      (SAV) in Chesapeake Bay, particularly in the 1960's and

                      1970's, have been attrib uted to changes in water quality,

                      primarily increased eutrophication and turbidity from

                      anthropogenic activity (Orth and Moore 1983; 1984;

                      Stevenson and Confer 1978). The decline in areal coverage

                      and number of species affected has been unprecedented.

                      However, studies of SAV in lakes have shown that

                      eutrophication and turbidity are not always followed by

                      a decline in SAV abundance. Rather this kind of

                      disturbance    tends   to    promote   the    growth     of

                      environmentally tolerant, eutrophic species with a

                      widespread distribution, at the expense of local, endemic

                      species, while a concomitant decline in species diversity

                      occurs (Ehrenfeld 1983; Jupp and Spence 1977; Morgan and

                      Phillip 1986; Stuckey 1971; 1978).



                      One such SAV which is widespread geographically         and

                      appears to have a tolerance to eutrophication and human

                      disturbance is Zan_nichellia palpstris. It is nearly

                      cosmopolitan in distribution, occurring over a wide

                      temperature and- salinity gradient. Populations have

                      increased or remained constant in eutrophic waters of

                      western Europe (Van Vierssen 1982b), Scotland (Jupp and

                      Spence 1977), and in lakes in the central United States




                                                                                   2



                        (Lind and Cottam 1969; Stuckey 1971). In Chesapeake Bay,

                        Zannichellia is not present in some eutrophic tributaries

                        and since the 1960's has been increasing in other.

                        nutrient-rich areas, leading some investigators to

                        believe that Z., palustris is an ephemeral, pioneer

                        species (Stevenson and Confer 1978).



                        The fossil record of Zannichellia palustris seeds

                        however, shows that the species has been a persistent

                        occupant of Chesapeake Bay for over 2000 years, with some

                        fluctuations in populations related to climatic events

                        and human activities (Brush, Hilgartner and Thor    ton in

                        prep). Changes in fossil seed numbers indicate a general

                        expansion during European colonization in the mid-1700 I a,

                        when increased siltation and nutrients from runoff of

                        agricultural land occurred throughout much of Chesapeake

                        Bay (Brush 1984a; 1984b; 1986; 1989; Brush and Davis

                        1984). Following this period and until about 1970, seed

                        influxes decreased with intensification of agriculture

                        and expansion of'urban development. Since the 197019, the

                        range of Zannichel-lia Valustris     has expanded in the

                        lower tributaries of the western shore and in Chester

                        River (Fig. 1), while declining in the upper stretches of

                        many tributaries.



                        While an appreciable amount of information concerning the

                        autecology of Zannichellia is available (see Stevenson





                                                                                 3



                       and Confer 1978; Van Vierssen 1982a; 1982b; 1982c),,

                       knowledge of its precise ecological requirements in North

                       America is lacking. Both growth forms have been described

                       from Europe, but the ecology in Europe differs from what

                       has. been observed in Chesapeake Bay (Hilgartner pers.
                       obs.). For example, Z. palustris in Europe is generally

                       confined to freshwater, a stratification period of 2
                       months at 40C is required for the seeds to germinate in

                       early spring, and the tall form is considered a perennial

                       while the short form is considered an annual (Van

                       Vierssen 1982a). In Chesapeake Bay, 1. @alustris is most

                       common in brackish water with a salinity tolerance of up

                       to 20 ppt.,- germination appears to occur in late summer

                       when no stratification period is required, and the tall

                       form is evidently annual, dying back by early June

                       (Stevenson and Confer 1978; Hilgartner, pers. obs.) . The

                       relationship of disturbance,, sediment, wave action, water

                       depth, and water quality as well as seed production and

                       fossilization, with growth patterns of Zannichellia,

                       Palustris needs to be more clearly defined.



                       The purpose of this study was to explore the possibility

                       of using population characteristics of Z. palustris as

                       an indicator of water quality in Chesapeake Bay.

                       Zannichellia vegetation and associated SAV were compared

                       in two sites that differed in the degree of anthrop  ogenic,

                       disturbance. The relationship of plant cover, seed





                                                                               4



                      production and seed abundance in surface sediments of

                      Zannichellia was compared to plant cover and seed

                      abundance of associated species. The broad spatial

                      distribution of Zannichellia, its abundant seed record in

                      sediments, a nd response . to changes in water quality

                      suggest that a few simple measurements of plant growth

                      and/or seeds in surface sediments might serve as a water

                      quality monitoring tool. Additionally, seed numbers along

                      with associated flora, could be used to refine analyses

                      of environmental changes in the paleoecological record.











                      GROWTH FORMS AND ECOLOGY OF ZANN ICHELLIA PALUSTRIS



                      zannichellia palustris, is cosmopolitan in distribution,

                      occurring throughout Eurasia and the Sahara, North

                      America from Alaska to Guatemala in the northern

                      hemisphere, and in South Africa, India, Madagascar, and
                      New Zealand in the southern hemisphere, being absent only

                      from Australia and the tropics (Haynes and Holm-Nielson

                      1987;   Ridley   1930).  This   wide   distribu
                                                                      tion    of.

                      zannichellia has presented problems concerning its

                      taxonomy and ecology (Van Vierssen 1982a) . In western

                      Europe, where there are four taxa. of Zannichellia,





                                                                                5


                       palustris occurs in two growth forms       (Van Vierssen

                       1982a,1982b). The short, creeping form, Z-12. repens, is

                       an annual that occurs in northern latitudes. in a wide

                       range of water depths from near water edge to depths

                       greater than 1 meter. These plants are tolerant of

                       disturbances by current and wave action. The tall form,

                       7.p. palustris, grows more than one meter in length in

                       water depths of 1.85 m, and behaves as a perennial. Both

                       forms are found primarily in fresh water, being

                       intolerant of salinities > 3.5 ppt. Seeds must undergo a
                       stratification period of two months at 4      0 C before

                       germination the following spring.



                       By contrast, in North America, Zannichellia consists of

                       a single annual species YL. valustris, which reproduces

                       solely by seeds (Haynes 1988; Haynes and Holm-Nielsen

                       1987). Like its counterpart in Europe,, there are two

                       growth forms in Chesapeake Bay, a prostrate form and an

                       upright form (Hurley 1990). Stevenson and Confer (1978)

                       noted that the species is never found where wave action

                       is significant.



                       Zannichellia generally grows in shallow, quiet water 0.5

                       to 1.5 m deep and occurs in a wide salinity range from

                       freshwater lakes high in sulfate ions in Minnesota to

                       mesohaline waters of estuaries in salinities up to 20 ppt

                       (Lind and Cottam 1969; Moyle 1945; Stevenson and Confer





                                                                               6



                      1978; Hurley 1990). Seed germination can occur during the

                      year of deposition. Two fruiting and growth periods, one

                      in late spring and one in late summer have been reported

                      (Stevenson and Confer 1978), but Z. palustris has been

                      observed in fruit each month from May to October in

                      Chesapeake Bay (Hilgartner, personal observation).



                      It is possible that the short and tall forms in

                      Chesapeake Bay are homologous to the two subspecies

                      Z-2.repens and Z-2-palustris found in Europe. However, it

                      has been suggested that these two forms could also

                      represent two species (Haynes, pers comm) . Also possible

                      is that these forms represent ecotypes or climatic races

                      (Clausen et al 1941) or environmentally induced growth

                      forms called ecophenes by Mooring et al (1971), similar

                      to those which occur in the two growth forms of gRartina

                      alterniflora.









                      AREA OF STUDY




                      To assess the effects of human activity on Zannichellia

                      palustris, populations were examined in a disturbed and.

                      undisturbed tributary.     In this study, disturbance

                      includes heavy recreational use and proximity to

                      -residential development.   Recreational   factors that




                                                                                  7


                       directly affect submerged vegetation include motorboats,

                       which tear and uproot plants and produce exhaust gases

                       and engine oil which have detrimental effects    on plants.

                       Dredging, retaining walls, boat docks and foot traffic

                       all affect shallow-water habitats (Stuckey 1971; 1978).

                       The residential community also stresses organisms by

                       affecting water    quality through septic systems and

                       runoff. The Chester River on the eastern shore and Severn

                       River on the western shore of Chesapeake Bay were chosen

                       for the study (Fig. 1) . Human activity along the Chester

                       River is primarily rural. Large tracts of privately owned

                       land are used for agriculture, game management' and

                       private use. There are numerous isolated coves and

                       tributaries. On the other hand, heavily residential

                       development including the city of Annapolis characterize

                       the environs of the Severn River.



                       Brewer Creek,, a small tributary of the Severn River,

                       supporting heavy boat traffic and dense residential use,

                       is the study site for the disturbed tributary. Robin

                       Cove, near the confluence of the Corsica and Chester

                       Rivers, surrounded by marshland and loblolly pine is the

                       study site for the relatively undisturbed environment. Z.

                       nalustris grows in both tributaries.




                                                                                                                                  8



                                                                                        W1001








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                                                                                                tdr -
                                                                                                                                      39'
                                                    WASHINOTON':-*.:@-'@!'-'
                                    Me









                                                                                                 :17












                                     Oly

















                                     370
                                                                                                                                       00f


                                                                                            A -
                                                                                         FOLX'
                                                                                        R
                                         L
                                                      7 =POIY                               76-100!                          7 5. loop
                                   r






























                                     Figure 1.     Map of Chesapeake Bay, showing           location of Chester and Severn Rivers





                                                                                  9


                       Robin Cov2 (39*04"N and 76*09'W) (Fig.2a)



                       This protected tidal tributary runs through Corsica Neck,

                       a peninsula at the confluence of the Corsica and Chester

                       Rivers. It is underlain predominantly by Quaternary

                       lowland deposits of gravel, sand, silt and clay (Cleaves

                       et al 1968), and surrounded by tidal marsh on the north,

                       east and south sides, and forest dominated by Pinus taeda

                       (loblolly pine) and Licruidambar styraciflua (sweetgum) on

                       the southeast side. The cove has been privately owned at

                       least    since    1928    (Peter    Sheaffer,,     personal

                       communication). Maps   from 1860, 1915., and 1951 show

                       virtually no change in the configuration of Robin Cove or

                       in the surrounding land use during.the past 130 years. On

                       the Besley Map of 1915, the pine forest is clearly shown

                       where it exists today. On the north and east  sides of the

                       cove is a private game management farm abutting the

                       surrounding marsh. The closest residence is about 0.5 km

                       distant.   A wooden structure built in the 1950's,

                       prevents boats from entering the mouth of the cove, but

                       does not disrupt the natural ebb and flow of tides.



                       The sediment where SAV grows is predominantly soft clay

                       mixed with some sand, into which a person can sink to 25

                       cza in some places. Dominant emergent vegetation growing

                       in, or just beyond the intertidal zone includes Spartina

                       alterniflora,    patens, fi. cyansuroides, Lva frutescens.
























                                              LANGFORD  CREEK




                                                                .76
                                                                -7,












                                          CHESTER RIVER                                                             CORSIC

                                                                J-1





                                                                                 ROBIN COVE








                                                                                                              Corsica Nee

                                   Figure 2a. Map showing location               of  Robin Cove







                       Acnida cannibina and Aster tenuifolius. Five species of
                       submerged angiosperms were observed growing along the

                       northeast shore: Zannichellia palustris (both short.and

                       tall    forms),    Elodea   cf.    nuttallii,     Potamogeton

                       perfoliatus, Myriophyllum spicatum and Ruppia inaritima.

                       The above suite of species is typically found in an

                       average annual salinity range of 9-14 ppt (Phillip and

                       Brown 1965).



                       Elodea nuttall-A was distinquished from        canadensis on

                       the basis of leaf size and salinity Aolerance.

                       nutal lii is found in salinities of 14 ppt; B. canadensis

                       cannot tolerate salinities > 3.6   ppt (Cook and Urmi-Konig

                       1985; Phillip and Brown 1965).






                       Brewer Creek (39002'N and 76*32'W) (Fig.3a)



                       Brewer Creek, a tidal tributary of the Severn River, is

                       surrounded by steep slopes of upper Cretaceous fine to

                       coarse grained sand (Cleaves et al 1968; Vokes and

                       Edwards 1974). Sherwood Forest, a community of summer

                       homes established in 1920's is surrounded by mature

                       Quercus spp. (oaks) and Liriodendron tulipifera, (tulip

                       tree). Boat traffic is heavy and is accomodated by boat

                       marinas. There is frequent foot traffic on the firm, fine









































                                             ZRMnM CR=













                                                            SL"n= RIVER











                          km



                                Figure 3a. Map showing location of Brower Creek




                                                                                13


                       intertidal sand. Scirpum americanus and an unidentified

                       grass are the dominant emergent plants growing in the

                       intertidal zone. The short form of Z. nalust  ris was the

                       only SAV observed at the site during the summers of 1987

                       and 1990.










                       METHODS




                       Field sampling



                       Vegetation:   Percent cover for all SAV was determined

                       from 1 m quadrats spaced at 5 m intervals along transects

                       ranging in length from 10 to 40 m. In Robin

                       Cove, 16 quadrats were sampled along 4 -transects. The

                       transects were made by walking one meter away from the

                       transect line in order to minimize disturbance of plants

                       within the quadrat. Two transects, were run through beds

                       of tall Zannichellia. palustris adjacent to a sand bar,

                       and 2 transects, were run through beds of short 7,L.

                       valustris in shallower water (Fig. 2b). In Brewer Creek,

                       nine quadrats were sampled along three transects

                       positioned perpendicular to the shoreline and 1 transect

                       parallel to shore (transect 4) (Fig.3b). Data collected

                       from quadrats in transect 4 included only plant cover and

                       buried seeds. Each 1 m2 quadrat was divided into one





                                                                                                14














                                                                        4
                                                                           5



                                          high marsh


                                                              Tr eect 3


                             wooden             Zplf           ZpT
                             bulkhead

                                             Tr &an 0 e"o t      Zp?


                                                        Trangect 2          ROBIN COVE
                              high marah" -L


                                                        loblolly pine
                                                        woodlan






                           ZpS, Zamichellia plLustris (short form)
                           ZpTi Zannichellia p1ju_strie (Tall form)
                               4 Quadrat











                            Fl&re 2b. Location of transects in Robin Cove



















                                                                         Tulip-oak forest




                                                                                             zPS           1 2 3




                                                zPS                             boat pier


                                      Transoot 3            Transoot I
                                                Traftsect 2

                     b oat piers








                                          ZpSs   Zamichellia yalustrLe Cabe" form)

                                          *-I Quadrat






                                           Figure 3b. Locations of transects in Brewer Creek




                                                                                 16



                      hundred 10 cm X 10 cm units. The number of units in which

                      a species occurred in each quadrat provided the measure

                      of percent cover for that particular species. Total

                      percentage in each quadrat could exceed 100%. Height of

                      plants within quadrats and along transects was also

                      measured: Depth of water at high tide was measured.

                      Samples of  both forms, of Zannichellia were collected.

                      other species growing at the site but not included in the

                      transects were recorded. Transect cross-sections are

                      shown in Figs. 4 and 5.



                      Sediment: Surface sediment samples were collected from

                      randomly chosen points within each quadrat for seed

                      analysis. A short tube with a piston was inserted into

                      the sediment,, which when extruded, provided a sample 2 cm

                      long. The sediment sample was placed in a ziploc bag,
                      labeled, and stored at 4*C in the laboratory.



                      Laboratory Analysis



                      Seeds (fruits) on plants:      The fruiting structure of

                      Zannichellia has been referred to as an endocarp, achene,,

                      and nutlet (Fernald 1970; Gleason 1952; Haynes and Holm-

                      Nielsen 1987; Montgomery 1977; Pierce and Tiffney 1986;,

                      Ridley 1930). The general term 'fruit' is used here (Fig.

                      6). Morphometrics conforming with Van Vierssen (1982a)

                      include number of fruits, fruit length, fruit rostrum



                                                                             mm man










                    Zannichellia 'Dalustris (Ull form)


                    Transect I                              Quadrat I             Quadrat 2               Quadrat 3
                                                                                     10 A                   15 a

                                                                                                                     W.

                                                                                        +
                                S 41 *a--




                             2
                           F-med sand j   I   pasid  I                      sort =CAY





                     Transect 2                              Quadrat I             Quadrat 2               Quadrat 3
                                                                                     10 a                    15A






                              2 a

                              mod  *an?i I  I sand I                         soft CIOX




                                   Zannichgllift RAIUSIcks           44 Xyrimllyll- siAc

                                   mode nutta""                           UAW& G&CLIL"



                                            Figure 4 a. -Crose-s*ctions ok Transects I and 2 in            Robin Cove













                       Zasmichellia Ralustri (short @orm)



                 Transect 3
                                      Qu@dr I                  Qua rat     W.I. at high tide
                                                                 74a




                                                  si6nd im clay






                 Transect 4                          4U&4rat I             Quadrat 2             Quadrat 3
                                                       5a                   10 a                   15 a




                           peat                                         son clay# silt and sand


                            Quadrat              Quadrat 6            Quadrat 7
                             25's                  30 a                 35a

                                                       2k


                                         Soft GI!q, Gilt WA SAA4               r P*&



                            Figure 4 b. Cross-sections of Trans*c-ts 3 and 4 In Robin Cove




                                                                                                                        19








                                                                                        Quadrat I                     Quadrat 2
                                    Tmneect 1                                              5 a                           10
                                                     bank           lal


                                                  L 2 a



                                                                                        Quadrat I                      QuWat 2
                                    Transect 2                                                                            10







                                                  L







                                                                                                                       Quadrat 2
                                      Transect                                          Quadrat 1                        10 a









                                                                                 silt and sar





                                                                                pi         (ah
                                                                                 klustris    ort form)

                                                                  SeIrpus americanue







                                                   Figure 5. Cross-section's of transects In Brewer Creek
                                                     bmk




                                                                                           20











































                         Figure 6. Morphology of fruits of Zannichellia Palustris. Fruits on
                                   left show location of rostrum and fruit length measurements.
                                   Fossil seed on right shows the typical appearance of seeds
                                   found in sedimentl with teeth along the convex margin.





                                                                                 21


                       length, and the ratio of rostrum to fruit length. Number

                       of fruits per cm of internode is multiplied by the mean

                       height of plants in the quadrats to arrive at an estimate

                       of the mean number of fruits per plant. Morphological

                       features, such as teeth along the convex margin of the

                       fruit, were also noted, in an attempt to distinquish the

                       seeds of the two growth forms.



                       Seeds in Sediment:       The term 'seed' includes any

                       angiosperm   fruiting   body   retrieved    from    surface

                       sediments,   often   referred    to   in   paleoecological

                       literature as macrofossils. A subsample of each sediment

                       sample was placed in a measured volume of 10% HN03. The

                       volume of the subsample was measured by the amount of

                       displaced liquid. The sediment was allowed to remain in

                       the acid for 2 hours, whereupon it was wet-sieved through

                       two nested sieves. Seeds were isolated and examined under

                       1OX   and    40X   magnification.    Identification     was

                       accomplished using the seed reference collection at the

                       Johns Hopkins University and seed identification keys

                       (Gleason 1952, Martin and Barkley 1973, Montgomery 1977).



                       Sediment: Sediment samples from selected transects were

                       examined under 15X magnification to estima  te the percent

                       sand in the substrate. Randomly chosen sand grains from

                       each sample were measured with a dial caliper to arrive

                       at a mean grain size for sand.





                                                                               22



                       Statistical Analysis




                       A Pearson-r  test was used to examine the correlation

                       between seed numbers in the sediment and percent cover of

                       Zannichellia in each quadrat. A t-test was used to test

                       the difference in means between rostrum-fruit ratios of

                       the short and tall forms of Zannichellia, the null

                       hypothesis being that the rostrum: fruit -ratios are the

                       same for both forms. A t-test was also used to test the

                       difference between mean number of seeds of Zannichellia

                       in all sediment samples in Robin Cove and Brewer Creek,

                       the null hypothesis being that there is no difference

                       between seed numbers in either area.







                       RESULTS



                       SAV ComRosition And Cover (Tables la and lb):



                       Five species of SAV were identified in Robin Cove where

                       greatest diversity occurred along transect 4. Percent

                       relative cover was highest for Zannichellia palustris in

                       transects 1 and 2, and Elodea.nuttallii in transects 3

                       and 4. Potamogeton Derfoliatus. Mvriophyllum spicatuM and

                       Ruppia maritima were each represented by < 10 relative

                       cover. Zannichellia palustris was the only SAV observed

                       in Brewer Creek.














                  Table IA.. Percent cover and percent relative cover of SAY in Robin Cove and Brewer Creek.
                             Zps Zanh@cheljja galustris (ZpS      short form* ZPT - tall form)l Rm a RUDDia marlilmat
                             Me a Myrio    llum spicatuml En    Elode nuttalliii PP - Potamoxeton T)erfolTatus.

                  Robin Cove (Percent cover)
                                             Tall form beds                             Short form beds
                             Transects       Tr I            Tr 2                   Tr 3             Tr  4
                             Quadrats*    1   2   3        1   2    3   4         1   2         1   2    3   4    5   6    7

                             ZP           24  68  20       60  34   20  43        0   52        25  0    0   20   10  40   0
                             RM           0   0   0        0   0    0   0         0   0         0   0    0   17   15  0    0
                             Ms           1   8   13       2   0    0   2         3   2         3   1    12  8    2   6    0
                             En           100 1   0        58  16   12  0         12  0         19  26   4o  8    14  50  100
                             PP           0   0   0        0   15   0   0         0   20        0   24   0   0    20  0    0
                  Robin Cove   (Percent relative  cover  of SAV)
                             Zp           ig  88  61       50  52   62  96        0   70        53  0    0   38   16  42   0
                             Rm           0   0   0        0   0.   0   0         0   0          0  0    0   32   24  0    0
                             Ms           1   10  39       2   o    o   4         20  3         6   2    23  15   3   6    o
                             En           80  1   0        48  23   37  0         80  0         40  63   77  13   23  52 100
                             PY,          0   0   0        0   23   0   0         0   27        0   58   0   0    33  0    0
                  Robin Cove (Mean percent    cover for  each transect)           (@Iean percent relative  cover  - tranGects)
                             Transects    1   2    3     4--  Mean                1   2    3   4.  Mean
                             ZpT          37  Z9   0     0    38                  36  63   0   0   60
                             zPS          0   0    26    V+   20                  0   .0   35  21  28
                             RM           0   0    0     5    1                   0   0    0   8   2
                             Me           7   1    2     5    4                   17  15   11  8   9
                             En           34  21   6     37   24                  27  28   40  39  33
                             Pp           0   4    io    6    5                   o   6    13  13  8





                                                                                      25


                         The short form of YL. 2alustrin (ZpS) occurred in

                         transects 3 and 4 in Robin Cove, and in all transects in

                         Brewer Creek. The tall form of yL. 2alustris (ZpT)

                         occurred in transects 1 and 2 in Robin Cove and was not

                         observed in Brewer Creek. At Robin Cove, Zp   T was dominant

                         in transects 1 and 2 until ' 15 June; &. nuttallii was

                         dominant and ZpS was second dominant in transects 3 and

                         4. After - 15 June when ZpT died back, Elodea became

                         dominant in transects 1 and 2. Although ZpS populations

                         changed somewhat in transects 3 and 4 throughout the

                         sum,mer, Elodea remained dominant.



                         Water Depth and the Occurrence gf Zannichellia (Table 2):



                         In Robin Cove, ZpT grows in depths ranging f    rom. 0.70 and

                         1.20 meters, but grows most abundantly about 1 meter

                         (between 0. 96 and 1. 10 m) . ZpS grows in shallower water

                         ranging from 0. 35 to 0. 60 m, occurring most abundantly at

                         0.4 m. In Brewer Creek, where only ZpS was observed, it

                         was  found in water ranging from 0. 3 to 1. 4 ri and was

                         most abundant between 0.65 to 0.70 m.





                         Seed Num bers in Surface Sediments (Table 3):



                         six species of SAV and eleven species of emergent plants

                         are represented by seeds buried in surface sediments at




















                  Table 2. Mean depth at high tide for all transects perpendicular to shore, and depth at which
                            Zannichellia has the highest percent cover along each transect. Tidal range is 0.50                      m.



                                                                              Robin Cove                               Brewer Crook


                                                                          2            3                                        2            3

                  LenjIth of transect (a)                     is          20                        38            to            10           10'
                  Mean depth along Transect. (a)              0.94        0.94         o.48         o.46          0.78          0.78         0.72
                  Standard deviation (t)                      0.23        0.24         0.07         0.12          0.39          0.45         0.39
                  Range of depth where Zp occurs (m)     0.71-1-19    0.94-1.14    0.35-0-46    0.42-0.59    0.33-1-40     0.32-0.94    0.29-0-87
                  Depth of highest % cover - ZPT (m)          1.10        o.96
                  'Depth of high'est % cover - ZPS (a)                                 o.43         0.44          0.71          o.68         o.65
                  Highest   cover                             68          60           52           40            79            82           25
















                         Table 3.    Number of weds 2W m' of emorpent and submerged veptafion in "diments aloog WSMOCEL. Oubdrats am          5 mcccr inter4ah, cxccpt in trw@ 3.
                                     the 2 quadrats am 7 vactm apaxt           kadvAuk ") Rum- XMIUMA M4116). EQMM= 201WWW (E. Md,). Pot-o-tan 22%iMW M 921Z).
                                     Eotamoret2a 6P. M OP,). HUM OAdd=MVi (U@6 SO= &M M&). SO= M?l (& SP6). In frutesce- (Lf.). rbagmitu Sp. Irphraff- Sp.). G
                                     (Gram.), P-ly-on- 02ga= M21m 2MI.). Cyporacew (CYPcrw-). CAM SP- fkQdWkdA 2M32k CP-&)- RRbM RIM V- LldQdMW= DJiWfM G;&)- Q=
                                     lan" (Q.). ZWMMM OP- (EMU SP-N IMM OP- MM SOAQ= AWQ9W

                                                                                                   Robin Crock


                                             Tr I                         Tr 2                     Tr 3                      Tr 4
                         quads           2        3          1       2       3       4           1       2           1       2       3       4    5    6         7

                         M2.             173      11S        2V      144     71      223         13      64          67      105     4W      197  &S   83        69
                         a.m.            50       20         12      83      35      64          9       59          48      24      91      25   6    12        20
                         E-22d-          9        10         25      6       12      5           4       14          24              9       17   13   4
                         E-22Z.                                                                                                      .13     12
                                                  5          4               5
                                         5        5          19      27      29      73                              14      19      74      4    9      4       4
                         12.                                                                                                 5       35      17   18     29      06
                         5-Sp.                               4                                                               9                    24
                         1-f-                     5                                              4                   5       9
                         Eunip.                                                                  9       5           5       5
                         Gram.                    5                                                      9                   9       9                           4
                         f2bi.m.                                                                         5           5               4                   4
                         Cypcrac.                                                                        9                           9                   4
                         Cum 'p-                                                                                             5
                         Liz.                                                                                                9       13      4                   4
                         Rub                                                                                                         9
                         EUM Sp.                                                                                                     4
                         Unknown                             12              6                   5       9                   5       26      4

                                                                                                   Bnmor Crock

                                             Tr I                           Tr 2                         Tr 3                                   Tr 4
                         quadrats            1    2                       1     2                        1   2 3                             1    2    3

                         L2-                24    17                      25    11                       10  6 6                             11   21 5
                                            8                             11                             5   17
                                                  4
                                                                                                         5
                         Gram.                                                                           5
                         EM-sp-                                                                              6
                                                                                                                                                       10




                                                                                28



                       Robin Cove. Greatest diversity occured along transect 4,

                       where 16 species of seeds were recovered. Seeds of

                       Zannichellia represented the highest percentage of buried

                       seeds in all .4 transects. Seeds of Ruppia were the next

                       most common. Seeds of emergent species represented 13% of.

                       all seeds recovered, but represented 23% of the seeds in

                       transect 4. The      most abundant     emergent    species

                       represented by seeds was Scirpus olneyi.



                       The only SAV species represented by seeds in Brewer Creek

                       is Zannichellia. This is-consistent with the plant cover

                       for  Brewer Creek.   In addition,, six other species

                       represented by a few seeds included sedges, grasses, and

                       tulip tree from the neighboring shoreline vegetation.




                       RelationshiR Of Pla6t, Cover to Seed Number (Table 4):



                       A greater number of species were represented by seeds

                       than by plants at both locations. In Robin Cove, 5

                       species of plants were recorded in the vegetation and 17

                       species by seeds in the sediment. The five species

                       represented in the vegetation quadrats were SAV, while 6

                       of the 17 species from seeds belonged to SAV. The

                       remaining eleven species were   represented by seeds of

                       nearby marsh emergents not represented in the quadrats.

                       Highest number of both plants and seeds, were found along




                                                .*Nam MMMMMMMM MM









                Tabl e 4. Comparison of mean percent relative cover and mean PDrOGnt of relative        seed number in
                          Ro*bin Cove. C w covers S a seeds$ (a)       submerged plants (e)    emergent plant.




                                                                                                                          Mean
                                          Tr 1                Tr 2                Tr 3                Tr 4                Total
                                          C,                  C        S          C                   C        S          C .  S
                                          56       72         63       59         35       34         21       33        .44   55
                                          0        17         0,       20         0        30                  12         2    20
                MXrio h llum (a)          17       0          1        0*         11       0                   0          9    0
                Elodea 9                  27       0          27       0          40       0          39       0          33   0
                =Oamoget. Perf.    (a     0        5          6        4          13       8          13       3
                Potamoset. R!Lct.  (S@    0        0          0        0          0        0          0        1
                FotamgAe    op. (S)       0        1          0        0          0        2          0        0
                                          0        2          0        14         0        2          0        7          0
                 gJaS guad (a)                                                                                            0    36
                      *-- -- nqyl to)     0        0          0        0          0        0          0        14         0    1
                -11va f                   0        1          0,       0          0        2          0        1
                      rutes. (e)                   0          0        0          0        6          0        0          0    1*
                -f-hraZTt7e--q (a)                                                                             a          0    7
                Others (e)                0        1          0        2          0        16         0





                                                                               31


                     Fruit  Morphology Aad Production 2f Zannichellia:



                     Measurements of rostrum length and fruit length of both

                     forms of ZannichelliA (Fig.6) were made in an attempt to

                     separate the two forms by seed morphology (Table 5). The

                     mean ratio of rostrum length to fruit length in ZpT is

                     0.64 and in ZpS is 0.59. A t-test shows no significant

                     difference between the two means (t(81) = 0.325, p> .05).

                     Both forms produced fruits that were dentate or entire

                     along the convex margin.



                     Number of iruits per cm of internode was 0.2 for ZpT and

                     0.4 for ZpS (Table   6). When frui ts per cm of internode

                     are multiplied by raean height of the plants,           ZpT

                     produces a mean of 13.2 fruits per plant, and ZpS 4.2

                     seeds per plant (Table 7).



                     Sediment Description (Table 8):



                     The preliminary analysis of sediment indicates that ZpT

                     grows primarily in mud with 5 - 15% sand. In Robin Cove,

                     ZpS grows in a sand-mud mixture, with sand comprising ca.

                     75% of the sediment. In Brewer Creek, ZpS grew in

                     sediment that was 100% very fine to coarse-grained sand.

















                            Table    Comparison of fruit length, rostrum length
                                     and the ratio of rDstrum to. fruit length in
                                     Zannichellia valustris.

                                     Mean fruit        Mean rostrum       Rostrums
                                     length (mm)       length (mm)        Fruit ratio
                            ZpT          2.99             I-.go              0.64
                            (n-40)
                            ZPS                           1.69               0.59
                            (n=43)

















                                                                                                        bj


















                                                   ers of fruits in Zannichelli palustriS-
           Table 6. Comparison of stem lenXth to numb



                   Total length     Total         Number of          Mean hei4it    Mean number
                   of all           number of     fruits per         of plants in   Of fruits
                   internodes       fruits        internode          quadrats       per plant
                   (cm)                           length uits/cm)    (cm)
                                                  (no. fr

            ZpT    25o.6            49            0.2                66.0.          13.2
            ZPS     99.6            43            o.4                io.4            4.2














                        Table 7. Maximum beigm of                          *m&%%wmwU inems. P6nuinUwwd                   4 w= Stesumd CVWY 5 Mdal. at SR Ww MA=Wcb- PW" Wwe acowed
                                        at I meter intervNIL


                                                                                                           RoWn Cove


                                                             tau fam                                        abort form
                              meters                 trails" I        umsea 2                                3          amnscot 4

                              0                          0                 0                            0
                              1                          0                 0                            0
                              2                          0                 0                            0
                              3                          45                60                           0
                              4                          87                60                           0
                              5                          56                55                           0                 20
                              6                          100               50                           0
                              7                          70                0                            10
                              8                          70                65
                              9                          66                58
                              10                         75                60
                              11                         70                0
                              12                         78                45
                              13                         as                60
                              .14                        LID               0
                              15                                           40
                              16                                           60
                              17                                           70
                                                                           66
                              19                                           58
                              20                                                                                         10


                                                                                                          Bovww Crook


                              meters                                                                                    2                                   auvaoct 3
                                                                           0                                            0                                   0
                              2                                            0                                            0                                   0
                              3                                            0                                            25                                  0
                              4                                            13                                           9                                   8
                              5                                            9                                            16                                  20
                              6                                                                                         8                                   24
                              7                                                                                         9
                              8                                                                                         0                                                                                           A.
                              9                                            6                                            0                                   0
                              10                                           .6                                           0                                   0














             Table 8. Sediment descriptions. Sediment type, estimated % sand, and sand grain size,
                        where Zannichellia is rooted. All measurements made at 15X magnification.




                    Tributary          Sediment type &         Estimated       Sand grain
                    transect &         general descrip.        percent         size
                    quadrat                                    sand            (mm)


             ZpT    Robin Cove         mud; material           5                not measured
                    Tr 1, 15 m         too fine to
                                       discern indiv.
                                       grains
                    Tr 1, 10 m         mud; with some          15               range - 0.1-0.8
                                       sand                                     mean - 0.43

             ZpS    Robin Cove         sand--=d                75               range - 0.25-0-70
                    Tr 3, 7 m          mixture                                  mean = 0.44

                    Tr 4. 5 m          sand-mud,               75               range = 0.20-0.60@
                                       mixture                                  mean = 0-37

                    Tr 4, 30 m         sand-mud                75               range = 0.10-1.10
                                       mixture                                  mean = 0.53


                    Brewer Creek       fine to med             100              range    O.o5-o.6
                    Tr 3, 5 m          sand                                     mean     0.22
                                                                                                                 Ln





                                                                                36




                      DISCUSSION



                      Differences in seeds and plant cover of the short and

                      tall forms of Zannichellia nalustris suggest that this

                      plant may be an indicator of disturbance. In the

                      relatively undisturbed tributary, plant    cover includes.

                      both ZpT and ZpS. ZpT coexists with 3 other species of

                      SAV and is dominant, and ZpS coexists with 4 other

                      species and is the second dominant. In the disturbed
                      tributary, ZpS is the sole SA'V. Seeds recovered from

                      surface sediments were significantly fewer in the

                      disturbed locale.



                      The relationship of Zannichellia to water depth is

                      equivocal. Where both forms occur, ZpT occurs in deep

                      water and ZpS in shallow water and the intertidal zone,

                      but where ZpS occurs alone, it is found in depths ranging

                      from the intertidal zone to 1.4 m. ZpS is not restricted

                      to shallow water, and ZpT is absent from the deep water

                      of Brewer Creek, the disturbed area. Water depth is

                      important because it affects the amount of light required

                      for germination and growth, as well as affecting the

                      amount of exposure of the plants to evaporation and

                      increased salinity that can occur in shallow water. In

                      unpolluted waters 2% of the surface light, the minimum

                      light requirement for submerged aquatic plants, occurs at

                      depths of 1.3 to 1.6 'meters (Southwick and Pine 1975). In





                                                                               37


                      polluted waters light becomes a limiting factor in depths

                      of 0. 6 to 1. 0 meters. Light does not appeat to be a

                      factor affecting the two growth forms of Zannichellia in

                      the depths studied in Robin Cove and Brewer Creek. ZpS

                      occurs in the well-lit shallow zone in Robin Cove as well

                      as depths of 1.4 meters in Brewer Creek. Shallow water

                      areas, including the intertidal zone, can experience

                      evaporation, increased salinity and increased chance of

                      dessication. These factors influence the growth forms of

                      Ruppia in New Hampshire tidal marshes (Richardson 1980).

                      There , plants growing in shallow pannes have a creeping,

                      spreading habit, while those growing in deeper water have

                      an ascending habit.



                      Sediment may be an important factor  on the distribution

                      of Zannichellia. In both areas ZpS was found growing in

                      sediment that was 75% to 100% sand. ZpT was found in mud

                      containing < 15 -% sand. These observations, though

                      preliminary, are in agreement with Van Vierssen (1982a) ,

                      who observed an increase in stem length with increased

                      clay percentage for both forms of Zannichellia palustris

                      in Europe. The restriction of ZpS to Brewer Creek may be

                      due to the high percentage of sand and near absence of

                      clay in the substrate. A sediment core collected at the

                      south shore of Brewer Creek also supports this conclusion

                      (Brush et al in prep). Sediment deposited prior'to 1940

                      consisted of silt and clay, and after 1940 was





                                                                                 38



                      predominantly silt and sand.    Seeds of Zannichellia are

                      common in sediment deposited between 1800 and 1930, when

                      there is a decline, followed by disappearance in 1940
                      (Fig. 7). Seeds of @annichellia reappear around 1955 and

                      continue in smaller numbers to the present. The core

                      shows a switch from mud to sand about the time the

                      community of Sherwood was established. Increased runoff

                      from construction could have resulted in high influxes of

                      sand, the predominant sediment type of the surrounding

                      hillsides, and could have led to   a recent establishment

                      of ZpS. However, since the     seeds of these two forms

                      cannot be distinguished morphologically, this possibility

                      remains conjectual.



                      The two growth forms of Zannichellia cannot               be

                      distinquished on the basis of fruit morphology. Both ZpS

                      and ZpT produce fruits which are dentate and entire or

                      slightly crenate along the convex margin. Nor are there

                      differences in fruit and rostrum length or in the ratio

                      of rostrum to fruit length. Van Vierssen (1982a) reported

                      that the   rostrum-fruit ratio is the most distinctive

                      morphological feature in separating several species of

                      Zannichellia in Europe. The mean ratio of 0.62 in this

                      study conforms to Zannichellia Pedunculata in Europe,

                      where rostrum-fruit ratios >0..5, and not to X. pal  ustris,

                      where ratios are <0.5. The mean rostrum length of 1.69 mm

                      for ZpS samples in this study are identical to the' mean


















                                                             Depth (CM)
                                                     year

                                                      1987 0
                                                 silt
                                                  with 1945
                                                 sand


                                                      1905     20



                                                 silt

                                                 with
                                                      1850
                                                  mud          4,0

                                                      1805
                                                 //Z  1783

                                                               60
                                                      1750
                                                                   0           100          200


                                                                      Seed Number/100 cc




                        Figure 7. Core SR3a from Brewer Creek showing changing abundance of
                                     Zannichellia Ralustris from ca. 1750 to 1987. (from Brush.
                                     Hilgartner and Thorton, in prep)





                                                                               40



                      rostrum length of Yj. pedunculata in Europe. The taxonomic

                      importanc e of this requires further study, but fruit

                      dimensions and morphology alone indicate that the two

                      growth forms are variations of the same species, and may

                      be more closely related to Z.
                                                       Pedunculata than to Z.

                      Dalustris.



                      There are some important differences in fruit production

                      and preservation in sediments between.the two forms. ZpT

                      produces three times more fruits than'ZpS. This greater

                      production is reflected by a greater abundance of

                      Zannichellia seeds in sediments where ZpT grows. However,

                      it cannot be inferred that an abundance of seeds in

                      sediment represents ZpT. High seed numbers in sediments

                      where ZpS occurs in Robin Cove could have been dispersed

                      from nearby ZpT beds.



                      Duration of growth differs for the two growth forms, with

                      ZpT growing only during the spring, and ZpS growing well

                      into July and returning in fall.



                      The high diversity of both SAV plant cover and seeds in

                      the undisturbed tributary contrasted sharply with the low

                      diversity in the disturbed environment. Zannichellia was

                      the only SAV species present at the disturbed site.

                      Discrepancies did occur between plant cover and seeds in

                      sediment, with some dominant plants not being represented





                                                                                41


                     by seeds such as Elodga and Myriophyllum. In other cases,,

                     seeds were present in the sediment where there were no

                     plants, e.g. Najas and Potamogeton pectinatus. Both of

                     these genera have been overlooked in vegetation surveys,

                     yet are represented by seeds in surface sediments of

                     lakes (Birks 1973; Birks and Birks 1980).



                     Despite these discrepancies between plant cover and the

                     seed record, the local vegetation was fairly well

                     represented by the seed record in terms of numbers of

                     species. seventy-one percent of the taxa recovered as

                     seeds were common components of the vegetation within a

                     30 meter radius of the sampling sites. Annuals were more

                     abundant among the seed taxa. than perennials, which

                     contrasts with the fact that perennials are among the

                     most important components of submerged and emergent

                     vegetation in wetlands (Van der Valk 1981). The selective

                     predominance of seeds of annuals buried in surface

                     sediments has been reported in paleoecological and seed

                     bank studies elsewhere (Birks 1973; Birks and Birks 1980;

                     Leck 1989; Parker and Leck 1985).



                     In this study,       low diversity     is indicative of

                     disturbance. Stuckey (1971) observed a decline in

                     diversity in Put-In-Bay Harbor, Lake Erie, during 70

                     years of human activity. Morgan and Phillip (1986) found

                     a similar pattern in the New Jersey Pine Barrens.





                                                                                    .42


                       Ehrenfeld (1983) found that species diversity increased

                       in some disturbed wetlands of New Jersey even while

                       eutrophic species were favored, suggesting that patterns

                       of plant diversity reflect a particular habitat and will

                       vary between sites. In this study as well' as others,

                       species favored by human disturbance including both

                       eutrophication and mechanical disturbance, are species

                       with broad ecological tolerances that respond positively

                       to increased nutrient inputs. Besides Zannichellia, one

                       such species is Sciryus americanus, a dominate shoreline

                       emergent with a broad tolerance ra     nge found in a series

                       of sites along the Patuxent River and elsewhere (Anderson

                       et al 1965). This species is the dominant shoreline

                       emergent in Brewer Creek.



                       Understanding the relationship b     etween plant cover and

                       seed production is important in interpreting the

                       paleoecological record -(Birks 1973; Birks and Birks 1980;

                       Watts 1978). Davis (1985) found Zannichellia vegetation

                       overrepresented by seeds in Leeds Creek, a tributary of

                       Chesapeake Bay, but admitted that- his values for plant

                       cover may have been low, since data were collected after

                       the peak growing period. In the undisturbed site for this

                       study Zannichellia represented 44% of 5 species in the.

                       plant cover and 55% of 17 species in    the seeds in surface

                       ,sediments.   In    the   disturbed     site,     Zannichellia

                       represented 100% of the SAV plant cover and 72% of 7





                                                                                  43


                      species in the seeds recovered from sediment samples.

                      This indicates that Zannichellia is more closely

                      represented in the seed record than has been thought.



                      Seeds preserved in surface sediments closely approximate

                      plant cover in an embayment or cove, even when there is

                      virtually no correlation between individual quadrats and

                      a sediment sample taken from the quadrat. Macrofossils

                      within a sediment core therefore represent the vegetation

                      of the embayment, at least within a 30 meter radius of

                      the coring site, for different time intervals (different

                      depths) . Periods of high and low disturbance can

                      therefore be interpreted on the basis of the number of

                      fossil seeds at particular depths within the core.



                      Paleoecology provides a long-term perspective for modern

                      ecological problems (Brush 1986; Foster et al 1990). In

                      an extensive stratigraphic analysis of SAV in the upper

                      Chesapeake Bay, Brush et al (in preparation) have found

                      Zannichellia seeds common throughout many sediment cores,

                      but found that they varied in abundance through        time.

                      Assuming that seed abundance reflects plant cover,

                      correlations between the abundance of fossil Zannichellia

                      seeds and particular periods of land u.se were used to

                      infer the response of Zannichellia populations to

                      different kinds and intensity of disturbance (Fig. 8).

                      The most significant increase in seed numbers occurred





                                                                                                                                  44

                                                               Z(7nniCheffi;9 PGIUSITI@



                                                                        A,












































                                                                                                          LEGEND

                                                                                                          SCALC


                                                                                                               "0

                                                                                                      Tim* laletwols

                                                                                                 A   Pee - 1720
                                                                                                 8
                                                                                                 C
                                                                                                 0    30- 70
                                                                                                 C
                                                                                                 No  of Steds 100cm-syr-I


                                                                                                     ?5-2.00

                                                                                                 0   2.01-4.00
                                                                                                 0   1, 4, C*
                                                                    N=
                                                                  E

                                           Figure 8. The distribution of Zannichellia Palustri                         from core
                                                         analy  ses, showing changing abundance through time
                                                         (from Brush, Hilgartner & Thornton, in prep.).





                                                                                45



                      during the period from 1650  -1780, when agriculture and

                      land clearance expanded. Initial land clearance by early

                      colonists was followed later by a clustering of small

                      farms into tobacco plantations during this period.

                      Sedimentation rates increased along with an increase in

                      nutrients and fertilizers. It appears    that the initial

                      response of Zannichellia to increased nutrients was an

                      increase   in plant cover. However,         with    further

                      intensification of land clearance and increase in the
                      human population from the 'mid-1800's into the 20th

                      century, Zannichelli steadily declined. The precipitous

                      decline of the 1960's and 1970's is revealed by the seed

                      record. Plant cover expanded again in the 1980's perhaps

                      in response to reduced sedimentation rates in some

                      tributaries in recent years. There appears to have been

                      a positive response of Zannichellia to moderate land use

                      .and disturbance, and, a negative   response to intense

                      agriculture and urban land use. Cores from the Chester'

                      River and Severn River illustrate this pattern (Fig     s.9

                      and 10) . The paleoecological pattern allows inferences to

                      be made about the cause and effect of disturbance. The

                      hypothesis that Zannichellia is a newcomer to Chesapeake

                      Bay (Stevenson and Confer 1978) is erroneous. Historical

                      perspectives therefore, provide a background in which to

                      analyze plant populations including SAV.


















                                                             Depth (ca)

                                                     Year
                                                      1987      0-1


                                                                  VIP-
                                                      1939

                                                               20-



                                                      1930




                                                Mud
                                                      1850



                                                      1750      60-


                                                      1650



                                                     .1210      90i
                                                                  0           100          200           300           400

                                                                                  Seed Nusb*r/ 100 a*


                                    Figure 9.      Core CHR6c from the mouth of Langford Creek near its confluence
                                                   with the Chester River,, showing the changing abundance of
                                                   Zannichellia Ralustria from ca. 1210 to 1987 AD. (from Brush.
                                                   Hilgartner and Thorton. in prep).
















                                                    Depth (ca)
                                            Year
                                               1987     0@
                                       black 1970
                                        AU4



                                                          K
                                              1880     20-%,





                                        dark           40
                                        foray
                                        mud    1770


                                                        60-
                                               1720





                                                                                                               loom-
                                               1200
                                      7                80
                                      *O℞*


                                       &rain


                                      L       300    1001
                                                          0           100          200          300           400

                                                                                    Seed Number/ 100 cc
                                     Figure 10. Core SRIa from the upper Severn River. showing the changing
                                                     ?
                                                     opulations of Z-annichellia Palustris from ca- 300 to 1987 AD
                                                     from Brush, Hilgartner and Thorto-n@-Jn prep).;





                                                                                  48




                       CONCLUSION




                       Differences in the distributions of two growth forms of

                       Zannichellia valustris in a disturbed and undisturbed

                       estuary indicate that this species is a potential

                       indicator of environmental disturbance. Both the short

                       and.tall growth forms occur in the undisturbed estuary,

                       but only the short form was found in the disturbed site.

                       Along with this distribution, it was noted that the short

                       form was found growing on substrates of predominantly

                       sand, whereas the tall form grows on substrates that are

                       predominantly mud. The species was also separated by

                       water depth in the undisturbed area, with the tall form

                       growing in deeper water, but in the disturbed area, the

                       short form grew in a wide range of water depths.



                       Neither form is identifiable by seed morphology, but the

                       tall form produces about 3x the number of seeds as the

                       short form. Lack of any identifying morphological traits

                       prevents the identification of these forms in the fossil

                       record. However, a comparison of seed abundance in

                       sediment cores with the history of land use indicates

                       that the response of Zannichell  ia to moderate land use is

                       positive, while the response to intense land use is.

                       negative. Also, an abundance of seeds of Zannichellia in

                       conjunction with a high diversity of other species in the

                       sediment can be used to indicate relatively      undisturbed





                                                                             49



                     conditions.



                     Both  modern and paleoecological distributions of

                     Zannichellia Ralustris indicate strongly that the species

                     is.an indicator of disturbance. This conjecture is now

                     being tested by mapping the distributions of the two

                     forms over a wide range of environmental conditions,

                     including both substrate and  disturbance history.





                                                                                    50






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