Aspects of succession in Big Marsh, Kent County, Maryland, a marsh/swamp forest ecosystem impacted by peat mining

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ASPECTS OF SUCCESSION IN BIG
MARSH. KENT COUNTY, MD
A MARSH/SWAMP FOREST ECOSYSTEM
IMPACTED BY PEAT MINING

1982

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ASPECTS OF SUCCESSION IN BIG MARSH, KENT COUNTY, MARYLAND ?

A MARSH/SWAMP FOREST ECOSYSTEM IMPACTED BY PEAT MINING

.John B. Williams

Coastal Resources Division.

,Edward C. Pendleton

University of Maryland, Horn P6int Lab

Coastal Resources Division Report
1982
V-

Introduction

In general the majority of Maryland's coastal wetlands are located in

Dorchester and Somerset Counties on its lower eastern shore of Chesapeake Bay

(McCormick and Somes 1982). These marshes are characterized by broad flat

expansives of grasses dominated by Spartina, Scirpus, Juncus, or other genera.

The size and species composition of these marshes is largely a function of the

low topography, watershed hydrology, and salinity regimes of this region. In

contrast to these southern shore counties, the marsh acreage of counties along
Maryland's upper eastern shore is considerably less (McCormick and Somes 1982).

These upper shore areas are bordered by rolling terrain with marsh areas often

restricted to the low areas between bluffs. Although these smaller - upper bay

marshes may contribute less organic matter to total Chesapeake Bay production

than their southern counterparts, they are stil I important in providing critical

habitat for different wildlife, bird, and plant species.

Considering the well documented value of marshes in their roles of nutrient

cycling, storm water buffering, detritus production, and waterfowl ha bitat,

destruction of marsh acreage is of great concern to coastal managers. Marsh',-losses

have been attributed to a variety of natural causes including sea level rise and

recent investigations initiated by Maryland's Coastal Zone Management Program.

have attempted to document cause and effect relationships (Pendleton and Stevenson

1982). Natural causes of marsh loss are sometimes beyond the scope of man's

control, however human activities directly or indirectly impacting marshes can be
controlled. These man-made impacts may range from dredge and fill activities to

the alteration of watershed drainage characteristics.

In the past decade peat mining operations in a freshwater marsh/swamp

forest ecosystem in northwestern Kent County, Maryland (Figure 1) were

implicated in vegetation changes reported for the lower marsh. Big Marsh is

contained in a relatively short watershed draining agricultural lands and

borders Chesapeake Bay just south of Howell Point. In the late 1960's peat

mining operations were conducted in the upper drainage basin of Big Marsh and

created several trench-like ponds in the swamp forest (Figure 2). In August

1971 a'long trench was excavated along the length of the marsh towards the Bay.

Mining operations were halted after this activity following a court order. The

long trench excavated in 1971 intersected a natural creek channel meandering

through Big Marsh at several locations and altered drainage patterns.

Local residents reported changes in the plant species composition of the

marsh i n 3ucceedi ng years and f el t the dredged channel was responsibl e. In order

to divert water back into the natural creek channel-, two bulkheaded check dams

were constructed at strategic creek intersections (Figure 3). However, after
several growing seasons following dam construct.ion up through 1978 residents
still. reported a shift in marsh conditions from a cattail marsh, Typha angustifolia,

to a marsh thicket with alder, Alnus serrulata, black willow, Salix nigra, and

other species appearing more frequently. In order to deteminL- what role the'

peat mining operations had had in changing the cattail stands in Big Marsh, the

Coastal Resources Division of Maryland's Department of Natural Resources in

cooperation with the University of Maryland Horn Point Environmental Laboratory

undertook an ecological study of the marsh.

The main objective of our study was to determine what plant species. changes

had occurred over time in Big Marsh and what role peat mining had played in
producing these changes superimposed upon natural succession processes.

Figure 1. Location of Big Marsh along
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Figure 2. Trenches dredged by peat mining operations.

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The questions we were seeking to answer were: 1. How had the mining directly

impacted the marsh? 2. Had natural ecological succession been occurring prior

to peat mining? and 3. What role did mining play in the successional process

relative to nature? We hypothesized that succession had been occurring in

-Big Marsh prior to the mining, but that. the channels may have accelerated its

rate.

Based upon our study results, we would develop ma nagement recommendations

addressing what actions the State could take, if any, to preserve or restore

Big Marsh.

Methods

In order to determine the general marsh species composition and plant
distribution in the lower marsh area along its border with Chesapeake Bay,

we established six randomized transects with stations randomly set at 64 yards

along the transects. At each station measurements were made of water depth,

species identification, and phytosociological (Wood.1970) associations among

plants., Observations were also made of muskrat presence and other animal activity.

These preliminary results were used to determine what additional studies should be

developed.

We surveyed the direct impacts of the peat mining operations by entering the

water-filled trenches by canoe and also traveling the le.ngth,of the exit channel.

Measurements were made of water depth, aquatic and terrestrial vegetation, and

marsh drainage patterns (Figure 4).

Based upon the preliminary transects, we selected sites at different distances

into the marsh to measure ages of
Woody vegetation to help determine succession

rates@ Samples.were taken by coring.device.and.c.hain saw. In addition to tree

aging, -succession rates were determined from aerial photographs-of, the. marsh. ta.ken
in 1936, 1957 and 1978. The 1978 photograph was ground-truthed by our field

observations and used to compare the earlier photographs. Succession rates were
determined by'comparing the areal.c.hanges-of'the different plant zones (swamp

forest, marsh thicket., marsh, and open water) from each year using a@-leaf area

index instrument.'

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Figure 4. Vegetated banks of former mi.ni.ng areas.

Results and Conclusions

The general vegetation zones of Big Marsh included examples of some of

the wetlands types described by McCormick and Somes (1982) including shrub

swamp and fresh marsh. Large bog areas were also observed. Plant species

diversity was general.ly high throughout the marsh except in pure cattail stands.

Most of Big Marsh's nearly 2000 acres are composed of a shrub swamp dominated by

red maple, Acer rubrum, and marsh thicket dominated by red maple, Acer rubrum,

smooth alder, Alnus serrulata, posion ivy, Rhus radicans., and swamp rose, Rosa

palustris.

Results from our preliminary transects of the western lower marsh area

revealed that large areas of the marsh displayed transition stages of succession

from marsh to shrub thicket. The northern'most half of this marsh zone was .still

mainly pure cattail marsh (Figure 5), while the southern half displayed frequent,

distributions of alder, swamp rose, Hibiscus, poison ivy, and scattered red

maples (Figure.6). T. angustifolia was still present throught much of the southern

half except in dense stands of alder and poison ivy. In some parts of this southern

successional.area,cattail stands exhibited typical freshwater ma rsh vegetation

including arrowarum, Peltandra vir' d the royal fern,,Osmunda reqalis- Our
ginica an

initial transects; were made early in the growing season, 1980, however fresh

new shoots of T. anguttifolia werieseen emerging from the maeslh"surface (Figure

We nieasured water depths throughout these successional marsh areas to d,eterm:ine-
whether marsh drainage was inhibiting cattail growth. All areas 'contained [email protected]

,or flowing water, apparently sufficient for cattail growth, except in dense stAnd.s-

of alder andwillow where dense root and sediment mats blocked cattail growth.

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Figure 5. Pure cattail marsh in
northern marsh area.
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Figure 6. Southern area of marsh containing mixed marsh and
shrub species.

Figure 7. New cattail growth amon
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old shoots.

Of particular interest in this cattail marsh portion of Big Marsh

were small groves of red maples observed growing in the middle of almost pure

stands of T. angustifolia. We felt tree ages from these maple stands might

be an indicator of how long ago succession had been occurring in this portion

of the marsh. Samples from these trees and other species in the marsh indicated

some of these trees had become established in the marsh as early as 1960, prior

to peat mining. Once established, these pioneer trees, would have provided a

seed source and helped trap sediment to make it easier for new trees to colonize

the area (Figure 8).

In the area of Big Marsh actually mined for peat, primarily shrub marsh

habitat, we found that the dredged ponds were now bordered with luxuriant aquatic

plant.growth and provided a very scenic view. Particularly notable were- dense
beds.of water.lilly, Nymphaea odorata, (Figure 9). We found that the bul.kheaded,
dams were diverting water flow from the dredged channel into. the natural stream

bed. Water levels were higher on the upstream side of the dam (Figure 10) and
flowed through a break"in the channel's peat berm into the marsh stream. We also

found evidence.that during times of extreme rainfall water flow in the channel

partially bypassed the stream entrance and passed over-the dam. Nearly all plant

growth*was absent from the heavy peat berm crest, however cattails were observed

growing on the lower outer slope of the berm (Figure 11).

Based upon our field measurements and aerial photography analyses, we

determined that succession had been occurring in Big Marsh prior to-the peat
mining operations in the late 1960's and channel dre dging in 1911. Tree ages

in maple stands within the marsh predated mining operations and thus showed parts

of lower Big Marsh were in a successional transitional stage from a cattaiT marsh

to a shrub marsh. However, channel dredging may have speeded up the rate of

succession in the early 1970's by altering marsh drainage patterns. If the water

table were-lowered enough in some of the marginal marsh areas, shrub species such

as alders would have colonized areas more quickly than before; producing the

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Figure 8. Island of maples growing withi-ng cattail marsh.

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Figure 9. Water lillies growing within former dredge channel.

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Figure 10. Check dam on dredge channel showing higher
upstream water level.

Figure 11. Berm bordering channel. Note cattails growing
along lower border in background.

vegetation changes observed by local residents. This observation is supported

by the changes in marsh acreage between 1936 and 1978. Nearly 539 acres of

marsh were present in 1936, while only 274 acres were present in 1978. We

estimated that ma rsh loss through succession to shrub tUcket had occurred at

a rate of about.5.2 acres per year from 1936 to 1957, but had increased to
nearly 7.4 acres per year from 195) to 19-78'.' Although this increased rate

c
0 Id have resulted primarily from th-e. earlier established adult trees acting
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as seed sources and soil b4nders, the role of the temporarily altered drainage

in the marsh from peat dredging during 1971 cannot be discounted.

TKe check -dams.along, ttLe dredged channel are diverting water into the. natural.

creek channel and water flow into the lower marsh appeared adequate for cattail

growth-. Renewed cattail growth, was observed at most sites in lower Big Barsh

except under canopies of dense older. growth. From these observations we concluded

that succession ha's always been occurring in B-ig Marsh and that wKil e. -rates may

have increased prior.to check dam construction, more natural conditions now seem

to exist in the marsh.

4ig Marsh-appears to be an excellent example of small lake or pond ecological

succession from open water. through. marsh.,. bog, and swamp -forest stages. In; colonial

days. Big Marsh- was formerly named Great Pond, attesting to the presence of open

water. W.1th- fntensive agriculture occurring in its watershed, sedimentation probably

filled th-e open water -areas -eventually leading to the swamp forest and thickets..

observed todiy. As natural success'i,on continues the red maple swamp-forest should

continue to.s@pread into the lower marsh- areas replacing most of.the cattail' Marsh-.

except in the northern most area whe r*e water levels are deep enough to ressist

invasJon.by more terrestrial species.

Management Recommendations

Since large portions of the cattail marsh areas of Big Marsh have developed

into the early stages of a shrub swamp, relatively drastic measures such as

burning would be required to reverse the successional process. However, this

measure would only be temporary and natural succession would continue once again.

The burning process would also destroy habitat diversity in the marsh possibly

reducing some bird and wildlife species. Big Marsh represents a very classic

example of pond/marsh succession and the areas of cattail marsh in transition to

a shrub marsh help complete the full natural picture.

The two existing check dams in the dredged channel are adequately diverting

water into the natural creek channels. These dams sho0d be periodically checke d

to ensure protection is maintained.

Use of Big Marsh as a natural field laboratory should be encouraged by the

State. Coordination of f iel d trips into the marsh -should carried out through

the Echo Hill Outdoor School, adjacent to the marsh.

References

McCormick, J. and H.A**Somes 1982. The coastal wetlands of Maryland.
Maryland Department Natural Resources Report 243p.

Pendleton, E.C. and J.C. Stevenson, 1982. Further investigations of marsh
losses and analysis of marsh reestablishment alternatives at Blackwater
National Wildlife Refuge. Maryland Department Natural Resources
Report 106p.
Wood,*R.D. 1970. Hydrobotanical Methods. University of Rhode Island. 176p.

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