Flax Pond, a Long Island Salt Marsh
Flax Pond, a Long Island Salt Marsh
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| Snowy Egret |
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| Flax Pond Location |
The geologic history of Flax Pond is reflected in the layers of sediment that
lie below its surface. In the 1970s, a group of researchers from the Department
of Earth and Space Sciences at the State University of New York at Stony Brook
used a peat auger to probe the surface of the marsh in order to sample this sedimentary
record. From the data, they computed average thicknesses of 42 centimeters
for the salt marsh peat and 14 centimeters for the freshwater marsh peat. Dividing each of
these numbers by the number of years of deposition yielded average accumulation rates
of 2.4 millimeters per year for the salt marsh peat and 0.07 millimeters per year for the
freshwater marsh peat.
Since 1966 the Flax Pond marsh has been owned by the State of New York and is jointly administered by the New York State Department of Environmental Conservation and the University at Stony Brook. The building and the marsh of about 146 acres are used by the University’s Marine Sciences Research Center for studies of shellfish, finfish, marine algae, and salt marsh ecosystems. New York State's Department
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| Map of Flax Pond |
Salt marshes are some of the most productive environments in the world. They produce a greater amount of organic matter per acre than any crop except cultivated rice and sugar cane. This material is utilized by a large variety of fish, plants, shellfish and other invertebrates such as insects. These in turn are utilized by a great variety of birds, and mammals, including foxes and raccoons, and the diamondback terrapin, a type of turtle. Most of the fish and shellfish harvested worldwide live in salt marshes or estuaries nourished by salt marshes for at least part of their lives. Salt marshes also help protect against storm damage and act as a filter that absorbs certain types of pollutants including heavy metals. They serve as a barometer for measuring sea level rise and are used for scientific research. Salt marshes also are aestheticaally pleasing and can be used for nature study, birdwatching, photography and recreation.
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| Spartina alterniflora |
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| Tussocks on the mudflats |
Adjacent to the mudflats, and higher in elevation is the zone where salt marsh cordgrass grows. This is called the low marsh and its upper limit, as far as elevation is concerned, corresponds to the average height of the high tide (mean high water). Where the low marsh meets the mudflats is where the tallest Spartina alterniflora grows. If you look closely at the grasses in a salt marsh you may see the salt marsh snail (Melampus bidentatus). These snails are referred to as pulmonate snails because they have a lung and breathe air. At low tide they can be found at the base of the grasses. The snails have an internal clock which enables them to anticipate the rise in tides and thus climb the stalks ahead of the rising tides. They are capable of holding their breath for long enough that they can survive if the grass they are on is submerged at high tide.
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| Spartina patens and Distichlis spicata |
Often, portions of marshes are covered by straw-colored dead stems of salt marsh cordgrass. Bare patches are often created by these rafts, which smother any vegetation that they come to rest upon. This type of bare area is frequently filled with holes made by fiddler crabs. Male fiddler crabs can be recognized by their one greatly enlarged claw. This claw is used for fighting and is waved about to attract females. These areas tend to be colonized first by annual glasswort (Salicornia europaea). Glasswort has fleshy, jointed stems. Its name comes from the Greek and means "salt horn", it has a pleasant salty taste and can be used to make salt pickles. Salicornia is a member of the goosefoot family which also includes spinach and beets.
The stands of grass that grow in the salt marsh slow down the movement of the seawater as it is brought in by rising tides. This causes suspended silt to trickle out of the water and become deposited on the marsh as mud. Gradually, the roots and rhizomes of the grasses bind the sediment together to form a spongy substance called peat, which makes up a large part of the marsh surface. The vertical accumulation rate of peat is variable, but averages about three millimeters per year. This is about equal to the current rate of sea level rise.
Flax Pond is separated from Long Island Sound by a gravel beach. This beach protects the marsh from the large waves that form in Long Island Sound during storms. The beach lies between two rocky headlands, Crane Neck and Old Field Points, that are part of the Harbor Hill Terminal Moraine. As waves erode these headlands, littoral currents carry the pebbles onto the beach and sort them by size. The great variety of rock types along Long Island’s North Shore is a reflection of the varied source areas visited by the glaciers on their journey here from New England.
The beach is cut by an inlet that supplies water to Flax Pond as the tide rises and drains the nmarsh as the tide falls. The inlet is currently stabilized by the jetties. There is evidence that before the jetties were constructed, the inlet migrated and at one time, a second inlet formed. The environment created here is called a rocky intertidal zone. The rocks and the crevices between them provide homes for barnacles, blue mussels, starfish and sea anemones.
The back beach area is a very harsh environment. Except during and shortly after a rain, the sand is very dry like a desert. During the summer, this area is very hot and in the winter it is subjected to fierce, biting winds. During storms, the back beach may be washed by waves which can cover the area with gravel.
Some of the hardy plants that are able to grow in this area are wormwood (Artemisia caudata), bayberry (Myrica pensylvanica), dune grass (Ammophila breviligulata), beach pea (Lathyrus japonicus), halberd-leaved orach (Atriplex patula), sea-blite (Suaeda maritima), saltwort (Salsola kali), beach plum (Prunus maritima), sea lavender (Limonium carolinianum), evening primrose (Oenothera biennis), great mullein (Verbascum thapsus), dusty miller (Artemisia stelleriana) and soapwort (Saponaria officinalis). Saltwort has fleshy stems that store water for use during dry periods, and spines to protect the plant from animals that might covet this water. The leaves of dusty miller are covered by fine white hairs that protect them against the drying effects of wind and bright sunlight.
In coastal areas woody plants are subjected to salt spray that is blown against them by the wind At Flax Pond, post oaks (Quercus stellata) along the beach have been severely affected by salt pruning. The salt in the wind kills young shoots that try to rise above the level of the surrounding growth. The result is a thick, low, bushy growth of leaves and stems along the tops of the trees. This dense growth pattern helps the trees to survive in this harsh environment by reducing the effect of the wind.
Episodic events like storms can cause erosion in some parts of the marsh, while they bring rapid deposition of sediment in others. Accumulations of gravel have formed on the back side of Flax Pond Beach, wher it meets the salt marsh. These are called storm washover lobes. During severe storms, waves carry this coarse sediment over the beach and into the marsh.
At the edge of Flax Pond and in other coastal areas, you may see dead red cedars and other dead trees that are remnants of what were once uplands. The death of these trees presents evidence of a rising sea level. As sea level rises at a rate of about 3 millimeters per year these trees become more frequently affected by salt water during storms and at spring high tides. As sea level continues to rise, damage from salt water will result in further loss of uplands which border high marsh areas. Eventually, these former upland areas become part of the marsh as they experience regular inundation by tides. Accumulation of peat then commences, and subsequently proceeds at approximately the same rate as the rise of sea level.
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| Iva frutescens |
Another shrub that grows along the edge of the marsh is groundsel tree (Baccharis halimifolia). In the late summer and early fall it is covered with white clusters of flowers which attract a large number of monarch butterflies. It can be distinguished from marsh elder by its alternate leaves and by its small white flowers which are upright rather than nodding. Groundsel tree is a member of the composite family. This is the same family to which asters and dandelions belong. The bushes bear either all male or all female flowers and in the late fall the female shrub appears white due to the abundance of silky white hairs that are attached to the mature seeds. The alternate leaves help distinguish it from marsh elder, which has opposite leaves.
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| Toxicodendron radicans |
Salt spray rose (Rosa rugosa) also grows in many shore ares on Long Island. It has 3 to 4-inch wide flowers which may be either white or deep pink. The branches are entirely covered with dense bristles. The dark red fruits or rose hips are an excellent source of vitamin C and a good source of food for birds.
In some places along the periphery of salt marshes, a fringe of freshwater marsh forms due the the presence of groundwater. In these places, the common reed (Phragmites australis) can often be found. The common reed has become a nuisance plant in many areas because it outcompetes many other plants. This leads to decreased plant diversity and it can be detrimental to wildlife. For example, cattails (Typha spp.) provide an excellent food source for many animals and when they are crowded out by the common reed this food source is lost.