Flax Pond: A Long Island Salt Marsh

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Flax PondA Long Island Salt Marsh
Created by Glenn A. Richard Mineral Physics
Institute Stony Brook University Glenn.Richard_at_sun
ysb.edu
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What is a tidal wetland?

• A vegetated area covered by tidal water at high
  tide
• Exposed to air at low tide
• A tidal wetland is defined by the presence of
  particular plant species that serve as evidence
  of the effects of tides.

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Flax Pond, a local tidal wetland, lies on Long
Islands North Shore within the Village of Old
Field.The Flax Pond Laboratory, a research
facility adjacent to Flax Pond, pumps in its
seawater from a shallow well in the marsh.
Example of a Local Tidal Wetland
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Geologic Features of Long Island
Flax Pond is adjacent to the hilly Harbor Hill
Moraine, created by the pushing of sediment by a
continental ice sheet that reached its maximum
extent about 20,750 years ago.
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Map of Flax Pond
Glacial Moraine
Glacial Moraine
The salt marsh occupies a depression, partially
surrounded by the more elevated Harbor Hill
Moraine. Flax Pond has an area of about 120
acres, and is connected to Long Island Sound by a
single inlet.
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Flax Pond at Low Tide
Low tide in the interior of Flax Pond occurs
about 1.5 hours later than in adjacent Long
Island Sound.
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Flax Pond at High Tide
Flax Pond has a vertical tidal range of about 5.5
feet.
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Flax Pond Digital Orthophoto Mosaic
A salt marsh can form where tides carry sediment
through an inlet and into an area that is
protected from waves and strong currents.
Orthophotos were assembled in ArcGIS after being
downloaded from http//www.nysgis.state.ny.us/gat
eway/mg/htmls/suffolk/01ic_o_suffolk_l06col.htm
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Why call it Flax Pond?

• 1700s - Flax grown in the area for making linen.
• Flax was harvested in the fall and placed in the
  marsh for a couple of weeks of retting.
• Retting requires fresh water not salt.
• Retting removed the pectins, and fibers remained
  which could be made into linen.
• Late 1700s Local flax industry collapsed as
  the Russian flax industry thrived.

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Why conserve tidal wetlands?
Eugene P. Odum (1961) The Role of Tidal marshes
in Estuarine Production
Ecosystem Pounds of living organic matter
produced on an acre per year Deep oceans
and deserts Hundreds Grasslands,
temperate forests, typical agriculture.. Thousand
s Tidal marshes, coral reefs, tropical rain
forests... Tens of thousands
deltas, intensive agriculture
Producers ?rooted plants, benthic algae (on mud
and peat), and phytoplankton.
Salt marshes are also habitat, feeding, and
breeding areas for many species.We cannot afford
to lose our salt marshes.
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Santapogue Creek, Lindenhurst, 1930
Aerial view prepared by Sandy Richard from
Suffolk County imagery
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Santapogue Creek, Lindenhurst, 20041930 tidal
wetlands outlined in red
Aerial view prepared by Sandy Richard from
Suffolk County imagery
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Golf Course Under Development,Long Beach Island,
1930
Aerial view prepared by Sandy Richard from Nassau
County imagery
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Golf Course in Long Beach, 2004
Aerial view prepared by Sandy Richard
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New York State Tidal Wetlands Act, 1974

• It is the public policy of the State, as set
  forth in the Tidal Wetlands Act, to preserve and
  protect tidal wetlands, and to prevent their
  despoliation and destruction, giving due
  consideration to the reasonable economic and
  social development of the State. It is the
  purpose of this Part to implement that policy by
  establishing regulations that allow only those
  uses of tidal wetlands and areas adjacent thereto
  that are compatible with the preservation,
  protection and enhancement of the present and
  potential values of tidal wetlands (including but
  not limited to their value for marine food
  production, wildlife habitat, flood and hurricane
  and storm control, recreation, cleansing
  ecosystems, absorption of silt and organic
  material, education and research, and open space
  and aesthetic appreciation), that will protect
  the public health and welfare, and that will be
  consistent with the reasonable economic and
  social development of the State.

A permit is required for filling, dredging or
otherwise damaging a tidal wetland in New York
State.
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But Long Island is still losing salt marsh
habitat.
Western portion of Flax Pond
Mid-1970sabundant tussocks
1999few tussocksimage from Fred Mushacke, NYSDEC
Marsh loss, 1974 to 1999Lost areas in redimage
from Fred Mushacke, NYSDEC
Slumping of peat and Spartina alternifloraoccurs
both naturally and as a result of disturbance
(Summer, 2004).
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Complex interactions between physical and
biological factors govern marsh growth and loss.
Grasses and mussels trap and bind sediment
brought by tides.
Ice causes erosion of marsh habitat but may
create tussocks.
Storms cause erosion and deposition of sediment.
Peat and mud form the substrate of the marsh.
Tussocks may either grow or perish on the
mudflats.
The marsh is a rich learning laboratory.
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Large Sediment from HeadlandsThe Gravel Beach
waves
sediment
Much of the gravel on the beach that separates
Flax Pond from Long Island Sound is carried there
by wave action from both Crane Neck Point (in
background) and Old Field Point headlands due to
the direction of wave approach and the arc shape
of the beach.
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Plants of the Beach Adapted to Drought
Photo by Sandy Richard
Dune Grass (Ammophila breviligulata) has deep
rhizomes and roots. Great Mullein (Verbascum
thaspsus) has a covering of hairs on its leaves.
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The Inlet

• The inlet controls the flow of the tides.
• It was dug around 1803
• The position and the form of the inlet change
  over time.
• The flood tide is about 4.5 hours, while the ebb
  tide is about 7.5 hours because the flood tide
  delta deposited near the inlet impedes the flow
  of water, especially around the time of low tide.

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Rock Barnacles
Photo by Sandy Richard
These Rock Barnacles (Balanus balanoides) are
arthropods that feed on plankton from the
seawater.
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Blue Mussels
Photo by Sandy Richard
Blue Mussels (Mytilus edulis), formerly abundant
on the flood tide delta, were greatly reduced in
number by 2008, possibly due to predation by the
now common Asian Shore Crab (Hemigrapsus
sanguineus).
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Softshell Clam and Eastern Oyster
The Softshell Clam (Mya arenaria) on the left and
the Eastern Oyster (Crassostrea virginica) on the
right are filter feeders that use their gills to
feed on tiny plankton from the seawater.
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Tidal Channel
Snowy Egret
Water is always present in the tidal channels,
even at low tide. Tidal channels carry water with
sediment between the inlet and the interior of
the marsh.
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Vegetational Zonation
Photo by Sandy Richard

• The tides control the zonation of vegetation in
  the salt marsh.
• High marsh in foreground
• Low marsh in background

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Mudflats
Mudflats are submerged by water during much of
the tidal cycle. Fiddler crabs are abundant here
at low tide.
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Tussocks on a Flax Pond Mudflat

• Tussock a mound of Spartina plants with their
  roots and rhizomes, peat, and ribbed mussels with
  their byssal threads. The byssal threads, roots
  and rhizomes bind the tussock together.

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Low Marsh

• Salt Marsh Cordgrass (Spartina alterniflora)
  inhabits the low marsh at Flax Pond.

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High Marsh at Flax Pond
Spike Grass in Bloom
The high marsh at Flax Pond, in the foreground,
is dominated by the recumbent Salt Meadow Grass
(Spartina patens) and Spike Grass (Distichlis
spicata). Low marsh is in the background.
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Marsh Elder
Marsh Elder grows in the highest part of the
marsh, adjacent to the uplands.
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Glasswort
Glasswort often becomes abundant in areas of the
high marsh where other vegetation has died, often
because it was covered by wrack.
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Upland Adjacent to Flax Pond
Flax Pond is bordered by upland areas where
trees, such as Post Oak, Black Oak, Red Cedar and
Black Cherry, grow. Post Oak (Quercus stellata)
has leathery leaves that help it retain water. As
sea level rises, tidal marshes tend to invade the
upland.
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Salt Peat
A layer of salt peat forms as vegetation traps
and binds sediment from the tidal waters. The
salt peat overlies a layer of darker freshwater
peat that formed prior to 1803.
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Cross Section
Marsh Elder Black Grass
From A Field Guide to Long Islands
Seashore Richard, Springer-Rushia and Stewart,
2001 Illustrated by Maria T. Weisenberg
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Poison Ivy, Abundant in the Uplands
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Groundwater
Groundwater seeps from the Upper Glacial Aquifer
into the surrounding salt water where the water
table is at sea level at the shoreline.
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Map from 1797
This 1797 map shows Flax Pond with no inlet.
Without a connection to Long Island Sound, it was
a freshwater wetland.
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The Inlet
The inlet, which was dug in 1803, now allows
saline tidal waters to carry sediment into and
out of Flax Pond approximately twice daily.
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Sedimentary Profile of Flax Pond
Saltwater Peat
Freshwater Peat
Sand
A layer of salt peat forms as vegetation traps
and binds sediment from the tidal waters. The
salt peat overlies a layer of darker freshwater
peat that formed prior to 1803.
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Alternating Layers of Gravel and Peat near Inlet
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Inlet 1837 - 1885
The inlet has changed over time.
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Inlet 1885 - 1930
In 1930 there were two inlets.
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Inlet 1930 - 1938
In 1938 the inlet was connected to the eastern
end of the marsh.
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Inlet 1938 - 1969
Since the 1940s the inlet has been stabilized by
rock jetties.
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Flax Pond Inlet in 2005
Shoaling of inlet and growth of tidal delta may
be truncating lower portion of tidal range
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Peat Accretion Rates
Teachers using a peat auger to measure sediment
thickness.
Long term accretion rate Thickness / duration of
accretion ? rate of accretion
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1975 Peat Thickness Map
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Stratigraphy of Flax Pond
Measurements are from cores taken with a peat
auger. The average vertical accretion rate of
salt peat at Flax Pond is about 2.4 mm per year.
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1970s Aerial Photo Flax Pond Frozen
Several days of sustained below-freezing weather
cause the marsh to ice over.
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Ice with Sediment at Flax Pond
Ice can transport sediment from one place to
another.
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Tussocks and Ice in the Winter
Ice can bring about erosion, deposition, and the
formation of new tussocks.
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Tussock on Low Marshat Flax Pond- March, 2004
This tussock was picked up and deposited here by
ice. Ribbed Mussels (Geukensia demissa) and
Spartina alterniflora held the tussock together
while it was in place on the mudflats.
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Storm Washover Lobes
During storms, waves may wash gravel over the
beach and into the marsh.
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Long Island salt marshes in the future
From 1803 until the 1970s, the vegetated portion
of Flax Pond gradually expanded in area. Since
the 1970s this area has contracted. The future of
Flax Pond and other tidal wetlands, to a great
extent, will depend upon the relationships
between

• Sediment deposition rates
• Sediment erosion rates
• Sediment compaction rates
• Sea level rise
• Biological Factors
• Human activities