Additional Studies to Determine Causes of Vegetative Tidal Wetlands Loss At Flax Pond

Flax Pond is one of four tidal wetlands along Long Island's north shore that is part of a 4 component wetlands study. The study is a collaborative effort supported/funded by a NYC Nitrogen Settlement to DEC for nitrogen violations to Long Island Sound Study and includes the NYS Dept of Environmental Conservation (DEC), Stony Brook's Marine Sciences Research Center (MSRC) and the United States Geological Survey (USGS).

Tidal wetlands are one of the most productive environments in the world. They provide nutrients to our estuaries, habitat for wildlife, filter the estuary and buffer against storms. Recent trends analysis examining the effectiveness of our tidal wetlands regulations and regulatory program revealed that the regulations and the regulatory program were highly effective in stemming the tide of historic fill and build activities. However, the trends also revealed that tidal wetlands, specifically, low marshes, were disappearing. These studies are an attempt to define the causes.

In addition to Flax Pond, Old Field, the study will include embayments at West Pond, Glen Cove; East Creek, Manhasset; and Frost Creek, Lattingtown

The first component is the tidal wetlands trends analysis. In this part, Fred Mushacke, NYSDEC, will compare historic (1974) and contemporary aerial photos that are placed in GIS (Geographic Information System) software and geo-referenced. He will then identify and compare the tidal wetlands zones from each image. (see comparison video of 1974 - 2006 infrared images, Figure1) to determine changes.

The second component, conducted by Heather Young, DEC, is the monitoring of sediments on the surface of the marsh, specifically in the low marsh. Special devices called SETs (Surface Elevation Table; see http://www.pwrc.usgs.gov/set and Figure2) will measure the buildup or loss of sediment over time. SET analysis will be augmented by "marker horizon" measurements, Figure3, which employs feldspar or other light colored materials that are easily distinguishable from surrounding sediments and placed on the marsh surface. When simultaneously used with the SET, the marker horizons can provide information on below ground processes that influence elevation change, such as shallow subsidence (See www.pwrc.usgs.gov/set/theory.html#mh).

The third component, conducted by J. Kirk Cochran, PhD, MSRC, is two-fold: 1) evaluate the accretion history of the marsh over the past 100 years and compare it with long and short-term changes in sea level as well as with short-term accretion rates determined by the SETs. This involves core sampling and analysis for Pb-210 and solid phase geochemistry; 2) characterize the basic geochemistry of the marsh through analysis of hydrogen sulfide and nutrients (N, P) in the sediment pore water and reactive iron and solid phase sulfide pools in the sediment, Figures 4&5. These elements are critical in determining whether high concentrations of hydrogen sulfide in the marsh pore waters are leading to the decrease in plant biomass and ultimately death of the marsh plant and subsidence of the marsh peat.

The fourth component, conducted by the USGS, is the continuous monitoring of water elevation in each of the four embayments. This involves the installation and operation of real-time monitoring stations which will relay the collected data hourly via satellite telemetry to USGS offices where this information will be made available via the internet within a few minutes of arrival. At two of the sites—East Creek and Frost Creek—water temperature and salinity will also be collected and, at Flax Pond, will be supplemented by monitoring for other water-quality parameters including pH, dissolved oxygen, and turbidity (Figure 6, shows a rendition of the monitoring device on the wooden bridge at Flax Pond). All water-quality readings will be disseminated over the internet in real time through the same processes employed for the water elevations.

The ultimate goal of the project is to identify causes of vegetative tidal wetlands loss

Video overlay, 1974 infrared inventory aerial over 2006 aerial infrared note changes at inlet and to large island in center of images. Vegetation is red; mudflats are silver-blue in color.

SET device temporarily installed to measure accretion rate at site, once measurements are taken the “head” is removed

Feldspar companion measurement, measures amount of sediment deposited on marsh and compared to SET measurements, to check for marsh subsidence. A rod frozen with nitrogen is used to extract the sample from the marsh peat.