Monitoring Tidal Water Elevation and Water Quality to Assess Tidal Wetland Loss in Four Embayments of Long Island Sound, New York Active

Introduction

Recent trends analysis examining the effectiveness of tidal wetland regulations and the regulatory program of the New York State Department of Environmental Conservation (NYSDEC) revealed that the regulations and regulatory program were highly effective in stemming the historic "fill and build" activities. However, the trends also revealed that tidal wetlands—specifically, low marshes—were disappearing. To help determine the cause(s) of this loss, the NYSDEC, in collaboration with Stony Brook University's School of Marine and Atmospheric Sciences (SoMAS) and the U.S. Geological Survey (USGS), established a monitoring program in 2008 that has been conducted on and in the tidal wetlands of East Creek, Sands Point; West Pond, Glen Cove; Frost Creek, Lattingtown; and Flax Pond, Old Field (fig. 1).

Approach

The USGS has established and operated a monitoring station that collects data on tidal water elevation at each of the four wetland embayments of Long Island Sound (LIS). These data have been relayed hourly via satellite telemetry to USGS offices in real time and made publicly available via the Internet within a few minutes of their arrival. At two of the embayments—East Creek and Frost Creek—where structures (bridges) exist and enable emplacement of instruments directly in the waterway, data on water temperature and specific conductance, which are used to compute salinity, have also been collected and disseminated via the same processes employed for the water elevations. Because no structures exist in the vicinity of standing water at low tide in West Pond, a siphon gage that precludes placement of an instrument directly in the waterbody (and collection of representative data on chemical parameters) has been used at this embayment. The remaining embayment—Flax Pond—has been equipped with an add-on water-quality monitor that has collected data on temperature, specific conductance (used to compute salinity), pH, dissolved oxygen, and turbidity (fig. 2); these data have also been disseminated with the water-elevation data.

Tidal statistics (for example, mean high and low water elevations) are being published (online) annually for daily water-elevation records from all four stations in the USGS Water-Data Report for Long Island. In addition, daily statistics (for example, maximum, minimum, and mean values) are being published annually in this report for records of water temperature and salinity from all embayments except West Pond, and for records of pH, dissolved oxygen, and turbidity from Flax Pond.

To better understand the cause(s) of tidal wetland loss, the NYSDEC has installed sediment elevation tables at these and other tidal wetland sites to provide long-term marsh accretion rates and elevation data. Scientists from SoMAS have collected pore-water samples from marsh soils for analysis of sulfide, nitrate, nitrite, ammonia, dissolved phosphorus, pH, and Eh. They are also determining accretion rates for the past century from detailed ²¹⁰Pb chronologies.

Results

A comparison of tidal statistics at East Creek, Frost Creek, and Flax Pond (see fig. 3A, for example) indicates that mean lower low water (MLLW) elevation differs substantially among embayments and LIS. During October 2008 to September 2009, MLLW elevations at Frost Creek and Flax Pond averaged -0.30 and 0.22 feet above NGVD 1929 (National Geodetic Vertical Datum of 1929), respectively, whereas MLLW elevation at the East Creek control site averaged 3.35 feet above NGVD 1929. Differences between MLLW elevations at the sites are due to varying degrees of shoaling in inlets that connect the embayments to LIS (Cartwright and others, 2010). Despite the MLLW differences, mean temperatures and salinities were similar among embayments during this period; minor variations in these parameters are attributed to differences in tidal hydrology, and magnitude and mechanism of freshwater inflow (see fig. 3B, for example).

Marsh habitats are the result of long-term adaptations to local differences in tidal hydrology and water quality, such as those among the four embayments. Understanding these adaptations may provide clues to ongoing and potential future rates of tidal wetland loss.

Related Publications

Cartwright, Richard, Schubert, Christopher, Tagliaferri, Tristen, Mushacke, Fred, Young, Heather, and Cochran, Kirk, 2010, Monitoring tidal water elevation and water quality in four embayments of Long Island Sound, New York to assess tidal wetland loss, Seventh National Monitoring Conference—Monitoring From the Summit to the Sea, Conference Program, Denver, Colorado, April 25-29, 2010, p. 136, accessed June 10, 2010, at http://acwi.gov/monitoring/conference/2010/2010_NMC_Program_2010-04-13.pdf

Wagner, R.J., Boulger, R.W., Jr., Oblinger, C.J., and Smith, B.A., 2006, Guidelines and standard procedures for continuous water-quality monitors—Station operation, record computa-tion, and data reporting: U.S. Geological Survey Techniques and Methods 1-D3, 51 p. + 8 attachments; accessed April 10, 2006, at http://pubs.usgs.gov/tm/2006/tm1D3/pdf/TM1D3.pdf

Project
Location by County

Suffolk County, NY, Nassau County, NY