Nassau and Suffolk Counties
Trends in Wetland Loss
In order to evaluate the effectiveness of the state's tidal wetlands program in protecting wetlands under the Tidal Wetlands Act (Article 25 of the Environmental Conservation Law), a tidal wetlands trends analysis is being conducted by the New York State Department of Environmental Conservation. The analysis is using color infrared aerial photography and geographic information system (GIS) technology. GIS technology allows geographic data, such as aerial photography, to be computerized. Through the use of GIS, a tidal wetlands line can be drawn on a scanned aerial photograph. This information is then checked in the field by marine biologists. The area within the line can then be queried and the tidal wetlands area determined. Comparing differing years will yield trends that can be analyzed.
To date, the tidal wetlands trends analysis has shown that the regulatory program to protect tidal wetlands from the historic "fill and build" damage is extremely successful. In many areas, such as Shinnecock and Moriches Bay on Long Island, there is no detectable loss due to those activities. In fact, the wetlands have increased over 250 acres in Shinnecock and Moriches Bay due to the landward migration of the wetlands.
Losses have been detected however, in areas such as Jamaica Bay, (See Tidal Wetlands Loss Strategies) and, to a lessor degree, certain focus areas along the north and south shores of Nassau and Suffolk Counties (see table and photos below). In Jamaica Bay the losses are occurring at an unprecedented and accelerating rate of 44 acres/year. Sediment budget disruption and sea level rise are primary suspects. Research is continuing to determine the causes and design solutions. To this end the Department has developed marsh loss strategies for Jamaica Bay and for tidal wetlands loss in general.
To fulfill a marsh loss strategy requirement, as described in Tidal Wetlands Loss Strategies, the Department conducted an expedited trends analysis of tidal wetlands in Nassau and Suffolk Counties. The areas of interest covered harbors, bays and rivers on the north and south shore and Peconic Bay . On the north shore 5 areas were explored: Manhasset Bay, Nassau County, Nissequogue River, Stony Brook Harbor, Flax Pond and Mount Sinai Harbor, the latter four in Suffolk County. On the south shore western bays in Nassau and Suffolk were also studied including: South Oyster Bay (Gilgo Islands and Goose Island), Middle Bay (West Islands) and islands in East Bay. In Peconic Bay, Corey and Cedar Beach Creeks were analyzed. Target sites within these areas of interest were chosen because they showed signs of loss during flyovers and field inspections.
The trends analysis included examination of aerial infra-red photographs from 1974 (photos of the original tidal wetlands inventory) and contemporary aerial photography (1994 New York State Digital Ortho Quads, 1999 Suffolk County Planning aerial photographs, 1998, 2001, 2002 true color aerial photographs). All photographs showed the tidal wetlands boundary clearly. As with the Jamaica Bay work, the photos were digitized and placed in a Geographical Information System (GIS). The tidal wetlands boundary (TWB) was then digitized, creating a second component of the GIS by which the area of the tidal wetlands could be assessed. The following tables show the trends of targeted wetlands on the North Shore, South Shore and Peconic Estuary.
|Area||Targeted Wetland||1974 acreage||1994 acreage||1999 acreage||Acres Lost||% Loss||Acres Lost/Year|
|Manhasset Bay||Kings Point||2.3||0.48||*||1.82||79||0.091|
|South Manhasset Bay||5.34||1.28||*||4.06||76||0.2|
|Nissequogue River||Center Island and East Shore||61.14||*||54.18||6.96||11.4||0.278|
|Stony Brook Harbor||Youngs Island||70.58||*||29.96||40.62||57.5||1.62|
|Flax Pond||Entire Pond||73||*||58||15||20.5||0.75|
|Mount Sinai Harbor||Center Marsh Islands||95.32||*||48.65||46.67||48.96||1.86|
|Total Acres Lost||123.75|
|Area||Targeted Wetland||1974 acreage||2002 acreage||Acres Lost||% Loss||Acres Lost/Year|
|Peconic Bay||Corey Creek||28.16||20.41||7.75||27.5||0.28|
|Cedar Beach Creek||19.72||11.16||8.56||43.4||0.3|
|Total Acres Lost||16.31|
|Area||Targeted Wetland||1974 acreage||1998 acreage||2001 acreage||Acres Lost||% Loss||Acres Lost/Year|
|South Oyster Bay||Gilgo Islands||108||*||70||38||36||1.4|
|Middle Bay||West Islands||527||*||404||123||23||4.5|
|East Bay||East Bay Islands||606||498||*||108||18||4.0|
|Total Acres Lost||284|
* Acreage was not calculated for these years.
All wetland areas studied except the Nissequogue River(11%) greatly exceeded the 10% criteria set in the marsh loss strategy. While loss of tidal wetlands at the subject sites must be assessed on a case by case basis, no direct filling or dredging of the vegetated marsh was known to occur. Losses occurred for one or more of the following reasons: wave energy, erosion, sand accretion, sediment budget disruption, subsidence, dredging and sea level rise. Unlike Jamaica Bay, mussel dams were not a factor.
This preliminary expedited trends analysis focused on areas that represented qualitative losses discovered while conducting annual video and photographic inventories. While the losses are high in those target areas, they represent only those specific areas listed. The marsh loss phenomenon requires further study to determine the reasons for the losses, and the development of marsh management and restoration plans. Below are photographic comparative examples of the losses observed.
These photographs show the four acres of tidal marshes lost between 1974 and 1994 in the southern portion of Manhasset Bay.
The data indicates significant loss of intertidal marsh (especially islands and also along the shoreline). Reasons are speculative. At this site it appears that the marsh has drowned due to sea level rise. Some erosion along the dredged channel edge may have occurred but a careful look indicates that shoals and mudflats still exist. The dredging may have compromised the subaquatic base of the marsh causing accelerated subsidence.
Approximately five and a half acres were lost between 1974 and 1994 along Sheets Creek in Manor Haven (Nassau County).
Vegetated tidal wetlands along Sheets Creek have disappeared leaving exposed mudflats. The area immediately adjacent to the vegetated tidal wetlands has not been dredged, other alterations are not immediately apparent. Further analysis of this site and others like it is necessary. Because intertidal marsh is critical to estuarine productivity and New York State has lost much intertidal marsh historically, it is essential to give priority attention to the assessment of the problem marine-district-wide, and develop remediation/restoration/research and monitoring strategies where possible and necessary.
One hundred eight acres of tidal wetlands were lost on a section of East Bay Marsh complex between 1974 and 1998.
Target marsh complexes from Hewlett Bay to South Oyster Bay on the south shore are experiencing similar marsh losses.
On a target marsh in Middle Bay, 123 acres of tidal wetlands were lost between 1974 and 2001.