December 17, 1999

Contact: Geoff Ryan (718/595-5371)

Wetland Reports Released

The United States Fish & Wildlife Service (USFWS) has completed two reports for the New York City Department of Environmental Protection (DEP) that review wetland conditions over the last 30 years in the watersheds of the City's East-of-Hudson reservoirs. "Wetland Trends in the Croton Watershed, New York: 1960s to 1990s" traces the changes in wetland types, as well as wetland gains and losses in the 387-square-mile watershed during two periods — 1968-1984 and 1984-1994. From 1968 to 1984, the annual net loss of vegetated wetlands averaged 9.1 acres per year. During the 1984-1994 period, the rate dropped to 4.3 acres per year. Over the 26-year period, approximately 190 acres of vegetated wetlands were converted to uplands or ponds. Primarily as a result of residential development, almost 100 acres of the lost wetlands, 90 of which were forested, were converted to shallow, open- water ponds. The 190-acre loss represents 1.2 percent of the wetlands that existed at the start of the study period in 1968.

Although ponds perform some important water quality functions, it is not known how the increase in ponds at the expense of vegetated wetlands has affected water quality in the Croton Watershed. It is known, however, that vegetated wetlands provide significant benefits — filtering pollutants from the waters that flow into wetlands from surrounding uplands; slowing the flow of waters, which reduces soil erosion and other impacts of storms and floods; and nutrient cycling, which reduces nitrogen and phosphorus loads in the reservoirs.

The second report, "Wetland Characterization and Preliminary Assessment of Wetland Functions for the Boyd Corners and West Branch Sub-basins of the Croton Watershed," is technical in nature and presents a preliminary strategy for assessing wetland functions. As such, it is a progress report that outlines a remote sensing approach to wetland functional assessment that was recently developed by USFWS and implemented as a pilot study in the West Branch and Boyd Corners Reservoir sub-basins. USFWS interpreted maps and aerial photography to classify wetlands according to their landscape setting, land form and hydrologic flow paths. Wetland classifications were verified by field checking and then used to provide a preliminary evaluation of eight wetland functions: surface water retention, streamflow maintenance, nutrient cycling, sediment and particulate retention, shoreline stabilization, and habitat for fish, waterfowl, waterbirds and other wildlife. Maps were then produced that differentiate wetlands based on their potential to perform specified functions at significant levels.

This preliminary report will serve as the basis for further study by DEP scientists who will verify and quantify the water quality functions of wetlands in two pilot sub-basins. Assessment of wetland functions will help DEP develop wetland protection and non-point source pollution prevention programs, quantify the roles of wetlands for water quality modeling, provide guidance for regulatory permit decisions, and help to direct management of the City's own watershed wetlands.

In 1997, DEP published another USFWS study, "Wetlands in the Watersheds of the New York City Water Supply System: Results of the National Wetlands Inventory," which describes the variety and status of wetlands in both the East-of-Hudson and West-of-Hudson watersheds of the New York City Water Supply System. Copies of all three reports are available by phoning 914/773- 4422.