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NEW YORK CITY'S WATER SUPPLY: A 25 YEAR LANDSCAPE ANALYSIS OF THE CATSKILL/DELAWARE WATERSHEDS
Citation:
Mehaffey, M H., M S. Nash, T G. Wade, AND C M. Edmonds. NEW YORK CITY'S WATER SUPPLY: A 25 YEAR LANDSCAPE ANALYSIS OF THE CATSKILL/DELAWARE WATERSHEDS. Presented at The 16th Annual Symposium of the US Regional Chapter of the International Association of Landscape Ecology, Tempe, AZ, April 25-29, 2001.
Impact/Purpose:
The primary objectives of this research are to:
Develop methodologies so that landscape indicator values generated from different sensors on different dates (but in the same areas) are comparable; differences in metric values result from landscape changes and not differences in the sensors;
Quantify relationships between landscape metrics generated from wall-to-wall spatial data and (1) specific parameters related to water resource conditions in different environmental settings across the US, including but not limited to nutrients, sediment, and benthic communities, and (2) multi-species habitat suitability;
Develop and validate multivariate models based on quantification studies;
Develop GIS/model assessment protocols and tools to characterize risk of nutrient and sediment TMDL exceedence;
Complete an initial draft (potentially web based) of a national landscape condition assessment.
This research directly supports long-term goals established in ORDs multiyear plans related to GPRA Goal 2 (Water) and GPRA Goal 4 (Healthy Communities and Ecosystems), although funding for this task comes from Goal 4. Relative to the GRPA Goal 2 multiyear plan, this research is intended to "provide tools to assess and diagnose impairment in aquatic systems and the sources of associated stressors." Relative to the Goal 4 Multiyear Plan this research is intended to (1) provide states and tribes with an ability to assess the condition of waterbodies in a scientifically defensible and representative way, while allowing for aggregation and assessment of trends at multiple scales, (2) assist Federal, State and Local managers in diagnosing the probable cause and forecasting future conditions in a scientifically defensible manner to protect and restore ecosystems, and (3) provide Federal, State and Local managers with a scientifically defensible way to assess current and future ecological conditions, and probable causes of impairments, and a way to evaluate alternative future management scenarios.
Description:
A number of water bodies located within the New York City's water supply system are impaired
by nutrients, pathogens and sediment. The objective of this study was to investigate long term
landscape and water quality trends using multiple snap shots in time spanning two decades
(1975-1998). Biweekly water quality, rainfall and discharge data from 1987-1998 was used to
examine temporal and discharge relations at six locations within the watershed. Stepwise
multiple regression analyses (n-732) were used to determine the contribution of the landscape
metrics to surface water total nitrogen, total phosphorous, and fecal coliform. Percentages of
agriculture and urban development were the dominant landscape variables over the years and
explained 25-65% of the variability in water quality measurements. Barren, agriculture on steep
slopes and agriculture on erodible soils were also contributed significantly to water but explaining only a small portion (4-8%) of the overall variability. During the past two decades the release of agricultural fields from farming has returned a small percentage of land (2%) to
secondary growth forest. Most of the change in landscape took place from 1985 to 1998 and
corresponds to decreases in nitrogen (0.039 to 0.009 mg/L/month) and phosphorous (0.053 to 2.81 mu g/L/month). With over half of the remaining agriculture located within 240 meters of
streams, efforts to further decrease pollution would have the greatest impact by directing best
management practices and land acquisition within these riparian zones.