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Landscape template of New York City’s drinking-water-supply watersheds

350 210 Stroud Water Research Center

Arscott, D.B., C.L. Dow, and B.W. Sweeney. 2006. Journal of the North American Benthological Society 25(4):867–886.

doi:10.1899/0887-3593(2006)025[0867:LTONYC]2.0.CO;2

Abstract

New York City (NYC) receives >99% of its drinking-water supply from streams, rivers, and reservoirs north and northwest of the city (east or west of Hudson River [EOH or WOH, respectively]). As part of a large-scale enhanced water-quality monitoring project (the Project) in NYC’s drinking-water-supply watersheds, 60 stream and 8 reservoir sampling sites were established in the water-supply area (30 WOH and 30 EOH) and sampled from 2000 to 2002. Our study describes watershed characteristics (including climate and hydrology, land use, human population, and known point-source discharges) at each study site and provides an analysis of differences in land use quantified at 3 scales: 1) watershed, 2) riparian (30 m on each side of entire stream network upstream of a site), and 3) reach (same as riparian, but truncated 1 km upstream of the study site). Regression analysis was used to determine relationships among scales, and principal components analysis was used to describe spatial differences in watershed characteristics across the study region. EOH sites are on smaller streams than WOH sites because the WOH region is much larger than the EOH region. EOH sites had smaller mean annual area-specific discharges than WOH sites, reflecting differences in precipitation and in watershed hydrologic retention that were related to surficial geology and the presence of wetlands, lakes, and reservoirs. Population densities, point-source discharges, and flows from those discharges were higher in EOH watersheds than in WOH watersheds. Landuse values in the EOH watersheds ranged from 87% forest to 57% urban. Agricultural land use exceeded 16% in only one watershed. Landuse values in WOH watersheds indicated either largely forest (several sites near 98%) or agriculture and grassland (many near 25%, largely in pasture). Urban landuse values were never >11%. Values for most landuse categories were strongly correlated (most R2 > 0.75) between the watershed and riparian scales. In WOH watersheds, values for categories indicating human land use (e.g., agriculture, urban) were greater at the riparian than at the watershed scale, indicating that human land use was concentrated along the stream network. In EOH watersheds, values for categories indicating human land use were lower at the riparian than at the watershed scale. Values for most landuse categories were not correlated (typically R2 < 0.50 or not significant) between the reach and watershed scales, indicating that local landuse values described statistically different conditions than watershed- or riparian-scale landuse values.

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