Determinants of summer nitrate concentration in a set of Adirondack lakes,New York

Following reductions in the emission and deposition of sulfur compounds in the past decade, atmospheric deposition of nitrogen has become a focus of c oncern. Identification of watershed characteristics that mediate the effect of atmospheric nitrogen deposition can help evaluate the sensitivity of la kes to chronic and episodic nitrogen addition. Twenty four lakes in the sou thwestern portion of the Adirondack Park, New York, U.S.A., were classified into three N classes by cluster analysis of lakewater NO3-N concentration [N] during the summers of 1994-1996. The lake-N classes were best character ized as having (1) low [N] throughout the summer, (2) high [N] in early- bu t low [N] in late-summer, and (3) high [N] throughout the summer. The three lake-N classes were reconstructed perfectly by canonical discriminant anal ysis based mainly on lake average depth (AD), and lakewater concentrations of chlorophyll a [Chla] and SO4-S [S] in mid-summer. Increases in AD and [S ], but decrease in [Chla] corresponded with a transition from low- to high- N classes.