| The Adirondack region of New York, receiving among the highest rates of atmospheric nitrogen (N) deposition in the United States, is characterized by soils and surface waters that are highly sensitive to inputs of strong acids. With concerns associated with N deposition, elevated N concentrations in surface waters, and other adverse environmental effects, such as stress to trees and decreases in fish species, there are considerable scientific, policy, and managerial interests in the transport and fate of nitrogen (N) in the region. To evaluate the response of the Adirondack forested ecosystem to atmospheric N deposition, nitrate (NO3−), ammonium (NH4+) dissolved organic nitrogen (DON), and dissolved organic carbon (DOC) in fifty-two (52) Adirondack Long-Term Monitoring (ALTM) lake-watersheds were examined, using lake water samples collected monthly from 1998 to 2000. The lake inlet samples from two lake-watersheds located within 26 km to each other, Grass Pond and Constable Pond, were also examined from May to October in 1999 and 2000 to assist in evaluating terrestrial and in-lake processes.; Wet N deposition was estimated to increase from the northeast to the southwest in the region, in concert with precipitation quantity and NO 3− concentrations. N input-output budget analyses for the lake-watersheds revealed that N drainage loss exhibited a wider range of values than wet N deposition and that N drainage loss and retention did not show distinctive spatial patterns, despite some evidence of the influences of wet N deposition on N outputs and retention.; DON and DOC increased with increasing proportion of wetland area. Vegetation composition appeared to affect N solutes and DOC. While DON and DOC were strongly correlated, their differences in the strength of empirical relationships with wet N deposition, the proportion of wetland area, elevation, and hydraulic residence time suggest that DON and DOC exported from lake-watersheds had different sources and/or undergo different processing. The comparisons of N solutes or DOC/DON ratios between the lake inlets and outlets and the relationships between NO3− output or retention and the ratio of mean depth to water residence time suggest the importance of N sources and processing associated with lakes.; Nitrate concentrations were markedly high at the Grass Pond inlets, which appeared to be due to the contribution of groundwater inputs, while DON was the major N solutes at Constable Pond inlets. The decreasing NO3 − concentrations with increasing DOC/DON ratio in these two lake-watersheds with minimal differences in atmospheric N deposition suggests that NO3− - C/N relationship may not solely be associated with a N deposition gradient, but could be resulted from spatial variations of physical and environmental factors. |
