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Nitrate trends in the Adirondack Mountains, Northeastern US, 1993-2007
Citation:
OELSNER, G. P. Nitrate trends in the Adirondack Mountains, Northeastern US, 1993-2007. Presented at Proceedings of the 24th Meeting of the ICP Waters Programme task Force, Budapest, HUNGARY, October 06 - 08, 2008.
Impact/Purpose:
The Adirondack Mountains in New York State receive some of the highest rates of nitrogen deposition in the Northeastern U.S.
Description:
The Adirondack Mountains in New York State receive some of the highest rates of nitrogen deposition in the Northeastern U.S. Between 1993 and 2007, nitrogen deposition loads did not significantly change and average annual wet inorganic nitrogen deposition was 6 kg/ha (Figure 1). In general, nitrogen deposition is higher in southwest area of the park than in the northeast. To determine the effects of nitrogen deposition on surface water chemistry, the U.S. Environmental Protection Agency (EPA) has collected monthly samples from the outlets of 50 acid-sensitive lakes since 1993 (Figure 2). Nitrate trends were calculated for each lake using a linear regression model and monthly concentrations. Trend slopes with p-values less than 0.1 were considered significant. Although the lakes are located within the same geographic region and are all acid sensitive, they do not exhibit the same response to nitrogen deposition (Figure 2). Approximately half of the lakes (22/50) exhibited decreasing trends in nitrate concentrations while 4 lakes had increasing nitrate concentrations. No significant trend was observed for 24 lakes. We compared the nitrate trends to watershed characteristics including area, lake size, relief, elevation, percent wetland and forest cover and DOC trends to explain the spatial heterogeneity of the nitrate trends. No single watershed characteristic could account for the direction or magnitude of the nitrate trends (Figure 3). Trends in lake nitrate concentrations are likely due to multiple factors including watershed characteristics, soil chemistry and depth. This is an abstract and does not necessarily reflect EPA policy. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. Figure 1. Inorganic nitrogen deposition loads in the Adirondack Park 1993 – 2007 from 5 monitoring stations. Figure 2. Map of Adirondack Park showing monitoring lake locations and trends of nitrate concentrations in lake outlets 1993 – 2007. Figure 3. Comparison of nitrate trends at individual Adirondack lakes with watershed properties. Land cover (% Evergreen Forest and % Wetland), lake size and watershed size were not correlated with the magnitude or direction of nitrate trend slopes.