Assessment of Trends and Leaching of Nitrogen at ICP Waters Sites (Europe and North America) (ICP Waters report 54/2001)

Abstract

The ICP Waters database currently holds data for 204 sites in Europe and North America. These data were evaluated with respect to nitrate concentrations. About 50% of the sites currently have nitrate concentrations indicative of nitrogen saturation, that is, elevated level of nitrate above that expected in undisturbed systems not receiving significant amounts of N deposition. The relative importance of nitrate as an acid anion has increased at the ICP sites since the early 1990s, mostly due to the decrease in sulphate. The data indicate no major change in N saturation at the ICP sites during the 1990s, indicating that progression to increased N saturation is a slow process with a time scale of decades. There is no consistent pattern of trends in nitrate in the ICP waters sites. The overall lack of significant trends may be the result of 2 opposing factors (Wright et al. 2001) continued high deposition of nitrogen should tend to increase N saturation and give increased nitrate in runoff, whereas the decline in N deposition over the past 5-10 years in large parts of Europe should give decreased nitrate in runoff. Short and long-term variations in climate affect nitrate in streamwater, and thus contribute "noise" which masks long-term trends.