Input-output budgets at the NITREX sites

Abstract

The NITREX project entails large-scale manipulation of nitrogen deposition to whole, forested ecosystems at eight sites in Europe. Nitrogen is added at sites with low-to-intermediate ambient N deposition and removed at sites with high deposition. Changes in outputs of dissolved constituents reflect the integrated effects on ecosystem processes and changes in storage. At sites exhibiting clear symptoms of nitrogen saturation prior to treatment, the nitrate flux in leachate and runoff responded rapidly to changes in deposition. Reduced deposition gave immediate improvement in water quality. At sites with low nitrogen losses prior to treatment, the response to increased deposition was small and delayed. Together the results point to significant hysteresis in output response related to the nitrogen status of the ecosystem. The input-output budgets indicate that forest ecosystems require many years to adjust to changes in nitrogen deposition.