The NITREX project (Nitrogen saturation experiments)

The NlTREX (Nitrogen Saturation Experiments) project investigates the role of nitrate and ammonium in acidification of coniferous forest ecosystems across a pollution gradient in northern and central Europe. Nitrogen deposition is experimentally changed to entire forest ecosystems at 7 sites - nitrogen addition at sites of relatively low present-day deposition and nitrogen removal by roofs at sites with high present-day deposition. Ecosystem input-output budgets and each of the major components of the ecosystem are investigated - water, soil, vegetation, fauna - and integrated at two levels: 1) by studying the transfer of nitrogen within the entire ecosystem by means of 15N-tracer studies and nitrogen cycling models, and 2) by studying the response to treatments among the same components in different ecosystems in the network ("cross-site comparisons"). The first phase of NITREX (1991-93) involves 12 research institutions in 6 nations. NITREX is linked to several other EC projects such as EXMAN and ENCORE. Here we describe the individual sites and investigations in NITREX and briefly summarize preliminary results to date.