Long-term modelling of nitrogen turnover and critical loads in a forested catchment using the INCA model

摘要

Many forest ecosystems in Central Europe have reached thestatus of N saturation due to chronically high N deposition. In consequence, theNO₃ leaching into ground- and surface waters is often substantial.Critical loads have been defined to abate the negative consequences of the NO₃leaching such as soil acidification and nutrient losses. The steady state massbalance method is normally used to calculate critical loads for N deposition inforest ecosystems. However, the steady state mass balance approach is limitedbecause it does not take into account hydrology and the time until the steadystate is reached. The aim of this study was to test the suitability of anotherapproach: the dynamic model INCA (Integrated Nitrogen Model for EuropeanCatchments). Long-term effects of changing N deposition and critical loads for Nwere simulated using INCA for the Lehstenbach spruce catchment (Fichtelgebirge,NE Bavaria, Germany) under different hydrological conditions. Long-termscenarios of either increasing or decreasing N deposition indicated that, inthis catchment, the response of nitrate concentrations in runoff to changing Ndeposition is buffered by a large groundwater reservoir. The critical loadsimulated by the INCA model with respect to a nitrate concentration of 0.4 mg N l–1 as threshold value in runoff was 9.7 kg N ha–1yr–1compared to 10 kg ha–1yr–1 for the steady statemodel. Under conditions of lower precipitation (520 mm) the resulting criticalload was 7.7 kg N ha–1yr–1 , suggesting the necessityto account for different hydrological conditions when calculating criticalloads. The INCA model seems to be suitable to calculate critical loads for N inforested catchments under varying hydrological conditions e.g. as a consequenceof climate change. style="line-height: 20px;">Keywords: forest ecosystem, N saturation, critical load, modelling, long-term scenario, nitrate leaching, critical loads reduction, INCA