Many forest ecosystems in Central Europe have reached the
status of N saturation due to chronically high N deposition. In consequence, the
NO3 leaching into ground- and surface waters is often substantial.
Critical loads have been defined to abate the negative consequences of the NO3
leaching such as soil acidification and nutrient losses. The steady state mass
balance method is normally used to calculate critical loads for N deposition in
forest ecosystems. However, the steady state mass balance approach is limited
because it does not take into account hydrology and the time until the steady
state is reached. The aim of this study was to test the suitability of another
approach: the dynamic model INCA (Integrated Nitrogen Model for European
Catchments). Long-term effects of changing N deposition and critical loads for N
were simulated using INCA for the Lehstenbach spruce catchment (Fichtelgebirge,
NE Bavaria, Germany) under different hydrological conditions.
Long-term
scenarios of either increasing or decreasing N deposition indicated that, in
this catchment, the response of nitrate concentrations in runoff to changing N
deposition is buffered by a large groundwater reservoir. The critical load
simulated 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–1
compared to 10 kg ha–1yr–1 for the steady state
model. Under conditions of lower precipitation (520 mm) the resulting critical
load was 7.7 kg N ha–1yr–1 , suggesting the necessity
to account for different hydrological conditions when calculating critical
loads. The INCA model seems to be suitable to calculate critical loads for N in
forested catchments under varying hydrological conditions e.g. as a consequence
of climate change.
Keywords: forest ecosystem, N saturation, critical load, modelling,
long-term scenario, nitrate leaching, critical loads reduction, INCA |