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We used the interdisciplinary model network
REGFLUD to predict the actual mean nitrate
concentration in percolation water at the scale of the
Weser river basin (Germany) using an area—differentiated
(100 m 9 100 m) approach. REGFLUD
combines the agro-economic model RAUMIS for
estimating nitrogen surpluses and the hydrological
models GROWA/DENUZ for assessing the nitrate
leaching from the soil. The areas showing predicted
nitrate concentrations in percolation water above the
EU groundwater quality standard of 50 mg NO3/l,
have been identified as priority areas for implementing
nitrogen reduction measures. For these ‘‘hot spot’’
areas a backward modelling approach was used to
quantify the maximal permissible nitrogen surplus
levels in agriculture to guarantee a mean long-term
nitrate concentration in percolation water below
50 mg NO3/l. Research work will directly support
the implementation of the EU-Water Framework
Directive in the Weser basin, e.g. by using the
maximal permissible nitrogen surplus levels as a
framework for the derivation of regionally adapted
and hence effective nitrogen reduction measures.
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