| The integrated nitrogen model INCA (Integrated Nitrogen in Catchments) was used to analyse the nitrogen dynamics in a small
rural catchment in Western France. The agrosystem studied is very complex, with: extensive use of different organic fertilisers, a variety of
crop rotations, a structural excess of nitrogen (i.e. more animal N produced by the intensive farming than the N requirements of the crops and
pastures), and nitrate retention in both hydrological stores and riparian zones. The original model features were adapted here to describe this
complexity. The calibration results are satisfactory, although the daily variations in stream nitrate are not simulated in detail. Different
climate scenarios, based on observed climate records, were tested; all produced a worsening of the pollution in the short term. Scenarios of
alternative agricultural practices (reduced fertilisation and catch crops) were also analysed, suggesting that a reduction by 40% of the
fertilisation combined with the introduction of catch crops would be necessary to stop the degradation of water quality.
Keywords: diffuse pollution, nitrate, climate change, model |