Abstract : The EU directive has addressed ambitious targets
concerning the quality of water bodies. Predicting water quality
as affected by land use and management requires using
dynamic agro-hydrogeological models. In this study, an agronomic
model (STICS) and a hydrogeological model
(MODCOU) have been associated in order to simulate nitrogen
fluxes in the Seine-Normandie Basin, which is affected by
nitrate pollution of groundwater due to intensive farming systems.
This modeling platform was used to predict and understand
the spatial and temporal evolution of water quality over
the 1971–2013 period. A quality assurance protocol
(Refsgaard et al. Environ Model Softw 20: 1201–1215,
2005) was used to qualify the reliability of STICS outputs.
Four iterative runs of the model were carried out with improved
parameterization of soils and crop management without
any change in the model. Improving model inputs changed
much more the spatial distribution of simulated N losses than
their mean values. STICS slightly underestimated the crop
yields compared to the observed values at the administrative
district scale. The platform also slightly underestimated the
nitrate concentration at the outlet level with a mean difference
ranging from −1.4 to −9.2 mg NO3 L−1 according to the aquifer
during the last decade. This outcome should help the stakeholders
in decision-making to prevent nitrate pollution and
provide new specifications for STICS development.
