Paysages virtuels et analyse de scénarios pour évaluer les impacts ...

Conclusion
The study develops innovative approaches and results for the multi-resource and multi-criteria assessment of
environmental impacts of agricultural practices. We presented a methodology to derive agricultural virtual
landscapes from observed data and processes by framing the range of variation of the original landscape
features. By comparing the intensive and the moderate cropping systems, we showed that the change of
practices done by the farmers between the 1995-1997 and 2001-2003 period did improve the soil P budgets
and stream N concentration, but not enough to pass below the EU regulation level of 11.3 mg N.l -1 . However,
N concentrations (stream and groundwater) were less sensitive to practice change than climate change (mean
annual rainfalls differing by 0.2 m). Similarly, an extension of the waterlogged soil class in bottom wetland
valley reduced the N stream concentration more significantly than agricultural practices. Moreover,
interaction between soils and climate may reduce the effect of BMP with a wetter climate occurring on
waterlogged soils.
The study showed that although agricultural or hydrological indicators may serve their evaluation purposes
individually, understanding the fate of diffuse elements like nitrogen requires their combination since
transfer and transformation processes are interrelated. Hydrological fluxes of C and P were neglected in this
study although there are strong evidences that they also impact water quality. Phosphorus and dissolved
organic carbon models are being developed and similar multi-factorial experiments based on virtual
landscapes may provide a benchmark for hypothesis test. More generally, multi-factorial virtual landscapes
may be used to perform sensitivity analyses for all kinds of spatially distributed models.
Acknowledgments
The PhD of the first author was funded by the Région Bretagne and INRA. We are grateful to Safya
Menasseri, Fabien Ferchaud, Jordy Salmon-Monviola, and Laurence Lebouille (Chambre d’Agriculture du
Morbihan) for stimulating discussions and their insights on the agronomic data of Kervidy and Frémeur
catchments.
IV. Évaluation environnementale multi-critères et multi-ressources – p. 133