Efficience des bandes végétalisées pour réduire les transferts de pesticides et d'azote vers les cours d'eau

Abstract

International audienceDiffuse pollution from agricultural and urban sources is of concern for maintaining water bodies at a reasonably good quality status in line with the European Water Framework Directive. The drinking water catchment of Coulonge located within the 10,000 km² wide intensive agricultural Charente river basin in South-western France is threatened by such risks. Some most critical areas have been prioritized by local watershed resource managers. A 4-year program has been funded by the Water Agency for developing specific tools and methods to help water managers and local stakeholders reducing diffuse pollution on the most contributive areas, in an innovative and collaborative approach. Several land-use change scenarios have been built and tested. The assessment of their long term impact on the surface streams quality has been made with the eco-hydrological Soils and Water Assessment Tool (SWAT) model coupled with the GenLU2 application. In this contribution, we focus specifically on the 22 scenarios involving various different strip widths ranging gradually from the commonly used 5m to an extreme and theoretical 30m. Due to the lack of in-situ tests, effectiveness has statistically been evaluated for each of the nine pesticides and for nitrogen fluxes and concentrations in surface streams. We highlight the effect on the combination of the various and progressive widths of filter strips with organic, innovative and conventional cropping systems. We point out that reduction of pollutants clearly varies between molecules and buffer strip widths. We further discuss the prevailing effect of farming systems in pollutant transfers. However, beyond the operational water management concerns, clearly remains the question on the SWAT Filter Strip sub-routine calculations based on empirical assumptions and implemented in the non-distributed Hydrological Response Unit, the SWAT smallest calculation unit. This question of the buffer strips efficacy is also of great expectation for farmers and local watershed managers willing to apply the CAP’s cross-compliance and greening 2010 standards