Modeling Flow and Nitrate Fate at Catchment Scale in Brittany (France)

Abstract

In the intensive pig-farming (Sus scrofa) area of Brittany (western France), many surface and subsurface water resources are contaminated by nitrate (NO₃) with concentrations that chronically exceed the European Community 50 mg L⁻¹ drinking standard. To ensure sustainable water supply, the fate of NO₃ must be considered in both surface water and ground water. The fate of N was investigated in a Britain catchment, the Coët-Dan watershed, with an integrated management tool: the hydrological SWAT model coupled with the ground water model MODFLOW, and its companion contaminant and solute transport model MT3DMS. The model was validated with respect to water quantity during a 6-yr period and for the NO₃ concentration during a 44-mo period, at two gauging stations in the catchment. The coupled models reproduced accurately the measurements. At the basin outlet, the Nash-Sutcliffe coefficients were 0.88 for monthly flow for the entire period and 0.87 for monthly N load. Alternative scenarios were simulated and showed potential benefits of decreasing manure application from 210 to 170 kg N ha⁻¹ as required by the European Commission Nitrates Directive. Copyright © 2003. American Society of Agronomy, Crop Science Society of America, Soil Science Society . ASA, CSSA, SSSA