SOLUTE TRANSFER IN AGRICULTURAL CATCHMENTS - THE INTEREST AND LIMITS OF MIXING MODELS

This paper deals with the applicability of the endmember mixing analys is (EMMA) to agricultural catchments. The basic assumptions of the met hod are discussed in the case of semi-natural and rural ecosystems. EM MA was applied to two storm events in a farmland catchment in Brittany (France) using four endmembers and three tracers. The results were va lidated using additional tracers. The sensitivity of the method to unc ertainty in the endmember composition was analysed using a Monte-Carlo procedure. The results were satisfactory although the method is very sensitive when the endmember composition is close to the streamwater c hemistry. It is concluded that mixing analysis is a valuable tool for studying water pathways in agricultural areas, provided it is applied over short periods and used with other hydrological approaches.