PHOSPHORUS LOSS FROM AGRICULTURAL CATCHMENTS - PATHWAYS AND IMPLICATIONS FOR MANAGEMENT

The contribution non-point P sources make to the total P loading on wa ter bodies in agricultural catchments has not been fully appreciated. Using data derived from plot scale experimental studies, and modelling approaches developed to simulate system behaviour under differing man agement scenarios, a fuller understanding of the processes controlling P export and transformations along non-paint transport pathways can b e achieved. One modelling approach which has been successfully applied to large UK catchments (50-350 km(2) in area) is applied here to a sm all, 1.5 km(2) experimental catchment. The importance of scaling is di scussed in the context of how such approaches can extrapolate the resu lts from plot-scale experimental studies to full catchment scale. Howe ver, the scope of such models is limited, since they do not at pre:len t directly simulate the processes controlling P transport and transfor mation dynamics. its such, they can only simulate total P export on an annual basis, and are not capable of prediction over shorter time sca les. The need for development of process-based models to help answer t hese questions, and for more comprehensive UK experimental studies is highlighted as a pre-requisite for the development of suitable and sus tainable management strategies to reduce nonpoint P loading on water b odies in agricultural catchments.