b'Challenges in reducing nutrient and sediment losses in agricultural catchments Bieroza M11Department of Soil and Environment, Swedish University of Agricultural Sciences, 75007 Uppsala, SwedenFreshwater ecosystems are subjected to multiple pressures in agricultural catchments resulting in gradual deterioration of their chemical and ecological status. One of the major pressures is nutrient and sediment loss to receiving waters. These can be reduced by appropriate changes in land/crop/fertiliser management at farm and field scale and implementation of mitigation measures in the drainage and stream network. The drainage and stream mitigation measures aim at slowing down water flow (e.g. by increasing retention time) and increasing the rates of physical and biogeochemical processes removing nutrients and sediments from water. However, the effectiveness of drainage and stream mitigation measures shows a large spatial (between catchments) and temporal (between seasons and years) variation. In this paper we discuss the effects of changing weather and legacy sources on effectiveness of mitigation measures for a small clay-soil agricultural catchment in Sweden. We show how mitigating a single pollutant can lead to pollution swapping effects and how difficult it is to achieve satisfactory improvements in water quality in the short-term.7'