Monitoring catchment scale agricultural pollution in Norway: policy instruments, implementation of mitigation methods and trends in nutrient and sediment losses

Agricultural management and losses of nitrogen (N), phosphorus (P) and suspended sediments (SS) from eight small (85–2830 ha) catchments in Norway were analysed. The catchments represent areas with different agricultural production systems, soils and climate. Results from the long-term (9–16 years) in-stream monitoring show (i) large differences in levels of losses between the catchments, (ii) large interannual variability and (iii) few time-trends in losses. These results are discussed in relation to changes in agricultural policies and the implementation of soil management practices, such as reduced autumn-ploughing, catch crops, constructed wetlands and changes in nutrient application. Overall, these data demonstrate changes in farmer behaviour driven by economic incentives in combination with active extension services stimulating environmental friendly management practices. However, despite the increased implementation of mitigation methods by farmers, improvements in water quality at the catchment scale can be attenuated. More long-term monitoring programmes are clearly required.