Effects of lowering nitrogen and phosphorus surpluses in agriculture on the quality of groundwater and surface water in the Netherlands

The small improvement in the quality of surface waters upon lowering surpluses in agriculture is related to the relative importance of other nutrient sources, including wastewater discharges, nutrient imports via rivers, seepage of nutrient-rich 'old' groundwater and sediments. The relative contribution of other sources to the loading of surface waters varies between water districts, and as a result N and P concentrations in surface waters vary regionally. For improving the ecological state of surface waters, we recommend a combination of low N and P surpluses in agriculture, with dredging P rich sediments, flushing of ditches, and decreasing discharges from other sources.