Towards ecohydrological nutrient management for river basin districts

Nitrogen and phosphorus emissions to ground- and surface waters must be drastically reduced to achieve the environmental objectives of the Water Framework Directive (WFD) in Europe. In order to reach the targets a four-step strategy must be followed by water managers. First, target nutrient concentrations for groundwater and surface water bodies must be defined. The second step is the quantification of nitrogen and phosphorus inputs to water bodies and the identification of dominant input pathways. Measures are planned and implemented during the third stage, and are most effective when they focus on nutrient emission pathways that are quantitatively important at river basin scale. Finally, the effect of measures must be evaluated using monitoring data, and if there is still a large distance to target the policy for implementing measures must be modified. In Germany, nitrogen and phosphorus emissions to ground- and surface waters arise mostly from agriculture. It is estimated that improving agricultural practice via a renewed Fertilization Ordinance will lower nitrogen emissions by 10–15%. Many agricultural measures aim to improve nutrient efficiency by using manure and biogas digestate as fertilizer, which has positive economic benefits for the farmer because it reduces the requirement for mineral fertilizers. However, it is clear that the WFD objectives cannot be achieved through agricultural measures alone. Therefore, nutrient retention must be improved by restoring rivers and wetlands. In areas where there is insufficient space for cost-effective natural solutions, ecohydrotechnical solutions such as drainage ponds, denitrification barriers or filter systems can be employed.