River and lake nutrient targets that support ecological status: European scale gap analysis and strategies for the...

Eutrophication caused by an excessive presence of nutrients is affecting large portions of European waters with more than 60% of the surface water bodies failing to achieve the primary ambition of water management in Europe, that of good ecological status (GES) with diffuse emission from agriculture being the second most important pressure affecting surface waters. We developed EU wide and regional nutrient targets that define the boundary concentrations between good and moderate status for river and lake total P (TP) and total N (TN) and assessed the gap between actual nutrient concentrations and these targets and considered strategies of nutrient reductions necessary to achieve GES and deliver ecosystem services. The nutrient targets established for rivers ranged from 0.5-3.5 mg/L TN and 11-105 μg/L TP and for lakes 0.5-1.8 mg/L TN and 10-60 μg/L TP. Based on the EU wide targets, 59% of the TN and 57% of the TP river monitoring sites and 64% of the TN and 61% of the TP lake monitoring sites exceed these value and are thus at less than GES. The PCA and step-wise regression for EU basins clearly showed that the basin nutrient export is predominantly related to agricultural inputs. In addition, the step-wise regression models for TN and TP provided the ability to extrapolate the results and quantify the input reductions necessary for reaching the nutrient targets at the EU level. The results suggest that a dual water management strategy would be beneficial and should focus a) on those less polluted rivers and lakes that can easily attain the GES goal and b) on the more highly polluted systems that will improve the delivery of ecosystem services.