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.

The hydrologic response of a river basin pertains to how precipitation is partitioned into streamflow, evapotranspiration, and infiltration. The reliability of all these components is essential for the sustainable use of water resources. This paper seeks to understand if the prediction of the main components of the water balance from the SWAT model can be controlled and interpreted by a simple Darwinian approach: the Budyko framework. The Danube Basin was selected to assess the SWAT model green (evapotranspiration) and blue water fluxes (water yield or water that runs off the landscape into rivers) in a diagnostic approach based on two mono-parametric Budyko curve-type equations. This analysis was conducted comparing the evaporative index (EI) and the base flow index (BFI) predicted by Budyko’s equations based on observed data from 418 gauging stations with those simulated by SWAT. The study demonstrated that SWAT evapotranspiration estimations were in good agreement with those of the Budyko curves, whereas SWAT baseflow underestimated the Inn and Austrian Danube regions. The analysis of the Budyko equations in each water management region of the Danube provided a pioneering understanding of the relationship between EI and BFI in the study area, leading to an improvement of the hydrological simulations and providing a more reliable water balance in each water management region.

Water contamination caused by the presence of excessive amounts of nitrate can be catastrophic for aquatic ecosystems and human health. Due to these high risks, a great deal of emphasis has been placed on finding effective measures to reduce nitrate concentrations in rivers and aquifers. In this study, we used the SWAT model based on grid-cells of 5 minutes of resolution for assessing the processes involved in nitrate loads generation and transport into aquifers and rivers and for providing basin management strategies of nitrate reduction. We applied the model in the Po River Basin (Italy), one of the most densely populated and highly agriculturally exploited area in the Mediterranean basin. The model was successfully calibrated and validated in eight monitoring stations along the Po River for the period 2000–2012. Simulated monthly streamflow and nitrate concentrations were in good agreement with observations, obtaining values of bias around ±25% in both calibration and validation. Among the tested scenarios of nitrogen reduction from agricultural sources, red clover cover crop after corn, coupled with a targeted reduction of mineral fertilizers and the limitation of nitrogen manure leads to a reduction of nitrate leaching and nitrogen emissions of around 37%.

Nitrogen and phosphorus are key to human life and crop production. However, excessive nutrient losses from agriculture affect air, soil, and water quality, with significant negative effects on terrestrial and aquatic ecosystems. Domestic nutrient emissions, in particular untreated wastewater, also negatively affect water ecosystems. European policies had a crucial role in contrasting nutrient pollution, but the assessment of the impact of these regulations requires an understanding of nutrient inputs and losses from land to sea. In this study, we quantified nutrient inputs in a cross-continental domain (Europe–Africa–Asia) in all regions discharging into the European seas. We reconstructed the time series for the 1979–2019 periods of high spatial resolution anthropogenic nutrient pressures including nitrogen atmospheric deposition, mineral fertilizers and organic N and P fertilizers, N and P from sewer connection, and improved and unconnected systems from urban and rural populations. We investigated regional differences and how existing legislation has affected nutrient inputs.

In Europe, excessive nutrient pollution in freshwater and marine ecosystems poses a significant threat to human uses of water resources and disrupts aquatic ecosystems, compromising essential ecosystem services. The effectiveness of existing EU policies aimed at mitigating nutrient pollution will be influenced by the combined impact of climate variability and change. It remains uncertain whether current policies will suffice to reduce nutrient pollution to levels compatible with good environmental conditions in freshwaters and coastal waters. This study quantifies nitrogen and phosphorus fluxes in European freshwater systems and their delivery to the sea, considering the effects of existing EU policies and climate change up to 2050. Using the GREEN model, we simulated total nitrogen and phosphorus loads from 1990 to 2021 and projected future changes until 2050 using climate projections from 11 regional climate models (EURO-CORDEX) under the RCP 4.5 scenario. Our results indicate that implementing current EU policies—Common Agricultural Policy, Urban Waste Water Treatment Directive, FitFor55 package for climate neutrality—will reduce nutrient loads to European seas by 2050, with a 10% decrease in nitrogen and 8% decrease in phosphorus loads compared to 2020 values, albeit with significant uncertainty related to climate variability. Regional differences are also explored. Nutrient concentrations in the EU river network are expected to decrease slightly, as well as the potential risk for coastal eutrophication (ICEP index). However, further reductions of 10%–20% beyond existing policies may be necessary to achieve good conditions in large rivers. These reductions could come from improved agricultural practices, nature-based solutions and wetland restoration. Our study suggests that while current measures will lead to improvements by 2050, additional efforts will be required in some regions to achieve good environmental conditions, highlighting the need for integrated nutrient management to avoid imbalances between nitrogen and phosphorus in receiving waters.

Excessive nutrients in rivers, lakes and aquifers are still threatening environmental health in Europe. Stringent regulations have led to progress in water quality, however hotspots with high nitrate concentrations still exist in Europe and understanding the impact of management on the nitrate concentrations and trends in these critical areas is still challenging. In this paper, we use the Exploration and Graphics for RivEr Trends (EGRET) statistical tool to eliminate the impact of flow variation, both short- and long-term, on nitrate concentration. We apply this tool to the south of France where water quality and quantity monitoring data is readily available. We compare the Mann–Kendall non-parametric approach to estimate trend and a methodology commonly used by Member States of the European Union when they report their progress in implementing the Nitrates Directive (referred to MSD approach hereafter). We showed that using the latter approach for the period 2008–2015 and the Mann–Kendall test leads to similar results in percentage of stations exhibiting trends, however with a significant disagreement on the stations exhibiting these trends. We further showed that when using flow-weighted nitrate concentrations instead of the simple mean nitrate concentration, the MSD approach results in a significant underestimation of the stations with an increasing trend. We also demonstrated that most of nitrate concentration time series are characterized by a bell-shaped curve with an increase of concentration from 1990 to mid-2000 and then a significant decreasing trend due to the implementation of management measures from mid-2000 to 2017. Most of the significant decreasing nitrate concentration trends are localized in Nitrate Vulnerable Zones that correspond to areas where strict nutrient management is required, highlighting the efficiency of the policy in place.