The ecohydrological approach, SWAT modelling, and multi-stakeholder engagement - A system solution to diffuse pollution in the Pilica basin, Poland.

The reduction of diffused nutrient pollution from agriculture is one of the defining challenges of our time, demanding system solutions. A nitrogen and phosphorus (N&P) reduction strategy at the catchment scale is the most realistic and effective long-term approach to eutrophication management. In this study, a voluntary programme for the reduction of diffuse pollution was developed for the Pilica catchment and the Sulejów Reservoir in Poland. The Action Plan was based on the ecohydrological approach, which strives to use ecosystem processes as a management tool. One fundamental element of the Plan was a SWAT model, used to estimate N&P emissions and to determine the priority areas in the catchment. Strong cooperation between water managers, interdisciplinary researchers, and stakeholders helped to catalyse the capacity-building process of public participation, through dialogical interaction including a critical exchange of knowledge. Finally, a list of selected spatially-targeted mitigation measures was generated based on the modelling results and following measure acceptance by stakeholders. The key assumption in the creation of the measure list was that ecohydrological nature-based solutions (NBS) should be used complementarily to good agricultural practices. Such an approach has contributed to a faster achievement of 'good ecological status' of water bodies.

Climate change and agricultural development: adapting Polish agriculture to reduce future nutrient loads in a coastal watershed.

Currently, there is a major concern about the future of nutrient loads discharged into the Baltic Sea from Polish rivers because they are main contributors to its eutrophication. To date, no watershed-scale studies have properly addressed this issue. This paper fills this gap by using a scenario-modeling framework applied in the Reda watershed, a small (482 km²) agricultural coastal area in northern Poland. We used the SWAT model to quantify the effects of future climate, land cover, and management changes under multiple scenarios up to the 2050s. The combined effect of climate and land use change on N-NO3 and P-PO4 loads is an increase by 20-60 and 24-31 %, respectively, depending on the intensity of future agricultural usage. Using a scenario that assumes a major shift toward a more intensive agriculture following the Danish model would bring significantly higher crop yields but cause a great deterioration of water quality. Using vegetative cover in winter and spring (VC) would be a very efficient way to reduce future P-PO4 loads so that they are lower than levels observed at present. However, even the best combination of measures (VC, buffer zones, reduced fertilization, and constructed wetlands) would not help to remediate heavily increased N-NO3 loads due to climate change and agricultural intensification.

How effective are River Basin Management Plans in reaching the nutrient load reduction targets?

Riverine nutrient loads are among the major causes of eutrophication of the Baltic Sea. This study applied the Soil & Water Assessment Tool (SWAT) in three catchments flowing to the Baltic Sea, namely Vantaanjoki (Finland), Fyrisån (Sweden), and Slupia (Poland), to simulate the effectiveness of nutrient control measures included in the EU's Water Framework Directive River Basin Management Plans (RBMPs). Moreover, we identified similar, coastal, middle-sized catchments to which conclusions from this study could be applicable. The first modelling scenario based on extrapolation of the existing trends affected the modelled nutrient loads by less than 5%. In the second scenario, measures included in RBMPs showed variable effectiveness, ranging from negligible for Slupia to 28% total P load reduction in Vantaanjoki. Adding spatially targeted measures to RBMPs (third scenario) would considerably improve their effectiveness in all three catchments for both total N and P, suggesting a need to adopt targeting more widely in the Baltic Sea countries.