BONUS SOILS2SEA – Reducing nutrient loads from agricultural soils to the Baltic Sea via groundwater and streams

Jens Christian Refsgaard1, Jørgen E. Olesen2, Przemyslaw Wachniew3, Anders Wörman4, Alena Bartosova5, Nico Stelljes6, Hubert De Jonge7, Boris Chubarenko8, Rasmus Jakobsen1

 

1 Geological Survey of Denmark and Greenland, Copenhagen, Denmark

2 Aarhus University, Tjele, Denmark

3 AGH University of Science and Technology, Krakow, Poland

4 KTH Royal Institute of Technology, Stockholm, Sweden

5 Swedish Meteorological and Hydrological University, Norrköping, Sweden

6 Ecologic Institute, Berlin, Germany

7 Eurofins Environment, Galten, Denmark

8 Atlantic Branch of the P.P. Shirshov Institute of Oceanology of the Russian Academy of Sciences, Kaliningrad, Russia

 

BONUS SOILS2SEA assesses the nutrient load to the Baltic Sea under changed climate and land use in 2050. Furthermore, BONUS SOILS2SEA develops and tests the concept of spatially differentiated regulation of agriculture as a smart way of reducing nutrient loads by exploiting the fact that the retention (removal by biogeochemical processes or sedimentation) of nutrients in groundwater and surface water systems shows a significant spatial variation, depending on the local hydrogeological and riverine regime. Data and knowledge from field study catchments in Denmark, Sweden, Poland and Russia have been used to improve the HYPE model simulating water flows and nutrient transport for the entire Baltic Sea drainage basin. This has in particular focused on improving HYPE’s capability to predict the effect of spatially differentiated regulatory measures. To support this, BONUS SOILS2SEA has produced a new map of N-retention in groundwater throughout the Baltic Sea drainage basin.

Preliminary results suggest that the nutrient loads to the Baltic Sea are likely to increase between 4% and 10% for N and between 6% and 20% for P as a response to climate change, while the ranges are substantially larger for individual catchments. Similarly, preliminary results suggest that land use change, depending on socio-economic developments, may lead to either a decrease (19% and 6% for N and P, respectively) or an increase (11% and 9% for N and P, respectively) in nutrient loads.

Analyses of differentiated regulation with spatially targeted measures for the agricultural cultivation areas and in streams/wetlands indicate that the N and P loads can be decreased substantially without significantly affecting the agricultural production. Preliminary results suggest that the potential gain in terms of decrease in nutrient loads vary considerably between individual catchments from a few percentage up to 25 % depending on spatial variation in groundwater retention and land use. Analyses also show that it will be difficult to exploit the full potential in practice due to constraints in agricultural land use and management as well as the uncertainties associated with groundwater retention at finer spatial scales.

The differentiated regulation with spatial targeting of measures within catchments implies that farmers are affected differently. Except for economic compensation, a precondition for this to be acceptable by stakeholders, if enforced by central authorities through traditional top-down regulations, is that the local scale information on the spatial variability of nutrient removal is reasonably accurate. As this will require more local data than is typically available today, new governance concepts are required to exploit the full potential gain from differentiated regulation. Results from a series of stakeholder workshops in the three study areas followed by regional stakeholder workshops suggest that the governance regime should be tailored to the local socio-economic and cultural context. Furthermore, in some countries with a strong tradition for local cooperation and a high level of societal trust, a co-governance system with delegation of some decision power to local stakeholders may be better capable of handling the large uncertainties in local scale data and hence better exploit the potential gain from spatially differentiated regulation.