Nitrogen leaching losses from two Baltic Sea catchments under scenarios of changes in land use, land management and climate

Jørgen E. Olesen1, Dominika Bar-Michalczyk2, Thomas Bosshard3, Christen D. Børgesen1, Anne Lausten Hansen4, Mohamed Jabloun5, Jens Christian Refsgaard4 and Przemyslaw Wachniew2

 

1 Department of Agroecology, Aarhus University, Tjele, Denmark

2 AGH University of Science and Technology Faculty of Physics and Applied Computer Science Krakow, Poland

3 Swedish Meteorological and Hydrological Institute, Norrköping, Sweden

4 Department of Hydrology, Geological Survey of Denmark and Greenland, Copenhagen K, Denmark

5 University of Nottingham, Nottingham, UK

 

The Baltic Sea Action Plan and the EU Water Framework Directive requires further reductions in nitrogen (N) loadings to the sea, a large part of which originates from agricultural land. Also the geology in the catchments influences N flows and the N reduction processes affecting loading. Measures therefore need to be taken to reduce N loadings. However, future climate change and changes in socioeconomic developments will affect the baseline on top of which mitigation measures for reducing N loadings need to be taken.

We analysed the effect of a combination of land use and climate scenarios on N leaching from two catchments in the Baltic Sea: Norsminde in Denmark and Kocinka in Poland. The two catchments vary greatly in time lag of the groundwater flow and the related N retention and reduction processes. For each catchment the effects on N leaching were analysed with the NLES leaching model, which at Norsminde was linked to a physically-based distributed groundwater model (MIKE SHE). The land use changes were based on three selected future scenarios taken from the Shared Socioeconomic Pathways (SSP), i.e. SSP1 (sustainability), SSP2 (middle of the road) and SSP5 (fossil fuelled development). For each SSP quantitative effects were given for changes in land use and agricultural activities, including fertilisation. The agricultural land use was maintained in SSP2 compared to baseline, reduced by 10% in SSP1 and increased by 10% in SSP5. Livestock density was maintained in SSP2, reduced by 50% in SSP2 and increased by 50% in SSP5. The climate change scenarios cover a 20 year period for 2041-2060 compared with baseline period of 1991-2010, and four different climate model runs were used based on the RCP8.5 emission scenario. The N leaching estimation with the NLES model was recalibrated for the temperature changes in the climate change scenarios using representative model runs with the dynamic Daisy simulation model.

For Norsminde the mean N leaching from agricultural areas was 54-60 kg N/ha in the baseline land use and climate, which increased to 71-88 kg N/ha under projected climate change. Under baseline climate, SSP1 has a reduced N leaching of 9-10 kg N/ha and SSP5 has an increased leaching of 10-11 kg N/ha. These differences increase under projected climate change due to the higher leaching level. These effects are moderated at catchment scale by different land use in the different SSPs. The range of N leaching in the catchment compared with baseline therefore ranges from 5% decrease to 23% increase and for N-load from the catchment between 6% decrease and 26% increase for SSP1. For SSP2 N-leaching is predicted to increase 23%-60% and N-load 20%-59%. For SSP5 N-leaching increases 63%-113% and N-load 52%-106%.

For Kocinka the mean N leaching from agriculture land was 28-34 kg N/ha in SSP2 under baseline climate, and this increases to 38-52 kg N/ha under projected climate change. The leaching in SSP1 was reduced by 2-3 kg N/ha under baseline climate and 3-5 kg N/ha under future climate. In SSP5 N leaching was increased by 3 kg N/ha under baseline climate and 4-5 kg N/ha under projected future climate.

A scenario analysis was conducted for Norsminde to explore how large agricultural area would be needed for spatially targeted set-aside to meet an N-load reduction target of 20% compared to baseline. For SSP2 this set-aside area is about 850 ha under baseline climate increasing to 1400-2200 ha under future cliimate. For SSP1 and SPP5 this range is 650-1400 ha and 2150-3000 ha, respectively, for future climate.