Interactions between climate change impacts and nutrient mitigation measures: Comparison of the Selke (Germany) and Berze (Latvia) catchments

Seifeddine Jomaa1, Arturs Veinbergs2, Xiaoqiang Yang1, Ainis Lagzdins2, Kaspars Abramenko2 and Michael Rode1

 

1 Department of Aquatic Ecosystem Analysis and Management, Helmholtz Centre for Environmental Research ˗ UFZ, Magdeburg, Germany (seifeddine.jomaa@ufz.de)

2 Department of Environmental Engineering and Water Management, Latvia University of Agriculture, Jelgava, Latvia (arturs.veinbergs@llu.lv)

There is an increasing concern about the environmental deterioration of streams due to the growing anthropogenic pressures as well as the impacts of land use and climate changes. Hydrological water quality modelling has been proven to be an appropriate decision supporting tool to improve the physical understanding of processes and then to test the effects of different nutrient mitigation measures and their interactions with climate change impacts. This study is a part of the MIRACLE-Bonus project, where the Hydrological Predictions for the Environment (HYPE) model was used to test the interactions between preventive nutrient mitigation measures, suggested by stakeholders, and climate change effects in two different catchments. Two agricultural-dominant land use catchments (≈ 50%), but distinct in terms of topography, soil type and climate conditions; the Selke (463 km2 in Germany) and Berze (872 km2 in Latvia) were used as implementation sites.

First, the HYPE model was successfully tested to mimic the baseline simulations (for the period 2005-2014) for discharge (Q), Nitrate-N (NO3-N) and Total Phosphorus (TP), for both catchments. Multi-site and multi-objective calibration approach was considered. Second, the effects of different stakeholders-designed mitigation measures on nutrient loads were simulated. Mitigation measures include both agricultural targeting measures, e.g., buffer strips, reduced tillage and optimized fertilizer application rates, as well as point-sources controlling inputs such as increased number of households connected to wastewater treatment plants and improved wastewater treatment efficiency. The scenario modelling was delivered in close cooperation with cost-benefit assessments. Third, the interactions between climate change effects and mitigation measures were investigated in the horizon of 2016-2045. Particularly, modelling results of how much the suggested measures by stakeholders in each case study can mitigate the climate change effects were evaluated.

For the Selke case study, results showed that, the implementation of 10-m buffer strips close to the streams reduces the TP loads by 10% at the catchment outlet. Also, it was found that reduced tillage’s is more efficient than the implementation of contour ploughing’s measure, where the TP loads were reduced by about 12% and 6%, respectively. For NO3-N loads, findings showed that 20% reduction of nitrogen fertilizer decreases the loads by about 6% compared to the baseline simulations. Results revealed that climate change will increase the TP loads due to the amplified storm events occurrence in the near future.

For the Berze case study, the implementation and maintenance of 10-m buffer strips along waterways and 2-m along open drainage ditches in agricultural lands could reduce the TP loads by 6%. Also, it was found that improvements in three existing municipal wastewater treatment plants according to the HELCOM recommendations for increased treatment efficiency would reduce the TP and TN loads at the outlet of the Berze River catchment by 2% and 0.1%, respectively. In addition, it was obtained that reduced application rate of mineral fertilizer by 20% would result in reduced TN loads by 13%.