H135-0014
The recent droughts as a time window for future investigation of climate change effects on water quality at the catchment scale

Monday, 14 December 2020
Poster
Xiangqian Zhou, Helmholtz Centre for Environmental Research-UFZ, Department of Aquatic Ecosystem Analysis and Management, Magdeburg, Germany, Seifeddine Jomaa, Helmholtz Centre for Environmental Research - UFZ, Department of Aquatic Ecosystem Analysis and Management, Magdeburg, Germany, Xiaoqiang Yang, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Aquatic Ecosystem Analysis, Berlin, Germany; Helmholtz Centre for Environmental Research UFZ Magdeburg, Magdeburg, Germany and Michael Rode, Helmholtz Centre for Environmental Research - UFZ, Department of Aquatic Ecosystem Analysis and Management, Magdeburg/Leipzig, Germany
Abstract:
Germany has recently experienced summer heatwaves, where the average temperature rose 1.5 °C between the period 1881 and 2018, resulting in severe droughts and ban on water pumping during the low-flow conditions in different regions. This study aims to investigate the effect of the recent drought events that occurred in the period 2015-2018 on the nitrate-N concentrations and loads in the Bode catchment (3300 km2) located in the transition areas of central uplands and northern lowlands of Germany. Also, the capability of a nitrate catchment model to predict the measured concentration under varying weather conditions and using different gauging stations, reflecting catchment heterogeneity, was tested. To this end, the fully-distributed, grid-based catchment water quality model (mHM-Nitrate) was implemented in the Bode catchment.

Measured data showed that in recent periods (2015-2018), there was a declining trend of river nitrate-N concentration in the lower Bode catchment, which is intensively used by arable land. In contrast, there was no trend of river nitrate concentration in the upper Bode catchment, which is mountain area dominated by forest. The model simulation could capture well the dynamics of measured daily discharge and instream nitrate concentration for both calibration (2010-2014) and validation (2004-2009 and 2015-2018) periods at six gauging stations in the Bode catchment, with Nash-Sutcliffe efficiency (NSE) above 0.69 and -0.61 (discharge and nitrate-N, respectively) and percentage bias (PBIAS) less than 30% and 16.8% (discharge and nitrate-N, respectively). The model simulation well represented the decreasing trend of nitrate concentration at Selke sub-catchment outlet (Hausneindorf) and Bode catchment outlet (Stassfurt) stations. Furthermore, results revealed a decrease of nitrate concentration due to reduced lateral nitrate leaching in the lower Bode catchment, which results from a combination of decreased precipitation and increased temperature. This study showed that the recent extreme weather conditions and their effects on nitrate concentration could be used a time window for future scenarios, shedding light on climate change impact on river water quality.

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