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Projection of groundwater nitrate evolution under different climate scenarios in NW Germany

IWRA 2020 Online Conference - Addressing Groundwater Resilience under Climate Change
THEME 2. Climate Change Effects on Groundwater Resilience (Pollution and Remediation)
Author(s): Ortmeyer, F., Mas-Pla, J., Banning, A.

Mr. Felix Ortmeyer,
Ruhr-Universität Bochum, Hydrogeology Department,
Universitätsstraße 150, 44801 Bochum

Dr. Josep Mas-Pla
Catalan Institute for Water Research & University of Girona

Keyword(s): Climate change, climate projection, groundwater pollution, nitrate, modelling


Climate change effects must be taken into account in investigating future nitrate (NO3-) concentrations in groundwater. Climate projections forecasts for the different climate scenarios permit simulating the future water balances that will control the aquifer behavior and, consequently, the fate of NO3- in groundwater. In this paper, the evolution of NO3- concentration in the Lodshof aquifer (NW Germany) is simulated based on the expected climate scenarios, RCP 2.6, RCP 4.5, and RCP 8.5.

Downscaled precipitation and temperature data for the 21st century are used to estimate the annual groundwater recharge for the three scenarios. Afterwards, these recharge values and the expected fertilization regimes are incorporated in a lumped-parameter model to estimate NO3- evolution. In order to obtain the best mapping resolution, the investigation area is divided into 1000 x 1000 m cells. To further adapt the model to the real aquifer, each cell is assigned with a specific NO3- input rate and a NO3- degradation capacity. In addition, land use in each individual cell is considered to calculate the actual evapotranspiration rates (ET).

Results show the effect of the distinct climate scenarios on the evolution of the NO3- concentration. Distinct temperature, and consequently actual ET, and precipitation tendencies, produce distinct NO3- concentration trends. For instance, NO3- increases considerably in the model with RCP 8.5 showing a final (2099) increase of total NO3- mass by 89 % as compared to 2020, whereas NO3- concentrations increase less with RCP 4.5 (50 %) and RCP 2.6 (67 %). For all scenarios, additional measures will have to be applied in the future to manage the NO3- problem.

Furthermore, model results suggest that a 20 % reduction of agricultural NO3- input, as intended by German authorities for the next decades, will not be sufficient to reach the drinking water limit value of 50 mg/l in the long run for any climate scenario. This result challenges the assumption that reduction in NO3- input is the right and only way to reduce NO3- levels in groundwater under the expected climate conditions. This study shows that climatically driven changes on the aquifer water balance also modify its hydrogeological behavior and, finally, its resilience to pollution impacts. Therefore, NO3- input reduction must consider the future hydrological dynamics of each particular aquifer to effectively attain stated environmental goals.

Funding: RUB Research School PLUS (B_2019_04_003) and the Spanish Research Program project PACE-IMPACT(FEDER-MCIU-AEI/CGL2017-87216-C4-4-R).

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