Checking the Plausibility of Modelled Nitrate Concentrations in the Leachate on Federal State Scale in Germany

Tim Wolters,Frank Wendland,Nils Cremer,Michael Eisele,Ralf Kunkel,Peter Kreins,Frank Herrmann

doi:10.3390/w13020226

Abstract

In Germany, modelled nitrate concentrations in the leachate are of great importance for the development of scenarios for the long-term achievement of the groundwater quality target according to the specific requirements of the EU Water Framework Directive as well as within the context of the recently adopted general administrative regulation for the designation of nitrate-polluted areas in Germany. For the German federal states of North Rhine-Westphalia (NRW) and Rhineland-Palatinate (RLP), an area-covering modelling of mean long-term nitrate concentrations in leachate with high spatial resolution was carried out using the model system RAUMIS-mGROWA-DENUZ. Hotspot regions with nitrate concentrations in the leachate of 50 mg NO3/L and more were identified for intensively farmed areas in the Münsterland, Lower Rhine, and Vorderpfalz. The validity of modelled values was checked using measured values from 1119 preselected monitoring stations from shallow springs and aquifers filtered near to the surface with oxidizing properties. For the land use categories of urban areas, arable land, grassland, and forest, an at least good agreement of modelled nitrate concentrations in the leachate and measured nitrate concentrations in groundwater was obtained at numerous sites. An equally good agreement was obtained for 1461 measuring stations from the area of responsibility of the Erftverband, which is a major water supplier in the Lower Rhine region. Here, discrepancies have been analyzed in detail due to profound regional knowledge on observation sites. It turned out that in most cases, accuracy limitations of input data (e.g., N balance surpluses of agriculture at the municipal level, 1:50,000 soil map) have been the reason for larger deviations between observed and modelled values. In a broader sense, the case study has shown on the one hand that the model system RAUMIS-mGROWA-DENUZ is able to reliably represent interrelationships and influencing factors that determine simulated nitrate concentrations in the leachate. On the other hand, it has been proven that observed nitrate concentrations in groundwater may provide a solid data source for checking the plausibility of modelled nitrate concentrations in leachate in cases where certain preselection criteria are applied.

Highlights

Introduction and ObjectiveDue to the fact that the nitrate threshold limit value for groundwater of 50 mg NO3 /L is continuously exceeded in some regions of Germany, the EU Commission already determined in 2016 that the Federal Republic of Germany had failed to take stricter and harmonized measures against water pollution by nitrates at the federal level, Germany would have been obliged to do so according to the EU Nitrates Directive [1]by 2012 at the latest
In Germany, the modelled nitrate concentration in leachate plays a central role in the cultural statistics included in the RAUMIS model do not contain any information on the dimensioning of nitrogen mitigation measures to achieve the groundwater quality objective illegal import of liquid manure from the neighboring Netherlands
According to the specific requirements of the EU Water Framework Directive [8] as well portant additional N source in the calculation of the nitrate concentration in the leachate as within the context of the recently adopted general administrative regulation for the is an explanation for the deviation from the observed higher nitrate concentrations in designation of nitrate-polluted areas [6]

Summary

Introduction

Due to the fact that the nitrate threshold limit value for groundwater of 50 mg NO3 /L is continuously exceeded in some regions of Germany, the EU Commission already determined in 2016 that the Federal Republic of Germany had failed to take stricter and harmonized measures against water pollution by nitrates at the federal level, . Due to these omissions, Germany was sued by the EU Commission in 2016 for excessively high nitrate levels in groundwater [2], which was ruled by the European Court of Justice (CJEU) in 2018 [3]. In June 2020, the Federal Republic of Germany reacted to this situation in accordance to § 13a paragraph 1 of the German Fertilization Ordinance [5]. By drafting a general administrative regulation for standardized designation of nitratepolluted and eutrophicated areas in Germany [6]. A nationwide uniform methodology for the designation of nitrate polluted areas (“red areas”), where further requirements for groundwater protection are necessary, was introduced

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Conclusion