Validation of denitrification models
Validation of modeled nitrate reduction by the direct measurement of denitrification in groundwater in Northwest German river basins
Denitrification is of great importance for reducing agricultural nitrogen in aquatic systems. For the first time, we apply direct quantification of denitrification in groundwater to validate regional denitrification models.
Background and Objective
In Europe, about 20 million tons of nitrogen (N) were applied as mineral and organic fertilizers to agricultural soils. A substantial part of the N input is discharged into surface and ground water providing a significant hazard for water resources.
This nitrogen load can be reduced by denitrification in soils and groundwater. Denitrification is therefore of central importance for the protection of groundwater and of surface waters. Similarly, denitrification is important for the control of emissions of the greenhouse gas N2O from aquatic systems ("indirect N2O emissions").
The aim of the project is to validate existing models for denitrification in soils and groundwater (DENUZ and WEKU, respectively (Kunkel Wendland 1997 and 2006)) by measuring dissolved N2 from denitrification in groundwater (N2/Ar-method). Moreover, the potential lowering of indirect N2O emissions by denitrification in groundwater will be derived from the determined removal of N loads.
Science, Federal Ministry of Food and Agriculture, professionals in the field of water supply, agriculture and environmental protection.
During the project 612 groundwater monitoring wells distributed all over Lower-Saxony, Germany were sampled. Major groundwater parameters are analyzed and quantified. Denitrification elapsed during groundwater residence time is quantified using the N2 / Ar method, which is based on the measurement of gaseous reaction products of denitrification in groundwater samples. At selected groundwater monitoring wells, groundwater age is determined (Helium-Tritium method). From these data, denitrification rates in groundwater as well as nitrate input are derived.
The collected data will be processed in a database and loaded into ArcGIS. The modeled nitrate leaching (DENUZ) and the modeled nitrate reduction on the groundwater flow path (WEKU) are then compared with the project data. Based on this, model adjustments are finally performed.
Our Research Questions
Concerning the comparison of the N2 / Ar-method with DENUZ:
- Are modeled nitrate inputs comparable with the results of the N2 / Ar method?
- What is the influence of the setting of the groundwater measuring wells on comparability of measured and modeled values?
- Are there regional differences in the goodness of fit between modeled nitrate emissions and the N2/Ar-method?
- How does the heterogeneity of soil properties and/or of land use in the vicinity of a measuring well influence the comparability of model and measurement?
Concerning the comparison between the N2/Ar-method and WEKU:
- How is the agreement of the modeled and the measured nitrate reduction in groundwater?
- What is the influence of aquifer types on the comparability between model and measurement?
Involved external Thünen-Partners
- Landesamt für Bergbau , Energie und Geologie (LBEG)
Federal Ministry of Food und Agriculture (BMEL)
11.2011 - 9.2014
Eschenbach W, Budziak D, Elbracht J, Höper H, Krienen L, Kunkel R, Meyer K, Well R, Wendland F (2018) Möglichkeiten und Grenzen der Validierung flächenhaft modellierter Nitrateinträge ins Grundwassermit der N2/Ar-Methode. Grundwasser 23(2):125-139, DOI:10.1007/s00767-018-0391-6
Eschenbach W, Well R, Krienen L (2013) Validation of modelled denitrification in selected river catchment areas of northern Germany by direct measurement of denitrification in groundwater. In: Volume of Abstracts: International Interdisciplinary Conference on: Land Use and Water Quality ; 10-13 June 2013, The Hague, The Netherlands. pp 86-87