Water fluxes and diffuse nitrate pollution at river basin scale: coupling of agro-economic models and hydrological approaches

Abstract

An integrated model system has been developed to estimate the impact of nitrogen reduction measures on the nitrogen load in groundwater and in river catchment areas. The focus lies on an area-wide, regionally differentiated, consistent link-up between the indicator "nitrogen balance surplus" and nitrogen charges into surface waters. As a starting point of the analysis actual nitrogen surpluses in the soil were quantified using the agro-economic RAUMIS-model, which considers the most important N-inputs to the soil and N-removals from the soil through crop harvest. The most important pathways for diffuse nitrogen inputs into river systems are modelled with the water balance model GROWA. Additionally, the time-dependent nitrogen degradation along the nitrogen pathways in soil and groundwater are modelled using the WEKU-model. The two selected river basins in Germany cover a variety of landscape units with different hydrological, hydrogeological and socio-economic characteristics. The results indicate a wide range of annual nitrogen surpluses for the rural areas between than 10 kg N ha(-1) x a(-1) and 200 kg N ha(-1) x a(-1) or more, depending on the type and intensity of farming. The level of nitrogen inputs into the surface waters is reduced because of degradation processes during transport in soil and groundwater. Policy impact analyses for a nitrogen tax and a limitation of the livestock density stress the importance of regionally adjusted measures.

Research at the Agrosphere Institute: From the Process Scale to the Catchment Scale

“…Mathematical modeling at the Agrosphere Institute involves the upscaling of water and solute transport processes (Vanderborght et al, 2006; Vereecken et al, 2007), the development of models to describe flow and transport processes in the groundwater–soil–plant–atmosphere continuum (Herbst et al, 2005a,b; Wendland et al, 2007), and the development and implementation of numerical models to run on the supercomputing facilities of the Jülich Forschungszentrum (Hardelauf et al, 2007). The institute also has much expertise in establishing and running complex and large field experiments from the local to the catchment scale (Bogena et al, 2006; Kasteel et al, 2007; Weihermüller et al, 2007).…”

“…Mathematical models can play an important role in integrating a wide range of processes operative in terrestrial systems, in planning and interpreting experimental studies conducted at various scales (Vanderborght and Vereecken., 2007a,b; Javaux et al, 2006a,b; Herbst et al, 2006), in the upscaling of parameters and processes of terrestrial systems across scales (Vereecken et al, 2007), and in analyzing the impact and effectiveness of different management and mitigation strategies (Kunkel et al, 2008; Wendland et al, 2007; Tetzlaff et al, 2007). The final two papers in this special section present modeling activities that encompass the local scale (Schröder et al, 2009) and the lysimeter scale (Mertens et al, 2009).…”

“…In addition to improving the mathematical modeling of terrestrial systems, novel observations and measurement technologies (e.g., remote sensing, hydrogeophysical methods, imaging techniques) are needed that will enhance our understanding of flow, transport, and biogeochemical processes in terrestrial systems (e.g., Rubin and Hubbard, 2005; Wagner et al, 2007; Vereecken et al, 2008). This will help improve the required accuracy of predictive terrestrial models for different purposes and scales of application (e.g., Herbst et al, 2005a,b; Vanderborght and Vereecken, 2007a; Wendland et al, 2007). As the ability to observe the state of terrestrial systems increases, we are also facing a gap between information obtained from these systems (often considered to be indirect or auxiliary information), and information required to run environmental and terrestrial models (e.g., the model parameterization and the initialization).…”

Assessing necessary nutrient reduction for measurement planning in groundwater bodies

“…The model has been developed to support practical water resources management issues of large river basins and has already been applied in different regions of different sizes with different perspectives Kunkel et al 2005;Tetzlaff et al 2007;Wendland et al 2003Wendland et al , 2005Wendland et al , 2007. It employs an empirical approach with a temporal resolution of one or more years.…”

Determination of nitrogen reduction levels necessary to reach groundwater quality targets in large river basins: the Weser basin case study, Germany

“…In this project the REGFLUD model network (Gömann et al 2004;Wendland et al 2007) was developed by coupling the agricultural sector model RAUMIS with the water balance model model GROWA (Kunkel and Wendland 2002), the DENUZ model approach (Kunkel and Wendland 2006) for assessing denitrification rates in the soil and the reactive nutrient transport model for groundwater WEKU (Kunkel and Wendland 1997). In the REGFLUD project in particular, the input and reactive transport of actual excess nitrogen fertilizers from agricultural use in soil and groundwater was simulated .…”