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•Denitrification conditions in groundwater derived based on redox-sensitive parameters.•Inverse distance weighting (IDW) combined with a grid based overlay method.•Integration with a ...reaction kinetics model to quantify denitrification in aquifers.•Modeled denitrification show good agreement with results from the N2/Ar method.
Denitrification in groundwater is an important process that helps to maintain environmental standards, yet there are very few studies that determine the spatial variation of denitrification conditions in aquifers on a regional scale. We introduce a procedure to derive spatially continuous estimates of denitrification conditions in groundwater based on the interpolation of measurements of the redox-sensitive parameters oxygen, nitrate, iron, manganese and DOC, combined with the quantification of denitrification using a 2D-hydrodynamic model based on first-order reaction kinetics. We applied this procedure to Germany, using measured values from more than 24,000 groundwater monitoring sites from 2007 to 2016. Annual concentrations of the five parameters at the monitoring sites were regionalized using an optimized, iterative inverse distance weighting procedure within 15 aquifer typologies for spatial delineation. The annual grids (2007–2016) of each parameter were then overlaid and a median over time was calculated. Discrete ranks were then assigned to the concentrations of each parameter based on their redox class, and ultimately, after overlaying the five parameters, a mean value was calculated describing the nitrate degradation conditions in groundwater. After assigning half-life times and reaction constants to those denitrification conditions, we quantified denitrification in groundwater using the hydrodynamic model WEKU.
To assess the plausibility of the derived denitrification in groundwater, we compared our results with the proportion of denitrified nitrate determined with the N2/Ar method at 820 groundwater monitoring wells in three German Federal States, which showed an overall good agreement. Accordingly, the method presented here is suitable to be used for the regionally differentiated derivation of denitrification conditions in groundwater. For regions with denitrifying groundwater conditions, the results provide an explanation for frequently observed discrepancies between high nitrate emissions from the soil and low nitrate concentrations in the groundwater of intensively used agricultural areas.
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.
For the first time, the AGRUM model consortium—consisting of the agro-economic model RAUMIS, the water balance model mGROWA, the hydrological nutrient transport models DENUZ, WeKu and MEPhos, and the ...urban emission model MONERIS—was jointly set up throughout Germany (357,000 km2). This provided a nationwide consistent nutrient model to capture the current status of N and P inputs to surface waters from diffuse sources and urban areas. Diffuse nutrient emissions were quantified in high spatial resolution for the input pathways’ groundwater, drainage runoff, and natural interflow (100 m × 100 m), as well as for water erosion and wash-off (25 m × 25 m). The sum of diffuse nutrient inputs to surface waters is about 385,000 metric tons N/yr and ca. 11,530 metric tons P/yr. Urban emissions were quantified either as point source inputs (wastewater treatment plants, industrial direct dischargers) or at municipality scale for different collection and treatment systems, e.g., rainwater sewers or decentralized treatment plants, and sum up to ca. 95,000 t N/yr and 7500 t P/yr. As modelled, total N and P inputs into surface waters correspond well with observed N and P loads in rivers. The model results represent valuable information for water managers, being responsible for the preparation of management plans for the third management cycle of the EC Water Framework Directive spanning from 2021 to 2027.
Reaching the EU quality standard for nitrate (50 mg NO3/L) in all groundwater bodies is a challenge in the Federal State of North Rhine-Westfalia (Germany). In the research project GROWA+ NRW 2021 ...initiated by the Federal States’ Ministry for Environment, Agriculture, Nature and Consumer Protection, amongst other aspects, a model-based analysis of agricultural nitrogen inputs into groundwater and nitrate concentration in the leachate was carried out. For this purpose, the water balance model mGROWA, the agro-economic model RAUMIS, and the reactive N transport model DENUZ were coupled and applied consistently across the whole territory of North Rhine-Westfalia with a spatial resolution of 100 m × 100 m. Besides agricultural N emissions, N emissions from small sewage plants, urban systems, and NOx deposition were also included in the model analysis. The comparisons of the modelled nitrate concentrations in the leachate of different land use influences with observed nitrate concentrations in groundwater were shown to have a good correspondence with regard to the concentration levels across all regions and different land-uses in North Rhine-Westphalia. On the level of ground water bodies (according to EU ground water directive) N emissions exclusively from agriculture led to failure of the good chemical state. This result will support the selection and the adequate dimensioning of regionally adapted agricultural N reduction measures.
For the Hessian river basins, an area-differentiated modeling of the nitrogen input to the groundwater and surface waters was carried out for six diffuse input pathways and six point source input ...pathways on the basis of the geodata available at the state level. In this context, extensive plausibility checks of the model results were carried out using the data from several official monitoring networks at the state level. These include the comparison of modeled runoff components and input pathways for nitrogen using the data from the network of discharge monitoring stations. For the validation of the modeled nitrate concentrations in the leachate, the data from groundwater monitoring wells for controlling the chemical status of groundwater were used. The validation of the modeled nitrate inputs to the groundwater and denitrification in the groundwater was carried out using the data from a special monitoring network of groundwater monitoring wells that include N2/Ar measurements. The data from the Surface Water Quality Monitoring Network were used to verify the plausibility of the modeled total N inputs to the surface waters from diffuse sources and from point sources. All of the model results evaluated by the plausibility checks prove that the nitrate pollution situation in Hesse is adequately represented by the model. This is a prerequisite for accepting the model results at the state level as a basis for developing and implementing regionally appropriate mitigation measures. The Hessian State Agency for Nature Conservation, Environment and Geology uses the model results in the broader context of the work on implementing the EU Water Framework Directive and the EU Nitrate Directive.
•We introduce a model for highly resolved simulations of water balance quantities.•Soil moisture dynamics is simulated using a multi-layer soil water balance module.•The model has been successfully ...applied on the Federal State level in Germany.•The groundwater recharge map is used in regional water resources management.•Groundwater withdrawals in NRW do not exceed groundwater recharge in large areas.
Study region: The Federal State of North Rhine-Westphalia (NRW), Germany.
Study focus: On behalf of the Federal State Agency for Nature, Environment and Consumer Protection of North Rhine-Westphalia, Germany (LANUV) the mGROWA model is applied, in order to simulate the water balance components actual evapotranspiration, total runoff, direct runoff and groundwater recharge at Federal State level. mGROWA-simulations were performed in daily time steps for the hydrological reference period 1971–2000 and in a spatial resolution of 100 by 100m. mGROWA results for groundwater recharge and State-wide recorded groundwater withdrawal rates have been used to assess the extent of groundwater exploitation in NRW.
New hydrological insights: Simulated groundwater recharge levels are presented as long-term annual averages and as long-term monthly values in order to indicate the seasonal fluctuation of groundwater recharge rates. Quantitative statistics indicate that mGROWA enables the simulation of total runoff and groundwater recharge without significant tendency of over- or underestimation. Against this background mGROWA simulation results are used by LANUV to support regional water resources management, e.g. for determining the status of groundwater exploitation in NRW. The majority of groundwater bodies in NRW are at present not at risk of unsustainable groundwater usage. A small number of groundwater bodies along the river Rhine, however, have been assessed as being close to unsustainable groundwater exploitation.
Within a collaborative project between Slovenian Environment Agency （ARSO） and Research Center Jfilich （FZJ）, nitrogen reduction levels necessary to reach groundwater quality targets in Slovenia were ...assessed. For this purpose the hydrological model GROWA- DENUZ was coupled with agricultural N balances and applied consistently to the whole territory of Slovenia in a spatial resolution of 100 x 100 m. GROWA was used to determine the water balance in Slovenia for the hydrologic period 1971-2000. Simultaneously, the displaceable N load in soft was assessed from agricultural Slovenian N surpluses for 2011 and the atmospheric N deposition. Subsequently, the DENUZ model was used to assess the nitrate degradation in soil and, in combination with the percolation water rates from the GROWA model, to determine nitrate concentration in the leachate. The areas showing predicted nitrate concentrations in the leachate above the EU groundwater quality standard of 50 mg NO3/L have been identified as priority areas for implementing nitrogen reduction measures. For these ＂hot spot＂ areas DENUZ was used in a backward mode to quantify the maximal permissible nitrogen surplus levels in agriculture to guarantee a nitrate concentration in percolation water below 50 mg NO3/L. Model results indicate that additional N reduction measures should be implemented in priority areas rather than area-covering. Research work will directly support the implementation of the European Union Water Framework Directive in Slovenia, e.g., by using the maximal permissible nitrogen surplus levels as a framework for the derivation of regionally adapted and hence effective nitrogen reduction measures.
The target of the Open Geospatial Consortium (OGC) is interoperability of geographic information, which means creating opportunities to access geodata in a consistent, standardized way. In the domain ...of sensor data, the target will be picked up within the OGC Sensor Web Enablement Initiative and especially reached through the Sensor Observation Service (SOS) standard. This one defines a service for a standardized access to time series data and is usually used for in situ sensors (like discharge gauges and climate stations). Although the standard considers raster data, no implementation of the standard for raster data exists presently. In this paper an OGC-compliant Sensor Observation Service for a standardized access to raster data is described. A data model was developed that enables effective storage of the raster data with the corresponding metadata in a database, reading this data in an efficient way, and encoding it with result formats that the SOS-standard provides.
The worldwide Sensor Web comprises observation data from diverse sources. Each data provider may process and assess datasets differently before making them available online. This information is often ...invisible to end users. Therefore, publishing observation data with quality descriptions is vital as it helps users to assess the suitability of data for their applications. It is also important to capture contextual information concerning data quality such as provenance to trace back incorrect data to its origins. In the Open Geospatial Consortium (OGC)'s Sensor Web Enablement (SWE) framework, there is no sufficiently and practically applicable approach how these aspects can be systematically represented and made accessible. This paper presents Q-SOS--an extension of the OGC's Sensor Observation Service (SOS) that supports retrieval of observation data together with quality descriptions. These descriptions are represented in an observation data model covering various aspects of data quality assessment. The service and the data model have been developed based on open standards and open source tools, and are productively being used to share observation data from the TERENO observatory infrastructure. We discuss the advantages of deploying the presented solutions from data provider and consumer viewpoints. Enhancements applied to the related open-source developments are also introduced.
The need to develop and provide integrated observation systems to better understand and manage global and regional environmental change is one of the major challenges facing Earth system science ...today. In 2008, the German Helmholtz Association took up this challenge and launched the German research infrastructure TERrestrial ENvironmental Observatories (TERENO). The aim of TERENO is the establishment and maintenance of a network of observatories as a basis for an interdisciplinary and long‐term research program to investigate the effects of global environmental change on terrestrial ecosystems and their socio‐economic consequences. State‐of‐the‐art methods from the field of environmental monitoring, geophysics, remote sensing, and modeling are used to record and analyze states and fluxes in different environmental disciplines from groundwater through the vadose zone, surface water, and biosphere, up to the lower atmosphere. Over the past 15 years we have collectively gained experience in operating a long‐term observing network, thereby overcoming unexpected operational and institutional challenges, exceeding expectations, and facilitating new research. Today, the TERENO network is a key pillar for environmental modeling and forecasting in Germany, an information hub for practitioners and policy stakeholders in agriculture, forestry, and water management at regional to national levels, a nucleus for international collaboration, academic training and scientific outreach, an important anchor for large‐scale experiments, and a trigger for methodological innovation and technological progress. This article describes TERENO's key services and functions, presents the main lessons learned from this 15‐year effort, and emphasizes the need to continue long‐term integrated environmental monitoring programmes in the future.
Plain Language Summary
This paper discusses the importance of creating comprehensive environmental observation systems to better understand and address global and regional environmental changes. In 2008, a German research infrastructure named Terrestrial Environmental Observatories (TERENO) was established to build and maintain a network of observatories. The goal is to conduct interdisciplinary, long‐term research on the impacts of global environmental changes on terrestrial ecosystems and their socio‐economic effects. The TERENO network employs advanced methods from environmental monitoring, geophysics, remote sensing, and modeling to study various environmental aspects. Over the past 15 years, four observatories have been part of this network, contributing to valuable experience in overcoming challenges and exceeding expectations. Today, TERENO is a crucial component for environmental modeling and forecasting in Germany, serving as an information hub for practitioners and policymakers. It also fosters international collaboration, supports large‐scale experiments, and drives methodological and technological advancements. The article highlights key lessons learned from this 15‐year effort and emphasizes the importance of continuing such integrated environmental monitoring programs in the future.
Key Points
Integrated observatories ensure a holistic Earth Systems perspective, offering data for current and future ecological challenges
The scientific and societal value of observatories is invaluable, but their design, construction and operation require considerable effort
For assured long‐term data collection, research infrastructure must have flexible design for adapting to changing research needs
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