Grundwasser

Die Studie untersucht die Entwicklung der Grundwasserstände in Deutschland anhand von 5844 Messstellen sowie deren Reaktionsdynamik gegenüber klimatologischen Antrieben im Referenzzeitraum 1991–2020. Zusätzlich wird die Entwicklung seit 2018 im Kontext der außergewöhnlichen Dürreperiode betrachtet, um die Reaktionsfähigkeit und Vulnerabilität der Grundwassersysteme gegenüber extremen klimatischen Bedingungen zu bewerten. Erstmals erfolgt diese Auswertung bundesweit einheitlich und in enger Zusammenarbeit mit den zuständigen Landesbehörden. An 43

Water in the Kiel Canal flows from the Baltic Sea westward to the Lower Elbe, crossing three hydrogeological areas: the eastern hilly region, the Geest, and the marsh. In contrast to the other two areas, direct hydraulic contact can be observed in the Geest area between the Kiel Canal and surrounding groundwater, as determined by the analysis of hydrogeological storage conditions. The high salinity levels in the east (greater than 10 PSU; practical salinity units), which exceed the local groundwater concentrations, decrease with increasing flow distance to the west and are already nearly balanced in the marsh, often falling below 5 PSU. Data from over 1000 official, and third-party operated groundwater monitoring wells have been reviewed, and a multi-stage selection algorithm was developed to identify a likely saline influence from the Kiel Canal. At 40 monitoring wells close to the canal (less than 3 km away), influent conditions may exist - temporarily in the hilly region and the Geest, and even locally permanent in the marsh - and saline transport from surface water into the groundwater is possible, as the hydraulic potentials of the groundwater are temporarily or permanently lower than those of the Kiel Canal. In the hilly region, only two monitoring wells show higher salinities due to construction measures at the eastern section of the Kiel Canal. However, this finding clearly demonstrates the potential risk that the Kiel Canal poses to the groundwater. In the marsh, some state monitoring wells show elevated salt concentrations in groundwater. These concentrations are not caused by the Kiel Canal but have a geogenic origin, and exceed the salt concentrations in the Kiel Canal.

The temperature of groundwater affects its quality and thus influences groundwater ecosystems and drinking water supply. Numerous studies have demonstrated a dependency of groundwater temperature on surface temperature, which can also be derived from remote sensing data. This study focuses on extending this approach from single measurements to monthly mean values from time series, which is considered essential for tracking the warming of groundwater bodies under the influence of climate change. The Upper Rhine Plain serves as study area, as it is a groundwater-rich region of great importance for regional drinking water supply and is located in one of the warmest regions in Germany. Here, we examine the relationship between satellite-based land surface temperature (LST) measurements and local groundwater temperatures over a five-year period. Specifically, data from 19 groundwater monitoring stations and air temperature data from four nearby climate stations for the period November 2016 to April 2022 were used and combined with LST data from the MODIS Terra satellite. Pronounced seasonal temperature variations were observed down to depths of 9 m, with depth-dependent time lags of 2 to 8 months between groundwater temperature signals relative to air and land surface temperatures. The time lag could be determined and accounted for at 15 sites, resulting in strong and highly significant (p < 0.001) positive correlations of groundwater temperature with both AT and local LST. Our findings demonstrate that monthly mean air and land surface temperatures can be used to estimate shallow groundwater temperature trends in the Upper Rhine Plain, also suggesting a broad applicability of this approach in other regions.

There is still an urgent need to reduce nitrogen inputs into surface water and groundwater. This study examines ammonium and nitrate losses from agricultural grasslands into connected drainage ditches of the northwest German coastal region. For this purpose, the soils of the characteristic geest, peatland, and marsh area landscapes are analyzed for ammonium and nitrate contents. In addition, surface drainage, subsurface drainage and ditch waters are analyzed for ammonium and nitrate concentrations. The peatlands are divided into bogs, fens and organo-mineral transition sites. High ammonium contents are found primarily in peat soils and organo-mineral soils, with values between 22.2 and 25.9 kg NH4+-N ha(-1) in 0-30 cm depth. Lower contents are found in the mineral-dominated soils of the geest and marsh areas. Ammonium losses through surface drainage mainly occur from soils of the geest area with a mean value of 4.7 NH4+-N mg l(-1) and via subsurface drainage primarily from fens and raised peatland bogs, with concentrations of 3.9 and 2.3 NH4+-N mg l(-1). The ditches adjacent to fen sites also show the highest ammonium concentrations with 3.5 mg NH4+-N l(-1). The nitrate contents of the soils are similar across all landscape areas. The highest contents are found in fens and organo-mineral sites, with values of 21.4 and 20.3 kg NO3--N ha(-1), respectively. Nitrate occurs in highest concentrations within surface drainage with 4.4 mg NO3--N l(-1) as well as in subsurface drainage with 4.6 mg NO3--N l(-1) from geest soils. This is also reflected in the ditches of the geest, with the highest mean NO3--N concentrations of 3.3 mg NO3--N l(-1). Soil organic matter was identified as a significant influence factor for the leaching of ammonium and nitrate. In addition, the amount and timing of N fertilization also play a significant role.

Die Temperatur des Grundwassers hat Auswirkungen auf dessen Qualität und beeinflusst damit unter anderem Grundwasserökosysteme und die Trinkwasserversorgung. Vielfach konnte eine Abhängigkeit der Grundwassertemperatur von der Oberflächentemperatur nachgewiesen werden. Der Fokus dieser Arbeit liegt auf der Ausweitung dieses Ansatzes von Einzelmessungen auf Monatsmittelwerte aus Zeitreihen, was als Voraussetzung gilt, um Erwärmungen von Grundwasserkörpern unter dem Einfluss des Klimawandels raumzeitlich verfolgen zu können. Das Oberrheinische Tiefland dient dabei als Untersuchungsgebiet, da es als grundwasserreiches Gebiet von großer Bedeutung für die regionale Trinkwassergewinnung ist und sich gleichzeitig in einer der wärmsten Regionen Deutschlands befindet. Hier wird der Zusammenhang zwischen satellitengestützten Messungen der Oberflächentemperatur mit den lokalen Grundwassertemperaturen über einen Zeitraum von fünf Jahren betrachtet. Konkret wurden Daten von 19 Grundwassermessstellen und Daten zur Lufttemperatur von vier nahegelegenen Klimastationen für den Zeitraum November 2016 bis April 2022 verwendet und mit Daten des MODIS Terra-Satelliten zur Landoberflächentemperatur kombiniert. Ausgeprägte saisonale Temperaturschwankungen konnten dabei bis in Tiefen von 9 m beobachtet werden, wobei die Temperatursignale gegenüber der Luft- und Landoberflächentemperatur durch einen mit der Tiefe zunehmenden zeitlichen Versatz von zwei bis acht Monaten geprägt waren. Der zeitliche Versatz gegenüber den Lufttemperaturen konnte bei insgesamt 15 Messstellen bestimmt und berücksichtigt werden, sodass sich für die Grundwassertemperaturen stark positive und hochsignifikante (p < 0,001) Korrelationen sowohl mit der Lufttemperatur, als auch mit den lokalen Landoberflächentemperaturen ergaben. Somit können Monatsmittelwerte zu Luft- und Landoberflächentemperaturen zur Abschätzung von Temperaturentwicklungen der oberflächennahen Grundwasserkörper im Oberrheinischen Tiefland genutzt werden, was großräumige Einsatzmöglichkeiten auch für andere Gebiete eröffnet.

Es besteht nach wie vor der Bedarf der Minderung von Stickstoffeinträgen in Oberflächen- und Grundwässer. Diese Studie befasst sich mit den Ammonium- und Nitratausträgen aus Grünlandflächen in die angeschlossenen Entwässerungsgräben der nordwestdeutschen Küstenregion. Dazu werden die Böden der charakteristischen Landschaftsräume der Geest, Moore und Marschen auf die Gehalte und die Grüppen‑, Drainage- und Grabenwässer auf die Konzentration an Ammonium und Nitrat untersucht. Die Moore werden dabei unterteilt in Hoch- und Niedermoore sowie organo-mineralische Übergangsstandorte. Hohe Ammoniumgehalte sind vor allem in Moorböden und organo-mineralischen Böden mit Gehalten zwischen 22,2 und 25,9 kg NH4+-N ha−1 in 0–30 cm u. GOK anzutreffen. Niedrigere Gehalte liegen in den mineralisch geprägten Böden der Geest und Marsch vor. Über Grüppen wird Ammonium im Mittel mit 4,7 mg NH4+-N l−1 vor allem aus der Geest und über Drainagen vor allem aus Nieder- und Hochmooren mit 3,9 und 2,3 mg NH4+-N l−1 ausgetragen. Die Niedermoore erreichen mit 3,5 mg NH4+-N l−1 die höchsten Ammoniumkonzentrationen in den Gräben. Die Nitratgehalte in den Böden sind über alle Landschaftsräume hinweg ähnlich. Die höchsten Gehalte liegen an Niedermoor- und organikreichen Übergangsstandorten mit Werten von 21,4 und 20,3 kg NO3−-N ha−1 vor. Nitrat wird über Grüppen mit 4,4 mg NO3−-N l−1 und über die Drainagen mit 4,6 mg NO3−-N l−1 insbesondere aus Böden der Geest ausgetragen. Dies spiegelt sich auch in den Gräben der Geest mit den höchsten mittleren Nitratkonzentrationen von 3,3 mg NO3−-N l−1 wider. Als bedeutender Einflussfaktor auf die Austräge von Ammonium und Nitrat wurde die organische Bodensubstanz identifiziert. Jedoch nehmen auch die Höhe und der Zeitpunkt der N‑Düngung maßgeblich Einfluss.

This study demonstrates that it is possible to assess and visualize the thermal impacts of urban subsurface structures on a groundwater system, using the city of M & uuml;nster (North Rhine-Westphalia, Germany) as an example. Ongoing urbanization increasingly leads to subsurface use conflicts, particularly due to thermal stress from buildings, underground garages, sewer systems, and sealed surfaces. The aim was to quantify these effects using geological, hydrogeological, and thermal datasets and to visualize them in 4D using monthly-resolved 3D subsurface models. Heat fluxes were calculated based on temperature profiles and Fourier's law of heat conduction. The results indicate the presence of distinct subsurface urban heat islands (SUHI) in densely built-up areas, whereas water bodies and green spaces partly exhibit cooling effects. Buildings account for approximately 90% of the positive heat input into groundwater, especially in areas with shallow water tables. The presented methodology forms a foundation for further in-depth analyses and supports sustainable thermal groundwater management in urban environments.

Quantifying the permissible technical groundwater heat pump (GWHP) use potential is important for informing policy decisions. This study introduces a transferable and efficient methodology to quantify the permissible technical GWHP use potential and its uncertainty using existing hydrogeological data. The methodology is applied to the deep aquifer in the Baar-Zug-Steinhausen area (Canton of Zug, Switzerland). To address the computational demands of strategies based on 3D numerical groundwater flow and heat transport simulations, the aquifer is classified into distinct hydrogeological “clusters”. This clustering is based on key hydrogeological parameters such as aquifer thickness, permeability, and hydraulic gradient. For each cluster, groundwater flow and heat transport are simulated for a single GWHP doublet in 3D box models with homogeneous properties and a constant hydraulic gradient. Small, medium, and large demands, including both balanced and unbalanced energy load profiles are considered. Thermal and hydraulic influence zones are delineated using 0.1 K isotherms and Darcy flow deviation from natural conditions. A spatial packing algorithm is then applied to place the influence zones within their cluster such that they are aligned with hydraulic gradient direction and treating them as non-overlapping hard boundaries. The permissible technical GWHP use potential is defined by the total number of GWHPs that can be accommodated within each cluster without interference. Uncertainty on the permissible technical potential is quantified through additional simulations. This approach also underscores the importance of quantifying and communicating the range of possible permissible technical heat use potentials to stakeholders, guiding future development towards optimized and environmentally sound groundwater heat use.

Accelerated by urbanization, as well as by agricultural intensification and climate change, increasing nutrient fluxes towards surface waters and increasing water temperatures are increasing the probability for cyanobacterial harmful algal blooms. Significant deterioration of water quality occurs with such events when microcystins (MCs) are released as the most prominent algal toxins. Despite the typical assumption that MCs are removed during percolation, studies have found significant concentrations in groundwater bodies. In this article, advances and challenges associated with monitoring and modeling techniques for characterizing the fate of MCs are discussed. Missing insights in the mechanisms leading to elevated MC concentrations in the subsurface—ultimately limiting the reliability of risk assessments—are identified. An important aspect is the a priori identification of environmental conditions and corresponding events that support bloom formation in surface waters and subsequent transport into groundwater. Challenges associated with required improved monitoring and simulation techniques are formulated. In particular, the role of environmental conditions in urban regions as major drivers for heat and nutrient emissions controlling bloom formation, potentially limiting MC retardation, needs to be further investigated. Based on existing experimental studies on MC reactive transport in porous media, existing monitoring methods need to be refined and combined with suitable modeling approaches. A thorough data analysis can then support efforts for sustainable water management of urban regions under threat by algal toxins.

As urbanization and transport demands rise, railway systems face higher risks from operational disruptions due to system failures and climate-related impacts, especially in urban areas. Understanding water flow and distribution beneath railway embankments is crucial not only for assessing potential contaminant transport in soil and groundwater but also for identifying possible structural weaknesses. This study implements numerical simulations to investigate these dynamics, focusing on a standard railway embankment designed according to German norms. The model setup includes ballast, a low-permeability protection subgrade surface layer (PSS), a subgrade (embankment base), and a subsurface to a depth of 10 m. Numerical simulations were conducted following a univariate approach. Variation parameters included key hydraulic characteristics of the embankment and subsurface. Further parameters were groundwater recharge rate, groundwater level, existence of a less permeable horizontal layer at multiple depths, and thickness of the embankment. The most sensitive parameters shaping water percolation fronts are identified as empirical coefficients (especially the Van Genuchten shape variable α), groundwater levels and hydraulic conductivity. The results indicate that the PSS layer retains the greatest amount of water from the rail system, particularly beneath the ballast. Low α values (0.8 m–1 to 7.7 m–1) led to total retention of water within the embankment, with no visible percolation fronts and the lowest values observed at the PSS layer. Shallow groundwater increased initial water content up to 0.30 at the PSS layer, rapidly approaching near fully water-saturated conditions. Embankments with low hydraulic conductivities (0.048 m d−1 to 1.207 m d−1) show the highest water contents, reaching up to 0.46, forming a clogging area prone to retain contaminants.

The cooling demand of cities is currently increasing due to urban heat island effects which could be covered with renewable energy to reach climate goals. An efficient solution is thermal cooling using groundwater. This approach involves introducing waste heat into the aquifer, which, at the same time, also raises some concerns among water authorities about potential impacts on groundwater quality. Hence, strict regulations were imposed on temperature spreading and maximum injection temperatures, limiting the thermal use of groundwater for cooling. However, regulations vary widely by country, because the influence of such temperature changes on groundwater conditions is still uncertain. In the present study, a summary of country-specific regulations is presented and evaluated with respect to possible impacts. Based on the review, a novel approach for the comparative assessment of the influence of different legal frameworks on city-wide relevant thermal impact areas is presented and implemented in three urban case studies in Germany, Switzerland and Spain, with various hydrogeological conditions. The results demonstrate that in the cities with higher hydraulic conductivities and strict regulations, the thermally impacted areas, defined by a 3K-isotherm, affect only a low percentage of the aquifer, comparable to those with less strict regulations. However, extensive thermal groundwater use by large systems, relatively high temperature spreading and aquifers with low hydraulic conductivities, lead to moderate percentages of impacted aquifer areas, especially by considering real operation data. The presented methodological approach provides a simplified tool to help city managers and local water authorities to define operational thresholds related to thermal-cooling use of groundwater.

Current practices to measure the impact of human activity on groundwater quality, as part of the EU Water Framework Directive (WFD), focus on diffuse sources of pollution from agriculture (i.e. mainly nitrate and pesticides). Here, we use the results of a systematic program for monitoring quality, covering more than 15 years of observations at 64 wells within a medium sized European city to understand how groundwater quality is affected by urban land use. In summary, a total of 115 different substances of concern (e.g., pesticides, neonicotinoids, per- and polyfluorinated compounds (PFAS), flame-retardants, explosives, pharmaceuticals, hydrocarbons, solvents, personal care products) have been analyzed. The results show that there is not a single well without detection of an emerging contaminant. We found, on average, 14 (ranging from 4 to 25) substances per well. Trifluoroacetic acid (TFA) was most abundant with a detection rate of 97

Diese Untersuchung zeigt, dass es möglich ist, die thermischen Auswirkungen urbaner Untergrundstrukturen auf das Grundwassersystem am Beispiel der Stadt Münster (NRW) zu bewerten und räumlich-zeitlich zu visualisieren. Die fortschreitende Urbanisierung führt zunehmend zu Nutzungskonflikten im Untergrund – insbesondere durch thermische Belastungen infolge von Gebäuden, Tiefgaragen, Kanalnetzen und versiegelten Flächen. Ziel war es, diese Einflüsse mithilfe geologischer, hydrogeologischer und thermischer Datensätze zu quantifizieren und über 3D-Untergrundmodelle mit monatlicher Auflösung in 4D abzubilden. Auf Basis von Temperaturprofilen und Fourier’s Wärmeleitungsgesetz wurden Wärmeflüsse berechnet. Die Ergebnisse deuten auf ausgeprägte unterirdische Wärmeinseln („subsurface urban heat islands“, SUHI) im Innenstadtbereich hin, während Gewässer und Grünflächen teilweise kühlende Effekte aufweisen. Gebäude verursachen mit ca. 90

Seasonal heat storage has been studied in Germany for over 30 years, but to date only a few pilot plant facilities have been built, such as those for borehole geothermal energy storage, pit storage or aquifer storage. A promising yet underutilized approach is the use of abandoned, groundwater-flooded mines for thermal energy storage. These offer high storage capacities due to their large volumes and extensive contact surfaces with the surrounding rock. Since cities often develop near mining sites, this could present a viable solution for energy supply in urban areas. A feasibility study in the city of Freiberg investigates the suitability of a former silver mine for this purpose. The storage efficiency depends on geological and thermal conditions, such as the accessible mine volume, water flows, and temperature limits. Initial results show that storage efficiencies of 50–60

Urban groundwater is a vital and sensitive resource, essential for drinking and industrial water supplies in densely populated areas. Due to the population distribution, the most frequently used groundwater in Switzerland originates from urban or urban-influenced aquifers. Its sustainability is threatened by contamination, temperature changes, and especially by irreversible damage from large-scale underground construction. Despite its critical importance, awareness of urban groundwater's vulnerability remains limited due to its invisibility. This article highlights the need to preserve urban groundwater for future generations through comprehensive assessment and early planning of construction projects. Strengthening process understanding and recognizing the complexity of the subsurface are key to sustainable groundwater management. Recent legal rulings emphasize the importance of balanced decision-making that integrates ecological, economic, and social values to protect this indispensable resource.

This study presents a tube passive sampler (TPS) for integrative monitoring at various stages of the urban water cycle. The device enables the determination of time-integrated average concentrations in pressurized systems. To achieve this, the sampler is operated via a bypass of the water stream, allowing for a load-based in situ calibration through a mass flow controller. In monitoring campaigns downstream of a wastewater treatment plant, it was possible to quantify not only substances with constant concentrations such as metoprolol and diclofenac, but also highly fluctuating industrial chemicals such as benzotriazole and tolyltriazole. In particular, the tube passive sampler allowed us to retroactively detect sporadic and isolated occurrences of dichlorprop in the wastewater effluent. Using weak anion exchange disks in the tube passive sampler, substance-specific in situ calibrations for 13 perfluoroalkyl and polyfluoroalkyl substances (PFAS) were carried out in five consecutive experiments at a drinking water treatment plant (not operated by Berliner Wasserbetriebe). Subsequently, time-weighted average values in a concentration range of 0.5 to 439 ng/l could be determined, which were comparable to parallel mixed water samples over the same period. Due to the accumulation of material on the passive sampler, it was also possible to determine a semi-quantitative average concentration of PFNA, even though the concentration in individual water samples was below the limit of quantification.

Aufgrund hoher Stickstoffeinträge überschreiten Nitratkonzentrationen im Grundwasser in Deutschland teils Trinkwassergrenzwerte, was präzisere Vorhersagemodelle und Managementstrategien erfordert. Diese Studie kombiniert Random-Forest-Modelle mit Explainable AI (SHAP-Werten), um die räumliche Verteilung der Nitratkonzentration im Grundwasser von Baden-Württemberg und Niedersachsen vorherzusagen und den Einfluss des Denitrifikationspotenzials zu analysieren. Die Ergebnisse zeigen, dass geodatenbasierte Modelle für Baden-Württemberg gute, für Niedersachsen jedoch fehlerhafte Vorhersagen liefern. Die Diskrepanzen sind auf nicht erfasstes Denitrifikationspotenzial zurückzuführen. Durch SHAP-Werte wird der Einfluss des Denitrifikationspotenzials quantifiziert und sichtbar gemacht. Die Einbeziehung chemischer Parameter wie Eisen und Kalium, die eng mit Denitrifikationsprozessen verknüpft sind, erhöht die Modellgüte in Niedersachsen signifikant (R2 = 0,06 auf 0,72) und bestätigt die zentrale Rolle anoxischer Bedingungen und spezifischer Elektronenakzeptoren für den Nitratabbau. SHAP zeigt zudem, dass ohne chemische Parameter räumliche Prädiktoren in Niedersachsen zufällige Muster widerspiegeln, statt kausale Zusammenhänge abzubilden. Random-Forest-Modelle kombiniert mit SHAP-Analysen liefern wertvolle Einblicke in die komplexe Wechselwirkung zwischen Nitratdynamik und Denitrifikation im Grundwasser.