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.
