Spring water monitoring in the Upper Harz Mountains: Precipitation, runoff and specific electrical conductivity

Due to extreme weather events and deforestation the physical and chemical characteristics of watersheds in mountain areas could exceed the known variations. Therefore, the spring water of the Innerste river in the Western Harz Mountains (Germany) was monitored from 2020 to 2023. The monitoring approach is simple and can be directly transferred to other watersheds of springs which are connected to the meteoric water cycle. The specific electrical conductivity (SEC) of the water is compared to daily precipitation data. The SEC values range between 50 and 100 μS/cm. In September 2020 and July 2022 the spring dried out. A hysteretic relationship between spring runoff and spring water mineralisation was found. The SEC values of the spring water are rising during dry periods or in winter seasons with a long ice cover in the catchment area. The highest SEC values are typical for long dry periods and flush events after the drying out of the spring. The relationship of SEC and major ions of the spring water (especially bicarbonate) indicates that biogeochemical processes within the soil zone and water-rock interactions in fractured shales and greywackes of the catchment area control the chemical composition of the spring water. Comparing the obtained results with data measured before the first observed drying out of the spring, no unexpected new values and correlations of runoff, SEC values and ion concentrations were found.