Runoff characterisation by SEC measurements in spring water

Extreme weather periods in the Harz Mountains with heavy rain events (e.g., July 2017) and long dry periods (September 2016, May – November 2018, September 2020) trigger extreme changes in surface runoff. However, such events do not lead to unknown, unpredictable chemical changes of the spring water in the Upper Harz Mountains (Bozau et al., 2013 and 2021). In order to obtain more information on the chemical evolution and to predict drying out events, spring waters of several catchment areas of the Harz Mountains were monitored. Every spring has a typical runoff pattern combined with specific chemical variations. The order of drying out during long droughts depends on the catchment size of the individual spring and did not change in the observation period.

Since February 2020, the specific electrical conductivity (SEC) of the spring "Innerstesprung" near Clausthal has been systematically measured at least once a week. This spring has its source in fractured Paleozoic greywacke, flows at the surface for about 30 m in a little artificial channel and then passes into the reservoir lake "Entensumpf". The measured SEC data are compared with daily precipitation rates. Drying out and first flush events show specific SEC trends. Furthermore, frozen snow covers are reflected by the SEC data. The SEC values of the spring water range between 55 and 100 µS/cm. Minimum values are typical for long rainy periods and snow melt in February. Only in 2017 (with about 300 mm precipitation during one week of July) 57 µS/cm were found in summer time. The maximum values of SEC are measured immediately before the drying out of the spring. Furthermore, a special effect of SEC enrichment after the first flush event has been observed. An impact of the enhanced deforestation which started in 2020 was not seen during the monitoring period. The spring runoff, precipitation and evaporation rates during the drying out events can be used for the calculation of the catchment areas. Furthermore, water-rock interactions along the flow path of spring water were investigated by batch tests.

References:

Bozau, E., Stärk, H.-J., Strauch, G., 2013. Hydrogeochemical characteristics of spring water in the Harz Mountains, Germany. Geochemistry, 73, 283-292.

Bozau, E, Bauer, G., Licha, T., Lojen, S., 2021. Hydrochemical response of spring and mine waters in the Upper Harz Mountains (Germany) after dry periods and heavy rain events. ZDGG, 172(1), 73-82.