Reservoir lakes in the Upper Harz Mountains (Germany): GIS Implementation and hydrochemical development

Dam reservoirs were used for the continuous water supply to the ore mines in the Upper Harz Mountains. The first reservoirs were built in the 16th century. The dam heights reach up to 15 m and the stored water volumes are between 10,000 and 600,000 m³. There are about 70 of such lakes around Clausthal-Zellerfeld now. Hydrogeochemical data of the lakes have been investigated for about ten years (Bozau et al., 2015). A data management system combining GIS and hydrochemical data is prepared to facilitate data collection and interpretation.

The specific electrical conductivity (SEC) of the lake water ranges between approx. 30 and 280 µS/cm and can be used for the classification of these lakes. SEC lower than 50 µS/cm are typical for lakes mainly filled by rain water. SEC higher than 200 µS/cm are found in lakes near urban and anthropogenic influences. Due to the long dry periods of the last years an increase of the SEC is seen in the majority of lakes especially between spring 2015 and 2023. Because of extraordinary high precipitation in autumn 2023 this trend stagnates or even decreases in some lakes, but is still observable in the comparison between autumn 2015 and autumn 2023.

Especially those lakes with catchment areas strongly changed by forest decline are expected to show higher values of the SEC. In order to investigate this, spatial comparison with forest damage maps is planned. Furthermore, the concentrations of main ions will be investigated in addition to SEC values. Nitrate and potassium concentrations of the lake water should be the most sensitive indicators for forest decline and anthropogenic influences. A first evaluation of organic trace components (Bozau et al., 2022) did not confirm the classification based on the SEC.

 

Bozau, E., Licha, T., Stärk, H.-J., Strauch, G., Voss, I., Wiegand, B. (2015): Hydrogeochemische Studien im Harzer Einzugsgebiet der Innerste. Clausthaler Geowissenschaften, 10, 35-46.

Bozau, E., Licha, T., Warner, W. (2022): Natürliche und anthropogene hydrochemische Parameter der Oberharzer Bergbauteiche. FH-DGGV-Tagung, Jena, März 2022.