Back to German pageThis study is an extension of research studies conducted within the framework of the Federal Ministry for Research and Technology Project "Case Study Harz" (BMFT Project), initiated in 1989 and begun in the Söse catchment. It was expanded to include the area to the east thus providing an overall survey for all of the Upper Harz mountains. Particular attention was devoted to elevations 500 m above sea level. Aim of the study was to determine input and fate of selected major and trace elements in the aquatic ecosystem on the basis of the analysis of stream water, sediments, and atmospheric deposition. Additionally, the spatial and temporal trends as well as distribution of elements from 1992 to 1994 had to be documented.
The geological background was elaborated by determining the compositions of 49 rock samples from the major geological units of the area dealt with. In addition 243 samples of stream sediment (fraction < 63 mm) and 318 surface water samples from the Brocken Massif area were analysed. Contribution by atmospheric processes was determined by the study of 24 collector samples located in the Sankt Andreasberg area. X-ray Fluorescence Spectrometry (XRF) and Inductively Coupled Plasma-Mass-Spectrometry (ICP-MS) were used to determine the concentrations of trace elements in the rocks, stream sediments and surface water. Ion-chromatography was used to determine anions. The ions Na2+, K+, Ca2+ and Mg2+ in the water samples were determined by Optical Emission Spectrometry with Plasma-Excitation (ICP-OES).
Distribution of element concentrations in the sediments shows depletion for Al2O3 (0.7), Na2O (0.3), K2O (0.4), Ba (0.7) and Rb (0.3) in comparison with the rocks which is attributed to the decomposition of the feldspars and removal of these elements. Stream sediments show enrichment for Cd (19), Cr (12), As (5), Co (5), Cu (5), Pb (5), Ni (4) and Zn (3) which reflects local and regional anthropogenic inputs.
The concentrations of metals heavily depend on grain size and can easily be released by lowering the pH-value. This occurs effectively at an elevation between 500 and 600 m above sea level with pH-values decreasing. This level of elevation characterizes the horizontal acidification front and is similar to the watershed and acidification front of the Söse catchment. At this altitude metal concentration in the surface water decreases sharply due to an increase in the pH-value up to > 5.0 and the heavy metal contents increase in the stream sediments. This acidification front is dynamic and moves downwards during events causing temporal acidification (snow thaw, heavy rainfall).
The pH-values of the surface water range between 2.2 and 8.1 with a mean of pH 6.0 and lay in the permanently acid range (84 % of the samples measured). Airborne acid deposition with high metal contents is responsible for the low pH-values of the surface water. SO42- comprises the highest equivalent percentage (69.2 % meq/L) of the strong mobile anions, Cl- with 21.2 % meq/L and NO3- with 9.6 % meq/L play a minor role only.
The concentrations of Al, Zn, Pb, Cu, Cr, Co and Cd in surface waters are strongly dependent on the pH-values. In some parts of the study area levels of Al, Cd, Fe and Mn are far above the maximum values set by the German Safe Drinking Water Act (TVO-BRD). The distribution patterns of the rare earth elements (REE) in the rocks and the associated surface water show similarities. Their concentrations are negatively correlated with the pH-values. In contrast to the non-bog areas, bog waters show low concentration of Na, Ca, Mg, Sr, SO42-, Cl- and NO3-. However, numerous metals and metalloids, for example Al, Fe, Mn, Cd, Co, Cr, Pb, Zn, As and REE are enriched in bog waters.
Classification according to the percentage of main ions shows similar water chemistry in all cases studied. The majority of the waters are earth-alkaline fresh water bodies. Electrical conductivity (minimum 17, mean 87, maximum 480 mS/cm) depicts very weak or weak mineralisation of the surface water on the Brocken Massif. Only the Al concentrations become spatially and temporarily close to values indicating the saturation of water with respect to gibbsite. Otherwise, water bodies on the Brocken Massif have very low ion activity products.
Studies of precipitation show that the mean value of pH of throughfall deposition (pH 3.8) in conifer stands is lower than in deposition in open areas (pH 4.1). The median value (130 mS/cm) of electrical conductivity in throughfall deposition in conifer stands is more than twice as high as that for bulk deposition (60 mS/cm) and discloses the interceptive effect of forests. Except for Mn, element of throughfall deposition are higher on the average by the factor 3.5 in comparison with open area deposition.
The low element contents of the surface water on granite are attributed to the short residence time of surface waters and slow weathering. The main source of heavy metals in the sediments of streams of the Brocken Massif and its environment is the deposition of airborne particulates. High average precipitation rates are responsible for high atmospheric acid input, low buffer capacity coupled with the thin soil cover on the granite bedrock and strong soil erosion on the weather side of the massif cause acidification of the soil, the aquatic environment and large-scale damage to the ecosystem of the Brocken Massif.
