Groundwater of the Quaternary unconsolidated sediments in the catchment area of the waterworks of Liebenau II (NW-Germany) is characterized by heterogeneous distributions of dissolved constituents. In order to determine sources of solutes and to estimate flowpaths, Sr isotope analyses were carried out on groundwater, precipitation, and soil samples. 87Sr/86Sr ratios of the groundwater samples vary between 0.708 and 0.719 and allow to discriminate four groundwater levels. The near-surface groundwater level is characterized by low 87Sr/86Sr ratios in the range of 0.7099 and 0.7130. At greater depths 87Sr/86Sr ratios increase up to a value of 0.7187 in the intermediate groundwater level. Deep groundwaters which can be divided into two levels exhibit a remarkable decrease of 87Sr/86Sr ratios. Groundwater of deep level I shows Sr isotope ratios between 0.7118 and 0.7128, whereas deep level II shows 87Sr/86Sr ratios of 0.7082 to 0.7087.
Differences in the 87Sr/86Sr ratios are the result of varying sources of dissolved strontium in the groundwater. These encompass mineral weathering, precipitation, and anthropogenic inputs. Low 87Sr/86Sr ratios of 0.710 to 0.713 indicate the influence of precipitation and probably fertilizers on the near-surface groundwaters. At greater depths, groundwater chemistry is dominated by weathering processes. Due to significant differences in the 87Sr/86Sr ratios the dissolution of silicate minerals can be distinguished from the dissolution of carbonate minerals. For the intermediate groundwater level a dominant influence of silicate weathering is confirmed by radiogenic 87Sr/86Sr ratios between 0.713 and 0.719 and saturation indices < –3.5 for calcite. In contrast, low 87Sr/86Sr ratios of 0.708 to 0.709 indicate dissolution of carbonate minerals in the deep groundwater, where saturation for calcite is observed.
|Journal||Acta hydrochimica et hydrobiologica|
|Publication status||Published - 2001|
Treatment code (Nähere Zuordnung)
- Basic - Fundamental (Grundlagenforschung)