Since reservoirs can act as sinks for potential contaminants, such as metal(loid)s, sediment management is a challenge for reservoir operators. To exemplify the variability of concentrations of arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), vanadium (V) and zinc (Zn), the sediments of two differently constituted reservoirs located in the Ore Mountains (Saxony, Germany) were comparatively investigated. In the sediments of the Einsiedel Reservoir, which has a catchment area dominated by forestry, the median values showed an enrichment of Cd (6.7 mg/kg), Co (31.4 mg/kg), Hg (0.57 mg/kg), Ni (39.0 mg/kg) and Zn (283 mg/kg), mainly due to an elevated geogenic background and a preferential input of these elements from the soils of the catchment area. Sediments of the Berthelsdorf Smelter Pond, which has a predominantly agricultural catchment, had relatively high median concentrations of As (62.9 mg/kg), Cd (10.3 mg/kg), Cr (43.1 mg/kg), Cu (50.2 mg/kg), Hg (0.51 mg/kg), Pb (204 mg/kg), V (57.0 mg/kg) and Zn (626 mg/kg), which was due to an elevated geogenic background and heavy anthropogenic metal(loid) inputs over the past. Statistical analyses indicated that site-specific differences (e.g., in the content of organic matter or in the physicochemical properties of sediments) may influence the sink and source functions of the reservoirs for metal(loid)s. In this context, a strong influence of the specific catchment characteristics on the sediment composition of the reservoirs was concluded. Based on the German Federal Soil Protection Ordinance, the status quo of the metal(loid) contamination of the two reservoirs was evaluated and recommendations for further management and investigations were derived.

Sediment management is a fundamental part of reservoir operation, but it is often complicated by metal(loid) enrichment in sediments. Knowledge concerning the sources of potential contaminants is therefore of important significance. To address this issue, the concentrations and the mobile fractions of metal(loid)s were determined in the sediments and the respective catchment areas of six reservoirs. The results indicate that reservoirs generally have a high potential for contaminated sediment accumulation due to preferential deposition of fine particles. The median values of the element-specific enrichment factor (EF) demonstrates slight enrichments of arsenic (EF: 3.4), chromium (EF: 2.8), and vanadium (EF: 2.9) for reservoir sediments. The enrichments of cadmium (EF: 8.2), manganese (EF: 3.9), nickel (EF: 4.8), and zinc (EF: 5.0) are significantly higher. This is enabled by a diffuse element release from the soils into the impounded streams, which is particularly favored by soil acidity. Leaching from the catchment soils partially enriches elements in stream sediments before their fine-grained portions in particular are deposited as reservoir sediment. We assume that this effect is of high relevance especially for reservoirs impounding small streams with forested catchments and weakly acid buffering parent material of soil formation.