Comparison of heavy metal contamination in sediment, water and Gammarus spp. (Crustacea: Amphipoda) in small streams with respect to anthropogenic discharges

Abstract

Abstract The entry of heavy metals into rivers affects both the water quality and the biocoenosis of the water bodies. Heavy metals that are discharged with wastewater are distributed with the current and can be stored downstream in the sediment of the watercourse and absorbed by aquatic organisms. The aim of the study is to examine how heavy metals entering water bodies are found in samples of water, sediment, and freshwater amphipods (Gammarus spp.). Several smaller rivers in Hesse and Bavaria are being investigated, establishing a connection to existing wastewater discharge points. For the examined rivers, it is determined that the concentration of heavy metals in sediment is about 10,000 times higher than in a scoop sample of water from the same section of the water body. In the species Gammarus fossarum, G. pulex and G. roeselii, heavy metal concentrations are about 1,000 times higher than those found in the investigated river water. A comparison of heavy metal contents in gammarids and in sediment shows no linear relationship. Gammarids inhabit the bottom of water bodies and the bank area, accumulating heavy metals with their food throughout their lifetime. Due to their high abundance, they serve as accumulation indicators in most smaller rivers. However, the sampling process is labor-intensive, requiring sufficient sample weight and the removal of other macrozoobenthos species. Sampling sediment in water bodies with gravel or fine sediment requires less effort. Water samples can be obtained quickly from any water body. The investigations of the Kössein and Röslau rivers in Bavaria, known for their mercury contamination, show a decrease in heavy metal concentrations over a period of about ten years. Due to the low flow velocity at the Wölsauerhammer weir, elevated levels can still be observed in the settled sediment. Dredging the riverbed and securing the banks of previously heavily contaminated sections lead to an overall decrease in concentrations throughout the river system. Sediment analyses from several sampling sites along the Wieseck river near Trohe, where untreated sewage was discharged for a week, indicate that an increase in heavy metal contamination due to the event can still be detected about a year later. The example of Rosbach in the Taunus region illustrates the suitability of combining different types of samples. Water analysis shows an increase in heavy metal concentrations (including zinc) downstream of a wastewater treatment plant's discharge point, which can be found in the sediment further along the watercourse. The examination of water samples is mainly suitable for short-term monitoring of known contamination events. Conversely, environmental media such as sediment and Gammarus spp. can be used to assess past wastewater discharges. The increase in heavy metal contamination in water bodies due to wastewater discharges is confirmed for both sediment and gammarids.