Role of River–Lake System Sediments and Microbial Activity in the Hyporheic Zone

The effect of river–lake systems on the surface water self-purification process is a significant and not fully recognised scientific issue. The conditions prevailing in the hyporheic zone of these ecosystems are of great importance in the process of component exchange between water and sediments. The aim of this study was to investigate the influence of the type of sediments located at the bottom of the riverbed being part of a river–lake system on microbial activity in the hyporheic zone. An ex situ experiment was used to study the microbiological activity and the transformation of components in the collected river sediments. It was found that the specific properties of sediments varied depending on their location in the riverbed between the lakes comprising the system and that the prevailing meteorological conditions can also have an effect on microbial activity in the hyporheic zone, e.g., aerobic conditions. These conditions determined the intensity of component conversion in the sediments due to microbial metabolism. A closer understanding of the processes occurring in the hyporheic zone may allow the processes of water self-purification within river–lake systems to be supported in the future, which will contribute to the improvement of surface water quality

Heavy Metal Contamination in the Surface Layer of Bottom Sediments in a Flow-Through Lake: A Case Study of Lake Symsar in Northern Poland

River-lake systems most often behave as hydrographic units, which undergo complex interactions, especially in the contact zone. One such interaction pertains to the role of a river in the dispersal of trace elements carried into and out of a lake. In this study, we aimed to assess the impact of rivers on the accumulation of heavy metals in bottom sediments of natural lakes comprised in postglacial river-lake systems. The results showed that a river flowing through a lake is a key factor responsible for the input of the majority of available fraction of heavy metals (Zn, Mn, Cd and Ni) into the water body and for their accumulation along the flow of river water in the lake. The origin of other accumulated elements were the linear and point sources in catchments. In turn, the Pb content was associated with the location of roads in the direct catchment, while the sediment structure (especially size of fraction and density) could have affected the accumulation of Cr and Zn, which indicated correlations between these metals and fine fraction. Our results suggest that lakes act as filters and contribute to the self-purification of water that flows through them. As a result, the content of most metals in lake sediments showed a decrease by approx. 75% between the upstream (inflow) and downstream (outflow) sections. The increased content of two metals only, such as chromium and cadmium (higher by 2.0 and 2.5 times, respectively, after passing through the lake), was due to the correlation of the metals with fine sand. Both the content and distribution pattern of heavy metals in lake sediments are indicative of the natural response of aquatic ecosystems to environmental stressors, such as pollutant import with river water or climate change. The complex elements creating the water ecosystem of each lake can counteract stress by temporarily removing pollutants such as toxic metals form circulation and depositing them mostly around the delta

Role of River–Lake System Sediments and Microbial Activity in the Hyporheic Zone

The effect of river–lake systems on the surface water self-purification process is a significant and not fully recognised scientific issue. The conditions prevailing in the hyporheic zone of these ecosystems are of great importance in the process of component exchange between water and sediments. The aim of this study was to investigate the influence of the type of sediments located at the bottom of the riverbed being part of a river–lake system on microbial activity in the hyporheic zone. An ex situ experiment was used to study the microbiological activity and the transformation of components in the collected river sediments. It was found that the specific properties of sediments varied depending on their location in the riverbed between the lakes comprising the system and that the prevailing meteorological conditions can also have an effect on microbial activity in the hyporheic zone, e.g., aerobic conditions. These conditions determined the intensity of component conversion in the sediments due to microbial metabolism. A closer understanding of the processes occurring in the hyporheic zone may allow the processes of water self-purification within river–lake systems to be supported in the future, which will contribute to the improvement of surface water quality