Floating photovoltaic (FPV) systems are increasingly deployed on gravel pit lakes to generate renewable energy and mitigate land-use conflicts. However, their environmental impacts on hydrological and ecological processes remain insufficiently studied. This study investigates the effects of a 1.5-MWp FPV system covering 8% of a 19-ha gravel pit lake in Germany. The General Lake Model (GLM-AED2) and Delft3D-FLOW were used to simulate FPV-induced changes. Meteorological data—including irradiance, air temperature, wind speed, and relative humidity—were recorded above and below the PV modules. Water quality data—including water temperature, dissolved oxygen, pH, dissolved organic carbon, and chlorophyll-a—were collected beneath the FPV and in open water. Mussel colonisation of the FPV substructure was assessed, and its filtration impact on water quality analysed. Macrophyte distribution was assessed beneath the FPV system and along the shorelines. Results showed a modelled 88% solar irradiance and 57% wind speed reduction beneath the FPV system. Water quality impacts were minimal and primarily influenced by mussels colonising the substructure. Macrophytes occurred in littoral zones up to 5.25 m deep up to 5.25 m deep, but habitat-typical species were scarce due to gravel extraction and herbivorous fish. These findings highlight complex interactions between FPV, mussel filtration, macrophytes, and human activities, suggesting that other anthropogenic factors may outweigh FPV impacts. Model simulations indicated that FPV coverage above 45% could destabilise thermal stratification and alter primary production. This study underscores the need for empirical monitoring and modelling to optimise FPV deployment and inform regulatory frameworks for sustainable development.

The increasing number of reservoirs around the world today reaches a surface area of around 500,000 km², equaling one third of that of non-artificial surface water bodies. By impounding rivers through the construction of dams, riverine systems and biochemical cycles are disrupted. Different types of transported materials are trapped behind the dams and form layers of sediment. A method to characterise the spatially extensive sediment volumes with an EA 400 echo sounder was tested in the Vossoroca reservoir in the southeast of Brazil, Paraná State. A number of core and grab samples was taken and analysed for a variety of chemical and physical parameters. These data served as ground truthing for the hydro-acoustic assessment of the sediment. Eight hydro-acoustic parameters were derived from the echo signals using the Sonar5-Pro software. The major objective of defining the optimal survey parameters for the echo sounder as well as determining the difference between core and grab samples was reached by correlating the various single parameters and identifying the best combinations. Density and grain size distribution represented the best detectable sediment features with r-values of 0.94 and 0.95. The lower 38 kHz frequency generally had a better performance than the 200 kHz frequency. Results show that core samples reached a significantly higher quality of correlation for sediment characterisation. Additionally, it is was found that shorter pulse lengths yield a better characterisation. The results underline the potential of single beam echo sounders for extensive sediment characterisation. This methodology may be used for future mass balance estimations of large reservoirs.