Microplastic (MP) occurrence is a growing concern in environmental research, with significant attention focused on its presence in various ecosystems worldwide. While much research has centered on large lakes and water bodies, remote alpine lakes remain relatively unexplored in terms of microplastic occurrence. Studying microplastic occurrence in remote alpine lakes is important to understand the global spread of pollution, assess its impact on pristine ecosystems, and inform conservation efforts in these vulnerable environments. This study investigates microplastic presence in the sediment of Lake Cadagno, a remote alpine lake situated in the Piora Valley of southern central Switzerland. The lake has no effluents, and its meromictic nature means that the water on the bottom is not mixed with the water above, which can potentially lead to an enhanced accumulation of microplastics in the sediments that perpetuate in the lake system. Through sediment core sampling and analysis, we aim to identify the sources and deposition trends of microplastics in this pristine alpine environment. Our findings reveal the presence of microplastic within Lake Cadagno: in total, 186 MP particles were extracted from 756 cm³ of processed sediment (0.24 MP/cm³) with an average of 19.5 MP/sample (SD ± 11.8 MP/sample). Our results suggest that microplastics are predominantly attributable to localized sources associated with nearby human activities. The absence of synthetic fibers and the limited polymer types detected suggest a minimal contribution from atmospheric deposition, reinforcing the significance of local anthropogenic influences. Spatial clustering of microplastic particles near potential sources underscores the impact of surrounding land use activities on microplastic distribution. Overall, this study highlights the importance of addressing microplastic contamination even in remote and relatively unmodified ecosystems like Lake Cadagno, to elucidate the need for strict adherence to waste management and correct disposal actions to reduce the impacts of microplastic contamination.

Mountain lakes are highly sensitive to climatic change, yet the extent to which alpine aquatic communities respond to recent warming remains uncertain. We used a palaeolimnological approach based on analysing the remains of non‐biting midge (chironomid) larvae preserved in surface sediments from 24 Swiss mountain lakes to assess species‐environment relationships of chironomids and compare our results to previous, detailed survey data from similar campaigns in 1993/2002. This allowed us to determine changes in chironomid assemblages relative to lake physicochemistry and increasing temperatures over the past decades. We show that high‐elevation oligo‐ to mesotrophic lakes generally experienced a shift towards warmer chironomid assemblages, expansion of taxa with larger thermal range, and a simultaneous reduction in cold‐stenothermic taxa, consistent with rising air and water temperatures. However, 9 out of 24 lakes, mainly in the lower‐elevational range, exhibited stable assemblages or, in some cases, shifts towards colder chironomid communities. This is likely related to local catchment and lake conditions such as shading, changing human activities such as pasturing or hydrological inputs from snow and ice, indicating highly individual, lake‐specific responses. Environmental parameters accounting for the highest variability in the modern distribution of chironomid assemblages include variables representing lakewater organic matter content and elevation, as well as oxygen, total nitrogen, and total phosphorus concentrations, demonstrating the sensitivity of chironomid assemblages to temperature and associated limnological variables. Overall, our findings highlight that both large‐scale climatic drivers and local environmental heterogeneity shape chironomid assemblages in alpine environments, and that the majority of Swiss mountain lakes are showing responses in aquatic insect communities due to increasing temperatures. We conclude that shifts in chironomid populations are expected to further increase in amplitude under continued warming in the Alps, as rising temperatures increasingly affect alpine ecosystems and progressively cross critical thermal thresholds and tipping points.