Neolithic human activity caused eutrophication in small central European lakes

Human activities during the Early Neolithic have had major influences on central European terrestrial ecosystems through deforestation, burning, animal husbandry and agriculture. However, much less is known about how these landscape-scale changes affected aquatic ecosystems. In this study, we examined diatom assemblages preserved in radiocarbon dated and intermittently laminated sediment cores collected at Burgäschisee and Moossee, two small lakes on the Swiss Plateau, and compared the results with archaeological evidence for Neolithic lakeshore settlements and palaeobotanical records indicating distinct catchment scale phases of changing land use. The new diatom records were used to reconstruct changes to the lake ecosystem and of lake water nutrient concentrations from 6600 to 3800 calibrated radiocarbon years BP (cal yr BP). Blooms of small sized Stephanodiscus spp. together with algal remains (Cyanobacteria, Chlorophyta) indicate distinct phases of lake nutrient enrichment particularly during a land use and settlement phase associated with the Cortaillod culture (5800–5500 cal yr BP). In contrast, other land use phases were not associated with clear indications of water quality changes. Diatom response to human impact in the catchment was more pronounced at Burgäschisee relative to Moossee, notably for the phase corresponding to the Cortaillod culture. The new results agree with previous studies that provided evidence of Neolithic human impact on lake ecosystems in central Europe. For small lakes, such as Moossee and Burgäschisee, the establishment of Neolithic lakeside settlements and land uses did not only lead to pronounced terrestrial ecosystem changes in the catchment but apparently influenced the lake ecosystems themselves. The different response of the diatom assemblages in the two lakes also suggests that the impact of land use on nutrient concentrations and algal communities varied between lakes during the Neolithic, presumably due to different intensities of human impact at different sites, but likely also due to differences in geographical and hydrological settings of the lakes (basin morphologies, stratification, and mixing regimes).