Sedimentary DNA record of eukaryotic algal and cyanobacterial communities in a shallow Lake driven by human activities and climate change.

Global freshwater lakes are changing due to human activities and climate change. Unfortunately, sufficient long-term monitoring is lacking for most lakes. However, lake sedimentary archives can extend the instrumental record and reveal historical environmental trends. In particular, sedimentary DNA analysis of lacustrine sediment cores can aid the reconstruction of past trends in eukaryotic algal and cyanobacterial communities, as was conducted in this study for Lake Chaohu in China. The results presented here indicate that the construction of the Chaohu Dam in 1963 is associated with decreased richness of eukaryotic algal and cyanobacterial communities. Several groups, including the eukaryotic algal taxa, Chlorophyceae, and cyanobacterial groups like Dolichospermum, Microcystis, Planktothricoides, Cyanobium, Pseudanabaena, and Synechococcus, increased in abundance following inferred historical nutrient enrichment. Nutrient concentrations and hydrologic conditions were further implicated as the dominant controls on communities based on Random Forest and generalized additive modeling statistical analyses. In particular, significant increases in lake hydraulic residence times after the construction of the Chaohu Dam were significantly associated with altered biological community structures. Further, phosphorus enrichment was positively associated with increased richness and diversity of these communities following the 1980s. In addition, effects from increased atmospheric temperatures on eukaryotic algal and cyanobacterial communities were apparent. Here, high-throughput sequencing analysis of sedimentary DNA allowed the inference of long-term biodiversity dynamics of Lake Chaohu. These results underscore the important impacts of anthropogenic activities and climate change on aquatic ecosystems at the decadal scale.