Effect of nutrient enrichment and climate change on historical changes of the cyanobacterial community in a shallow north temperate lake in China

Quantitative ecological reconstructions in lakes can be potentially significant for providing long-term environmental records and the information generated would become invaluable source for comprehensive understanding of the effects of human disturbances and climate change on lake ecosystem. Our aim is to explore the drivers of historical changes of the cyanobacterial community in a shallow temperate freshwater system, Baiyangdian Lake Complex (BLC), in northern China. We used a multi-proxy approach (e.g., sedimentary DNA, subfossil diatom assemblages) to establish the historical changes of the cyanobacterial community in BLC over different stages as accurately as possible. At Stage 1 (similar to 1902-2012), the cyanobacterial co-occurrence network analysis revealed more complex interactions among different genera than at Stage 2 (similar to 2012-2021) in all three sampling sites. The reconstructed cyanobacterial community correlated well with changes of the sedimentary diatom species composition, geochemical indices and historically documented events in the watershed. The cyanobacterial abundance in two advanced hydrologically-connected sampling sites (Shaochedian, Caiputai) was mainly regulated by the dynamics of TP and TN, while the other relatively weak hydrologically-connected site (Zaozhadian) was regulated by precipitation. Therefore, a reduction in nutrient inputs is still the most prudent option to avoid risk of the outbreak of cyanobacterial blooms in BLC. Meanwhile, intact hydrological connectivity within the wetland complex is also essential to reduce pollution and cyanobacterial blooms through mixing and flushing. Although the fate of cyanobacterial blooms in BLC has been greatly reduced over the recent time, resource managers should not only adopt conventional approaches (e.g., nutrient control) but also incorporate a landscape scale limnological-based monitoring approaches to resolve the long-lasting cyanobacterial bloom problem induced by coupled human and climate change disturbances.