Lake ecosystem regime shifts induced by agricultural intensification: A century scale paleolimnological investigation from the Huai River Basin (China)

Abstract

Regime shifts of freshwater ecosystems driven by fast-changing multiple stressors are increasingly occurring. However, lake regime shifts across intensive agricultural landscapes are less explored, especially how different aquatic communities respond to multiple environmental forcings through time is poorly understood. Using a century scale paleolimnological record from Gaoyou Lake in the Huai River Basin, one of the most intensively cultivated areas in China, we analyzed high-resolution sedimentary subfossil pigments and cladoceran assemblages to investigate the dynamic trajectories of plankton communities and detect the potential occurrence of ecological shifts across different aquatic trophic levels. Furthermore, we explored how these shifts were driven by anthropogenic and climatic stressors, and examined the rates of ecological change through time. Our results revealed a significant ecological shift in the cladoceran community around the 1970s associated with the hydrological regulation through damming within the basin. Subsequently, a regime shift for the whole-lake ecosystem occurred in the 1990s, which was characterized by the onset of eutrophication with elevated primary production and decreased water clarity. Redundancy and variance partitioning analyses identified agricultural intensification with substantial anthropogenic nutrient loading as the main driver of lake ecological dynamics. Rising temperature played an additional role. Moreover, we detected two significant acceleration phases of lake primary productivity (in the 1990s and after the 2000s), which were asynchronous with the variability of external environmental drivers. This finding probably indicated Gaoyou Lake has switched from a slow-to a fast-response system with decreasing ecological stability. Our study offers new challenges and insights for incorporating rate-focused management strategies to minimize the risk of catastrophic ecological shifts in aquatic ecosystems.