Regime shifts revealed by paleoecological records in Lake Taibai's ecosystem in the middle and lower Yangtze River Basin during the last century

Abstract

Shallow lakes in the middle and lower Yangtze River Basin are greatly influenced by human activities during the last century, subsequently ecological regime shifts have occured and some ecosystem services are degraded in some shallow lakes. In order to provide more scientific and efficient lake management, it is necessarily urgent to understand the transforming process of the lake ecosystems. In this study, we focus on a typical eutrophic shallow lake sited in the middle reach of Yangtze River Basin, namely Lake Taibai, and combine its related geochemistry proxies, grain size and fossil diatom assemblages from a sediment core dated in 210Pb and 137Cs chronology based on paleolimnology with the basin's historical documents and monitoring data, to analyze specific regime shifts occurred in its ecosystem and changes of feedbacks inside driven by hydrodynamic changes and nutrient enrichement process. Results of diatom assemblages using STARS, a T-test based algorithm, revealed that at least two ecological shifts took place in the late 1950s and 1990s, respectively. The sudden shift in the late 1950s is supposed to be influenced hydrological change caused by dam and sluice constructions in 1950s and another shift in the late 1990s should be a critical transition due to the alternation of cultured fish community and consistent nutrient enrichment, which led to gradual decrease in ecosystem resilience in Lake Taibai. Through analyzing the changes of feedbacks among main function groups in the ecosystem influenced by the change of hydrodynamics and euthrophication, we can have a deeper understand of the process of ecosystem structural changes disturbed by anthropogenic driversand lay the fundation for building a shallow lake ecosystem dynamic model in future researches.