Anthropogenically driven changes to organic matter input in sediments of Lake Chaohu, Eastern China, over the past 166 years

Characterizing how and to what extent human activities have influenced organic matter (OM) input in lake sediments is essential for a thorough study of the carbon cycle and carbon burial in lake systems, but this issue has not yet been addressed. Here, the source and composition of OM in sediments of Lake Chaohu, Eastern China, over the past 166 years, were determined by analyzing stratigraphic variations in aliphatic hydrocarbons and OM pyrolysis parameters in a dated sediment core. These data, coupled with documental records, were further used to elucidate the pattern and controlling factors of OM input in the sediments. The lowest hydrogen index (HI), lowest long-chain n-alkane concentrations, and highest Paq (proxy of aquatic macrophyte input) in sediments prior to ca. 1956 indicate a minimal input of OM from phytoplankton and terrestrial plants and a larger input from submerged macrophytes. This may represent the features of OM input in primitive conditions given the mild human activities around the lake before the 1950s. In sediments from ca. 1962 to 1985, elevated HI and C17/C16 n-alkane ratios indicate a greater input from phytoplankton, while the high abundances of long-chain n- alkanes and & alpha;& beta;-hopanes reflect an anomalously high input from terrestrial plant and fossil OM. These variations might have been caused by the rapid development of agriculture during this period, which accelerated catchment erosion and petroleum contamination and promoted the transport of allochthonous OM and nutrients to the lake. The lowest Paq in sediments during this period indicates reduced input from submerged macrophytes, probably resulting from a dam installation that modified the water to an unfavorable plant depth. In sediments after ca. 1989, the highest values of HI, short-chain n-alkane abundances, and C17/C16 n-alkane ratios indicate a further increase in OM input from phytoplankton, a response to domestic and industrial discharge and subsequent lake eutrophication.

Automated summary

Characterizing the input of organic matter (OM) in lake sediments and understanding its source and composition is crucial for studying the carbon cycle and burial in lake systems. This study analyzed stratigraphic variations in aliphatic hydrocarbons and OM pyrolysis parameters in Lake Chaohu sediments over the past 166 years to determine the pattern and controlling factors of OM input. The results indicate a minimal input of OM from phytoplankton and terrestrial plants before the 1950s, an increase in input from phytoplankton and terrestrial plant/fossil OM during the 1960s-1980s, and a further increase in input from phytoplankton after 1989 due to domestic and industrial discharge and lake eutrophication.