Sedimentary macrophyte delta C-13(cellulose) record of environmental evolution over the past century in East Taihu Lake, China

At present, East Taihu Lake has been profoundly affected by human interventions. However, the earlier limnological conditions such as the occurrence of temporal nodes and the cause of eutrophication remain unclear due to the short temporal range covered by the instrumental record. The stable carbon isotope ratio of plant residue alpha-cellulose (delta C-13(cellulose)) is a sensitive proxy indicator of palaeoproductivity, but this proxy index is rarely used in Chinese lakes. In order to test whether delta C-13(cellulose) can be used as a lake ecological environment changes indicator, we investigated the relationship between the delta C-13(cellulose) and several geochemical proxies from a similar to 30 cm core extending 100 years obtained from a shallow lake: East Taihu Lake, China. Here, the changes in delta C-13(cellulose) of plant residues in sediments from East Taihu Lake were coupled analysis with geochemistry indexes to identify the response of delta C-13(cellulose) from plant residues to the past environmental changes. Combined with the results of C/N ratios, delta C-13(cellulose) and other related studies, the big plant residues in the sediments of East Taihu Lake may be derived from autochthonous aquatic macrophytes. In addition, the delta C-13(cellulose) showed a significant negative correlation with total organic carbon, probably indicating the changes of primary productivity of the lake. The delta C-13(cellulose) and geochemical proxy records revealed that the environmental changes in East Taihu Lake have undergone three distinct periods. The first period (1900s-1960s) represented a natural state without intensive human disturbance. The acceleration of lake eutrophication from the middle period (1960s-1995s) was a consequence of intensive local human activities. The late stage (1995s-2010s) represented a minor decline in nutrient levels after the implementation of ecological protection and restoration. By comparing the results with historical documents and measurements from East Taihu Lake, we inferred that anthropogenic pressures were the primary cause of the changes in the aquatic macrophyte communities and environments. This study provides a unique approach to the ecological environment evolution of East Taihu Lake. At present, Taihu Lake still suffers from annual cyanobacterial blooms due to economic growth (urbanization and industrialization). There is an urgent need for interventions to reduce nutrient inputs in order to enhance ecosystem resilience. Finally, the results of study of East Taihu Lake in China reveal the potential of combining delta C-13(cellulose) and other geochemical proxies to study palaeoenvironmental change, which provides new perspectives for understanding lake ecological environmental change in lakes.

Automated summary

By studying the changes in δC-13(cellulose) and other geochemical proxies in plant residues from East Taihu Lake in China, it was revealed that the lake's environment has undergone three distinct periods. The results showed that human activities were the main cause of the environmental changes, and interventions are needed to reduce nutrient inputs and enhance ecosystem resilience.