Sedimentary macrophyte δ13Ccellulose record of environmental evolution over the past century in East Taihu Lake, China

Abstract

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 α-cellulose (δ13Ccellulose) is a sensitive proxy indicator of palaeoproductivity, but this proxy index is rarely used in Chinese lakes. In order to test whether δ13Ccellulose can be used as a lake ecological environment changes indicator, we investigated the relationship between the δ13Ccellulose and several geochemical proxies from a ∼ 30 cm core extending 100 years obtained from a shallow lake: East Taihu Lake, China. Here, the changes in δ13Ccellulose of plant residues in sediments from East Taihu Lake were coupled analysis with geochemistry indexes to identify the response of δ13Ccellulose from plant residues to the past environmental changes. Combined with the results of C/N ratios, δ13Ccellulose 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 δ13Ccellulose showed a significant negative correlation with total organic carbon, probably indicating the changes of primary productivity of the lake. The δ13Ccellulose 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 By comparing the results with historical documents and measurements from East Taihu Lake, we inferred that anthropogenic pressures were the primary cause of the changes in the aquatic macrophyte communities and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. Atpresent, 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 δ13Ccellulose and other geochemical proxies to study palaeoenvironmental change, which provides new perspectives for understanding lake ecological environmental change in lakes.