MICROBIAL MOLECULAR RECORDS IN RESPONSE TO LACUSTRINE EUTROPHICATION IN MIDDLE YANGTZE REGION IN CENTRAL CHINA

The East Lake in Wuhan, Central China, is a multiple functional lake that has been seriously affected by human activities since the 1950s with algal blooms occurred annually during the 1970s and 1980s. In contrast, the Liangzi Lake, the second largest freshwater lake near Wuhan, is a macrophytic lake but shows a relatively moderate eutrophication during the same time period. The two lakes enable us to compare their microbial responses due to the change of environmental conditions. Here, we use gas chromatography and gas chromatography – mass spectrometry to investigate variations of microbial biomarkers using 145 samples collected from three cores in the two lakes, which span a period of the recent 100 years based upon on Pb²¹⁰ dating.

The molecular record displays different courses of eutrophication in the two lakes. Prior to the 1950s, the microbial-derived compounds, such as the short chain iso- and anteiso-fatty acids, fatty alcohols, wax esters and hopanoids, were present in low abundance in comparison with the medium- and long-chain normal alcohols and n-alkanes, indicative of the presence of the floating-leaved, submergent and emergent plants or terrestrial higher plants. Biomarkers from bacteria and algae increase sharply, especially in one of the East Lake cores with abundant isomers from bacterial lipids after 1970s when the local anthropogenic activities intensified. The presence of abundant esters and high TOC content indicates that the aquatic environment favors the preservation of organic matter. The eutrophicational level of the Liangzi Lake is lower in intensity than that of the East Lake, and algae and aquatic vegetation were the main composition of the lake ecosystem. Our data indicate that molecular lipids can serve as an effective tool to reconstruct trophic levels for lacustrine environments.