Sedimentary record of nutrients and sources of organic matter in the Shuanglong reservoir, Dianchi watershed, China.

In the last few decades, the eutrophication of lakes has been a serious issue in the middle and lower reaches of the Yangtze River watershed. To explore the relationship between lake systems and anthropogenic activities, sediments were collected from the Shuanglong reservoir in the Dianchi watershed in Southwest China. Total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), and the carbon isotopic ratio (δC) were analyzed in sediment cores to reconstruct the effects of natural succession and human activities on the past lacustrine environmental conditions. A reliable chronology of the sediment core was established by using the Pb dating technique, which indicated that the age span of the 70-cm sediment core is from the years 1871 to 2011. Above - 31 cm depth in the core, TN, TP, TOC, C/N, and δC increased significantly, indicating that eutrophication has occurred since the 1980s. By combining the indicators of δC and C/N, it was shown that terrestrial and lacustrine components were the main sources of organic matter (OM) in the reservoir, which was mostly controlled by terrestrial C plants and algae. Since the 1980s, increased sewage discharge, fish aquaculture, fertilizer application, population, and economic strength have sped up the eutrophication process, and the eutrophication was further intensified in 2001.