Abstract: Based on the analysis of organic C, N stable isotope, C/N ratio, TOC, and TN from core sediments (YLH-1) in Lake Yilong, combined with the stage features of human activities, we analyzed the origin of organic matter and the stagebased evolution process of lake ecosystem during the past 100 years. The results showed that the organic C and N stable isotope values varied from -25.9‰ to -22.5‰ and 0.5‰ to 4.7‰, respectively, and the range of C/N ratio was between 16.4 and 20.4. Such results suggested that aquatic macrophyte was main origin of organic matter, with relatively little contribution of algae and terrestrial sources. The decline in δ¹³C values suggested that the process of intensified eutrophication, which may be related to CO₂ produced by algae due to the degradation of organic matter. The increase in δ¹⁵N was attributed to the increasing sewage, the application of fertilizers, and atmospheric nitrogen deposition. The historical evolution of Lake Yilong ecosystem could be divided into three stages. From the 1880s to the early 1960s, primary production level was relatively low and water quality was good, with weak human influence. From the mid1960s to 1990s, with the intensified human activities, the lake productivity rapidly increased, eutrophication was aggravated, water quality was deteriorated, and the intensity of algal blooms increased. Since the 1990s, the lake was at high production level and serious eutrophication state. Future work should pay attention to the impacts of human activities on the lake ecological environment. The management of lake ecosystem should be emphasized to improve the quality of eco-environment.  

Key words: polyacrylamide (PAM), compost, urban green soil, biochar, pollution reduction, soil permeability improvement, stable isotopes of carbon and nitrogen, organic matter, environmental evolution, human activity, Lake Yilong.