Abstract Lakes in the middle and lower reaches of the Yangtze River (MLY) are important freshwater ecological zones in China; investigating organic matter (OM) sources can deepen our understanding of regional carbon cycling and human effects on carbon storage. We compiled sediment core data from previous studies to determine the proportion of OM originating from endogenous sources and exogenous sources using a Bayesian mixing model supported by measurements of TOC, TN, C/N ratio, δ 13 C, and δ 15 N from five lakes (Lake Tai, Lake Cao, Lake Poyang, Lake Longgan, and Lake Changshou) in the MLY. Most C/N ratios ranged from 5 to 12, suggesting that sediment OM came from both autochthonous and allochthonous sources. Some ratios exceeded 12, indicating a strong terrestrial input. We used δ 13 C and C/N ratios for qualitative analysis. The results indicated that soil OM, algae, aquatic vascular plants, domestic sewage, and C₃ plants influenced sediment OM in the MLY lakes. Subsequently, we employed a Bayesian mixing model to estimate the contributions of autochthonous and allochthonous sources. Domestic sewage (29.2%) and soil OM (28.5%) were the main sources. Aquatic vascular plants (16.7%), algae (14.1%), and terrestrial C₃ plants (11.6%) served as secondary sources. These findings suggest that the lake ecosystems in the MLY are mainly affected by severe soil erosion and pollution from domestic sewage. Rapid urbanization in the basin has altered land‐use patterns in surrounding areas, increasing soil erosion and intensifying organic pollution from industrial wastewater and nutrient runoff from domestic sewage.
Zhang et al. (Thu,) studied this question.