Isotopic constraints on sources of organic matter in surface sediments from two north-south oriented lakes of the Yunnan Plateau, Southwest China

Purpose Lake sediment is an important carbon reservoir, and knowledge of organic carbon distribution and its controlling factors can provide insights into the effects of natural processes and anthropogenic pressures on carbon dynamics in drainage basin. Materials and methods Here, we combined total organic carbon (TOC), total nitrogen (TN), and their stable isotopes (delta C-13 and delta N-15) with a Bayesian isotope mixing model to identify the origin of organic matter (OM) and the key factors influencing OM accumulation in surface sediments from Lake Yangzong (YZ) and Lake Chenghai (CH), located on the Yunnan Plateau, SW China. Results and discussion The delta C-13 values in surface sediments from YZ showed a gradual increase from south to north, with an asynchronous decrease in delta N-15, suggesting an increasing contribution of pollutants originating from the Yangzong River. In contrast, CH was characterized by a rapid decrease in delta C-13 and an increase in delta N-15 values occurring in the deepest part of the lake, indicating that water depth may play an important role in OM accumulation in the lake. Allochthonous OM (C3 plant and soil OM) was the dominant sediment OM source for surface sediments in YZ, while substantial contributions of OM originated from plankton, soil OM, and sewage in CH. Conclusions These findings suggest that trophic state and terrestrial input may exert large impact on OM accumulation in deep lakes, which results in different distribution patterns of OM sources.

Automated summary

Lake sediment is an important carbon reservoir, and its distribution is influenced by trophic state and terrestrial input, resulting in different patterns of organic matter sources in different lakes.