Impact factors of dissolved organic carbon and the transport in a river-lake continuum in the Tibet Plateau of China

As a significant fraction of carbon in inland waters, dissolved organic carbon (DOC) plays a crucial role in carbon cycling at a global scale. Understanding the linkages between variations in DOC and its dominant factors in lakes is critical for estimating its concentration on a larger scale. This study characterized the concentrations of DOC in the lakes of Tibet Plateau and explored the major underlying influencing factors. The overall mean concentration of DOC in these closed lakes had a mean value of 21.80 +/- 30.82 mg/L (mean +/- S.D.) and was higher than open lakes (F = 174.1, p < 0.05). The potential drivers for the concentration of DOC in the lakes of Tibet Plateau were conducted by the correlation analysis of DOC with the observed landscape, water quality variables, and climatic factors. The multiple regression model showed that 78% of DOC concentrations across the lakes could be explained by Shannon evenness index (SHEI) of landscape, slope, and landscape dominance index (LDI), of which SHEI explained the most substantial variations for the concentration of DOC. The changes in the concentrations of DOC in river-lake interaction were analyzed in Qinghai Lake watershed. The concentration of DOC in the Qinghai Lake water was higher than the surrounding rivers. Slope and the density of soil organic matter (SOM) in the Qinghai Lake watershed were responsible for the higher DOC in lake than rivers. The landscape had a significant influence on DOC in the lakes, and the dominant factor was SHEI. The results observed from this investigation further supplement the information of DOC in the inland waters with plateau lakes. Further, this study is expected to improve the understanding of the transport of DOC in the river-lake ecosystem.