Carbon concentrations and their stable isotopic signatures in the upper Han River, China.

Carbon (C) in riverine ecosystems play an important role in regulating terrestrial carbon reservoir to the oceans and atmosphere, thus, understanding C dynamics in riverine ecosystem are essential for understanding global carbon cycle. Here, we investigated the seasonal and spatial variations in concentrations of dissolved inorganic carbon (DIC), particulate organic carbon (POC), and their carbon isotopic signatures (i.e., δC-DIC, δC-POC) in the tributaries and main channel of the upper Han River, China. Dissolved organic carbon (DOC), total suspended solid (TSS), and other physicochemical parameters including water temperature, pH, dissolved oxygen (DO), and electrical conductivity (EC) were also measured. We found that POC concentration was significantly higher in wet season and in main channel, and DIC concentration did not show significant spatiotemporal variability. DIC and POC were positively related to DOC, and they were also positively correlated with water temperature and TSS, respectively. δC-DIC and δC-POC had significant seasonal and spatial variations, and δC-DIC was significantly higher in dry season and δC-POC was significantly higher in the tributaries and in dry season. δC-DIC was negatively related to the TSS concentration, while δC-POC was negatively correlated with water temperature, DIC, and DOC concentrations. Our results suggest that water temperature and TSS are the primary factors in regulating C concentrations, and their stable isotopic signatures are primarily affected by aquatic photosynthesis and riverine respiration in the upper Han River, China.