Dissolved inorganic carbon isotopes of a typical alpine river on the Tibetan Plateau revealing carbon sources, wetland effect and river recharge

Abstract

The Nyangqu River, the largest right bank tributary of the Yarlung Zangbo River in the Qinghai-Tibet Plateau, was representative of an alpine riverine carbon cycle experiencing climate change. In this study, dissolved inorganic carbon (DIC) spatial and seasonal variations, as well as their carbon isotopic compositions (δ 13 C DIC ) in river water and groundwater were systematically investigated to provide constraints on DIC sources, recharge and cycling. Significant changes in the δ 13 C DIC values (from À2.9‰ to À23.4‰) of the water samples were considered to be the result of different contributions of two dominant DIC origins: soil CO 2 dissolution and carbonate weathering. Three types of rock weathering (dissolution of carbonate minerals by H 2 CO 3 and H 2 SO 4 , and silicate dissolution by H 2 CO 3 ) were found to control the DIC input into the riverine system. In DIC cycling, groundwater played a significant role in delivering DIC to the surface water, and DIC supply from tributaries to the main stream increased from the dry season to the wet season. Notably, the depleted δ 13 C DIC 'peak' around the 88.9 longitude, especially in the September groundwater samples, indicated the presence of 'special' DIC, which was attributed to the oxidation of methane from the Jiangsa wetland located nearby. This wetland could provide large amounts of soil organic matter available for bacterial degradation, producing 13 C-depleted methane. Our study provided insights regarding the role of wetlands in riverine carbon cycles and highlighted the contribution of groundwater to alpine riverine DIC cycles.

Carbon dioxide partial pressures and emissions of the Yarlung Tsangpo River on the Tibetan Plateau

“…Yan et al (2018) showed that the littoral zones of lakes on the Tibetan Plateau were supersaturated and acted as sources of greenhouse gases. Research on the alpine riverine dissolved inorganic carbon (DIC) of Nyangqu River found that rock weathering controlled the DIC input into the riverine system and groundwater played a significant role in delivering DIC to the surface water (Ge et al, 2021). However, the degassing effect of plateau rivers might be still unclear.…”

Moving Bedforms Control CO2 Production and Distribution in Sandy River Sediments

“…In‐stream CO 2 is controlled by CO 2 exchange with the atmosphere, in‐stream metabolic processes, and input from external sources (Hope et al., 2004; Stumm & Morgan, 1996). The latter includes the import of CO 2 via shallow groundwater exfiltration that originates from root respiration, soil organic matter decomposition, soil CO 2 dissolution, and carbonate weathering (Amiotte‐Suchet et al., 1999; Ge et al., 2021; Hope et al., 2004). On the one hand, several studies report the external input of CO 2 as the major contributor to the overall pool in the water column of rivers and streams (Gu et al., 2021; Peter et al., 2014; Rovelli et al., 2022).…”