Changes in dissolved inorganic carbon in river water due to urbanization revealed by hydrochemistry and carbon isotope in the Pearl River Delta, China

Spatial and temporal variability of <i>p</i>CO<sub>2</sub> and CO<sub>2</sub> emissions from the Dong River in south China

“…For small rivers, the highest pCO 2 value was observed in April (Fig. 4), which is consistent with the rapid surge of terrestrial C inputs, usually occurring at the onset of the wet season (Hope et al, 2004;Yao et al, 2007;Johnson et al, 2008). However, such increase in pCO 2 was not observed in large rivers (Fig.…”

“…This seasonal pattern is similar to that observed in the Xi and Daning rivers (Yao et al, 2007;Ni et al, 2019) but different from that observed in the Jinshui River in the upper Yangtze River, where pCO 2 is high in winter and low in summer (Luo et al, 2019), although all four rivers are in the East Asian Monsoon climate region. The seasonal differences in CO 2 emissions are largely caused by the pCO 2 variability, which in turn is regulated by external carbon inputs, internal production of CO 2 (Yao et al, 2007), and the dilution effect caused by precipitation (Johnson et al, 2007). For rivers where pCO 2 is lower in summer than in winter, the dilution effect overrides the effect of increased carbon inputs and internal CO 2 production (Luo et al, 2019).…”

“…As the wind speed decreases, the impact of flow velocity on k 600 becomes increasingly predominant (Borges et al, 2004). Therefore, the accuracy of k 600 estimation based on wind speed in nearby regions should be examined using measurement data (Yao et al, 2007;Li et al, 2018). The temporal heterogeneities of k 600 between small and large rivers reveal the differences in flow regime.…”

“…In addition, the controlling processes of the Dong River could be different even when compared with rivers with similar seasonal variations in the same climatic zone. For instance, the DO in the Xi River was supersaturated, indicating that its aquatic photosynthetic activities predominated aquatic metabolism and tended to reduce its CO 2 concentration (Yao et al, 2007). Therefore, other carbon sources like soil respiration and carbonate weathering should be responsible for the high pCO 2 in summer (Zhang et al, 2019).…”

“…The Dong River (DJR), located in subtropical south China, is one of the three tributaries of the Pearl River. Previous studies on riverine carbon transport and emissions in the Pearl River system mainly focused on the Xi River, which is characterized by widely distributed carbonate rocks, and the estuary area of the Pearl River delta (Yao et al, 2007;Zhang et al, 2015Zhang et al, , 2019Zhang et al, , 2021. Although some studies on chemical weathering and dissolved inorganic carbon (DIC) transport in the Dong River basin (DJRB) have been conducted (Tao et al, 2011;Fu et al, 2014), there is still a lack of understanding of the characteristics of catchment-wide CO 2 emissions from the DJRB.…”