Dissolved carbon storage and flux dynamics in China's inland waters over the past 30 years

Inland waters (lakes, reservoirs, and rivers) serve as important regulators of global climate change and carbon (C) cycling. China's inland water systems significantly regulate regional C budgets. However, our understanding of the long-term spatiotemporal patterns and underlying mechanisms of dissolved carbon (DC) storages and fluxes in inland waters remains limited. This study examined lake and reservoir DC storage and river DC flux, quantifying their changes in China over the past three decades. We found that inland water DC stocks in China increased from 96 Tg C in the 1990s to 142 Tg C in the 2010s while DC river flux did not significantly change (13.2 ± 0.4 Tg C/yr). Findings also showed that a combination of climate change, anthropogenic disturbance, and water chemistry collectively drove inland water DC dynamics. River DC was more directly driven by climate and anthropogenic factors (>50%) while lakes and reservoirs were more directly influenced by water chemistry (>70%). Additionally, climate factors can explain changes in dissolved inorganic carbon (DIC) concentrations via water chemistry factors (i.e. electrical conductivity (EC) and pH), while, collectively, climate and the nutrient status can typically explain changes in dissolved organic carbon (DOC) concentrations. This study emphasizes the important role that inland water plays in the global C balance and underscores the necessity of considering it in future C budgets.