Rapid urbanization effects on partial pressure and emission of CO2 in three rivers with different urban intensities

Rapid urbanization has been reported to affect carbon biogeochemical cycle of waterways, contributing to even higher carbon dioxide (CO2) outgassing from rivers to the atmosphere. However, knowledge on the magnitude and extent of the urbanization influence on riverine CO2 dynamics is still limited. In this study, we investigated partial pressure of CO2 (pCO(2)) and CO2 degassing rate in the surface water of three rivers that drain land areas with varied urban coverages. Field sampling and measurements were conducted in the Taohua, Nan and Puli Rivers in China's mountainous Three Gorges Reservoir (TGR) area during winter 2018 and summer 2019 to determine the effect of urbanization intensity on riverine CO2 degassing. We found that pCO(2) level was significantly higher in the river with increased proportion of urban land. Both pCO(2) level and CO2 flux rate of the Taohua River (3872 mu atm and 574 mmol m(-2) d(-1)) with the highest urban land coverage were significantly higher than those of the Nan River (1737 mu atm and 218 mmol m(-2) d(-1)) and Puli River (1218 mu atm and 130 mmol m(-2) d(-1)) that drain less urbanized land areas. No significant seasonal difference in pCO(2) was found in these subtropical rivers (2402 +/- 1421 vs 2112 +/- 1254 mu atm in the summer and the winter). Overall, pCO(2) was positively correlated with the concentration of chlorophyll-a (Chl-a), nutrients (i.e., TDN and TDP), dissolved organic carbon (DOC) and colony-forming units (CFU), and was negatively correlated with pH and dissolved oxygen (DO). We found that pH and DOC loading were the better parameters for predicting pCO(2) in the river draining more urbanized land area, and pH and Chl-a were the better parameters for predicting pCO(2) in the river draining less urbanized area. These findings highlight the role that urbanization plays in increasing riverine pCO(2) through increasing nutrient and DOC inputs from the drainage basin under urban development.

Automated summary

This study investigated the pCO(2) and CO2 degassing rate in rivers in the Three Gorges Reservoir area, finding that pCO(2) levels were significantly higher in rivers with more urban land coverage. Urbanization was found to play a role in increasing riverine pCO(2) through nutrient and DOC inputs from the drainage basin.