Carbon and nutrients as indictors of daily fluctuations of pCO2 and CO2 flux in a river draining a rapidly urbanizing area

Carbon dioxide (CO2) emission via water-air interface from fluvial networks plays a central role in the global carbon budget. Large uncertainties, however, exist because field measurements are often spatially and temporally biased, while aqueous carbon (C) processing can be strongly affected by anthropogenic activities in rapidly urbanizing areas. Information of controls on riverine CO2 emission in an area of rapid urbanization is limited. In this study, we conducted field surveys in high time intervals to unravel the characterization of riverine partial pressure of CO2 (pCO(2)) and CO2 emission rates and their associations with C and nutrients. We found distinct variations in inter-/intra- daily and monthly pCO(2). pCO(2) and CO2 fluxes averaged 904-3157 mu atm and 80-1137 mmol/m(2)/d, respectively, with significantly higher levels in the period with higher nutrients. Increasing organic carbon and nutrients loading sped up aqueous CO2 production as reflected by the strong relationships between pCO(2) and dissolved organic carbon (DOC) and nitrogen and phosphorus. C and nutrients as indicators of pCO(2) were further developed. We highlight that urbanization is potentially increasing eutrophication and shifting DOC quantity and quality, and the resulting changes in C geochemical process and CO2 areal fluxes will hamper the CO2 accurate estimation from global rivers. In view of the increasing intensive and extensive urbanization, the resulting changes in extent and magnitude to CO2 emission in the frame of regional or global C budgets warrant future work.