CO2 partial pressure and CO2 degassing in the Daning River of the upper Yangtze River, China

Rivers and streams are important agents for global and regional carbon cycle, which represent a nonnegligible carbon source to the atmosphere. However, carbon dioxide (CO2) degassing via water-air interface from inland waters currently has a large uncertainty in estimation. Here we examined the CO2 partial pressure (pCO(2)) and CO2 degassing in the Daning River, a main tributary of the Yangtze in the Three Gorges Reservoir (TGR) region. The riverine pCO(2 )showed obvious spatial and temporal variations on the main stem and its tributaries, ranging from 483,2 +/- 293.9 mu atm (May) to 2183.3 +/- 1309.2 mu atm (August) with an average of 1198.2 +/- 1122.9 mu atm. pCO(2) increased with the intensive agricultural practices and population on the lower reach of the tributary. The daytime average water-air CO2 flux was 329.8 +/- 470.2 mmol/m(2)/d, and yielded a total CO2 efflux approximately 0.12 Tg CO2/y. The results also indicated that carbon loss via atmospheric exchange accounted for 38.8% of riverine dissolved carbon fluxes. There were close relations between pCO(2) and environmental parameters such as total dissolved nitrogen (TDN), total dissolved phosphorus (TDP) and water temperature in the rainy season, but not in the dry season. Our results demonstrated the essential need to highlight the importance of anthropogenic activities on global and regional CO2 outgassing, and it is urgent to underscore the detailed biogeochemical processes in riverine pCO(2), as well as the couplings between pCO(2) and environmental parameters.