Elevated nitrogen loadings facilitate carbon dioxide emissions from urban inland waters.

Carbon dioxide (CO 2) production and emissions from inland waters play considerable roles in global atmospheric CO 2 sources, while there are still uncertainties regarding notable nutrient inputs and anthropogenic activities. Urban inland waters, with frequently anthropogenic modifications and severely nitrogen loadings, were hotspots for CO 2 emissions. Here, we investigated the spatiotemporal patterns of partial pressure of CO 2 (p CO 2) and CO 2 fluxes (FCO 2) in typical urban inland waters in Tianjin, China. Our observation indicated that p CO 2 values were oversaturated in highly polluted waters, particularly in sewage rivers and urban rivers, exhibiting approximately 9 times higher than the atmosphere equilibrium concentration during sampling campaigns. Obviously, the spatiotemporal distributions of p CO 2 and FCO 2 emphasized that the water environmental conditions and anthropogenic activities jointly adjusted primary productivity and biological respiration of inland waters. Meanwhile, statistically positive correlations between p CO 2 /FCO 2 and NH 4 +-N/NO 3 −-N (p < 0.05) suggested that nitrogen biogeochemical processes, especially the nitrification, played a dominant role in CO 2 emissions attributing to the water acidification that stimulated CO 2 production and emissions. Except for slight CO 2 sinks in waters with low organic contents, the total CO 2 emissions from the urban surface waters of Tianjin were remarkable (286.8 Gg yr−1). The results emphasized that the reductions of nitrogen loadings, sewage draining waters, and agricultural pollution could alleviate CO 2 emissions from urban inland waters. [Display omitted] • CO 2 emissions from urban inland water contributed largely to atmospheric CO 2. • Land use affected the spatiotemporal variations of CO 2 emissions. • Nitrogen loading increases stimulated CO 2 production and emissions. • Acidification in the nitrification processes enhanced the CO 2 production and degassing. • Improving water quality could cut down CO 2 emissions from urban inland waters. [ABSTRACT FROM AUTHOR]