Natural and anthropogenic N2O emissions. (IMAGE)
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Anthropogenic sources constitute the primary component of N2O emissions in global rivers and are mainly manifested as two patterns: baseline emissions and localized hotspots. The k values of the EF lines for natural, agricultural, and urban rivers were determined at 0.02, 0.09, and 0.05, respectively, indicating increasing nutrient levels and basic N2O emissions in the different types of rivers. The corresponding median ΔN2O concentrations were 0.02, 23.9 and 21.7 nM, respectively. The median NH4+, NO3- and DOC concentrations for the basic emissions (blue) and localized hotspots (red) are shown for the different rivers. Additionally, the median ΔN2O concentration at localized hotspots reached 204.0 nM (11%) and 231.4 nM (14%) in agricultural and urban rivers, respectively. The priority control of organic and NH4+ pollution could eliminate hotspots and reduce the emissions of agricultural and urban rivers by 51.6% and 63.7%, respectively. However, further restoration of baseline emissions on nitrate removal is a long-term challenge.
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