Effects of land use on the concentration and emission of nitrous oxide in nitrogen-enriched rivers.

Nitrous oxide (NO) is a potent greenhouse gas that contributes to climate change and stratospheric ozone destruction. Nitrogen-enriched rivers are significant sources of atmospheric NO. This study conducted a one-year field campaign in seven N-enriched rivers draining urban, rural, and agricultural land to determine the link between the production, concentrations, and emissions of NO and land use. Estimated NO fluxes varied between 1.30 and 1164.38 μg NO-N m h with a mean value of 154.90 μg NO-N m h, indicating that rivers were the net sources of atmospheric NO. Concentrations of NO ranged between 0.23 and 29.21 μg NO-N L with an overall mean value of 3.81 μg NO-N L. Concentrations of ammonium and nitrate in urban and rural rivers were high in the cold season. The concentrations were also high in agricultural rivers in the wet season. NO concentrations and emissions in rural and urban rivers followed a similar pattern to ammonium and a similar pattern to nitrate in agricultural rivers. A strong link between the concentrations and emissions of NO and land use was observed. NO concentrations in and emissions from the rivers draining the urban and rural areas were significantly higher than the rivers draining the agricultural areas (P < 0.01). Stepwise regression analysis indicated that dissolved NO were primarily influenced by NH in agricultural rivers and by NO in rural rivers; while dissolved NO in urban rivers was primarily predicted by temperature and reflected the integrated impact of sewage input and river hydrology. Nitrate-N and NO-O isotope data and linear regression of NO and river water variables strongly indicated that dissolved NO was mainly derived from nitrification in agricultural rivers and denitrification in rural and urban rivers.