;Nitrification is an important intermediate process in nitrogen cycle that oxidizes ammonia to nitrite and/or nitrate and produces N2O as byproduct. Currently, nitrification has been recognized as the major source of N2O, which is regarded as one of the main greenhouse gases. Since 19th century, excessive use of chemical synthesized nitrogenous fertilizer has elevated the total amount of nitrogen in environments. The excess nitrogen remained in soil and leached into aquatic environments may be transformed to N2O through nitrification. In addition, the enhanced soil erosion can elevate the suspended particles in aquatic environments. In this dissertation we determined the rate of nitrification (NR) in turbid environments by the stable isotope tracer method to investigate the role of suspended particles on nitrification and N2O production. In the subtropical mesotrophic Feitsui Reservoir, high NR and N2O were recorded in the aphotic zone where rare ammonium and high particle sinking flux occurred. These fast-sinking particles in the aphotic zone was dominantly brought from the turbid interflows induced by heavy precipitation during cold season and typhoon periods. The light-sensitive nitrifying microorganisms may utilize the remineralized organics on those particles as substrate source for nitrification and also N2O production. In Chang Jiang River plume, simultaneous measurement of NR and community respiration rate (CR) revealed that the oxygen demand of nitrification was greater than that of community respiration. However, the amounts of reactive Fe/Mn oxide of suspended particles seemed enough to support oxidant demand of nitrification. Meanwhile, the reactive Fe/Mn was significantly positive correlated to NR, indicating that the reactive Fe/Mn may serve as an alternative electron acceptor in nitrification. Moreover, the production rate of N2O from ammonium in the turbid river mouth is significantly higher than that in other relatively clear regions. The results suggested that the elevated suspended particles in aquatic environment due to soil erosion may enhance nitrification and also N2O production. Consequently, the increasing N2O may potentially accelerate the global warming.
