Spatiotemporal Variations Of Nitrous Oxide （N₂O） Concentrations And Flux In17Reservoirs And Their Input Rivers Of Guangdong Province

Environmental problems were caused by atmospheric N₂O concentration risingthrough global temperature increasing and ozone destruction. Clearing atmosphericN₂O emission sources, their N₂O distribution and release characteristics issignificance to control atmospheric warming. The reservoirs are widely distributed inlarger quantities, but the reservoir whether N₂O emission source remaining incontroversy.In order to decide whether the reservoirs and their input rivers can be consideredas the N₂O emissions source, and understanding the distribution characteristics ofN₂O of reservoirs and their input rivers, this study chose the six River Basin ofGuangdong Province （coastal western Guangdong, the Xijiang River, the North Riverbasin, the East River basin,17large and medium-sized reservoirs in the Pearl RiverDelta and eastern Guangdong coastal） as the research objectives, the N₂O distributionand release characteristics, source and sink and their influencing factors wereresearched. The major findings of this paper were as follows:The concentrations and water-atmosphere fluxes of dissolved N₂O in17reservoirs and rivers of Guangdong Province were investigated during the wet seasonand the dry season,2011. N₂O concentration in the surface waters were measured bypurge and trap-gas chromatography. The results demonstrated that reservoirs and theirinput rivers kept lower N₂O concentration in the wet season than the dry season, withsignificant seasonal variations （P<0.01）. Seeing from Spatial variation, changingtrends of dissolved N₂O concentrations was Pearl Delta area> Coastal area in westGuangdong> Coastal area in east Guangdong> Beijiang watershed> Dongjiangwatershed. In flooded season, N₂O concentration in the surface waters were lowerthan in the bottom waters（P<0.01）. At the same time, vertical distribution of reservoirN₂O dissolved concentrations were significantly different both in the dry season andin the wet season. In addition to Changhu and Songmushan Reservoirs, the N₂Odissolved concentrations of other reservoirs were all lower in the surface water than in the bottom water （P<0.01）, had layered phenomenon. The N₂O dissolvedconcentrations of the surface water and bottom water in reservoirs had no significantrelationships （P>0.01） in dry season. Deposit concentration compared with otherwaters, N₂O dissolved concentrations of reservoirs and their input rivers were in themedium level.The saturations of reservoirs and their input rivers were calculated through N₂Odissolved concentration. The results demonstrated that reservoirs and their input riverskept lower N₂O saturations in flooded season than dry season, with significantseasonal variations （P<0.01）. Seeing from Spatial variation, changing trends of N₂Osaturations was Pearl Delta area> Coastal area in west Guangdong> Coastal area ineast Guangdong> Beijiang watershed> Dongjiang watershed. In wet season, N₂Osaturations in the surface waters were lower than in the bottom waters （P<0.01）. Atthe same time, vertical distribution of reservoir N₂O saturations concentrations weresignificantly different both in the dry season and in the wet season. In addition to Hedi,Nanshui, Fengshuba, Tiegang and Tangxi Reservoir, the N₂O saturations of otherreservoirs were all lower in the surface water than in the bottom water （P<0.01）, hadlayered phenomenon. The N₂O saturations of the surface water and bottom water inreservoirs had no significant relationships （P>0.01） in dry season. Depositconcentration compared with other waters, N₂O saturations of reservoirs and theirinput rivers were over-saturationed.N₂O water-atmosphere fluxes were estimated by the Liss&Meriivat （1986）and Wanninkhof （1992） formula. The results demonstrated that reservoirs and theirinput rivers kept lower N₂O water-atmosphere fluxes in wet season than dry season,with significant seasonal variations （P<0.01）. Seeing from Spatial variation, changingtrends of N₂O water-atmosphere fluxes was Pearl Delta area> Dongjiang watershed>Coastal area in west Guangdong> Coastal area in east Guangdong> Beijiangwatershed. Based on the reservoir surface area and average annual N₂O flux, theannual N₂O emission from the studied area was about3.88×10-5Tg·a-1, account for0.0037%of the total N₂O emissions of China.Make analysis between N₂O concentration, saturations, water-atmosphere fluxes and water physical and chemical characteristics,The correlation analysis suggestingthat in the wet season, inorganic nitrogen, were key factors to affect the produce anddistribution of N₂O, which were also affected by factors such as temperature,dissolved oxygen, pH and chlorophyll in the dry season.