Research Of Greenhouse Gases Fluxes Between Water-Air Interface In Main Rivers Of Shanghai And The Influencing Factors

The increasing concentration of greenhouse gases in the atmosphere,which leads to global climate warming,has attracted much attention.The increased carbon and nitrogen loading in river ecosystem has become an important source of greenhouse gases in the atmosphere due to human activities.Therefore,the Shanghai was selected as a typical study area to analyze the concentration of CO₂,CH₄ and N₂O in river water and calculate the CO₂,CH₄ and N₂O fluxes across water-air interface,and then analyze the associated controlling factors.On the basis of above results,we estimated greenhouse gas warming potential（GWP）and emissions potential of Shanghai rivers,providing some references for greenhouse gas emissions calculations of river ecological system and global greenhouse gases contribution.The main results of this study were as following:（1）The dissolved concentrations of CO₂,CH₄ and N₂O in Shanghai river water ranged from 116.28±7.94 to 325.91±19.71 μmol L-1、0.65±0.17 to 10.94±2.1μmol·L-1 and 322.87±40.61 to 918.78±101.55nmol·L-1 in winter,respectively.In summer,the dissolved concentrations of CO₂,CH₄ and N₂O in Shanghai river water ranged from 13.66±1.61 to 196.75±4.22μmol·L-1、0.06±0.00 to 17.50±0.87 μmol·L-1 and 97.19±8.22 to 1476.53±109.15 nmol·L-1,respectively.The concentration of CO₂ in river water were significantly higher in winter than in summer.However,the concentrations of CH₄ and N₂O had no significant seasonal variations.The concentrations of CO₂ and CH₄ in river water were greater in urban area than in the suburbs.（2）The concentrations of greenhouse gases in Shanghai river water were effected by air humidity,temperature,NO3-,NH₄+,Eh,pH and DO of water.The air humidity were significantly negative correlated with N₂O concentration in winter,and CO₂ concentration in summer.The water temperature was significantly negative correlated with N₂O concentration in summer.Water NO3-concentration was significantly and positively correlated with CH₄ concentration in winter,the concentration of NH₄+ in water body,was positive correlated with CO₂ concentration in winter and significantly positive correlated with CO₂ and CH₄ concentrations in summer.Eh was significantly and negatively correlated with CO₂ concentration in winter.The pH had significantly influenced on CO₂ concentration.DO was negatively correlated with CO₂ concentration only in winter.（3）The average fluxes of CO₂、CH₄ and N₂O across water-air interface in Shanghai river water ranged from 21.24±0.24 to 144.73±17.83 mmol·m-2·h-1,1.241±0.33 to 41.94±14.06μmol·m-2·h-1 and 6.54±1.42 to 41.93±1.30 μmol·m2·h-1 in winter.The average fluxes of CO₂,CH₄ and N₂O across water-air interface in summer ranged from 2.06±0.93 to 134.61±1.63 mmol·m-2·h-1、0.30±0.01 to 111.23±5.56 μrmol·m-2·h-1 and 7.42±0.63 to 77.28±5.71μmol·m-2·h-1.The river is the source of greenhouse gases in the atmosphere of Shanghai.In terms of temporal variation,CO₂ flux across water-air interface were higher in winter than in summer,no seasonal variation of CH₄ flux was observed and N₂O flux in summer was higher in summer than in winter.Spatial distribution characteristicsis shown as:（1）in winter,CO₂ fluxes across water-air interface was lower in Baoshan,central urban area and the north of Pudong new area,while high in Songjiang and Minhang district.In summer,CO₂ fluxes across water-air interface were higher in central urban area and Baoshan,while were low in other region.（2）CH₄ fluxes across water-air interface was the highest in central urban area and Baoshan in summer,while was low throughout other in both winter and summer.（3）In winter,N₂O fluxes across water-air interface was higher in Songjiang,Minhang,Jinshan and Fengxian and Jinshan district was higher in summer.（4）CO₂,CH₄ and N₂O emission fluxes of Shanghai riveres across water-air interface were effected by wind speed,air humidity,air temperature,water temperature,the concentration of NO3" and NH₄+,Eh,and pH.The main factor differed in seasons.In terms of meteorological factors,wind speed was significantly and positively correlated with CO₂,CH₄ and N₂O emission fluxes across river water-air interface in winter and were significantly and positive correlated with CH₄ and.N₂o fluxes across.water-air.interface in summen Air.relative humidity in summer was very significantly negative correlated with CO₂ flux across water-air interface.The temperature was significantly correlated with CO₂ and N₂O fluxes across water-air interface in winter.Water temperature was very significantly negative correlated with CO₂ flux across water-air interface in winter.NO3-concentration in water body and Eh were significantly correlated with CO₂ flux across water-air interface in winter.NH₄+concentration in water body and pH were significantly correlated with CO₂ flux across water-air interface in summer.The concentration of NH₄’ in water body was significantly positive correlated with CH₄ flux across water-air interface.（5）No difference of CO₂,CH₄ and N₂O fluxes across water-air interface was in river orders.Water quality pollution had significant impacts on CO₂,CH₄ and N₂O fluxes across water-air interface.The greenhouse gases fluxes in V order rivers across water-air interface were higher than III order river,indicating that river pollution was likely to contribute greenhouse gases emission across water-air interface.（6）The greenhouse gases warming potential of Shanghai river was 18738.92 g CO₂·m-2·2-1 at the scale of 100 years,and CO₂ contributed mostly.The N₂O emission factor in Shanghai rivers is 0.0373.CO₂ and CH₄ fluxes across water-air interface showed rivers>reservoirs>lakes,N₂O flux ranked rivers>lakes.Total carbon fluxes across water-air interface ranked rivers>reservoirs>lakes,and total nitrogen flux ranked rivers>lakes.The output of three carbon in water was the main form of CO₂.