冬季平原河网水体溶存甲烷和氧化亚氮浓度特征及排放通量

Methane and nitrous oxide dissolved concentration and emission flux of plain river network in winter

以长江三角洲上海地区和海河流域天津地区水网为研究对象,对冬季河网表层水体溶存甲烷(CH4)和氧化亚氮(N2O)浓度、饱和度及水-气界面排放通量进行了研究.结果表明,冬季我国平原河网水体溶存CH4和N2O的浓度值都很高,呈高度过饱和状态:CH4浓度均值为0.86mol/L(饱和度:758%),范围在(0.043±0.001)～(25.3±9.32)μmol/L之间;N2O浓度均值为86.8nmol/L(饱和度:488%),范围在(9.71±0.41)～(691±35.2)nmol/L之间变化.天津排污河水体CH4和N2O浓度显著高于其他河流(均值分别为38.4mol/L和88.9nmol/L).水体溶存CH4和N2O浓度、饱和度存在很大的地区差异,上海河网的CH4和N2O浓度和饱和度均值高于天津河网.河网水体水-气界面CH4和N2O排放通量变化范围很广,CH4通量在(1.35±0.22)～(665±246)mol/m2h之间,平均值为24.1mol/m2h,N2O通量在(0.19±0.02)～(22.6±5.05)mol/m2h之间,平均值为2.28mol/m2h.相关分析发现,河网水体溶存CH4浓度与DO显著负相关,与NH4+显著正相关;N2O浓度则与NH4+和NO3+NO2显著正相关.河网水-气界面CH4和N2O排放通量均呈现出市区高郊区和农村低的空间分布规律,污染严重的河流已显然成为大气CH4和N2O的潜在排放源.

Methane （CH4 ） and nitrous oxide （N2O） concentration,saturation and fluxes in river network of Shanghai city （Yangtze Delta） and Tianjin city （Haihe watershed） were investigated in winter.Results showed that CH4 and N2O concentration were high in river network and supersaturated.The average of CH 4 concentration was 0.86 mol/L （saturation：758%）,and ranged from 0.043±0.001 to 25.3±9.32 mol/L.The average of N2O concentration was 86.8 nmol/L （saturation：488%）,and ranged from 9.71±0.41 to 691±35.2 nmol/L.CH4 and N2O concentration in two sewage draining rivers of Tianjin city were clearly higher than other rivers （Average CH4 and N2O concentration were 38.4 mol/L and 88.9 nmol/L,respectively）.There is significant spatial variation of CH4 and N2O concentration and saturation,data of concentration and saturation in Shanghai river network was significant higher than in Tianjin city.Air-water interface fluxes of CH4 and N2O widely varied from 1.35±0.22 to 665±246 mol/m2 h （Average was 24.1 mol/m2 h）,and from 0.19±0.02 to 22.6±5.05 mol/m2 h （Average was 2.28 mol/m2 h）,respectively.CH4 concentration had significant negative correlation with dissolved oxygen （DO）,but positive with ammonium （NH4＋ ）,and N2O concentration had significant positive correlation with NH4＋ and nitrate and nitrite （NO3-＋NO2-）.Air-water interface fluxes of CH4 and N2O in urban area were evidently higher than in suburban and rural area,implicating that seriously polluted river is a potential source of atmospheric CH4 and N2O.