Concentration And Flux Of N₂O In Different Types Of Pollution Rivers In Chaohu Basin

With the increasing trend of global warming, greenhouse gas emissions have causedpeople’s attention. N2O is an important greenhouse gas, and is also one of the mainsubstances to destroy atmospheric ozone. Affected by human activities, river nitrogenload has increaseddramatically, and greatly contributed to the production and release ofN2O. A large number of studies have shown that the river has become a major sourceof atmosphericN2O.Three different kinds of pollution of rivers in Chaohu lake basin (urban wastewaterpollution rivers: Nanfei river、Ershiburiver; Village and township wastewater pollutionrivers: Dianburiver, Shiwuli river; agricultural non-point source pollution rivers: Pairiver, fengle river, Hangbu river)are selected for the study, and in January2013toDecember2013monthlyare taken regular sampling and observation. This conducts theresearch of the main pollution factor of river water quality and relationships betweentime variation of different types of river pollution concentrations of N2O, seasonalchanges, and the impact factors, with estimates of different types of river water-airinterface N2Orelease flux of time variation and seasonal variation.Taking acomparative analysis of different models to estimate differences in N2O release fluxes,different ecosystem N2O fluxes are summarized. The study uses IPCC recommendedmethod and the revised method tocalculate N2O emissioncoefficients and differenttypes of river pollution N2O emission coefficient measured value and IPCCrecommended values were compared and analyzed. The main conclusions are asfollows:（1） To seven rivers, pollution factors were measured. Ammonia, nitrate, totalphosphorus, CODMn, BOD5,dissolved oxygen, and pH changes in the range of valueswere0.06~32.13mg/L,0~17.90mg/L,0.035~3.436mg/L,3.3~22.1mg/L,0.8~38.5mg/L,0.20~14.72mg/L,6.60~8.56; mean values respectively were（7.78±8.40）mg/L,(2.27±3.24) mg/L,(0.825±0.845) mg/L,(9.39±4.82) mg/L,(8.1±7.6) g/L,(3.83±2.93) mg/L,7.59±0.43. Among them, the most pollutedriver is Shiwuli, and except for Fengle River and Hangbu, the remaining five rivers，the primary pollutants，are ammonia.（2）Comparison of the dissolved concentration of N2O and saturation of threedifferent types of river pollution, the largest is urban wastewater polluting rivers, followed by the settlement wastewater polluting rivers, and agricultural sourcespolluting rivers are minimum value. Dissolved concentration of N2O and saturationmean respectively are (266.27±292.30)、(145.84±193.24)、(42.72±38.06) nmol/L,（2964±3267）、（1426±1717）、（497±473）%. The N2O saturation of seven riversinto the lake is greater than100%, which is a release source of atmospheric N2O. Thelowest is in summer and winter maximums.（3）Using the BO04method to calculate the river water-air interface N2O fluxes,three kinds of polluted rivers N2O emission mean respectively are (741.01±826.46)、(405.38±564.61)、(101.54±112.62) μg N2O-N/(m2·h). Seasonal trends were as same asconcentration of dissolved N2O, and the lowest is in summer and winter maximums.（4）In municipal wastewater polluting rivers, concentrations of N2O dissolved andtemperature were negatively correlated; In villages and towns wastewater Rivers,there is a positive correlation between N2O dissolved concentration and nitrate with pHnegatively correlated;In agricultural sources polluting rivers, N2O dissolvedconcentration and ammonia,nitrate, permanganate index showed a positive correlation.N2O release fluxes of three types of pollution rivers and environmental factors hadsome correlativity which were similar with N2O concentrations.（5）With the use of five different models to estimate the flux of river water-airinterface N2O emissions, the results vary greatly. The highest flux was calculated bythe BO04model, which was24,3.1,3.9, and2.4times of LM86, W92a, W92b, andRC01model result.（6）By summarizing and comparing N2O release fluxes of the different ecosystems inthis year, the results of the comparison showed that: the amount of N2O released fromwater ecosystem and the farmland ecological system，including rivers，were higher.Forest and grassland ecosystems released N2O, which had relatively lower volumes.（7）Using IPCC methods to estimate N2O emission factor of the river, all three typesof river pollution N2O emission coefficients are respectively0.0070±0.0109,0.0046±0.0094,0.0020,0.0023. In addition to agricultural sources polluting rivers, IPCCmeasured values of releasing factor and IPCC recommended value was closer to0.0025, and the remaining two types of pollution rivers measured values of emissioncoefficients were significantly higher than the IPCC Rivers suggested values.