Research On The Characteristics And Influencing Factors Of Greenhouse Gas Emissions In Typical Urban Polluted Rivers

With the acceleration of urbanization and the increasing frequency of human activities,global warming has become an inevitable environmental problem for human beings.Urban river as an important component of urban ecological system,has long been high impact load pollution from human activities,seriously affected the urban river water balance of carbon and nitrogen and phosphorus,lead to greenhouse gas in the urban river(N₂O,CH₄and CO₂)content in saturated state,all the year round city river has become a source of greenhouse gas emissions.Therefore,it is particularly important to explore the production and emission of greenhouse gases in different nutrient load water bodies of urban river.Taking Zhibang of Liangxi River and Wu Dacheng branch as an example,this study studied the characteristics and influencing factors of greenhouse gas emissions in water bodies with different nutrient loads through field investigation and laboratory simulation experiments,and reached the following conclusions:(1)The seasonal variation of greenhouse gas emission(N₂O,CH₄ and CO₂)in typical polluted urban river channels is obvious.The emission fluxes of N₂O and CH4 were high in winter and spring,and low in summer and autumn,mainly influenced by p H.The highest value of N₂O emission fluxes was 270?g m^-2 h^-1 in January,and the lowest value was-15?g m^-2 h^-1 in September.The highest CH₄emission flux was 386 mg m^-2 h^-1,and the lowest was 0.09 mg m^-2 h^-1.The CO₂ flux was high in summer and autumn,and low in winter,mainly affected by p H,DO and ORP.The highest value of CO₂flux was 148 mg m^-2 h^-1 in June,and the lowest value was 5 mg m^-2 h^-1 in November.(2)The sediment nutrient load has a significant impact on GHG release by changing the characteristics of organic matter and nutrient release.The exchange fluxes of greenhouse gases(N₂O,CH₄ and CO₂)in river channels decreased gradually with the decrease of water pollution.The exchange fluxes of greenhouse gases(N₂O,CH₄ and CO₂)in the northern section with severe pollution loads are higher than those in the southern section with relatively light pollution loads.Among them,the average monthly N₂O exchange fluxes at the overweight and heavy pollution points in the northern section of the river course with heavy pollution load are 91 and 116?g m^-2 h^-1,respectively,which are about 1?2 times of those at the middle pollution point in the southern section with relatively light pollution load.However,the light pollution spot located at the junction of Liangxi River and the southernmost part of the river is N₂O sink in the atmosphere in most months.The monthly average CH₄ exchange flux at the overweight pollution point with the most serious pollution load in summer is 350 mg m^-2 h^-1,which is about 10,273 and 320times of that at the heavy pollution point,the moderate pollution point and the light pollution point.However,in autumn and winter,the monthly average CH₄ exchange flux at the overweight pollution point is about 5,29 and 40 times of that at the heavy pollution point,the moderate pollution point and the light pollution point,respectively.During the whole observation period,the monthly average CO₂ exchange fluxes from the heavy pollution point to the light pollution point were about 76,66,43 and 23 mg m^-2 h^-1,respectively.The increase of organic matter and nutrients caused by human activities greatly promoted the greenhouse gas emission in river water.(3)The sediment nutrient load has a significant effect on the release of organic matter,nutrient and greenhouse gases(N₂O,CH₄ and CO₂).The yield of greenhouse gases(N₂O,CH₄ and CO₂)in the water was positively correlated with the degree of nutrient load in the water,and the effect of nutrient load degree in the sediment on greenhouse gases(N₂O,CH₄ and CO₂)was greater than that of nutrient load degree in the water.Among them,the treatment group with the highest pollution load of water and sediment has the largest production of greenhouse gases(N₂O,CH₄ and CO₂),and the existence of water and sediment with high pollution load greatly promotes the production of N₂O,CH₄ and CO₂.