Methane Cycling Process And Functional Microorganism In Lakeside Wetlands Of Dianchi Lake In Different Non-point Source Pollution Areas

Methane is an important greenhouse gas that contributes significantly to global warming.The lakeside zone is an important source of methane emission.Studying the CH₄ cycle in the lakeside has important theoretical significance for understanding global warming.According to different land use types in the Dianchi basin,this study selected the different non-point source pollution area of Dianchi lake:the agricultural non-point source pollution area like Bai Yu river(BY),the agricultural non-point source pollution area like Ci Xiang river(CX),the urban nonpoint source pollution area like Da Qing river(DQ),the urban and agricultural non-point source pollution crisscross area like Lao Yu river(LY),the Xi Hua wetland(XH).By measuring the CH₄ production and oxidation rates of sediments,the abundance and community structure of functional microorganisms,and combined with the chemical characteristics of sediments,overlying water and plants.The study discussed the differences of CH₄ production and oxidation rate and its influencing factors in the Dianchi Lake littoral zone under different pollution types.And,to provide theoretical guidance for the effective emission reduction of greenhouse gases in Dianchi Lake.The main conclusions are as follows:(1)The chemical characteristics of different non-point source pollution areas in the Dianchi Lake littoral zone were significantly different(p<0.05),and the chemical characteristics of different non-point source pollution areas were higher than that of the control Xihua wetland area.(2)There were significant differences in methane production rate and methanogen mcrA gene abundance among different non-point source pollution areas in the Dianchi Lake lakeside(p<0.05),the methane production rate in all non-point source pollution areas was significantly higher than that in the Xi Hua wetland(p<0.05).The highest and lowest CH₄ production rates were found in Bai Yu River(17.648 ?g/(g·d))and Xi Hua wetland(0.262 ?g/(g·d)),respectively.The highest and lowest abundances of mcrA gene are the region of the agricultural non-point source pollution Bai Yu River(2.671E+10 copies/g)and the urban non-point source pollution Da Qing River(1.265E+09 copies/g),respectively.Methanogens in different non-point source pollution areas at order level were composed of Bathyarchaeia,Methanobacteriales,Methanocellales,Methanofastidiosales,Methanomassiliicoccales,Methanomethyliales,Methanomicrobiales and Methanosarcinales.Bathyarchaeia was the dominant species of methanogen in Ci Xiang River,Xi Hua Wetland and Lao Yu River,while Methanosarcinales was the dominant species in Bai Yu River and Da Qing River.Methane production rate was significantly positively correlated with mcrA gene abundance,soil total P and ammonium N,plant total P,microbial biomass C,Ammonium nitrogen and COD in overlying water(p<0.05),and significantly negatively correlated with microbial biomass phosphorus(p<0.05).The abundance of mcrA gene in methanogens was significantly positively correlated with microbial biomass carbon,nitrate nitrogen,ammonium nitrogen,total nitrogen and total phosphorus in overlying water(p<0.05).(3)There was no significant difference in the aerobic oxidation rate of methane among different non-point source pollution areas in the Dianchi Lake littoral zone,and the abundance of pmoA gene in aerobic methane-oxidizing bacteria was significantly different(p>0.05).The pmoA gene of aerobic methane-oxidating bacteria in the Xi Hua wetland area is the most significant(5.450E+07 copies/g).The pmoA gene of aerobic methane-oxidizing bacteria from the different non-point source pollution areas was composed of Beijerinckiaceae,Methylacidiphilaceae,Methylococcaceae,Methyloligellaceae,Methylomonaceae,Methylophilaceae at the family level.The dominant species of aerobic methane-oxidizing bacteria in Bai Yu River and Xi Hua Wetland is Beijerinckiaceae,the dominant species of aerobic methane-oxidizing bacteria in Da Qing River and Lao Yu River is Methyloligellaceae,and the dominant species of aerobic methane-oxidizing bacteria in Ci Xiang River is Methylomonaceae.There was no significant correlation between the aerobic oxidation rate of methane and the pmoA gene of aerobic methane oxidizing bacteria,but it was significantly positively correlated with soil total carbon,chlorophyll in overlying water,and microbial biomass phosphorus(p<0.05).(4)The anaerobic methane oxidation rate and the abundance of ANME archaea and NC10 bacteria were significantly different among different non-point source pollution areas in the Dianchi Lake lakeside(p<0.05).Anaerobic methane oxidation rates were significantly highest in the agricultural non-point source pollution area like Ci Xiang River(27.294 ?g/(g·d))and lowest in the urban and agricultural non-point source pollution intersecting area like Lao Yu River(7.771 ?g/(g·d)),respectively.The abundance of ANME archaea is significantly highest in agricultural non-point source pollution area like Ci Xiang river(8.901E+05 copies/g)and lowest in the urban non-point source pollution area like Da Qing river(9.925E+04 copies/g),respectively.The abundance of NC10 bacteria is significantly highest in the Xi Hua wetland(6.852E+09 copies/g)and lowest in the agricultural non-point source pollution area like Bai Yu River(9.545E+05 copies/g),respectively.At order level,the ANME archaea in different nonpoint source pollution areas are composed of Methanomicrobiales and Methanosarcinales.The dominant species of ANME archaea in Xi Hua Wetland and Ci Xiang River are Methanomicrobiales,and the dominant species of ANME archaea in Da Qing River,Bai Yu River and Lao Yu River are Methanosarcinales.NC10 bacteria in different non-point source pollution areas are composed of Methylomirabilaceae and Rokubacteriales at the family level.The dominant species of NC10 bacteria in Bai Yu River,Xi Hua Wetland,Ci Xiang River and Da Qing River area is Rokubacteriales,and the dominant species of NC10 bacteria in Lao Yu area is Methyl omirabilaceae.There was a significant positive correlation between the anaerobic methane oxidation rate and the abundance of ANME archaea(p<0.05)and had no significant correlation with the abundance of NC10 bacteria.Anaerobic methane oxidation rate was significantly positively correlated with soil ammonium nitrogen and total nitrogen,and total phosphorus in overlying water(p<0.05),had a significant negative correlation with plant total phosphorus(p<0.05).Through the above studies,the characteristics of CH₄ cycle process and its driving factors in different non-point source pollution areas of the lakeside zone have been deeply understood,providing theoretical support for revealing the correlation between non-point source pollution and methane cycle process and controlling CH₄ emission in eutrophic lakes.