Spatio-temporal Distribution Patterns Of Dissolved Methane And The Influencing Factors In The Gutian Reservior Fujian Province, China

In order to reveal the spatial-temporal distribution of dissolved CH₄ in subtropical reservoirs,the study examined and analyzed of concentrations of dissolved CH₄ and its environmental factors in the water body of the Gutian reservoir,Fujian Province,and upper and lower reaches during the high flow,the low flow and the medium flow.The results show that:?i?The concentrations of dissolved CH₄ in Gutian Reservoir ranged from 0.05 to0.40?mol·L^-1,and listed as high flow>low flow>medium flow.During three periods,were higher during the high flow compared with dry and medium flow.During the high flow,the concentrations of dissolved CH₄ was higher in the north and lower in the east,while the concentrations were lower at the inlet and higher in the middle area during the dry season.During the medium flow,the concentrations of dissolved CH₄ were lowest in the north and east and highest in the south of the reservoir.The difference of the concentrations of dissolved CH₄ was significant between north and south.The concentrations of NO₃^–and pH were the main factors affecting the spatial differentiations of dissolved CH₄ concentrations during the high flow,the concentrations of NO₃^–and NH₄⁺were closely related to dissolved CH₄ concentrations in the low flow.Lastly,during the medium flow,the concentrations of dissolved CH₄ were mainly affected by the concentrations of Chla and NO₃^–.?ii?During the high flow,the concentrations of dissolved CH₄ in the reservoir were higher than those in the upstream and downstream,while the concentrations of NH₄⁺and NO₃^–are significantly lower than those in the upstream.During the low flow,the concentrations of dissolved CH₄ in the reservoir were comparable than those in the upstream and were slightly higher than those in the downstream.The concentration of DIC and NO₃^–in the reservoir area is significantly lower than that in the upstream and downstream rivers.During the medium flow,the concentrations of dissolved CH₄ were higher in the river compared with the reservoir.Across three periods,all the pH and the concentrations of Chla were higher in the reservoir than all the streams.?iii?According to the model LM86?CW03?MY95 and RC01,the CH₄ emission fluxes of reservoir were 0.41±0.29,1.09±0.79,1.33±0.99 and 5.54±3.74?mol·m^-2·h^-1.Different with the concentrations of dissolved CH₄,the CH₄ emission fluxes listed as follow:high flow>medium flow>low flow.During the high flow,the spatial distributions of CH₄ emission fluxes were similar with the concentrations of dissolved CH₄.During the other periods,the CH₄ emission fluxes were higher in the south and lower in the north and east of the reservoir.Combined,this result suggested that the reservoir is the source of CH₄ emission.The concentrations of dissolved CH₄ of the reservoir and the CH₄ emission fluxes changed across different periods and across the reservoir.The concentrations of NH₄⁺,NO₃^–and Chla and pH are the main environmental factors to determine the distributions of CH₄emission fluxes.In the future,the spatial-temporary changes of dissolved CH₄concentrations should be considered in the predicting CH₄ fluxes.