Study On The Change Of Soil Methane Flux In Freshwater Herbaceous Wetland With Different Anthropogenic Disturbance Intensities

Global warming caused by the ecological environment changes to the survival of life poses a serious threat to the survival of life,the greenhouse effect is the main cause of global warming,since the industrial revolution since the continuous increase in the concentration of three greenhouse gases led to the continuous enhancement of the greenhouse effect,so reduce the concentration of greenhouse gases,weaken the greenhouse effect,Curbing the continuous rise in temperature has become an important issue facing all mankind by slowing down the earth’s warming and thus improving the environment in the context of climate change.CH₄is the world’s second largest carbon-based greenhouse gas,wetlands are a major natural source of methane emissions,control CH₄emissions can reduce the rate of global temperature rise by 25%,so accurate assessment of wetland soil methane output into the atmosphere,clear mechanism of action is an important premise for the implementation of emission reduction policies.According to the frequency of anthropogenic activities in the estuary area of Jingxin Wetland in the lower reaches of the Tumen River,three herbaceous wetlands with different anthropogenic interference intensities were selected,and the daily changes of soil CH4 fluxes of three herbaceous wetlands with anthropogenic disturbance degrees were observed in 2021 using a fully automatic portable respiratory system（PS-3000）,and the physical and chemical property indexes were determined and the plant biomass was measured after processing soil and plant samples were collected at the end of the growing season.The data collected above were used to study the temporal variation characteristics of soil methane emission fluxes in herbaceous wetlands under different human activity intensities and to analyze and explain the changes in methane fluxes in combination with changes in environmental factors.The findings are as follows:（1）Methane flux has spatiotemporal heterogeneity.At the seasonal scale,the soil-atmosphere methane gas exchange rates of three herbaceous wetlands of the lower reaches of the Tumen River showed"inverted U-shaped"seasonal fluctuations,which were manifested by the highest methane flux in the full growth period of vegetation in September,followed by the lowest freezing period of vegetation growth in June,and the lowest freezing period of complete withering vegetation in November（P<0.05）.（2）Effects of seasonal changes of soil hydrothermal factors on soil methane fluxes.The regression analysis results showed that the contribution of soil temperature and water content to soil methane flux in wetlands was 53.7%and 21.2%,respectively,and all showed significant positive correlations.Temperature inhibits/promotes the production process of methane by changing the activity of wetland anaerobic methane-producing bacteria,soil moisture content will change soil permeability to affect the oxidation and transmission process of methane,and the seasonal fluctuation of wetland soil hydrothermal factors（temperature,water content）with temperature and rainfall can explain the seasonal changes of methane flux.When the production efficiency of methane is much higher than the consumption rate of methane oxidation,it is manifested as a strong methane emission flux,when the methane production rate is similar to the oxidation rate of methane,it is characterized by weak emission characteristics,and when the production rate of methane is less than the oxidation rate of methane,it is shown as an absorption state.（3）Effect of human activity intensity on methane flux in herbal wetlands.Comparing the soil physicochemical properties of the three herbaceous wetlands with the degree of human interference,it was found that the soil organic carbon and microbial biomass carbon of the severe anthropogenic disturbance wetland were significantly smaller than those of the mild and moderate anthropogenic disturbance wetland（P<0.05）,while the content of the soil total nitrogen,ammonium nitrogen and nitrate nitrogen was significantly higher than that of the mild and moderate anthropogenic disturbance wetland（P<0.05）,and the soil texture of the severe anthropogenic disturbance wetland was more compact,and the water content was significantly lower than that of the mild and moderate disturbance wetland The absence of carbon nutrients in the soil limits the production of methane,while ammonium nitrogen has an inhibitory effect on the production of methane,nitrate nitrogen participates in the oxidation process of methane,and the shallow water accumulation on the wetland soil has a buffer effect on the change of air temperature and can change the permeability of the soil.In summary,due to the heavy anthropogenic interference of the wetland’s carbon loss,increased nitrogen pollution and soil texture changes,the soil methane production capacity became weaker,the oxidation capacity was enhanced,and the soil response to changes in temperature and precipitation was more sensitive,so it finally manifested as a lower methane exchange rate and the daytime performance of the methane absorption sink nighttime emission source when the soil entered a short day-night freeze-thaw alternation period in November.