The Relationship Between Sediment And CH₄,CO₂ Production And Sink Under Different Concentrations Of Carbon And Nitrogen Input In The Main Section Of The Yangtze River In Chongqing

The natural carbon cycle process is persecuted due to frequent human activities,causing a series of current environmental problems.The reservoir ecosystem is an important part of the natural carbon cycle.In order to further understand the natural carbon cycle in the reservoir ecosystem,this study selected The main urban section of the Yangtze River in Chongqing is the main research object,to study the basic water quality indicators of the water body and the content of various forms of carbon in the water body and sediment sediments in the basin and typical tributaries（Jialing River）.Changes in distribution,key ways of CH₄ production and main sources of CO₂in water;indoor Carbon,Nitrogen concentration variation parameter simulation experiments using sediments,and analysis of different concentrations of Carbon and Nitrogen sources combined with changes in water quality indicators and carbon stable isotopes during the experiment Inputting the relationship between the production and sinking of sediment,CH₄ and CO₂in the background,the following conclusions are obtained:（1）The variation range of CH₄ concentration in the water body in the study area and time period is 0.099μmol/L to 0.144μmol/L,the CH₄ stable carbon isotope in the water body ranges from-43.25‰to-50.14‰;the variation range of the CO₂concentration in the water body is 23.051μmol/L～30.143μmol/L,the stable carbon isotope of CO₂fluctuates greatly in the water body,and the fluctuation range is-11.07‰～-14.97‰;the downstream water body is obviously affected by the upstream water body transfer,and the Tangjiatuo and Guojiatuo points in the middle and lower reaches of the main stream are affected by external sources.The influence of C and N input is more obvious.The concentrations of CH₄ and CO₂and their carbon isotopes are generally higher than those of the upstream point,and the methane production intensity is stronger.（2）The key pathways of CH₄ production are mainly acetic acid fermentation,the proportion of which fluctuates from 84%to 97%along the way,and the average is90.6%.The proportion of acetic acid fermentation at the tributary point is（97%）was significantly higher than that of the mainstream point;the source analysis of CO₂in water mainly considered three situations:carbonate weathering,substrate organic matter decomposition,and terrigenous input.（3）The concentration of CO₂ in the water body has a significant positive correlation with dissolved oxygen DO,dissolved inorganic carbon DIC,and nitrous nitrogen NO₂^--N;CH₄ carbon isotopeδ¹³C-CH₄ has a significant positive correlation with dissolved oxygen DO;while CO₂carbon The isotopeδ¹³C-CO2 was significantly negatively correlated with dissolved oxygen DO.（4）Exogenous Carbon（C）input will promote the production of CH₄ in the sediment,and reduce the oxidation rate of methane,so that the concentration of CH₄ increases;the higher the concentration of C source input,the higher the production rate of CH₄ ,and the methanogens in the 8th The hourly activity was the highest,and the yield reached the peak value;C₁（10 mg/L）concentration of carbon source input was the most suitable for bacterial growth,and methanogens had the highest methane production rate.The input of exogenous C will make the respiration of microorganisms in the water body more obvious,and the decomposition of organic matter will produce more CO₂;the higher the concentration of C source input will make the final concentration of CO₂in the water body higher,the C source input of C₁（10 mg/L）concentration will affect CO₂.The impact of the output and sink is more obvious;the higher concentration of C source input will make the final overall CH₄ and CO₂concentration in the water body higher.（5）Exogenous nitrogen（N）input significantly improved the activity of functional bacteria,so the concentration of CH₄ would increase significantly,and the C/N value and inorganic nutrient environment in the water body and sediment were changed,resulting in changes in the number of biological populations in the sediment;low concentrations The N source input showed a more obvious effect on the CH₄ production and sink 6 hours before the reaction;the N1（1 mg/L）concentration nitrogen source input was more suitable for functional bacteria to play an advantage in the core stage of the reaction;the high concentration N source input made the water CO₂The production and consumption mechanism of slough becomes more complex,and the CO₂concentration in the water body fluctuates continuously,and the impact on the reproduction,respiration,functional bacterial community and quantity of sediment microorganisms,and CH₄ and CO₂sinks lasts for a longer time.