Study On The Spatial And Temporal Distribution Of Carbon Isotope In The Main City Section Of The Yangtze River In Chongqing

The carbon cycle in the reservoir ecosystem is essential for the transportation of terrestrial carbon pools to the ocean,that is,the atmospheric carbon pool.Understanding the dynamic characteristics of the carbon cycle in the reservoir ecosystem is of great significance to fully grasp the global carbon cycle.This study selects the Yangtze River in the main Chongqing section of the Yangtze River as the research object,and selects two time periods in summer,June and autumn,to determine the carbon content of various forms of water（particulate organic carbon POC,dissolved organic carbon DOC,and dissolved inorganic carbon DIC）.),research on relative abundance and main influencing factors,traceability research through carbon stable isotope technology,and use mass balance model to analyze the contribution of each source of carbon;analyze the production and sink of carbon source gases（CH₄,CO₂）The characteristics and sources of seasonal changes and the key production pathways of CH₄,and the following main conclusions are obtained:（1）Water body carbon is dominated by soluble inorganic carbon（DIC）.Summer DIC content varies from 94.28mg/L to 126.73mg/L,with an average value of 113.11mg/L;DOC content varies from 1.31 mg/L to 2.57 mg/L,with an average value of 1.74 mg/L;The variation range is 0.3 mg/L～1.03 mg/L,and the average value is 0.57 mg/L.The variation range of DIC content in autumn is 52.86mg/L～67.87mg/L,the average value is58.99 mg/L;the variation range of DOC content is 1.98 mg/L～4.7 mg/L,the average value is 2.68 mg/L;POC The content varies from 0.45 mg/L to 1 mg/L,with an average value of 0.59 mg/L.（2）Approximately 55%of the observation points in summer are mainly from soil organic matter,18%are from plankton,and 27%are from aquatic plants;in autumn,about18%of the observation points are from aquatic plants.,18%source is plankton,74%source is soil organic matter.The contribution of soil CO₂ to the source of DIC in summer is 42.98%,and the contribution of carbonate water is 57.02%;the contribution of soil CO₂ to the source of DIC in autumn is 51.29%,and the contribution of carbonate water to the source of DIC is 51.29%.It accounts for 48.71%.The sources of DOC are mainly heterogeneous soil organic matter degradation and domestic sewage.（3）The variation range of CH₄ concentration in summer is 0.04μmol/L～0.16μmol/L,with an average value of 0.08μmol/L;the variation range of CH₄ concentration in autumn is 0.11μmol/L～0.23μmol/L,with an average value of 0.13μmol/L.The fluctuation range ofδ¹³C-CH₄ in summer water is-59.27‰～-43.4‰,with an average of-58.61‰;the fluctuation range ofδ¹³C-CH₄ in autumn water is-49‰～-38.4‰,with an average of-45.82‰.（4）Both summer and autumn CH₄ production pathways have been dominated by the acetic acid fermentation process.The fluctuation range of the acetic acid fermentation pathway in summer is 58.66%～98.94%,with an average value of 71.89%;in autumn,the fluctuation range is 86.71%～97.32%,with an average value.It is 92.21%,and the proportion of CO₂ reduction pathways is much smaller than that in summer.（5）The fluctuation range of CO₂ concentration in summer is 50.7～65.84μmol/L,with an average value of 57.05μmol/L;the fluctuation range of CO₂ concentration in autumn is 33.77～46.15μmol/L,with an average value of 41.11μmol/L;the surface layer is all high At the bottom.The fluctuation range ofδ¹³C-CO₂ in summer is-15.0‰～-9.9‰,with an average value of-11.8‰;the fluctuation range ofδ¹³C-CO₂ in autumn is-17.4‰～-14.4‰,with an average value of-16.1‰.The CO₂ in surface waters mainly comes from the upward diffusion of CO₂ produced in the bottom layer.