Study On The Emission Patterns And Influencing Factors Of Carbon Dioxide And Methane From Urban Freshwater Wetland

Greenhouse gas emissions are one of the important influences to accelerate climate change,and the contribution of greenhouse gas emissions from global freshwater ecosystems has attracted widespread attention.In this study,three aspects of outdoor observation,indoor incubation,and carbon emission estimation from water bodies were thoroughly investigated.In the first part,four types of water bodies,namely artificial lakes,rivers,lakes and reservoirs,and aquaculture ponds,were selected as typical water bodies in Jiangbei New District,Nanjing and the spatial and temporal differences in greenhouse gas emissions from different types of urban freshwater wetlands were investigated.The results of the study show that:1 greenhouse gas fluxes have strong seasonal characteristics,showing a trend of"high in summer and low in winter".2 farming ponds and artificial lakes are the hotspots of greenhouse gas emissions,while rivers and reservoirs have relatively small greenhouse gas fluxes.3temperature,wind speed,dissolved oxygen,and dissolved organic carbon have important effects on greenhouse gas emissions.However,the relationship between eutrophication and greenhouse gas emission is not consistent in all types of water bodies,and further research is needed.In the second part,based on the results of field observation experiments,the Yangtze River floodplain soil in Pukou Riverside Wetland Park was selected as the experimental object,and the differences in greenhouse gas emission patterns under different sediment substrates,different temperature backgrounds,and different flooding conditions were systematically simulated and explored through indoor microcosm incubation experiments.UV-Visible spectroscopy and fluorescence spectroscopy were used to explore the key driving mechanisms of the biogeochemical processes of dissolved organic matter in the greenhouse gas emission process.The results showed that:1 greenhouse gas emissions were significantly correlated with the inundation state and soil water content.The emission capacity of CH₄ was highest in the flooded state,which was 6.85-199.48 times higher than that of CH₄ in the dry state,and the emission capacity of CO₂ was also highest in the flooded state,which was 86.76 times higher than that of the dry state.2 Temperature was closely correlated with GHG emissions,and the carbon emission rate was up to 22.75 times higher at 30°C compared with 20°C.3 In the wetland soil is more wet,wetland soil microorganisms can be good access to organic matter,organic matter availability is higher,conducive to greenhouse gas emissions.4 River wetland carbon storage is low,but shows the characteristics of a mixture of endogenous and exogenous sources,the freshness index is higher conducive to greenhouse gas emissions.Finally,the greenhouse gas emissions of urban water bodies in Nanjing were comprehensively estimated using outdoor greenhouse gas observation flux data,microcosm simulation incubation data under indoor control conditions,and combined with the area of water bodies extracted from Landsat 8 satellite image data in the abundant/deepwater season.The results show that:1 the carbon emissions of Nanjing urban water bodies are underestimated after considering inundation changes compared with those without considering inundation changes,underestimating about 1%CO₂-equivalent emissions.2 the carbon emission potential of urban water bodies in the context of warming is not negligible.According to the scenarios of 1.5°C and 2°C warmings,the GHG emissions of Nanjing urban water bodies can increase by 22.2%-101.4%per year.3 compared to two typical cities with different urbanization rates,Berlin and Mexico City,the total GHG emissions of Nanjing urban water bodies are relatively low.However,it can still be optimized in terms of water body area planning,surrounding land use,etc.