Contribution Of Carbon Sequestration On CH₄and Co₂production In Coastal Wetland Of The Yangtze River Estuary

Global warming caused by greenhouse gases?GHGs?has attracted more attention in current.Wetland plants can fix CO₂ in the atmosphere by photosynthesis,and therefore have strong carbon storage and carbon sequestration capabilities and play an important role in global carbon cycle.Although the global wetland area accounts for a small proportion?5%⁸%?of the surface area of the earth's land,its contribution to greenhouse gas emissions can not be ignored.Wetlands account for70% of all natural CH₄ sources.In the estuarine coastal wetlands,strong anaerobic reduction environment was formed due to its high vegetation cover and long-term flooding.The decomposition of vegetation and litter residues produced a large amount of C.Some of them were converted into soil organic matter?SOM?,and the other part is released into the atmosphere as greenhouse gases.Plant litter and vegetation burial?fresh organic carbon input?contribute significantly to the generation of greenhouse gases in wetland sediments.This study select Dongtan wetland of the Yangtze River estuary as the research site.Phragmites australis,Spartina alterniflora,and Scirpus mariqueter plant together with their soil sediments were subjected to simulate experiments of plant litter decomposition to investigate the effects of vegetation addition on the production of CH₄ and CO₂ under temperature and salinity incubation.The contribution of carbon inputs and the contribution of freshly buried organic carbon inputs to the generation of CH₄ and CO₂ gases.The main conclusions were obtained from laboratory anaerobic incubation experiments:?1?CH₄ and CO₂ production under vegetation input were positively correlated with temperature.The higher the temperature,the greater amount of CH₄ and CO₂ production generated.The amount of CH₄ and CO₂ production with Phragmites australis and Scirpus mariquete input featured with the order of 5? < 20? < 35?during incubation period.The amount of CH₄ and CO₂ production with Spartinaalterniflora input featured with the order of 20? < 35? during incubation period.The maximum CH₄ productions with Phragmites australis input were 73.2,2749.3and 4435.9 ? mol and the maximum CO₂ productions with Phragmites australis input were 470.2,2154.8 and 2986.2 ? mol under 5?,20? and 35? incubation,respectively.The maximum CH₄ productions with Spartina alterniflora and Scirpus mariqueter input were 3485.4 and 7046.5 ? mol,3708.2 and 4377.7 ? mol and the maximum CO₂ productions with Spartina alterniflora and Scirpus mariqueter input were 2933.0 and 5989.2 ? mol,2795.1 and 3473.9 ? mol under 20? and 35?incubation,respectively.?2?Higher salinity inhibited the production of CH₄ and CO₂ under the addition of vegetation.However,the addition of vegetation under certain salinity?0‰²0‰?promoted the production of CH₄ and CO₂.The maximum productions of CH₄ during incubation period with the input of organic carbon from three vegetation?S.alterniflora,P.australis and S.mariqueter?were 1480.6,1560.4,1117.1 and 880.0 ?mol,2491.3,2669.2,2121.7 and 1746.4 ? mol,4057.6,3890.5,4010.7 and 3574.7 ?mol under the salinity of 0‰,10‰,20‰ and 30‰ incubation,respectively.The maximum productions of CO₂ were 1221.7,998.1,791.4 and 701.6 ? mol,2713.4,2680.4,2919.7 and 2105.5 ? mol,2973.5,3056.7,3318.4 and 3108.7 ? mol under the salinity of 0‰,10‰,20‰ and 30‰ incubation,respectively.?3?The addition of vegetation significantly increased the production of CH₄ and CO₂ under temperature and salinity incubation compared to the non-added control group.The remnant TOC content in the sediments with vegetation additions was higher than that in the non-added control group,indicating that the vegetation addition increased the input of fresh organic carbon and provided sufficient carbon sources for the generation of CH₄ and CO₂.The more the amount of vegetation added,the higher concentration of organic carbon content in sediment remained.?4?The maximum conversion rates of per unit mass of organic carbon input at temperature incubation were 16.1%,9.7%,18.5% for CH₄ and 11.0%,6.7%,12.2%for CO₂?at 35? incubation?with the addition of three vegetation?P.australis,S.alterniflora and S.mariqueter?,respectively.The maximum conversion rates of CH₄ and CO₂ per unit mass of organic carbon input at salinity incubation were 5.5%,5.7%,16.9% and 4.3%,4.3%,11.7% with the addition of three vegetation,respectively.?5?The maximum conversion rates of CH₄ and CO₂ per unit mass of organic carbon input at temperature incubation were 9.7%¹8.5% and 6.7%¹2.2%.The maximum conversion rates of CH₄ and CO₂ per unit mass of organic carbon input at salinity incubation were 5.5%¹6.9% and 4.3%¹1.7%.Considering the warming potential of CH₄ is relatively 28 times of CO₂,the conversion of burial organic carbon converted to CH₄ producing greenhouse effect which offset the carbon sequestration function and becomes a source of greenhouse gas emissions in coastal wetlands.