Emissions Of Methane And Carbon Dioxide At Cyperus Malaccensis Marsh With Freshwater And Brackish Water In The Minjiang River Estuary

Salinity is one of the most important influencing factors in the process of biogeochemistry at the estuarine tidal wetland ecosystem, which also plays an important role in generations and emissions of greenhouse gases in wetland. Based on this, this paper takes Cyperus malaccensis-dominated tidal wetland of Daoqingzhou (freshwater) and Shanyutan (brackish water) in Minjiang River estuary in the coastal region of Southeast China as a typical area to study. Methane and carbon dioxide fluxes with its influencing factors (air temperature, soil physicochemical properties and anions in porewater and tidewater) in the two sampling sites was measured in situ from November 2013 to October 2014 by using static chamber-gas chromatography technique. In addition, soil production rates of methane and carbon dioxide and physicochemical indicators in Daoqingzhou and Shanyutan was determined simultaneously in the four seasons (November 2013, February 2014, May and August represent Fall, Spring, Winter and Summer respectively) by collecting undisturbed soil column cultivated under the anaerobic conditions in laboratory. The results show that: ① The obvious monthly variations of methane and carbon dioxide fluxes were existed in Daoqingzhou and Shanyutan. The maximum and minimum of methane flux in Daoqingzhou appears in April and August respectively, while carbon dioxide flux appears in April and January respectively. In Shanyutan wetland, the maximum and minimum of methane flux appears in April and February respectively, and carbon dioxide flux appears in July and March respectively.② There were obvious seasonal variations of methane and carbon dioxide fluxes in the two sampling sites. The maximum and minimum of methane flux in Daoqingzhou appears in summer and spring respectively, and carbon dioxide flux appears in summer and winter respectively, In Shanyutan wetland, the maximum and minimum emission fluxes, both methane and carbon dioxide appears in summer and winter respectively.③ The emission fluxes of methane and carbon dioxide in the two sampling sites is mainly determined by a combination of the temperature (including soil temperature and air temperature)and soil electric conductivity, as well as the SO42-、Cl-and NO3--N in the porewater and tidewater, and the correlations between the two greenhouse gases and its environmental factors showed high consistency.④ Like the change law of methane and carbon dioxide emission fluxes, the production rates of the two greenhouse gases in soil at the 0-15cm depth range also exhibited an obvious seasonal variation. The maximum and minimum of methane production rates, both in Daoqingzhou and Shanyutan all appears in summer and winter respectively, and carbon dioxide production rates appears in July and March respectively.⑤ The main environmental factors which may influence the methane and carbon dioxide production rates over the four seasons are culture temperature, soil electric conductivity, soil TN and TP.⑥ The seasonal variations of emission fluxes and production rates of methane and carbon dioxide in the two sampling sites shared a comparatively unanimous tendency. Statistical analysis showed that the emission fluxes and production rates of methane in Daoqingzhou is significantly higher than that in Shanyutan, and there was no significant difference in emission fluxes and production rates of carbon dioxide between Daoqingzhou and Shanyutan.