Diurnal Variations of Concentration of Porewater Dissolved CH4 and CO2 in a Brackish Marsh Dominated by Cyperus malaccensis and Phragmites australis During Neap and Spring Tidal Days in the Minjiang River Estuary

: Understanding of diurnal variation of soil porewater dissolved CO2 and CH4 concentration plays an important role in revealing carbon cycling in estuarine wetlands.During neap and spring tidal days in April and September 2010,the diurnal variations of soil porewater dissolved CO2 and CH4 concentrations and main impacting factors in a brackish marsh ecosystem dominated by two species of Cyperus malaccensis(brevifolius) and Phragmites australis(common reed) were determined in the ShanYutan in the Min River estuary,southeast China.The results showed that:① the soil porewater dissolved CH4 concentration during the spring and neap tidal days in April and September ranged from 88.20 to 190.74,53.42 to 141.24,16.27 to 81.89 and 44.90 to 88.53 μmol·L-1,respectively.The mean of dissolved CH4 concentration was higher at nighttime than at daytime during the spring and neap tidal days in April,but the mean of dissolved CH4 concentration was higher at daytime than at nighttime during the spring and neap tidal tidal days in September.② the soil porewater dissolved CO2 concentration during the spring and neap tidal days in September ranged from 19.33 to 40.1 μmol·L-1 and 9.69 to 29.96 μmol·L-1,respectively,and the dissolved CO2 concentration during daytime was lower than that at night;③ the mean of dissolved CO2 concentration was lower during the inundation period than in the exposed soil surface period,but the mean of dissolved CH4 concentration was higher during the inundation period than in the exposed soil surface period.