Characteristics of Temperature Sensitivity of Methane Flux from the Shanyutan Tidal Wetlands in Min River Estuary

Methane(CH_ 4)is a kind of important greenhouse gases.Methane emission is recognized that biogenic sources account for more than 70% of the total global methane emission,and the single largest methane source is from natural wetlands.Coastal and estuary marsh ecosystems have high net primary productivity,and the CH_ 4 flux from them had being paid attentions to.Temperature sensitivity(Q_ 10 value)is a key parameter in carbon cycling process(including methane cycling).In 2007,the enclosed chamber technique was used and the measurements on methane flux from 4 kinds of wetlands were taken during 2 different tidal periods(before the flood and after the ebb)in the Shanyutan tidal wetlands in Min River Estuary.The climate in the wetlands is warm and wet,with mean annual temperature of 19.6 ℃ and annual precipitation of 1 350 mm.Based the data set of CH_ 4 fluxes from the wetlands,and the data of environmental factors were measured at the same time in 2007,the Q_ 10 values of CH_ 4 emission fluxes were calculated,and the effect of environmental factors on Q_ 10 values was analyzed.The relationships between CH_ 4 flux and air,soil temperature were fitted well using the exponential function model.Estimated air Q_ 10 values(Q_ a10)ranged from 2.89 to 7.78,and soil Q_ 10(Q_ s10)values from 3.22 to 11.10,the averaged Q_ a10 value and Q_ s10 value of 4 kinds of wetlands were 3.95 and 5.41.The Q_ s10 values of Phragmites australis marsh,Cyoerus malaccensis marsh,Scirpus triqueter marsh and mudflat were 3.22,5.23,4.79 and 11.0,and their Q_ a10 values were 2.89,3.96,3.84 and 7.78.The average Q_ a10 value of the 4 types of wetlands in the period before flooding and after ebbing were 3.53 and 4.39 respectively,and the averaged Q_ s10 values of the wetlands were 4.82 and 6.15 in the two tidal stages,the differences of Q_ 10 values in 2 tidal stages were not significant(p0.05).The average Q_ a10 value and Q_ s10 value of CH_ 4 emission fluxes during plant main growing season were 1.28 and 2.29,and average Q_ a10 value and Q_ s10 value in other months were 4.31 and 7.03,the temperature sensitivity during plant main growing season was lower than that in other months.The results also showed that soil pH had a control on Q_ s10 and Q_ a10 of methane emission fluxes of the wetlands,the Q_ a10 value and Q_ s10 value both dropped with the increase of soil pH.