Anaerobic Oxidation Of Methane And Its Mechanism In The Minjiang River Estuarine Wetland

Wetland is one of the most sensitive ecosystems responses to global climate change and human activities.Wetland is also an important source of methane emission. Diverse electron transfermediators and electron acceptors come into wetland via acid deposition, salt water intrusion, soil erosion, sewage and other channels, and affecting the methane metabolism. Anaerobic oxidation of methane is an important process of methane metabolism. In this study we aimed to deep investigate several variables related to estuarine wetland anaerobic oxidation of methane, and to advance the knowledge of the possible management to reduce methane emissions. The Minjiang River estuarine wetland was selected as the study area which located in the transition zone between mid-subtropical and south subtropical regions. The processes and mechanisms of anaerobic oxidation of methane in the wetlands of salt-freshwater gradient were studied by the field collection and laboratory experiments. The main results were as follows:(1) The profiles of the concentration of methane and electron acceptors, isotope of methane, and the results of laboratory incubation of the anaerobic oxidation of methane after inhibitor addition,δ13C-CO2variation with the increment of incubation time from natural abundance and stable isotope pool-dilution together proved that the existence of anaerobic oxidation of methane in the estuarine wetlands of salt-freshwater gradient.(2) The results from experiments of stable isotope pool-dilution methods showed that the electron acceptors such as nitrate, nitrite, ferric and sulfate all play a role in the anaerobic oxidation of methane, and ferric was the driver of the anaerobic oxidation of methane in the wetlands of salt-freshwater gradient. Furthermore, the results also showed anaerobic oxidation of methane by microbe was the main pathway.(3) Rate of anaerobic oxidation of methane was highest in January with the value of41.76μg g-1d-1and lowest in August with the value of3.46μg g-1d-1, and the averaged value was10.97μg g-1d-1. The averaged values of anaerobic oxidation of methane in a soil depth of0-100cm were1.53,1.59,1.00μg g-1d-1and1.90,1.54,1.23μg g-1d-1in the Shanyutan wetland, Bianfuzhou wetland and Tajiaozhou wetland of salt-freshwater gradient in summer and winter, respectively. Pore water dissolved methane, soil ferric, pH, Eh, salinity and root activity were the most important factors controlling seasonal variation of anaerobic oxidation of methane, while the spatial variations of anaerobic oxidation of methane was influenced by the salt-freshwater gradient in the Minjiang River estuarine wetland.(4) Rate of anaerobic oxidation of methane was significantly positively correlated with methane production rate (R=0.750, P<0.001) and rate of aerobic oxidation of methane (R=0.768, P<0.001) in the Minjiang River estuarine wetland.