Factors influencing CO2 and CH4 emissions from coastal wetlands in the Liaohe Delta, Northeast China

[摘要] Many factors are known to influence greenhouse gas emissions from coastalwetlands, but it is still unclear which factors are most important underfield conditions when they are all acting simultaneously. The objective ofthis study was to assess the effects of water table, salinity, soiltemperature and vegetation on CH₄ emissions and ecosystem respiration(R_eco) from five coastal wetlands in the Liaohe Delta, Northeast China:two Phragmites australis (common reed) wetlands, two Suaeda salsa (sea blite) marshes and a rice (Oryza sativa) paddy.Throughout the growing season, the Suaeda wetlands were net CH₄ sinks whereasthe Phragmites wetlands and the rice paddy were net CH₄ sources emitting 1.2–6.1 g CH₄ m⁻² yr⁻¹.The Phragmites wetlands emitted the most CH₄ perunit area and the most CH₄ relative to CO₂. The main controllingfactors for the CH₄ emissions were water table, temperature, soilorganic carbon and salinity. The CH₄ emission was accelerated at highand constant (or managed) water tables and decreased at water tables belowthe soil surface. High temperatures enhanced CH₄ emissions, andemission rates were consistently low (< 1 mg CH₄ m⁻² h⁻¹) at soil temperatures < 18 °C. At salinity levels> 18 ppt, the CH₄ emission rates were always low (< 1 mg CH₄ m⁻² h⁻¹) probably because methanogens wereout-competed by sulphate-reducing bacteria. Saline Phragmites wetlands can, however,emit significant amounts of CH₄ as CH₄ produced in deep soillayers are transported through the air-space tissue of the plants to theatmosphere. The CH₄ emission from coastal wetlands can be reduced bycreating fluctuating water tables, including water tables below the soilsurface, as well as by occasional flooding by high-salinity water. Theeffects of water management schemes on the biological communities in thewetlands must, however, be carefully studied prior to the management inorder to avoid undesirable effects on the wetland communities.

[学科分类] 地球化学与岩石