Effect of water table level on CO2, CH4 and N2O emissions in a freshwater marsh of Northeast China

We quantified the effects of the water table on CO2, CH4 and N2O emissions from microcosms in a freshwater marsh in Sanjiang Plain, Northeast China. From July to September in 2005, CO2, CH4 and N2O emission rates were measured in an undisturbed natural marsh (in natural) and microcosms of three manipulated water table treatments: a reference, a high water table (HW) and a low water table (LW). The averages of CO2, CH4 and N2O emissions were 360.2 mg m−2 h−1, 7.43 mg m−2 h−1 and 12.84 μg m−2 h−1, respectively, close to those in reference (p < 0.05), averaging 394.5 mg m−2 h−1, 8.92 mg m−2 h−1 and 13.3 μg m−2 h−1. This means microcosm installation had no significant effect on CO2 efflux. Averaged CO2 (p = 0.03) and CH4 (p = 0.001) emissions were significantly different across the treatments, but that of N2O emission (p = 0.36) was not. To quantify the effects of water table position, three typical classes of water table were considered, i.e. +2 to +14 cm, –11 to 0 cm and −28 to −11.3 cm (+, above the soil surface. –, below the soil surface). Mean CO2 and N2O emissions were lowest at the higher water table positions (+2 to +14 cm) and increased by 120% and 60% at the lower water table positions (−11 to 0 cm), respectively, and the corresponding CH4 emissions decreased by 75%. However, at lowest water table positions (−28 to −11.3 cm), little additional effects on gas emissions were not found. Our results suggested that there could be considerable changes of greenhouse emissions as a response of water drawdown due to wetland drainage.