Key factors affecting spatial variation of methane emissions from freshwater marshes

Abstract

To understand the mechanism for spatial variation of CH 4 emissions from marshes grown with different type of plants in a region and plots within a certain marsh grown with one type of plants, we measured CH 4 emissions from a region in which eutrophic freshwater marshes were divided into three types: Carex lasiocarpa, Carex meyeruana and Deyeuxia angustifolia according to plant type as well as CH 4 concentration in porewater, aboveground plant biomass and stem density in situ in Sanjiang Plain of Northeast China in August 2001. Spatial variation of CH 4 emissions from both different marshes in a region and different plots within a certain marsh was high. The flux rates of CH 4 emissions from three marshes ranged from 17.2 to 66.5 mg CH 4 m −2 h −1 with 34.76% of variation coefficient, whereas the values in Carex lasiocarpa, Carex meyeriana and Deyeuxia angustifolia marshes varied from 21.6 to 66.5 (39.61%), from 17.2 to 45.0 (29.26%) and from 19.1 to 33.0 mg CH 4 m −2 h −1 (17.51%), respectively. Both the flux rates and spatial variation of CH 4 emissions strongly increased as standing water depth increased significantly. Standing water depth greatly governed the spatial variation of CH 4 emissions from different marshes in a region by changing the amount of plant litters inundated in standing water, which provided labile organic C for methanogens and controlled CH 4 concentrations in porewater. Moreover, the aboveground plant biomass determined spatial variation of CH 4 emissions from plots within a certain marsh by controlling the pathways (stem density) of CH 4 emissions from the marsh into the atmosphere.