Key factors affecting spatial variation of methane emissions from freshwater marshes

To understand the mechanism for spatial variation of CH4 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 CH4 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 CH4 concentration in porewater, aboveground plant biomass and stem density in situ in Sanjiang Plain of Northeast China in August 2001. Spatial variation of CH4 emissions from both different marshes in a region and different plots within a certain marsh was high. The flux rates of CH4 emissions from three marshes ranged from 17.2 to 66.5 mg CH4 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 CH4 m(-2) h(-1) (17.51%), respectively. Both the flux rates and spatial variation of CH4 emissions strongly increased as standing water depth increased significantly. Standing water depth greatly governed the spatial variation of CH4 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 CH4 concentrations in porewater. Moreover, the aboveground plant biomass determined spatial variation of CH4 emissions from plots within a certain marsh by controlling the pathways (stem density) of CH4 emissions from the marsh into the atmosphere. (C) 2003 Elsevier Science Ltd. All rights reserved.