Methane Emissions From Created Riverine Wetlands

We measured methane emissions over a two-year period (2006-08) from two 12 to 14-year-old created freshwater marshes in central Ohio, one initially planted and the other allowed to self-colonize. Overall, methane emissions in the two created wetlands were different (p < 0.05), with the plant self-colonized wetland having higher annual methane (median and mean) emissions of 19 and 68 g CH4-C m(-2) y(-1) than the planted wetland (6 and 17 g CH4-C m(-2) y(-1)). Since hydrology and soil/water temperature were identical for the two wetlands, we hypothesize that differences in carbon accumulation due to higher net primary productivity in the self-colonized wetland may be causing higher methane emissions in that wetland. Net primary productivity in the self-colonized wetland was higher 7 out of 11 years prior to the study. Methane emissions from the created wetlands were lower than the average methane emission of 82 g CH4-C m(-2) y(-1) in a natural wetland in Ohio with similar hydrologic patterns. Methane emissions increased at a slower rate in the planted wetland (4 g CH4-C m(-2) y(-1)) than in the self-colonized wetland (16 g CH4-C m(-2) y(-1)) over a four-year period. Early methane emissions from created wetlands may depend as much or more on the methods used to create the wetlands, e.g. planting v. self colonization, as on their hydrogeomorphic conditions.