Methane emissions from freshwater riverine wetlands

To better understand methane emissions from freshwater riverine wetlands, seasonal and spatial patterns of methane emissions were measured over a 1-year period from created freshwater marshes and a river division oxbow, and at a river-floodplain edge (riverside) in central Ohio, USA. Plots were distributed from inflow to outflow and from shallow transition edges to deep water zones in the marshes and oxbow. Median values of CH4 emissions ranged from 0.33 to 85.7 mg-CH4-C m−2 h−1, at the riverside sites and 0.02–20.5 mg CH4-C m−2 h−1 in the created marshes. The naturally colonizing marsh had more methane emissions (p = 0.047) than did the planted marsh, probably due to a history of higher net primary productivity in the former. A significant dry period and lower productivity in the oxbow may explain its low range of methane emissions of −0.04 to 0.09 mg CH4-C m−2 h−1. There were significantly higher rates of methane emissions in deep water zones compared to transition zones in the created marshes. Overall CH4 emissions had significant relationships with organic carbon and soil temperature and appear to depend on the hydroperiod and vegetation development. Riparian wetlands can be designed to minimize greenhouse gas emissions while providing other ecosystem services.