Science Serving Maryland's Coasts
Laura Lapham, Ph.D.
Chesapeake Biological Laboratory
Characterizing the Distribution of Methane Flux from Sediment to the Water Column in the Chesapeake Bay
Methane production is the last stage of organic matter decay. Several microorganisms take part in organic matter decomposition, including aerobic bacteria, sulfate-reducing bacteria, and the methane-producing methanogens themselves. Another group of microorganisms, the methanotrophs, reverses this process of methanogenesis with methanotrophy, where sulfate is reduced and the methane is oxidized back into carbon dioxide. Methanotrophic activity determines methane flux, and sulfate availability determines methanotrophic activity. It was originally hypothesized that the Chesapeake Bay's salinity gradient should therefore control methane flux. The flux-salinity data did not support this idea, however; it actually showed flux increasing as salinity increased. Another possible hypothesis was developed: dissolved oxygen content may serve as a control over methane flux, rather than salinity. While methanotrophs oxidize methane anaerobically in the sediment, methane can also be oxidized aerobically by bacteria both in the top layer of the sediment or in the water column, provided there are oxic conditions. The Chesapeake Bay undergoes hypoxic conditions seasonally, during which times there should be increased methane flux. We did not acquire sufficient data to explore this possibility, so further study must be devoted to tracing methane's movement after it passes from the sediment into the water column.
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