Waving Vegetation Facilitates Gas Transfer in Wetland Surface Water

Abstract:

Wind-driven movement of flexible vegetation has been an overlooked mechanism in wetland gas models. To understand the magnitude of this effect, a laboratory experiment was conducted. An array of plastic tubes, representing vegetation, was mechanically forced at a range of frequencies and amplitudes matching those observed in the field. Starting from deoxygenated water, we measured dissolved oxygen at mid-depth in the water column using a YSI ProODO as the water re-equilibrated with the atmosphere. From this DO timeseries, we calculated the gas transfer velocity, k, using the thin film gas transport model. This measurement of k was independent of the water-wall interactions, which can be significant in laboratory-scale tanks. Our experiments have shown that the movement of vegetation stirs the water column and thus contributes to the transfer of dissolved gases across the air-water interface. Increased transfer was observed with movements of higher frequency and amplitude. To estimate the occurrence of this phenomena in natural systems, data (e.g. velocity profiles) from a long-term monitoring project in the Florida Everglades will be analyzed. The results can help improve current gas budgets and predict biogeochemical processes.