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Heterogeneous redox conditions in saturated soils: implications for ecological impact if oxbow wetlands are impounded for managed aquifer recharge
Proceedings of the 2023 Mississippi Water Resources Conference
Year: 2023 Authors: Adele Bolaji B., Davidson G., Hossain M.R., Mamus M.L., Hickey C.J.
Over-drafting of regional aquifers such as the Mississippi Valley River alluvial aquifer (MRVA) has prompted a greater focus on methods of managed aquifer recharge. Previous work has demonstrated that oxbow lake-wetland systems on the floodplain of the Mississippi River can serve as significant sources of recharge, which could be enhanced by impounding water. Subsequent attention is needed on the potential ecological impacts of altering the natural hydroperiod. While it is typically assumed that flooding quickly results in anoxic soil conditions that diminish plant growth, some studies have reported increased in growth of wetland-adapted trees, such as bald cypress (Taxodium distichum), with increasing water level. A possible cause is a flux of oxygenated surface water through the root zone under greater vertical hydraulic gradients. Given the heterogeneous nature of forested wetland soils, caused in large part by buried decomposing tree remains, it is anticipated the soil redox response to rising water levels is highly variable, with the greatest increases corresponding to localized zones of higher permeability (preferential flow pathways). Preliminary data from redox and temperature probes deployed at two different elevations in the forested perimeter of Sky Lake, MS, are consistent with the hypothesis. Wet but aerated soils of some probes show rapid increases in redox potential following rainfall events, with smaller increases observed even if the soil is already saturated. Other probes indicate very little response, suggesting placement in zones of very low permeability. Under deeper water conditions, response to changes in water level and precipitation appear to be more complex.