Groundwater recharge from an oxbow lake-wetland system in the Mississippi Alluvial Plain

Authors: GRATZER, MICHAEL - University Of Mississippi; DAVIDSON, GREGG - University Of Mississippi; O'REILLY, ANDREW - University Of Mississippi; Rigby Jr, James

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2019
Publication Date: 12/18/2019
Citation: Gratzer, M., Davidson, G.R., O'Reilly, A.M., Rigby Jr, J.R. 2019. Groundwater recharge from an oxbow lake-wetland system in the Mississippi Alluvial Plain. Hydrological Processes. 34(6):1359-1370. https://doi.org/10.1002/hyp.13680.
DOI: https://doi.org/10.1002/hyp.13680

Interpretive Summary: Groundwater decline is a major challenge facing the Mississippi River alluvial plain. Oxbow lakes are a common feature of this landscape and are generally thought to be of limited impact on regional groundwater recharge. Despite this assumption, there is little data on the flow of water between oxbow lakes and the regional aquifer or an accounting of the total contribution of all oxbow lakes to annual recharge. This study used field data to estimate the recharge from an oxbow lake in Humphreys Co, MS over a two-year period and estimate the potential contribution from all oxbow lakes in the region. Flow to the aquifer was greater than expected and suggests that oxbows may be an important resource for augmenting local groundwater recharge. This work will be of interest to farmers and water resource managers in the region for more effective groundwater management.

Technical Abstract: The Mississippi River Valley Alluvial Aquifer ranks among the most over-drafted aquifers in the United States due to intensive irrigation. Concern over declining water levels has increased focus on understanding the sources of recharge. Numerous oxbow lakes overly the aquifer which are often considered hydraulically disconnected from the groundwater system due to fine-grained bottom sediments. In the current study, groundwater levels in and around a 445-ha oxbow lake wetland in Mississippi were monitored for a two-year period that included an unusually long low-water condition in the lake (>17 mo), followed by a high-water event lasting over four months before returning to earlier low water levels. The high water pulse (>4 m rise) provided a unique opportunity to track the impact in the underlying alluvial aquifer. During low-water conditions, groundwater flowed westward beneath the lake. Following the lake rise, groundwater beneath and near the perimeter responded as quickly as the same day, with more delayed responses moving away from the lake. Within two months, a groundwater mound formed near the center of the oxbow (>3 m increase), with a reversal in the local hydraulic gradient toward the east. Flow returned to a westward gradient when the lake level dropped back below 0.5 m. Analysis of precipitation and nearby river stage could not account for the observed behavior. Recharge to the aquifer is attributed to rising water levels spreading over point bar deposits and into surrounding forested wetlands where preferential flow pathways are likely to exist due to buried and decomposing tree remains. An earlier study in the wetland demonstrated increasing redox potential in isolated zones, consistent with the existence of preferential flow pathways through the bottom sediments. Retaining high water levels in oxbow lakes could be a relatively low cost water-management practice for enhancing aquifer recharge.