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Detangling Tanglewood: Characterizing vertical, horizontal, and longitudinal hydrologic connectivity in a Coastal Plain headwater stream
Proceedings of the 2022 Mississippi Water Resources Conference
Year: 2022 Authors: Peterson D.M., Jones C.N., Shogren A.J., Plattner A., Godsey S.E., Atkinson C.L., Benstead J.P.
Upstream hydrologic processes affect the chemical, physical, and biological function of downstream aquatic ecosystems. However, there are systematic gaps in our understanding of watershed storage and connectivity dynamics that limit our ability to effectively manage downstream waters—particularly in Coastal Plain landscapes. We are working to bridge this gap by characterizing drivers of vertical, horizontal, and longitudinal hydrologic connectivity in a 90-ha headwater stream in the Upper Coastal Plain of western Alabama. We first identified three distinct hydrogeomorphic features based on varying degrees of stream incision. We then installed a network of nested shallow groundwater wells across these features and performed seasonal stream network surveys to capture variable scales and dimensions of water movement. Additionally, we used an Electrical Resistivity Tomography (ERT) survey to characterize subsurface structure. Results suggested that vertical connectivity is constrained by discontinuous clay layers based on observed water table perching and evidence of preferential flow through the clay confining units. Horizontal connectivity (i.e. both hillslope storage and connectivity) was driven by the degree of incision; the incised reach consistently received water from the hillslope, whereas the depositional reaches were consistent sources of water to the hillslope. Finally, longitudinal connectivity was a function of both stream incision and season, as stream drying was variable across seasons, but stream width distributions followed unique seasonal patterns that were variable across stream hydrogeomorphology types. Our results provide an initial characterization of how upstream processes impact downstream water quality in low-gradient, Coastal Plain watersheds.