Temporal Patterns in Soil Redox Potential Vary Across a Freshwater Coastal Delta

Journal Article · Mon Nov 24 00:00:00 EST 2025 · Hydrological Processes

DOI:https://doi.org/10.1002/hyp.70338· OSTI ID:3020930

Herndon, Elizabeth ^[1]; Berens, Matthew J. ^[2]; Pilla, Rachel M. ^[1]; Schwaner, Geoff ^[1]

---

1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
2. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); North Carolina Department of Agriculture & Consumer Services, Raleigh, NC (United States)

Widespread and persistent flooding is submerging coastal ecosystems, particularly along the Louisiana Gulf coast, where flooding results from the compounding effects of ground subsidence and rising sea level. Restoration projects aim to mitigate land loss by diverting sediment loads from rivers into degraded areas to increase ground elevation. To predict how coastal ecosystems will change over time in response to projected changes in relative sea level and restoration, it is necessary to understand how subsurface biogeochemical processes respond to dynamic hydrologic forcings. Here, this study evaluates how environmental parameters that integrate biogeochemical processes vary with water table fluctuations in the freshwater Wax Lake Delta (WLD) in Louisiana, USA, where water diversions have formed one of the only active deltas along the coast. High‐frequency observations of water level, soil redox potential, specific conductance and pH were made for 1 year along elevation transects located on the older, proximal and younger, distal ends of a deltaic island. Redox responded rapidly to changing water tables, with fluctuations occurring primarily in shallow soils (< 20 cm) and at higher elevations. Deeper soils and those at lower elevation remained inundated and reduced. Semi‐diurnal tidal fluctuations were pronounced in younger, distal soils, presumably due to rapid groundwater exchange with the river channel. Tidal signals were muted in older soils that instead exhibited seasonal variability associated with river discharge and evapotranspiration. Although much of the delta sediments are persistently reducing and anoxic, redox fluctuations in the natural levees that border the deltaic islands likely drive high rates of biogeochemical activity. Evaluating how hydrology drives the frequency and duration of redox fluctuations provides a basis for understanding how biogeochemical processes might vary with complex hydrological interactions in coastal systems.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC05-00OR22725
• Other Award/Contract Number: ERKPA45; FOA-0002563
• OSTI ID: 3020930
• Journal Information: Hydrological Processes, Journal Name: Hydrological Processes Journal Issue: 11 Vol. 39; ISSN 0885-6087; ISSN 1099-1085
• Publisher: Wiley
• Country of Publication: United States
• Language: English