Kennedy Okioghene Doro

Oxygen plays a central role in regulating biogeochemical processes across terrestrial and aquatic ecosystems. However, its dynamics in hydrologically and redox‐dynamic ecosystems remain poorly characterized due to high spatiotemporal variability and the lack of field‐ready instrumentation capable of long‐term, depth‐resolved deployments required to capture these dynamics. Here, we present a practical, modular system for measuring high‐frequency in situ dissolved oxygen time series across multiple soil depths in both unsaturated and saturated conditions. The platform integrates commercially available optical oxygen sensors with a portable logging and power system housed in a weatherproof enclosure. This system is cost‐effective and designed for rapid assembly, flexible deployment, and robust operation under harsh field conditions. We demonstrate system performance across contrasting environmental settings, including an experimental flooding event in an upland forest and king tide‐driven inundation in a coastal marsh, capturing rapid transitions between oxic and anoxic states and revealing depth‐dependent oxygen dynamics. To support broader adoption, we provide open‐source code for data processing and visualization, and outline pathways for future development, including integration with commercial dataloggers. By lowering technical and logistical barriers to depth‐resolved in situ soil oxygen monitoring, this approach facilitates improved characterization of short‐term oxygen dynamics and associated biogeochemical processes across a wide range of fundamental and applied research settings.

Study RegionThe Oak Openings Region (OOR) is characterized by a unique ecosystem sustained by a complex shallow groundwater system. Developing plausible groundwater models to simulate flow for managing groundwater resources within the region is challenging due to its multilayered post-glacial aquifer systems that require accurate representations of the aquifer’s hydrostratigraphy and boundary conditions.Study FocusThis study evaluated the impact of hydrostratigraphic complexities, model boundary conditions, and domain extent on simulating groundwater flow within the multilayered aquifer system. We developed three MODFLOW models with different complexities to simulate groundwater flow based on [1] a two-layer conceptual model combining sand, rhythmite, and till units into a single upper layer over bedrock, [2] a three-layer model that treats the rhythmites and till as a single hydraulic unit, and [3] a four-layer model that maintains the distinct hydrostratigraphic units. The models were calibrated and validated using transient hydraulic head and pumping test data.New Hydrological Insights for the RegionThe results demonstrated that groundwater flow, drawdown, aquifer storage and yield, and particle transport path are strongly influenced by stratigraphic heterogeneity. The model, which included more details of stratigraphic heterogeneities, improved simulation predictions over the simplified models. The findings show that simplified models risk under- or over-predicting transient processes in the OOR. Incorporating drawdown and head measurement enhanced model validation as both static and stress conditions are represented.

Coastal upland forests are exposed to intensifying precipitation regimes and sea level rise, increasing tree mortality and transforming these coastal forests into wetland ecosystems. While the ultimate outcome of long-term exposure to these perturbations is known to be an ecosystem state change from upland forest to wetland, the resistance of forests to the first novel exposure to flooding and salinity is relatively unknown. The Terrestrial Ecosystem Manipulation to Probe the Effects of Storm Treatments (TEMPEST) experiment uses ecosystem-scale (2000 m ² ) experimental flooding plots to decouple two distinct disturbances associated with hydrological extremes: (1) freshwater saturation of soils and flooding (e.g., from heavy precipitation) and (2) salinization from storm surge by saturating and flooding soils with brackish water. Here we describe the immediate effects of the experimental flooding treatments on hydrologic, biogeochemical and vegetation ecosystem components following the first novel experimental ecosystem-scale flooding event in TEMPEST. Following a 9-hour experimental treatment, the system’s hydrology was temporarily and significantly impacted, but there were subtle effects on biogeochemical and vegetation components of the ecosystem. This suggests that this temperate deciduous forest was resistant to a single novel flooding event, even if the water is saline. Most biogeochemical parameters monitored in the soil, porewater, and groundwater responded similarly between freshwater and saltwater treatments relative to the control plot. However, we show that even a single episodic event can cause large transient shifts in belowground conditions that drive physiological changes in coastal forest functions, such as soil moisture and oxygen levels. Such responses may impact how the system responds to future perturbations.

Hydrological disturbances, including intense precipitation and sea level rise along coastal interfaces, lead to freshwater flooding and saline water overwash that changes the soil saturation and salinity and, in turn, alters subsurface biogeochemical reactions and soil-plant-atmosphere exchanges. The extents of these state changes are not well known, limiting their accurate representation in earth system models. In this study, we combined the spatial-temporal parameter measurements advantage of geophysical imaging with discrete in-situ and laboratory measurements and petrophysical relationships to quantify changes in soil moisture and salinity at an improved spatial scale. We simulated a concurrent freshwater and estuarine water flooding at two adjacent 2,000 m2 forested plots by inundating them with 265 m3 of freshwater and estuarine water with salinities of 0.06 and 8.1 practical salinity units (PSUs), respectively. The flooding experiment was conducted over a single 10-hour cycle for year 1 and for two and three flooding cycles for years 2 and 3, respectively, with a 14-hour pause between each cycle. During each flooding experiment, repeated electrical resistivity and induced polarization measurements were used to image the water and solute infiltration fronts along two 100 m and 42 m transects while soil moisture, temperature, and electrical conductivity were monitored every 15 minutes with soil sensors installed at 5, 15 and 30 cm depths and co-located with the geophysical transects. Petrophysical models derived from laboratory multi-salinity electrical measurements were used to estimate changes in soil moisture and fluid salinity from field measurements of real and imaginary conductivity during the flooding experiment. During flooding, the real electrical conductivity increased by ~100% in the freshwater plot and ~570% in the estuarine water plot. The change in imaginary conductivity in the freshwater plot was < 1 mS/m, whereas that of the estuarine water plot was ~5 mS/m. The real conductivity shows a dependence on soil moisture content with a coefficient of determination (R2) >0.7, while the imaginary conductivity shows a dependence on soil salinity with R2 >0.6. Repeated monitoring over 3 years shows >60% change in ambient soil electrical conductivity at the estuarine water plot, indicating an increase in soil salinity over time. These results validate the use of electrical resistivity for estimating changes in coastal soils' moisture content in response to flooding. Combining the electrical resistivity with induced polarization measurements provides the possibility to account for changes in pore fluid conductivity. The intermittent geophysical monitoring limits the comparison of geophysical data with in-situ soil parameters measurement to develop a more robust petrophysical model. This study would benefit from the use of continuous automatic electrical resistivity and induced polarization monitoring, which is becoming increasingly popular for ecohydrological studies.

Coastal ecosystems along the Great Lakes play an important role in critical element cycling between land and lake ecosystems. Because lake water levels are highly dynamic, the dominant ecosystems (marsh, swamp, upland forest) constantly respond to the varying water line. Flood pulses are important controls on plant community zonation, as well as their respective biogeochemical functions, setting the boundary between herbaceous wetlands, forested wetlands, and/or upland forest based on the respective flooding tolerance. Because lake levels are predicted to increase in future decades (e.g. 2040-2049 vs. 2010-2019), shifts in ecosystem boundaries are expected but the change in ecosystem function is currently unknown.To understand the impact these flood pulses have on soil biogeochemistry and plant function, we are implementing an ecosystem-scale manipulative experiment to create increasingly intense flood pulses by pumping water across an elevation gradient from forested wetland to upland (DELUGE - Disturbance and Ecohydrological Legacies in Upland Great-lakes Ecosystems). We follow a before-after-control-impact design using two diked parcels in the Ottawa National Wildlife Refuge at the coast of Lake Erie, one of which will be untreated and serve as a reference. The main objective is to gain a mechanistic understanding of how the effects of freshwater flooding and subsequent drainage propagate through water, soils, microbes, and plants to cause ecosystem state changes such as tree mortality and changes in biogeochemical cycling. Here we present the experimental design, site characterization, and results from sensor-based baseline measurements which started in June, 2025. Results from DELUGE will be incorporated into multi-scale process and Earth system models, with the overarching goal of an improved predictive understanding of coastal ecosystems.

Coastal soils are increasingly impacted by hydrologic intensification in the form of rising sea level and flooding from storm surges and precipitation. Alternating saltwater (SW) and freshwater (FW) exposure has the potential to disperse colloids, which can lead to disintegration of soil structure, clogging of pore spaces, and reduction in ecologically and biogeochemically important functions like infiltration or gas exchange. To investigate how hydrologic intensification affects soil structure and oxygen dynamics, we conducted a series of laboratory‐based flood simulations. Intact soil cores of the A and B horizons (22 total) from the toe slope of an upland coastal forest along the western shore of Chesapeake Bay. We subjected the cores to 24 h of saturation with either FW or alternating brackish SW and FW, with a 24‐h draining event in between flood events. Oxygen diffusion into soil during draining was reduced by up to 30% for soils flooded alternating SW‐FW compared to soils flooded only with FW. We attributed the reduced oxygen diffusion to clogging of smaller pores by colloids, with colloid redistribution observed as an increase in specific surface area down the core profile of up to 59%. After three SW‐FW floods (six floods total), there were significant changes in pore size distribution, significant redistribution of colloids, and the A horizon became sodic. We concluded that a small number of SW flooding events can induce a measurable change in soil physical properties that directly impacts the biogeochemical dynamics.

Geophysical methods provide high‐resolution spatial measurements of physical quantities sensitive to changes in soil moisture and salinity and can be used to monitor soil hydrological responses to flooding. However, extracting quantitative hydrological information from geophysical data remains challenging. In this study, we extended existing petrophysical models to estimate soil moisture and salinity from electrical measurements to address this challenge. We manipulated two hydrologically isolated 2000 m ² experimental plots by simultaneously inundating them with 265 m ³ of either freshwater or estuarine water. Repeated electrical resistivity and induced polarization measurements were used to image the water and solute infiltration along two transects that are 100 and 42 m in length. Petrophysical models derived from laboratory multi‐salinity electrical measurements were used to estimate changes in soil moisture and fluid salinity from field measurements of real and imaginary conductivity during the ecosystem‐scale flooding experiment. The real conductivity increased by ∼100% in the freshwater plot and ∼570% in the saltwater plot. The change in imaginary conductivity in the freshwater plot was 0.7, while the imaginary conductivity shows a dependence on soil salinity with R ² > 0.6. The results validate the use of electrical resistivity for estimating changes in soil moisture content in response to flooding. Combining electrical resistivity imaging with induced polarization measurements provides the possibility to account for changes in pore fluid conductivity.

Coastal soils are a significant but highly uncertain component of global biogeochemical cycles. These systems experience spatial and temporal variability in biogeochemical processes, driven by marsh‐to‐upland gradients and hydrological fluctuations. These fluctuations make it difficult to understand and predict biogeochemical processes in these highly dynamic systems. We studied coastal soil biogeochemistry and its variability (a) at regional scales and (b) across transects from upland forest to marsh, in two contrasting regions—Lake Erie, a freshwater lacustrine system, and Chesapeake Bay, a saltwater estuarine system. Salinity‐related analytes were a key source of variability in soil biogeochemistry, not just in the saltwater system, but surprisingly, also in the freshwater system. We had hypothesized linear trends in biogeochemical parameters along the TAI—however, contrary to expectations, transition soils were not consistently intermediate between upland and marsh endmembers; the non‐monotonic trends of C, P, Fe along our transects suggest that these do not behave as expected and may be difficult to model and predict—thus these are key analytes to study in our regions. Rapidly changing soil factors across coastal gradients (e.g., Ca, K, CEC, and TS) may act as precursors to ecosystem shifts. Our comprehensive soil characterization represents a snapshot of a single timepoint of surface soils and provides essential data for mechanistic modeling of ecosystem dynamics across coastal transects.