Wetland Connectivity Thresholds and Flow Dynamics From Stage Measurements

Abstract

Depressional wetlands are dominant features in many low‐gradient landscapes, where they provide water storage and exchange. Typical basin morphology enables water storage during drier periods, when surface flow paths are disconnected and exchange is limited to slower groundwater flow paths. Under wetter conditions, wetland stage can exceed surface connection thresholds, activating surface flow paths to downstream waters. Empirical methods are needed to quantify these dynamics and thus to assess their role in landscape hydrology and associated functions. We developed a new water budget‐based approach to enumerate connectivity thresholds and flows from stage measurements. We propose that this approach, termed Connectivity and Flow from Stage (CFS), has broad applicability across wetlandscapes. We applied the CFS method in the Big Cypress National Preserve, where we hypothesized that surface connectivity episodes control water and solute flux, with consequences for exported carbonate weathering products and thus for karst landform evolution. Across five study wetlands, this analysis detected surface connectivity thresholds and assessed temporal flow dynamics. Imputed connectivity thresholds were clear from stage‐dependent net flow dynamics and aligned well with LiDAR‐derived thresholds. Water export occurred overwhelmingly when stage exceeded these thresholds, indicating that water and solute export from these wetlands is dominated by periods of enhanced landscape connectivity. Notably, the presented CFS method can quantify wetland connectivity thresholds from stage data, even without supporting geomorphic information. This approach is useful for understanding hydrologic controls on biogeomorphic evolution in this particular karst landscape, and more broadly for inferring wetland connectivity patterns and magnitudes in other wetlandscape settings.

Local Storage Dynamics of Individual Wetlands Predict Wetlandscape Discharge

“…It also indicates that the topography in BICY is statistically stationary (Figure 4), resulting in conditions where a limited sampling of basin‐scale topography using a single DEM of 500 m radius, which contains multiple wetlands (pattern period ≈ 200 m), is sufficient to characterize whole‐landscape variability and patterns in elevation. Moreover, stage dynamics were highly correlated among wetlands (Figure 3) despite often large distances between them, which is consistent with our model conceptualization of distributed wetland storage acting as a single reservoir, and with recent work highlighting synchronous wetland stage and imputed spill dynamics among multiple BICY wetlands (McLaughlin et al, 2019). This, in turn, enables the fitting of a consistent “rating curve” for the stage‐discharge relationship across all wetlands (Figure 2 and Equation ).…”

“…The hydroperiod varies with elevation across the landscape, with many domes being perennially inundated, while the surrounding uplands, at approximately 50 cm higher elevation, are dry most of the year (Cohen et al, 2011). Flow patterns and surface connectivity depend on stage, with connected surface flow among domes at high stage in contrast to limited wetland‐groundwater exchange at low stage (McLaughlin et al, 2019). Construction of roads for logging, oil drilling, and recreation over the last century has resulted in augmented landscape drainage through canals.…”

Scale‐Dependent Patterning of Wetland Depressions in a Low‐Relief Karst Landscape

“…While it is broadly tenable that the observed pattern is contemporary and that local divergence in elevation is induced by markedly differing weathering environments between wetlands and uplands (i.e., the positive dissolution feedbacks are clear), the negative feedbacks that inhibit dissolution features, preventing continual expansion either vertically (collapse sinkholes) or laterally are less clear. One key recent insight is that vertical expansion is limited by the absence of subsurface drainage (McLaughlin et al, ) as well as persistent shallow water table conditions. Moreover, vertical weathering rates are self‐limiting as insoluble residual materials accumulate as wetland sediment (Watts et al, ), effectively sealing carbonic acid production in the shallow sediments from unweathered bedrock at depth (Dong et al, ).…”

Understanding Catchment‐Scale Forest Root Water Uptake Strategies Across the Continental United States Through Inverse Ecohydrological Modeling

“…Recent research provides some evidence that catchment‐scale RWU strategies could be derived from surface water observations. McLaughlin et al () observed evapotranspiration signals within wetland stage measurements. Similarly, Tashie et al () demonstrated that streamflow recessions in a headwater catchment in the southern Appalachian Mountains reflected both gravity‐driven groundwater outflow to surface waters as well as forest transpiration.…”