The Peculiar Hydrology of West-Central Florida’s Sandhill Wetlands, Ponds, and Lakes – Part 2: Hydrogeologic Controls

This study investigates hydrogeologic controls on a peculiar, poorly studied type of geographically isolated wetland in west-central Florida, USA, locally referred to as “sandhill wetlands.” Their peculiarity lies in their connectivity to a large, regional aquifer, which controls their hydrology and influences their ecological expression. Six wetlands and one wetland-pond complex were examined using geophysical, lithologic, hydrologic, and ecological data. These data were used to configure site-specific hydrogeology, from which two conceptual models were developed. The first model depicts mechanisms of sandhill wetland connectivity to the regional aquifer. Three mechanisms of connectivity are proposed based on the degree and depth of aquifer confinement: 1) direct - due to wetland embedment directly in the unconfined regional aquifer; 2) indirect - due to embedment in a surficial aquifer, where groundwater exchange with the regional aquifer occurs through breaches in the semi-confining unit; and 3) none - due to embedment in a surficial aquifer where groundwater exchange with the regional aquifer does not occur because the semi-confining unit is too deep. The second model conceptualizes fundamental sandhill wetland ecohydrology. It depicts how the geomorphology of a sandhill depression relative to the range of the regional water table determine whether that feature will manifest as a wetland or as a pond, lake, sink, or upland. Findings from both models contribute to the limited understanding of sandhill wetland, pond, and lake ecohydrology and may be used to improve how they are classified, assessed, managed, and preserved as valuable natural resources.

The interactive pedological-hydrological processes and environmental sensitivity of a tropical isolated wetland in the Brazilian Cerrado

In seasonal flooding isolated wetlands, the degree of wetness suggests a close synergy between soil processes, landscape evolution and hydrology along space and time. Until now, that subject has received insufficient attention despite natural wetlands supply essential environmental services to society and are surrounded by intensive agriculture that uses agrochemicals and fertilizers in their management. The objectives of this study were to propose an infiltration architecture model based on local surface and subsurface water-fluxes in isolated wetland embedded in lateritic plateau covered by savanna and qualify the environmental sensitivity as an area of aquifer recharge. Grain size, soil bulk density, and hydraulic conductivity were determined in five profiles in a soil catena. Unmanned Aerial Vehicle high-resolution images were obtained to generate a digital elevation model and discriminate areas with different vegetation, water accumulation, and environmental sensitivity. Electrical tomography was performed to unveil the soil architecture and infiltration. The soils (Plinthosols) developed on aquic conditions determine the linkage between the surface–subsurface hydrodynamics with the soil's physical properties. We have identified vertical and lateral water-flows in the soil architecture. Vertical flow occurs exclusively at the center, where the wetland is characterized as a recharge zone. Lateral flow towards the borders characterizes a discharge zone. The recharge zone is a depression surrounded by crops; therefore, it is a point of high environmental sensitivity. This hydrodynamic model is essential to support studies related to the dispersion of contaminants since soybean agriculture dominates the whole area of well-drained soils in the Brazilian Cerrado.

Quantifying hydrologic connectivity of wetlands to surface water systems

Hydrologic connectivity among wetlands is poorly characterized and understood. Our inability to quantify this connectivity compromises our understanding of the potential impacts of wetland loss on watershed structure, function and water supplies. We develop a computationally efficient, physically based subsurface–surface hydrologic model to characterize both the subsurface and surface hydrologic connectivity of geographically isolated wetlands and explore the time and length variations in these connections to a river within the Prairie Pothole Region of North America. Despite a high density of geographically isolated wetlands (i.e., wetlands without surface inlets or outlets), modeled connections show that these wetlands are not hydrologically isolated. Subsurface connectivity differs significantly from surface connectivity in terms of timing and length of connections. Slow subsurface connections between wetlands and the downstream river originate from wetlands throughout the watershed, whereas fast surface connections were limited to large events and originate from wetlands located near the river. This modeling approach provides first ever insight on the nature of geographically isolated wetland subsurface and surface hydrologic connections to rivers, and provides valuable information to support watershed-scale decision making for water resource management.

Quantifying hydrologic connectivity of wetlands to surface water systems

Hydrologic connectivity of wetlands is poorly characterized and understood. Our inability to quantify this connectivity compromises our understanding of the potential impacts of wetland loss on watershed structure, function and water supplies. We develop a computationally efficient physically-based subsurface-surface hydrological model to characterize both the subsurface and surface hydrologic connectivity of "geographically isolated" wetlands and explore the time and length variations in these connections to a river within the Prairie Pothole Region of North America. Despite a high density of geographically isolated wetlands (i.e., wetlands without surface outlets), modeled connections show that these wetlands are not hydrologically isolated. Hydrologic subsurface connectivity differs significantly from surface connectivity in terms of timing and length of connections. Slow subsurface connections between wetlands and the downstream river originate from wetlands throughout the watershed, whereas fast surface connections were limited to large events and originate from wetlands located near the river. This modeling approach provides first ever insight on the nature of geographically isolated wetland subsurface and surface hydrological connections to rivers, and provides valuable information to support watershed-scale decision making for water resource management.