A Hydrologic Landscapes Perspective on Groundwater Connectivity of Depressional Wetlands
Research into processes governing hydrologic connectivity of depressional wetlands has advanced rapidly in recent years. Nevertheless, a need persists for broadly-applicable, non-site-specific guidance to facilitate further research. Here we explicitly use the hydrologic landscapes theoretical framework to develop broadly-applicable conceptual knowledge of depressional-wetland hydrologic connectivity. We used a numerical model to simulate groundwater flow through five generic hydrologic landscapes from Winter (2001). Next, we inserted depressional wetlands into the generic landscapes and repeated the modeling exercise. Results strongly characterize groundwater connectivity from uplands to lowlands as being predominantly indirect. Groundwater flowed from uplands and most of it discharged to the surface at a concave-upward break in slope, with a relatively small percentage discharging to the surface in the lowland at the simulated drain. Additionally, we found groundwater connectivity of the depressional wetlands was primarily determined by the slope of the adjacent water table. However, we identified certain arrangements of landforms that caused the water table to fall sharply and not follow the surface contour. We attribute the decline in water table to a dramatic concave-down surface contour that commonly exists on the down-gradient side of depressional wetlands. The lower water table in these areas often causes depressional wetlands to recharge groundwater or to serve as flow-through wetlands by receiving groundwater discharge on the up-gradient side and recharging groundwater on the down-gradient side. Finally, we synthesize our findings and provide guidance to practitioners and resource managers regarding the management significance of indirect groundwater discharge and the effect of depressional wetland groundwater connectivity on pond permanence and connectivity.