Citation:

Neff, B., D. Rosenberry, S. Leibowitz, D. Mushet, Heather E Golden, M. Rains, J Renee Brooks, AND Charles R Lane. A Hydrologic Landscapes Perspective on Groundwater Connectivity of Depressional Wetlands. WATER. MDPI, Basel, Switzerland, 12(50):1-29, (2020). https://doi.org/10.3390/w12010050

Impact/Purpose:

One of EPA’s long-term goals is reducing the number of square miles of watersheds not meeting surface water standards. Since watershed management of wetlands and wetland connectivity types could help realize this goal, a better understanding of connectivity of depressional wetlands through groundwater flowpaths would be useful. This study builds on an approach that used the Hydrologic Landscapes (HL) framework, in order to develop further insights into hydrologic connectivity of depressional wetlands, with a primary focus on groundwater flow. We numerically simulate linkages between groundwater and surface water flows within five generic HL landforms, and then evaluate how the presence of depressional wetlands affects hydrologic connectivity, producing results that are broadly applicable over the conterminous US. Connectivity of the depressional wetlands was primarily determined by the slope of the adjacent water table. However, results also reveal several processes related to nesting of landforms – embedding one landform such as a depressional wetland within a broader landform such as a playa – that strongly affect the water table and therefore groundwater connectivity of depressional wetlands. Regarding water-resource management, the application of this HL approach toward groundwater connectivity could improve a practitioner’s understanding of wetland connectivity and guide more resource-efficient measurement and modeling efforts to support decision-making. Through its models and conclusions, this research could also be useful in the development of tools and guidance related to groundwater connectivity.

Description:

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.

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