Hydrologic connectivity in a prairie hillslope seep system, Texas, USA

Groundwater seeps are characteristic hydrological and ecological features of many landscapes, yet their hydrology remains poorly understood. Within the North Central Texas Grand Prairie Ecoregion, seep systems developed in soils over interbedded limestone and marl are prevalent. However, previous attempts to gather data on runoff generation from these systems, and to assess their connectivity and contribution to headwater stream hydrology, have been unsuccessful due to widespread drought across the state, principally between 2010 and 2015. A priori reasoning suggests that seeps must contribute flow to headwater streams, but no work to date has been able to document or quantify those contributions.

In this paper, we document a hitherto undiscovered hillslope seep system in Somervell County, Texas. The overall aim of our research is to gain a deeper understanding of the hydrology of these seep systems and to determine whether they function (and can therefore be classified) as wetlands. To achieve this, we (1) quantify the spatial and temporal variability of soil moisture and matric potential across the hillslope seep system; (2) assess the relationship between changes in soil moisture and vegetation; and (3) quantify the magnitude and timing of runoff generation from the seep system to channel flow. We hypothesized that these systems might qualify as isolated wetlands during non-drought conditions, and our field measurements and wetland delineations demonstrate this to be true. The findings of this study indicate that, while these wetlands are separated by a glade and barrens, they are hydrologically connected to the associated headwater stream via overland flow occurring during storm events. Moreover, they remain hydrologically connected to the main channel for prolonged periods via seeping after a precipitation event. Our research provides a more complete understanding of how these seep systems behave as intermittent wetlands which could serve to improve habitat management and conservation of riparian areas within Texas.