Imaging Hydrological Processes in Headwater Riparian Seeps with Time-Lapse Electrical Resistivity.
Delineating hydrologic and pedogenic factors influencing groundwater flow in riparian zones is central in understanding pathways of water and nutrient transport. In this study, we combined two-dimensional time-lapse electrical resistivity imaging (ERI) (depth of investigation approximately 2 m) with hydrometric monitoring to examine hydrological processes in the riparian area of FD-36, a small (0.4 km2) agricultural headwater basin in the Valley and Ridge region of east-central Pennsylvania. We selected two contrasting study sites, including a seep with groundwater discharge and an adjacent area lacking such seepage. Both sites were underlain by a fragipan at 0.6 m. We then monitored changes in electrical resistivity, shallow groundwater, and nitrate-N concentrations as a series of storms transitioned the landscape from dry to wet conditions. Time-lapse ERI revealed different resistivity patterns between seep and non-seep areas during the study period. Notably, the seep displayed strong resistivity reductions (∼60%) along a vertically aligned region of the soil profile, which coincided with strong upward hydraulic gradients recorded in a grid of nested piezometers (0.2- and 0.6-m depth). These patterns suggested a hydraulic connection between the seep and the nitrate-rich shallow groundwater system below the fragipan, which enabled groundwater and associated nitrate-N to discharge through the fragipan to the surface. In contrast, time-lapse ERI indicated no such connections in the non-seep area, with infiltrated rainwater presumably perched above the fragipan. Results highlight the value of pairing time-lapse ERI with hydrometric and water quality monitoring to illuminate possible groundwater and nutrient flow pathways to seeps in headwater riparian areas.
Mark R
MR
Williams
Pasture Systems & Watershed Management Research Unit, USDA-ARS, 3702 Curtain Road, University Park, PA 16802.
Anthony R
AR
Buda
Department of Hydrologic Science and Engineering, Colorado School of Mines, Golden, CO 80401.
Kamini
K
Singha
Pasture Systems & Watershed Management Research Unit, USDA-ARS, 3702 Curtain Road, University Park, PA 16802.
Gordon J
GJ
Folmar
Department of Agricultural & Biological Engineering, The Pennsylvania State University, 111 Hastings Road, University Park, PA 16802.
Herschel A
HA
Elliott
Champaign Research Center, DuPont Pioneer, 985 County Road 300 East, Ivesdale, IL 61851.
John P
JP
Schmidt
D004784:Environmental Monitoring; D060587:Groundwater; D062070:Hydrology; D009566:Nitrates; D010414:Pennsylvania; D060753:Water Quality
D009566:Nitrates