Electrical geophysical monitoring of subsurface solute transport in low-relief agricultural landscapes in response to a simulated major rainfall event

Authors: THOMPSON, JOSHUA - Rutgers University; Buda, Anthony; SHOBER, AMY - University Of Delaware; NTARLAGIANNIS, DIMITRIS - Rutgers University; COLLICK, AMY - Morehead State University; Kennedy, Casey; MOSESSO, LAUREN - Environmental Protection Agency (EPA); Reiner, Michael; TRIANTAFILIS, JOHN - Landcare Research; POKHREL, SAPANA - University Of Delaware; SLATER, LEE - Rutgers University

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2024
Publication Date: 11/16/2024
Citation: Thompson, J., Buda, A.R., Shober, A., Ntarlagiannis, D., Collick, A., Kennedy, C.D., Mosesso, L., Reiner, M.R., Triantafilis, J., Pokhrel, S., Slater, L. 2024. Electrical geophysical monitoring of subsurface solute transport in low-relief agricultural landscapes in response to a simulated major rainfall event. Journal of Hydrology. 646,132313. https://doi.org/10.1016/j.jhydrol.2024.132313
DOI: https://doi.org/10.1016/j.jhydrol.2024.132313

Interpretive Summary: Describing the hydrologic pathways that connect farm fields with surface waters is essential to controlling phosphorus losses from agriculture. Such knowledge is especially vital in flat landscapes with open ditch drainage, where the bulk of phosphorus transport often occurs in subsurface groundwater flow. In this study, we injected a conductive salt tracer into shallow groundwater and then simulated a large rainstorm with a sprinkling system. During the storm, we used advanced electrical sensing methods to track the movement of the tracer over time. Results showed that groundwater preferred to move rapidly through a thin layer of coarse gravels embedded within the fine sandy aquifer materials. The speed of tracer transport in the preferential groundwater flow path approached 50 feet per day, while transport through the surrounding fine sands covered the same distance in about a year. Findings show that subsurface transfers of water and associated nutrients like phosphorus can be rapid, even in flat agricultural fields, which has key implications for nutrient management in these settings.

Technical Abstract: The Delmarva Peninsula contributes significantly to nutrient loading of the Chesapeake Bay predominantly from excessive Phosphorus (P) historically applied to low-relief agricultural fields with artificial drainage. Subsurface P transport is recognized as a primary pathway for P loss from the artificially drained agricultural systems, especially during high intensity rainfall events. This study used time-lapse electrical resistivity imaging (ERI) to monitor an ionic (salt) tracer in a low-relief, artificially drained agricultural field with a sprinkler system to simulate a 20-year rainfall event for Princess Anne, MD. Conductivity breakthrough curves (BTCs) from the time-lapse electrical datasets were compared against relative concentration BTCs of a solute transport model. The results show rapid lateral transport via high permeability pathways within the experimental plot, emphasizing the role of soil heterogeneity in the potential for subsurface P transport during high intensity rainfall events. The critical sources areas for P loss, where high soil P concentrations coincide with hydrologic connectivity with ditch waters, have the potential to be farther from the field edges than previously recognized. The heterogeneous nature of the agricultural field soils and locations of critical source areas can inform existing nutrient management decisions.