Subsurface sediment transport in the shallow vadose zone of fine-textured soils with heterogenous preferential flows

Authors: FORD, WILLIAM - University Of Kentucky; Williams, Mark; MUMBI, ROSE - Purdue University

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2024
Publication Date: 11/10/2024
Citation: Ford, W.I., Williams, M.R., Mumbi, R.C. 2024. Subsurface sediment transport in the shallow vadose zone of fine-textured soils with heterogenous preferential flows. Hydrological Processes. https://doi.org/10.1002/hyp.15327.
DOI: https://doi.org/10.1002/hyp.15327

Interpretive Summary: Rainfall intensity and soil moisture are known to influence surface soil erosion, but there is not very much information on how these factors influence sediment transport through the soil profile to tile drains. In this study, we conducted seven laboratory rainfall simulations on undisturbed soil columns (1ft3) to determine the effect of rainfall intensity and soil moisture on surface and subsurface erosion. Results showed that sediment leachate concentration and loss was related to the filtration capacity of the soil columns, with more that 2/3rd of the sediment loss from a single soil column despite similar leachate volumes. Higher rainfall intensity resulted in greater sediment loss compared to low rainfall intensity. When soils were covered to prevent surface erosion from occurring, subsurface erosion was very small, but dry and wet soil moisture conditions were equally important for sediment loss. Findings highlight the importance of soil cover such as residue and cover crops for decreasing subsurface sediment loss and how future weather patterns may influence sediment delivery to tile drains.

Technical Abstract: Subsurface sediment transport in tile-drained landscapes occurs through macropores; however, little is known regarding how heterogeneous preferential flows influence fluxes. Generally, it’s well recognized that surface erosion is heavily influenced by rainfall intensity and subsurface erosion of macropores is strongly influenced by antecedent rainfall conditions. We performed laboratory rainfall simulations on ten in-tact core lysimeters from a tile-drained field in Indiana, USA to study the impacts of surface and subsurface erosion on sediment leachate in heterogeneous preferential flow paths. Seven rainfall simulations were conducted to assess the impact of rainfall intensity on leachate of surface eroded sediments (three-events), and the impact of antecedent conditions on subsurface eroded sediments (four events). Three lysimeters with negligible flow during the initial rainfall intensity study received large artificial macropores prior to subsurface erosion simulations to enhance hydrologic connectivity. Sediment concentrations and flowrates were measured, and flow weighted mean concentrations and sediment yield were calculated for each lysimeter in each event, as well as the collective flux from all lysimeters. Analytical methods included cumulative sediment yield, linear mixed effects modeling, and hysteresis analysis. Results were presented in a series of four case studies. Results showed that sediment leachate concentration and yield was tightly linked to filtration capacity of lysimeters, with more than 2/3rd of sediment originating from a single lysimeter despite similar flow contributions from each. Rainfall intensity had a significant impact on transport of surface eroded sediment with the greatest concentrations and loadings during the high-intensity event. Nevertheless, we observed negative feedback between rainfall intensity, and subsurface sediment leachate, likely due to enhanced turbulent mixing within macropores at greater velocities. Subsurface sediment erosion from natural macropores was low compared to surface soils but we found alternating controls on sediment concentrations at both low and high antecedent moistures that were equally important to sediment leachate yields. Artificial macropores produced comparable sediment yields to surface erosion. These large macropores behaved similarly to soil pipes in terms of erosion mechanics and could be important features in areas that experience tile blowouts. Hysteresis results generally highlighted contrasting results for surface and subsurface sources but suggest that prominence of slow-flow, low concentration water sources may strongly influence interpretation of results in field-scale applications.