Dye tracers reveal potential edge-flow effects in undisturbed lysimeters sealed with petrolatum

Authors: Williams, Mark; McAfee, Scott; Kent, Brittany

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2019
Publication Date: 8/29/2019
Citation: Williams, M.R., McAfee, S.J., Kent, B.E. 2019. Dye tracers reveal potential edge-flow effects in undisturbed lysimeters sealed with petrolatum. Vadose Zone Journal. 8:190040. https://doi.org/10.2136/vzj2019.04.0040.
DOI: https://doi.org/10.2136/vzj2019.04.0040

Interpretive Summary: Undisturbed soil lysimeters, also known as soil columns, are commonly used to study water and nutrient transport through the soil in a laboratory setting. Unnatural preferential flow can occur during leaching experiments at the interface between the soil and the lysimeter casing that is typically made of either steel or PVC. This edge flow can produce unrealistic results. The purpose of this study was to test the effectiveness of petroleum jelly in limiting flow along the inside edge of the lysimeters. Dye tracers were used to visualize the flow pathways through the soil during a rainfall simulation using lysimeters that were either unsealed or sealed with petroleum jelly. As expected, unnatural preferential flow occurred along the edge in the lysimeters that were not sealed. The petroleum jelly limited flow between the soil and the lysimeter casing, but cracks that formed in the soil where the petroleum jelly had infiltrated resulted in a 'new' edge that created in preferential flow. Findings suggest that when using petroleum jelly to limit edge flow, soil moisture must be maintained in order to prevent soil cracking and unnatural preferential flow pathways through the soil.

Technical Abstract: Undistributed soil lysimeters are widely used to study water and solute transport. During or following lysimeter collection, it is common to implement measures aimed at limiting edge-flow at the interface between the soil and the lysimeter casing. The objective of this study was to evaluate the effectiveness of petroleum jelly in suppressing edge-flow in lysimeters using dye tracers. Eight undisturbed lysimeters (900 cm2) with removable spacers lining the inside of the casing were collected from an agricultural field. Spacers were removed from four lysimeters and liquified petroleum jelly was poured into the gap created after spacer removal. Lysimeters air dried over 150 d when two sealed and two unsealed lysimeters were re-saturated. All lysimeters were then subjected to a 1 h rainfall simulation (3.3 cm h-1), with dye added to the rainfall. Rewetting both sealed and unsealed lysimeters resulted in less horizontal dye coverage compared to the dry treatments likely due to reduced matrix-macropore interaction. Dye staining patterns for unsealed lysimeters showed that edge-flow was the predominant flow pathway through the soil regardless of soil moisture status. While sealing lysimeters with petroleum jelly largely limited flow between the soil and the casing, shrinkage cracks formed during drying that coincided with the extent of petroleum jelly infiltration into the soil. This new hydrophobic edge served as a preferential flow pathway in the sealed lysimeters under both dry and rewetted conditions. Findings suggest that maintaining adequate soil moisture before and after petroleum jelly addition is critical to avoiding edge-flow in sealed lysimeters.