Dye Tracers Reveal Potential Edge-Flow Effects in Undisturbed Lysimeters Sealed with Petrolatum

Abstract

Undisturbed 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 use dye tracers to evaluate the effectiveness of petroleum jelly in suppressing edge flow in lysimeters. Eight undisturbed square lysimeters (900 cm) with removable spacers lining the inside of the casing were collected from an agricultural field. Spacers were removed from four lysimeters and liquefied petroleum jelly was poured into the gap created after spacer removal. The lysimeters were air dried for 150 d, after which two sealed and two unsealed lysimeters were resaturated. All lysimeters were then subjected to a 1-h rainfall simulation (3.3 cm h), with dye added to the rainfall. Rewetting both sealed and unsealed lysimeters resulted in less horizontal dye coverage compared with the dry treatments 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 avoid preferential flow along the hydrophobic edge in sealed lysimeters.