Tillage effect on hydrophobicity and hydrological properties of oil-contaminated sediments in a hyper-arid region

Abstract

A crude oil spill in 2014 led to the contamination of an extensive area in the Evrona Nature Reserve at the hyper-arid Arava Valley of Israel. In 2015, as a part of the restoration efforts, the oil-polluted braided ephemeral stream channels underwent a single session of tillage, to a depth of 10 cm. The rationale of this treatment was to break the hard, impermeable crust of the residual oil, aiming to reduce soil hardness and water repellency, and to improve the hydrological properties of the soil. In 2017, a study was conducted to assess the effect of chiseling tillage on the soil's hydrophobicity, mechanical strength, and infiltration capacity. Water drop penetration time, critical surface tension, penetration resistance, and near-saturated hydraulic conductivity were measured on-site, at depths of 0, 5, and 10 cm in contaminated-tilled, contaminated-non-tilled, and clean plots. We found that at the ground surface, tillage had a slight and non-significantly positive effect on the nearly-saturated hydraulic conductivity and a negative effect on the penetration resistance, while no improvement was recorded for the other properties. Further, some of these properties were inferior in the contaminated-tilled sediments compared to those in the contaminated-non-tilled sediments, an effect that could be attributed to the: (1) tillage-induced inversion of the most polluted surface layer into the sub-soil, (2) absence of a clayey sublayer, and (3) limited oil degradation due to the extremely dry conditions. Therefore, the results indicate that tillage is not an effective practice for restoring oil-polluted soils and sediments in hyper-arid regions.