Effects of Oil Pollution on Water Movement in Soils with Different Textures

Exploring water movement characteristics in oil-polluted soils could facilitate the understanding of soil stress resistance. The aim of the present study was to evaluate the effects of oil pollution on water movement in soils with different textures and explore the underlying mechanisms. A heavy loam (Earth-cumuli-Orthic Anthrosols, EOA), a light loam (Hapli-Ustic Cambosols, HUC), and a sandy loam (Usti-Sandic Primosols, USP) were spiked with different levels of crude oil (0, 0.5, 1, 2, and 4%, w/w). Soil water movement parameters, including saturated hydraulic conductivity, unsaturated hydraulic conductivity, and specific water capacity were measured. Soil water availability under different levels of oil pollution was also analyzed. According to the results, saturated hydraulic conductivity of all three soils decreased with an increase in the level of oil pollution, as did the unsaturated hydraulic conductivity of HUC and USP. Under 4% oil pollution, the saturated hydraulic conductivity of the EOA, HUC, and USP decreased by 52.8%, 81.7%, and 39.6%, compared with their respective unpolluted soils, while the unsaturated hydraulic conductivity of HUC and USP decreased by 78.0% and 39.9% at 20% soil water content. In addition, the unsaturated hydraulic conductivity of EOA decreased with an increase in oil pollution level when the soil water content was >25%; however, a reverse trend was observed at soil water content <25%. The specific water capacity of all soils increased first and then decreased with an increase in water suction, while it decreased with an increase in the level of oil pollution. The suction ranges corresponding to the available water content in the three soils were reduced by oil pollution, and the corresponding water-holding capacities were weakened. Oil pollution had major negative impacts on water movement in the soils with different textures, causing a decline in water infiltration and supply capacities, which could hamper soil drought resistance. However, the effects of soil texture on water movement were greater than the effects of oil pollution under the experimental conditions.