Influence of contamination with diesel oil on water sorptivity and hydrophobicity of sandy loam soil

This paper shows the changes in water sorptivity (S-w) and hydrophobicity following soil contamination with petroleum hydrocarbons (PHs) under different soil moistures. Laboratory experiments were carried out to verify that contamination with PHs reduces S-w, thus affecting the infiltrability, which in practice influences the field water capacity and the availability of water for plants. Soil water repellency (SWR) was estimated by the repellency index (R) and water drop penetration time (WDPT). The increase in PHs contamination contributed to SWR and caused a significant decrease in S-w. With the decrease in moisture, the water sorptivity of the soil increased, reaching its maximum at 0.12-0.15 cm(3) cm(-3), which was the threshold value in the case of the analysed soil, and then decreased drastically. The R index and the WDPT revealed a similar trend, inversely related to the level of soil contamination with PHs. The increase in SWR and the accompanying decrease in S-w made the soil less resistant to drought. The total amount of water available to plants in the control soil was 19.04%, whereas contamination with PHs equal to 100 g kg(-1) caused a decrease to 6.36%. The almost threefold decrease in the total amount of water has a fundamental influence on increasing the risk of soil drought. The results obtained indicated that the interrelationship presented between the level of contamination with PHs, water sorptivity, SWR and soil moisture are the keys to predicting the environmental effects of contamination with PHs. The obtained results indicate that the undertaken remediation measures aimed at restoring the hydrological function of the soil system should be preceded by an assessment of soil hydrophobicity.