Relationship between the severity, persistence of soil water repellency and the critical soil water content in water repellent soils

Soil water repellency (SWR) causes reduced soil water storage and enhanced runoff and reduced ecosystem productivity. As such, characterization of SWR is a prerequisite for effective environmental management. The objectives of this study were to determine the relationship between the severity of SWR and its persistence and to determine the soil critical water content (CWC). Soils were collected from thirteen soil sites; five from natural jack pine (Pinus banksiana) ecosites (AE1, AE2, SV 10, 26 and 27), six from reclaimed/disturbed sites (ALFH, CPA, SS trial, ATS, SCB, and SW30) located in the Athabasca Oil Sands region and two from agricultural sites (Goodale and Melfort) in Central Saskatchewan, Canada. The severity of SWR as a function of persistence was assessed by measuring the change of water drop contact angles (modified sessile drop method) with time (WDPT, water drop penetration time). The CWC was determined for all the soils by measuring water drop contact angles on soils with predetermined water contents from oven dried to 20% (kgkg−1). In natural, reclaimed and agricultural soils, a high severity (contact angle) of repellency does not necessarily denote long persistence (WDPT) or high CWC. Measurement of severity and persistence is related to the differences and changes in surface energy between water and the soil surface respectively. Although the CWC gives us the water content at which above it SWR is negligible, the trend between contact angle and increasing water content proved to be more informative. Characterizing and understanding the severity, persistence and CWC together are valuable when determining the effects of SWR on hydrological processes as they have different mechanisms compared to one another.