Assessing changes in physical and biological properties in a soil contaminated by oil sludges under semiarid Mediterranean conditions

Abstract

We have studied the changes in biological and physical properties of a soil, in a semiarid area, contaminated by hydrocarbons in order to predict the potential for bioremediation of this soil. The microbial biomass C, the basal respiration and the metabolic quotient ( qCO 2) of contaminated soil were significantly higher than that of the control soil, which points to a markedly reduced efficiency of substrate use and to a possible toxic effect of hydrocarbons in the soil. The low global rate of mineralisation in the contaminated soil also indicates the presence of hydrocarbons resistant to biodegradation. The dehydrogenase activity and the activities of hydrolases involved in the N and P cycles (urease, protease and phosphatase) were stimulated by the contamination with hydrocarbons. Soil total porosity was increased by the contamination, about 15-fold in comparison with the control soil. The contamination by hydrocarbons led to an increase in cracks in the 100–200 μm size classes, which can be regarded as a reservoir to hold water for plants and microorganisms. The biodegradation of hydrocarbons in this soil would require long periods of time, and it would be advisable to apply methods of bioremediation to this contaminated soil.