Effects of crude oil on the biological activity of chernozem soils

Abstract

The article investigates the effect of crude oil on soil microorganisms and the enzymatic activity of chernozem soils. Experiments were carried out on podzolized medium loamy chernozem in the Samara region using high-sulphur crude oil of medium density. Per 1 kg of soil, 10.00 g (1%), 30.00 g (3%) and 50.00 g (5%) of oil were applied. According to the obtained results, the native soil microbiota contains a wide variety of microorganisms capable of oxidizing both individual hydrocarbons and crude oil in general. Bacteria of the Acinetobacter, Bacillus, Mycobacterium, Pseudomonas and Streptomyces genera, filamentous fungi of the Aspergillus and Penicillium genera, as well as Candida yeast showed the greatest activity in the degradation of both individual hydrocarbons and crude oil in general. The soils freshly polluted with oil demonstrated an increase in the number of bacteria that consume organic forms of nitrogen, actinomycetes, fungi and hydro-carbon-oxidizing microorganisms. In addition, a growing trend in the number of autochthonous microorganisms participating in the mineralization of humic substances was observed. Following 3 months of experiments, a decrease in the number of bacteria consuming organic forms of nitrogen and actinomycetes was revealed. The number of fungi showed the most pronounced decrease upon addition of 3 and 5% of oil, while the number of autochthonous microorganisms participating in the mineralization of humic substances and hydrocarbon-oxidizing microorganisms grew with an increase in the degree of oil pollution. Inhibition of various microorganisms by means of physical or toxic action of hydrocarbons contained in crude oil can cause a decrease in the activity of enzymes present in chernozem soils. Oil hydrocarbons inhibit the activity of polyphenol oxidase, catalase, invertase, phosphatase and lipase present in chernozem soils, although slightly stimulating the peroxidase activity. A decrease in the soil humification coefficient indicates that the oxidation of humic substances prevail over the decomposition of organic aromatic compounds into soil humus components, as well as a decrease in soil fertility as a result of its contamination with crude oil hydrocarbons.