Enzyme Activity of Oil-Contaminated Chernozem and Soddy-Podzolic Soil

The enzyme activity of oil-contaminated chernozem and soddy-podzolic soil is assessed for a set of 20 enzymes in the arable horizon of ordinary chernozem and the humus-accumulative horizon of soddy-podzolic soil under forest. Oil (1, 5, and 10%) is added to the soil to simulate hydrocarbon contamination. For this purpose, the activities of 20 oxidoreductases and hydrolases involved in the biogeochemical cycles of C, N, O, P, and S were determined. Cellulase and cysteine reductase are the most sensitive to the oil contamination of ordinary chernozem and adenosine triphosphatase and nitrate reductase, of soddy-podzolic soil. All studied enzymes (except for protease and β-glucosidase in ordinary chernozem) appear highly informative, displaying a tight correlation with the oil content in soil (r > 0.65). The integral index of enzyme activity (IIEA), geometric mean (GMEA), and integral pollution index (AP) are calculated. Of the integrated characteristics, IIEA (r = –0.9 to –0.98) and GMEA (r = –0.98 to –0.99) are highly informative for both soils, whereas AP is poorly informative for soddy-podzolic soil (r = –0.46). IIEA and GMEA are recommended for enzyme diagnostics of the soil ecological state after oil pollution. The impact of oil contamination on the N, P, and C cycles is stronger than that on the S and O cycles. In the case of oil contamination, C-cycling (invertase, polyphenol oxidase, and dehydrogenases), N-cycling (urease), P-cycling (acid and alkaline phosphatases), and O-cycling (catalase and peroxidase) enzymes display the highest mean applicability score for soil health assessment. The enzyme assessment is effective and helpful for assessing the ecological state of soils contaminated with oil hydrocarbons.