Assessment of the ecological state of soil above an underground natural gas storage using bioassay

Soils in areas of underground natural gas storage facilities (UGS) can become contaminated with hydrocarbons, which impacts negatively on soil properties and functions of soil biocenosis. The purpose of this study was to biodiagnose soil samples from the territory of an UGS (Stepnoye district, Saratov region) using bioassay. For microbiological analysis of the soil samples, the following parameters were selected: The total number of heterotrophic microorganisms, the content of hydrocarbon-oxidizing and methylotrophic bacteria, as well as the number of iron-oxidizing bacteria given that in the area of this natural gas storage facility clusters of bacteriomorphic magnetite may have been formed. Dehydrogenase, catalase and β-fructofuranosidase activities were studied as informative and sensitive indicators. The biodiagnostic results showed reduced levels of heterotrophic microorganisms in the soil samples from the area of this UGS compared to the background samples obtained outside the UGS. A high content of indicator organisms: Hydrocarbon-oxidizing and methylotrophic bacteria, not only facultative, but obligate was observed in some soil samples which suggests the emission of methane into the upper layers of the soil. The presence of iron-oxidizing microorganisms in the soil samples was confirmed by an increased activity of dehydrogenases and catalases. The observed correlations between the studied biological and physico-chemical parameters of soil confirmed the presence of hydrocarbon pollution.   Key words: Underground gas storage, bioassay, soil microorganisms, soil enzymes, magnetic susceptibility.