Biodiagnostics of Soil under a Low Level of Anthropogenic Impact (by the Example of the Urban Settlement of Stepnoe, Saratov Oblast)

Abstract

Abstract—Biodiagnostics of soil in a settlement with low technogenic impact was performed by the example of the urban settlement of Stepnoe. The number of microorganisms was evaluated in 30 soil samples by inoculation on solid nutrition media: on meat peptone agar for the calculation of the total heterotrophic microorganisms and on the corresponding selective media for hydrocarbon-oxidizing and iron-oxidizing microorganisms. We also analyzed the activity of several soil redox and hydrolytic enzymes (dehydrogenases, catalases, peroxidases, and invertases). The content of the mobile forms of copper, zinc, lead, cadmium, chromium, and nickel was determined to assess the anthropogenic impact on the soil, and the total soil contamination coefficient (Z_c) was calculated. The excess of the MPC of mobile forms of Ni, Cu, and Pb was revealed in the area studied. In general, the total soil contamination coefficient did not exceed 16, indicating favorable environmental and geochemical conditions in the settlement. The analysis of the total number of heterotrophic microorganisms and the amounts of hydrocarbon-oxidizing and iron-oxidizing microorganisms showed deviations from the norm in some regions of the area surveyed, which pointed to anthropogenic transformation of the soil biocenoses. The maximum deviations were typical for the index of hydrocarbon-oxidizing microorganisms, which pointed to soil contamination by hydrocarbons. Our data on the evaluation of the activity of indicator soil enzymes did not exclude possible functional disturbances in the soil. It was found that the activity of soil dehydrogenases and invertases corresponded to low and very low levels of soil enrichment with these enzymes. The activity of soil catalases and peroxidases corresponded to the moderate and high levels of the enzymes, which indicated the absence of pathological changes in the soil. It has been shown that the studied soil microbiological and biochemical parameters are promising for soil health biodiagnostics in areas with low anthropogenic impact.