Microbial characteristics of soils depending on the human impact on archaeological sites in the Northern Caucasus

Abstract

Anthropogenic impact in prehistoric settlements results in a considerable alteration of soil microbial communities depending on intensity and the character of human activities. This paper present a case study from a Late Bronze Age settlement located in the high-mountain part of the North Caucasus (Russia). The site represents a community, which presumably specialized in intensive livestock herding. Samples from settlement soils anthropogenically affected in the past and unmodified background soils were taken and studied. Of particular interest were divergences in soil microbial communities, expected to indicate different activities and animal presence in the site. The total microbial biomass, their respiratory activity, the biomass of fungal mycelium and the proportion of dark-colored hyphae were determined, as well as the quantitative state of keratinophilic fungi.The microbial characteristics vary considerably within the settlement locations, and contrast sharply with the reference soils exterior to the archaeological site. The cultural layer has higher percentage of active metabolizing microorganisms, whereas the total microbiological biomass is considerably lower than in the unmodified soils from the surroundings. A determining factor to transform the respiratory activity of microorganisms, in both qualitative and quantitative aspects, is the composition of the organic material which has been accumulated in the ground as a result of various human activities in the past. The cultural layers contain microorganisms, which can be reactivated when glucose is added. In the anthropogenically unmodified soils surrounding the prehistoric settlement, in contrast, 97% of the cells cannot be reactivated. Based on the mycological characteristics of the studied cultural layers and unmodified soils, in particular with regard to the total biomass of fungi mycelium, the dark pigmented fungal biomass, and the existence of keratin-decomposing soil fungi, detailed information about activity areas and their specific usage is given. The use of bio-indicators allows not only diagnosing anthropogenic impact in soils as such, but also significantly complements description of cultural layers of activity areas in the settlement, specifying their purpose. The paper presents the microbiological analyses applied and, moreover, discusses the potential of this approach as a non-destructive prospecting method on archaeological sites.