Soils and Carbon Pools on Shungite Rocks of South Karelia under Different Types of Land Use

Abstract

Azonal organo-accumulative soils (Umbrisols) on shungite rocks and the influence of type of land use on their properties and ecosystem carbon stocks were investigated. Сhanges in soil profile structure, basic agrochemical and microbiological indicators of upper horizons, Corg and Cmik stocks in a meter layer of soils and sites carbon pool structure were analyzed. Pine forest as a control, arable land, hayfield, as well as young alder and middle-aged mixed forest were studied. Land use change does not lead to a significant transformation of the properties of shungite soils in contrast to zonal soils. The removal of stones has the greatest influence, leading to the formation of developed arable horizons. The soils are characterized by a high stony, a weak-divided thin profile, low density values, and a pH close to neutral. The wide range of Corg content values from 1.6% to 11.7% is due to the heterogeneous composition of parent rocks. Agricultural development contributes to the accumulation of exchangeable bases, available potassium and phosphorus, the content of which are initially increased in schungite soils. All sites are characterized by a high rate of organic matter mineralization (C/N ratio not higher than 17). A small content of Cmic (84–245 mg C/kg) was noted in the soils, which may be due to the low availability of substrate because of lithogenic origin of carbon and the increased concentrations of heavy metals and lanthanides in schungite rocks. The structure of Corg and Сmic stocks depends on carbon content, keep of stones and presence of dense bedrock. Soil organic carbon stocks range from 17–251 t C/ha, while Cmic stocks range from 6–43 g C/m2. The total ecosystem carbon stocks are maximum in hayfield (259 t C/ha) and minimum in young forest (74 t C/ha). The stocks of carbon in the sites of arable land, middle-aged and control forests are within 169–211 t C/ha.