The effect of technogenic contamination on carbon dioxide emission by soils in the Kola Subarctic

Abstract

Carbon dioxide emission (CO2) is the most important part of carbon turnover, which characterizes the biological activity of soils. This parameter was investigated in background ecosystems and those that have undergone atmospheric contamination in the subarctic zone of the Kola Peninsula, the large industrial region. The Pechenganikel’ plant located in the region is the largest source of sulfur dioxide and heavy metals in northern Europe. Long-term contamination by its waste products has resulted in a technogenic digression of forest ecosystems: destruction and death of the tree layer, poorer species composition of phytocenoses, lower soil biota activity, soil contamination, disturbance of biogeochemical cycles of elements, and a drop in ecosystem productivity. Technogenic wastelands have been formed near the plant. Field studies have shown a slowing down of CO2 emission by soils in situ from 190–230 C–CO2/m2 h in the background pine forests to 130–160 mg C–CO2/m2 h in pine forests at the defoliation stage, to 100 mg C–CO2/m2 h in a technogenic pine thin forest, and to 5–20 mg C–CO2/m2 h in technogenic wastelands. CO2 emission from soils is more intensive in birch forests when compared to pine forests, and there is a tendency to decrease with soil contamination from 290 mg C–CO2/m2 h in the background soils to 210–220 mg C–CO2/m2 h in birch forests at the defoliation stage and to 170–190 mg C–CO2/m2 h in technogenic thin forests. The CO2 emission by soils of technogenic thin soils and wastelands differs significant from the background levels. Soil CO2 emission is characterized by a great spatial variability within biogeocenoses. It becomes lower in pine forests upon a rise in soil contamination. Soil respiration (CO2 emission) shows the total production of carbon dioxide as a result of autotrophic (plant roots) and heterotrophic (soil microorganisms and animals) respiration. A decrease in part of the root respiration, contrary to soil contamination, was revealed in the region for the first time: it comprises from 38–57% in the background forests to 0% in wastelands. This is evidence that plants in biogeocenoses die first, while microorganisms are more resistant. Correlation analysis shows that soil respiration, and the role of roots in it, are directly related to the distance from the plant, the mass of small roots, and the content of carbon and nitrogen. An adverse correlation is seen for the content of available nickel and copper compounds in soils. The remediation of technogenic wastelands has favored intensification of biological activity of the soils. Soil respiration becomes more active, and the role of roots in it is more effective under willow plantations with grass cover formed on man-made fertile soil layer than in contaminated soils after lime and fertilizer application (chemo-phytostabilization).