Summary of Iuliias work
Permafrost-affected environments are characterized by slow biogeochemical cycles due to their low temperatures. The slow rates of biogeochemical processes in Arctic landscapes lead to a high susceptibility to contamination and to a low pollution resistance. Trace metals are one of the major groups of industrial pollutants and can reach the Arctic by different paths, namely through local human activity and via long-range atmospheric transport. At present, the knowledge about the background levels of trace metals and their behavior in soils of the Arctic Regions is very limited, and in particular research is needed to understand the effect of permafrost conditions on trace metal mobility and distribution. This question is particularly interesting in the light of anticipated changes of climatic conditions. The predicted temperature increase in the Arctic region may lead to an increase of the annual thaw depth of the soils and a change of the groundwater table, which may affect the spatial distribution of contaminants. Therefore, there is a special need to study the processes that govern trace metal distribution in soils affected by permafrost. This knowledge may also help to gain more information about the ecological state of Arctic ecosystems and to estimate possible effects from direct anthropogenic pollution and, subsequently, predicted climate change.
Northeast Siberia represents an area remote from evident anthropogenic trace metal sources. This fact affords an opportunity to investigate trace metal levels in pristine environments. Soil samples from the Lena River Delta region and its hinterland, collected in 2009, 2010, and 2011 were analysed. The element concentrations in studied soils varied greatly ranging, for example, from 0.01 to 0.71 mg kg-1 for Cd, from 0.6 to 65.0 mg kg-1 for Cu, from 0.9 to 55.4 mg kg-1 for Ni, from 2.14 to 38.9 mg kg-1 for Pb, and from 12.1 to 440 mg kg-1 for Zn. It could be shown that the Lena River Delta and its hinterland are pristine and can serve as a reference region for determining human influences on permafrost-affected landscapes.
The obtained results showed that element properties and soil physical and chemical characteristics are one of the major factors controlling the element distribution in studied landscapes. Furthermore, topography features (e.g. microrelief forms) and water drainage are likely to govern more intensive element migration to adjacent landscapes and their accumulation on natural physico-chemical barriers. This study also showed that the accumulation of trace elements by different vegetation types reflects mainly the plant’s biogeochemical characteristics. Furthermore, the soil geochemical composition of natural tundra landscapes presumably controls the element uptake by plants.
A laboratory experiment was performed to determine how the temperature regime affects the contaminant distribution within the soil matrix at the boundary between a contaminated surface soil layer and an uncontaminated deeper soil layer. The hypothesis was that the water transfer to the freezing front will be accompanied by a downward migration of water soluble metals within the soil column. The results of this experiment showed that diffusion along the concentration gradient seemed to be the most important mechanism controlling the migration of water soluble forms of Cd and Pb in unsaturated soils. In the frozen soils, no clear relation between water migration and the metal distribution was found. A decrease of the Cd mobility in the lower parts of the frozen columns in comparison with the unfrozen columns, suggests that frozen soils acted as a temporal geochemical barrier restricting further downward Cd transport. However, the experimental data obtained is still not enough to understand all the mechanisms of transport processes that occur under natural conditions. To gain a better understanding of these mechanisms, further investigations are needed to provide explanations, which which allow to quantitatively asses element transport and could be introduced to existing analytical modelling methods.
The results of this research enable a better assessment of the ecological state of permafrost-affected soils as one of the major components of Arctic ecosystems in changing climatic conditions.