Trace elements accumulation in cryoconites and periglacial soils of the Central Caucasus

The problem of retreating glaciers is pronounced in almost all high-altitude and high-latitude landscapes. Black carbon is considered as one of the most important pollutants that contributes to global climate change and the melting of glaciers, especially in polar and mountainous regions due to formation of cryoconite. It is a supraglacial sediment which represents a mixture of black carbon, mineral particles and organic matter. Cryoconites are considered as accumulators of various pollutants such as polycyclic aromatic hydrocarbons, trace elements and radionuclides, which can be transported by aeolian and water flows to the downstream ecosystems and affect the safety of the region both directly and indirectly, through the cultivation of crops and grazing. Moreover, cryoconites considerably reduce the albedo of the glacier and take part in formation of primary soils after its retreat which is especially important in the context of global climate change.

The main purpose of this research is to study the pollution of cryoconites, other sediments and soils by trace elements at the Central Caucasus mountainous region, Russia. Cryoconite, moraines and mudflows were sampled from the biggest valley glacier at the Caucasus mountains, Bezengi Glacier; cryoconite derived soils were collected from the Khulamo-Bezengi Gorge. Chernozems and fresh mudflow samples were collected at Baksan Gorge. Trace elements content was determined by flame and electrothermal atomic absorption spectrometric method according to the standard ISO 11047-1998 at Atomic absorption spectrophotometer. We determined concentrations of Cu, Pb, Zn, Ni, Cd due to the facts that they are the most toxic for human health as well as they are mostly accumulated in a black carbon.

High concentrations of Zn (70.9 mg/kg) and Pb (30.0 mg/kg) in cryoconites have been determined on the Bezengi Glacier, which may be due to both local human activities and allochthonous pollution associated with the arrival of contaminated air masses from other regions. The content of Cu (max. 17.4 mg*kg), Ni (max. 19.0 mg*kg) and Cd (max. 0.052 mg*kg) was relatively low. However, concentrations of Zn (max. 89.2 mg*kg) and Cd (max. 0.313 mg*kg) in cryoconite derived soils were higher than in cryoconite which indicates high input of polluted material from the glacier into downstream ecosystems. The highest level of pollution with some trace elements has been determined in fresh mudflow: Cu = 40.7 mg*kg, Zn = 89.3 mg*kg, Ni = 42.0 mg*kg which also indicates that sediments act as a source of pollutants for mountain ecosystems. Pollution of Chernozems with trace elements was higher than in moraine sediments, however, it was lower than in cryoconites which shows possible impact of these sediments on pollution status of soils in mountainous region.

This work was supported by Russian Foundation for Basic Research, project No 19-05-50107 “The role of microparticles of organic carbon in degradation of ice cover of polar regions of the Earth”.