Micromorphological features of organic and mineral parts of tundra soils in the Lena river delta

Abstract

The aim of the study was to define the unique micromorphological properties and mechanisms responsible for the development of stable organomineral pedofeauteres in the soils of the Lena River Delta.

Location and time of the study. The study area is located on Samoylovsky Island and a newly formed, Ivovyi island in the Lena River Delta, Yakutia, Russia. Fieldwork was conducted during the summer field season of 2021.

Methods. Standard micromorphological methods were employed for soil analysis. Determination of minerals took place on polarisation microscope Leica DM750P, calculation of organomineral particles took place in software complex ImageJ ver. 1.54m.

Results. This study identified key patterns in the influence of cryogenesis and river activity on soil formation within the first terrace of the Lena River delta. On micromorphological level it was revealed that soils under river influence are characterized by large organomineral aggregates composed of thin organic matter, quartz, mica, and undecomposed plant residues. The formation of these organomineral aggregates is attributed to active humification of plant residues and a limited influence of cryogenesis. Soils out of the active floodplain exhibit a prevalence of undecomposed plant residues, indicating slow rates of organic matter transformation. Under the conditions of degradation of polygonal structures, active processes of cryogenic mass exchange and cracking are observed, which lead to the destruction of the organomineral matrix of soils and release of organic matter from the frozen state. According to the assessment of physical stabilisation of SOM, it was found that the degradation of polygonal structures can lead to a reduction in the stable carbon pool in soils due to the active occurrence of cryogenic processes, thus increasing the potential labile carbon pool, which can be subject to biodegradation.

Conclusions. As a result of the river action and cryogenic processes in the Lena River delta there is a significant transformation of soils, which is associated with the features of organic matter accumulation and formation of organomineral matrix of soils. The analysis of soil microstructure composition has shown that in soils under the active influence of the river the formation of organomineral pedofeatures takes place, despite the low degree of elaboration of the material. In soils out of annual flooding, thermokarst processes result in the release of soil organic matter, which increases the risk of biodegradation. Permafrost degradation demonstrates the vulnerability of cryogenic soils to carbon loss under climate change.