Soil Isotopic Signatures in the Diagnostics of Aridization Processes in Landscapes of the Republic of Dagestan

摘要

The planetary climate system is currently unstable, and its challenges manifest themselves primarily in 'marginal' parts of the biosphere, including mountain landscapes. Mountain ecosystems in arid regions are especially susceptible to natural or anthropogenic external impacts, and their recovery after disturbances takes the longest amount of time. The purpose of this study was to examine the natural and specific features of impacts exerted by climatic and anthropogenic factors alternating with each other or acting cumulatively throughout the Holocene on the ecosystems of Inner Dagestan with the stable isotope technique and to assess their contributions to the modern progressive aridization of landscapes in the eastern Caucasus. The soil cover in vertical zones (2000-4000 m a.s.l. (Baltic Elevation System)) of the eastern Caucasus was studied in the Akhtyn district, Inner Dagestan, in areas affected by different types of economic activity (pastures of varying grazing intensity, hayfields, and natural meadows). The following soil parameters were determined: general chemical properties (actual acidity and carbon and nitrogen content), magnetic susceptibility, humus state of the soils, isotopic composition of carbon (delta C-13) and nitrogen (delta N-15) (via mass spectrometry), and soil age (via humus radiocarbon dating). It is established that the conditions of dynamic soil formation result in the appearance of a polygenetic soil cover: the epochs of surface stabilization correspond to buried horizons and soils, while epochs of exogenesis activation correspond to layers with an elevated rubble content and rocky horizons. Like exposed and buried horizons, buried soils of different ages have contrasting properties. This indicates that different epochs of buried soil formation featured different climatic conditions: arid epochs of the early Boreal and Atlantic optima of the Holocene cyclically alternated with colder and more humid ones, while the medieval optimum featured a temperate climate similar to the modern one. The Little Ice Age was not clearly pronounced in Inner Dagestan. However, the identified climate humidification trend is negated by the 'steppification' of landscapes as a result of their anthropogenic use.