Role of hydrothermal conditions in the formation of water-stable aggregates in brown mountain forest soils

Abstract

The patterns of formation and stability of water-stable aggregates in brown mountain forest soils under changing hydrothermal conditions are examined through the example of the Pirgulu Biogeographical Station of the Institute of Geography of the Ministry of Science and Education of the Republic of Azerbaijan. The research goal was to evaluate the influence of soil temperature and moisture on the structural and aggregate state of soils and their resistance to degradation processes. The research targets were brown mountain forest soils classified as Leptic Calcic Cambisols (Clayic). The research was based on a set of field and laboratory studies. The content of water-stable aggregates larger than 0.25 mm was determined using the method of I.N. Savinov. Thermo-moisture conditions were characterized using the data from ground-based meteorological observations as well as the ERA5 global reanalysis dataset produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) with a spatial resolution of 0.25° × 0.25° and a temporal resolution of 6 hours. The research findings showed that soil moisture and temperature exhibited pronounced seasonal and vertical variability which significantly affected aggregation and disaggregation processes. The upper soil horizons are characterized by a higher proportion of large and water-stable aggregates providing favorable water-air conditions. With increasing depth, the proportion of water-stable aggregates decreases due to soil compaction and reduced biological activity. It was found that an increase in mean annual temperature led to a reduction of the content of water-stable aggregates, whereas an optimal range of accumulated active temperature (1000-2000°C) promoted the maximum structural stability. Extreme thermal and moisture conditions negatively affect soil structure increasing the risk of soil degradation and erosion. The obtained results are of scientific and practical importance for evaluation of the ecological stability of mountain forest soils and development of sustainable soil management strategies under the conditions of climate change.