Saline soils of the Rostov Lowland (Yaroslavl Volga region): current state, hydrological aspects of salinization and evolution trends in the context of climate change

Abstract

The hydrochemical composition of Lake Nero and its tributary streams is closely related to the soils in the catchment. This paper describes the current state of saline soils on the lakeside lower terraces. On average, the salinity of the soils surveyed in 2016–2018 ranged from 0.2 to 0.3 %. Soil salinization within the poorly drained lakeside part of the Rostov Lowland is confined to flat or low-lying waterlogged areas. The source of the salinity, which is completely uncommon for the humid climate of the Yaroslavl Volga region, is groundwater with a TDS content of more than 1.0 g/l. The brackish groundwater is a result of the hydrogeological features of the territory and the topographic position of the basin as the base level of salt accumulation. The soils exhibit a noticeable tendency for relative accumulation of SO4 2− and Ca2+, while the more migration-active Cl– and Na+ get washed out of the soil profile into the watercourses of the nearest hydrographic network. Some tributaries to Lake Nero showed a high TDS content (over 500 mg/l) and a significant share of Cl– and Na+ among macro-components. Such were rivers Mazikha, Ishnya, Kuchebesh’, and Sula. Lake Nero water TDS content varied significantly during the year and the contributions of Cl–, SO4 2–, and Na+ to its macro-component composition showed several rises. Compared to similar soils surveyed 30–40 years ago, saline soils of the Rostov Lowland exhibit a downward trend in salinity. The content of carbonates of hydrogenous origin and the ash content of peat soils, on the contrary, increased over this time period. Climate change is hypothesized as the main cause of the soil transformation over the past 30–40 years. Saline soils are sensitive components of the lakeside landscape and can serve as indicators of changes in environmental conditions.