The Ecological Status of Soils of Ust'-Ilimsk (Irkutsk Oblast).

Abstract—Experimental investigations were made into the basicity–acidity indices (pH) and soil biochemical activity (SBA) in the industrial city of Ust'-Ilimsk in conditions of Eastern Siberia. A cartographic representation of the distribution of values of integral indicators of soils in the city is presented for the first time. The significance of the method of mapping urban soils that are experiencing urbanization and technogenesis is emphasized. The investigation was made by using the express method of determining the soil biochemical activity. In addition to this indicator, pH conditions of soils were identified. The study encompassed the main functional zones of two parts of Ust'-Ilimsk: the Old Town (Levoberezhie) and the New Town (Pravoberezhie). The neutral and weakly alkaline soils are of widespread occurrence on the territory. The pH values vary from 7.4 to 7.8; in the control soils, they vary from 6.3 to 6.9. A significant area of the city (43.9%) is occupied by weakly alkaline soils. The level of soil biochemical activity permitted us to categorize the soils as active and very active. The proportion of very active soils makes up 32.9% of the total territory of the city. This indicates a trend of ecological regression, namely a loss of a biogenic element, nitrogen. The study revealed trends of a weak but positive dependence of SBA on pH. The coefficients of approximation are positive and vary, according to the zones of the city, from 0.2 to 0.5. The absolute and relative distribution of the areas with pH and SBA values is shown. A comparative analysis of data revealed a difference of the Ust'-Ilimsk soils from the soils in other cities of the Angara region. [ABSTRACT FROM AUTHOR]