Atmospheric Solid Fallouts as a Source of Hydrophobicity of Urban Soils and Material for Their Formation

In urban conditions, the soil is exposed to a number of adverse effects that have a great impact on its hydrophobic and hydrophilic properties. The water-repellent properties of urban dust and soil samples were determined using a WDPT test, the process of hydrophobization of Albeluvisols in the conditions of a megalopolis was modeled and its speed was estimated. The study used three dust samples with different values of the WDPT test from 420 to 850 seconds. According to the results of the model experiment it is shown that with an increase in the amount of solid atmospheric precipitation in the Retisols material, the level of its hydrophobicity also increases. The rate of increase depends on the water-repellent properties of the dust sample. When polluted with the most hydrophobic dust, the maximum hydrophobization of the humus-accumulative soil horizon is achieved at a 70-year load. For other dust samples, an increase in the time of absorption of a drop was observed up to the maximum period of aerial soil contamination within the model experiment (200 years). Values of the WDPT test for the studied soil horizons ranged from 2.4 s for background soil, to 1493.5 s for urban soil formed near a major highway for 90 years. In the soil of residential buildings of 40 years of age, the value was 237.1 s. The correspondence of the levels of hydrophobicity, the degree of anthropogenic load and the residence time of sites in the urban environment in the model experiment and in samples of real urban soils at the study sites indicates that solid atmospheric fallouts is a component of humus-accumulative horizons of urban soils and has a significant impact on their water-repellent properties.