Rainfall intensity and aggressiveness have a major influence on the soil erosion. In order to develop efficient prevention and protection methods regarding the soil erosion, it is essential to comprehend the rainfall washing consequences in the presence of a series of mineral components (carbonates, sulfates, nitrates, nitrites, ammonium ion).
The continuous soil aridization in the Republic of Moldova results in changing dynamics of pluvial processes: rain becomes more intense, but shorter in time. Thus, the soil washing processes intensify, escalating erosion. Growing quantities of rainwater mineral components increases the aggressive capacity, further accelerating the degradation processes of soils (especially lands). Assessing the ability of soil erosion by rain and storage of the mineral particles in the suspended form for a long time allows elucidating the main effects of silting ponds and lakes and clogging the adjacent areas.
Using three models of rainwater and its diluted solutions, under laboratory conditions, the capacity of washing, hydration and maintaining of limestone particles in the suspended form has been investigated. The hydration of CaCO3 particles, as one of the main causes of their storage in suspension for a long time, has been demonstrated by the pH-metric titration and quantitative determination of total calcium concentration in rainwater samples, containing the limestone particles.
The paper proposes a classification of rainwater, depending on the content of hydrogen carbonate, ammonium ion and anions of mineral acids. It has been found that after ten minutes of washing, the most aggressive is the ―acidic‖ rainwater, in which the anions of strong acids prevail, along with HCO3-. By decreasing the concentrations of these components, the aggressiveness capacity of ―acidic‖ rainwater becomes lower. The ―moderate‖ rainwater (in which HCO3- anions prevail in comparison with the anions of strong acids) has a lower aggressiveness, decreasing much more slowly in comparison with ―acidic‖ water. A slightly less aggressiveness, compared to that of ―acid‖ water, has the ―ammonia‖ rainwater, in which the NH4+ ion concentration exceeds the concentrations of anions of strong acids. Due to high concentrations of NH4+, the accumulation of HCO3- takes place, by capturing the carbon dioxide in rainwater [1,2]. The dilution of the ―ammonia‖ rainwater decreases more slowly the rainwater capacity of hydration, dissolving and keeping the suspended particles of CaCO3. The calcium carbonate particles are kept suspended for a longer time in the ―ammonia‖ rainwater. At the same time, the suspensions are more unstable in the ―acidic‖ rainwater, especially in its dilute solutions.
Therefore, the aggressiveness of ―acidic‖ rainwater increases with increasing amounts of mineral components. At the same time, the strongest washing effect exhibits the rainwater with a predominant content of ammonia in the series of investigated main mineral components.
1. Zhuangjie L., Baoquan Z., J. Phys. Chem. A, 116 (2012) 8989−9000. 2. Hafner S.D., Sommer S.G., Petersen V., Markfoged R., Heat and Mass Transfer, 53 (2017) 1335–1342.