Ion's association in soil and vadose zone of Azov-Black sea region

The assessment of soil and vadose zone as the drains for carbon sink, proper modelling of the effects and extremes of biogeochemical cycles in terrestrial biosphere are the key components to understand the carbon cycle, global climate system, aquatic and terrestrial systems uncertainties. Carbonate-calcium equilibrium causes saturation of solution with CaCO.sub.3, determines its material composition, migration and accumulation of salts. In solution are formed electrically neutral ion pairs СаСО.sub.3 °, CaSO.sub.4 °, MgCO.sub.3 °, MgSO.sub.4 °. Charged ion pairs CaHCO.sub.3 .sup.+, MgHCO.sub.3 .sup.+, NaCO.sub.3 .sup.−, NaSO.sub.4 .sup.−, CaOH.sup.+, MgOH.sup.+ are developed the carbonate-calcium equilibrium algorithm, mathematical model and original software to calculate the real equilibrium forms of ions and determine the nature of carbonate-calcium balance in solution. An approach conducts the quantitative assessment of real ion forms of solution in solonetz soil and vadose zone of dry steppe taking into account the ions association at high ionic strength of saline soil solution. The concentration of free and associated ion form were calculated according to analytical ion concentration in real solution. In iteration procedure were used the equations of ion material balance, a linear interpolation of equilibrium constants, a method of ionic pairs, the laws of initial concentration preservation, operating masses of equilibrium system, the concentration constants of ion pair dissociation. The coefficient of ion association γ.sub.e was determined as a ratio of ions free form to analytical content of ion γ.sub.e =C.sub.ass /C.sub.an . Depending on soil and vadose zone layer, concentration and composition of solution in the ionic pair's form are: 11--52% Ca.sup.2+ ; 22.2--54.6% Mg.sup.2+ ; 1.1--10.5% Na.sup.+ ; 3.7--23.8 HCO.sub.3 .sup.−, 23.3--61.6% SO.sub.4 .sup.2−, up to 85.7% CO.sub.3 .sup.2− . The carbonate system of soil and vadose zone water solution helps to explain the evolution of salted soils, vadose and saturation zones, and landscape, improve the soil maintenance, plant nutrition and irrigation. The association of ions in soil solutions is one of the drivers, promoting transformation of solution, excessive fluxes of carbon in the soil, loss of carbon from soil through vadose zone.