267-285
Ion’s Association in Soil Solution among the Drivers of Biogeosystem Dynamics
Authors: Anatoly P. Endovitsky, Angrey G. Andreev, Taniana M. Minkina, Valery P. Kalinichenko
Number of views: 563
Biogeosystem change is linked to ion’s association in soil solution. The concern of carbon sequestration problem is a soil as carbon sink drain. The carbonate calcium equilibrium (CCE) in soil solutions is important to characterize the degree soil solutions saturation with CaCO3 as a factor of terrestrial system carbonate geochemical cycle. CCE depends on the state of the chemical composition, pH, Eh, buffering properties of soil liquid phase, dissolution, migration, precipitation of carbonates in the soil profile and landscape, ion exchange processes at the interface of solid and liquid phases. At high ionic force in soil solution are formed electrically neutral ion pairs СаСО3°; CaSO4°, MgCO3°, MgSO4°, charged ion pairs CaHCO3+, MgHCO3+, NaCO3-, NaSO4-, CaOH+, MgOH+.
The object of research – Southern Russia; saline chestnut soil, dry steppe zone; non-saline chernozem, steppe zone. The soil solution was extracted from soil layers 0-150 cm. Composition of soil solution was determined using standard analytical methods. The soil system is the object of mathematical thermodynamic modeling, because it is impossible to remove the solution from dry soil, on the other hand, the extraction of solution change the chemical equilibrium in solution. The approach to soil disperse system model is proposed as a discreet partially insulated form one another micro-water-basins on the internal surfaces of soil. This approach gives a new understanding of water-salt transfer, geochemical barrier functions and ecological properties of soil.
On the basis of CCE algorithm, the computer programs were developed to calculate the real equilibrium ion forms and determine the nature of carbonate-calcium balance in the soil solution. The mathematical model shows the real state of associated ions at different ionic strength of low saline and saline soil solution. The concentration of free and associated macro-ion forms were calculated in iteration procedure according analytical ion concentration considering ion material balance, linear interpolation of equilibrium constants, method of ionic pairs, laws of: initial concentration preservation, operating masses of equilibrium system. Concentration constants of ion pairs dissociation were calculated following the law of operating masses. Were determined the quantity of ion free form and coefficient of ion association γe as a ratio of ions free form to its analytical contents . The association of ions is higher in saline soil layers. Depending on composition and ionic force c of soil solution in the form of ionic pairs are: 11-52% Ca2+; 22.2-54.6% Mg2+; 1.1-10.5% Na+; 3.7-23.8 HCO3-, 23.3-61.6% SO42-, up to 85.7% CO32-.
To interpret a behavior of heavy metal in soil solution an additional equation for microelements is proposed for the mathematical model of macro-ions.
The proposed thermodynamic calculation method for the real ion forms quantitative assessment in soil solution shows that in salted soils a chemical equilibrium in the soil solution causes a dissolved carbonate forms at high concentration of soil solution. It determines a high mobility of carbonates. Carbonate system of the soil solution is most important because on its state depends the nature of basic processes affecting formation and development of a certain type of soil. The nature of the calcium carbonate equilibrium soil is a cause why using an analytical concentration of ions only is observed the high calculated saturation degree of soil solutions with CaCO3. The association of ions in soil solutions is one of the geochemical drivers promoting transformation of solution, salt and heavy metal migration and accumulation in disperse system, soil genesis, excessive fluxes of carbon into soil, carbon sink from soil and biosphere to lithosphere and other geospheres.