Home – Home – Jornals – Chemistry for Sustainable Development 2012 number 5

Studies were performed concerning the seasonal dynamics of major ions (Na⁺, Mg²⁺, K⁺, Ca²⁺, SO₄^2-, Cl^-, HCO₃^-), Si, 52 trace elements, organic carbon, pH, O₂ in the Selenga River, the main tributary of Lake Baikal and the rivers flowing into the Selenga in the Russian territory, the flow paths and lakes of the delta within the barrier area of Lake Baikal (up to 7 km from the mouth of the Selenga River). Using the factor analysis we revealed four main groups, those differ from each other in the spatial and temporal distribution of the components in the Selenga River. The first group comprises the water salinity, the major ions and trace elements, some conservative trace elements (B, Br, Sr, Mo, Ba, Re, U). The concentration values for these components are maximal within the ice period (March) and minimal within the flood period (May), exhibit an increase on the frontier with Mongolia reducing towards the mouth as being diluted by less saline water of the tributaries of the Selenga River. The elements of the second group are connected with the content of dissolved organic matter capable of mobilizing difficultly soluble and almost insoluble elements (Be, Al, Ti, Fe, Ni, Cu, Ga, Y, Zr, Nb, Hf, REE, Pb, Th) to produce fine-dispersed organomineral complexes. The concentration values for these elements demonstrate increasing in the spring, in the course of the snowmelt and of an active removal of organic matter from the catchment area. The third group of the elements (Si, Li, Cr, Mn, Co, Zn, Ge, Rb, Ag, Cd, Sn, Cs, Bi) reflects the processes of water acidifying against the background of seasonal dynamics inherent in the dissolved oxygen. Concentration values for these elements increase towards the mouth (except for Co within the period of spring and autumn, as well as Ge in winter), being to a significant extent increased in the winter. The fourth group of the elements (V, As, Sb, I, W, Cu) represents a marker of a weak cross-border transfer in summer. Increased concentration values of these elements are observed in July, especially on the upper section of the river (0–120 km from the frontier with Mongolia). The maximum and average weighted concentrations of the most of trace elements in the Selenga River are lower than those inherent in the global natural river background. Exceeding the maximum background concentration values is observed for Mo (10 %), Mn (10 %) and Ge (60 %). Average weighted background concentration values exhibit a 2- to 5-fold exceeding in Zr (2.1), Nb (2.1), Sr (2.5), Ti (2.9), U (3.5), Y (3.5), Zn (3.7), Mo (3.8) and Sn (4.9), which could be caused by the geological structure of the basin and the naturally occurring processes of mobilizing the elements. The concentration of Mo, Mn, Cu, Al, Fe, V in the general river station of the Selenga River and the tributaries thereof in some seasons are slightly higher than Russian standards established for fish-industry water basins (in 80 % of cases less than 2 MPC). Within the barrier zone of Lake Baikal there is an excess over the fish industry water standards in Mo registered to be constant (1.2–2.1 MPC): for Cu in winter (up to 1.8 MPC), in summer (up to 1.9 MPC), in autumn (up to 1.3 MPC); for V in summer (up to 1.6 MPC); for Mn in winter (up to 2.2 MPC).