Modern State of Water in the Selenga river at the Territory of Russia over Major Components and Trace Elements
The dynamics of major ions (Na<sup>+</sup>, Mg<sup>2+</sup>, K<sup>+</sup>, Ca<sup>2+</sup>, SO<sub>4</sub><sup>2-</sup>, Cl<sup>-</sup>, HCO<sub>3</sub><sup>-</sup>), Si, 52 trace elements, organic carbon, pH, O<sub>2</sub> was studied in the main tributary of Lake Baikal the Selenga river and the rivers flowing into it at the territory of Russia, channels and lakes of the delta, in the barrier zone of Lake Baikal (up to 7 km from the mouth of the Selenga). With the help of factor analysis, four major groups were revealed, differing from each other in the character of spatial-temporal distribution of components in the Selenga. The first group includes water mineralization, major ions and some conservative trace elements (B, Br, Sr, Mo, Ba, Re, U). The concentrations of these components are maximal during the ice period (march) and minimal during high water period (may), increase at the border with Mongolia and decrease to the mouth while the water gets diluted with less mineralized water of the tributaries of the Selenga. The elements of the second group are connected with the content of dissolved organic substance which is able to mobilize hardly soluble and almost insoluble elements (Be, Al, Ti, Fe, Ni, Cu, Ga, Y, Zr, Nb, Hf, РЗЭ, Pb, Th) into fine organomineral complexes. The concentrations of these elements are increased in spring, during snow melting and active carry-oover of the organic matter from the catchment basin. The third group of elements (Si, Li, Cr, Mn, Co, Zn, Ge, Rb, Ag, Cd, Sn, Cs, Bi) depicts the processes of water acidification at the background of the seasonal dynamics of dissolved oxygen. The concentrations of these elements increase towards the mouth (except Co during the period from spring to autumn and Ge in winter) and are substantially increased in winter. The fourth group of elements (V, As, Sb, I, W, Cu) marks a weak transboundary transport during summer. Increased concentrations of elements are observed in July, especially in the upper region of the river (0-120 km from the border with Mongolia). Maximal and average weighted concentrations of the majority of trace elements in the Selenga river are lower than the corresponding parameters for the global river background. The maximal background concentrations were exceeded by Mo (10 %), Mn (10 %) and Ge (60 %). The average weighted background concentrations were exceeded by a factor of 2-5 for 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 is connected with the geological structure of the basin and natural processes of element mobilization. The concentrations of Mo, Mn, Cu, Al, Fe, V in the main range of the Selenga and its tributaries during some seasons insignificantly exceed the Russian standards established for water reservoirs for fish industry purposes (in 80 % of cases not more than 2 MPC). In the barrier zone of Lake Baikal, the standards for fish industry water reservoirs were observed to be exceeded permanently for Mo (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).