Comparative analysis of the calculation methods of the background concentrations of major ions in the left tributaries of the Middle Ob River

The average seasonal and multi-year concentration of macro-nutrients of river water and their spatial and temporal changes in wetland watersheds of the northeastern the Great Vasyugan Mire is calculated in this paper. The change of the ion-salt structure of the surface water is considered based on data of the Federal Service for Hydrometeorology and Environmental Monitoring (12 hydro-logical stations for 13 years (1997-2009)). A comparative analysis of the calculations of the background concentrations by various methods - the arithmetic mean, the weighted average arithmetic, the geometric mean - is presented. The calculation of the background concentrations of major ions by the weighted average arithmetic based on the idea of the unity of the formation of the water and the chemical runoffs of a river due to the genetic heterogeneity of the nourishment sources of the rivers in the different phases of the water regime [1; 12]. The weights that were used are: when calculating the mean concentration per year the volume shares of water runoff in hydrological phases; when calculating the average long-term concentrations the volume shares of the annual runoff in the total for a long-term period. With this approach, it is easy to single out background concentrations of warm and cold periods of the year. For each macro-component a map of the spatial distribution of concentrations for the studied area was built. For Mg +, Ca +, Cl , and HCO3 macro-components, these estimates comply with those obtained by a less costly method - the simple geometric mean. The quantitative differences of the concentrations of macro-components depending on the phase of the water regime in the river basins of different swampiness are analyzed. The distribution of the average content of the main ions in river waters as a whole is quite understandable and well correlated with the intensity of water exchange. A linear dependence was determined between the long-term average sum of major ions and the runoff rate of the left bank tributaries of the Middle Ob during the observation period of 19972009 with the quality of the approximation of S/a= 0.6. The analysis of the trends in the row of concentrations revealed statistically significant ones for some of them. The long-term dynamics of the anion HCO ₃" has a statistically significant trend for the Iksa River. The concentration of ions Na++ K+ during the observation period from 2002 to 2009 are characterized by a significant trend for an increase in the Iksa and the Parabel rivers. It is concluded that although obtaining estimates of background concentrations and mineralization based on the volume of the runoff in different phases of the water regime is time-consuming are complex, yet it yields more reliable, genetically-based results.

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