The effects of long-term drainage and wildfires on water table level and water chemistry of the Great Vasyugan Mire

Abstract

In this paper, we assessed long-term changes in water table level of the Great Vasyugan Mire, water chemistry and the removal of mineral and organic substances in the mire-river system in the taiga zone of Western Siberia under the conditions of forest reclamation, pyrogenic factor and climate change. In the drained area of the Great Vasyugan Mire, a significant decrease in water table levels and an increase in the amplitude of their fluctuations by 1.6 times were noted. The effect of the pyrogenic factor is expressed, on the contrary, in an increase in water table levels due to surface burnout. In the water of the drained part of the Great Vasyugan Mire, an increase in the concentrations of Са2+, Mg2+, Fetotal, Cl–, К+, Na+, Cl–, SО4 2–, NO3 –, DOC was noted. An increase in the content of NH+ 4, Fetotal , Cl–, SO4 2–, NO– 3, and DOC is observed in river waters. An indicator of the effect of the pyrogenic factor on the chemical composition is an increase in the pH value and the content of K+, Na+, SО4 2–, NО– 3, HCО– 3 ions, as well as Са2+, Mg2+, Fetotal. In connection with the overgrowth of the ditches, the process of self-healing of the mire is observed, and backwater zones are formed near the ditches and the amplitude of level fluctuations increases, as a result, the chemical composition of the waters of the drained and natural areas of the Great Vasyugan Mire in certain periods has minimal differences. Studies have shown that the removal of mineral and organic substances from the drained area of the great Vasyugan Mire prevailed in the high-water year 2018 and amounted to 2054 tons, of which the removal of DOC was equal to 47 % or 969 tons. In the future, climate change, an increase in air temperature and precipitation in the region are likely, will contribute to the removal of biogenic elements and organic substances from mires and increase their concentration in river waters.