Hydrogeochemical features of Lake Kotokel

The purpose of this study is to determine the main hydrochemical parameters of Lake Kotokel deep waters, to identify the role of groundwater feeding it, as well as to establish the features of spatial distribution of macro- and microelements in the lake. Field work was carried out during the ice and ice-free seasons. A special sampler was used to take water samples from the bottom of the lake. Water samples were filtered through the filters with a pore size of 0.45 μm at the sampling site. Plastic bottles were used for the water samples for analysis. Polypropylene containers (15 ml) pretreated with 0.1 N nitric acid were used for the water samples for trace elements. The analysis of the macrocomponent composition of water was carried out in a certified Laboratory of Hydrogeology and Geoecology of the Geological Institute of the Siberian Branch of the Russian Academy of Sciences (Ulan-Ude) according to the standard methods intended for fresh and saline waters. Cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) were determined by atomic absorption, F^-, SiO₂ – by the colorimetric method, HCO_3^- , CO₃^2- and Cl^- – by the titrimetric method, SO₄^2- – by the turbidimetric method. The analysis of the trace element content was carried out in the Laboratory of Aquatic Microbiology at the Limnological Institute of the Siberian Branch of the Russian Academy of Sciences (Irkutsk) by the method of inductively coupled plasma on Agilent 7500ce quadrupole mass spectrometer. Conducted research made it possible to determine an inhomogeneous chemical composition of lake water associated with the discharge of fissure-vein waters along the faults that bound the depression from the southeast and northeast and intersect the lake water area from the island to the Istok river. The highest content of dissolved substances was recorded in the strait between Monastyrsky island and the western shore of the lake; the maximum values of hydrocarbonate ion and total mineralization were found here. The maximum content of sulfate ion was found in the southern and southeastern parts of the lake. The dispersion in microelement distribution reaches several mathematical orders. The most variable concentration is characteristic of iron, manganese, copper, zinc, lead, phosphorus, molybdenum, tungsten, strontium. Their high contents were found in the lake water within the location of faults of northeast strike. Therefore, the chemical composition of the water of Lake Kotokel is largely formed by fissure-vein waters. This water is discharged along the tectonic faults of the northeastern strike. The research revealed two centers of subaqueous discharge, which are characterized by the formation of two different associations of microelements in the lake water. The composition of microelements in fissure-vein waters is determined by their interaction degrees with rocks.

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