The Hydrogeochemistry of the Shira Region, Republic of Khakassia, Southern Siberia, Russian Federation - Data Report

Abstract

The groundwater chemistry of the aquifers around and within the Devonian rift basin of the Shira area is very different from that of the Permian Oslo Rift. The anionic chemical composition in the Russian Devonian Aquifers is often dominated by apparently evaporite-derived sulphate and chloride salinity. The composition of the more saline ground- and lake-waters is typically of sodium sulphate (-chloride) type. This sodium sulphate signature appears be present even in non-evaporite-bearing aquifers and to pervade the entire hydrological cycle, probably by the presence of evaporite-dust and lake spray in local precipitation. It is postulated that the sodium-sulphate-(chloride) hydrochemical signature is characteristic for inland, semi-arid, partially closed drainage basins, being derived from silicate water-rock interaction, halite and gypsum dissolution, coupled with calcium, magnesium and bicarbonate removal via calcite\/dolomite precipitation. Evaporite-derived saline groundwaters feed lake systems, where further evaporite up-concentration occurs such that maximum salinites of over 100 g\/L are reported in the most saline lake (Lake Tus). The Khakassian groundwaters do not, even the granitoids contain the high levels of natural health-related minor\/trace elements (F,U,Th, Be,T1) characteristics of the granites in and around the Oslo rift. Fluoride concentrations exceeding drinking water norms are not encountered in the Shira region, even in the granitoid complexes. In town areas in the Shira region, nitrate concentrations often exceed drinking water norms, suggesting possible contamination from latrines or sewerage. This result suggests that a systematic microbiological survey of the regions's public supply wells for faecal micro- organisms would be advisable.