Lake Urmia Brine Evolution from 2007 to 2019

Lake Urmia is presently the second-largest hypersaline lake on Earth and is in NW Iran. The lake experiences an extremely rapid water level fall of about 6 m in the last two decades due to human intervention. The rapid water level fall has affected the lake area, the water volume, the lake water composition, and the brine type. To investigate human activity on lake brine evolution, water samples from the lake water and major rivers entering the lake were collected annually (in both wet and dry seasons) from 2007 to 2012 and 2018 to 2019. Besides, various lake water physicochemical parameters were measured at the same time. The major cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) and anions (Cl⁻, SO42−,CO32−,HCO3− ) of both river and lake waters were analyzed. The riverine water depends on the lithology of the catchment and supplies different types and amounts of anions and cations to the lake. Results indicate that the eastern-northeastern rivers are rich in Na⁺, K⁺, and Cl⁻, while the western and southern rivers are dominated by Ca²⁺, Mg²⁺, CO32−,HCO3−. Results show a distinct variation in brine type over time. The lake brine of the Na⁺–Mg²⁺–Cl⁻ type in 2007–2011 (comparable with the Great Salt Lake) changed to a Mg²⁺– SO42− –Cl⁻ type from 2012 to 2018. These changes agree with a continued lake water level fall during that time, with a salinity increase, and consequently a rapid salt deposition between 2007 and 2018. However, in 2019 along with increasing freshwater input and water level rise, the lake salt crust has partly dissolved and the amount of Na⁺ and Cl⁻ ions increased in the lake brine. The lake brine changed to a Na⁺–Mg²⁺–Cl⁻ type, which is similar to conditions before 2011.