Lake Van and Lake Tuz are two prominent bodies of water in Turkey, geographically separated but sharing unusual environmental characteristics. Lake Van is a vast, deep lake in the east, while Lake Tuz is a large, shallow salt flat in central Anatolia that often dries up seasonally. Despite differences in size and physical state, both lakes share rare hydrological, chemical, and biological traits.
Shared Endorheic Basin Status
Both Lake Van and Lake Tuz are classic examples of endorheic or closed-basin lakes, meaning they have no natural outflow to the sea. Water entering the basins, primarily from streams and rainfall, can only exit through evaporation or seepage. This lack of drainage is the fundamental physical constraint that drives the lakes’ unique chemistry. Tectonic activity contributes to the formation of these deep, contained basins, such as Lake Van, which is a tectonic lake formed by faulting and volcanic activity.
The consequence of this closed system is the perpetual accumulation of dissolved minerals and salts over millennia. As water evaporates, non-volatile elements remain behind, increasing the concentration of solutes. This continuous process, coupled with high evaporation rates, ensures the water chemistry becomes progressively more extreme. The geological setting, including volcanic influences, introduces specific mineral components that feed into this concentration process.
Hypersaline and Alkaline Chemistry
The endorheic nature results in the lakes’ shared status as both hypersaline and alkaline water bodies. Hypersaline defines water significantly saltier than seawater, a trait pronounced in Lake Tuz, which contributes 60% of Turkey’s total salt production. Lake Van, while highly saline, is famous for its extreme alkalinity, being the world’s largest soda lake with a pH around 10.
This alkalinity is caused by high concentrations of sodium carbonate and bicarbonate species. In both basins, calcium and magnesium carbonates precipitate first, leaving sodium and carbonate ions to dominate the remaining water. Both lakes thus share a highly mineralized water composition that is chemically challenging for most forms of life due to high salt content and high pH.
Specialized Biological Adaptation
The extreme chemical environment selects for a low-diversity but highly specialized community of life forms known as extremophiles. These organisms have evolved unique molecular mechanisms to cope with the dual stress of high salinity and alkalinity. In Lake Tuz, the microbial community is dominated by halophilic (salt-loving) archaea and bacteria, which employ osmoadaptation strategies like potassium accumulation.
Lake Van also hosts a unique community of alkaliphilic and halophilic microorganisms, including those that form the largest known modern microbialite deposits. The high concentration of salts and carbonates requires organisms to possess specialized proteins and enzymes that function without denaturation under these harsh conditions. These biological communities represent a rare ecological niche dictated by the lakes’ shared geological and hydrological past.