Asalt lake orsaline lake is a landlockedbody of water that has aconcentration ofsalts (typicallysodium chloride) and other dissolvedminerals significantly higher than mostlakes (often defined as at least three grams of salt per liter).[1] In some cases, salt lakes have a higher concentration of salt thansea water; such lakes can also be termedhypersaline lake, and may also bepink lakes on account of their color. An alkalic salt lake that has a high content ofcarbonate is sometimes termed asoda lake.[2]
Salt lakes are classified according tosalinity levels. The formation of these lakes is influenced by processes such as evaporation and deposition. Salt lakes face serious conservation challenges due to climate change,pollution and water diversion.
The primary method of classification for salt lakes involves assessing the chemical composition of the water within the lakes, specifically its salinity,pH, and the dominant ions present.[2]
Hyposaline lakes exhibit salinities from 3 to 20 g/L,[3] which allows for the presence of freshwater species along with some salt-tolerant aquatic organisms.[2]Lake Alchichica in Mexico is a hyposaline lake.[4]
Hypersaline lakes possess salinities greater than 35 g/L,[2][6] or 50 g/L,[3] often exceeding 200 g/L. The extreme salinity levels create harsh conditions that limit the diversity of life, primarily supporting specialized organisms such ashalophilic bacteria and certain species ofbrine shrimp.[6] These lakes can have high concentrations of sodium salts and minerals, such as lithium, making such lakes vulnerable to mining interests.[6] Hypersaline lakes can be found in theMcMurdo Dry Valleys in Antarctica, where salinity can reach ≈440‰.[7]
Lake Hillier shoreline with microorganisms includingDunaliella salina, red algae which cause the salt content in the lake to create a red dye
Salt lakes form through complex chemical, geological, and biological processes, influenced by environmental conditions like highevaporation rates and restricted water outflow. As water carrying dissolvedminerals (sodium,potassium, andmagnesium) enters these basins, it gradually evaporates, concentrating these minerals until they precipitate as salt deposits.[8] Then, specificions interact under controlled temperatures, which leads to solid-solution formation and saltcrystal deposition within the lake bed.[8] This cycle of evaporation anddeposition is the main process to the unique saline environment that characterizes a salt lake.[8]
Soltan lake in Iran with salt mounds
Environmental factors further shape the composition and formation of salt lakes. Seasonal variations in temperature and evaporation drive mineral saturation and promote saltcrystallization.[9] In dry regions, water loss during warmer seasons concentrates the lake's salts.[9] This creates a dynamic environment where seasonal shifts affect the salt lake's mineral layers, contributing to its evolving structure and composition.[9] Groundwater rich in dissolved ions often serve as primary mineral sources that, combined with processes like evaporation and deposition, contribute to salt lake development.[10]
Salt lakes host a diverse range of animals, despite high levels of salinity acting as significant environmental constraints.[11] Increased salinity worsens oxygen levels and thermal conditions, raising the water's density andviscosity, which demands greater energy for animal movement.[11] Despite these challenges, salt lakes support biota adapted to such conditions with specialized physiological and biochemical mechanisms.[12] Common salt lake invertebrates include various parasites, with around 85 parasite species found in saline waters, includingcrustaceans andmonogeneans.[11] Among them, the filter-feeding brine shrimp plays a crucial role as a keystone species by regulatingphytoplankton andbacterioplankton levels.[13] The Artemia species also serves as an intermediate host for helminth parasites that affect migratory water birds like flamingos, grebes, gulls, shorebirds, and ducks.[13]Vertebrates in saline lakes include certain fish and bird species, though they are sensitive to fluctuations in salinity.[12] Many saline lakes are also alkaline, which imposes physiological challenges for fish, especially in managing nitrogenous waste excretion.[14] Fish species vary by lake; for instance, the Salton Sea is home to species such as carp, striped mullet, humpback sucker, and rainbow trout.[14]
Stratification in salt lakes occurs as a result of the unique chemical and environmental processes that cause water to separate into layers based ondensity.[15] In these lakes, high rates of evaporation often concentrate salts, leading to denser, saltier water sinking to the lake's bottom, while fresher water remains nearer the surface.[15] These seasonal changes influence the lake's structure, making stratification more pronounced during warmer months due to increasing evaporation, which drives separation between saline and fresher layers in the lake, leading a phenomenon known asmeromixis (meromictic state), primarily preventsoxygen from penetrating the deeper layers and create thehypoxic (low oxygen) oranoxic (no oxygen) zones.[16] This separation eventually influenced the lake's chemistry, supporting only specialized microbial life adapted to extreme environments with high salinity and low oxygen levels.[17] The restricted vertical mixing limitsnutrient cycling, creating a favorable ecosystem forhalophiles (salt-loving organisms) that rely on these saline conditions for stability and balance.[17]
The extreme conditions within stratified salt lakes have a profound effect onaquatic life, as oxygen levels are severely limited due to the lack of vertical mixing.[17]Extremophiles, including specificbacteria andarchaea, inhabit the hypersaline and oxygen-deficient zones at lower depths.[18] Bacteria and archaea, for example, rely on alternative metabolic processes that do not depend on oxygen.[18] These microorganisms play a critical role in nutrient cycling within salt lakes, as they break down organic material and release by-products that support other microbial communities.[18] Due to limited biodiversity, the restrictive environment limitsbiodiversity, allowing only specially adapted life forms to survive, which creates unique, highly specialized ecosystems that are distinct fromfreshwater or less saline habitats.[18]
Salt lakes declined worldwide in recent years. TheAral Sea, once of the largest saline lakes with a surface area of 67,499 km in 1960, diminished to approximately 6,990 km in 2016.[19] This trend is not limited to the Aral Sea; salt lakes around the world are shrinking due to excessive water diversion, dam construction, pollution, urbanization, and rising temperatures associated with climate change.[19] The resulting declines cause severe disruptions to local ecosystems and biodiversity, degrades the environment, threatens economic stability, and displaces communities dependent on these lakes for resources and livelihood.[19]
In Utah, if the Great Salt Lake is not conserved, the state could face potential economic and public health crises, with consequences for air quality, local agriculture, and wildlife.[20] According to "Utah’s Great Salt Lake Strike Team", in order to increase the lake's level within the next 30 years, average inflows must increase by 472,00 acre-feet per year. This is approximately 33% more than the amount that has been reaching the lake in recent years.[21]
Water conservation is viewed as being the most cost-effective and practical strategy to save salt lakes like the Great Salt Lake.[21] Implementing strong water management policies, improving community awareness, and ensuring the return of water flow to these lakes are additional ways that may restore ecological balance.[21] Other proposed methods of maintaining lake levels includecloud seeding and the mitigation of dust transmission hotspots.[22]
^abFinlayson, C. M. (2016), Finlayson, C. Max; Milton, G. Randy; Prentice, R. Crawford; Davidson, Nick C. (eds.),"Salt Lakes",The Wetland Book: II: Distribution, Description and Conservation, Dordrecht: Springer Netherlands, pp. 1–12,doi:10.1007/978-94-007-6173-5_255-1,ISBN978-94-007-6173-5, retrieved2024-11-16
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