A pink lake is a lake that has a red or pink colour. This is often caused by the presence of salt-tolerant algae that produces carotenoids, such as Dunaliella salina , usually in conjunction with specific bacteria and archaea, which may vary from lake to lake. The most common archaeon is Halobacterium salinarum .
Pink lakes arise from a combination of factors, which include climate and hydrology of the continent beneath them, in particular the level of salinity. The orange/pink colour of salt lakes across the world has often been attributed to the green alga Dunaliella salina , but other work has shown that bacteria or archaea are also involved. [1]
Dunaliella salina is the most halophilic (salt-tolerant) alga known and can grow in salinity as high as 35% NaCl [2] [3] (in comparison to seawater, which contains approximately 3% NaCl). [4] The single-celled green alga plays a key role in primary production in hypersaline environments around the world. At high salinity, temperature and light, this alga accumulates the red carotenoid pigment, beta-carotene. This is the same pigment that gives carrots, which contain 0.3% of beta-carotene, their colour. [2] D. salina can adapt to a very wide range of concentrations of salt. The beta-carotene protects the alga against damage from high light, coating the green chlorophyll and giving the alga an orange/red colour. The alga, which was found not to contain a high intracellular concentration, was named after Michel Félix Dunal who first recognised the red colour of certain salt lakes in France was due to an organism. [3]
It was thought for a long time that the colour of pink lakes was the result of this alga, as it has been found in many pink lakes. [5]
Some bacteria and archaea also produce a carotenoid pigment within their cell membranes, which may either contribute to or be the only cause of the pink colouration. [2]
In some of the hundreds of Australian pink lakes, a red bacterium, Salinibacter ruber , may be involved in producing their colour. Work done by molecular biologist Ken McGrath at on Lake Hillier, on Middle Island in Western Australia led by molecular biologist Ken McGrath in 2015 showed that, while D. salina was present in only tiny quantities (0.1% of DNA sampled), while S. ruber formed 20 [1] to 33% [6] [7] [5] [lower-alpha 1] of the DNA recovered from the lake. [1] They found 10 species of halophilic bacteria and archaea as well as several species of Dunaliella algae, nearly all of which contain some pink, red or salmon-coloured pigment. [7]
Environmental scientist Tilo Massenbauer, while researching the loss of colour of the lake since the 1990s (attributed to excessive salt harvesting from it), has a hunch that all pink lakes are caused by S. ruber, rather than D. salina, but proving this is challenging, because bacteria are so much smaller and more difficult to find than algae. A project is being planned to pump more salt into the lake from local agricultural land, where high salinity is a problem. [1] Lake Retba in Senegal, in West Africa, contains the same bacterium. [2]
S. ruber produces a pigment called bacterioruberin, which helps it to trap and use light for energy in the photosynthesis process. While the pigments in algae are contained within the chloroplasts, bacterioruberin is spread across the whole cell of the bacterium. This makes it more likely that the colour of the lake is that of S. ruber. [5]
The archaea Halobacterium salinarum (formerly Halobacterium cutirubrum), which is pink in colour and generally grows within the salt crust on the bottom of the lake, has been found to be involved in the colour of some pink lakes, such as the lake in Melbourne's Westgate Park. The exact colour of the lake depends on the balance between D. salina and H. salinarium, with salt concentration having a direct impact. [8] [9]
The majority of pink salt lakes change their colour which is often linked to rainfall. A lake in Westgate Park, Melbourne, Australia, was coloured pink in March 2017 [10] and then again in September 2019, but since then and as of January 2022 [update] had taken on a dark green hue. Warmer weather and lower rainfall appears to make it turn pink. [1] As water evaporates, the salinity increases, but salinity is not the only factor at work. Sediment and the organisms living in the lake affect its colour, and the shade of pink that it takes on. [10]
Pink lakes such as Lake Hillier can be up to ten times saltier than seawater (the Dead Sea in Israel is around nine times so). [10] It is safe to swim in pink lakes, but it is not advisable to drink it owing to the effect of its hypersalinity on the human body, and the possibility of micro-organisms which may be harmful to human health. [2]
The term carotene (also carotin, from the Latin carota, "carrot") is used for many related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but in general cannot be made by animals (with the exception of some aphids and spider mites which acquired the synthesizing genes from fungi). Carotenes are photosynthetic pigments important for photosynthesis. Carotenes contain no oxygen atoms. They absorb ultraviolet, violet, and blue light and scatter orange or red light, and (in low concentrations) yellow light.
A halophile is an extremophile that thrives in high salt concentrations. In chemical terms, halophile refers to a Lewis acidic species that has some ability to extract halides from other chemical species.
The Murray-Sunset National Park is the second largest national park in Victoria, Australia, located in the Mallee district in the northwestern corner of the state, bordering South Australia. The 633,000-hectare (1,560,000-acre) national park is situated approximately 440 kilometres (270 mi) northwest of Melbourne and was proclaimed in 1991. It is in the northwestern corner of the state, bordering South Australia to the west and the Murray River to the north. The Sturt Highway passes through the northern part of the park, but most of the park is in the remote area between the Sturt Highway and the Mallee Highway, west of the Calder Highway.
Carotenoids are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, canaries, flamingos, salmon, lobster, shrimp, and daffodils. Over 1,100 identified carotenoids can be further categorized into two classes – xanthophylls and carotenes.
A salt evaporation pond is a shallow artificial salt pan designed to extract salts from sea water or other brines. The salt pans are shallow and expansive, allowing sunlight to penetrate and reach the seawater. Natural salt pans are formed through geological processes, where water evaporating, leaving behind salts deposits. Some salt evaporation ponds are only slightly modified from their natural version, such as the ponds on Great Inagua in the Bahamas, or the ponds in Jasiira, a few kilometres south of Mogadishu, where seawater is trapped and left to evaporate in the sun.
Lake Retba, also known as Lac Rose, lies north of the Cap Vert peninsula in Senegal, some 35 km (22 mi) north-east of the capital, Dakar, in northwest Africa. It is named for its pink waters caused by Dunaliella salina algae and is known for its high salt content, up to 40% in some areas. Its colour is usually particularly strong from late January to early March, during the dry season; however, flooding in September 2022 not only disrupted salt harvesting activities on the lake, but because it caused the lake to lose its colour, had a negative effect on tourism.
Halobacterium is a genus in the family Halobacteriaceae.
Dunaliella salina is a type of halophile unicellular green algae especially found in hypersaline environments, such as salt lakes and salt evaporation ponds. Known for its antioxidant activity because of its ability to create a large amount of carotenoids, it is responsible for most of the primary production in hypersaline environments worldwide, and is also used in cosmetics and dietary supplements.
Haloarchaea are a class of the Euryarchaeota, found in water saturated or nearly saturated with salt. Halobacteria are now recognized as archaea rather than bacteria and are one of the largest groups. The name 'halobacteria' was assigned to this group of organisms before the existence of the domain Archaea was realized, and while valid according to taxonomic rules, should be updated. Halophilic archaea are generally referred to as haloarchaea to distinguish them from halophilic bacteria.
Halobacterium salinarum, formerly known as Halobacterium cutirubrum or Halobacterium halobium, is an extremely halophilic marine obligate aerobic archaeon. Despite its name, this is not a bacterium, but a member of the domain Archaea. It is found in salted fish, hides, hypersaline lakes, and salterns. As these salterns reach the minimum salinity limits for extreme halophiles, their waters become purple or reddish color due to the high densities of halophilic Archaea. H. salinarum has also been found in high-salt food such as salt pork, marine fish, and sausages. The ability of H. salinarum to survive at such high salt concentrations has led to its classification as an extremophile.
Dunaliella is a single-celled, photosynthetic green alga, that is characteristic for its ability to outcompete other organisms and thrive in hypersaline environments. It is mostly a marine organism, though there are a few freshwater species that tend to be more rare. It is a genus in which certain species can accumulate relatively large amounts of β-carotenoids and glycerol in very harsh growth conditions consisting of high light intensities, high salt concentrations, and limited oxygen and nitrogen levels, yet is still very abundant in lakes and lagoons all around the world.
Lake Hillier is a saline lake on the edge of Middle Island, the largest of the islands and islets that make up the Recherche Archipelago in the Goldfields-Esperance region, off the south coast of Western Australia. It is particularly notable for its pink colour. A long and thin shore divides the Southern Ocean from the lake.
Hutt Lagoon is a marine salt lake located near the Indian Ocean coast 2 kilometres (1.2 mi) north of the mouth of the Hutt River, in the Mid West region of Western Australia.
Pink Lake is a salt lake in the Goldfields-Esperance region of Western Australia. Although historically the water in the lake was visibly pink, as of 2017 it had not been pink for over ten years. Salt concentration is vital to Pink Lake's pink hue, and Pink Lake may turn pink again as conditions change. It lies about 3 kilometres (2 mi) west of Esperance and is bounded to the east by the South Coast Highway.
Halobacterium noricense is a halophilic, rod-shaped microorganism that thrives in environments with salt levels near saturation. Despite the implication of the name, Halobacterium is actually a genus of archaea, not bacteria. H. noricense can be isolated from environments with high salinity such as the Dead Sea and the Great Salt Lake in Utah. Members of the Halobacterium genus are excellent model organisms for DNA replication and transcription due to the stability of their proteins and polymerases when exposed to high temperatures. To be classified in the genus Halobacterium, a microorganism must exhibit a membrane composition consisting of ether-linked phosphoglycerides and glycolipids.
Salinibacter ruber is an extremely halophilic red bacterium, first found in Spain in 2002.
Archaerhodopsin proteins are a family of retinal-containing photoreceptors found in the archaea genera Halobacterium and Halorubrum. Like the homologous bacteriorhodopsin (bR) protein, archaerhodopsins harvest energy from sunlight to pump H+ ions out of the cell, establishing a proton motive force that is used for ATP synthesis. They have some structural similarities to the mammalian GPCR protein rhodopsin, but are not true homologs.
Pink Lake is a small, circular, salty pink lake on the Western Highway just north of Dimboola in Australia. Granville Stapylton, part of the explorer Thomas Mitchell's 1836 expedition into western Victoria, reconnoitered Pink Lake on 20 July 1836.
Kobeituz is a salt lake in Yereymentau District, Akmola Region Kazakhstan.
Lake Lemuria, also known as Pink Lake, is a small lake in the western part of Syvash Bay in the Kherson region of Ukraine. It is located near the villages of Hryhorivka and Novovolodymyrivka, Lemuria lake has pink water due to the action of an algae which produces large amounts of beta-carotene. Lake Lemuria is a healing resort of international importance.
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