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|year=2008|title=A renaissance for the pioneering 16S rRNA gene
|year=2008|title=A renaissance for the pioneering 16S rRNA gene
|journal=Curr Opin Microbiol |volume=11
|journal=Curr Opin Microbiol |volume=11
|pages=442–446. }}
|pages=442–446.
|doi=10.1016/j.mib.2008.09.011}}
</ref> Culture-independent surveys have confirmed what was already indicated by many culturing studies before them, namely that the diversity of microorganisms in soda lakes is very high, with [[species richness]] (number of species present) of individual lakes often rivaling that of freshwater ecosystems.
</ref> Culture-independent surveys have confirmed what was already indicated by many culturing studies before them, namely that the diversity of microorganisms in soda lakes is very high, with [[species richness]] (number of species present) of individual lakes often rivaling that of freshwater ecosystems.


Revision as of 07:28, 8 May 2014

A soda lake or alkaline lake is a lake on the strongly alkaline side of neutrality (in other words, a pH value above 7, typically between 9 - 12). They are characterized by high concentrations of carbonate salts, typically sodium carbonate (and related salt complexes), giving rise to their alkalinity. In addition, many soda lakes also contain high concentrations of sodium chloride and other dissolved salts, making them saline- or hypersaline lakes as well. High pH and salinity often coincide, because of how soda lakes develop (see "Geology, geochemistry and genesis"). The resulting hypersaline and highly alkalic soda lakes are considered some of the most extreme aquatic environments on Earth.[1] In spite of their apparent inhospitability, soda lakes are often highly productive ecosystems, compared to their (pH-neutral) freshwater counterparts. Gross primary production (photosynthesis) rates above 10 g C m−2 day−1 (grams carbon per square meter per day), over 16 times the global average for lakes and streams (0.6 g C m−2 day−1), have been measured.[2] This makes them the most productive aquatic environments on Earth. An important reason for the high productivity is the virtually unlimited availability of dissolved carbon dioxide.

Soda lakes occur naturally throughout the world (see Table below), typically in arid and semi-arid areas and in connection to tectonic rifts like the East African Rift Valley. The pH of most freshwater lakes are on the alkaline side of neutrality and many exhibit similar water chemistries to soda lakes, only less extreme.

Lake Shala, in the East African Rift Valley

Geology, geochemistry and genesis

In order for a lake to become alkalic, a special combination of geographic, geological and climatic conditions are required. First of all, a suitable topology is needed, that limits the outflow of water from the lake. When the outflow is completely prevented, this is called an 'endorheic basin'. Craters or depressions formed by tectonic rifting often provide such topological depressions. The high alkalinity and salinity arise through evaporation of the lake water. This requires suitable climatic conditions, in order for the inflow to balance outflow through evaporation. The rate at which carbonate salts are dissolved into the lake water also depends on the surrounding geology and can in some cases lead to relatively high alkalinity even in lakes with significant outflow.

Tufa columns at Mono Lake, California

Another critical geological condition for the formation of a soda lake is the relative absence of soluble magnesium or calcium. Otherwise, dissolved magnesium (Mg2+) or calcium (Ca2+) will quickly remove the carbonate ions, through the precipitation of minerals such as calcite, magnesite or dolomite, effectively neutralizing the pH of the lake water. This results in a neutral (or in slightly acidic) salt lake instead. A good example is the Dead Sea, which is very rich in Mg2+. In some soda lakes, inflow of Ca2+ through subterranean seeps, can lead to localized precipitation. In Mono Lake, California and Lake Van, Turkey, such precipitation has formed columns of tufa rising above the lake surface.

Many soda lakes are strongly stratified, with well-oxygenated upper layer (epilimnion) and an anoxic lower layer (hypolimnion), without oxygen and often high concentrations of sulfide. Stratification can be permanent, or with seasonal mixing. The depth of the oxic/anoxic interface separating the two layers varies from a few centimeters to near the bottom sediments, depending on local conditions. In either case, it represents an important barrier, both physically and between strongly contrasting biochemical conditions.

Biodiversity

A rich diversity of microbial life inhabit soda lakes, often in dense concentrations. This makes them unusually productive ecosystems and leads to permanent or seasonal "algae blooms" with visible colouration in many lakes. The colour varies between particular lakes, depending on their predominant life forms and can range from green to orange or red.[1]

Compared to freshwater ecosystems, life in soda lakes is often completely dominated by prokaryotes, i.e. bacteria and archaea, particularly in those with more "extreme" conditions (higher alkalinity and salinity, or lower oxygen content). However, a rich diversity of eukaryotic algae, protists and fungi have also been encountered in many soda lakes.[3]

Multicellular animals such as crustaceans (notably the brine shrimp Artemia and the copepod Paradiaptomus africanus) and fish (e.g. Alcolapia), are also found in many of the less extreme soda lakes, adapted to the extreme conditions of these alkalic and often saline environments. Particularly in the East African Rift Valley, microorganisms in soda lakes also provide the main food source for vast flocks of the Lesser Flamingo (Phoeniconaias minor). The cyanobacteria of the genus Arhtrospira (formerly Spirulina) are a particularly preferred food source for these birds, owing to their large cell size and high nutritional value.

Microbial diversity surveys and species richness

Lesser Flamingos (Phoenicopterus minor) feeding on cyanobacteria in Lake Nakuru, Kenya

In general, the microbial biodiversity of soda lakes is relatively poorly studied. Many studies have focused on the primary producers, namely the photosynthesizing cyanobacteria or eukaryotic algae (see Carbon cycle). As studies have traditionally relied on microscopy, identification has been hindered by the fact that many soda lakes harbour poorly studied species, unique to these relatively unusual habitats and in many cases thought to be endemic, i.e. existing only in one lake.[4] The morphology (appearance) of algae and other organisms may also vary from lake to lake, depending on local conditions, making their identification more difficult, which has probably led to several instances taxonomic confusions in the scientific literature.

Recently, a number of studies have used molecular methods such as DNA fingerprinting or sequencing to study the diversity of organisms in soda lakes.[4][5][6][7][8] These methods are based on DNA extracted directly from the environment and thus do not require microorganisms to be cultured. This is a major advantage, as culturing of novel microorganisms is a laborious technique known to seriously bias the outcome of diversity studies, since only about one in a hundred organisms can be cultured using standard techniques.[9] For microorganisms, the phylogenetic marker gene Small Subunit (SSU) Ribosomal RNA is typically targeted, due to its good properties such as existence in all cellular organisms and ability to be used as a "molecular clock" to trace the evolutionary history of an organism.[10] Culture-independent surveys have confirmed what was already indicated by many culturing studies before them, namely that the diversity of microorganisms in soda lakes is very high, with species richness (number of species present) of individual lakes often rivaling that of freshwater ecosystems.

Biogeography and uniqueness

In addition to their rich biodiversity, soda lakes often harbour many unique species, adapted to alkalic conditions and unable to live in environments with neutral pH. These are called alkaliphiles. Organisms also adapted to high salinity are called haloalkaliphiles. Culture-independent genetic surveys have shown that soda lakes contain an unusually high amount of alkaliphilic microorganisms with low genetic similarity to known species.[5][6][7][8] This indicates a long evolutionary history of adaptation to these habitats with few new species from other environments becoming adapted over time.

In-depth genetic surveys also show an unusually low overlap in the microbial community present, between soda lakes with slightly different conditions such as pH and salinity.[3][7] This trend is especially strong in the bottom layer (hypolimnion) of stratified lakes,[4] probably because of the isolated character of such environments. Interestingly, diversity data from soda lakes suggest the existence of many endemic microbial species, unique to individual lakes.[3][7] This is a controversial finding, since conventional wisdom in microbial ecology dictates that most microbial species are cosmopolitan and dispersed globally, thanks to their enormous population sizes, a famous hypothesis first formulated by Lourens Baas Becking in 1934 ("Everything is everywhere, but the environment selects").[11]

Ecology

Carbon cycle

Cyanobacteria of the genus Arthrospira (synonymous to "Spirulina")

Photosynthesis provides the primary energy source for life in soda lakes and this process dominates the activity at the surface. The most important photosynthesizers are typically cyanobacteria, but in many less "extreme" soda lakes, eukaryotes such as green algae (Chlorophyta) can also dominate. Major genera of cyanobacteria typically found in soda lakes include Arhtrospira (formerly Spirulina) (notably A. platensis, Anabaenopsis,[12] Cyanospira, Synechococcus or Chroococcus.[13] In more saline soda lakes, haloalkaliphilic archaea such as Halobacteria and bacteria such as Halorhodospira dominate photosynthesis. However, it is not clear whether this is an autotrophic process or if these require organic carbon from cyanobacterial blooms, occurring during periods of heavy rainfall that dilute the surface waters.[1]

Below the surface, anoxygenic photosynthesizers using other substances than carbon dioxide for photosynthesis also contribute to primary production in many soda lakes. These include purple sulfur bacteria such as Ectothiorhodospiraceae and purple non-sulphur bacteria such as Rhodobacteraceae (for example the species Rhodobaca bogoriensis isolated from Lake Bogoria.[14])

The photosynthezising bacteria provide a food source for a vast diversity of aerobic and anaerobic organotrophic microorganisms from phyla including Proteobacteria, Bacteroidetes, Spirochaetes, Firmicutes, Themotogae, Deinococci, Planctomycetes, Actinobacteria, Gemmatimonadetes, and more.[1][3] The stepwise anaerobic fermentation of organic compounds originating from the primary producers, results in one-carbon (C1) compounds such as methanol and methylamine.

At the bottom of lakes (in the sediment or hypolimnion, methanogens use these compounds to derive energy, by producing methane, a procedure known as methanogenesis. A diversity of methanogens including the archaeal genera Methanocalculus, Methanolobus, Methanosaeta, Methanosalsus and Methanoculleus have been found in soda lake sediments.[1][15] When the resulting methane reaches the aerobic water of a soda lake, it can be consumed by methane-oxidizing bacteria such as Methylobacter or Methylomicrobium.[1]

Sulfur cycle

Sulfur-reducing bacteria are common in anoxic layers of soda lakes. These reduce sulfate and organic sulfur from dead cells into sulfide (S2-). Anoxic layers of soda lakes are therefore often rich in sulfide. As opposed to neutral lakes, the high pH prohibits the release of hydrogen sulfide (H2S) in gas form. Genera of alkaliphilic sulfur-reducers found in soda lakes include Desulfonatronovibrio and Desulfonatronum.[1] These also play important an ecological role besides in the cycling of sulfur, as they also consume hydrogen, resulting from the fermentation of organic matter.

Sulfur-oxidating bacteria instead derive their energy from oxidation of the sulfide reaching the oxygenated layers of soda lakes. Some of these are photosynthetic sulfur phototrophs, which means that they also require light to derive energy. Examples of alkaliphilic sulfur-oxidizing bacteria are the genera Thioalkalivibrio, Thiorhodospira, Thioalkalimicrobium and Natronhydrogenobacter.[1]

Nitrogen and other nutrients

Nitrogen is a limiting nutrient for growth in many soda lakes, making the internal nitrogen cycle very important for their ecological functioning.[16] One possible source of bio-available nitrogen is diazotrophic cyanobacteria, which can fix nitrogen from the atmosphere during photosynthesis. However, many of the dominant cyanobacteria found in soda lakes such as Arthrospira are probably not able to fix nitrogen.[1] Ammonia, a nitrogen-containing waste product from degradation of dead cells, can be lost from soda lakes through volatilization because of the high pH. This can hinder nitrification, in which ammonia is "recycled" to the bio-available form nitrate. However, ammonia oxidation seems to be efficiently carried out in soda lakes in either case, probably by ammonia-oxidizing bacteria as well as Thaumarchaea.[16]

List of soda lakes

The following table lists some examples of soda lakes by region, listing country, pH and salinity. NA indicates 'data not available'

Name Country pH Salinity
Africa
Wadi El Natrun lakes Egypt 9.5 5%
Malha Crater Lake Sudan 9.5-10.3 NA
Lake Arenguadi (Green Lake) Ethiopia 9.5-9.9[3] 0.25%
Lake Basaka Ethiopia 9.6[3] 0.3%
Lake Shala Ethiopia 9.8[3] 1.8%
Lake Chitu Ethiopia 10.3[3] 5.8%
Lake Abijatta Ethiopia 9.9[3] 3.4%
Lake Magadi Kenya 10 >10%
Lake Bogoria Kenya 10.5 35%
Lake Turkana Kenya 8.5-9.2[17] 0.25%
Lake Nakuru Kenya 10.5 NA
Lake Logipi Kenya 9.5-10.5 2-5%
Lake Sonachi (Crater Lake) Kenya NA NA
Lake Manyara Tanzania 9.5-10[18] NA
Lake Natron Tanzania 9-10.5 >10%
Lake Rukwa Tanzania 8-9[18] NA
Lake Eyasi Tanzania 9.3[18] 0.5%
Lake Ngami Botswana
Rombou Lake Chad 10.2[19] 2%
Asia
Kulunda Steppe Lakes Russia NA NA
Lake Khatyn Russia 10 NA
Lake Van Turkey 9.7-9.8 NA
Lake Salda Turkey NA NA
Lake Urmia Iran NA 30%
Lonar Lake (Crater Lake) India 9.5-10.5[5] 1%
Sambhar Salt Lake India 9.5 7%
Khyagar Lake[19] India 9.5 0.6%
Tso Moriri Salt Lake India 9.0 NA
Tso Kar Salt Lake India 8.8 NA
Lake Surigh Yilganing Kol Aksai Chin, India NA NA
Tso Tang Lake Aksai Chin, India NA NA
Aksayqin Hu Lake Aksai Chin, India NA NA[20]
Lake Hongshan Hu Aksai Chin, India NA NA
Tianshuihai lake Aksai Chin, India NA NA
North Tianshuihai lake Aksai Chin, India NA NA
Kushul lake Aksai Chin, India NA NA
Pangong Salt Lake India & China 9.4 0.9%[21]
Spanggur Tso (Pongur Tso) India & China NA NA
Guozha lake China NA NA
Qinghai Lake China 9.3[22] 2.2%
Namucuo Lake China 9.4[22] 0.2%
Lake Zabuye (Drangyer) China 10 NA
Taboos-nor Mongolia NA NA
Europe
Lake Fehér (Szeged) Hungary NA NA
Böddi-szék Hungary 8.8-9.8[23] NA
Lake Neusiedl (Fertö) Austria, Hungary 9-9.3[23] NA
Rusanda Serbia 9.3[23] NA
Kelemen-szék Hungary 9-9.7[23] NA
North America
Mono Lake USA 9.8[16] 8%
Big Soda Lake (Nevada) USA 9.7 NA
Soap Lake USA 9.7 0.7%
Baldwin Lake USA NA NA
Alkali Lake (OR) USA 11 NA
Summer Lake USA NA NA
Owens Lake USA NA NA
Borax Lake USA NA NA
Manitou Lake Canada NA NA
Goodenough Lake Canada 10.2 NA
Lake Texcoco Mexico 8.8-11.5 8%
Lake Alchichica Mexico 8.9 NA
South America
Antofagasta Lake Chile NA NA
Australia
Lake Werowrap[19] Australia 9.8 4%

Industrial use

Many water soluble chemicals are extracted from the soda lake waters worldwide. Lithium carbonate (see Lake Zabuye), potash (see lake Lop Nur and Qinghai Salt Lake Potash), soda ash (see Lake Natron), etc. are extracted in large quantities. Lithium carbonate is a raw material in production of lithium which has applications in lithium storage batteries widely used in modern electronic gadgets and the electricity driven auto mobiles. Water of some soda lakes are rich in dissolved uranium carbonate.[24] Algaculture is carried out on a commercial scale with soda lake water.

See also

References

  1. ^ a b c d e f g h i Grant, W. D. (2006). Alkaline environments and biodiversity. in Extremophiles, 2006, UNESCO / Eolss Publishers, Oxford, UK
  2. ^ Melack JM, Kilham P (1974). "Photosynthetic rates of phytoplankton in East African alkaline, saline lakes" (PDF). Limnol. Oceanogr. Retrieved 27 December 2012. {{cite web}}: Missing pipe in: |volume= (help)
  3. ^ a b c d e f g h i Lanzén A, Simachew A, Gessesse A, Chmolowska D, Øvreås L. "Surprising Prokaryotic and Eukaryotic Diversity, Community Structure and Biogeography of Ethiopian Soda Lakes". PLoS ONE. Retrieved 2 August 2013. {{cite web}}: Missing pipe in: |volume= (help)CS1 maint: multiple names: authors list (link)
  4. ^ a b c Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1007/s00248-010-9775-6, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1007/s00248-010-9775-6 instead.
  5. ^ a b c Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1002/jobm.201000001, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1002/jobm.201000001 instead.
  6. ^ a b Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1007/s00248-005-0228-6, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1007/s00248-005-0228-6 instead.
  7. ^ a b c d Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 22676420, please use {{cite journal}} with |pmid=22676420 instead.
  8. ^ a b Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 17070674, please use {{cite journal}} with |pmid=17070674 instead.
  9. ^ Handelsman J (2004). "Metagenomics: application of genomics to uncultured microorganisms". Microbiol Mol Biol Rev. 68, pages=669–685. {{cite journal}}: Missing pipe in: |volume= (help)
  10. ^ Tringe SG, Hugenholtz P (2008). "A renaissance for the pioneering 16S rRNA gene". Curr Opin Microbiol. 11: 442–446. doi:10.1016/j.mib.2008.09.011.
  11. ^ Baas-Becking, Lourens G.M. (1934), Geobiologie of inleiding tot de milieukunde, The Hague, the Netherlands: W.P. Van Stockum & Zoon
  12. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1016/j.limno.2011.12.002, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1016/j.limno.2011.12.002 instead.
  13. ^ Zavarzin GA, Zhilina TN, Kevbrin VV (1999). "Alkaliphilic microbial community and its functional diversity". Mikrobiologiya. 86: 579–599.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  14. ^ Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 10985738, please use {{cite journal}} with |pmid=10985738 instead.
  15. ^ Antony CP, Colin Murrell J, Shouche YS (July 2012). "Molecular diversity of methanogens and identification of Methanolobus sp. as active methylotrophic Archaea in Lonar crater lake sediments". 81 (1): 43–51. doi:10.1111/j.1574-6941.2011.01274.x. PMID 22150151. {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: multiple names: authors list (link)
  16. ^ a b c {{Cite doi|10.4319/lo.2008.53.6.2546}}
  17. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1016/0016-7037(83)90240-5, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1016/0016-7037(83)90240-5 instead.
  18. ^ a b c Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1016/j.bbr.2011.03.031, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1016/j.bbr.2011.03.031 instead.
  19. ^ a b c Hammer U.T. (1986). Saline lake ecosystems of the world, Kluwer Academic Publishers, Hingham MA
  20. ^ "Glacial and lake fluctuations in the area of the west Kunlun mountains during the last 45000 years" (PDF). Retrieved 23 July 2013.
  21. ^ T.V. Ramachandra & others. "EIA study near Pangong lake, India". Retrieved 27 December 2012.
  22. ^ a b Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1128/AEM.01544-09, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1128/AEM.01544-09 instead.
  23. ^ a b c d Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.4081/jlimnol.2009.385, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.4081/jlimnol.2009.385 instead.
  24. ^ "Uranium in Sambhar lake waters in India" (PDF). Retrieved 5 December 2013.
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