page_title: Soda lake
section_title: Carbon cycle
hierarchical_section_title: Soda lake / Ecology / Carbon cycle
caption_attribution_description: Spirulina sp.
context_page_description: A soda lake or alkaline lake is a lake on the strongly alkaline side of neutrality, typically with a pH value between 9 and 12. They are characterized by high concentrations of carbonate salts, typically sodium carbonate, 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. The resulting hypersaline and highly alkalic soda lakes are considered some of the most extreme aquatic environments on Earth.
  In spite of their apparent inhospitability, soda lakes are often highly productive ecosystems, compared to their freshwater counterparts. Gross primary production rates above 10 g C m⁻² day⁻¹, over 16 times the global average for lakes and streams, have been measured. 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.
context_section_description: 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, Cyanospira,
  Synechococcus or Chroococcus.  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.
  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-sulfur bacteria such as Rhodobacteraceae (for example the species Rhodobaca bogoriensis isolated from Lake Bogoria.)
  The photosynthezising bacteria provide a food source for a vast diversity of aerobic and anaerobic organotrophic
  microorganisms from phyla including Proteobacteria, Bacteroidetes, Spirochaetes, Firmicutes, Thermotogae, Deinococci, Planctomycetes, Actinobacteria, Gemmatimonadetes, and more.  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.  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.
caption: Cyanobacteria of the genus Arthrospira (synonymous to "Spirulina")
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