From: University of Amsterdam
Published October 6, 2017 11:46 AM

Microbes Dictate Regime Shifts Causing Anoxia in Lakes and Seas

Gradual environmental changes due to eutrophication and global warming can cause a rapid depletion of oxygen levels in lakes and coastal waters. A new study led by professors Jef Huisman and Gerard Muyzer of the University of Amsterdam (UvA) shows that microorganisms play a key role in these disastrous regime shifts. The researchers’ findings were published in the journal Nature Communications on 6 October.

Regime shifts are abrupt, large and persistent changes in the structure and function of ecosystems triggered by gradual changes in environmental conditions. Regime shifts have been described for a large variety of ecosystems. One type of regime shift may occur in lakes and coastal waters when a rapid depletion of the dissolved oxygen concentration leads to a lack of oxygen, which is detrimental to most aquatic organisms. Although this phenomenon is well known, the underlying mechanisms causing the transition from oxic to anoxic conditions are not fully understood.

Shifts in microbial composition

Scientists from the UvA and the University of Edinburgh developed a mathematical model to investigate interactions between the microbial species composition and the dissolved oxygen concentration. They discovered that lakes can be in two alternative stable states: one in which the lake is rich in oxygen, and another in which it lacks oxygen. Transitions from the oxic to the anoxic state occur in the form of a regime shift. ‘When the oxygen influx is gradually reduced, at first oxygen-producing cyanobacteria and algae still persist and the lake remains in the oxic state’, explains first author Tim Bush. ‘Below a critical threshold, however, sulfate-reducing bacteria and photosynthetic sulfur bacteria take over. These cause an increase in sulfide concentrations, which then kills the cyanobacteria and rapidly flips the lake from an oxic to an anoxic state.’

Read more at University of Amsterdam

Photo credit: Christian Fischer via Wikimedia Commons

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