Diatoms As Biological Indicators

The Oxford Dictionary of Science defines an indicator species as “a plant or animal that is very sensitive to a particular environmental factor, so that its presence (or absence) in an area can provide information about the levels of that factor.

There are many reasons why diatoms make excellent biological indicators, The Great Lakes Ecological Indicators website has compiled a list of reasons in their paper assessing the current usage of diatoms in order to use diatom metrics when monitoring lakes:

  • “ubiquitous; occur in virtually any aquatic environment
  • diverse; can provide a fine-grained assessment of environmental conditions
  • versatile; sensitive to a variety of stressors, particularly water chemistry
  • short turnover rate; respond rapidly to changing conditions
  • more time-integrative than “snapshot” environmental measurements
  • narrow tolerances and specific optima to environmental conditions”
The paper also mentions that because diatoms are easily preserved in sediments, they are of great use in paleolimnology, a subject which I have also discussed on the blog.
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Figure 1. An example of diatoms viewed at 1000x magnification, taken from my own research. (c) Cara Thompson 2014

Figure 1. An example of diatoms viewed at 1000x magnification, taken from my own research. (c) Cara Thompson 2014

The acid status of water bodies globally is a growing field of research, as the focus on climate change also increases. The United Kingdom Acid Waters Monitoring Network is responsible for tracking changes in the acidity of water bodies in the UK, and in 2004 the 15 year report was published in Environmental Pollution (Monteith & Evans 2005) discussing changes in pH, as well as how the communities of diatoms have altered. The data was collected from 22 sites across the UK, and sediment samples were taken from these sites for paleolimnological analysis to determine the historical composition.

The diatom samples were collected annually during the summer months, by scraping rocks that were permanently submerged. The samples were then mounted and identified using a microscope at 1000x magnification (Fig. 1). The report found that the type of diatoms found was largely predictable by the pH of the site (Fig. 2)

Figure 2. An example of the species of diatoms found at different acidity levels.

Figure 2. An example of the species of diatoms found at different acidity levels.

Published in the same issue of Environmental Pollution was a further discussion (Monteith et al. 2005) of how the organisms in a water body respond to rising pH. The species of diatom found changed over the 15 year study, in line with the changing pH. This suggests that diatoms are a suitable indicator of water pH. As the pH becomes more neutral, the species found tends towards the species identified using paleolimnology, suggesting recovery, however, there is still relatively low species diversity when compared to historic conditions.

In conclusion, as well as a measure of pH, diatoms are a very useful biological indicator for many water quality concerns.

Reference

Daintith, J. and Martin, E. (2010). A dictionary of science. 6th ed. Oxford: Oxford University Press, p.418.

Great Lakes Ecological Indicators: Diatoms. http://glei.nrri.umn.edu/default/documents/Pubs/Diatoms_1-pgr.pdf

Monteith, D. & Evans, C. (2005). The United Kingdom Acid Waters Monitoring Network: a review of the first 15 years and introduction to the special issue. Environmental Pollution, 137 (1), pp. 3–13.

Monteith, D., Hildrew, A., Flower, R., Raven, P., Beaumont, W., Collen, P., Kreiser, A., Shill & Winterbottom, J. (2005). Biological responses to the chemical recovery of acidified fresh waters in the UK. Environmental Pollution, 137 (1), pp. 83–101.

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