So what is this “trophic” stuff all about?

31 January 2012

Droplets makes frequent reference to the term “eutrophication”.  This is a term applied to waterbodies to describe the level of nutrients available.  The word stems from the Greek and means “well-fed”.  As with people (“you are what you eat”), lakes have a limit to how much food they can take before they start to become clogged up – in this case not rolls of fat but too many plants, unwanted algae, undesirable species of fish that can tolerate the mucky conditions, and so on.

Lakes progress naturally from a condition of very low nutrient enrichment (“oligotrophic”), to moderate enrichment (“mesotrophic”), and then it all becomes pear-shaped as we move into “eutrophic” and “hypertrophic”.  In South Africa, most of the dams in the most densely part of the country, Gauteng Province, are hypertrophic.

The natural process takes centuries.  Put people in the picture and it takes a few decades –  a problem that started with post-WWII industrialization and a lack of awareness about what dumping sewage could do! (Sewage is FULL of nutrients!).

The following set of images, sourced from the UWEX Lakes Partnership, illustrates the process – but the images don’t show the ultimate hypertrophic state of algal-dominance with little else (e.g. Hartbeespoort Dam).

Pay attention to what happens in the background, that is in the “catchment”:





Oligotrophic (Photo: Bill Harding)

Mesotrophic (Photo: Bill Harding)

Eutrophic to hypertrophic (Photo: Bill Harding)

An example of hypertrophic (Photo: Bill Harding)


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