South African Diatom Index published

21 May 2012

Diatoms are powerful indicators of water quality (Photo: Bill Harding)

Diatoms provide probably the most powerful biological indicator for assessing water quality in streams, rivers and wetlands.  Additionally, they can be used in a paleoecological application to determine historical conditions, an attribute which can be used in climate change assessments.  Globally, there is a massive database of information which supports the cosmopolitan use of these algae in aquatic assessments.

The culmination of a programme of research and method development, led by Bill Harding from DH Environmental Consulting, has been the formulation of the South African Diatom Index (SADI), a tool which allows the numerical composition of diatoms, collected from a specific site, to be translated into a value representing the water quality (and a whole lot of other ecological inferences as well simply not available from any other bio-indicator approaches).

The SADI has been made available as part of the global software package known as OMNIDIA, a collection of similar indices.  A report on the work has been published by the Water Research Commission, entitled “THE SOUTH AFRICAN DIATOM INDEX, A PRELIMINARY INDEX FOR INDICATING WATER QUALITY IN STREAMS AND RIVERS IN SOUTHERN AFRICA” (WR Harding and JC Taylor, Report 1707/1/11).

Why preliminary?  Well, the SADI so far has focussed on the 300 odd species of diatoms in this country that are the most common and likely to be encountered.  There is another layer to this work, which, most regrettably, has not been taken up by the WRC or the Department of Water Affairs, namely to augment the SADI with specific, regional and endemic information that would make it an even more powerful tool.  For example, the index needs to include those diatoms special to the Western Cape rivers.

The arrival of the index, already widely in use by water quality specialists, followed the development of a toolkit of methods and taxonomic keys, including an interactive key now available globally via the internet.  Given that Version 1.0 is of a cosmopolitan nature, it can be used pretty much anywhere in the world.

A parallel work testing the approach in wetlands will be published shortly.

Lots more information on this work can be found by searching Droplets for “diatoms”.


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