Diatoms: biomonitors for wetlands

Using these simple, central organisms, biologists are developing a new way of monitoring the ecological health of wetlands that can work in conjunction with existing tests. Chris Nel reports.
Issue date 7 September 2007

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The Water Research Commission’s National Wetland Research Programme, under the leadership of the University of Cape Town, is developing a technique that uses diatoms as a biological indicator to monitor the ecological health of wetlands. This new method can even reveal some of the history of certain wetlands.
Diatoms – microscopic, single-celled algae with silica walls – have been used to measure water quality since 1870. With technological advances, the techniques have become more sophisticated and reliable. Diatoms are used internationally in river biomonitoring and to measure the success of wetland restoration projects. Diatom methodology is now being developed for use in South African wetlands.

Around 70 000 fossil and recent diatom species are known. Diatoms are hyperabundant and crucially important. They comprise approximately 25% of plant life by weight and produce at least a quarter of the oxygen in the atmosphere. Living diatoms provide high quality nutrition for a wide range of animal life from microscopic protozoa to baleen whales. Dead diatoms fall to the ocean floor and create an oil-rich plasma layer that is, over thousands of years, transformed into petroleum. Their microscopic silica skeletons are commonly mined as a fine powder and used as filters and abrasives. In addition to their ecological and economic value, diatoms are crucial environmental indicators. Biologists use living diatoms to accurately assess pollution levels in certain ecosystems. Paleontologists use the remains of extinct diatoms to reconstruct ancient climates and interpret the environment in which certain strata were formed and deposited.

As they’re situated at the base of the food pyramid, diatoms are affected by everything that happens in a wetland, and can reveal detailed information about the system.
Dr Bill Harding of DH Environmental Consulting, who is leading the Diatoms in Biomonitoring team, explains: “The composition of diatom species and the presence of certain species reflects 50% to 70% of water chemistry. They grow on anything – rocks, snails, plants – and disperse widely, so you can take samples at any point in the wetland and get a reasonable result, as long as there are no major hydrological differences.”

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