The calibration of an artificial stream system used to investigate the tolerances of South African riverine invertebrates to selected water quality variables.

Water quality management in South Africa aims at the maintenance of water in a state that is "fit for use." This includes use for agriculture, industry, domestic supply, and recreation,together with the maintenance of the natural, functioning resource base:aquatic ecosystems. The water quality requirements of riverine ecosystems need to be established to fulfil this last aim. A first step is the investigation of the tolerances of a range of riverine organisms to key water quality variables or pollutants. However, riverine organisms require flowing water, and in order to provide a flowing water experimental facility, an artificial stream laboratory has been developed. The objective of calibrating this system was to establish the physical and chemical conditions in the streams before test organisms were introduced; then to monitor behavior of organisms in the streams before water quality conditions were experimentally altered. This paper introduces the concept of system calibration and reports on hydraulic and water quality calibration, and the effects of handling on test organisms.

Salinity tolerances of selected macroinvertebrates of the Sabie River, Kruger National Park, South Africa.

Salinization has been identified as the most important problem facing the managers of South African freshwaters. Laboratory-based toxicity tests were conducted to assess the tolerance of selected macroinvertebrates to elevated salt concentrations. Since the Kruger National Park is the focus of river research in South Africa, and the Sabie River is the least mineralized river in the park, 96-h acute toxicity tests were conducted using Sabie River water and an ephemeropteran mayfly Tricorythus sp. found in the river. Experiments were conducted inflowing water systems known as raceways. The tolerance of the mayfly to two sodium salts, sodium chloride and sodium sulphate, was assessed at a range of selected conductivity levels/concentrations. The results indicated that mortality cannot be linked only to conductivity or total dissolved solid(TDS) concentrations, but also to the nature of the salt. Sodium sulphate was considerably more toxic to Tricorythus sp. than sodium chloride. Causes of mortality and implications for the development of water quality guidelines for the natural aquatic environment are discussed.