The use of biological indices to assess the water quality of the Vaal River with specific reference to the Vredefort Dome area

Abstract

Water is one of South Africa's most limited resources and the Vaal River, as one of the country's hardest working rivers, provides water to a considerable proportion of the country's agricultural, industrial and household needs. The Vredefort Dome, one of the biggest meteorite impact sites on earth, is of great ecological significance. It maintains a unique ecosystem of biota that significantly differs from the surrounding area. The area has been proposed to receive World Heritage status, and has potential as an eco-tourism destination. From October 2001 - August 2002 the quality of the Vaal River in the Vredefort Dome was assessed with biological indices. SASS 5, IHAS and physical-chemical analysis were conducted along the Vaal River within the Vredefort Dome. From the results, it was evident that good to fair water quality prevailed in the Vredefort dome. The SASS and ASPT scores were in the fair to good range, and the number of taxa fell into the good to excellent range, indicating good overall river health. Seasonal patterns in the occurrence of macroinvertebrates were observed for this section of the Vaal River. Habitat scores were generally in the fair range, indicating adequate habitat conditions. The results of the physical/chemical analysis did not show any significant problems. The geomorphology of the Dome indicates a big slope between the first and last site, averaging a drop of 1.96m.km-1. Preliminary investigations into the occurrence of freshwater molluscs in the Vredefort Dome indicated the distribution of molluscs in the area. Problems encountered in the Dome area were of aesthetical importance, resulting from a high degree of eutrophication. More sampling is advised before any management proposals for the Dome area could be made. It is advisable that this area should be subjected to routine sampling to spot potential water quality problems as soon as possible.