THE DETERMINATION OF CHLOROPHYLL a IN WATER CONTAINING SEDIMENT

SUMMARY

The presence of sediment at concentrations of 0,2% by mass in water samples significantly lowered the amount of chlorophyll a that could be measured. Two types of sediment differed in their ability to lower the chlorophyll a concentration. The chemically more active sediment had a marked depressive effect on the chlorophyll a concentration and the relationship between chlorophyll a and cell numbers in the samples was non-linear. It is recommended that the use of chlorophyll a as an indicator of biomass in water containing sediment should be approached with care.     

THE DISTRIBUTION AND ECOLOGY OF TWO MULLET SPECIES IN SOME FRESH WATER RIVERS IN THE EASTERN CAPE,SOUTH AFRICA

SUMMARY

Data on the relative abundance, penetration and breeding biology of the freshwater mullet Mugil cephalus and the flathead mullet Mugil cephalus in the freshwater reaches of some Eastern Cape coastal rivers are described. The differences found between the two species indicate that Myxus capensis is more specialized for a catadromous life history in an unstable riverine environment. Evidence showing the importance of the freshwater phase for the latter species is given and the disastrous effects of the erection of barriers to fish movement are stressed.     

AN HOLISTIC APPROACH TO THE MANAGEMENT OF WATER QUALITY IN FALSE BAY,CAPE TOWN,SOUTH AFRICA

Summary

An overview of the water quality status of False Bay identified the bacterial/viral water quality of stormwater and rivers discharging near contact recreation beaches to be the management concern of highest priority. A second water quality concern is the potential impact of nutrients being discharged into False Bay on the surf zone and bay ecosystems. Heavy metals, hydrocarbons and industrial chemical discharges into the Bay are not regarded as a serious water quality threat. Much of the future development planned for Metropolitan Cape Town will impact on the volume and water quality of rivers, groundwater, stormwater and wastewater flowing into False Bay; hence the need for an integrated catchment management approach to the management of the bay.

An assessment of the constraints facing the holistic management of the bay and catchment concludes that the four main concerns are: (1) a lack of key research information on the options for stormwater management, and on the loading and potential impacts of nutrients being discharged into the surf zone and bay ecosystems; (2) jurisdictional fragmentation, and the lack of coordinated policy and planning between different local and government authorities and other users; (3) legislative fragmentation; and (4) a lack of private sector and public consultation by authorities. Preliminary ideas on the structure of a management body for False Bay and its catchment which address the concerns listed above are presented.     

THE USE OF TOXICITY TESTING IN EFFLUENT REGULATION AND CONTROL: A NEW DIMENSION TO ASSESSMENT AND MANAGEMENT OF WATER QUALITY IN SOUTH AFRICA

Summary

Efficient management tools are continually required to cope with increasing demands placed on the quality and quantity of aquatic resources. Recent developments in environmental monitoring indicate the importance of incorporating biological indicators in assessment programmes. Aquatic toxicology has consequently become an important monitoring and regulatory science. Applications of aquatic toxicity testing include: deriving water quality criteria; toxicological evaluations of whole effluents and receiving waters; and the estimation of ecological risk. Toxicity testing can potentially play a significant role in improving water quality in years to come, especially through its application in effluent regulation. Currently however, few environmental laboratories in South Africa have the required expertise and facilities to carry out a representative range of toxicity tests. Training and funding are required to build the capacity for the necessary developmental research, before toxicity testing can routinely be implemented.

The significant problems we face cannot be solved at the same level of thinking we were at when we created them. Albert Einstein.     

SOME ASPECTS OF THE ECOLOGY OF THE FRESHWATER CRAB (POTAMONAUTES PERLATUS MILNE EDWARDS) IN THE UPPER REACHES OF THE BUFFALO RIVER,EASTERN CAPE PROVINCE,SOUTH AFRICA.

Summary

Freshwater crabs (Potamonautes perlatus) are the largest naturally occurring invertebrates in southern African rivers. The ecology of these animals in South African riverine ecosystems is little understood. This study investigates some aspects of the population and feeding ecology of P. perlatus in the upper reaches of the Buffalo River. The densities of crabs (carapace width larger than 25 mm) at two sites in the river ranged between 1.72 and 5.25 crabs m², higher than previously recorded for freshwater crabs in rivers in southern Africa and southern Italy. Twenty-four hour observations revealed that P. perlatus has a nocturnal habit. The diet of P. perlatus was established by examination of the contents of the fore-gut. Crabs with a carapace width smaller than 40 mm fed predominantly on aquatic invertebrates while larger crabs fed on allochthanous material (leaf litter), detritus and algae. Through feeding, crabs reduced the surface area of leaves in the stream by 99.95%.