Wetlands of South Africa
Abstract
South Africa's only significant natural standing waters are its coastal lakes, mostly formed by the drowning of deep estuarine valleys. They include totally isolated lakes and lakes with surface connections to the marine environment but without tidal inflows, through to those with either continuous or intermittent tidal connections. Three major regional groups exist. Subtropical lakes on the north-eastern seaboard; warm temperate lakes on the Cape south coast, and a more disparate array in the south-western Cape, experiencing a Mediterranean climate. Total surface areas decline consecutively between these groups. As may be seen from Table 1, morphometric and physico-chemical characteristics vary widely between the lakes. Mean depths range from -1 m to 14 m, surface areas from 10 to 41 700 ha, salinities from <0.1 to >35 %o, and Secchi depth transparencies from <0.1 m to >5 m. Because
they are mostly shallow, and/or face high wind exposure, the lakes do not stratify vertically, apart from two ectogenically meromictic systems (KuHlange, Swartvlei), in which vertical stability is imposed by salt-water intrusions. Nutrient levels in most of the lakes are reasonably low, although eutrophication impacts are
increasingly apparent in lakes lying in catchments experiencing prominent human population and/or agricultural developments. The lakes vary significantly in biotic structure. Some are definitely macrophyte-based systems, while phytoplankton production is the principal primary energy basis of others. Differences in the autotrophic base are reflected in the resulting faunal communities, in the principal food web structures, and in consequent ecological
dynamics. Several isolated lakes are especially interesting in retaining an array of estuarine relicts, while presently
open systems with episodic or regular tidal connections with the marine environment provide important habitat (juvenile nursery or adult feeding grounds) for various euryhaline fish in particular. Some of the northern coastal lakes are still almost pristine, whereas the southern lakes collectively have to face major adverse anthropogenic impacts or perturbations.
Management and research needs are difficult to generalize. Management should be targeted to specified objectives. Once formalized, appropriate research needs can be identified. The diversity and inherent natural variability of the coastal lakes necessitates a rather individual approach. But in general terms, recognition that these iakes mirror their catchments leads to the certainty that only an essentially holistic approach to management will be successful. Some basic research needs are specifically identified.
GI Cowan (ed).1995.
South African coastal lakes
RC Hart
| If you have any comments on this page, or need more information, please contact John Dini at nat_jd@ozone.pwv.gov.za. |
| This page is maintained by the South African Wetlands Conservation Programme and was last updated on 12 January 1999. |