MANAGEMENT OPTIONS FOR SHALLOW HYPERTROPHIC LAKES, WITH PARTICULAR REFERENCE TO ZEEKOEVLEI, CAPE TOWN

Abstract

Zeekocvlei, a freshwater coastal lake, is an important regional recreation area in the south-western Cape, South Africa. The lake is hypertrophic, experiences perenially dense populations of cyanobacteria (Microcystis), invasive bulrush and reed encroachment, and has a thick benthic layer of sediments rich in organic matter. User and scientific surveys have indicated that management problems centre around the dense phytoplankton population and the nutrient loading of the lake. Both in-lake and catchment-based management options for improving the water quality of the lake were evaluated. Given the present socio-economic constraints in South Africa, only catchment-based management can be recommended before any rehabilitation measures are undertaken in the lake itself. This would entail the investigation and implementation of measures to reduce levels of catchment-derived nutrient loading by managing the water quality of agricultural (predominantly horticulture) and urban catchment runoff.