ECOLOGICAL PROBLEMS IN HARTBEESPOORT DAM

Abstract

In Hartbeespoort Dam ecological problems arise primarily as a consequence of the reservoir's hypertrophic condition. The development of anaerobic conditions, high primary productivity and blue-green algal dominance have many detrimental influences on ecosystem structure and function. With high rates of production, the underutilized phytoplankton biomass accumulates into nuisance hyperscums. Zooplankton biomass and succession are limited by low food quality and the inability of filter-feeders to ingest large blue-green algal colonies. Fish production whilst high, is limited in species diversity. Many of the fish species preferred by anglers are virtually absent and the fish community shows signs of stress. A typical symptom of hypertrophy, which is also a direct consequence of the reduced efficiency of energy transformation along ecosystem pathways, is the shift away from the phytoplankton/-zooplankton/fish pathway to a series of indirect pathways via decomposition processes of the detritus cycle. Events in Hartbeespoort Dam indicate ecological instability (massive algal blooms, reduced species diversity, potential whole-lake anoxia).