An investigation of ecosystem regime shifts caused by regulated water release into Phongolo River from the Pongolapoort Dam, Kwazulu-Natal, South Africa

Abstract

Rivers have disturbance regimes of which flooding forms a major part. Scouring floods alters nutrient content, in-channel habitat, benthic macro-invertebrate assemblage structure and water quality in genera!. A novel macro-invertebrate regime or regime shift created by the artificial flood releases in the Phongolo River was determined by comparing the pre- and post-flood in situ physico-chemical aspects, primary production and benthic macro-invertebrate composition of two sites immediately downstream of the dam. nMDA results showed that there is no variation between the pre- and post-flood benthic macro-invertebrate composition of two sites immediately downstream but the sites were significantly difference (P < 0.05). The benthic macro-invertebrates were affected by the electric conductivity, oxygen level, ammonium concentration, nitrite concentration and pH when using RDA, and phosphate was correlated with the chlorophyll-a when using Person's correlation. lt was found that flood reduced the standing stock producers, organic matter and benthic macro-invertebrates abundance, diversity and biomass and therefore a novel of macro-invertebrate regime or regime shift was created by the artificial flood releases in the Phongolo River.