Causes and consequences of algal blooms in Loch Logan, an urban impoundment

Abstract

Loch Logan is situated at the “Waterfront” in the city centre of Bloemfontein. During the rainy season it collects stormwater from the surrounding catchment areas as well as other urban runoff water. During summer, Loch Logan frequently experiences
algal blooms. The system can be classified as eutrophic due to high dissolved reactive phosphate (PO4-P) and chlorophyll-
a (Chl-a) concentrations. Nitrogen is probably the limiting factor to algal growth. The consequences of the eutrophication
are algal blooms, oxygen depletion, fish kills, excessive macrophyte growth, odour problems and extreme oscillations occur in physical and chemical parameters.

Water SA Vol.31 (3) 2005: pp.385-392