Limnochemistry and Biological Characteristics of Small High Altitude Reservoirs in a Sub-Tropical Region, Nyanga, Zimbabwe

Abstract

The ecological characteristics of ten small reservoirs in the high-altitude Eastern Highlands region of Zimbabwe, were studied. Water quality and sediment quality for a range of parameters and also the phytoplankton, zooplankton, macrophyte communities were described. The water quality of the reservoirs was in near pristine condition and their trophic status was oligotrophic and ultra-oligotrophic. In contrast, the sediments especially of the Connemara reservoirs had unusually high levels of phosphorus. Given the high levels of dissolved oxygen in the reservoirs, most phosphorus is likely to be bound to the sediment but its present source was not immediately clear. Phytoplankton densities were very low indicative of low productivity. The major phytoplankton taxa identified included Cyanophyta, Euglenophyta, Chrysophyta, Bacillariophyceae, Pyrrophyta and Chlorophyta. The least abundant taxa were the Euglenophyta while the most abundant was the Chlorophyta. Zooplankton taxa comprised of Daphniidae, Chydoridae, Bosminidae, Sididae, Macrothricidae, Cyclopoida and Calanoida. The daphniids were the most abundant species, while the rotifers were not identified further in this study. Several macrophyte species were identified but the reservoirs showed low similarity in macrophytes composition. There were no clear environmental gradients to explain the patterns. The results of this study provide an important baseline from which future studies especially on the impact of climate change and landuse can be assessed.