Impact on water quality of land uses along Thamalakane-Boteti River: an outlet of the Okavango Delta

Abstract

Botswana is a semiarid country and yet has one of the world’s famous wetlands: the Ok­avango Delta. The Thamalakane- Boteti River is one of the Delta’s outlets. The water quality of the Thamalakane-Boteti River was determined and related to its utilisation. The major land uses along the Thamalakane River within Maun are residential areas, lodges, hotels, and grazing by cattle and donkeys. The water is used as a source of water for livestock, wildlife in a game park, horticulture and domestic applications including drink­ing. The river is also used for fishing. To check whether these activities negatively impact on the water quality, pH, electrical conductivity, dissolved oxygen, temperature, total dissolved nitrogen and phosphorus, Faecal coli­forms and Faecal streptococci and selected metals were determined from July 2005 to January 2006. The pH was near neutral except for the southern most sampling sites where values of up to 10.3 were determined. Dissolved oxygen varied from 2 mg/l to 8 mg/l. Sodium (range 0.6–3.2 mg/l), K (0.3–3.6 mg/l), Fe (1.6–6.9 mg/l) conductivity (56–430 lS/cm) and Mg (0.2–6.7 mg/l) increased with increased distance from the Delta, whereas lead showed a slight decline. Total dissolved phosphorus was low (up to 0.02 mg/l) whereas total dissolved nitrogen was in the range 0.08–1.5 mg/l. Faecal coli­form (range 0–48 CFU/100 ml) and Faecal streptococci (40–260 CFU/100 ml) were low for open waters with multiple uses. The results indicate that there is possibility of pollution with organic matter and nitrogen. It is recommended that more monitoring of water quality needs to be done and the sources of pollution identified.