Coliforms as a measure of sewage contamination of the River Zambezi

Abstract

The effect of releasing untreated sewage from Victoria Falls Town into the Zambezi river was determined by bacteriological examination of water samples collected upstream of Victoria Falls and for 22 km downstream. Most probable numbers of faecal coliforms and Escherichia coli were estimated. Water upstream of the falls, on the Zimbabwe side of the river, contained between seven and 130 E. coli per 100 ml. This section of the river was free from major sources of faecal pollution. Below the falls, but before the Victoria Falls Town sewage outfall, numbers of E. coli were between 1.8 X 10(2) and 1.4 X 10(4)/100 ml, indicating the existence of a sewage discharge other than that from Victoria Falls Town. The river was also highly polluted from the Victoria Falls Town sewage outfall to a point 18.6 km downstream. The highest E. coli count was 3.3 X 10(4)/100 ml and declined slowly to 1.4 X 10(3)/100 ml 18.6 km downstream of the outfall.

Development of a risk-based index for source water protection planning, which supports the reduction of pathogens from agricultural activity entering water resources

“…Direct voiding of faeces into streams can increase survival rates (Davies et al, 1995) as rapid sorption onto bed sediment can occur (Whiteley, 1998). Nevertheless, bacterial concentrations of 10 mL À1 have been found 20 km downstream from a source of contamination (Feresu and Van Sickle, 1990). Access to streams also allows animals to disturb the sediment, causing the release of stored pathogens into the water.…”

Kariba Reservoir: Experience and lessons learned

“…Masundire (1998) reported that the bulk of untreated wastewater from Livingstone (population of 100 000; annual growth rate of 2.6% in 1990) and Victoria Falls (population of 32 000; annual growth rate of 14% in 1990) is largely discharged into the Zambezi with little or no treatment. Feresu and Van Sickle (1990) traced a plume of faecal coliform bacteria for a distance of >20 km along the Zambezi River downstream of Victoria Falls.…”

Phytoplankton biomass and primary production dynamics in Lake Kariba

“…Eutrophication tends to have more impact on shallow lake systems than on deeper tropical lakes such as Lakes Malawi, Victoria and Kariba. Incidences of localized pollution, for example, are only occasionally reported in Lakes Malawi and Victoria, or in Lake Kariba (Feresu & Van Sickle 1989; Magadza & Dhlomo 1996; Verschuren et al. 1998; Hecky et al.…”

“…The water in Lake Kariba has changed from an initial eutrophic state to that of its current oligotrophic state, with phosphorus limiting its PP (Moyo 1991; Lindmark 1997; Ndebele‐Murisa 2011). The high concentrations of faecal coliform bacteria recorded in Zambezi waters above Victoria Falls, however, along the northern shoreline of Lake Kariba, infer that the lake waters are shifting towards a mesotrophic condition (Feresu & Van Sickle 1989; Magadza & Dhlomo 1996; Phiri et al. 2006; Ndebele‐Murisa 2011).…”

“…Eutrophication tends to have more impact on shallow lake systems than on deeper tropical lakes such as Lakes Malawi, Victoria and Kariba. Incidences of localized pollution, for example, are only occasionally reported in Lakes Malawi and Victoria, or in Lake Kariba (Feresu & Van Sickle 1989;Magadza & Dhlomo 1996;Verschuren et al 1998;Hecky et al 1999;Odada et al 2006). The water in Lake Kariba has changed from an initial eutrophic state to that of its current oligotrophic state, with phosphorus limiting its PP (Moyo 1991;Lindmark 1997;Ndebele-Murisa 2011).…”