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The Limpopo River Basin
Climate and Weather
Water Quality
 Principles of Water Quality
 Human Impacts to Water Quality
 Agricultural Impacts
 Industry and Mining
 Heavy Metals
 Persistent Organic Pollutants
 Water Temperature
 Case Study: Upper Olifants River
 Water Quality Fitness for Use
Ecology and Biodiversity
Sub-basin Summaries



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Water Quality: Microbiological Organisms and Pathogens  

Microbiological organisms and pathogens are linked to water pollution and the problems of eutrophication and sanitation. In Africa there are "over 50 communicable diseases associated with water and inadequate sanitation (Donkor 2003)." Water borne diseases such as dysentery, cholera, typhoid, gastro-enteritis and hepatitis are the primary cause of disease and poor health in the SADC region (SADC 2009b). Micro-organisms enter rivers via untreated and partially-treated sewage and can cause various diseases in downstream users. Potential costs to society include:

  • Increasing burden on healthcare facilities
  • Loss of income to families
  • Cost of funerals
  • Loss of production in the economy
  • Adverse media attention and its effect on overseas tourism

A study by Gundry et al. (2009) looks at the incidence of child dysentery in Vhembe District in South Africa and Zaka District in Zimbabwe, both districts had below average access to improved sanitation and water sources and Vhembe District has a higher incidence of childhood diarrhoeal disease than the national average. This is explained by the fact that for unimproved sources (unimproved groundwater sources and surface water) E. coli counts were below the recommended maximum of 10 cfu/100mL in only 26 % of cases.

Nutrient enrichment can promote algal growth.
Source: Vogel 2010
( click to enlarge )

Mycrocystis in the Olifants River

Harmful microorganisms can impact the environment and wildlife in as much as they can impact human health. An article was published in Farmer's Weekly (2008) that details the death of the Olifants River. Acid drainage from abandoned coal mines, agricultural flow returns, and the inflow of untreated effluent from cattle feedlots and human sewerage have all contributed to the deteriorating water quality and some the prolific spread of Microcystis.

Microcystis is cyanobacteria that blooms in low-flow, nutrient-rich waters. When the cyanobacteria die, it creates hypoxic or anoxic conditions, depleting the water of oxygen. Microcystins bind metals present in the water column and are hepatotoxins meaning that they act upon the liver; they are also known to promote tumour growth (Fish and Wildlife Research Institute 2010). 

In the Olifants River system, especially near the polluted Lake Loskop, water buffalo (Farmer's Weekly 2008) and crocodiles (Oberholster et al. 2010) have been found dead. The crocodile population went from 30 individuals to 6 in 2008 because they consumed toxic fish fat resulting in pansteatitis. The fish consume phytoplankton contaminated by chemical compounds (associated with acid mine drainage, etc.) and when the fish are then consumed by the crocodiles, the chemical compounds are biomagnified to deadly levels. Microcystitis is only one of many phytoplankton populations present in the Olifants River system consumed by the local biota; however, its association with the new hypertrophic state of the environment now overshadows all other impacts from the many pollutants that enter the system (Oberholster et al. 2010).

A New Trophic State

[...] the development of the Microcystis bloom in the riverine zone of Lake Loskop at the end of February was possible due to a switch in trophic states. This change appears to have caused the aquatic system to pass the upper critical threshold for high concentrations of nutrients and enter an alternate hypertrophic regime, which now overshadows the adverse effects of high concentrations of heavy metals, sulphate and low pH values. Possible drivers in the aquatic system that could have triggered the system to cross this threshold were nutrient-enriched runoff from agricultural land, as well as inflows of untreated and partially treated domestic sewage.

Source: Oberholster et al. 2010



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