ENVIROMENTAL ISSUES -WATER QUALITY

The physico-chemical requirements of some users, including domestic, irrigation, livestock watering, recreation, and aquatic ecosystems, have been defined in the Water Quality Guidelines issued by the DWAF (1996).

The Reserve Determination Process being undertaken by the DWAF for each water resource indicates basic requirements for human needs, aquatic ecosystem maintenance, and international obligations. The Reserve specifies a required flow for each resource, as well as required physico-chemical (ground and surface water) and biological (surface waters only) qualities. Water quality variableThe Water Research Commission has funded several research initiatives to collate information into the DWAF’s Water Management System (WMS) database.

Water samples from about 1 600 surface water sites and 450 groundwater sites across the country are currently being collected and analysed, and the results are being added to the WMS.

The DWAF published a National Water Resource Quality Status Report in 2002. This study used data from over 150 representative sites (selected from the WMS) to determine the suitability (from a physico-chemical perspective) of surface-water resources for domestic, irrigation, and recreational uses. Other than for aquatic ecology, the criteria for these uses are the most stringent. The results were based on data collected between 1996 and 2000, so they are now out of date. The report will probably be updated in 2006/2007, however, using data from 2001 to 2005.

The restriction on the fitness for use imposed by the physico-chemical water quality standards of the different WMAs regarding domestic, irrigation, and recreational use is given in this table.

The data are consolidated for each WMA and conceal the inherent vulnerability that exists within these large areas. The table also includes the conservation status, as determined by the National Spatial Biodiversity Assessment.

Median values from the WMS for the years 2000–2004 indicate that nitrate levels tend to be stable or are improving, with an indication of deterioration evident at only 10% of the sites (see map below).

Surface water quality trends for nitrate at 150 Water Management System sampling sitesSource: Brendan Hohls, Department of Water Affairs and Forestry

Urban wastewater significant pressure

Diminished fitness for use is generally associated with the activities of humans but can also arise from natural causes, such as underlying geology (higher mineral content), biological phenomena (evapo-transpiration or pH shift and anoxia associated with the breakdown of organic matter), atmospheric deposition and evaporative loss, with consequent increase in dissolved solid content, particularly salts.

Other factors that can have an effect on water quality include:

•Industry and mining. Mining can result in change of pH (acidity of the water), increased salinity, increased metal content, and increased sediment load. Industrial contributions are more varied, depending on the industrial process, but can include poisonous and hazardous chemicals, nutrients, elevated salinity, and increased sediments.

•Increased urbanization and deteriorating standards in wastewater management. Little or no treatment of wastewater takes place in some circumstances, such as at informal settlements. Where treatment is available, sewer reticulation can be inadequate or poorly maintained, resulting in uncontrolled releases such as leakage and overflow to the natural environment. Urban runoff can contain high organic and nutrient loads that contribute to problems in urban streams and impoundments. The consequence is increased nutrient and organic load, plus microbial contamination. An urgent need exists for adequate and improved urban wastewater treatment, to minimize the negative impact, including the cost of damage to our critical inland water resources.

•Agricultural drainage. This includes irrigation return flows and seepage, which may contain salts that include nutrients (fertilizers), other agro-chemicals (including herbicides and pesticides), and runoff or effluent from animal husbandry locations such as feedlots, piggeries, dairies, or chicken farms, which also contribute to contamination.

•Waste disposal. Industry, mining, and urban development result in increased production of waste, creating a need for additional and improved waste-management facilities (see Chapter 9). Although techniques for containing waste are available, and are being applied to new facilities, older waste repositories (industry and mining) and landfill sites (domestic) had no structured lining systems, and they have released contaminated leachate into adjacent water resources.

•Land use. Increase in the laying of impervious surfaces in urban areas diminishes rainwater recharge to groundwater. Lack of the dilution effect that would otherwise take place can lead to a rise in solute concentrations of the existing underlying aquifers. Overgrazing and clearance of natural vegetation increases the risk of erosion and the entry of sediment into surface waters.

Consequences of poor quality

Pollution of water resources results in reduced fitness for use. This affects the resource directly by making the water less acceptable for consumption (either for food production or any other identified use), depending on the extent, severity, and temporal nature of the pollution. It can also affect the resource indirectly by curtailing recreational activities in badly affected water bodies.

A consequence of these impacts is that water may need to be processed before it can be used. This increases water-supply cost, particularly if the process is technically complex and expensive.

This is particularly relevant for saline water, common to mine wastewater discharge. Any desalination process, itself, generates a salt-enriched and aggressive waste liquor, that presents its own disposal problems and costs.

Eutrophication is an impact that is directly associated with nutrient loading. It can take millenia to occur naturally, but can appear quickly as a consequence of human activity. Classification of a trophic status of dams and lakes is given in the table below.

The number of dams within each trophic status, as monitored by the DWAF (a total of 76 dams and lakes are currently monitored), is also given. Where possible, a comparison has been made between the trophic status of the dams during the period 1990–2000. Of the 34 dams, 18 improved in status (became less eutrophic), 11 remained unchanged, and 5 deteriorated (the paucity of data could invalidate this comparison).

The dams and lakes with higher trophic status are generally located near urban areas such as Gauteng, Durban, and Bloemfontein, or on highly exploited rivers (such as Crocodile West, Vaal, and Umgeni).