Water Resources

Lecture 9

Degradation of the Water Resource

Sources of degradation

• Urbanisation

• Alien invasion

• Industrialisation

• Afforestation

• Agriculture

• Unsustainable rangeland farming

Alien invasives: additional info

Woody alien incremental water use: 1900 m3 /year

Commercial plantation incremental use: 930 m3 /year

Dye et al, 2001

Total streamflow reduction by Alien Invasives Versveld et al

1988

Industrialisation

• Types of industry affecting water resources:– Mining – Energy– Chemical – Metal and non-metal manufacture– Waste treatment

Mining• Release of toxins into freshwater systems:

– over 1 million tons/y of effluent containing cyanide and other poisons is generated by gold-mining

– the mining industry is directly responsible for 100% of highly toxic, 78% of toxic, and 66% of slightly toxic pollutants entering South Africa's water.

• Climate change– coal mines contribute 35% of the 2.25 million tons of the methane which

South Africa emits into the atmosphere every year

• Acid rain– coal dump fires are responsible for 5.24% of the 1.95 million tons of sulphur

dioxide released per year.

Mining• Acidification

– Headwater of Olifants: pH = 2.9

• Water demand– Mining accounts for 2.5% of SA’s water demand

• Wetland degradation– Open cast mining– Dumping on wetlands

• Increased salinity– Pumping of high salinity groundwater into surface water

systems

• Increased turbidity

Other impacts by industry

• Thermal pollution – Eg cooling towers of coal power stations

Afforestation

Pine species – reduced streamflow

Afforestation in Maclear, EC:Effect on MAR

Forsythe et al, 1997

Afforestation in Maclear: Effect on low flow

Forsythe et al, 1997

Afforestation: Statistics for SA

• 1.44 million hectares

• Water use: 1 399 milion m3 /year

• 3.2% MAR

• 10% change in cover of pines/eucalypts = 40mm change in water yield (Bosch and Hewlett, 1982)

Afforestation• Pines and Eucalypts have high rates of

evaporation – leads to stream flow reduction• Planting often occurs in the high moisture areas of

a catchment• Planting often occurs in wetlands or in riparian

zones. • Reduced biotic diversity• Reduced pH• Impacts of logging and hauling

Agriculture

Agriculture• Tilling

– Increased removal of topsoil– Crusting– Reduced infiltration– Donga erosion

• Fertilizers

• Pesticides

Agriculture

• Irrigation

• Dumping

• Draining of wetlands

• Invasion by alien vegetation

• Feedlot pollution

PoorRangeland Farming

Poor Rangeland Farming Practices

• Overgrazing– Reduced vegetation cover

– Reduced infiltration

– Increased rill and gully erosion

– Increased susceptibility to alien vegetation invasion

• Destruction of the riparian habitat• Destruction of wetlands• High frequency fires