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 m 3 /year Commercial plantation incremental use:930 m 3 /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: milion m 3 /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

Tilling –Increased removal of topsoil –Crusting –Reduced infiltration –Donga erosion Fertilizers Pesticides

Agriculture Irrigation Dumping Draining of wetlands Invasion by alien vegetation Feedlot pollution

Poor Rangeland 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