Learning Unit 7: Rivers, lakes and wetlands

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Learning Outcomes Discuss the impact of human activities on rivers Explain how the damage caused by pollution to rivers can be reversed Discuss relevant considerations in the management of rivers Explain how lakes are affected when the flow patterns of rivers are altered by people and give an example Explain how the indigenous aquatic life of a lake is affected by the introduction of exotic species and give an example Explain how eutrophication is accelerated by pollution and what the final outcome is for the aquatic life in lakes Discuss the relevant considerations that are applicable in managing lakes Explain what a wetland is and why it is of value to people and nature Explain where and why wetlands are destroyed as a result of human activities Explain what is being done and suggest what can be done to protect wetlands

Introduction of the exotic Nile perch into Lake Victoria Page 177 in Middleton Ecological implications: Dramatic decline of endemic fish called cichlids Approximately 200 cichlid species were driven to extinction Economic implications: Nile perch suddenly increased Nile perch generated considerable benefits – expanding the fishery into a multimillion dollar export industry for Nile fillets and improving incomes of lakeside communities Annual fish landings rose from 40,000 tons in the 1970s to 500,000 tons in the 1980s

Pages 103, 173-175 and 244 in Middleton Aral Sea tragedy Pages 103, 173-175 and 244 in Middleton The diversion of water from the Amu Darya and Syr Darya rivers in Kazakhstan and Uzbekistan (under the governance of the Soviet Union at the time) for irrigation of cotton plantations, has resulted in the diminishing water levels of the Aral Sea. In 1960, the Aral Sea was the fourth largest lake in the world, but its surface area has shrunk by 75%, it has lost 90% of its volume and its water level has dropped by more than 25m. Average water level in 1960 was 53m above sea level, by 2003 it was 30m above sea level. This has resulted in salinization.

Aral Sea tragedy

Aral Sea tragedy In some parts of the Aral Sea, the water is several times saltier than the sea water in the open ocean. Drainage from salinized areas can increase the concentration of salts in streams, rivers and wetlands, which negatively affects biodiversity and aquatic organisms The Aral Sea commercial fishing industry ceased to exist, since most of the native organisms died out The diversion of river water also resulted in widespread lowering of groundwater levels The receding sea affected the local climate – the exposed sea bed has become a dust bowl from which tons of saline material is deposited on surrounding areas The dust contaminates agricultural land and may have negative effects on human health

Aral Sea tragedy The irrigated cropland has also been subject to salinization and waterlogging due to poor management Drainage water from the irrigation schemes also contain high salinity and high concentrations of fertilizer and pesticide residues. Regional climate changes took place: the climate has warmer summers and cooler winters, later spring frosts and earlier autumn frosts than previously occur, there has been a decrease in humidity and a shorter growing season. The desire to be self-sufficient in textiles, combined with the Soviet belief that humans were capable of complete domination over nature overrode any fears of the associated environmental impacts. The Aral Sea tragedy is regarded as the most extreme example of human-induced environmental degradation in the modern era. It is also an example of the dangers of an extreme technocentric approach to the environment

Wetland destruction Pages 180-182 in Middleton Causes Examples Agriculture USA (Great Lakes, lakes in the Mississippi River, along the Gulf of Mexico and Chesapeake Bay) Belarus (Marshes along the Pripyat River) Botswana (Okavango delta) Disease prevention Albania (fight against malaria) Land reclamation Netherlands Urban expansion Mexico City Water utilisation South Sudan (Sudd Swamps drained) The exploitation of energy sources (eg collection of wood for fuel) Central America, Africa and Asia (mangroves) Northern European countries such as Ireland, Russia, Finland and Belarus (production of peat)