Sunday, June 24, 2012

Wetlands

The wetland ecosystem- rivers, streams, lakes, ponds and swamps- is under threat. Currently covering about 6 percent of the Earth’s surface, wetlands are shrinking rapidly. Destruction of wetlands may seem to bring nothing but benefit. Draining a marsh creates fertile land for cultivations and reduces breeding areas for insects such as mosquitoes. Damming a river provides a water supply, and may mean a source of power as well.
But many changes to water system carry seeds of disaster.
 The Aswan Dam on the upper Nile, completed in 1963 and fully effective by the 1970s, was meant to regulate the river’s flow and provide hydro electric power. However, the traditional fertility of the Nile valley was dependent on over 100 million tones of silt deposited annually as the river flooded. The silt is now silting up the artificial Lake Nasser, forcing farmers downstream to rely on fertilizers, and robbing local brick makers of raw materials; around 35 percent of Egypt’s cultivated land is suffering from salination. Deprived of nutrients, the fish stocks of the eastern Mediterranean are declining while the Nile delta is being eroded steadily. Schistosomiasis is a disease common in newly irrigated areas, has spread explosively, causing debilitation and death; in 1990 between five and six million people were affected.
Surviving wetlands are often badly damaged: by engineering schemes; by eutrophication, when nutrients flow off the land causing huge growths of weeds that over whelm other plant life; by pollution from sewage or toxic industrial waste; or by thermal pollution from water used for cooling.