If water is extracted more rapidly than it is naturally replenished, wetland ecosystems will, in extreme cases, collapse, with a complete loss of ecosystem services. The effect of such extreme cases is costly in terms of human health. A well-documented example is the Aral Sea where water abstraction for irrigating crops reduced a vibrant wetland to dust - causing loss of livelihoods in the short term and, in the longer term, seriously impairing the health of communities that lived around the sea through the health effects of dust storms, erosion, and poor water quality for drinking and other purposes.
While this may be an extreme example, there are many cases where a dramatic reduction in water availability results in significant negative effects on human health. In Lake Chad, a lake shared by Cameroon, Chad, Nigeria and Niger, climate change, the demand for irrigation water upstream, and poor management decisions in the basin have reduced the size of the lake by 90% over the past 40 years. The net effect on the 20 million people, mainly fishers and farmers, who rely directly on the lake is rising levels of malnutrition, in turn leading to a much increased vulnerability to diseases.
We've been saying it for years - inland wetlands (rivers, lakes, ponds, marshes, etc.) perform a vital function in filtering and purifying freshwater, rendering it 'clean' for human consumption. And never has it been a more valuable service for human populations than today when over one billion people lack access to clean water supplies. But wetlands can only provide us with clean water if we keep them healthy through effective management. What happens when we destroy our wetlands is obvious - we lose this source of clean water, as well as all the other ecosystem services they provide.
Despite the capacity of freshwater wetlands in purifying water, they do have their limits. They can only deal with so much agricultural runoff, so much inflow from domestic and industrial wastes. And of course the human species is capable of adding much more - toxic chemicals (such as PCBs, DDT and dioxins), antibiotics from animal husbandry, untreated human sewage, pesticides that act as 'endocrine disrupters' . . . and more. We can, and do, readily move beyond the purifying powers of wetlands so that these sources of freshwater, and the food they supply, are rendered unfit for consumption and a danger to human health.
Of particular concern are the 2.6 billion people today who lack access to adequate sanitation. Poor sanitation adds to the microbial contamination of drinking water provided by wetlands - and then to sickness and sometimes loss of life.
Wetlands act as filters or traps for many pathogens - when the passage of water through wetlands is long enough, pathogens lose their viability or are consumed by other organisms. Human-made wetlands are being constructed in urban and rural areas to perform just this function and thus prevent untreated sewage reaching natural wetlands that are used as an immediate source of drinking water.
In many parts of the world, human health is closely linked to water-related diseases. Malaria, because mosquitoes breed in wetlands, and diarrhea infections (including cholera) because of sewage contamination are globally the worst in terms of their severity of impact, accounting for 1.3 and 1.8 million deaths respectively in 2002, and affecting the health of many, many more. Fatalities are almost entirely in children under 5 years of age. Diarrheal diseases affect both African and south Asian countries, whereas malaria's impact is largely in Africa but also significant in many parts of Asia and the Americas.
Controlling malaria was one of the driving forces for wetland destruction in the past, especially in Europe, but this has led to the loss of vital ecosystem services such as water and food and is not considered an option today. Solutions that are working, at least in some areas, range from the use of fish that consume the mosquito larvae and bacterial larvicides that kill them without affecting other organisms, to better design, management, and regulation of dams and irrigation schemes and water drainage systems that can reduce breeding sites.
Look for more information on World Wetlands Day also at the site of the Ramsar Convention on Wetlands: www.ramsar.org
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