East (Shiklomanov and Rodda 2003) [well established]. Regulation of the world’s rivers has altered water regimes, with substantial declines in discharges to the ocean (Meybeck and Ragu 1997). Long-term trend analysis (more than 25 years) of 145 major world riv- ers indicates that discharge has declined in one-fifth of cases (Walling and Fang 2003). Worldwide, large artificial impoundments hold vast quantities of water and cause signifi- cant distortion of flow regimes (Vörösmarty and others 2003), often with harmful effects on human health (box 6.5).
Water diversion and the construction of hydraulic infrastructure (reservoirs, physical barriers) have altered downstream ecosystems through changes in the quantity and pattern of water flows and the seasonal inflows of freshwater (see global summaries in Vörösmarty, Lévêque, and Revenga 2005 and Finlayson and D’Cruz 2005). Negative effects include the loss of local livelihood options, fragmentation and destruction of aquatic habitats, changes in the composition of aquatic communities, loss of species, and health problems resulting from stagnant water. Less flooding means less sedimentation and deposition of nutrients on floodplains and reduced flows and nutrient deposition in parts of the coastal zone (Finlayson and D’Cruz 2005).
Water management and human health
Many water-related diseases have been successfully controlled through water management (for ex- ample, malaria in some places), but others have been exacerbated by the degradation of inland waters through water pollution and changes in ow regimes (the spread of schistosomiasis). Where diseases have spread, the adverse effects on human health are due to a complex mix of environmen- tal and social causes. The Millennium Ecosystem Assessment reported many instances where water management practices contributed to a decline in well-being and health (MEA 2005a; Finlayson and D’Cruz 2005). This includes diseases caused by the ingestion of water contaminated by human or animal feces; diseases caused by contact with contaminated water, such as scabies, trachoma, and typhus; diseases passed on by intermediate hosts such as aquatic snails or insects that breed in aquatic ecosystems, such as dracunculiasis and schistosomiasis, as well as dengue fever, lariasis, malaria, onchocerciasis, trypanosomiasis, and yellow fever; and diseases that occur when there is insufcient clean water for basic hygiene.
In addition to disease from inland waters, waterborne pollutants have a major effect on human health, often through their accumulation in the food chain. Many countries now experience problems with elevated levels of nitrates in groundwater from the large-scale use of organic and inorganic fertil- izers. Excess nitrate in drinking water has been linked to methemoglobin anemia in infants.
There is increasing evidence from wildlife studies that humans are at risk from a number of chemi- cals that mimic or block the natural functioning of hormones, interfering with natural bodily processes, including normal sexual development. Chemicals such as DDT, dioxins, and those in many pesticides are endocrine disruptors, which may interfere with human hormone functions, undermining disease
resistance and reproductive health.
The draining and burning of forested peat swamps in Southeast Asia have had devastating health effects (see box 6.6 later in this chapter) that extend across many countries and that may be long- lasting. The investigation of environment-related health effects linked with the ongoing degradation of the forested peat swamps is a major issue for health services in the region.