Water for people.pdf - WHO Thailand Digital Repository

1 3 4 / C H A L L E N G E S T O L I F E A N D W E L L - B E I N GProtecting Ecosystems for People and Planetarise from point sources, such as discharge pipes, or be morediffuse in nature, arising for example from agricultural land use.Pollutants can be classified into a number of classes (table 6.3).The most frequent sources of pollution are human waste (with2 million tons a day disposed of in water courses), industrial wastesand other chemicals including agricultural pesticides and fertilizers.It has been calculated that humans currently use about 26 percentof total terrestrial evapotranspiration and 54 percent of accessiblerunoff (Postel et al., 1996). By some estimates (Tilman et al.,2001), the expansion of agricultural demand for food by a wealthierand 50 percent larger global population could drive the conversionof an additional billion hectares of unmodified ecosystems toagriculture by 2050. This could result in nitrogen- and phosphorusdriveneutrophication of terrestrial, freshwater and near-shoremarine ecosystems being more than doubled, with comparableincrease in pesticide use. An example of current and predictedemissions of nitrogen and organic pollutants from different sectorsis shown in figure 6.1.Impacts of water use on quality differ between sectors and arenot symmetrical between uses. Thus, recreational use such asswimming and fishing upstream will have no impact on downstreamwaste disposal; inversely, waste disposal upstream can have animpact on recreational use downstream. Water conditions, includingFigure 6.1: Emissions of water pollutants by sectorTable 6.3: Types of pollutants affecting freshwater ecosystemsNutrients such as nitrogen and phosphorus from fertilizers and manuresFaecal and other pathogens from livestock and human wasteSoil particles from farming, upland erosion, forestry, urban areas andconstruction and demolition sitesPesticides, veterinary medicines and biocides from industrial, municipal andagricultural useOrganic wastes (slurries, silage liquor, surplus crops, sewage sludge andindustrial wastes)Oil and hydrocarbons from vehicle use and maintenanceChlorinated solvents from industrial areasMetals, including iron, acidifying pollutants and chemicals from atmosphericdeposition, abandoned mines, industrial processesEndocrine-disrupting substances (particularly oestrogenic steroids deriving fromhuman contraceptive pills, linked to feminization of male fish)sediment load and volume of inflow, may also be affected by landuse decisions applied to terrestrial parts of the catchment basin.Many uses of aquatic ecosystems (e.g. fisheries, recreation, waterpurification, biodiversity maintenance, some forms of floodreduction) depend on ecosystems that are at or close to naturalconditions. Other uses (e.g. hydropower, irrigation, transport) areless dependent on ecosystem condition, and often lead to highlyengineered environments.Mega tonsTotal % change 1995-2020BOD loading towaterways by sectorOECDNon-OECDAgricultureHouseholdIndustryAgricultureHouseholdIndustry0AgricultureHouseholdIndustryAgricultureHouseholdIndustry50 100 150 200 0% 100% 200%Nitrogen loadingto waterwaysfrom agricultureOECDNon-OECDOECDNon-OECD0 10 20 30 40 50 0% 100% 200%1995 2010 2020The figures give current and predicted pollutant percentages by sector. In 1995, agriculture was responsible for a more or less equivalent amount of biological oxygendemand (BOD) in both OECD (Organization for Economic Cooperation and Development) and non-OECD countries; yet this trend is reversing, and agriculture in non-OECDcountries is expected to load two times more BOD in waterways than OECD countries by 2020.Source: OECD, 2001.