Water for people.pdf - WHO Thailand Digital Repository

1 3 2 / 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 PlanetTable 6.1: Simplified classification of services provided by waterecosystemsProductionWater (drinking, irrigation)Food (fish, rice)*Raw materials (reeds)*Energy (hydroelectric)Species habitatGenetic resources*RegulationBuffering (storm protection, flood control, storage)*Biogeochemical cycling (oxygen production, carbon storage, methane)*Waste removal (filter-feeding invertebrates, sediment micro-organisms)*Climate (local)Biological control (pest control, pollination)*OtherRecreation and tourism*Cultural uses*Transport* Ecosystem services include all functional results of ecosystem processes. All items marked withan asterisk depend on elements of biodiversity, that is, on the presence of species and communitiesof organisms, and their ecological attributes.Source: Modified from IUCN, 2000.Maintenance of the entire range of goods and services derivedfrom any ecosystem depends on the continued presence of keycomponents (e.g. water, key fishery species, sediment communities,marginal vegetation) and continuation of ecosystem processes (e.g.water retention, removal of pollutants). In the case of naturalfreshwaters – unmodified systems with all components, processes andattributes essentially intact at all relevant scales are generally of thegreatest intrinsic value and can be considered to have high ecologicalintegrity. In different terms, this may be taken as broadly equivalent togood ‘ecosystem health’ status. In artificial systems, however,ecosystem integrity is best reflected by the purpose they are designedto serve and the quality of the specific goods or services derived. Whilepristine natural systems may be of greatest value, particularly in termsof biodiversity and hence their potential use for future humangenerations, it is important to note that systems with some degree ofimpact are often also of high significance. Highly modified systems mayhave their own value (for example the low-intensity grazing marshes ofsouthern England). Degraded systems may be restorable where this canbe identified as a shared societal goal.Pressures on Freshwater EcosystemsA wide range of human uses and transformations of freshwater orterrestrial environments has the potential to alter, sometimesirreversibly, the integrity of freshwater ecosystems. Activities and theirpotential impacts on ecosystem health are summarized in table 6.2.It is a familiar observation that human numbers, biomass andtechnological capacity have had enormous impacts on the biosphere,mainly through land conversion, consumptive use of resources anddisposal of waste. Persistence of the human species will, as aconsequence of simple ecological principles, continue to exert suchpressures, leading to a number of challenges:■ potential conflict between the interests of upstream users versusdownstream users, at local, national or international levels; and■ the need to assess and prioritize the range of water uses, inparticular those that can immediately support local humandevelopment (for example. drinking water, irrigated agriculture,hydroelectric power, fisheries) in relation to those with benefitsthat may be realized mainly at larger scales or over longerperiods of time such as flood control, recreation, biodiversitymaintenance. An interesting illustration is the historic approachof wetland drainage for malaria control (see box 6.1).Water is a resource that is not permanently transformed by use inthe same way that many other natural resources (e.g. timber,fisheries, rubber) are. At the global level, essentially the sameamount remains after use as before; although it can be reused, itsquality is likely to decline progressively without processingthrough industrial or natural biological systems. Regardless of theglobal stock of water, at a local (or catchment) level it is commonfor water to be either in very short supply, or in great excess, atany one time or place, and water uses can be regarded asconsumptive (e.g. irrigation) or non-consumptive (e.g.hydropower). Some uses of water, for example for irrigation,power generation or industrial cooling, do not have narrow waterquality requirements. Other uses, of which the single mostimportant is human drinking water, require water of a certainquality (in terms of solutes, micro-organism populations, etc.).Potential conflicts of interest arise when any given stock of wateris used for different purposes and at different times and places(see chapter 12 on sharing water).From the water quality and human environmental healthperspectives, control of chemical and biological pollution is of keysignificance in protecting ecosystems. Many human activities, fromwater supply and sanitation to transport, mining and the chemicalindustry, have the potential to pollute water. This pollution may