Water for people.pdf - WHO Thailand Digital Repository

P R O T E C T I N G E C O S Y S T E M S F O R P E O P L E A N D P L A N E T / 1 3 5In addition to considerations of water quality, the integrity andhealth of aquatic ecosystems depend on the maintenance ofadequate quantities of water. Increasingly it is clear that the timingof water availability, for example flow regime and flooding events, isas important as absolute minimum quantities for most naturalsystems. While natural aquatic systems are typically able towithstand seasonal or annual variation in water supply, and hencehave a degree of resilience to artificial perturbations, sustainedreductions in water quantity can dramatically alter ecologicalbalances and degrade the system. A major challenge in waterresource management is therefore to identify critical ecosystemrequirements in order to deliver appropriate water quantities forhuman social and economic needs, within the temporal and spatialconstraints of environmental protection. This is the first step torestoring ecosystem health in such circumstances.Taking the Measure of EcosystemHealthAppropriate measures (or indicators) of ecosystem health, whetherdirect or indirect, are a prerequisite of holistic water management.With a key policy focus on environmental protection, measuresmust include tools for assessing status or monitoring trends interms of public health, water quality, natural resource productionand biodiversity.To date, much discussion of terrestrial ecosystems has focusedon changes in total area. At a gross level, loss of habitat (forexample the loss of wetland through drainage) provides a usefulgeneral indicator of global trends in freshwater ecosystemcondition, particularly in the context of natural resource provision.Rivers however are essentially linear systems and area is thereforeinappropriate as an indicator. In addition, it is clear that moresophisticated measures of overall condition are needed, which areable to integrate extent and ‘quality’ of freshwater systems to allowtracking of changes over time. Ecosystem ‘quality’ as discussedearlier is reflected by the overall state of ecosystem processestogether with the relative value of the individual components and/orthe biodiversity of the system as a whole. A range of indicators andmethodologies have been developed towards this goal. Broadlyspeaking, these can be divided into water quality indicators (bothphysico-chemical and biological), hydrological information andbiological assessment, including measures of biodiversity. There area few other indirect approaches that are of use in specificsituations. These include evidence of change derived from observedchanging patterns of human use of an aquatic ecosystem: forexample, a decline in the number of fishers might indicate declinein the availability of target fish species.Water quality indicatorsMonitoring physico-chemical water quality has historically been a keymeans of assessing ecosystem health. In providing a direct measureof the concentration of substances known or believed to affecthumans or other species, water quality provides an essential linkbetween ecosystem health and environmental health (in its traditionalsense of public health). Water quality monitoring standards have beeneffective in comparing sampled water for compliance, and regulatingpoint and non-point source pollution. Other physico-chemicalvariables provide useful indicators of risk to human health, or waterquality issues that might compromise other uses or the needs of aparticular ecosystem component. These indicators include measuringthe amount of faecal coliforms (as an indicator of potentialpathogens from human or animal waste) and biological oxygendemand (BOD), which indicates organic loading and the capacity of ariver system to purify industrial or other effluents.Biological water quality indicators have been adopted, forexample, by the United States Environmental Protection Agency (USEPA), by Environment Australia, by the United Kingdom EnvironmentAgency and by many other similar national and subnational bodies(see figure 6.2 for an example of these indicators taken for UnitedKingdom rivers). These provide a complementary measure tochemical water quality and are useful in assessing intermittentpollution or impacts of unknown contaminants. The procedures usedfor analysis can vary significantly, and there is a growing technicalliterature on sampling and related statistical issues (Lillie et al.,2002; Wright et al., 2000; Barbour et al., 1999; TNC, 1999).Community structure indicators (such as the numbers and kinds oforganisms dwelling adjacent to the bottom sediment) rather thanindividual-species indicators, may give greater accuracy and lessuncertainty in detecting water quality change, but may also increaseresources needed for data collection and analysis. Similarly,composite indices based on a numerical integration of multipleseparate indicators of a range of ecological attributes can, in somecircumstances, strengthen data interpretation and yield a morerobust assessment of overall biological condition. In the UnitedKingdom, the River Invertebrate Prediction and Classification Scheme(RIVPACS) enables biological indices for benthic macro-invertebratesto be predicted, based on unimpacted sites in rivers of similarphysical and chemical characteristics. Significant differences betweenobserved and predicted scores can be used to highlight potentialissues and biological classifications of rivers produced (see table6.4). A similar approach is used in several catchment- and state-levelprogrammes in the United States, for example, applying protocolsdeveloped by the US EPA (Barbour et al., 1999).