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 4 3Figure 6.4: Living Planet Index 1999: inland waters120Index value1008060402001970 1975 1980 1985 1990 1995 1999This figure shows a consistently declining number of inland freshwaterspecies over the last thirty years. The system is based on estimates ofpopulation size of wild species available in the scientific literature. Theindex is calculated as a percentage of the population size estimated at1970; the mean value of the index is calculated as an average of allthe species included in the assessment at each time interval.Vertebrates other than fish (water birds, turtles, crocodilians,amphibians) are disproportionately represented.Source: Loh et al., 1999.The World Wide Fund for Nature (WWF) Living Planet Report(Loh et al., 2000, 1999, 1998) provides the overall trend in a largesample of inland water species for which indicators of populationchange are available. Some of the species represented had beenassessed as globally threatened while several populations wereactually increasing during the period, sometimes very steeply (manyof these being waterbirds subject to management for hunting). Thesample included a large number of wetland and water marginspecies in addition to truly aquatic forms. The method is designedto represent the average change in the size of sampled populationsfrom one five-year interval to the next, starting in 1970. The samplein 1999 represented 194 species of mammals, birds, reptiles andfish associated with inland waters, and the index suggests adeclining trend over the last three decades of the twentieth century(figure 6.4).These global and national data on the status of species providea strong indication that inland water biodiversity is widely in decline,and because in most cases the principal threats arise from habitatdisturbance, rather than excess harvesting or other factors extrinsicto the ecosystem, this can be taken as evidence of decliningecosystem condition.LakesThe changing condition of freshwater lakes since 1970 has beenassessed in a semi-quantitative global study using publishedinformation (Groombridge and Jenkins, 1998; Loh et al., 1998). Abaseline was provided by Project Aqua, initiated by the SocietasInternationalis Limnologiae in 1959, which collated and publishedinformation from local specialists on more than 600 water bodies(Luther and Rzóska, 1971). Many of these lakes were treated inlater information sources relating to the 1980s and 1990s, and insome ninety-three cases it was possible to make an assessmentthat may be taken as indicative of changing conditions. Each lakewas scored according to whether its condition appeared to havedeteriorated (or impacts increased), or to have improved or whetherno change was reported. Improvement was reported in a very smallnumber of lakes, but the overwhelming trend was for deteriorationin condition (see figure 6.5).WetlandsThe most recent attempt to summarize information on wetland areas(Finlayson and Davidson, 1999) concluded that the information ispatchy, inconsistent and not adequate to provide a precise picture ofglobal change. Nevertheless it was reported that around 50 percentof the world’s wetlands present in 1900 had been lost by the late1990s, with conversion of land to agriculture being the main causeFigure 6.5: Changes in lake condition, 1960s–1990s100%80%60%40%20%0%Africa Asia Central andSouth AmericaWorseNo changeBetterAustralia Europe TotalThis figure is based on a sample of ninety-three lakes. Although there has beenimprovement of lake water condition in some areas of all regions, theoverwhelming trend illustrated here is deterioration in quality, most notably inCentral and South America where close to 80 percent of sampled lakes deterioratedin the studied period.Source: Data collated for Loh et al., 1998.