EarthTrends: Featured Topic Title: Freshwater Biodiversity in Crisis Author(s: Carmen Revenga and Greg Mock Source Adapted from PAGE: Freshwater Systems 2000 and world Resources 1998-99 Date written: October 2000 In a world in which it seems that (Kristensen and Hansen 1994: 90) wetlands in 1999-about 9 percent nearly every natural ecosystem is Due to their limited area of the worlds total fish catch(not under stress. freshwater freshwater ecosystems only contain including aquaculture)(FAO 2000: 6) ecosvstems-the diverse about 2. 4 percent of all Earth's plant Rivers and lakes are also crucial as communities of species found in and animal species(Reaka-Kudla ansportation and shipping routes, as lakes, rivers, and wetlands-may be 1997: 90). On a hectare-for-hectare power sources, and, unfortunately, as the most endangered of all basis, however, they are richer in waste sinks. All of these human uses Freshwater ecosystems have lost a species than the more extensive take their toll on freshwate greater proportion of their species terrestrial and marine ecosystems. ecosystems. and habitat than ecosystems on land (See Figure 1. To date, scientists or in the oceans, and they face have discovered some 44,000 aquatic Why is Freshwater Biodiversity creasing threats from dam pecies in freshwater ecosystems, but Endangered? erextraction, pollution, and this probably only represents a overfishing portion of all freshwater spec Threats to species in freshwater ( Reaka-Kudla 1997: 90). In the last ecosystems are widespread. Habitat How Crucial Are Freshwater 18 years, scientists have described degradation, physical alteration from Ecosystems: about 309 new freshwater species dams and canals, water withdrawals, each year(Nelson 1976, 1984, 1994). overharvesting of fish and shellfish, Freshwater systems occupy only 0.8 In addition to being biologically rich, pollution, and the introduction of rcent of Earth's surface(McAllister freshwater ecosystems play a vital nonnative species have all increased et al. 1997 5), but they are rich in role in the lives of many people, in scale and impact in the last species and vital as habitat. An providing a source of drinking and century.(See Figure 2: Alteration of estimated 12 percent of all animal irrigation water, food, recreation, and Freshwater Systems Worldwide. )As a species live in fresh water employment. Indeed, the majority of consequence, the capacity of (Abramovitz 1996: 7). Many others, the world's population lives near and freshwater ecosystems to support including humans, depend on fresh depends on freshwater environments, biodiversity-the natural variety, water for their survival. In Europe with most inland cities located next abundance and distribution of for example, 25 percent of birds and to a waterway (Moyle and Leidy pecies across the aquatic 11 percent of mammals use 1992: 130). The world's fishe environment-is highly degraded at a freshwater wetlands as their main harvested some 8.2 million metric global level breeding and feeding areas tons of fish from lakes rivers and In a recent study of freshwater h, Harrison and Stiassny(1999) Teeming with Life found that while many factors can Figure 1: Species Richness by Ecosystem, 1997 simultaneously contribute to Percent of extinctions. habitat alteration and th introduction of nonnative spec Percent of Species* were the major causes driving the Relative extinction of fish species. Building Total Ecosystem Species Habitat Contains Richness** dams and water diversions channelizing riverbeds, and draining Freshwater wetlands are typical habitat 0.28 0.775 2.7 ns. The study reported that habitat alteration contributed to 71 percent of extinctions; nonnative Sum does not add to 100 percent because 5.3 percent of known pecies(which can compete with or ymbiotic species are excluded feed on native species)contributed to **Calculated as the ratio between the percent of known species and the 54 percent; overfishing contributed of ar by th t;and pollution to 26 Source: McAllister et al. 1997: 29 Stiassny1999298299) OEarthTrends 2001 World Resources Institute. All rights reserved. Fair use is permitted on a limited scale and for educational purposes©EarthTrends 2001 World Resources Institute. All rights reserved. Fair use is permitted on a limited scale and for educational purposes. EarthTrends: Featured Topic Title: Freshwater Biodiversity in Crisis Author(s): Carmen Revenga and Greg Mock Source: Adapted from PAGE: Freshwater Systems 2000 and World Resources 1998-99 Date written: October 2000 In a world in which it seems that nearly every natural ecosystem is under stress, freshwater ecosystems—the diverse communities of species found in lakes, rivers, and wetlands—may be the most endangered of all. Freshwater ecosystems have lost a greater proportion of their species and habitat than ecosystems on land or in the oceans, and they face increasing threats from dams, overextraction, pollution, and overfishing. How Crucial Are Freshwater Ecosystems? Freshwater systems occupy only 0.8 percent of Earth’s surface (McAllister et al. 1997:5), but they are rich in species and vital as habitat. An estimated 12 percent of all animal species live in fresh water (Abramovitz 1996:7). Many others, including humans, depend on fresh water for their survival. In Europe, for example, 25 percent of birds and 11 percent of mammals use freshwater wetlands as their main breeding and feeding areas (Kristensen and Hansen 1994:90). Due to their limited area, freshwater ecosystems only contain about 2.4 percent of all Earth’s plant and animal species (Reaka-Kudla 1997:90). On a hectare-for-hectare basis, however, they are richer in species than the more extensive terrestrial and marine ecosystems. (See Figure 1.) To date, scientists have discovered some 44,000 aquatic species in freshwater ecosystems, but this probably only represents a portion of all freshwater species (Reaka-Kudla 1997:90). In the last 18 years, scientists have described about 309 new freshwater species each year (Nelson 1976, 1984, 1994). In addition to being biologically rich, freshwater ecosystems play a vital role in the lives of many people, providing a source of drinking and irrigation water, food, recreation, and employment. Indeed, the majority of the world’s population lives near and depends on freshwater environments, with most inland cities located next to a waterway (Moyle and Leidy 1992:130). The world’s fishers harvested some 8.2 million metric tons of fish from lakes, rivers, and wetlands in 1999—about 9 percent of the world’s total fish catch (not including aquaculture) (FAO 2000:6). Rivers and lakes are also crucial as transportation and shipping routes, as power sources, and, unfortunately, as waste sinks. All of these human uses take their toll on freshwater ecosystems. Why is Freshwater Biodiversity Endangered? Threats to species in freshwater ecosystems are widespread. Habitat degradation, physical alteration from dams and canals, water withdrawals, overharvesting of fish and shellfish, pollution, and the introduction of nonnative species have all increased in scale and impact in the last century. (See Figure 2: Alteration of Freshwater Systems Worldwide.) As a consequence, the capacity of freshwater ecosystems to support biodiversity—the natural variety, abundance, and distribution of species across the aquatic environment—is highly degraded at a global level. In a recent study of freshwater fish, Harrison and Stiassny (1999) found that while many factors can simultaneously contribute to extinctions, habitat alteration and the introduction of nonnative species were the major causes driving the extinction of fish species. Building dams and water diversions, channelizing riverbeds, and draining wetlands are typical habitat alterations. The study reported that habitat alteration contributed to 71 percent of extinctions; nonnative species (which can compete with or feed on native species) contributed to 54 percent; overfishing contributed to 29 percent; and pollution to 26 percent of extinctions (Harrison and Stiassny 1999:298–299). Teeming with Life Figure 1: Species Richness by Ecosystem, 1997 Ecosystem Percent of Earth’s Total Habitat Percent of Known Species* Each Ecosystem Contains Relative Species Richness** Freshwater 0.008 0.024 3 Terrestrial 0.284 0.775 2.7 Marine 0.708 0.147 0.2 *Sum does not add to 100 percent because 5.3 percent of known symbiotic species are excluded. **Calculated as the ratio between the percent of known species and the percent of area occupied by the ecosystem. Source: McAllister et al. 1997:29