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Global Biodiversity Outlook 3

Biodiversity in 2010
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Inland water ecosystems
Inland water ecosystems have been dramatically altered in recent decades. Wetlands throughout the world have been and continue to be lost at a rapid rate.

Rivers and their floodplains, lakes and wetlands have undergone more dramatic changes than any other type of ecosystem, due to a combination of human activities including drainage for agriculture, abstraction of water for irrigation, industrial and household use, the input of nutrients and other pollutants, introduction of alien species and the damming of rivers.

Verifiable global data for loss of inland water habitats as a whole are not available, but it is known that shallow-water wetlands such as marshes, swamps and shallow lakes have declined significantly in many parts of the world. Documented examples of loss include:

  • Between 56% and 65% of inland water systems suitable for use in intensive agriculture in Europe and North America had been drained by 1985. The respective figures for Asia and South America were 27% and 6%.
  • 73% of marshes in northern Greece have been drained since 1930.
  • 60% of the original wetland area of Spain has been lost.
  • The Mesopotamian marshes of Iraq lost more than 90% of their original extent between the 1970s and 2002, following a massive and systematic drainage project. Following the fall of the former Iraqi regime in 2003 many drainage structures have been dismantled, and the marshes were reflooded to approximately 58% of their former extent by the end of 2006, with a significant recovery of marsh vegetation.

Water quality shows variable trends, with improvements in some regions and river basins being offset by serious pollution in many densely-populated areas.

Water quality in freshwater ecosystems, an important biodiversity indicator, shows variable trends, and global data are very incomplete. Relevant information about pollution loads and changes in water quality is lacking precisely where water use is most intense - in densely populated developing countries. As a result, the serious impacts of polluting activities on the health of people and ecosystems remain largely unreported.

In some areas, depletion and pollution of economically important water resources have gone beyond the point of no return, and coping with a future without reliable water resources systems is now a real prospect in parts of the world. UNESCO's Third World Water Development Report predicts that nearly half of humanity will be living in areas of high water stress by 2030.

Pollution control through sewage treatment and regulation of industrial effluent has had significant success in improving water quality in many inland water ecosystems [See Figure 11], although such progress has so far been very limited in developing countries. Pollution originating from diffuse or non-point sources (particularly from agriculture) remains a significant and growing problem in many parts of the world.

Of 292 large river systems, two-thirds have become moderately or highly fragmented by dams and reservoirs.

Rivers are becoming increasingly fragmented, often with severe disruption to their flows. The most fragmented rivers are in industrialized regions like much of the United States and Europe, and in heavily-populated countries such as China and India. Rivers in arid regions also tend to be highly fragmented, as scarce water supplies have often been managed through the use of dams and reservoirs. Rivers flow most freely in the lesspopulated areas of Alaska, Canada and Russia, and in small coastal basins in Africa and Asia.

This fragmentation is important because so much of the variety of freshwater life is determined by the connections formed between different parts of a river basin, as water, sediments and nutrients flow in dynamic rhythms of flood and interaction with tidal zones on the coast. More than 40% of the global river discharge is now intercepted by large dams and one-third of sediment destined for the coastal zones no longer arrives. These large-scale disruptions have had a major impact on fish migration, freshwater biodiversity more generally and the services it provides. They also have a significant influence on biodiversity in terrestrial, coastal and marine ecosystems.

Inland water ecosystems are often poorly served by the terrestrial protected areas network, which rarely takes account of upstream and downstream impacts. Governments are reporting increased concern about the ecological condition of wetland sites of international importance (Ramsar sites).

Assessing the proportion of inland water biodiversity covered effectively by the existing network of protected areas is difficult. The Millennium Ecosystem Assessment estimated that 12% of the area of the world's inland waters was included within protected areas. This does not, however, give an accurate indication of the proportion of the world's river basins that enjoy protection, since the state of freshwater biodiversity at a particular location will often depend on activities far upstream or downstream - such as pollution, abstraction of water, the building of dams and deforestation.

Governments of 159 countries have ratified the Ramsar Convention on Wetlands, currently committed to conserving 1,880 wetlands of international importance, covering over 1.8 million square kilometres, and to the sustainable use of wetland resources generally. The condition of these wetland protected areas continues to deteriorate, with the majority of governments reporting an increased need to address adverse ecological changes in 2005-8, compared with the previous three-year period. The countries reporting the greatest concern about the condition of wetlands were in the Americas and Africa.

In many countries, steps are being taken to restore wetlands, often involving reversals in land-use policies by re-wetting areas that were drained in the relatively recent past. A single freshwater ecosystem can often provide multiple benefits such as purification of water, protection from natural disasters, food and materials for local livelihoods and income from tourism. There is a growing recognition that restoring or maintaining the natural functions of freshwater systems can be a cost-effective alternative to building physical infrastructure for flood defenses or costly water treatment facilities.

  • United Nations
  • United Nations Environment Programme