The values of maintaining ecosystems that function in an unaltered and interconnected way are paramount. The importance of controlling introduced species and the controls that must be placed on fishing have to be emphasized. Habitat loss is a major problem. Without secure habitats, the ecosystem services are degraded. Ecosystems have structure and function . If one sees the many facets that make up a well functioning ecosytem with negative feedback loops keeping it in a steady state, then they may have a better idea about how impacts on the ecosystem can have far-reaching effects.
Reference FROM:” WATER” http://www.unep.org/geo/geo4/report/04_Water.pdf
Ecosystem integrity
Since 1987, many coastal and marine ecosystems and most freshwater ecosystems have continued to be heavily degraded, with many completely lost, some irreversibly (Finlayson and D’Cruz 2005, Argady and Alder 2005) (see Box 4.3). It has been projected that many coral reefs will disappear by 2040 because of rising seawater temperatures (Argady and Alder 2005). Freshwater and marine species are declining more rapidly than those of other ecosystems (see Figure 5.2d). Wetlands, as defined by the Ramsar Convention, cover 9–13 million km2 globally, but more than 50 per cent of inland waters (excluding lakes and rivers) have been lost in parts of North America, Europe, and Australia (Finlayson and D’Cruz 2005). Although data limitations preclude an accurate assessment of global wetland losses, there are many well- documented examples of dramatic degradation or loss of individual wetlands. The surface area of the Mesopotamian marshes, for example, decreased from 15 000–20 000 km2 in the 1950s to less than 400 km2 around the year 2000 because of excessive water withdrawals, damming and industrial development (UNEP 2001) but is now recovering (see Figure 4.12). In Bangladesh, more than 50 per cent of mangroves and coastal mudflats outside the protected Sunderbans have been converted or degraded.
Reclamation of inland and coastal water systems has caused the loss of many coastal and floodplain ecosystems and their services. Wetland losses have changed flow regimes, increased flooding in some places, and reduced wildlife habitat. For centuries, coastal reclamation practice has been to reclaim as much land from the sea as possible. However, a major shift in management practice has seen the introduction of managed retreat for the marshy coastlines of Western Europe and the United States. Although limited in area compared to marine and terrestrial ecosystems, many freshwater wetlands are relatively species-rich, supporting a disproportionately large number of species of certain faunal groups. However, populations of freshwater vertebrate species suffered an average decline of almost 50 per cent between 1987 and 2003, remarkably more dramatic than for terrestrial or marine species over the same time scale (Loh and Wackernagel 2004). Although freshwater invertebrates are less well assessed, the few available data suggest an even more dramatic decline, with possibly more than 50per cent being threatened (Finlayson and D’Cruz 2005). The continuing loss and degradation of freshwater and coastal habitats is likely to affect aquatic biodiversity more strongly, as these habitats, compared to many terrestrial ecosystems, are disproportionately species-rich and productive, and also disproportionately imperiled.
The introduction of invasive alien species, via ship ballast water, aquaculture or other sources, has disrupted biological communities in many coastal and marine aquatic ecosystems. Many inland ecosystems have also suffered from invasive plants and animals. Some lakes, reservoirs and waterways are covered by invasive weeds, while invasive fish and invertebrates have severely affected many inland fisheries. Declines in global marine and freshwater fisheries are dramatic examples of large-scale ecosystem degradation related to persistent overfishing,
http://www.maweb.org/documents/document.358.aspx.pdf
Mitigation of climate change. Sea level rise and increases in
storm surges associated with climate change will result in the
erosion of shores and habitat, increased salinity of estuaries and
freshwater aquifers, altered tidal ranges in rivers and bays,
changes in sediment and nutrient transport, and increased coastal
flooding and, in turn, could increase the vulnerability of some
coastal populations. Wetlands, such as mangroves and flood-
plains, can play a critical role in the physical buffering of climate
change impacts.