Tundi Agardy, Ph.D.
Freshwater Ecosystems and Their Condition
Surprisingly, the extent and distribution of freshwater ecosystems or inland waters is unevenly or even poorly known at the global and regional scales, partly due to difficulties in delineating and mapping habitats with variable boundaries due to fluctuations in water levels. In some cases, such as the extent and location of wetlands, there is no comprehensive documentation, even at the regional or national levels. On the whole, the larger wetlands and lakes and inland seas have been mapped along with the major rivers, however for many parts of the world the smaller, immensely valuable wetlands are not well mapped or delineated, despite the importance of the services they provide for human wellbeing7.
Freshwater ecosystems provide many ecosystems to support mankind and maintain human well-being. In addition to freshwater for drinking, bathing, cleaning, etc., inland water systems provide provisioning services in the form of food substances, especially fish; materials such as timber, fiber and fuel, including peat; energy from hydro-electric facilities; and novel products from biodiversity. Within river basins, inland waters provide many hydrological functions and support public good functions that are "free of charge" and extremely expensive to replace8.
Additional ecosystem services provided by inland waters include: biological regulation; biodiversity habitat; nutrient cycling and soil fertility; local atmospheric and climatic regulation; waste processing and detoxification; bank stabilization; and support vectors of human infectious diseases. In addition, freshwater ecosystems have significant aesthetic, artistic, educational, cultural and spiritual values, and provide invaluable local opportunities for recreation and, increasingly, tourism.
Biodiversity in freshwater ecosystems is largely unknown and undervalued, much like marine biodiversity. But unlike the patterns of life in the sea, which are widespread, freshwater ecosystems are living labs in speciation, and demonstrate notably high levels of endemism. This means that each freshwater body threatened by overuse, pollution, landscape changes, or removal of water, threatens an uncommon and sometimes unique set of living beings. According to a newly released study done by the World Wildlife Fund (WWF) and The Nature Conservancy (TNC), parts of major rivers such as the Amazon, Congo, Ganges, Yangtze, and the rivers and streams of the Southeastern United States are outstanding for rich fish populations and high numbers of species found nowhere else. In addition, several smaller systems that had not been identified in previous global assessments, such as Congo's Malebo Pool, the Amazon's western piedmont, and Cuba and Hispaniola, were determined to have high numbers of fish species unique to those ecosystems9.
As water demand is increasing, pollution from industry, urban centers, and agricultural runoff is limiting the amount of water available for domestic use and food production. Water quality degradation is most severe in areas where water is scarce because the dilution effect is inversely related to the amount of water in circulation. Toxic substances (e.g. chemical pollution from urban domestic and industrial sources and from herbicides & pesticides) are a serious and increasing threat as land use in watersheds changes. The regulation capacity of inland waters has often been used for waste disposal or remediation, but not always within the capacity of the system to assimilate such materials indefinitely. Eutrophication and pollution have degraded both habitats and services, and contribute to the reduction in human wellbeing10.
Major trade-offs have occurred between various sorts of ecosystem services provided by inland waters, leading to substantial adverse changes in habitats and species, and services, such as freshwater and food supply. Such trade-offs occur because utilizing freshwater systems for energy generation, for example, can diminish the ability of these ecosystems to support biodiversity. Such trade-offs are clearly shown in the case of river fragmentation (i.e. modification of a river through dams, reservoirs, interbasin transfers, and irrigation consumption).
It is true that these changes have improved transportation, provided flood control and hydropower, and boosted agricultural output by making more land and irrigation water available. At the same time, physical changes in the hydrological cycle disconnect rivers from their floodplains and inland water systems and slow water velocity in riverine systems, converting them to a chain of connected reservoirs. This, in turn, impacts the migratory patterns of fish species and the composition of riparian habitat, opens up paths for exotic species, changes coastal ecosystems, and contributes to an overall loss of freshwater biodiversity and inland fishery resources.
Irrigation has similarly led to increased food production in drylands, but this in many cases is unsustainable without extensive public capital investment as waterlogging, pollution, especially eutrophication and salinization, degrade the system and other services. Changes in natural flow regimes have caused a decline in biodiversity and services provided by inland water systems, and those provided by coastal systems.
Threats to freshwater diversity are thus numerous and widespread. In the WWF/TNC study described above, agriculture, industry, drinking and livestock were found to place freshwater ecosystems in 55 (out of a total of 426) ecoregions under high stress, threatening the species and habitats they support11. This represents more than 10 percent of the world’s ecoregions, which are defined by a large area encompassing one or more ecoregions that contains a distinct assemblage of natural communities and freshwater species. And, damage is already widespread: more than half the area in another 59 ecoregions has already been converted from natural habitats to cropland and urban areas.
In the United States, news outlets recently reported a looming water supply crisis in the western states, escalated by human-caused climate change that already has altered the region's river flows, snow pack and air temperatures12. Since 1960, thermoelectric, self-supplied industrial, and irrigation water withdrawals increased, reaching a peak in 1980. Demand for municipal and rural use has grown steadily over the past few decades, with municipal demand increasing more rapidly. Total water withdrawals declined about 10% between 1980 and 1985, and then grew slightly from 1985-2000, equaling about 345 billion gallons per day in 200013. Small streams are disappearing not only because of water withdrawls or overdrafts, but also from mining and damming. However, because there is no widely accepted way to classify streams for ecological monitoring, no national dataset exists for reporting on their gains or losses14. Thus many freshwater ecosystems in the U.S., and the biodiversity and other ecosystem services they provide, are at risk from physical alteration, freshwater overdraft, alien species invasions, chemical pollution, sedimentation, and climate change impacts that affect recharge and source water15.
Prospects for the future of freshwater ecosystems and their noteworthy biodiversity are dim. In the next few decades, some 3 billion people will live in countries classified as water stressed16. As competition for freshwater resources increases around the world, freshwater habitats and species are among the most imperiled.
7 Millennium Ecosystem Assessment (MEA). 2005. Ecosystems and Human Well-Being. Ch. 20 Inland Water Systems. Island Press, Washington p563-4
8 Ibid. p 561-563
9 See http://www.feow.org/ for more information and an online copy of the report
10 This and the following three paragraphs are adapted directly from Ch. 20, Inland Water Systems. In MEA. 2005. Ecosystems and Human Well-Being; pp 561-580
12 Tim P. Barnett, David W. Pierce, Hugo G. Hidalgo,Celine Bonfils,Benjamin D. Santer, Tapash Das,Govindasamy Bala, Andrew W. Wood, Toru Nozawa, Arthur A. Mirin, Daniel R. Cayan, Michael D. Dettinger.. 2008. Human-Induced Changes in the Hydrology of the Western United States. Science 319 (5866): 1080 – 1083
13 State of the Nation update by the Heinz Center, available at http://www.heinzctr.org/ecosystems/intro/updates_05_ecosys.shtml#26
14 See www.epa.gov index of landscape changes
15 See www.feow.org
16 Postel, S. and B. Richter. 1993. Rivers for Life: Managing Water for People and Nature. Island Press, Washington DC
