Components. The components of wetland systems include such economically beneficial goods as fish, timber, peat, and wildlife. Wetlands likewise provide water supply for domestic, agricultural, and industrial uses, and the structure of wetlands may allow for economical water transport. Some wetland systems offer enriched agricultural land as a result of improving the soil fertility through periodic inundation of flood waters. Fish and wildlife provide opportunities for leisure fishing activities and tourism. Barbier et al. (1997) report that two-thirds of the fish we eat depend upon wetlands at some stage of their life cycle. In Vietnam and Thailand, the Melaleuca wetland forests provide many diverse products, including medicine (Barbier et al. 1997).
Functions. Wetlands also fulfill important functions, such as flood control, groundwater recharge and discharge, water purification through retention of sediments and pollutants, storm protection, water table maintenance, and stabilization of climate. Nutrient retention occurs when nutrients such as nitrogen and phosphorus accumulate in the sub-soil or vegetation and allow eventual circulation back into the atmosphere. Wetland may serve as sediment settling ponds.
By absorbing the force of strong winds and tides, wetlands protect terrestrial areas adjoining them from storms, floods, and tidal damage. Wetlands remove nutrients from surface and ground water by filtering and by converting nutrients to unavailable forms. Denitrification is arguably the most important of these reactions because humans have increased nitrate worldwide by applying fertilizers. Increased nitrate availability can cause eutrophication, but denitrification converts biologically available nitrogen back into nitrogen gas, which is biologically unavailable except to nitrogen fixing bacteria. Denitrification circulates the nitrogen back into the atmosphere. Denitrification can be detected in many soils, but denitrification is fastest in wetlands soils (Ullah and Faulkner 2006).
Attributes. An attribute of wetlands is biodiversity. Being transitional between aquatic and terrestrial environments, and involving complex interactions among such components as water, soils, topography and biotic communities, wetlands help to preserve biodiversity. This provides not only for a more stable system, but tourism and aesthetic appreciation also are often tied to biodiversity. Many wetlands also provide habitats for resident and migratory fish and wildlife. There also are cultural aspects. For example, the Marsh Arabs of southern Iraq have lived in harmony with the marshes at the confluence of the Tigris and Euphrates rivers and they have a spiritual connection that goes beyond the direct use of the wetland products (Barbier et al. 1997). Likewise, the Fens of East Anglia and Somerset levels in the United Kingdom are important for cultural heritage (Barbier et al. 1997).The Pantanal in Brazil, near Pantanal National Park
The Pantanal of South America provides an example of the above. As a wetland system of exceptional size, the Pantanal embodies many of the aforementioned values in a big way. It has one of the most impressive freshwater fisheries on the earth, serving an exceptional biogenetic reservoir. The Pantanal supports a large number of species and also an abundantly high concentration of animals, perhaps the highest in the New World and comparable to the densest animal populations in Africa (Andrade et al. 1985; Pádua 1991). The Pantanal not only provides an extensive water supply and transport system for its inhabitants, but it serves to remove sediments and pollutants, thus improving the water quality for millions of people downstream. The reduced water velocity in the Pantanal, and its storage of water, create excellent circumstances for mineral uptake by plants, microbial processing, and the settlement of sediments and chemicals such as heavy metals, which are sorbed to sediments (Gottgens 1998). Flood control is another major value of the Pantanal. The Pantanal has a regulatory effect on the Rio Paraguay, extensively reducing and delaying the height of the flood peak and thus reducing the flood risk downstream. Because of the Pantanal, the flood peak of the Paraguay is as much as two to three months later than the Paraná into which it empties, avoiding the cumulative impact of these two flood peaks combining downstream.Small wetland in Marshall County, Indiana.
Intertidal wetlands provide an excellent example of invasion, modification, and succession. The invasion and succession process is establishment of seagrasses. These help stabilize sediment and increase sediment capture rates. The trapped sediment gradually develops into mud flats. Mud flat organisms become established encouraging other life forms changing the organic composition of the soils.
The mangroves establish themselves in the shallower water upslope from the mudflats. Mangroves further stabilize sediment and over time increase the soil level. This results in less tidal movement and the development of salt marshes. The salty nature of the soil means it can only be tolerated by special types of grasses (e.g. saltbush, rush, and sedge). There is also changing species diversity in each succession.
In the salt marshes, there is greater species diversity, nutrient recycling, and niche specialization making it one of the most productive ecosystems on Earth.
In intertidal wetlands, the majority of natural stress comes from salinity and tidal movements. The intertidal wetlands must be able to survive extreme conditions of mainly salt water at high tide, fresh water at low tide, and times of flood and brackish water at other times. The saline water is a very difficult condition for plants to survive in. The gray mangrove accomplishes this by excluding salt in the root system, salt glands in the leaf, and waxy leaves to minimize water loss. However, it is vulnerable to changes in salinity levels.
Changes to tidal movements through increased run-off or altered drainage can cause the roots of mangroves to be inundated for longer than normal periods affecting their pneumatophones. It can also be pushed past its threshold level if water quality is changed. Thus, even healthy ecosystems are vulnerable to change.
Some species such as oysters and mollusks have been used as indicator species, with any decline in their numbers indicating the ecosystem is under stress. A change in nutrient levels may also affect primary productivity and thus bring about change.
Protecting or rehabilitating wetlandsA temperate wetland in Britain, with shallow open water and reedbeds.
Historically, humans have made large-scale and small-scale efforts to drain wetlands for development or flood them for use as recreational lakes. Wetlands are often filled in to be used by humans for everything from agriculture to parking lots, in part because the economic value of wetlands has only been recognized recently. For example, the shrimp and fish that breed in salt water marshes are generally harvested in deeper water.
As a result, 50 percent of the world's original wetlands are believed to have been lost. Barbier et al. (1997) report that in Portugal 70 percent of the Western Algarve has been converted for agricultural and industrial development and that in the Philippines, 67 percent of the country's mangrove resources were lost between 1920 and 1980. they likewise report a loss of 67 percent of the wetlands in France between 1900 and 1993, 66 percent of the wetlands in Italy between 1938 and 1984, and 60 percent in Spain between 1948 and 1990. They report 54 percent of the United States's original wetlands have been lost, while the Environmental Protection Agency (2004) notes that the United States loses an additional 60,000 acres of wetlands every year, and this is a leading cause of species extinction.
Humans can maximize the area of healthy, functioning intertidal wetlands by minimizing their impacts and by developing management strategies that protect, and where possible rehabilitate those ecosystems at risk.
Since the 1970s, more focus has been put on preserving wetlands for their natural function-sometimes also at great expense. One example is the project by the U.S. Army Corps of Engineers to control flooding and enhance development by taming the Everglades, a project that has now been reversed to restore much of the wetlands as a natural habitat and method of flood control. Fifty years after ditching and diking the Everglades and affecting the flood-and-drought cycle, over 50 percent of the "River of Glass" has been lost, largely due to conversion to intensive residential and agricultural purposes, and the number of one-legged wading birds plunged by up to 95 percent or more (Swarts 2000). The estimated price tag to restore this is in the many billions of dollars.
Among approaches for protection of wetlands:
- Exclusion-Those responsible for the management of wetland areas often facilitate public access to a small, designated area while restricting access to other areas. Provision of defined boardwalks and walkways is a management strategy used to restrict access to vulnerable areas, as is the issuing of permits whilst visiting.
- Education-In the past, wetlands were regarded as wastelands. Education campaigns have helped to change public perceptions and foster public support for the wetlands. Due to their location in the catchment area, education programs need to teach about total catchment management programs. Educational programs include guided tours for the general public, school visits, media liaison, and information centers.
- Andrade, C. D., A. Magnanini, L. C. Marigo, A. de Oliveira Gomes, and P. H. Britto. 1985. Pantanal. Rio de Janeiro: Assessoria de Comunicação e Marketing.
- Barbier, E. B., M. Mike Acreman, and D. Knowler. 1997. Economic Valuation of Wetlands: A Guide for Policy Makers and Planners. Gland, Switzerland: Ramsar Convention Bureau. ISBN 294007321X.
- Cowardin, L. M., V. Carter, F. C. Golet, and E. T. LaRoe. 1979. Service wetlands definition. U.S. Fish and Wildlife Service. Retrieved July 24, 2007.
- Environmental Protection Agency (EPA). 2006a. What are wetlands?. U.S. Environmental Protection Agency. Retrieved July 24, 2007.
- Environmental Protection Agency (EPA). 2006b. Wetlands definitions. U.S. Environmental Protection Agency. Retrieved May 3, 2008.
- Environmental Protection Agency (EPA). 2004. Wetlands overview. U.S. Environmental Protection Agency EPA 843-F-04-011a (December 2004). Retrieved July 24, 2007.
- Gottgens, J. F., et al. 1998. The case of the Paraguay-Paraná waterway ("Hidrovia") and its impact on the Pantanal of Brazil: A summary report to the Society of Wetland Scientists. Wetlands Bulletin 12-18.
- Mitsch, W. J., and J. G. Gosselink. 1993. Wetlands, 2nd edition. New York: Van Nostrand Reinhold. ISBN 0442008058.
- Pádua, M. T. 1991. Quoted in Vic Banks, The Pantanal: Brazil's Forgotten Wilderness. San Francisco: Sierra Club Books. ISBN 0871567911.
- Swarts, F. A. 2000. The Pantanal is the 21st Century: For the planet's largest wetland, an uncertain future. In F. A. Swarts (ed.) The Pantanal. St. Paul, M.N.: Paragon House. ISBN 1557787913.
- Ullah, S., and S. P. Faulkner. 2006. Denitrification potential of different land-use types in an agricultural watershed, lower Mississippi valley. Ecological Engineering 28(2): 131-140.