Antecedentes a una ley de humedales

"A Global Overview of Wetland Loss and Degradation"
Michael Moser, Crawford Prentice, and Scott Frazier

1. The rapid and continuing worldwide loss and degradation of wetlands has been the basis for the development of the Ramsar Convention and other wetland conservation initiatives. Wetland loss is the loss of wetland area, due to the conversion of wetland to non-wetland habitats, as a result of human activity; wetland degradation is the impairment of wetland functions as a result of human activity. The loss and degradation of wetlands reduces their ability to provide goods and services to humankind and to support biodiversity, .and are therefore associated with economic costs.

2. This paper provides an overview (but not a full review) of the causes and extent of wetland loss and degradation throughout the world. The proximate and ultimate causes of wetland loss and degradation are discussed, and the types are reviewed. The frequency of different factors causing wetland loss and degradation are compared between different regions of the world using data from published wetland directories and from the Ramsar sites database. Case studies are also presented to show the extent of wetland loss and degradation in certain countries and for certain types of wetland.

3. The paper concludes by assessing how the Ramsar Convention can better address the continuing problem of loss and degradation of wetlands. It concludes that at Ramsar site level, this must be addressed by effective integrated management including restoration and rehabilitation measures, while at national level it must be addressed by effective policies for wetland conservation. The measurement of wetland loss and degradation, and the evaluation of management actions and wetland policies depends, upon baseline information on wetland resources and effective monitoring programmes. Recommendations are made as to how to improve. these requisites through the Ramsar Convention.

This paper provides a global overview, but not a full review, of the issue of loss and degradation in wetlands; it defines these terms, looks at the consequences, describes the types and causes of loss and degradation in wetlands, and examines the extent of these changes around the world. The presentation aims to provide a background to the many issues that are to be covered in this workshop, and to suggest how the Ramsar Convention might be improved to address this paramount issue.

Some definitions
"Wetland loss" is the loss of wetland area, due to the conversion of wetland to non- wetland areas, as a result of human activity.

"Wetland degradation" is the impairment of wetland functions as a result of human activity. In practice, wetland loss is rarely independent of wetland degradation, since loss of part of a wetland is likely to impair the functions of the remaining wetland area. Conversely, wetland degradation frequently occurs without the loss of wetland area, through upstream impacts on hydrology and water quality, etc.

Generally, wetland loss is difficult and costly to reverse, although wetland restoration (the reinstatement of some, or all, pre-existing functions to "lost" wetlands (Hollis 1993)) and wetland creation (the introduction of some wetland functions to formerly non-wetland areas) are increasingly popular applied sciences and conservation tools. Changes resulting from wetland degradation are more easily reversed through rehabilitation (the enhancement of the remaining functions and the reintroduction of past functions to degraded wetlands) than is wetland loss.

Thus, both wetland loss and degradation relate to the change in quantity and/or quality of the wetland resource around a baseline.

Some consequences of wetland loss and degradation
The processes of loss and degradation reduce the ability of wetlands to provide goods and services to humankind and to support biodiversity. Examples of the impacts of the loss and degradation of wetlands have been graphically portrayed by Davies & Claridge 1993, and these may include impaired or reduced:

All of these impacts are associated with economic costs, and with a reduction in the opportunities for sustainable economic development. The subject of the economic evaluation of wetlands (and therefore of wetland loss and degradation) is covered elsewhere in the proceedings of this conference.
In industrialized countries, the consequences of the loss and degradation of wetlands have often been mitigated with expensive artificial constructions, such as major flood protection schemes or water purification plants. However, losses of wetlands in developing countries are likely to have a more direct impact than in richer countries, because mitigatory measures are less likely to be implemented due to financial and technical constraints. In addition, the consequences of wetland loss and degradation are likely to be more severe in arid and semi-arid countries (Kotze, Breen and Quinn 1995) because of the scarcity of wetland resources.

Principal Causes of Wetland Loss and Degradation
The vast majority of the world's wetlands are being used by people in a broad spectrum of activities. Through these activities, and factors emanating from activities occurring outside the sites, wetlands are subject to a range of factors which can lead to loss of wetland area and degradation of wetland quality. Not all activities performed in a wetland or its catchment are necessarily wise or sustainable, and it is these activities which can lead to loss and degradation.

Apparent and underlying causes
While it is important that the proximate causes of wetland loss and degradation are identified, the underlying causes are largely socio-economic and political (Kotze, Breen and Quinn 1995, Hollis 1992, Anon. 1996). These include: poverty and economic inequality; population pressures from growth, immigration and mass tourism; social and political conflicts; sectoral demands on water resources; centralized planning processes; and financial policies. The apparent causes are merely the outward expression of the underlying causes. It should be remembered that success in addressing the proximate issues of ecological change is unlikely if the underlying processes are not also addressed.

Types of ecological change
At a workshop on ecological change in 1992, IWRB (1993) found that the main categories of processes producing ecological change were:

Analyses of the causes of wetland loss and degradation must be considered at two levels: the direct loss and degradation that occurs to the wetland itself; and the indirect loss and degradation which occur as a result of changes outside (upstream) of the wetland. It should be noted that while a protected area or an effective management plan may be able to tackle those threats occurring within the wetland; such measures will be totally ineffective for threats whose origins are outside the wetland.
The types and frequency of ecological change factors leading to wetland loss and degradation vary in relation both to region and to wetland type.
Scott and Poole (1989) in their Status Overview of Asian Wetlands analysed the frequency of major threats recorded in wetlands of international importance in Asia, and similar data were presented by Scott and Carbonell (1985), based on the Directory of Neotropical Wetlands. In the Asian study, threats were recorded at 85% of the 734 sites for which information was available, and in the Neotropics the figure was 81% of 620 wetlands. Hunting, pollution, drainage and settlements/urbanization all occurred within the top five major threat categories in both regions.
Dugan and Jones (1993) calculated that data provided by the Ramsar Contracting Parties showed that 84% of Ramsar sites had undergone or were threatened by ecological change. Since Ramsar sites are probably better protected against wetland loss and degradation than most other wetlands with a lower conservation status, there can be few wetlands today which are not under some form of anthropogenic threat.
The analysis of Frazier (1996) (based on the Ramsar Database) shows that the frequency of occurrence of ecological change factors at Ramsar sites varies between each Ramsar region. In every region, agricultural and pollution impacts, and factors adversely affecting habitats (general habitat loss, conversion, certain species invasions/infestations) figured prominently, albeit at different positions within the top categories.

Extent and rates of loss and degradation
While the threats of change or potential change in ecological character described above affect most of the remaining wetlands in the world, this is just a "snapshot" of the current situation. Current threats very rapidly turn into wetland loss, and in a historical perspective, these losses have occurred on a massive scale.
In most industrialized countries, extensive losses have already occurred; as a consequence, public awareness of wetland values is increasing, and legislative and policy measures to reduce wetland loss are being introduced. In certain parts of the developing world, particularly those with lower population densities, the losses have been less extensive, but the potential for future loss and degradation remains great.

Measuring loss and degradation of wetlands
Unfortunately, much of the published information on wetland loss and degradation cannot be compared because of the different definitions and techniques employed by the various studies. There is an urgent need to adopt criteria which will enable standard measures of wetlands. For example, where does a wetland start and finish? How often must an area be flooded before it is classified as wetland? The most comprehensive study is that of the US National Wetlands Inventory, on account of its rigorous scientific approach to the identification and description of wetland habitats, standardized protocols for data collection and interpretation, and comprehensive coverage of all wetland habitats across the entire country. This system has been developed over two decades and has cost millions of dollars, an investment outside the immediate reach of most other countries.
Satellite remote sensing techniques, data management based on Geographical Information Systems, and improved international communication systems for data exchange and dissemination continue to make advances. However, the most recent studies (Silveira 1996) still suggest that the complexity of wetlands means that satellite data alone is usually not adequate for detecting change in wetlands, and that extensive ground truth data or mapping from aerial photographs is required.
These problems in assuring comparability between studies are even more severe when it comes to comparing regional and temporal differences in wetland quality.

Wetland losses by region
This section provides a brief overview of existing published quantitative studies of wetland loss, according to the Ramsar regions. Information was collected by keyword search from the Wetlands International library, and through contacts for different regions. Undoubtedly, the review is incomplete. At present, information for individual sites has been excluded, and the studies include those for whole regions, catchments, countries or wetland types. The studies differ in terms of time periods, and may also be biased toward regions where the greatest losses have occurred, and to industrialized countries which have greater resources to undertake such studies. Outside North America and a few European countries, very little effort has been made to document wetland loss on a systematic basis (Scott 1993). In a very generalized overview, OECD (1996) states:
"Some estimates show that the world may have lost 50% of the wetlands that existed since 1900; whilst much of this occurred in the northern countries during the first 50 years of the century, increasing pressure for conversion to alternative land use has been put on tropical and sub-tropical wetlands since the 1950s.
No figures are available for the extent of wetland loss worldwide, but drainage for agricultural production is the principal cause; by 1985 it was estimated that 56-65% of the available wetland had been drained for intensive agriculture in Europe and N America; the figures for tropical and subtropical regions were 27% for Asia, 6% for S America and 2% for Africa, making a total of 26% worldwide. Future predictions show the pressure to drain land for agriculture intensifying in these regions."

North America
By far the most comprehensive and comparable information on wetland losses are available for this Ramsar region when compared to all other parts of the world.
For the United States, Dahl and Allord (undated) describe the history of wetland losses since settlement of Colonial America in the early 1600s. The unique US National Wetland Inventory provides a wealth of detail on the quantitative scale of wetland losses, by region, by wetland type and over time.
The extent of wetland losses in the US makes depressing reading, by the fact that the losses are both widespread and severe. An analysis of losses between the 1780s and the 1980s (Dahl, 1990) indicates that a 53% loss occurred in the conterminous US (i.e., excluding Alaska and Hawaii). The least impact has occurred in Alaska, where the state's massive 170 million acres of wetland resources have only suffered a 1% loss. Next lowest losses occurred for Hawaii (12%), New Hampshire (9%) and Rhode Island (37%). Ten states have lost over 70% of their wetlands, Ohio and California having lost most at 90% and 91% respectively. Florida has lost approximately 9.3 million acres (46%).
For Canada, a high level of quantitative information on losses is also available (National Wetlands Working Group 1988). Since settlement, ca. 65% of Atlantic tidal and salt marshes, 70% of the lower Great Lakes-St. Lawrence River shoreline marshes and swamps, up to 71% of prairie potholes and sloughs, and 80% of Pacific coast estuarine wetlands are estimated to have been converted to other uses. Primarily, this is due to agricultural drainage and diking, to urban and industrial expansion, to construction of port, road and hydroelectric facilities, and to increased demands for recreational properties (National Wetlands Working Group, 1988). The intense conflict over the use of prairie wetlands for wildlife and waterfowl habitat versus their use for agricultural purposes is the most extensively documented wetland issue in Canada. The Minnedosa pothole region of SW Manitoba has been well studied, where 71% of wetlands have been lost in the period 1928-1982 due to clearance and cultivation of surrounding basins; infilling and road construction; and complete or partial drainage. Canada's boreal wetlands have primarily been influenced by conversion for hydro-electric power reservoirs and corridors, peat extraction for agriculture and energy, and forestry harvesting practices.
The information available for Mexico is less detailed, although Cervantes (personal communication) quotes losses of ca. 35% of original wetland area.

Neotropics
In the insular Caribbean, many wetland sites are degraded due to a long history of wetland reclamation and alteration, coupled with uncontrolled resource exploitation and general neglect. The current poor status of wetlands seriously influences the perception of their values, so governments have been reluctant to invest in their management. Furthermore, the small size of many of the region's wetlands has entailed their neglect by most international programmes. A survey of 220 Eastern Caribbean coastal wetlands (predominantly mangroves) between 1989 and 1991 revealed that virtually every site visited in the 16 islands showed evidence of damage, and over 50% showed severe damage (111 sites). (Bacon 1993)
Throughout the continent of South America, most wetlands remained more or less intact until recent decades, and it is only within the last few years that serious concern has been expressed concerning wetland loss. A few recent studies have revealed the alarming rate at which wetlands are disappearing in some areas, but reliable data over large areas and over many years are generally lacking (Scott, 1993).
In the Cauca River Valley system (Colombia), 88% of mapped wetlands were lost between the 1950s and 1980s. Land reclamation, drainage, river regulation, and pollution (Restrepo and Naranjo 1987) were cited as the major causes. In the Magdalena River delta (Colombia), 80% of mangrove forests died between 1970 and 1987 due to changes in the hydrological cycle (Naranjo 1993).

Europe
The most recent overview on the extent of wetland loss in Europe was provided by Jones and Hughes (1993), and little new information has been published since. While many published accounts exist at national and local scales, this was the first attempt to collate information at a Pan-European level. Some wetland types have been well covered in recent years, however, such as peatlands and lowland wet grasslands. Overwhelmingly, the available data comes from western Europe. A striking feature of the studies from Western Europe is the diversity of methodologies used to measure wetland loss, and the lack of coordination between studies in different countries or for different wetland types. This prohibits any overview at regional level.
Overall wetland losses exceeding 50% of original area have been reported by the Netherlands, Germany, Spain, Greece, Italy, France and parts of Portugal (see references in Jones and Hughes (1993) and European Commission (1995). In the UK, loss rates of 23% of estuaries and 50% of saltmarshes since Roman times (Davidson et al. 1991), and 40% of wet grasslands (RSPB 1993) have been reported. The only study allowing broad comparisons for a particular wetland type across the whole of Europe is that of Immirzi et al. (1992), which reports loss rates for peatlands in excess of 50% for 11 European countries).

Africa
The situation concerning wetland losses in Africa is characterized by an extreme paucity of published quantitative studies, similar to South America. This may reflect both the generally lower rates of losses than in industrialized regions, but also the lack of capacity to undertake such studies in many countries.
A review of wetland inventories in Southern Africa (Taylor et al. 1995), gives some information on the extent of wetland resources in 10 countries in the region. Loss figures are given for two areas in Natal – the Tugela Basin, where over 90% of the wetland resources have been lost in parts of the basin; and the Mfolozi catchment (10,000 sq.km), where 58% of the original wetland area (502 sq.km) had been lost.
The only other quantitative information arises from the wetland inventory of Tunisia, which reports an overall loss of 15% of wetland area, and 84% loss in the Medjerdah catchment (Hollis 1992).

Asia
The situation in the densely populated regions of southern and eastern Asia is very different from Africa and South America, in that here wetland loss has been occurring for thousands of years. Lowland rice cultivation began in SE Asia about 6,500 years ago, and sophisticated drainage and irrigation systems had been developed in parts of the Middle East by the 4th millenium BC.(Scott, 1993)
Over the centuries, vast areas of wetland in southern and eastern Asia have been converted into ricefields or drained for other forms of agriculture andhuman settlement. In some areas, this conversion or destruction of wetlands has been total. For example, no trace remains of the natural floodplain wetlands of the Red River delta in Vietnam, which originally covered 1.75 million hectares. Likewise, there is virtually nothing left of the one million hectares of natural floodplain vegetation which once covered most of the Sylhet Basin in Bangladesh or the six million hectares of floodplain wetlands in the lowlands of central Myanmar. Much of the 40 million hectares of rice cultivation in the central plains of India must have been developed at the expense of natural wetlands, and the same is true of the 1.9 million hectares of rice cultivation in the central plains of Thailand. In all of these regions, very little natural wetland vegetation has survived into the present century. (Scott 1993)
In his review, Scott (1993) quotes an overall loss of 31% of wetlands in Indonesia, with loss of mangroves in Singapore, Philippines and Thailand being 97%, 78% and 22% respectively. In their review of peatlands, Immirzi et al. quote losses for Israel (100%), Thailand (82%), West Malaysia (71%), Indonesia (18%), China (13%), Sarawak in East Malaysia (11%).

Oceania
Little published quantitative information exists for the extent of wetland loss in the small south Pacific islands, despite the recent wetland inventory for this region (Scott 1993).
For New Zealand, Cromarty (1996) estimates a loss of 90% of the original wetland area. For Australia, loss estimates are given for Victoria (26.8%), the southeastern part of South Australia (89%) and the Swan Plain Coast of South Australia in the recently published national wetland directory (Usback & James 1993). The most detailed study for Victoria shows losses of fresh water marshes exceeding 70%, whilst there have been gains through the creation of artificial wetlands such as sewage ponds and saltworks.

Strategies to Reverse Loss and Degradation
Wetland loss and degradation and the Ramsar Convention

The Ramsar Convention was established to address the issue of the loss and degradation of wetlands through concerted and coordinated action by the Contracting Parties, so that wetlands can contribute to the process of sustainable development. Almost the entire suite of obligations that are undertaken by the Contracting Parties relate to addressing this issue: the designation of sites to the Ramsar list, maintaining the ecological character of listed Ramsar sites; the establishment of reserves on wetlands, and making wise use of wetlands. Undoubtedly, the Ramsar Convention has succeeded in raising awareness and the level of actions for conservation of wetlands; yet wetlands continue to be lost and degraded at a rapid pace in many parts of the world. The remainder of this paper focuses on how the Ramsar Convention could be made more effective to address these issues, both at a national policy level and at the level of individual Ramsar sites. The paper concludes with a number of specific recommendations for consideration by the Ramsar Convention.

The adoption of a strategic plan by this conference, represents a clear indication of the increasing maturity of the Ramsar Convention, and a realization that such a strategic approach is the only way to address the issue of the global loss and degradation of wetlands. A comprehensive strategy should incorporate the following vital steps, which are applicable both to sites (through a management plan, as covered well by the Ramsar guidelines) and to whole countries (through a national wetland policy):

1. Set a measurable goal
Larson (1993) recommends that a measurable goal should be included in all national wetland policies. Goals that have been adopted or proposed to date include the "No Net Loss" goal of national wetland policies in the United States and Canada, which relate both to wetland area and function (see discussion in Larson 1993), and the goal of stopping and reversing the loss and degradation of Mediterranean wetlands, which is the goal of the Mediterranean Wetlands (MedWet) Initiative.
At present, the Ramsar Convention contains a measurable goal for the listed Ramsar sites, which is "to maintain their ecological character". While potentially measurable, the issue of "change in ecological character" is still poorly defined.
Unfortunately, at the national and international levels, neither the Convention text nor the draft Strategic Plan set measurable goals, making it difficult to measure the success of the Convention in future years. It is strongly recommended that each Contracting Party, and perhaps the Ramsar Convention as a whole, should include a measurable goal as it develops and adopts its national wetland policy.

2. Measure the resource baseline
Whether the goal is to maintain the ecological character of a wetland site, or to stop the loss and degradation of wetlands across the landscape as a whole, it is essential to measure the baseline of the wetland resource under consideration. This is achieved through a wetland inventory programme. A wetland inventory is one of the key elements in a conservation strategy for wetlands (WWF 1992). This is because (Costa et al. 1996) such inventories:

The Convention, through the wise use guidelines, already calls upon Contracting Parties to execute national wetland inventories. However, recent regional reviews such as Hecker and Tomas Vives 1995 (the Mediterranean), Taylor et al. 1995 (Southern Africa), and national reports to (former) IWRB suggest that such programmes are, as yet, poorly developed.

MedWet Monitoring Guide. The most comprehensive national wetland inventory programme to date has been that of the United States. Building on this and other experiences, and in order to assist the development of wetland inventories internationally, Wetlands International and the Instituto da Conservacao da Natureza (Portugal), as part of the MedWet initiative, have prepared comprehensive national wetland inventory tools for the Mediterranean region including: a Reference manual; Datasheets and their guidelines; a Habitat Description System; Photointerpretation and cartographic conventions; and a MedWet database and manual.
Two important issues have emerged during the preparation of these tools:

4. Prescribe and undertake actions
These two critical steps are the main subject of the Ramsar Convention Strategic Plan, and are not discussed here in any further detail.

5. Monitor performance against baseline
Monitoring the effects of the conservation actions undertaken should be an important feedback mechanism within any site management plan or national wetland policy. It is only through such monitoring programmes that the extent and causes of loss and degradation of wetlands can be determined, and the success of conservation actions be measured. However, the complexity and diversity of wetlands has been a serious constraint to the development of effective monitoring schemes, and it is notable that it is only after 25 years that the Convention is now beginning to address this issue systematically.
Monitoring programmes need to address both the issue of wetland integrity (i.e. change in wetland area) and change in wetland quality. While the Convention is addressing these needs at the level of individual Ramsar sites, a serious gap remains in the lack of quantitative information on changes in these parameters at national and therefore international level. Very few countries, with the notable exception of the United States, are able to provide information on the status of their wetlands or temporal trends in the rates of loss and degradation.
Given this lack of knowledge, it is recommended that Contracting Parties be encouraged to establish programmes to gather such information. Further investigation of the possibilities of using remote sensing to achieve these aims may provide the most cost-effective solution in the long term.

6. Report the results
The quality and quantity of information about the state of wetlands must be increased and communicated more effectively at all levels. Information on the loss and degradation of wetlands, and the consequences of this for people and for biodiversity, provide powerful tools for influencing public opinion and decision-makers. Thus, awareness of the US status and trends reports led to the Emergency Wetlands Resource Act of 1986 (Thompson and Tapson 1994).
It is strongly recommended that at both national and international levels, formal mechanisms are established for reporting on the status of the wetland resources. At international level, a first step would be to compile and publish a review of all the quantitative studies of wetland loss/gain.

1) There is a lack of information about loss and degradation in most countries; much of the information that does exist cannot be compared.
2) A global overview indicates that massive historical losses of wetlands have occurred worldwide, much of this prior to the launch of the Ramsar Convention. There are wide variations between regions, between wetland types and over time.
3) The majority of the remaining wetlands are degraded, or under threat of degradation. The intensity of these problems is closely related to the intensity of human activity in and around the wetland.
4) The loss and degradation of wetlands has severe economic consequences, and removes opportunities for sustainable development. Restoration and rehabilitation measures are very expensive, and unlikely to restore full natural functions.
5) We are not in a position to measure the global wetland resource baseline, nor to monitor the success of national and international programmes, including the Ramsar Convention.
6) Information on the loss and degradation of wetlands is essential to influence policy, through public awareness.

Acknowledgements
The authors are grateful to the many experts who have participated in numerous workshops (St Petersburg Beach, Florida (USA) 1992), Linz (Austria) 1993, and several workshops under the MedWet Initiative) which have led to the development of this work. They would like to thank Mauricio Cervantes, Ian Davidson, Tom Dahl (US National Wetlands Inventory) and Roger Jaensch for providing additional material at short notice.
References: Wetland Loss Bibliography

Anonymous. 1996. The Mediterranean Wetland Strategy: 1996-2006. Venice. 16pp.
Bacon, P.R. 1993. Wetland restoration and rehabilitation in the Insular Caribbean. In Moser, Prentice& van Vessem. 1992, pp. 206-9.
Begg, G.W. 1988. The wetlands of Natal (Part 2): The distribution, extent and status of wetlands in the Mfolozi catchment. Natal Town and Regional Planning Commission Report, 41.
Chiau, W-Y & Liu, C-C. "Coastal wetlands protection in Taiwan: issues and challenges." Unpublished manuscript.
Commission of the European Communities. 1995. Wise Use and Conservation of Wetlands. Communication from the Commission to the Council and the European Parliament. 53pp.
Costa, L.T., Farinha, J.C., Hecker, N. & Tomás Vives, P. (Eds.). 1996. Mediterranean Wetland Inventory: A Reference Manual. MedWet/Instituto da Conservaõ o da Natureza / Wetlands International Publication, Volume I.
Cowardin, L.M., Carter, V., Golet, F.C. & Laroe, E.T. 1979. Classification of wetlands and deep water habitats of the United States. US Fish and Wildlife Service, Washington DC.
Cromarty, P. 1996. New Zealand Country Report. pp79-92. In Jaensch, R. (ed.). 1996. Wetland Conservation in the PacificIslands Region. Proceedings of the Regional Workshop on Wetland Protection and Sustainable Use in Oceania, Port Moresby, Papua New Guinea, 6-10 June 1994. Wetlands International - Asia, Pacific, Canberra, Publication No. 118.
Dahl, T.E. 1990. Wetlands losses in the United States 1780's to 1980's. US Department of the Interior, Fish and Wildlife Service, Washington, D.C. 13pp.
Dahl, T.E. & Allord, G.J. Undated. Technical Aspects of Wetlands. History of Wetlands in the Conterminous United States. National Water Summary: Wetland Resources. US Geological Survey Water-Supply Paper 2425.
Davidson, N.C., d'A Laffoley, D., Doody, J.P., Way, L.S., Gordon, J., Key, R., Drake, M., Pienkowski, M.W., Mitchell, R. and Duff, K.L. 1991. Nature conservation and estuaries in Great Britain. NCC. Peterborough.
Davies, J. & Claridge, G.F. (Eds). 1993. Wetland Benefits: The potential for wetlands to support and maintain development. AWB publication 87, IWRB Publication 27, WA publication 11.
Dugan, P.J. & Jones, T.A. 1993. Ecological change in wetlands: a global overview. In Moser, Prentice, & van Vessem. 1992.
Frazier, S. 1996. An overview of the world's Ramsar sites. Wetlands International Publ. 39. 58pp.
Hecker, N. & Tomás Vives, P. (Eds.). 1995. The Status of Wetland Inventories in the Mediterranean Region. MedWet Publication/IWRB Publication 38. 146 pp,
Hollis, G.E. 1992. The causes of wetland loss and degradation in the Mediterranean. In Finlayson, C.M., Hollis, G.E. and Davis, T.J. (eds.). Managing Mediterranean Wetlands and Their Birds. Proc. Symp., Grado, Italy, 1991. IWRB Spec. Publ. No. 20, Slimbridge, UK, 285pp.
Hollis, G.E. 1993. Goals and objectives of wetland restoration and rehabilitation. In Moser, Prentice, & van Vessem. 1992.
Immirzi, C.P. & Maltby, E. with Clymo, R.S. (1992). The Global Status of Peatlands and their Role in Carbon Cycling. A report for Friends of the Earth by the Wetland Ecosystems Research Group, Department of Geography, University of Exeter. Friends of the Earth, London.
IWRB. 1993. Conclusions of a workshop on measuring ecological change in wetlands. In Moser, Prentice, & van Vessem. 1992.
Jones, T.A. & Hughes, J.M.R. 1993. Wetland inventories and wetland loss studies: a European perspective. In Moser, Prentice, & van Vessem. 1992.
Kotze,D.C., C.M. Breen & Quinn, N. 1995. Wetland losses in South Africa. In Cowan, G.I. (ed.). Wetlands of South Africa. Dept. of Environmental Affairs and Tourism, Pretoria, S. Africa. Pp. 263-272.
Larson, J. 1993. Is "No net loss" a useful concept for wetland conservation? In Moser, Prentice, & van Vessem. 1992.
Moser, M., Prentice, R.C. & van Vessem, J. (eds.). 1992. Waterfowl and wetland conservation in the 1990s: a global perspective. Proceedings of the IWRB Symposium, St. Petersburg, Florida, November 1992. IWRB Special Publication 26.
Naranjo, L. 1993. Ecological change in Colombian wetlands. In Moser, Prentice, & van Vessem. 1992.
National Wetlands Working Group, Canada Committee on Ecological Land Classification. 1988. Wetlands of Canada. Ecological Land Calssification Series, No. 24. Sustainable Development Branch, Canadian Wildlife Service, Environment Canada.
OECD/IUCN. 1996. Guidelines for aid agencies for improved conservation and sustainable use of tropical and sub-tropical wetlands. OECD, Paris.
Restrepo, C. & Naranjo, L.G. 1987. Recuento histórico de la disminución de humedales y la desparación de aves acuáticas en el Valle del Cauca, Colombia. In: Alvarez, H., Kattan, G. & Murcia, C. (eds.). Memorias III Congreso de Ornitolog!a Neotropical. Cali: ICBP-USFWS-SVO; pp.43-45.
RSPB 1993. Wet grasslands - what future? RSPB, Sandy, UK.
Saenger, P., Hegerl, E.J. & Davie, J.D.S. 1983. Global Status of Mangrove Ecosystems. IUCN Commission on Ecology Papers No.3. IUCN, Gland, Switzerland.
Scott, D.A. (ed.) 1993. A Directory of Wetlands in Oceania. IWRB, Slimbridge, UK and AWB, Kuala Lumpur, Malaysia. xvii+444pp, 16 maps.
Scott, D.A. 1993. Wetland inventories and the assessment of wetland loss: a global overview. In Moser, Prentice, & van Vessem. 1992.
Scott, D.A. & Carbonell, M. 1985. The IWRB/ICBP Neotropical Wetlands Project: a report on the completion of "A Directory of Neotropical Wetlands". In Scott, D.A., Smart, M. & Carbonell, M. Report of the XXXI Annual Meeting, Paracas, Peru, 10-16 February 1995. IWRB, Slimbridge, UK.. 194 pp.
Scott, D.A. & Poole, C.M. 1989. A Status Overview of Asian Wetlands. Asian Wetland Bureau Publication No.53. AWB, Kuala Lumpur, Malaysia.
Silveira, J.E. 1996. Methods for determining change in Florida wetland habitats using SPOT satellite data. Fla. Coop. Fish and Wildl. Res. Unit, US Nat. Biol. Serv. Tech. Rep. 52. Gainesville, Florida.
Taylor, R.D., Howard, G.W. & Begg, G.W. 1995. Developing wetland inventories in Southern Africa: a review. Vegetatio 118:57-79.
Thompson, M.W. & Tapson, A. 1994. Current and future trends in mapping and monitoring wetlands in South Africa using remote sensing. Unpublished report.
Usback, S. & James, R. (compilers). 1993. A Directory of Important Wetlands in Australia. Australian Nature Conservation Agency, Canberra, Australia.
WWF. 1992. Statewide Wetlands Strategies: A guide to protecting the resource. Island Press, Washington.

For further information about the Convention on Wetlands, please contact the Ramsar Convention Bureau, Rue Mauverney 28, CH-1196 Gland, Switzerland (tel +41 22 999 0170, fax +41 22 999 0169, e-mail

). Posted 18 February 1998, Dwight Peck, Ramsar.

Of the original 215 million acres of wetlands existing 200 years ago in the continental United States, less than 100 million acres remain. Check the map at EPA to find whether your state has experienced low, moderate, or high wetlands loss. Twenty-two states have lost at least 50 percent of their original wetlands. Seven states have lost over 80 percent (Indiana, Illinois, Missouri, Kentucky, Iowa, California, and Ohio). Since the 1970’s the most extensive wetlands loss has occurred in Louisiana, Mississippi, Arkansas, Florida, South Carolina, and North Carolina.

Wetland losses from the 1950’s to the 1970’s averaged about 458,000 acres per year. Agricultural development was responsible for about 87 percent of this loss. In the 1990’s wetland losses have averaged about 117,000 acres per year, due to passage of the Clean Water Act, state and local government wetland protections, and the vigilance of community conservationists who challenge the ongoing draining and filling of wetlands, mostly for residential and commercial development.

The remaining 100 million acres of wetlands in the continental U.S. comprise an area about the size of California. Alaska has an estimated 170 to 200 million acres, while Hawaii has 52,000 acres.

Of the 100 million acres of wetlands remaining in the continental U.S., Florida has the most, with 11 million acres. Next are Louisiana (8.8 million), Minnesota (8.7 million), and Texas (7.6 million).

The remaining wetlands, in millions of acres, are:
Coastal Wetlands - 5.1
Inland Marshes and Wet Meadows - 28.6
Inland Shrub Swamps - 10.4
Inland Forested Wetlands - 46.3
Other Inland Wetlands - 6.1

A lot of wetland loss is attributable to agricultural activities, such as draining, diking and plowing of wetlands. Other human activities that lead to wetlands destruction include:

Preventing wetlands loss is good for the economy, because filling or draining wetlands costs a lot of money in lost tourist dollars, reduction of fisheries, repairing flood damage. It also costs a lot more to restore a wetland that to just protect it in the first place. Destroying wetlands means fewer birds and less wildlife. It means we leave a damaged world behind us for our children to inherit.

The value of wetlands is grossly underestimated by many people. For many years, humans have perceived these ecosystems as unproductive hazardous places and have deemed them worthless. As a result of this attitide, many countries have had policies in place that subsidized the conversion of wetlands into other land-use types. In the last few decades, however, science has shown that wetland habitats provide us with some very important environmental functions. These important wetland functions include:

Canada is rich in wetland habitat. Approximately 14 % of Canada's land area is classified as this land-cover type. More than 60 % of Canada's wetlands are found in the provinces of Ontario and Manitoba and the Northwest Territory. British Columbia wetlands represent only about 2-3 % of the Canadian total. Some of the more significant freshwater wetlands are: the prairie potholes of Alberta, Saskatchewan, and Manitoba; the marshes of Lake St. Clair and Lake Erie; the St. Lawrence River, Peace-Athabasca River, and Red River marshes; the peatlands of Newfoundland and Vancouver Island; and the numerous wetlands of northern Manitoba, Saskatchewan, and Alberta. Some of the better known saltwater wetlands include the coastal regions of Hudson Bay and James Bay, the marshes of Kamouraska in Quebec and Tintamarre in New Brunswick, and the tidal marshes of the Fraser River estuary.

Table 3.4 describes the thirteen largest wetlands found on our planet. The majority of these wetlands are located along major river systems like the Nile, Amazon, Congo, and Mackenzie. Large areas of wetlands also occur on terrestrial habitats which have little topographic slope to enhance the drainage process. These wetlands include the West Siberian Lowlands, Hudson Bay Lowlands, North America Prairie Potholes, and the Hudson Bay Lowlands.

Wetland Name	Location	Approximate Size (square km.)	Wetland Type
West Siberian Lowlands	Eurasia	1,000,000 to 780,000	peat bogs, boggy forests, meadows
Amazon River	South America	800,000	swamps, marshes, floodplain
Hudson Bay Lowlands	North America	320,000 to 200,000	peatlands
Pantanal	South America	200,000 to 140,000	marshes, swamps, floodplain
Mississippi River System	North America	86,000	bottomland hardwoods
Upper Nile Swamps	Africa	90,000 to 50,000	swamps and floodplain
Chari-Logone River System	Africa	90,000	seasonal floodplain
Papua-New Guinea	Eurasia	69,000	swamp, bogs
Zaire-Congo River System	Africa	80,000 to 40,000	marshes, swamps, floodplain
Upper Mackenzie River	North America	60,000	marshes, swamps, floodplain


Chilean Fjordlands	South America	55,000	?
North America Prairie Potholes	North America	40,0000	marshes
Orinoco River Delta	South America	30,000	floodplain, swamp, marsh

Large quantities of this land-cover type have been altered or converted into other land-use types. Approximate 70 % of the potholes in the North America Prairies have been drained or filled in for agriculture. Wetlands found in our urban regions have been reduced by over 80 % in many cases. In the Fraser River estuary, more than 70 % of wetlands located in this area have been affected by farming or urban development.
From a national perspective, Canada has been slow in developing policy for wetland conservation. Almost all of the policy now in place was developed after 1980.

ver criterios norteamericanos . 4 . 5 . 6 . 7 . . . ¿sustentables? ver 3 textos . 8