2 Global Distribution, Diversity and Human Alterations of Wetland Resources
DENNIS F. WHIGHAM
Smithsonian Environmental Research Center, Edgewater, USA
INTRODUCTION Wetlands of International Importance Especially as Waterfowl Habitat, published in 1971, gives: This chapter outlines the distribution and ... wetlands are areas of marsh, fen, peatland or water, diversity of wetland resources and examines the whether natural or artificial, permanent or tempo types of human activities that have resulted in rary, with water that is static or flowing, fresh, brack widespread alteration. The term 'wetland' has a ish or salt, including areas of marine water the depth variety of meanings, and examples are given of of which at low tide does not exceed six metres. the terminology used to describe different types Another widely used wetland definition was of wetlands. The processes responsible for the for developed by the US Fish and Wildlife Service for mation and persistence of wetlands are indicated purposes of bringing consistency to an ongoing and consideration is given to human perceptions national debate related to inventory, regulation of these ecosystems and threats to them from and conservation of wetlands in the United States both natural and anthropogenic activities. (Cowardin et al. 1979; Mitsch and Gosselink 2000; Tiner 1996). The Cowardin et al. definition, developed as part of a classification system, is: DEFINITIONS AND CLASSIFICAnON ... lands transitional between terrestrial and aquatic Many definitions of wetlands have been devel systems where the water table is usually at or near the oped (Maltby 1991; Dugan 1993; Mitsch and surface or the land is covered by shallow water. For the purposes of this classification wetlands must have one Gosselink 2000; Tiner 1996) and some of them or more of the following three attributes: (1) at least have been changed over time, particularly in the periodically, the land supports predominantly hydro US, in response to an increased understanding phytes; (2.1 the substrate is predominantly undrained of wetland ecology and to political arguments hydric soil; and (3) the substrate is nonsoil and is satu (National Research Council 1995). Two examples rated with water or covered by shallow water at some of wetland definition demonstrate the range of time during the growing season of each year. ('nonsoil' considerations that have been used to describe simply means 'not soil' e.g. rock, undecomposed lit their characteristics. The most widely known and ter, or the sediments of a water body too deep for the internationally adopted wetland definition was growth of rooted plants (usually >2.m-3m)). developed for purposes of providing international Both definitions communicate the importance protection for waterfowl across the widest possible of vegetation and water in the identification, range of wetlands. The Ramsar Convention on development and persistence of wetlands, and the Cowardin et al. definition also recognises The Wetlands Handbook, 1st edition. Edited by the importance of substrate conditions. The two E. Maltby and T. Barker. © 2.009 Blackwell Publishing, descriptions collectively identify the essential ele ISBN 978-0-632.-052.55-4 ments of a robust definition of wetlands: hydrology, 44 DENNIS F. WHIGHAM vegetation and substrates. Most wetland defini marshes and mangroves. Inland wetlands were tions are not, however, particularly useful when freshwater marshes, northern peatlands, south there is a legal requirement to determine whether ern deepwater swamps and riparian wetlands. or not a given habitat should be classified as a While the wetland terms used by Dugan (1993), wetland or when wetland delineation is required. Maltby (1991) and Mitsch and Gosselink (2000) The issues of wetland identification and delin are widely recognised, the reader should be aware eation have been particularly contentious in that the use of common terms can lead to confu the United States and many efforts have been sion because names for a single type of wetland directed toward providing a definition that can can vary from one language to another (Scott be used to develop methods to identify and delin and Jones 1995). At times, common terms used eate wetlands (Tiner 2000). Tiner emphasised to describe types of wetlands can be confusing. that a robust wetland definition that can provide The Ramsar definition given above, lists fens and effective guidance toward wetland identification peatlands, suggesting that they are separate types and delineation must include the three elements of wetlands. Gore (1983) defined fens as peat accu listed above (hydrology, vegetation, soil). He also mulating wetlands that receive rainwater and suggested that a tiered approach be applied in drainage from surrounding mineral soil and usu application of identification procedures. Obvious ally support marsh-like vegetation. He defined wetlands can be identified by rapid assessments peatland as a generic term for any wetland that using vegetation, hydrology or soils alone, while accumulates partially decayed plant matter (Gore wetlands that are more difficult to identify require 1983), indicating that fens are a type of peatland. additional effort and multiple indicators of these It is preferred to describe all active peat-forming elements. No matter how wetlands are defined, it wetlands as mires, and separate them into fens is common practice to use Widely accepted terms and bogs according to whether they are fed pre to describe different types. dominantly by groundwater or rainfall. Despite Dugan described globally distributed wetland the danger of confusion it is nevertheless useful types based primarily on geomorphic position to examine the salient characteristics of the most (Dugan 1993). Estuaries, mangroves and tidal common categories found in the literature. flats are wetlands and wetland habitats associ ated with coastal features that are tidally influ Marshes enced. Floodplains and deltas are systems that contain wetlands associated with rivers with var Marshes (Figure 2.1) are wetlands dominated by ious flooding regimes. Marshes, lakes, peatlands herbaceous vascular plants, the stems of which and forested swamps are terms used by Dugan emerge above the water surface. Marshes occur to describe wetlands associated with non-tidal in areas that are frequently or continuously inland habitats. Maltby (1991) also described inundated with water and they are most often general wetland types based on broad features associated with mineral soils that do not accu such as dominant vegetation (marshes, swamps), mulate peat. Typically, dominant plant species soil characteristics (peatlands), geomorphic fea in marshes are reeds, rushes, grasses, and sedges tures (floodplain wetlands, lakes, estuaries and that are characterised by thin 'grass-like' leaves. lagoons), geographic location (mangroves, Nipa Marshes, however, can also contain a wide swamps (Nipa palm, Nipa fructicans), and tidal variety of plant species with many different life freshwater swamp forests) and human activi forms. Freshwater tidal marshes, for example, ties (artificial wetlands). Mitsch and Gosselink can be dominated by annuals and perennials (2000) recognised seven types of wetlands based that range in leaf form from grass-like to broad on whether they were associated with coastal leaved (Simpson et al. 1983). Marshes have been (tidal) or inland (non-tidal) habitats. Coastal wet studied extensively because of their importance lands included tidal salt marshes, tidal freshwater as waterfowl habitat (Weller 1994) and many Distribution and Diversity of Wetland Resources 45
Fig. 2.1 The author standing in a stream channel at Fig. 2.2 Richard Hauer in a freshwater swamp low tide in a freshwater tidal emergent wetland along dominated by Acer rubrum (Red Maple) and Nyssa the Delaware River (USA). Tidal amplitude is approxi aquatica (Water Tupelo) on the Pearl River in mately 3 m. The dominant emergent species in the fore Mississippi (USA). (Photo by the authoL) ground is Nuphar advena (Yellow waterlily). (Photo by Robert Simpson.) different types of marsh have been recognised both in the US (e.g. prairie potholes, playas, sali nas, salt marshes, brackish marshes, freshwater tidal marshes, vernal pools and Carolina bays) and elsewhere (Semeniuk and Semeniuk 1995).
Peatland (often called mire) This is a generic term for any wetland that has at some point accumulated partially decayed plant matter because of incomplete decomposition, usually to a depth less than 30 cm (Figure 2.2). Fig. 2.3 Seiichi Nohara in the Akaiyachi Mire (bog), The term 'mire' refers to those peatlands in central Honshu, Japan. Sphagnum dominated peat has which peat formation is still active. Many terms accumulated to a depth of 150 em. Below the Sphagnum have been developed to describe peat-forming peat are layers of Moliniopsis and Phragmites domi wetlands, particularly in Europe (Money). Fens nated peat overlying a layer of volcanic ash and sand can be dominated by herbaceous or woody plant with wood and Phragmites remains. Four Sphagnum species. Bogs are peatlands dominated by herba species dominate the existing peat mat. Abundant vas ceous or woody species, but they differ from fens cular plants are Phragmites australis, Ilex crenata vaL because the water chemistry resembles that of paludosa, Vaccinium oxycoccus, Moliniopsis japonica, precipitation and the peat is usually formed by Rhynchospora alba and Sasa palmata. (Photo by the the slow decomposition of mosses, especially authoL) species of Sphagnum. A complex and diverse Swamps terminology (Heathwaite and Gbttlich 1990; Verhoeven 1992; Glooschenko et 01. 1993) has Wetlands that are covered intermittently or per been developed in different countries to describe manently with water, and are dominated by trees different types of bogs. or shrubs, are swamps (Figure 2.3). In essence, 46 DENNIS F. WHIGHAM swamps are marshes that are dominated by Table 2.1 Classification of wetlands used in the woody vegetation. Swamps, like marshes, are Directory of Neotropical Wetlands (Scott and diverse and occur in many habitats from the Carbonell 1986). Identification of wetland types temperate zones to the tropics (Lugo et al. 1990). is based on geomorphic features (e.g. estuaries), Swamps that are associated with rivers typically habitat type (e.g. freshwater pond), vegetation type (e.g. mangrove), and substrate conditions (e.g. peat have inorganic substrates (Sharitz and Mitsch bogs). Vegetation type refers to the numbering system 1993; Junk 1997). Other swamps develop in areas used by Scott and Carbonell (1986). with little or no connection to flowing streams and rivers, and may develop peat substrates Vegetation Description (Richardson 1981; Richardson and Gibbons 1993). type Swamps represent a particularly threatened type of wetland in many parts of the world because of 01 Shallow sea bays and straits exploitation for wood products and conversion to 02 Estuaries, deltas 03 Small offshore islands, islets agricultural lands. 04 Rocky sea coasts, sea cliffs There have also been attempts to classify 05 Sea beaches (sand, pebbles) wetlands based mostly on hydrologic and hydro 06 Intertidal mudflats, sandflats geomorphic characteristics, thus eliminating 07 Coastal brackish and saline lagoons and marshes, some of the confusion associated with the use of salt pans common names based mostly on vegetation char 08 Mangrove swamps, brackish forest acteristics. Scott (1989) and Scott and Carbonell 09 Slow-flowing rivers, streams (lower perennial) (1986) developed a widely cited classification 10 Fast-flowing rivers, streams (upper perennial) system (Table 2.1 Lfor neotropical wetlands. They 11 Riverine lakes (including oxbows), riverine marshes used dominant vegetation type to describe three 12 Freshwater lakes and associated marshes (lacustrine) wetland types (08, 18, 19) but location within the 13 Freshwater ponds «8 hal, marshes, swamps landscape, or a combination of landscape position (palustrine) and vegetation, were used to classify most wet 14 Slat lakes, slars (inland systems) lands. Cowardin et al. (1979) developed a system 15 Reservoirs, dams to classify wetlands in the US that is hierarchi 16 Seasonally flooded grassland, savanna, palm cally based on geomorphic features (marine, estu savanna arine, riverine, lacustrine, palustrine) hydrologic 17 Rice paddies, flooded arable land, irrigated land conditions (subtidal, intertidal, tidal, perennial 18 Swamp forest, temporarily flooded forest streams, intermittent streams, limnetic, littoral) 19 Peat bogs, wet Andean meadows (bofedales), and several modifiers, such as substrate condi snow melt bogs tions and dominant vegetation type (Figure 2.4).
total wetland area on earth has been estimated to WETLAND DISTRIBUTION be 7-8.5 million km2, approximately 6% of the land surface (Maltby and Turner 1983; Mitsch Wetlands occur over wide range of altitudes and 1998; Mitsch and Gosselink 2000). The global latitudes, from the tropics to the arctic, and from estimates should, however, be viewed as mini below sea level to alpine environments (Figure 2.5). mum estimates of wetland coverage, because few They occur in almost all habitats, from tidally countries have completed any detailed national influenced coastal landscapes that flood once or wetland inventories and, even where inventories twice daily, to endorheic basins in interior areas have been completed, only the largest wetland of continents that most often have little or no areas have been identified. standing water but are transformed into produc Wetlands are found on all continents, and sev tive wetland systems when rainfall occurs. The eral publications have included summaries of Distribution and Diversity of Wetland Resources 47
System Subsystem Class ROCk bottom ,- Subtidal ------Unconsolidated bottom ~Aquatic bed Reef Marine--- AqUatic bed '------Intertidal ------i Reef ~Rocky shore Unconsolidated shore ROCk bottom Subtidal Unconsolidated bottom r------1 Aquatic bed GReef
Aquatic bed Estuarine Reef Streambed L------Intertidal ------1 Rocky shore nconsolidated shore Emergent wetland Scrub-shrub wetland Forested wetland
Rock bottom unconsOlidated bottom Tidal ------1 Aquatic bed Rocky shore ~Unconsolidated shore Emergent wetland ROCk bottom Unconsolidated bottom 1- Lower perennial Aquatic bed Rocky shore Unconsolidated shore Riverine ----I ---iEmergent wetland ROCk bottom Unconsolidated bottom f----- Upper perennial ------1 Aquatic bed ~Rocky shore Unconsolidated shore '------Intermittent ------Streambed
ROCk bottom ------Limnetic ------1 Unconsolidated bottom EAquatic bed Lacustrine ~ROCk bottom Unconsolidated bottom L- Littoral . Aquatic bed ---1 Rocky shore Unconsolidated shore Emergent wetland
ROckbottom Unconsolidated bottom Aquatic bed Palustrine ------Unconsolidated shore Moss-lichen wetland Emergent wetland ~ Scrub-shrub wetland Forested wetland
Fig. 2.4 Hierarchy of wetlands and deepwater habitats in the US wetland classification (Cowardin et a1. 1979), showing system, subsystems and classes. 48 DENNIS F. WHIGHAM
•• I , ..... , '*~I" -.
..-.~
Key • Major wetland areas
Areas with abundance O of wetlands
Note: Mapping of Russia based orl available butincompleledala
Fig.2.5 Distribution of major wetland areas and areas where wetlands are abundant. (Source: Mitsch 1994.) information on the distribution of the world's sites in all countries except Lybia, Syria and wetland resources. Most noteworthy are the Bulgaria; areas where important wetland habi edited volumes by Finlayson and colleagues tats are known to occur (Britton and Crivelli (Finlayson and Moser 1991; Finlayson and van 1993). Hughes considered most of the same der Valk 1995), as well as the illustrated volume countries as Hollis and Jones, and suggested a by Dugan (1993). Together with Lugo et a1. (1990) total of 7.41 million ha of wetlands in the region and Whigham et a1. (1993) they provide references (Hughes 1995). About half of the European and to many of the relevant sources of information on the Mediterranean countries have completed, the worlds wetlands. Wetlands International also are conducting, or are planning wetland invento offers many publications that describe wetlands ries. Unfortunately there has been little unifor at international and regional scales (http://www. mity in approaches to conducting inventories, wetlands.orgjpubs&jpubsMain.htm). and classification approaches vary widely, resulting in difficulties in making comparisons Regional overview among countries (Hughes 1995). Only about 18% of the wetlands identified in the region are Europe and the Mediterranean basin not threatened in some way by direct or indirect Hollis and Jones listed 200 major wetland areas pressures associated with development (Hollis in the region (Hollis and Jones 1991), including and Jones 1991). Distribution and Diversity of Wetland Resources 49
There is a wide diversity of wetland types Information on specific wetland types is avail in Europe and the Mediterranean. Arctic and able, for example for Pocosins, which are bogs boreal landscapes and alpine habitats sup found only in the south-eastern US dominated port many types of wetland. Extensive tracts by evergreen shrubs and small trees (Richardson occur in the Scandinavian countries, and large 1981; Sharitz and Gibbons 1982). The Florida wetland complexes are associated with the Everglades are subtropical marshes and forested Wadden Sea in the Netherlands, Germany and wetlands, including Cypress wetlands of vari Denmark. Important wetlands also occur in ous types (Ewel and Odum 1984; Gunderson and Russia, on the coast of the Black Sea and along Loftus 1993). Prairie Potholes wetlands occur in the North Atlantic Coast. Large and important seasonally- to permanently-flooded depression marshes and swamps are associated with river habitats in the upper Midwest. Pothole wet deltas such as the Volga, Danube and Nile River. lands are typically marshes and they provide Many countries in the region have developed breeding habitats for 50-75% of the continent's an extensive wetland literature that focuses waterfowl (van der Valk 1989). Martin et a1. on classification and ecology. Examples include (1993) describe wetland ecosystems of the south a discussion of mire classification in Finland eastern US where floodplain forests and swamps and Scandinavia (Parkarinen 1995), and of wet are especially abundant, along with extensive lands in the UK (Rodwell 1991, 1995). Recent coastal marshes. An example of a forested wetland regional descriptions of fens and mires are (swamp) that occurs only on the eastern coast of also available (Heathwaite and Gottlich 1990; the US is one dominated by Atlantic White Cedar Verhoeven 1992). (Laderman 1987, 1989). No national inventory has been compiled for Canadian wetlands, but a detailed classification system (Glooschenko North America et a1. 1993; Warner and Rubec 1998) has been Avast amount of information is available for wet developed, and inventories are available for some lands of the US and Canada and the two countries provinces and selected parts of the country (Zoltai have an estimated 14.2 million ha of wetlands and Vitt 1995). (Scott and Jones 1995). The two countries also have an enormous diversity of wetlands, includ Latin America and The Caribbean ing marshes and peatlands in the arctic and boreal zones, temperate-zone swamps, subtropical Wetlands in this region are also highly diverse, marshes and riparian wetlands in semi-arid and ranging from marshes along the coast to vast arid climates. Mitsch and Gosselink (2000) pro seasonally-flooded marshes and swamps asso vide an overview of the major types of wetlands ciated with the region's large river systems in the US and Canada, and Larson (1991) showed (McLain 2002). The region includes all major the locations of 137 important wetland areas. climate types ranging from tropical lowlands Wetland maps are available for most of the US to alpine habitats. Few of the III important through the National Wetland Inventory (NWIj wetland areas mapped by Scott (1991b) have of the US Fish and Wildlife Service National been studied in detail, and there has not been a Wetlands Inventory Center (2007), who also complete wetland inventory for any country in conduct assessments of wetland status and trends the region (Ellison 2004). The largest wetland at the national (e.g. Dahl 2000) and state levels complexes are associated with rivers such as the (e.g. Hefner et a1. 1994; Dahl 1999). The US Orinoco (Venezuela and Columbia), the Amazon Geologic Survey also reviewed the status of wet (Brazil), Pantanal (Brazil, Bolivia, Paraguay), lands in the US (Fretwell et a1. 1996). For wetlands Eastern Chaco (Paraguay, Argentina), Lower Rio in North America, publications are available for Parana and Rio Uruguay (Argentina, Uruguay) most of the major wetland types or wetland areas. and the Chilean Fjordlands (Chile). Most of 50 DEN~SF. ~G~ the information about wetlands in the region, Asia and the Middle East however, is based on a few detailed studies (Olmsted 1993; Naranjo 1995). The most com Wetlands in Asia and the Middle East range from plete inventory of wetlands in the region was extensive coastal swamps, such as those in the prepared by Scott and Carbonell [1986). The Sunderbans district in India and Bangladesh and Amazon and Orinoco basins contain enormous the Mesopotamian marshes of Iraq, to expansive wetland areas (Junk 1997) and other wetland arctic and subarctic wetland complexes in north complexes have received a large amount of ern Russia. Many of the 154 wetlands mapped by international attention because of proposed Scott (1991a) are marshes associated with dry or development activities such as the Hidrovia seasonal climates. The largest wetland complexes scheme (Junk). are associated with the Indus Valley and Deltas (Pakistan), the Ganges River and its floodplain, the Brahmaputra Delta and the Sunderbans (India Africa and Bangladesh), together with those in Russia Approximately 345000km2 of African wetlands (Tobol and Ismim lakes, Ob and Irtysh Rivers, occur in a geologically ancient landscape, and Taymyr Peninsula, Lena and Vilyuy Rivers, support 'the largest numbers and greatest vari Indigirka and Kolyma basins). There have been ety of wildlife in the world' Denny (1991). In few detailed studies and no complete inventories addition, they have important functions and of wetlands in the region (Scott 1989). Relevant values that support the livelihood of hundreds publications for Russian wetlands can be found on of thousands of people (Denny 2001). The esti the Wetlands International website (2007, http:// mate of wetland area offered by Denny (1991) is www.ramsar.org/profile/profiles_russia.htm). undoubtedly an underestimate of the total wet There has not been an inventory of wetlands in land resource, because there have not been any China, but a wetland classification system has coordinated inventories of wetlands on the conti been proposed [Lu 1995). Undoubtedly there are nent. The largest mapped wetland complexes are many important wetland complexes that were not marshes and swamps in the Zaire Basin (Zaire, among those listed by Scott (1991b). For example, Congo and Central African Republic), The Sudd the Kushiro wetland complex in south-central [Sudan, Ethiopia), Kafue Flats (Zambia), and the Hokkaido (Japan) was not listed but is a Ramsar Okavango Inland Delta (Namibia, Botswana and site but has been internationally recognised for Angola). Other summaries of wetlands in Africa the biodiversity that it supports. Several other are found in Denny (1985); Burgis and Symoens wetlands in Japan have been extensively stud (1987); Breen et 01. (1993); Denny (1993); and John ied (Iwakuma 1996) but most publications are in et 01. (1993). Britton and Crivelli (1993) sum Japanese and have not been readily available to marised information on wetland resources in the the international community. Japanese wetlands Mediterranean portion of North Africa. There range from coastal marshes, bogs and fens in tem have been a number of ongoing activities related perate areas, to subtropical coastal mangroves in to African wetlands, including a classification the Okinawaprefecture. Many important national and inventory of wetlands (Hughes and Hughes monuments and parks in Japan include large and 1992). Wetlands in South Africa have been evalu important wetlands. Gopal and colleagues have ated (Cowan 1995j Naranjo 1995; Cowan and van provided several summaries of wetland resources Riet 1998) and additional information is available in the Indian subcontinent, where the annual on the South African Wetlands Conservation monsoon climate dictates the distribution and Programme websites [1999, see also http://www. characteristics of most wewtlands (Gopal 1990; environment.gov.za/enviro-info/ sote/nsoer/ Gopal and Krishnamurthy 1993; Gopal and Sah resource/wetland/index.htm). 1995; Middleton 1999). Finlayson et 01. (2002) Distribution and Diversity of Wetland Resources 51 have developed a protocol for cataloguing Asian WETLAND FORMAnON AND wetlands. PERSISTENCE The Mesopotamian Marshes (Nicholson and Clark 2003) have been the focus of recent inter Wetland definitions have usually been non national efforts. Approximately 90% of the origi specific because they were designed to include a naIlS 000 km2 wetland area was drained between wide diversity of wetland types, especially wet 1985 and 2000, resulting in major impacts on lands that are important for waterfowl resting, indigenous people and millions of migratory feeding and reproduction. The Ramsar defini waterfowl. Recent studies, however, indicate that tion, in particular, is not especially useful if one 'the restoration potential for a substantial portion is interested in processes that are responsible for of the Mesopotamian marshes is high' even the formation and persistence of wetlands. A brief though there are concerns about water availabil review of the history of wetland definition in the ity, levels of soil salinity, and the bioaccumula US may help to understand the conditions that tion of selenium in the food chain (Richardson must be present for wetlands to form and persist. et al. 2005). Mitsch and Gosselink (2000) describe the his torical developments that led to the current definition of wetlands in the US, beginning in Australasia and Oceania 1965 and ending with the legal definition of wet Australasia and Oceania have the smallest lands used by the US Army Corps of Engineers total wetland area of any region according to as required by the 1977 Clean Water Act. More Finlayson and Moser (1991). The diversity of recently, a national Committee on Wetlands wetlands, however, is impressive and includes Characterisation of the National Academy of seagrass meadows, mangrove swamps, tidal Sciences reported a very similar definition: marshes and salt flats, monsoonal freshwater ecosystems that depend on constant or recurrent, floodplain wetlands, swamps, lakes, river chan shallow inundation or saturation at or near the surlace nels and bogs. Even though wetlands in this of the substrate. The minimum essential characteris region may be less extensive than in other parts tics of a wetland are recurrent, sustained inundation or of the world, they are no less important for their saturated at or near the surlace and the presence of uses by native peoples, for their biodiversity and physical, chemical, and biological features reflective of for societal services that they provide (Finlayson recurrent, sustained inundation or saturation. Common 1991). Overviews of wetlands and ecological diagnostic features of wetlands are hydric soils and processes in wetlands in Australasia are found hydrophytic vegetation. These features will not be pres ent where specific physio-chemical, biotic or anthro in McComb and Lake (1988), Jacobs and Brock pogenic factors have removed them or prevented their (1993), Finlayson and von Oertzen (19931, Brock development (National Research Council 1995). et al. (19941, Pressey and Adam (1995) and Giblett and Webb (1996). Numerous studies of Wetland hydrology is the essential element of individual wetlands and wetland complexes are the definition, since wetlands will only form and cited in Pressey and Adam (1995) and a directory persist, and hydric soils and hydrophytic vegeta of important wetlands in Australia has been pub tion (the other two criteria) will only occur when lished (Environment Australia 2001). Osborne water is present for a suitable period of time. (1993) has described wetlands in Papua New The formation and persistence of wetlands Guinea that range from marshes to swamps and may be viewed also from broader perspectives. mangroves. Wetland resources, and the effects of The range of climatic and landscape conditions anthropogenic activities, have been examined on that are suitable for wetland formation is enor a few Pacific Islands (e.g. Allen et al. 2001; Ewel mous. Geographically, wetlands can occur in et al. 2003). any landscape where there is an excess of annual 52 DENNIS F. WHIGHAM
Organic mat Loamy mantle Permafrost [SJ Massive ice Black spruce forest CLJ ~ Weathered bedrock
Fig.2.6 Cross-section showing disposition of Picea mariana (Black Spruce) dominated wetlands on steep slopes that are underlain by permafrost in the portion of Alaska (USA) that is characterised by discontinuous permafrost. The forested wetland is underlain by permafrost beneath an organic mat. Following disturbance that results in the disap pearance of the permafrost layer (e.g. fire) the wetland can be converted to a non-wetland habitat. Wetlands form on the site again following approximately 250 years of succession (Post 1996). (Source: Lee et al. 1999.) precipitation over losses from evaporation and including steep slopes (Figure 2.6) and hill tops as drainage. In areas where annual losses of water well as relatively flat valley bottoms (Figure 2.7). exceed total annual precipitation, wetlands can Fire is also an important element in the ecology still form where landscapes allow water accumu of Black Spruce wetlands. In parts of its range, lation for long enough periods for wetland plants Black Spruce wetlands form on substrates that are to persist. Wetlands are usually extensive and underlain by permafrost. Following fire, the per diverse in cool or cold climates where annual mafrost can melt, resulting in the conversion of a precipitation exceeds losses, mostly because of wetland habitat into a non-wetland habitat. The relatively low annual temperatures. More than loss of permafrost results in higher rates of water 62% of the total wetland area in the United States, loss through evaporation and internal drainage. for example, occurs in Alaska (Hall et al. 1994) Approximately 250 years of succession, how and many Alaskan wetlands occur in areas where ever, result in the conversion of the non-wetland the total annual precipitation is comparatively habitat into a wetland, once again underlain by low (less than 500mm). Wetlands dominated by permafrost (Post 1996). Permafrost forms after the Black Spruce (Picea mariana) are widespread in site becomes dominated by trees which insulate both Alaska and Canada and account for approxi the soil surface, and result in an accumulation mately 20% of all wetlands in Alaska. Because of organic matter, which retains moisture and of the excess of precipitation inputs compared lowers average soil temperatures. with water losses, Black Spruce wetlands occur In warmer climates, a greater amount of precipi in almost any landscape position (Post 1996), tation would be required for wetlands to form and Distribution and Diversity of Wetland Resources S3
Active .-- channel and --. ~4------ Terrace floodplain Abandoned Interfluve channel Interfluve Cleared Birch Black spruce forest shrub bog
~4------". ~4------+. 4 Endoaquic Eqiaquic Tanana river back channel (deep groundwater ~ Organic mat discharge) ~ Loamy mantle
~ Permafrost
Fig. 2.7 Cross-section showing disposition of Black Spruce dominated wetlands on alluvial floodplains in Interior Alaska. Black Spruce dominated sites are found on alluvial sites that are underlain by permafrost. (Source: Lee et a1. 1999.) persist because of warmer annual temperatures alluvial formations deposited by water and and greater losses of water through evaporation ancient volcanic mudflows (Zedler 1987). Vernal and evapotranspiration. Pocosin is an example pools in California are found mostly in depres of a type of non-tidal coastal wetland dominated sions on ancient soils that have an impermeable by evergreen shrub and tree species that is found subsurface layer, such as a hardpan, claypan or only in the south-eastern US (Richardson 1981; basalt. The impermeable layer allows the pool to Sharitz and Gibbons 1982). Pocosins form through retain water for much longer than the surround the process of paludification, a process that typi ing uplands, even though vernal pools typically cally only occurs in colder climates over several dry completely during the annual rainfall cycle. thousand years (Figure 2.8). Pocosins have formed While they are widespread, vernal pools are typi primarily because the Coastal Plain landscape cally small (<1 hal and occupy less than 10% of is flat, the water table is shallow because of most landscapes where they are found. They are proximity to estuarine habitats, and there are important for a variety of reasons, and have his large distances between streams, resulting in torical and cultural significance as sites that were slow runoff and accumulation of water (Daniels used by Native Americans for securing food and et a1. 1977). for use in ceremonial activities. Vernal pools also Wetlands also form in arid climates. Vernal provide wetland habitat for migrating waterfowl, pools are seasonally flooded depressions found in act to regulate seasonal flooding, maintain water many arid and semi-arid landscapes around the quality and contain a high proportion of endemic world. In the US, they are widespread in the west plant and animal species. ern states, especially California where they occur Mountainous regions provide an example of on a variety of landscape formations, including landscapes that contain habitats that include 54 DENN[SF. ~G~
Tall pocosin Short pocosin
2
Ombrotrophic Minerotrophic
Fig.2.8 Cross-section showing peat forming Pocosin - bay-gum wetland forests that develop over mineral soils on the lower Coastal Plain, south-eastern USA. The structure and species composition of the vegetation is determined, in part, by the nutrient status of the substrate. Short Pocosin, for example, develops on nutrient deficient deep peat accumulations. (Source: Martin et al. 1993.)
a wide diversity of wetland types due to large be explained using more straightforward geomor differences in altitude, slope, aspect and geo phic criteria. An example of geomorphic criteria logic substrata. Investigation of Mt. St Helens that was used to describe landscape positions following its eruption in 1980 has revealed 24 where wetlands will form is given by Semeniuk wetland types 14 years after the eruption (Titus and Semeniuk (1995). The geomorphic approach et al. 1999). Some wetlands occurred in locations to wetland classification for inland wetlands where they were present prior to the eruption, includes two essential elements: host landform while others formed as a result of primary suc and degree of wetness (Table 2.2). Five inland cession in habitats created by the eruption. This landforms (basins, channels, flats, slopes and research has found that stochastic events played hills or highlands) and three degrees of wetness a more important role than environmental fac (permanently inundated, seasonally inundated, tors in wetland formation. This may yet provide seasonally waterlogged) were used to develop a valuable lesson which managers need to con a matrix of wetland types. Thirteen wetland sider further when dealing more generally with types are recognised, with examples given in the effects of major events. parentheses: The relationship between landscape position • Permanently inundated basins (lakes); and wetland formation and persistence can also • Seasonally inundated basins (sumplands); Distribution and Diversity of Wetland Resources 55
Table 2.2 Example of a wetland classification system based on combining landform and hydroperiod attributes (Semeniuk and Semeniuk 1995).
Water longevity Landform
Basin Channel Flat Slope Highland
Permanent inundation Lake River Seasonal inundation Sumpland Creek Floodplain Intermittent inundation Playa Wadi Barlkarra Seasonal waterlogging Dampland Trough Palusplain Paluslope Palusmont
• Intermittently inundated basins (playas); developed to use natural and created wetlands, • Seasonally waterlogged basins (dampland); especially marshes, for purposes of water quality • Permanently inundated channels (rivers); management (Hammer 1989; Kadlec and Knight • Seasonally inundated channels (creeks); 1996; Hammer 1997). • Intermittently inundated channels (wadis); Societal benefits that emanate from wetlands • Seasonally waterlogged channels (troughs); only continue as long as ecological processes • Seasonally inundated flats (floodplains); continue (Whigham 1997). For this reason it is • Intermittently inundated flats (barlkarra); important to understand the differences between • Seasonally waterlogged flats (palusplains); ecological processes that occur in wetlands, and • Seasonally waterlogged slopes (paluslopes); and values that are placed on wetland resources and • Seasonally waterlogged highlands (palusmont). services by societies around the world. Wetland functions are the result of ecological processes that are necessary for the self-mainte- . GOODS AND SERVICES PROVIDED BY nance of ecosystems (Richardson 1994; Whigham WETLAND ECOSYSTEMS 1997). They occur in all types of ecosystem and occur without human intervention. Examples No matter where wetlands occur in the landscape, of ecological functions in wetlands are: storage and no matter the processes that were responsi of surface water; storage of subsurface water; ble for their formation and persistence, wetland reduction of the energy level of surface water; resources are used for a wide variety of purposes recharge and discharge of groundwater; transfor and all of the wetland-related goods and services mation of nutrients and maintenance of primary that benefit human societies emanate ultimately production. from natural ecological processes. Three such Wetland values result from the goods and examples of wetland resources are peat (wet services that emanate from natural ecological land soils), reed (wetland vegetation) and fish functions (Taylor et al. 1990). Each of the three (wetland-dependent animals). Benefits from eco broad types of wetlandprovide, to varying degrees, logical processes that occur in wetlands are not so these ecological functions. obvious and are often ignored when decisions are Marshes and peatlands almost always provide made to alter wetlands. Some types of wetland, long-term storage of surface water. The degree for example, store large amounts of water and to which swamps store surface water depends release it slowly, thus lowering flood peaks and primarily on landscape position. Some swamps minimising damaging floods (Hey and Philippi occur in areas that have standing water for 1995). Processes related to the cycling and stor extended periods of time and thus provide sig age of nutrients in wetlands are responsible for nificant surface water storage (Ewel and Odum water quality benefits, and techniques have been 1984). Other swamps occur along rivers, and 56 Df.NNIS F. WHIG~IAM provide only shorHcrm swmgc of surface w:ncr influences the amounts of plant and llllimal during flooding events; ;l time when they provide biomass available for human uses. the important function ofreducingtheenergy level of the flow (Lugoel 01.1990). Pcatl3nds typically do not reduce the energy level of surface water THREATS TO WETLANDS because precipitation is generally the primary source. Whether a wetland provides grollndw(ltcr Wetlands arc threatened in most areas of the recharge or disch:ngc depends on many factors, world and in some countries the majority of including landscape position and substrate char wetland resources have already been converted acteristics (Winter 2001; Rosenberry and Winter to other land uses (Fretwell el aI. 1996). In some 1997). Swamps usually occur in topographic31ly landscapes (c.g. the Gulf CoaSt of Louisiana, low areas and arc sites for groundwater discharge. USAl, wetlands arc threatened by direct and indi Since precipitation is often the dominant source rect activities (Mitsch ct (1/. 2(01) and recent hllT of water to peatlands, particularly bogs, they arc ricane d:llnagc in the region has exacerbated the usually not considered to be important sites for problem (Dean ct aI. 2005; Boesch el a/. 2(X}61. groundwater discharge or recharge. All wetlands The estimated costs of restoration and the pre tmnsform nutrients and mOSt arc habitats where vention of further losses are in the order of bil nutrients aecumulate IMitsch and Gosselink lions of dollars for wetlands in coastal Louisiana 2000). The level of primary production thar as well as the Florida Everglades lUahret tIl. 2005). occurs in wetlands varies considerably, primar Many losses occurred before there W.IS any gen· ily depending on the nutrient status of water that eral understanding of the importance of wetlands enters the wetland. Bogs typically have low lev to wider human needs. The primary challenges in els of primary production because of low nutri the present and future wil.l be to provide appro ent levels in precipitation, but nutrient-rich fens pri:lte infomlation to decision makers regarding and tropical papyrus communities arc among the the imp:lctS of ongoing or proposed activities most productive ecosystems,
Geomorphic setting
~"'r------,
Critical processes and mechanisms
Wetland functions Natural stressor
Commodities Intangibles
Extractable resources
Constructive
Human life Destructive support system
Fig. 2.9 The diagram broadly depicts the relationship between ecological functions of wetlands and the societal values of wetlands. The dashed line separates ecological processes (above linel from societal interactions (below the line) with wetlands. Ecological processes and the structure of ecosystems above the line continue in the absence of society. Items below the line do not continue, or are greatly diminished, if ecological processes above the line stop, or are degraded, owing to natural or anthropogenic activities. (Source: Brinson 1993.)
exist between wetland functions in the Pantanal upland habitats in the watershed, resulting in and human uses of the wetland complex. The increased rates of sedimentation, the develop integrity of the Pantanal wetland complex is ment of a major international waterway project now being threatened, however, by many factors that will significantly alter the hydrology of the that are typically encountered around the world. system, and river channelisation (Junk et a1., Threats to the Pantanal include conversion of Chapter 40). 58 DENNIS F. WHIGHAM
Wetland losses have slowed significantly in wetland destruction can be slowed or stopped. the US following the destruction and degrada Indigenous peoples require wetland resources tion of more than 50% of the nation's wetlands, for survival, yet continued destruction of those excluding Alaska and Hawaii, from the 1600s to resources will lead to greater and greater stresses the mid-1980s (Dahl and Allord 1996; Dahl 2000). on natural ecosystems and, eventually, societies. There are now numerous laws and regulations to It is paramount that effective methods for wet protect wetlands (Cylinder et al. 1995) but losses land education be developed for those parts of the continue to occur even though there is a national world. Educational modules need to be developed policy of 'No Net Loss' of wetlands (Whigham that focus on the relationships between wetland 1999). Wetland losses continue for many reasons. functions and societal values. With the rapid Some types of wetland, particularly 'dry end' wet expansion of electronic methods of communica lands (Whigham 1999) and isolated wetlands (see tion, educational materials can more effectively articles in special issue of Wetlands - Nadeau and be delivered to parts of the world where resources Leibowitz 2003) are lost because of inadequate are limited. One example is a recent interactive protection by existing regulations and laws. In web page (http://www.serc.si.edu/labs/animaL many states, permits for wetland destruction plant_interaction/Trail/VirtualTour.html) that is are given when only small wetland areas are a virtual tour through a Caribbean mangrove involved. Losses of dry end wetlands and small system. The Tangled Roots website could be wetland areas are often allowed to occur with used to teach a mangrove course anywhere in no mitigation requirement. When mitigation is the world and it has been used, for example, in required, there may be no net loss of wetland wetland training courses in Belize and Panama area, but there are concerns about the loss of (I. Feller, personal communication). In developed wetland function because many restorations are countries, wetland education efforts need to be never completed, or fail (Whigham 1999). expanded, to inform the public and to develop a broad-based understanding of the importance of wetlands to societies (Denny 2001). DISCUSSION In addition, a range of methods for conducting wetland assessments need to be developed to pro It is important for wetland scientists to develop a vide the vehicles required to manage wetlands so range of tools that can be used by wetland manag that their functions and values are both retained ers to assist in the decision making process. and restored. A number of assessment methods There are many threats to wetlands around the have been developed in the US (Bartoldus 1999; world. Some threats are natural and cannot be eas Fennessy et al. 2004) but none have proven to be ily avoided. Examples include wetland destruc completely satisfactory. The hydrogeomorphic tion resulting from volcanic eruptions (Titus approach to wetlands assessment, for example, et al., 1999), hurricanes (Michener et al. 1997; may prove useful in conducting assessments Alleng 1998; Boesch et al. 2006) and floods (Day at several levels of complexity (Whigham et al. et al. 1995; Stromberg et al. 1997; Patten 1998). 2007) but the method needs further develop Climate change related to human activities has a ment and testing (Brinson et al. 1998; Whigham high potential for impacting wetlands (Poiani and 1999; Hill et al. 2006; see Brinson). The hydro Johnson 1991), particularly coastal wetlands (Day geomorphic approach being developed for Europe et al. 1995; Michener et al. 1997). Direct impacts of (Functional Analysis of European Wetland human activities on wetlands due to drainage, con Ecosystems, FAEWE) is also promising (Maltby version to other uses and alterations of hydrologic et al. 1996; McInnes et al. 1998; see Maltby et al., conditions also have a significant impact on wet Chapter 23). lands (e.g. Richardson et al. 2005). In many areas How can we accomplish the dual and related of the world there is little hope that the ongoing tasks of wetland education and wetland Distribution and Diversity of Wetland Resources 59 assessment? There is little need to continue Boesch D.F., Shabman L., Antle L.G., Day J.W. Jr., to classify the world's wetlands using the Dean R.C., Galloway C.E., Groat C.C., Laska S.B., traditional approaches. Terms such as marshes, Luettich R.A Jr., Mitsch W.J., et al. 2006. A New swamps, peatlands, floodplain wetlands and Framework for Planning the Future of Coastal mangroves are meaningful and will certainly Louisiana after the Hurricanes of 2005. Integration and Application Network, University of Maryland continue to be used. While the traditional terms Center for Environmental Science, Cambridge, MD. to describe wetlands convey useful information, Breen e.M., Heeg J. and Seaman M. 1993. South Africa. they are insufficiently precise to be used to con In: Whigham D.F., Dykyjova D. and Hejny S. (edi vey information about the ecological processes tors), Wetlands of the World I: Inventory, Ecology that occur within wetlands. A hydrogeomorphic and Management. Kluwer Academic Publishers, approach to wetlands classification (Brinson Dordrecht, pp. 79-110. 1993; Semeniuk and Semeniuk 1995; Maltby Brinson, M.M. 1993. A Hydrogeomorphic ClaSSification et al. 1996) is much more effective in conveying for Wetlands. 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