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