ONE Ecology of Freshwater and Estuarine Wetlands: An Introduction RebeCCA R. SHARITZ, DAROLD P. BATZER, and STeveN C. PENNINGS WHAT IS A WETLAND? WHY ARE WETLANDS IMPORTANT? CHARACTERISTicS OF SeLecTED WETLANDS Wetlands with Predominantly Precipitation Inputs Wetlands with Predominately Groundwater Inputs Wetlands with Predominately Surface Water Inputs WETLAND LOSS AND DeGRADATION WHAT THIS BOOK COVERS What Is a Wetland? The study of wetland ecology can entail an issue that rarely Wetlands are lands transitional between terrestrial and needs consideration by terrestrial or aquatic ecologists: the aquatic systems where the water table is usually at or need to define the habitat. What exactly constitutes a wet- near the surface or the land is covered by shallow water. land may not always be clear. Thus, it seems appropriate Wetlands must have one or more of the following three to begin by defining the wordwetland . The Oxford English attributes: (1) at least periodically, the land supports predominately hydrophytes; (2) the substrate is pre- Dictionary says, “Wetland (F. wet a. + land sb.)— an area of dominantly undrained hydric soil; and (3) the substrate is land that is usually saturated with water, often a marsh or nonsoil and is saturated with water or covered by shallow swamp.” While covering the basic pairing of the words wet water at some time during the growing season of each year. and land, this definition is rather ambiguous. Does “usu- ally saturated” mean at least half of the time? That would This USFWS definition emphasizes the importance of omit many seasonally flooded habitats that most ecolo- hydrology, soils, and vegetation, which you will see is a gists would consider wetlands. Under this definition, it also recurring theme in wetland definitions. The U.S. Army seems that lakes or rivers could be considered wetlands. A Corps of Engineers (USACE), the primary permitting more refined definition is clearly needed for wetland sci- agency for wetlands of the United States, adopted a slightly ence or policy. different wording (Environmental Laboratory 1987): Because definingwetland is especially important in terms of policy, it is not surprising that governmental agencies The term “wetlands” means those areas that are inundated began to develop the first comprehensive definitions (see or saturated by surface or ground water at a frequency Chapter 8). One influential definition was derived for the and duration sufficient to support, and that under normal U.S. Fish and Wildlife Service (USFWS) (Cowardin et al. circumstances do support, a prevalence of vegetation 1979): typically adapted for life in saturated soil conditions. 1 UC-Batzer-TEXT_00-CH4.indd 1 6/7/14 10:56 AM Wetlands generally include swamps, marshes, bogs, and much as 1 meter of water (Fig. 1.1), yet competent delinea- similar areas. tors following USACE criteria determined that the major- ity of the floodplain area did not meet the legal US defini- This definition also incorporates hydrology, soils, and vege- tion of a wetland (hydric soil was not present). However, tation, but it is more restrictive than the USFWS definition. the determination that these floodplains were not jurisdic- The USACE definition requires all three features to be pres- tional wetlands did not affect the responses of soil-dwell- ent, while the USFWS Cowardin definition indicates that ing arthropods and herbaceous plants that were covered only one of the three conditions needs to occur. Despite its by the water or the functioning of waterfowl or fish that exclusive nature, the USACE definition has been adopted as were swimming and feeding in those habitats. Although the authority to define legal (or jurisdictional) wetlands of definitions do serve a purpose, especially for regulation (see the United States. Chapter 8), ecologists should not be constrained by them In Canada, a very similar definition forwetland is used by when studying wetlands. the National Wetlands Working Group (NWWG). This defi- Nonetheless, for ecologists seeking a biologically use- nition also focuses on hydrology, soils, and vegetation, but ful definition for wetlands, we recommend the simple, is more expansive, acknowledging that aquatic processes straightforward, yet inclusive, definition put forward by and biologic factors other than just soils and plants may Paul Keddy (2000): also be useful for classification (NWWG 1988): A wetland is an ecosystem that arises when inundation Wetland is defined as “land that has the water table at, by water produces soils dominated by anaerobic processes near, or above the land surface or which is saturated for and forces the biota, particularly rooted plants, to exhibit a long enough period to promote wetland or aquatic pro- adaptations to tolerate flooding. cesses as indicted by hydric soils, hydrophytic vegetation, and various kinds of biological activity that are adapted to the wet environment.” Why Are Wetlands Important? Wetlands comprise only about 6% of the earth’s land sur- The NWWG definition is not an official legal standard in face, but ecologically they are disproportionately impor- Canada but is widely used or adapted by various govern- tant. For example, 25% of the plant species in Malaysia mental agencies for setting policy about wetlands (personal occur in only one wetland type, peat swamps (Anderson communication, Barry Warner, University of Waterloo, 1983). Almost 10% of the world’s fish fauna occurs in the Ontario, Canada). Amazon basin (Groombridge and Jenkins 1998). The vast An international definition forwetland was developed majority of amphibians are linked to wetlands, even if only for the Ramsar Convention, an intergovernmental treaty for reproduction. Wetlands are particularly important hab- regarding wetland conservation initiated in 1971 (which itats for birds, with many species occurring only in asso- met in Ramsar, Iran). The most recent information (see ciation with wetlands. Bird watching and waterfowl hunt- www.ramsar.org) provides this definition: ing are major human activities related to wetlands. Because wetlands support both terrestrial and aquatic biota, they are Wetlands are areas of marsh, fen, peatland or water, unusually diverse (Gopal et al. 2000). Those taxa unique to whether natural or artificial, permanent or temporary, wetlands will contribute significantly to the overall diver- with water that is static or flowing, fresh, brackish or salt, sity of regions containing numerous wetlands. including areas of marine water the depth of which at low tide does not exceed six metres. Besides supporting the plethora of plants and animals of interest to ecologists and nature enthusiasts, wetlands The emphasis on soils and plant adaptations found in other provide an assortment of ecosystem services of consider- definitions is absent from this one, possibly because it tar- able value to all people. Costanza et al. (1997) estimated the gets non-scientists who may not be familiar with what con- economic values of services provided by the world’s ecosys- stitutes wetland conditions. However, hydrology remains tems and found that, on a per-hectare basis, estuaries and a focal tenet. This definition is currently being applied freshwater floodplains/swamps were the world’s two most to identify wetlands in countries in Asia (e.g., Gong et al. valuable ecosystem types (Table 1.1). The value of these 2010). wetlands to people stem primarily from their roles in nutri- As ecologists, we must realize that political definitions ent cycling, water supplies, disturbance (flood) regulation, may not cover all habitats that function ecologically as wet- and wastewater treatment. However, recreation, food pro- lands. For example, mud flats devoid of vegetation, flood- duction, and cultural (aesthetic, artistic, educational, spiri- plains that primarily flood in winter outside the “growing tual, or scientific) values are also important (Costanza et season,” and flooded areas of floodplains where anoxic soil al. 1997). Many of these services are accomplished by wet- conditions do not develop are all probably ecological wet- land biota (microbes, plants, and animals). In Canada, an lands but may not fit some legal definitions. In Georgia, for assessment of the economic values of the country’s wet- example, we have seen floodplains repeatedly covered by as lands (see NWWG 1988, Table 10-15) came up with an esti- 2 chapter one UC-Batzer-TEXT_00-CH4.indd 2 6/7/14 10:56 AM FIGURE 1.1. Flooded riparian wetland of the North Oconee River, Georgia. Although the site floods almost yearly, it does so in winter, out of the growing season. Additionally, hydric soils are not extensive. As such, using current criteria for delineating wetlands in the United States, most of the floodplain is not considered a jurisdictional wetland. table 1.1. mate of almost $10,000,000,000 (1985 Canadian dollars), Estimated Relative Economic Values per Hectare of of which almost half was attributed to recreational values Services Provided by the World’s Ecosystems (nature appreciation activities, fishing, and hunting). How- ever, despite the considerable economic value of wetlands, 1997 US$ there is a long history of humans destroying or degrading Ecosystem Type ha–1yr–1 the world’s wetland resources. Estuaries 22,832 Characteristics of Selected Wetlands Swamps/floodplains 19,580 Throughout the world, the types of plant and animal com- Coastal sea grass/algae beds 19,004 munities that occur in wetlands are a result of climate, geo- Tidal marsh/mangrove 9,990 morphology and landscape position, soils, water source and Lakes/rivers 8,498 chemistry, and numerous environmental factors including disturbance. Wetlands are found on every continent except Coral reefs 6,075 Antarctica and extend from the tropics to the tundra. Esti- Tropical forests 2,007 mates of the extent of the world’s wetlands vary, but gen- Coastal continental shelf 1,610 erally range from around 7 to 10 million square kilometers Temperate/boreal forests 302 (Mitsch and Gosselink 2007). Approximately 30% occur in tropical and 24% in subtropical regions, 12% in temperate Open oceans 252 areas, and 30% in boreal regions.