Ecology of Freshwater and Estuarine Wetlands
372
Ecology of Freshwater and Estuarine Wetlands
372eBook
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Overview
Prominent scholars help students understand both general concepts of different wetland types as well as complex topics related to these dynamic physical environments. Careful syntheses review wetland soils, hydrology, and geomorphology; abiotic constraints for wetland plants and animals; microbial ecology and biogeochemistry; development of wetland plant communities; wetland animal ecology; and carbon dynamics and ecosystem processes. In addition, contributors document wetland regulation, policy, and assessment in the US and provide a clear roadmap for adaptive management and restoration of wetlands. New material also includes an expanded review of the consequences for wetlands in a changing global environment.
Ideally suited for wetlands ecology courses, Ecology of Freshwater and Estuarine Wetlands, Second Edition, includes updated content, enhanced images (many in color), and innovative pedagogical elements that guide students and interested readers through the current state of our wetlands.
Product Details
| ISBN-13: | 9780520959118 |
|---|---|
| Publisher: | University of California Press |
| Publication date: | 12/06/2014 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 372 |
| File size: | 51 MB |
| Note: | This product may take a few minutes to download. |
About the Author
Rebecca Sharitz is Professor of Plant Biology at the University of Georgia and coeditor of two books for the US Atomic Energy Commission. She has taught courses in wetland ecology.
Read an Excerpt
Ecology of Freshwater and Estuarine Wetlands
By Darold P. Batzer, Rebecca R. Sharitz
UNIVERSITY OF CALIFORNIA PRESS
Copyright © 2014 The Regents of the University of CaliforniaAll rights reserved.
ISBN: 978-0-520-95911-8
CHAPTER 1
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 needs consideration by terrestrial or aquatic ecologists: the need to define the habitat. What exactly constitutes a wetland may not always be clear. Thus, it seems appropriate to begin by defining the word wetland. The Oxford English Dictionary says, "Wetland (F. wet a. + land sb.)—an area of land that is usually saturated with water, often a marsh or swamp." While covering the basic pairing of the words wet and land, this definition is rather ambiguous. Does "usually saturated" mean at least half of the time? That would omit many seasonally flooded habitats that most ecologists would consider wetlands. Under this definition, it also seems that lakes or rivers could be considered wetlands. A more refined definition is clearly needed for wetland science or policy.
Because defining wetland is especially important in terms of policy, it is not surprising that governmental agencies began to develop the first comprehensive definitions (see Chapter 8). One influential definition was derived for the U.S. Fish and Wildlife Service (USFWS) (Cowardin et al. 1979):
Wetlands are lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. Wetlands must have one or more of the following three attributes: (1) at least periodically, the land supports predominately hydrophytes; (2) the substrate is predominantly undrained hydric soil; and (3) the substrate is nonsoil and is saturated with water or covered by shallow water at some time during the growing season of each year.
This USFWS definition emphasizes the importance of hydrology, soils, and vegetation, which you will see is a recurring theme in wetland definitions. The U.S. Army Corps of Engineers (USACE), the primary permitting agency for wetlands of the United States, adopted a slightly different wording (Environmental Laboratory 1987):
The term "wetlands" means those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas.
This definition also incorporates hydrology, soils, and vegetation, but it is more restrictive than the USFWS definition. The USACE definition requires all three features to be present, while the USFWS Cowardin definition indicates that only one of the three conditions needs to occur. Despite its exclusive nature, the USACE definition has been adopted as the authority to define legal (or jurisdictional) wetlands of the United States.
In Canada, a very similar definition for wetland is used by the National Wetlands Working Group (NWWG). This definition also focuses on hydrology, soils, and vegetation, but is more expansive, acknowledging that aquatic processes and biologic factors other than just soils and plants may also be useful for classification (NWWG 1988):
Wetland is defined as "land that has the water table at, near, or above the land surface or which is saturated for a long enough period to promote wetland or aquatic processes as indicted by hydric soils, hydrophytic vegetation, and various kinds of biological activity that are adapted to the wet environment."
The NWWG definition is not an official legal standard in Canada but is widely used or adapted by various governmental agencies for setting policy about wetlands (personal communication, Barry Warner, University of Waterloo, Ontario, Canada).
An international definition for wetland was developed for the Ramsar Convention, an intergovernmental treaty regarding wetland conservation initiated in 1971 (which met in Ramsar, Iran). The most recent information (see www.ramsar.org) provides this definition:
Wetlands are areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres.
The emphasis on soils and plant adaptations found in other definitions is absent from this one, possibly because it targets non-scientists who may not be familiar with what constitutes wetland conditions. However, hydrology remains a focal tenet. This definition is currently being applied to identify wetlands in countries in Asia (e.g., Gong et al. 2010).
As ecologists, we must realize that political definitions may not cover all habitats that function ecologically as wetlands. For example, mud flats devoid of vegetation, floodplains that primarily flood in winter outside the "growing season," and flooded areas of floodplains where anoxic soil conditions do not develop are all probably ecological wetlands but may not fit some legal definitions. In Georgia, for example, we have seen floodplains repeatedly covered by as much as 1 meter of water (Fig. 1.1), yet competent delineators following USACE criteria determined that the majority of the floodplain area did not meet the legal US definition of a wetland (hydric soil was not present). However, the determination that these floodplains were not jurisdictional wetlands did not affect the responses of soil-dwelling arthropods and herbaceous plants that were covered by the water or the functioning of waterfowl or fish that were swimming and feeding in those habitats. Although definitions do serve a purpose, especially for regulation (see Chapter 8), ecologists should not be constrained by them when studying wetlands.
Nonetheless, for ecologists seeking a biologically useful definition for wetlands, we recommend the simple, straightforward, yet inclusive, definition put forward by Paul Keddy (2000):
A wetland is an ecosystem that arises when inundation by water produces soils dominated by anaerobic processes and forces the biota, particularly rooted plants, to exhibit adaptations to tolerate flooding.
WHY ARE WETLANDS IMPORTANT?
Wetlands comprise only about 6% of the earth's land surface, but ecologically they are disproportionately important. For example, 25% of the plant species in Malaysia occur in only one wetland type, peat swamps (Anderson 1983). Almost 10% of the world's fish fauna occurs in the Amazon basin (Groombridge and Jenkins 1998). The vast majority of amphibians are linked to wetlands, even if only for reproduction. Wetlands are particularly important habitats for birds, with many species occurring only in association with wetlands. Bird watching and waterfowl hunting are major human activities related to wetlands. Because wetlands support both terrestrial and aquatic biota, they are unusually diverse (Gopal et al. 2000). Those taxa unique to wetlands will contribute significantly to the overall diversity of regions containing numerous wetlands.
Besides supporting the plethora of plants and animals of interest to ecologists and nature enthusiasts, wetlands provide an assortment of ecosystem services of considerable value to all people. Costanza et al. (1997) estimated the economic values of services provided by the world's ecosystems and found that, on a per-hectare basis, estuaries and freshwater floodplains/swamps were the world's two most valuable ecosystem types (Table 1.1). The value of these wetlands to people stems primarily from their roles in nutrient cycling, water supplies, disturbance (flood) regulation, and wastewater treatment. However, recreation, food production, and cultural (aesthetic, artistic, educational, spiritual, or scientific) values are also important (Costanza et al. 1997). Many of these services are accomplished by wetland biota (microbes, plants, and animals). In Canada, an assessment of the economic values of the country's wetlands (see NWWG 1988, Table 10-15) came up with an estimate of almost $10,000,000,000 (1985 Canadian dollars), of which almost half was attributed to recreational values (nature appreciation activities, fishing, and hunting). However, despite the considerable economic value of wetlands, there is a long history of humans destroying or degrading the world's wetland resources.
CHARACTERISTICS OF SELECTED WETLANDS
Throughout the world, the types of plant and animal communities that occur in wetlands are a result of climate, geomorphology and landscape position, soils, water source and chemistry, and numerous environmental factors including disturbance. Wetlands are found on every continent except Antarctica and extend from the tropics to the tundra. Estimates of the extent of the world's wetlands vary, but generally range from around 7 to 10 million square kilometers (Mitsch and Gosselink 2007). Approximately 30% occur in tropical and 24% in subtropical regions, 12% in temperate areas, and 30% in boreal regions. These estimates do not include large lakes or deepwater coastal systems.
The classification and naming of wetland types is often confusing because names have evolved over centuries in different parts of the world and often reflect regional or continental differences. The wetlands described here reflect a North American perspective and are chosen to be representative of the variety of wetland types rather than totally inclusive of the range of wetland plant and animal communities that occur on this continent. We have grouped them ecologically, according to major sources of water (Fig. 1.2)—(1) precipitation, (2) groundwater, and (3) surface water—with the understanding that sources and amount of water may vary considerably within a wetland type and that most wetlands receive water from more than one source. A more detailed treatment of many North American wetland habitats is available in a companion volume by Batzer and Baldwin (2012).
Wetlands with Predominantly Precipitation Inputs
NORTHERN BOGS
Bogs are freshwater wetlands that occur on acid peat deposits throughout much of the boreal zone of the world (Fig. 1.3). They are frequently part of a larger complex of peatlands that includes fens, with readily apparent gradients of plant species distributions, biogeochemistry, and hydrology (Bridgham et al. 1996; Rochefort et al. 2012; Fens and Related Peatlands below). Bogs are distinguished from fens, however, because they receive water and nutrients exclusively from precipitation (ombrogeneous). Precipitation inputs are greater than evapotranspiration losses, and the slow decomposition of organic material under cold temperatures results in peat accumulation. Bog soils are organic, waterlogged, low in pH, and extremely low in available nutrients for plant growth (Chapter 2). In addition, growing seasons are short. Thus, a specialized and unique flora occurs in this wetland habitat.
Mosses, primarily Sphagnum, are the most important peat-building plants in bogs. Bogs can be open Sphagnum moss peatlands, Sphagnum-sedge peatlands, Sphagnum-shrub peatlands, or bog forests; these bogs often form a mosaic across the landscape with other peatlands such as fens, which are more influenced by groundwater. Plants often associated with Sphagnum in bogs include various sedges (Carex spp.); cottongrass (Eriophorum vaginatum); and a variety of ericaceous shrubs such as heather (Calluna vulgaris), leatherleaf (Chamaedaphne calyculata), cranberry and blueberry (species of Vaccinium), and Laborador tea (Ledum groenlandicum). Trees such as spruce (Picea spp.) and tamarack (Larix larcina) may occur in bogs, often stunted in growth to reach only a meter or two tall. Many northern peatlands show a considerable overlap of species along the hydrologic and chemical gradients from nutrient-poor bogs to more mineral rich fens (see Fens and Related Peatlands below).
Vegetation development in many bogs may follow the model of hydrarch succession, or terrestrialization, at least to some degree (see Chapter 5). Through the buildup of soil organic matter, vegetation in these peatlands has significant control over habitat development (Moore and Bellamy 1974). Primary production exceeds decomposition of the peat substrates (Clymo et al. 1998), and the accumulation of peat affects hydrologic conditions, chemistry, and plant community composition (Damman 1986; Bridgham et al. 1996; Bauer et al. 2003). As peat builds up, it is often colonized first by shrubs and then by trees. Paleoecological evidence from several studies suggests a sequence of plant associations from wet marshes to a Sphagnum bog or wet forest (Walker 1970). Other processes, such as paludification (which occurs when bogs exceed the basin boundaries and encroach on formerly dry land) (e.g., Moore and Bellamy 1974; Bauer et al. 2003; Yu et al. 2003) and fires (Kuhry 1994), complicate the patterns of bog successional development.
Sphagnum has the ability to acidify its environment, probably through the production of organic acids located on its cell walls (Clymo and Hayward 1982). The acid environment retards bacterial action and reduces decomposition rates, enabling peat accumulation. Sphagnum also maintains waterlogging in the substrate. Its compact growth habit and overlapping, rolled leaves form a wick that draws up water by capillarity. Many bog plants are adapted to waterlogged anaerobic (low oxygen) environments by aerenchyma production, reduced oxygen consumption, and a leakage of oxygen from the roots to the rhizosphere. Many bog plants also have adaptations to the low available nutrient supply; these include evergreenness, sclerophylly (thickening of the plant epidermis to minimize grazing), the uptake of amino acids as a nitrogen source, and high root biomass (Bridgham et al. 1996). In addition, carnivorous plants such as pitcher plants (Sarracenia spp.) and sundews (Drosera spp.) have the ability to trap and digest insects. Some bog plants, such as the sweet gale (Myrica gale) and alders (Alnus spp.) also carry out symbiotic bacterial nitrogen fixation in nodules on their roots.
POCOSINS
Pocosins are evergreen shrub bogs (Fig. 1.4; Richardson 2012) restricted to the southeastern US Atlantic Coastal Plain, chiefly in North Carolina. They occur on waterlogged, acidic, nutrient-poor sandy or peaty soils (Bridgham and Richardson 1993; Richardson 2003) and are located primarily on flat topographic plateaus of the outer Coastal Plain. Their source of water is precipitation, and most of their water loss is through evapotranspiration during the summer and fall, although surface runoff also occurs, especially during winter and spring (Richardson 2012).
Evergreen shrub and tree species dominate in pocosins, and the composition and stature of the vegetation is related to depth of the peat and nutrient availability. On deep peat accumulations (>1 m), roots do not penetrate into the underlying mineral soils, and ombrotrophic shrub bogs develop (Otte 1981). Ericaceous shrubs in these communities, called short pocosin, include titi (Cyrilla racemiflora), fetterbush (Lyonia lucida), and honeycup (Zenobia pulverulenta) as well as vines, particularly greenbriar (Smilax spp.). A sparse and often stunted canopy of pond pine (Pinus serotina) and loblolly bay (Gordonia lasianthus) may be present. Where organic substrates are shallower (approximately 50–100 cm), roots can penetrate into the underlying mineral soil and the vegetation grows somewhat taller. Additional species in these tall pocosins may include red maple (Acer rubrum), black gum (Nyssa sylvatica), and sweetbay (Magnolia virginiana). Fire during drought may also be an important factor in pocosin community development. Shallow peat burns allow the regeneration of pocosin species, although if the depth of the peat is reduced, roots of the recovering plants may be able to reach mineral soils. Severe burns that destroy peat substrates lead to development of a nonpocosin community, such as a marsh.
(Continues...)
Excerpted from Ecology of Freshwater and Estuarine Wetlands by Darold P. Batzer, Rebecca R. Sharitz. Copyright © 2014 The Regents of the University of California. Excerpted by permission of UNIVERSITY OF CALIFORNIA PRESS.
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Table of Contents
CONTRIBUTORSPREFACE
1. ECOLOGY OF FRESHWATER AND ESTUARINE WETLANDS: AN INTRODUCTION
2. WETLAND SOILS, HYDROLOGY, AND GEOMORPHOLOGY
3. ABIOTIC CONSTRAINTS FOR WETLAND PLANTS AND ANIMALS
4. WETLAND MICROBIAL ECOLOGY AND BIOGEOCHEMISTRY
5. DEVELOPMENT OF WETLAND PLANT COMMUNITIES
6. WETLAND ANIMAL ECOLOGY
7. CARBON DYNAMICS AND ECOSYSTEM PROCESSES
8. UNITED STATES WETLAND REGULATION, POLICY, AND ASSESSMENT
9. WETLAND RESTORATION
10. CONSEQUENCES FOR WETLANDS OF A CHANGING GLOBAL ENVIRONMENT
LITERATURE CITED
INDEX
What People are Saying About This
"The editors are to be highly commended for . . . the straightforward and honest writing style that continually weaves its way throughout this text."—Ecology
"Provides a comprehensive introduction to the great ecological breadth and complexity that wetlands exhibit ranging from microbial process to biogeography and global climate."—Wetlands