Environmental Engineering Reference
In-Depth Information
19
Freshwater Wetlands
An Introduction
“In the end, we will conserve only what we love, and we love only what we understand.”
Baba Dioum, Senegal
19.1 INTRODUCTION
Wetlands (see e.g., Figure 19.1) are typically transitional systems where land meets water. They are
deined by the following attributes:
•
Hydrology: wetlands are permanently or periodically looded or saturated with water.
•
Soils: wetlands have hydric soils that are frequently or periodically saturated with water.
•
Vegetation: wetlands support hydrophytes or plant species that are adapted to wet
environments.
As discussed in Chapter 16, wetlands could be considered an intermediate stage in the succession
of lakes toward some climax condition. One classical view is that lakes are temporary ecological
systems that are formed in a depression that will gradually ill in to become a terrestrial environment,
or become extinct. One of the intermediate stages in that succession is a wetland. However, while
wetlands may be transitional zones between aquatic and terrestrial environments, they may also
stand alone, be permanent or temporary, natural or man-made systems of considerable ecological
and hydrological importance. They are known to be valuable ecological systems that provide a wide
variety of ecological services, ranging from lood control, to providing habitats, to nutrient control.
Note that wetlands are very diverse systems and, as such, they are dificult to characterize and
identify. One of the problems for wetlands is in determining whether they are subject to protection
by law, such as under the Clean Water Act (CWA). Therefore, unlike other chapters, much of this
chapter will focus on the legal rather than the scientiic deinition of wetlands and how that deini-
tion has changed due to both the historical shifts in the nation's environmental ethics and the winds
and vagaries of national policy and politics.
19.1.1 d
efInItIon
First, what is a wetland? One of the issues associated with wetland management and protection is
deining speciically what wetlands are and how to identify them. Deinitions vary, often depending
on the speciic purpose of that deinition, such as research, general habitat classiication, natural
resource inventories, and environmental regulations (Tiner 1999). For example, the deinition used
to allow the U.S. Fish and Wildlife Service to inventory the nation's wetlands, and to determine
changes in that inventory over time, may vary with the deinition used by regulatory agencies to
protect those wetlands.
Deinitions may also vary with the technical background of the scientist composing those deini-
tions (Tiner 1999; Lefor and Kennard 1977). For example, a botanist's deinition may emphasize
plants while a soil scientist would focus on the soil properties and a hydrologist would focus on the
water table.
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