Environmental Engineering Reference
In-Depth Information
files that can be used and manipulated using software associated with Geographic
Information Systems (GIS). Historically, most wetlands (e.g., prairie potholes,
coastal marsh) have been identified and mapped by the U.S. Department of Interior,
Fish and Wildlife Service, National Wetland Inventory (NWI) ( http://www.fws.
gov/wetlands/ ) . The data from NWI are available electronically ( http://www.fws.
gov/wetlands/Data/index.html ) and used to produce periodic status and trends
reports of wetlands in the United States (e.g., Dahl 2011 ). Other potential sources
of wetland occurrence include individual joint ventures associated with the North
American Waterfowl Management Plan that focus on conservation of wetlands for
migratory birds, state-specific land cover data bases, U.S. Geological Survey
topographic maps ( http://nationalmap.gov/ustopo/index.html ), state highway
departments, and U.S. Department Agriculture, Natural Resources Conservation
Service (primarily at state and county levels) wetland determination and soils
mapping data. Most states and some nongovernmental organizations have layers
of GIS data available on regional location of wetlands; however, at times it requires
some searching to find the storage locations of these data.
Because of the variation among wetland types and, to some extent, within a
wetland type, it is important to fully describe the wetland(s) under study. The two
primary wetland classification/description approaches are the Cowardin et al. ( 1979 )
and hydrogeomorphic methods (Brinson 1993 ; Chap. 2 of Vol. 3). The Cowardin
method was developed to serve as a “classification, to be used in a new inventory of
wetlands and deepwater habitats of the United States, is intended to describe
ecological taxa, arrange them in a system useful to resource managers, furnish
units for mapping, and provide uniformity of concepts and terms. Wetlands are
defined by plants (hydrophytes), soils (hydric soils), and frequency of flooding.
Ecologically related areas of deep water, traditionally not considered wetlands, are
included in the classification as deepwater habitats” (Cowardin et al. 1979 : 1). This
classification approach is used by NWI and all users of these data need to be familiar
with the Cowardin et al. system. The hierarchical approach uses System, Subsystem,
Class, Dominance Types, and Modifiers, and understanding these is important to
maximize the use of NWI data and describe the study wetland using a common
language. The hydrogeomorphic classification approach emphasizes hydrologic and
geomorphic (i.e., abiotic) controls for wetlands using the three components of
(1) geomorphic setting, (2) water source and its transport, and (3) hydrodynamics
(Brinson 1993 ). The geomorphic setting refers to the topographic location of the
wetland within the surrounding landscape. The types of water sources are precipita-
tion, surface/near surface flow, and groundwater discharge. Hydrodynamics is the
direction of flow and strength of water movement within the wetland. A variety of
descriptive terms are available to classify each wetland using this approach. There
are many other classification approaches that have been developed, and local
wetlands experts should be consulted to determine what approach might work best
for the wetlands being studied.
Hydrology is the dominant force driving ecological mechanisms and patterns
within wetlands. Abiotic factors represent indices to the hydrology of the wetland
and biotic elements represent the response to wetland hydrology. All ecological
Search WWH ::




Custom Search