Wetlands Characteristics and Boundaries (1995) / Chapter Skim
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7 REGIONALIZATION
7 REGIONALIZATION
Pages 168-189
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From page 168... ...
Regionalization is "a method of reducing or eliminating details which do not, on the average, hold true over large areas" (Wiken, 19861. Regionalization for the purpose of wetland delineation, therefore, would require the identification of areas with some degree of homogeneity in wetland characteristics and the development of specific regional procedures or indicators.
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From page 169... ...
Physiographic region Among physiographic regions Among wetland classes Wetland class Size and connections to upland, aquatic, and other wetlands Intra-wetland Topographic position Climate Geomorphic setting, water sources, hydrodynamics Hydroperiod, soils, plant assemblages Plant species composition, hydrologic status, redoximorphic features
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From page 170... ...
Topographic position within the wetland along the wetness gradient accounts for variation at this scale. Combinations of plant species, inundation and saturation, and redoximorphic soil features as they occur along the wetland to upland continuum, make this scale of variation the major focus of wetland delineation.
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From page 171... ...
In humid and dry regions alike, wetlands can be perched above and isolated from the regional water table wherever wetland soils do not drain efficiently. Isolation of wetlands from the regional groundwater table particularly occurs where hydrology has been altered by control structures and artificial drainage, as is the case on the Mississippi River Delta.
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From page 172... ...
, whereas nonwoody vegetation dominates wetlands in drier regions, such as the prairie pothole area. Growing seasons for plants differ substantially among regions, and plant phonology reflects the correlated regional variation in light and temperature (Chapter 5~.
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From page 173... ...
Regional Variation in Abundance of Wetlands Differences in geomorphology and climate were the cause of variation in wetland abundance among the states before to extensive European settlement. Use of the land resulted in a greater reduction of wetland area in some states than in others, however (Figure 7.1J.
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From page 174... ...
In addition to seven types of prairie pothole wetlands, it contains six salinity classes and five hydrologic phases to account for long-term variation in hydrology, and it includes agriculture as a cause of variation. For the glaciated northeast, Golet and Larson (1974)
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From page 175... ...
Statistically distinct intrastate map units are identified by sampling that was done for the Soil Conservation Service 1982 National Resource Inventory (Lytle, 1993~. By acknowledging the influence of human activity, these subdivisions could more accurately portray current wetland status than do schemes based mainly on natural vegetation (Bailey, 1976; Omernik, 1987~.
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From page 176... ...
176 N I _ `16 i, , ,\ _' 1 ! 't ~, ~ , < r _ ' - ~ _ 1 tori a 11 At" ~I N ~an; Air/ ~ ~ ~ ' ' '' ~ ~ ~ /°~7o;)
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From page 177... ...
177 on C} o ~n ~.
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From page 178... ...
178 .3' : ~' I' ~, >:.: " am'" " " "'3""' 3""3'""""''""'> 3:: .~: .
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From page 179... ...
CURRENT APPROACHES Regionalization of Federal Agencies The four federal agencies involved in wetland delineation are regionalized administratively, although their regional boundaries do not coincide (Figure 7.4~. FWS has the fewest regions (seven)
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From page 180... ...
Although all USACE districts use the same manual, there are minor differences among the districts in its implementation. Consultants who perform wetland delineations become accustomed to the standards of a district through their interactions with the staff in the district office, and can adjust their delineations accordingly.
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From page 181... ...
Descriptors of the complex wetland hydrologic system are usually limited to the relative height and seasonal variation in the water table or standing water or to indirect indicators of recent flooding. Although hydrologic indicators are used nationally in wetland delineation, the frequency and duration of saturation required for wetland formation and maintenance have not been summarized by region (Chapter 5~.
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From page 182... ...
PUERTO RICO B FIGURE 7.4 Regions of the four federal agencies with wetland delineation mandates.
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From page 183... ...
As explained in Chapter 5, substantial regional variation would be expected both for duration and for growing season, but information on duration and growing season is insufficient to allow clarification of this issue. Until a more sophisticated assessment is possible, reliance on duration should be questioned wherever duration data seem to conflict with information on plant associations and soil properties, and application of the growingseason concept should be reviewed and revised (Chapter 51.
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From page 184... ...
If the plant lists that establish the relationship of hydric soils and their attendant indicators are constrained to application within relatively homogeneous climatic or physiographic regions, such as ecoregions (Omernik, 1987) , then growing season becomes a less critical variable, as does the saturation threshold.
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From page 185... ...
Regional Applicability of Current Delineation Methods Current delineation methods were developed predominantly in the eastern United States, and as a result are most applicable there. For example, some of the field indicators of wetland hydrology listed in the 1987 and 1989 manuals, such as water marks, drift lines, waterborne sediment deposits, water-stained leaves, buttressing, and multiple trunks are typically associated with floodplain forests of the southeastern United States, and are less applicable where wetlands are maintained by ground water rather than by flooding.
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From page 186... ...
There is no regional framework for hydrology, despite the acknowledged regional differences in frequency and duration of saturation required for a wetland to develop hydric plant communities and hydric soils. Any national protocol defining hydrologic thresholds for wetlands should acknowledge regional variation.
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From page 187... ...
The U.S. Geological Survey long-term research programs on lake and ground water interaction, water budgets, and limnology provide other examples.
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From page 188... ...
The Hydric Soils List is subdivided into state and county lists, but it does not represent an effective regionalization scheme because it is based on political boundaries. Regional indicators for wetland hydrology and hydric soils, both of which involve depth to water table, should be developed concurrently rather than separately.
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From page 189... ...
7. The process that has been used to develop the regional hydrophyte lists is sound, as is the use of fidelity categories as a means of indicating regional differences.
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