WETLANDS - Water Quality Engineering in Natural Systems - page 290

TABLE 8.2. Hydrologic Zones for Nontidal Areas

Zone Name Percent of Time Inundated Comments

I Permanently inundated 100% Inundation >2 m (6 ft) mean water depth.

Aquatic, not wetlands.

II Semipermanently to nearly

inundated or saturated

75-100%

Inundation defined as <2 m (6 ft) mean
water depth.

III regularly inundated or saturated 25-75%

IV Seasonally inundated or saturated 12.5-25%

V Irregularly inundated or saturated 5-12.5% Many areas having these hydrologic

characteristics are not wetlands.

VI Intermittently or never inundated

or saturated

<5% Areas with these hydrologic characteristics

are not wetlands.

drained of excess water and carefully managed, muck
soils are among the most important vegetable-producing
soils in the eastern United States.
When a hydric soil is drained, it may no longer
be referred to as a hydric soil, unless the supported
vegetation is hydrophytic, and indicators of hydrology
support the designation as a hydric soil.

8.2.2.3 Hydrology. Hydrologic factors that deter-
mine whether an area is a wetland are the frequency,
timing, and duration of inundation or soil saturation, as
shown in Table 8.2, for nontidal areas. Zone I is aquatic,
zones II, III, and IV are wetlands, and zone VI is upland.
Zone V may or may not be considered a wetland,
depending on the other indicators. recorded water level
data from adjacent streams and lakes, as well as model
predictions, can be used to establish the hydrologic con-
dition of an area.
If an area meets any of the wetland criteria regarding
vegetation, soils, and hydrology, the area can be classi-
fied as a wetland.

Figure 8.7. Canada geese. Source : Jackson Bottom Wetlands
Preserve (2005).

8.2.3 Water Budget

the major source of nutrients to wetlands. When hydro-
logic conditions in wetlands change, even slightly, the
biota may respond with massive changes in species com-
position, richness, and ecosystem productivity. Several
animals are particularly noted for their contributions to
hydrologic modifications and subsequent changes in
wetlands. Beavers are noted for building dams, muskrats
for burrowing, and geese (particularly Canada geese,
shown in Fig. 8.7) for consuming excessive amounts of
wetland vegetation.
The hydroperiod is the seasonal pattern of water
level in a wetland and can be considered a hydrologic
signature of each wetland type. Factors that affect the
hydroperiod include (1) the balance between inflows
and outflows, (2) the surface contours of the landscape,
and (3) the subsurface soil, geology, and groundwater

Wetlands are part of a landscape mosaic that provides
several watershed functions, and removal or alteration
of wetlands can significantly affect the health and func-
tion of the broader landscape. The hydrology of a
wetland creates the unique physicochemical conditions
that make such an ecosystem different from both well-
drained terrestrial systems and deepwater aquatic
systems. Hydrologic pathways such as rainfall, surface
runoff, groundwater flow, tides, and flooding rivers
transport energy and nutrients to and from wetlands.
Water depth, flow patterns, and duration and frequency
of flooding are the result of hydrologic inputs and
outputs, and these factors have a direct influence on the
biochemistry of soils and the biota of wetlands. Except
in nutrient-poor wetlands such as bogs, water inputs are