Environmental Engineering Reference
In-Depth Information
a need to determine whether a landscape has characteristics of a wetland setting for
regulatory or protection purposes. Hydrology is basically the study of water as it is
distributed over, on, and within the earth. All landscapes, and particularly wetlands,
have hydrologic properties that are an integration of all the water-related chara-
cteristics and processes that occur there. Wetland hydrology encompasses study of
the distribution and flow of all water that is added to, lost from, or stored in a wetland.
A wetland is a portion of a landscape that is wet for a period sufficiently long that
physical, chemical and biological conditions are indicative of a wet setting.
Wetlands occur in a wide range of settings where geological and hydrological
processes enhance the accumulation and retention of water (Winter 1988 ). Water,
therefore, is present at or just beneath land surface at a substantial percentage of the
time in wetland settings. Given that water is integral to wetland settings, an
overarching challenge in determining the type or persistence or quality of a
particular wetland setting is to determine the relative contributions of the various
components of wetland hydrology (i.e., precipitation or evapotranspiration or
surface-water inputs or groundwater inputs or overland flow). A water-budget
approach for making this determination is perhaps the best way to categorize and
describe the wide range of wetland types that exist in the world (Winter and Woo
1990 ; Winter 1992 ) and is the perspective from which this chapter is presented.
3.2 Wetland Hydrology from the Perspective
of a Water Budget
Knowledge and understanding of the storage and mass balance of water and
chemicals is critical to understanding a wetland ecosystem. This includes quanti-
fying all of the sources, losses, and changes in storage in the wetland. Simply
determining the relative magnitude of various hydrologic components can largely
determine a wetland type. For example, surface water may be the dominant source
and sink of water and solutes for a riparian wetland whereas overland flow and
evapotranspiration may dominate in a prairie wetland. One will have greatly
different water chemistry and biogeochemical processes than the other, all because
of the relative mix of sources and sinks of water and chemicals.
Wetland stage is an integrated response to all source- and sink-terms in a
hydrologic budget. It also incorporates temporal variability in the balance of all
hydrologic fluxes and is, therefore, strongly linked to wetland hydroperiod and
wetland hydrodynamics, both of which are important to most disciplines that
encompass wetland science (Euliss et al. 2004 ). Wetland stage and volume can
also provide a direct and often sensitive response when climate change may be
affecting the relative magnitude and importance of specific hydrologic components.
For these reasons and more, an accounting of hydrologic components of a wetland
water budget should be one of the first items on a wetland-scientist's agenda (LaBaugh
1986 ). Preliminary estimates of the relative volume associated with each hydrologic
component is often a valuable first step. These estimates will allow attention to be
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