Introduction to Stream Restoration - Hydro-Environmental Analysis: Freshwater Environments - page 266

that are degraded. Steps for the conservation of wetlands typically proceed irst through identiica-
tion and then through protection, by law or action. For example, wetlands directly connected to
navigable waterways are protected under Section 404 of the CWA, while the wetland conservation
compliance provisions (Swampbuster) in the 1985 Farm Bill (with amendments) provide protection
by removing certain incentives to produce agricultural commodities on converted wetlands. Much
of the loss of wetlands in the last century has occurred due to agricultural conversion.
Restoring riparian wetlands is often a critical component of river or stream restoration projects.
Riparian wetlands are not only important habitats in themselves, but they also affect stream channel
morphology and lows by providing temporary storage and buffering against the physical effects
of high lows. Generally, productivity is greatest in riparian wetlands with alternating periods of
inundation and drying (NRCS 2007a).
Two common methods for riparian wetland restoration are the “passive” and “active” approaches
(USEPA 2003a). The passive method involves identifying and then removing the factors causing
wetland loss. An example would be fencing to protect the wetland if cattle usage was identiied as a
contributing cause. Active methods would involve structural methods, such as restoring connectiv-
ity. A variety of causes for wetland degradation and corrective actions are listed in Table 8.6 from
the U.S. EPA (USEPA 2003a).
8.4.34 w etLand c onStructIon
Wetland conservation (or restoration), as discussed earlier, attempts to reestablish ecological pro-
cesses in damaged natural wetlands, while wetland construction is targeted toward the initiation of
wetland processes, or building new wetlands where none previously existed. One of the most com-
mon examples of constructed wetlands is that for wastewater or stormwater management. Wetland
construction as a BMP is an increasingly popular method for the treatment of stormwater control
(see the references in Sections 8.4.1 and 8.4.30 for guidance in wetland construction). Wetland
construction is also common as a mitigation measure to compensate for wetlands lost or destroyed,
such as due to construction projects. Wetlands are also commonly constructed for wildlife habitats,
by government agencies or private organizations (e.g., Ducks Unlimited).
Wetlands have long been known to naturally ilter the water of unwanted products. They can be
used just as effectively as treatment plants at treating water without the cost and maintenance. A
wetland ilters water by virtue of aquatic and nonaquatic plants, the absorptive capacity of the soil,
and by the different organisms and microorganisms found in water. Artiicially constructed wet-
lands are particularly versatile as a treatment option because they can be customized for a speciic
set of criteria. They can be designed for any coniguration, sediment load, pollutant load, or nutrient
load. They can also be designed much the same way as retention ponds, in the respect that the water
can be held for a short or long period of time depending on the level of treatment required. These
wetlands can also be of some scenic and aesthetic value.
Wetlands constructed for use as a stormwater management tool incorporate wetland plants in
shallow pools. Pollutants are removed from stormwater runoff by settling and biological uptake as it
lows through the wetland. Wetlands are among the most effective stormwater practices in terms of
pollutant removal, and also offer aesthetic value. Stormwater wetlands are fundamentally different
from natural wetlands in that they are designed speciically for the purpose of treating stormwater
runoff and usually have less biodiversity than natural wetlands. Wetlands are widely applicable
stormwater treatment practices. While they have limited applicability in highly urbanized settings
and in arid climates, they have few other restrictions (California Stormwater Quality Association
2003).
A constructed wetland is any area designed on a site that would not naturally support wetland
plants (Figure 8.50). Constructed wetlands can be used as the basic level of biological treatment for
stormwater. Wetland plants allow oxygen to develop at the plants root structure, allowing the water
to be oxygen rich. With oxygen-rich water, the hydraulic loading of nutrients creates the proper