Water: Coastal Zone Act Reauthorization Amendments
Management Measures for Wetlands - I. Introduction
A. What "Management Measures" Are
This chapter specifies management measures to protect and restore wetlands and riparian areas to protect coastal waters from coastal nonpoint pollution. "Management measures" are defined in section 6217 of the Coastal Zone Act Reauthorization Amendments of 1990 (CZARA) as economically achievable measures to control the addition of pollutants to our coastal waters, which reflect the greatest degree of pollutant reduction achievable through the application of the best available nonpoint pollution control practices, technologies, processes, siting criteria, operating methods, or other alternatives.
These management measures will be incorporated by States into their coastal nonpoint programs, which under CZARA are to provide for the implementation of management measures that are "in conformity" with this guidance. Under CZARA, States are subject to a number of requirements as they develop and implement their Coastal Nonpoint Pollution Control Programs in conformity with this guidance and will have some flexibility in doing so. The application of these management measures by States to activities causing nonpoint pollution is described more fully in Coastal Nonpoint Pollution Control Program: Program Development and Approval Guidance, published jointly by the U.S. Environmental Protection Agency (EPA) and the National Oceanic and Atmospheric Administration (NOAA).
B. What "Management Practices" Are
In addition to specifying management measures, this chapter also lists and describes management practices for illustrative purposes only. While State programs are required to specify management measures in conformity with this guidance, State programs need not specify or require the implementation of the particular management practices described in this document. However, as a practical matter, EPA anticipates that the management measures generally will be implemented by applying one or more management practices appropriate to the source, location, and climate. The practices listed in this document have been found by EPA to be representative of the types of practices that can be applied successfully to achieve the management measures. EPA has also used some of these practices, or appropriate combinations of these practices, as a basis for estimating the effectiveness, costs, and economic impacts of achieving the management measures. (Economic impacts of the management measures are addressed in a separate document entitled Economic Impacts of EPA Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters.)
EPA recognizes that there is often site-specific, regional, and national variability in the selection of appropriate practices, as well as in the design constraints and pollution control effectiveness of practices. The list of practices for each management measure is not all-inclusive and does not preclude States or local agencies from using other technically and environmentally sound practices. In all cases, however, the practice or set of practices chosen by a State needs to achieve the management measure.
C. Scope of This Chapter
This chapter contains management measures that address multiple categories of nonpoint source (NPS) pollution that affect coastal waters. The primary NPS pollutants addressed are sediment, nitrogen, phosphorus, and temperature. This chapter is divided into three management measures:
- Protection of Wetlands and Riparian Areas;
- Restoration of Wetlands and Riparian Areas; and
- Promoting the Use of Vegetated Treatment Systems, such as Constructed Wetlands and Vegetated Filter Strips.
Each category of management measure is addressed in a separate section of this guidance. Each section contains (1) the management measure; (2) an applicability statement that describes, when appropriate, specific activities and locations for which the measure is suitable; (3) a description of the management measure's purpose; (4) the basis for the management measure's selection; (5) information on management practices that are suitable, either alone or in combination with other practices, to achieve the management measure; (6) information on the effectiveness of the management measure and/or of practices to achieve the measure; and (7) information on costs of the measure and/or of practices to achieve the measure.
CZARA requires EPA to specify management measures to control nonpoint pollution from various sources. Wetlands, riparian areas, and vegetated treatment systems have important potential for reducing nonpoint pollution in coastal waters from a variety of sources. Degradation of existing wetlands and riparian areas can cause the wetlands or riparian areas themselves to become sources of nonpoint pollution in coastal waters. Such degradation can result in the inability of existing wetlands and riparian areas to treat nonpoint pollution. Therefore, management measures are presented in this chapter specifying the control of nonpoint pollution through (1) protection of the full range of functions of wetlands and riparian areas to ensure continuing nonpoint source pollution abatement, (2) restoration of degraded systems, and (3) the use of vegetated treatment systems.
The intent of the three wetlands management measures is to ensure that the nonpoint benefits of protecting and restoring wetlands and riparian areas, and of constructing vegetated treatment systems, will be considered in all coastal watershed water pollution control activities. These management measures form an essential element of any State Coastal Nonpoint Pollution Control Program.
There is substantial evidence in the literature, and from case studies, that one important function of both natural and human-made wetlands is the removal of nonpoint source pollutants from storm water. Much of this literature is cited in this chapter. These pollutants include sediment, nitrogen, and phosphorus (Whigham et al., 1988; Cooper et al., 1987; Brinson et al., 1984). Also, wetlands and riparian areas have been shown to attenuate flows from higher-than-average storm events, thereby protecting receiving waters from peak flow hydraulic impacts such as channel scour, streambank erosion, and fluctuations in temperature and chemical characteristics of surface waters (Mitsch and Gosselink, 1986; Novitzki, 1979).
A degraded wetland has less ability to remove nonpoint source pollutants and to attenuate storm water peak flows (Richardson and Davis, 1987; Bedford and Preston, 1988). Also, a degraded wetland can deliver increased amounts of sediment, nutrients, and other pollutants to the adjoining waterbody, thereby acting as a source of nonpoint pollution instead of a treatment (Brinson, 1988).
Therefore, the first management measure is intended to protect the full range of functions for wetlands and riparian areas serving a nonpoint source abatement function. This protection will preserve their value as a nonpoint source control and help to ensure that they do not become a significant nonpoint source due to degradation.
The second management measure promotes the restoration of degraded wetlands and riparian systems with nonpoint source control potential for similar reasons: the increase in pollutant loadings that can result from degradation of wetlands and riparian areas, and the substantial evidence in the literature on effectiveness of wetlands and riparian areas for nonpoint pollution abatement. In addition, there may be other benefits of restoration to wildlife and aquatic organisms. This measure provides for evaluation of degraded wetlands and riparian systems, and for restoration if the systems will serve a nonpoint source pollution abatement function (e.g., by cost-effectively treating nonpoint source pollution or by attenuating peak flows).
The third management measure promotes the use of vegetated treatment systems because of their wide-scale ability to treat a variety of sources of nonpoint pollution. This measure will apply, as appropriate, to all other chapters in this guidance. Placing the large amount of information on vegetated treatment systems in one management measure avoids duplication in most other 6217(g) measures and thereby limits the potential for confusion. All descriptions, applications, case studies, and costs are in one measure within the CZARA 6217(g) guidance and are cross-referenced in the management measures for which these systems are a potential nonpoint pollution control. Also, all positive and negative aspects of design, construction, and operation have been included in one place to avoid confusion in applications due to potential inconsistencies from placement in multiple measures.
D. Relationship of This Chapter to Other Chapters and to Other EPA Documents
- Chapter 1 of this document contains detailed information on the legislative background for this guidance, the process used by EPA to develop this guidance, and the technical approach used by EPA in the guidance.
- Chapter 3 of this document contains a management measure and accompanying information on forestry practices in wetlands and protection of wetlands subject to forestry operations.
- Chapter 8 of this document contains information on recommended monitoring techniques (1) to ensure proper implementation, operation, and maintenance of the management measures and (2) to assess over time the success of the measures in reducing pollution loads and improving water quality.
- EPA has separately published a document entitled Economic Impacts of EPA Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters.
- NOAA and EPA have jointly published guidance entitled Coastal Nonpoint Pollution Control Program: Program Development and Approval Guidance. This guidance contains details on how State Coastal Nonpoint Pollution Control Programs are to be developed by States and approved by NOAA and EPA. It includes guidance on the following:
- The basis and process for EPA/NOAA approval of State Coastal Nonpoint Pollution Control Programs;
- How NOAA and EPA expect State programs to provide for the implementation of management measures "in conformity" with this management measures guidance;
- How States may target sources in implementing their Coastal Nonpoint Pollution Control Programs;
- Changes in State coastal boundaries; and
- Requirements concerning how States are to implement their Coastal Nonpoint Pollution Control Programs.
E. Definitions and Background Information
The preceding five chapters of this guidance have specified management measures that represent the most effective systems of practices that are available to prevent or reduce coastal nonpoint source (NPS) pollution from five specific categories of sources. In this chapter, management measures that apply to a broad variety of sources, including the five categories of sources addressed in the preceding chapters, are specified. These measures promote the protection and restoration of wetlands and riparian areas and the use of vegetated treatment systems as means to control the nonpoint pollution emanating from such nonpoint sources. Management measures for protection and restoration of wetlands and riparian areas are developed as part of NPS and coastal management programs to take into consideration the multiple functions and values these ecosystems provide to ensure continuing nonpoint source pollution abatement.
1. Wetlands and Riparian Areas
For purposes of this guidance, wetlands are defined as:
Those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas.
Wetlands are usually waters of the United States and as such are afforded protection under the Clean Water Act (CWA). Although the focus of this chapter is on the function of wetlands in reducing NPS pollution, it is important to keep in mind that wetlands are ecological systems that perform a range of functions (e.g., hydrologic, water quality, or aquatic habitat), as well as a number of pollutant removal functions.
For purposes of this guidance, riparian areas are defined as:
Vegetated ecosystems along a waterbody through which energy, materials, and water pass. Riparian areas characteristically have a high water table and are subject to periodic flooding and influence from the adjacent waterbody. These systems encompass wetlands, uplands, or some combination of these two land forms. They will not in all cases have all of the characteristics necessary for them to be classified as wetlands.
Figure 7-1 illustrates the general relationship between wetlands, uplands, riparian areas, and a stream channel. Identifying the exact boundaries of wetlands or riparian areas is less critical than identifying ecological systems of concern. For instance, even those riparian areas falling outside wetland boundaries provide many of the same important water quality functions that wetlands provide. In many cases, the area of concern may include an upland buffer adjacent to sensitive wetlands or riparian areas that protects them from excessive NPS impacts or pretreats the inflowing surface waters.
Wetlands and riparian areas can play a critical role in reducing NPS pollution, by intercepting surface runoff, subsurface flow, and certain ground-water flows. Their role in water quality improvement includes processing, removing, transforming, and storing such pollutants as sediment, nitrogen, phosphorus, and certain heavy metals. Thus, wetlands and riparian areas buffer receiving waters from the effects of pollutants, or they prevent the entry of pollutants into receiving waters.
The functions of wetlands and riparian areas include water quality improvement, aquatic habitat, stream shading, flood attenuation, shoreline stabilization, and ground-water exchange. Wetlands and riparian areas typically occur as natural buffers between uplands and adjacent waterbodies. Loss of these systems allows for a more direct contribution of NPS pollutants to receiving waters. The pollutant removal functions associated with wetlands and riparian area vegetation and soils combine the physical process of filtering and the biological processes of nutrient uptake and denitrification (Lowrance et al., 1983; Peterjohn and Correll, 1984). Riparian forests, for example, have been found to contribute to the quality of aquatic habitat by providing cover, bank stability, and a source of organic carbon for microbial processes such as denitrification (James et al., 1990; Pinay and Decamps, 1988). Riparian forests have also been found to be effective at reducing instream pollution during flood flows (Karr and Gorman, 1975; Kleiss et al., 1989).
In highly developed urban areas, wetlands and riparian areas may be virtually destroyed by construction, filling, channelization, or other significant alteration. In agricultural areas, wetlands and riparian areas may be impacted by overuse of the area for grazing or by removal of native vegetation and replacement by annual crops or perennial cover. In addition, significant hydrologic alterations may have occurred to expedite drainage of farmland. Other significant impacts may occur as a result of various activities such as highway construction, surface mining, deposition of dredged material, and excavation of ports and marinas. All of these activities have the potential to degrade or destroy the water quality improvement functions of wetlands and riparian areas and may exacerbate NPS problems.
A wetland's position in the landscape affects its water quality functions. Some cases have been studied sufficiently to predict how an individual wetland will affect water quality on a landscape scale (Whigham et al., 1988). Wetlands that border first-order streams were found by Whigham and others (1988) to be efficient at removing nitrate from ground water and sediment from surface waters. They were not found to be as efficient in removing phosphorus. When located downstream from first-order streams, wetlands and riparian areas were found to be less effective at removing sediment and nutrient from the stream itself because of a smaller percentage of stream water coming into contact with the wetlands (Whigham et al., 1988). It has also been estimated that the portion of a wetland or riparian area immediately below the source of nonpoint pollution may be the most effective filter (Cooper et al., 1986; Lowrance et al., 1983; Phillips, 1989).
Although wetlands and riparian areas reduce NPS pollution, they do so within a definite range of operational conditions. When hydrologic changes or NPS pollutants exceed the natural assimilative capacity of these systems, wetland and riparian areas become stressed and may be degraded or destroyed. Therefore, wetlands and riparian areas should be protected from changes that would degrade their existing functions. Furthermore, degraded wetlands and riparian areas should be restored, where possible, to serve an NPS pollution abatement function.
2. Vegetated Buffers
For the purpose of this guidance, vegetated buffers are defined as:
Strips of vegetation separating a waterbody from a land use that could act as a nonpoint pollution source. Vegetated buffers (or simply buffers) are variable in width and can range in function from a vegetated filter strip to a wetland or riparian area.
This term is currently used in many contexts, and there is no agreement on any single concept of what constitutes a buffer, what activities are acceptable in a buffer zone, or what is an appropriate buffer width. In one usage, the term vegetated buffer refers to natural riparian areas that are either set aside or restored to filter pollutants from runoff and to maintain the ecological integrity of the waterbody and the land adjacent to it (Nieswand et al., 1989). In another usage, the term vegetated buffer refers to constructed strips of vegetation used in various settings to remove pollutants in runoff from a developed site (Nieswand et al., 1989). Finally, the term vegetated buffer can be used to describe a transition zone between an urbanized area and a naturally occurring riparian forest (Faber et al., 1989). In this context, buffers can be designed to provide value to wildlife as well as aesthetic value.
A vegetated buffer usually has a rough surface and typically contains a heterogeneous mix of ground cover, including herbaceous and woody species of vegetation (Stewardship Incentive Program, 1991; Swift, 1986). This mix of vegetation allows the buffer to function more like a wetland or riparian area. A vegetated filter strip (see below) can also be constructed to remove pollutants in runoff from a developed site, but a filter strip differs from a vegetated buffer in that a filter strip typically has a smooth surface and a vegetated cover made up of a homogeneous species of vegetation (Dillaha et al., 1989a).
Vegetated buffers can possess characteristics and functions ranging from those of a riparian area to those of a vegetated filter strip. To avoid confusion, the term vegetated buffer will not be discussed further in this chapter although the term is used in other chapters of this guidance.
3. Vegetated Treatment Systems
For purposes of this guidance, vegetated treatment systems (VTS) are defined to include either of the following or a combination of both: vegetated filter strips and constructed wetlands. Both of these systems have been defined in the scientific literature and have been studied individually to determine their effectiveness in NPS pollutant removal.
In this guidance, vegetated filter strips (VFS) are defined as (Dillaha et al., 1989a):
Created areas of vegetation designed to remove sediment and other pollutants from surface water runoff by filtration, deposition, infiltration, adsorption, absorption, decomposition, and volatilization. A vegetated filter strip is an area that maintains soil aeration as opposed to a wetland that, at times, exhibits anaerobic soil conditions.
In this guidance, constructed wetlands are defined as (Hammer, 1992):
Engineered systems designed to simulate natural wetlands to exploit the water purification functional value for human use and benefits. Constructed wetlands consist of former upland environments that have been modified to create poorly drained soils and wetlands flora and fauna for the primary purpose of contaminant or pollutant removal from wastewaters or runoff. Constructed wetlands are essentially wastewater treatment systems and are designed and operated as such though many systems do support other functional values.
In areas where naturally occurring wetlands or riparian areas do not exist, VTS can be designed and constructed to perform some of the same functions. When such engineered systems are installed for a specific NPS-related purpose, however, they may not offer the same range of functions that naturally occurring wetlands or riparian areas offer. Vegetated treatment systems have been installed in a wide range of settings, including cropland, pastureland, forests, and developed, as well as developing, urban areas, where the systems can perform a complementary function of sediment control and surface water runoff management. Practices for use of vegetated treatment systems are discussed in other chapters of this guidance, and VTS should be considered to have wide-ranging applicability to various NPS categories.
When properly installed and maintained, VFS have been shown to effectively prevent the entry of sediment, sediment-bound pollutants, and nutrients into waterbodies. Vegetated filter strips reduce NPS pollutants primarily by filtering water passing over or through the strips. Properly designed and maintained vegetated filter strips can substantially reduce the delivery of sediment and some nutrients to coastal waters from nonpoint sources. With proper planning and maintenance, vegetated filter strips can be a beneficial part of a network of NPS pollution control measures for a particular site. Vegetated filter strips are often coupled with practices that reduce nutrient inputs, minimize soil erosion, or collect runoff. Where wildlife needs are factored into the design, vegetated filter strips or buffers in urban areas can add to the urban environment by providing wildlife nesting and feeding sites, in addition to serving as a pollution control measure. However, some vegetated filter strips require maintenance such as mowing of grass or removal of accumulated sediment. These and other maintenance activities may preclude much of their value for wildlife, for example by disturbing or destroying nesting sites.
Constructed wetlands are designed to mimic the pollutant-removal functions of natural wetlands but usually lack aquatic habitat functions and are not intended to provide species diversity. Pollutant removal in constructed wetlands is accomplished by several mechanisms, including sediment trapping, plant uptake, bacterial decomposition, and adsorption. Properly designed constructed wetlands filter and settle suspended solids. Wetland vegetation used in constructed wetlands converts some pollutants (i.e., nitrogen, phosphorus, and metals) into plant biomass (Watson et al., 1988). Nitrification, denitrification, and organic decomposition are bacterial processes that occur in constructed wetlands. Some pollutants, such as phosphorus and most metals, physically attach or adsorb to soil and sediment particles. Therefore, constructed wetlands, used as a management practice, could be an important component in managing NPS pollution from a variety of sources. They are not intended to replace or destroy natural wetland areas, but to remove NPS pollution before it enters a stream, natural wetland, or other waterbody.
It is important to note that aquatic plants and benthic organisms used in constructed wetlands serve primarily to remove pollutants. Constructed wetlands may or may not be designed to provide flood storage, ground-water exchange, or other functions associated with natural wetlands. In fact, if there is a significant potential for contamination or other detrimental impacts to wildlife, constructed wetlands should be designed to discourage use by wildlife.