Over the last 23 years, the Clean Water Act has produced large improvements in the water quality of the nation's surface waters, most of which were achieved through reductions in pollutants from point sources. Despite these achievements, however, many surface waters still have not attained CWA goals. Further reductions in pollutants from point sources likely will not achieve those goals, because factors that now limit attainment of those goals primarily are derived from land uses within a watershed which result in ecological degradation. To achieve significant additional improvements in the nation's waters will often require some type of ecological restoration.
Ecological restoration is a tool that can produce improvements in the quality of our water resources to support diverse, productive communities of plants and animals that provide significant ecological and social benefits. This document focuses on restoration as it applies to stream quality. Ecological Restoration: A Tool to Manage Stream Quality asserts that stream quality can often be managed by using restoration techniques in conjunction with more traditional management approaches, such as point source permitting. Many restoration techniques can serve as more natural options for meeting CWA goals when they are appropriately applied to restore the natural dynamics of a stream system.
Ecological Restoration: A Tool To Manage Stream Quality has four related objectives: (1) explaining and clarifying CWA authorities for restoration of streams, (2) examining and illustrating linkages between selected restoration techniques and parameters often addressed in state water quality standards, (3) providing water program managers with a helpful guide to determine when to pursue restoration, and (4) investigating the cost-effectiveness of restoration in comparison to traditional water quality management tools.
Restoration Defined (Chapter 1)
Academic and philosophical distinctions could be made between habitat restoration and ecological restoration. However, for the practical purposes of this document, the reader may find both terms used interchangeably.
In this report, ecological restoration is the restoration of chemical, physical, and/or biological components of a degraded system to a pre-disturbance condition and is also an important tool for preventing environmental degradation. Strengthening structural or functional elements through restoration can help increase a stream system's tolerance to stressors which lead to environmental degradation. By so doing, water quality and aquatic and terrestrial habitat will be improved, which, in turn, will lead to improvements in the aquatic and terrestrial communities that depend on that water.
For streams, then, restoration is an integral part of a broad, watershed-based approach for achieving federal, state, and local water resource goals. Specifically, restoration is the re-establishment of chemical, physical, and biological components of an aquatic ecosystem that have been compromised by stressors such as point or nonpoint sources of pollution, habitat degradation, hydromodification, and others.
This document emphasizes and endorses the use of natural restoration techniques. Natural techniques to restore ecosystem components are distinct from treatment technologies or artificial structures that are inserted into the system. Natural restoration techniques use materials indigenous to the ecosystem and are linked or incorporated into the dynamics of a river system in an attempt to create conditions in which ecosystem processes can withstand and diminish the impact of stressors.
Three categories of restoration techniques have been identified for stream management activities:
- Instream techniques are applied directly in the stream channel (e.g., channel reconfiguration and realignment to restore geometry, meander, sinuosity, substrate composition, structural complexity, re-aeration, or stream bank stability).
- Riparian techniques are applied out of the stream channel in the riparian corridor (e.g., re-establishment of vegetative canopy, increasing width of riparian corridor, or restrictive fencing).
- Upland, or surrounding watershed, techniques are generally related to the control of nonpoint source inputs from the watershed, including hydrologic runoff characteristics from increased imperviousness of the watershed [e.g., urban, agricultural, and forestry best management practices (BMPs)].
Stream restoration can be a mosaic of instream, riparian, and upland techniques, including BMPs, to be used in combination to eliminate or reduce the impact of stressors (both chemical and nonchemical) on aquatic ecosystems and reverse the degradation and loss of ecosystem functions. Instream restoration practices often need to be accompanied by techniques in the riparian area and/or the surrounding watershed. For example, restoration may involve rebuilding the infrastructure of a stream system (e.g., reconfiguration of channel morphology, re-establishment of riffle substrates, re-establishment of riparian vegetation, and stabilization of stream banks, accompanied by control of excess sediment and chemical loadings within the watershed) to achieve and maintain stream integrity.
Restoration and the Clean Water Act (Chapter 2)
Restoration is a natural tool for meeting some CWA requirements. Water quality standards define specific objectives for restoring aquatic ecosystem integrity and are comprised of designated uses, numeric or narrative water quality standards to protect these uses, and an antidegradation provision.
Ecological restoration techniques can be effective in addressing water quality impairments that are typically characterized by state water quality standards. Water quality impairment is often indicated by excursions of numeric standards, which provide quantitative targets for particular parameters. Water quality impairment may also be identified based on narrative standards and designated uses, such as the ability to support a designated type of fishery.
The Watershed Protection Approach and its key technical component, the Total Maximum Daily Load (TMDL) process, provide an impetus for restoration activities. Restoration techniques can be applied as a management action within the context of the TMDL process in conjunction with traditional regulatory actions (such as point source permits) and voluntary programs (such as implementation of nonpoint source BMPs) to address any component of a water quality standard—a numeric or narrative criterion or a designated use. In the context of a TMDL, restoration can also address nonattainment of a designated use (e.g., a coldwater fishery) or a narrative criterion that refers explicitly to habitat quality or biological diversity. An optimal management strategy may combine some or all options involving point source load reductions, BMPs, and instream ecological restoration techniques.
Adequate understanding of the relationships among physical, chemical, and biological processes is critical for determining when habitat restoration can be used to improve stream quality and implement the CWA. The following discussion illustrates the relationship between several restoration techniques and specific water quality parameters.
- Altered Stream Geomorphology:
- In cases where habitat degradation is significant, restoring or improving the physical habitat can help attain the aquatic life designated use, while simultaneously improving water quality.
- Upland, riparian, and instream restoration techniques that can restore equilibrium to sediment loads to streams include changes in land-use practices that reduce sediment loading (e.g., conservation tillage, contour farming, sodding or wildflower cover during construction activities), restoring off-stream wetlands to intercept nonpoint sources of sediments during wet-weather conditions, and modifying operations of dams and water diversion structures.
- High Stream Flows:
- Instream techniques that can reduce the effects of high stream flows include restoring natural stream meander and channel complexity, increasing substrate roughness, promoting growth of riparian vegetation (which provides refuge for fish during high flows), restoring wetlands to restore natural hydrologic regimes, and modifying operations of dams. Upland techniques include reducing the percent impervious surface in the watershed, which reduces "flash" runoff, through development of guidelines.
- Low Stream Flows:
- Impacts from low stream flows can be reduced by several instream restoration techniques, including restoring the stream channel in a channelized stream, controlling evaporation through restoration of the riparian canopy, replacing exotic riparian plant species that have high evapotranspiration rates with native species that have lower transpiration rates, creating pools through the use of drop structures providing protection of aquatic life during low flow periods, and increasing channel depth and re-establishing undercut banks to provide areas for protection of fish and other species during periods of low flow. Minimum flows can also be addressed by applying techniques in the surrounding watershed, such as managing watershed land and water use to prevent excessive dewatering.
- Biological Integrity:
- Improvements in water quality and habitat quality generally lead to increases in biodiversity and improvements in ecological functions such as nutrient cycling, trophic relationships, and predator-prey relationships.
- Practices that reduce ammonia toxicity would, through similar mechanisms, reduce the toxicity of other substances, including hydrogen sulfide. In addition, wetlands can help reduce the toxicity of some metals by reducing metal concentrations and bioavailability. Together, these practices would help reduce the total toxicity of the water and help attain narrative water quality standards.
- Nuisance Algal Growths:
- Restoration practices that can reduce nuisance algal growth include drop structures and riffles to create turbulence to reduce attached algal growth, constructing wetlands to reduce nutrient input and subsequent algal growth s, planting trees and bushes to reduce the amount of sunlight available for algal growth, increasing channel depth, and re-establishing undercut banks to reduce the area available for algal growth.
- Dissolved Oxygen:
- Restoration practices that can increase dissolved oxygen (DO) concentrations include constructing small hydrologic drop structures that increase re-aeration rates, restoring wetlands to reduce nutrient inputs and plant growth, re- establishing trees and bushes along stream banks to reduce incident sunlight and water temperature, restoring stream depth and undercut banks to reduce aquatic plant growth and water temperatures, and restoring riffles to increase turbulence.
- Water Temperature:
- High water temperatures can be reduced by restoring trees and bushes along stream banks to reduce incident sunlight, restoring stream depth, re-establishing undercut banks, and narrowing stream width to reduce excessive solar warming.
- pH levels can be increased by restoring wetlands to intercept acid mine drainage and neutralize acidity by converting sulfates associated with sulfuric acid to insoluble non-acidic metal sulfides that remain trapped in wetland sediments. In addition, all techniques discussed above for increasing DO concentrations can be used to decrease high pH levels caused by high rates of photosynthesis.
- Restoration practices that decrease high pH or temperature will also decrease the potential toxicity of ammonia to aquatic life.
- Restoration practices can decrease inputs of metals to streams or reduce the ionic, dissolved phases of metals, which are considered to be toxic. Particulate phases have much lower toxicities. Techniques include those mentioned above for increasing pH; decreasing metal bioavailability by increasing particulate metals; restoring existing wetlands to treat acid mine drainage; and re-establishing vegetation in riparian areas.
A Decision-Making Guide for Restoration (Chapter 4)
Chapter 4 presents a decision-making guide that includes decision points integrating a broad range of program responsibilities and activities. The process assumes that impaired or threatened water resources have already been identified in accordance with relevant sections of the CWA, as well as requirements of any other relevant water programs. The decision-making guide begins with a selected site where water quality standards, which may include numeric or narrative criteria or designated uses, are not being met or are threatened. In Step 1, an inventory of the watershed is conducted to assess the potential value of ecological restoration techniques for addressing water quality impairment. Steps 2 and 3 provide an analysis of the availability, applicability, and relative costs of ecological restoration techniques to assist regional and state personnel in making informed decisions. In Step 4, an ecological restoration approach is implemented, where appropriate. In Step 5, post-implementation monitoring, an essential part of the decision-making guide, is conducted to determine whether impairment has been mitigated. Additionally, several steps in the decision-making guide call for stakeholder involvement.
Evaluating the Cost Effectiveness of Restoration (Chapter 5)
Selecting the most cost-effective techniques is critical to the success of any restoration project. Two possible approaches for evaluating the cost effectiveness of water quality measures are cost minimization and benefit maximization. The most cost-effective restoration technique either achieves the water quality objective at the lowest cost (cost minimization) or produces the greatest benefits for the same cost (benefit maximization). The two primary economic reasons why restoration may be more cost effective than point source controls alone are that (1) restoration often has lower marginal costs (i.e., the incremental costs of removing an additional unit of a pollutant) and (2) restoration provides a wider range of ecological benefits. Cost calculations are relatively straightforward and are the same for cost minimization and benefit maximization analyses.
Determining the benefits of each project to be evaluated is critical prior to comparing costs and benefits. Benefits fall into three general categories: (1) prioritized benefits (i.e., those that are ranked by preference or priority, such as best, next best, and worst), (2) quantifiable benefits (i.e., those that can be quantified but not priced), and (3) monetary benefits (i.e., those that can be described in monetary terms).
If all benefits can be quantified monetarily, total costs can be compared to benefits in two ways. The first comparison is expressed as a cost-to-benefits ratio, from which the alternative with the lowest cost-to-benefits ratio is selected. The second comparison is expressed in terms of net value (i.e., subtracting costs from benefits), from which the alternative with the highest net value is selected. Neither approach is the most appropriate in all cases. In many cases, considering as many measures as practicable—cost per unit, cost-to-benefits ratios, and net present value—is advisable. A clear understanding of objectives is essential for the analysis.
Finally, cost effectiveness is relative and may change with location and circumstances. For example, a certain combination of restoration practices in one location may produce great benefits at a low cost, whereas others may produce few benefits at a large cost. Some water quality problems (e.g., loss of habitat) are not amenable to a point source treatment approach at any cost; and some water quality problems cannot be reduced through any reasonable degree of restoration.
Case Studies (Chapter 6)
Chapter 6 presents seven case studies to demonstrate the effectiveness of using restoration techniques to achieve water quality goals. Common elements among the case studies that resulted in improvements to stream integrity are the reduction of stressors and the restoration of stream components (e.g., stream channel and riparian corridor). Each project does, however, offer unique lessons that may be beneficial in planning future projects. Presentation of case studies is therefore structured in accordance with the framework presented in this document to provide a common basis for evaluating individual examples and comparing different approaches. The following case studies are included in Chapter 6: Anacostia River, Metropolitan Washington, District of Columbia; Bear Creek, Iowa; Boulder Creek, Colorado; South Fork of the Salmon River, Idaho; Upper Grande Ronde River, Oregon; and Wildcat Creek, California.