California Coastal Commission

PROCEDURAL GUIDANCE FOR EVALUATING WETLAND MITIGATION PROJECTS IN CALIFORNIA'S COASTAL ZONE

One of the challenges in developing comprehensive wetland evaluation procedures is to produce methods that can be generally applied to a wide variety of individually proposed projects, yet provide enough specificity to ensure consistent and objective evaluation of both mitigation plans and the resulting projects. Thus, the methods must describe the essential elements in sufficient detail, and provide an overall framework that integrates the elements into an objective process that is generally applicable. To address these concerns, this section presents a description of the major elements critical to effective wetland evaluation procedures. An overall framework for these elements is described first, followed by more detailed descriptions of each element.

Although the information and procedures described here might suggest the evaluation of wetland performance is a simple and straightforward process, this is clearly not the case. These procedures, although generally accepted in theory, have had limited application. In fact, there are no generally accepted methods for some of the procedures, while project specific complexities can require —often substantial— deviations from the general procedures described here. In addition, the information presented in this document applies most directly to in-kind compensatory mitigation, which is defined as compensatory mitigation involving the same type of habitat as that impacted by the development activity. These procedures will have more limited use for out-of-kind compensatory mitigation projects and enhancement projects, as the procedures do not address methods for comparing different types of habitats, nor do they address the question of partial credit. The procedures described here also have more limited application to restoration projects completed for reasons other than compensatory mitigation, because restoration project goals and objectives are derived in a fundamentally different way. Yet, while the procedures presented here are most applicable as general guidance for achieving successful in-kind compensatory wetland mitigation, they do include information relevant to other types of activities involving wetlands.

4.1. The Overall Framework

The approach used here is to provide, within the context of local and regional needs, an objectively based framework that can provide guidance useful to development of wetland mitigation plans and to evaluation of the resulting projects. The framework is flexible enough to apply to any type of wetland occurring in the coastal zone, and consists of five major elements: 1) ecological assessment; 2) goals, objectives, and performance standards; 3) mitigation attributes; 4) monitoring program; and 5) performance evaluation (Figure 1). Critical decisions relating to each element are made by the project proponent and the resource and regulatory agency staff overseeing the project. Although each element must be considered in the design and implementation of any wetland mitigation project, the arrows in Figure one show how information flows within and among the elements. These arrows illustrate the need for taking a comprehensive and integrated approach in the design and implementation of any wetland mitigation project.

Figure 1. A Diagram of the Overall Framework for Developing Wetland Mitigation Plans and for Evaluating Wetland Mitigation Project Performance

Although compensatory wetland mitigation projects vary greatly in size and complexity, the basic features are in fact similar. All mitigation plans must clearly describe the wetland habitat and functions that will be affected by the proposed development. This information is then used to develop clearly defined goals, objectives, and performance standards for a mitigation project that provides a similar or greater quantity and quality of wetland habitat and functions. An appropriate monitoring program is used to collect the data necessary to evaluate the performance of the mitigation project. A performance evaluation includes an analysis of the monitoring data in relation to the established performance standards to determine the performance level of the mitigation site's habitat and functions. The monitoring program and performance evaluation also serve to identify the need for remediation and appropriate remedial actions. This procedural guidance document addresses these features in further detail, in an attempt to provide a more clear and consistent process for achieving successful compensatory wetland mitigation in the coastal zone.

4.2. Individual Elements of the Framework

This section contains a more detailed discussion of the five major elements identified in the overall framework. Each element is discussed separately, although it is important to remember that a successful mitigation project requires a comprehensive plan that integrates the information from each element.

4.2.1. Ecological Assessment

Completing an ecological assessment of a wetland prior to its disturbance is a critical first step to achieving a successful mitigation project. Wetland mitigation must be based on an understanding and quantification of the ecological functions that exist prior to disturbance (Richardson, 1994). Ecological assessment is defined here as an assessment of the entire wetland system and includes evaluation of both the biotic and abiotic components of a wetland. In the case of in-kind mitigation, an ecological assessment should be completed for both the adversely impacted wetland and the proposed mitigation site to assure development of an appropriate mitigation plan.

4.2.1.1. Assessing wetland habitat

In large measure, an ecological assessment requires an evaluation of the wetland's habitats and functions. A habitat is the place where a plant or animal lives, so an assessment of the habitats within a wetland will focus on the identification and evaluation of the factors that define the structure of the wetland. The amount of open water area, the depth of the water, and the type of water (e.g., fresh, brackish, or salt water) are all features of the open water habitat. In addition, the habitat for many organisms is a direct function of the type and form of other organisms present. For example, the number, type, location, and size of plants within the wetland largely define the vegetative habitat, which in turn affects the type of animals that occur in a wetland and how those animals use the wetland.

4.2.1.2. Assessing wetland functions

In contrast to habitat, function refers to what a wetland does, the processes it performs. All of the known functions of coastal wetlands are a manifestation of one or more physical, chemical, or biological attribute inherent to the system. The presence of a function is most directly evaluated by measuring or monitoring these attributes. For example, if provision of habitat for native fishes is identified as an important function, then the physical, chemical, and biological attributes that provide the correct conditions for a wetland to perform that function will have to be evaluated. Assessment of the biological attributes would include identifying the species of fish that occur in the wetland, identifying their life stages (e.g., young-of-the-year, juvenile, or adult), and determining the abundances of those species. Assessment of the chemical attributes would include quantification of the water quality conditions (e.g., salinity, temperature, and dissolved oxygen) important to the native fishes in the wetland. Assessment of the physical attributes would include characterization of the fish habitat, such as the proportion of open water habitat, the sources, timing, and amount of water, and the water depths. If this function is subsequently included as an objective in the mitigation plan, then the information gained from the ecological assessment can serve as the basis for one or more performance standards.

As indicated by the example above, an ecological assessment generally results in a description and quantification of the attributes of a specific function, rather than direct assessment of the function itself (Kentula, et al., 1992; Simenstad, et al., 1991). This approach requires knowledge of the relationship between the attribute and the function. Thus, an ecological assessment should clearly explain how the assessed attributes relate to the functions of interest.

The value of each function must also be taken into account in an ecological assessment of a wetland. Value refers to those characteristics resulting from a function that are perceived by society as desirable and worthy of protection, or those characteristics that contribute to the habitat quality of the resident biota (Hammer, 1992; Squires, 1992). Assessing the value of each function helps to prioritize the importance of the functions. In addition, the existence of a function and its current value must be assessed to determine the affects of historic adverse impacts. If the historic impacts are severe, the mitigation plan must provide for an improved level of function (i.e., increased value), instead of the current impaired level.

4.2.1.3. Assessing a wetland's ecological contribution to the landscape

In addition to providing information on a wetland's habitats, functions and values, an ecological assessment can also provide information on a wetland's ecological contribution to the landscape. Information from the ecological assessment may be used to assess habitat rarity. For example, how common is the habitat type in the region or immediate area? Or the information may be used to assess historic rarity. For example, what fraction of this habitat type has been lost regionally and locally? Completing this analysis, however, requires information from a regional assessment of wetland resources (see Box One). Such regional assessments of wetlands in the coastal zone are only just beginning.

4.2.1.4. Other issues to consider in an ecological assessment

Generally, the aim of any wetland mitigation project should be to provide the wetland habitat and functions lost at the affected site at an equivalent or greater level. However, it must be acknowledged that many projects propose development activities in previously degraded wetlands. In these cases, the ecological assessment should also attempt to determine in a regional context, the wetland functions most appropriately provided through mitigation. In this way, the mitigation project can work towards improving the compliment of wetlands within the region. Appropriate mitigation can only be achieved by providing appropriate habitat and functions at an appropriate location. The provision of appropriate habitat and functions is built into this process by integrating the information obtained from the ecological assessment into the goals, objectives, and performance standards. However, finding an appropriate location can be a major stumbling block to maintaining locally or regionally specific wetland attributes. Although some flexibility is necessary —especially in the coastal zone— potential sites must be examined in an ecological context to ensure maximization of regional- and site-specific considerations.

Unfortunately, a widely accepted, objective process for completing an ecological assessment does not exist. In the past, procedures such as the Habitat Evaluation Procedure (HEP) and the Wetland Evaluation Technique (WET) have been used, but only with limited success and acceptance, especially in California's coastal zone⁵. This is a continuing problem and a substantial source of contention, especially on larger projects. Nevertheless, even using basic scientific procedures to objectively evaluate the habitat and functions of a wetland can go a long way toward understanding the scope and magnitude of a project's potential impacts, and the appropriate level of mitigation.

4.2.2. Goals, Objectives, and Performance Standards

The goals, objectives, and performance standards form the foundation of the mitigation plan. Each component of a mitigation plan must relate back to the goals, objectives, and performance standards either through project design or through the performance evaluation process. Ensuring this relationship occurs throughout the plan is very important, and is one way to determine if the mitigation plan is consistent and relevant.

The purpose of compensatory wetland mitigation is to replace lost or adversely impacted wetlands with wetlands having similar functions of equal or greater ecological value. Thus, the goals, objectives, and performance standards of a specific mitigation project must be based on the information derived from the ecological assessment. Goals, objectives, and performance standards developed in this manner will contain site- and region- specific attributes. Developing clear project goals with specific objectives and quantifiable performance standards is critical to evaluating the success of any mitigation project. In fact, the lack of clear goals and evaluation criteria is among the most cited reason for why project success is never fully evaluated (Eliot, 1985; Josselyn, et al., 1993; Maguire, 1985; Race, 1985).

In practice, the goals, objectives, and performance standards consist of three parts (Figure 2), which are based on information obtained from the ecological assessment. The goal or goals are stated first, and describe the overarching purpose of the mitigation project. The objectives are stated second, and describe the steps necessary to reach the goal(s). The objectives can also be used to define the major components of the mitigation plan. Third, is a description of the performance standards, which state in quantifiable terms the level and extent of the attributes necessary to reach the goals and objectives. Sustainability of the attributes should be a part of every performance standard. Each performance standard must identify: 1) the attribute to be achieved; 2) the condition or level that defines success; and 3) the period over which success must be sustained. The performance standards must be specific enough to provide for the assessment of wetland performance over time through the measurement of attributes of wetland habitat and functions.

Figure 2. Relationship Between, Goals, Objectives, and Performance Standards

Although Figure Two depicts the goals, objectives, and performance standards as separate components, they are in fact interrelated (see Box Two for an example). Ultimately, permit compliance (i.e., success in a regulatory sense) occurs when the performance level of the mitigation wetland, as determined by the performance standards for each objective, meets or exceeds the stated goals.

The development of appropriate goals, objective, and performance standards is not a simple process. Even with the information from an ecological assessment, it is often difficult to clearly articulate what the mitigation project will achieve and the criteria used to evaluate performance. The three case studies presented later in this document illustrate some of the different approaches used. Ultimately, input from the project proponent and resource and regulatory agency staff is required to develop appropriate goals, objectives, and performance standards.

4.2.3. Mitigation Attributes

The type of compensatory mitigation, its location relative to the impact site, and the mitigation ratio are three attributes that affect the design and implementation of any mitigation project.

4.2.3.1. Types of compensatory mitigation

In developing information for this document it became necessary to develop operational definitions for three types of activities commonly included in compensatory wetland mitigation plans:

• Wetland Creation: This is an activity that results in the formation of a new wetland in an upland area.

• Wetland Restoration: This is an activity that re-establishes the habitats and functions of a former wetland.

• Wetland Enhancement: This is an activity that improves the habitats and functions of an existing wetland.

The terms enhancement and restoration are often used interchangeably, and in fact a mitigation plan may include both types of activities. However, enhancement and restoration are distinct processes with different results. In the context of compensatory mitigation, wetland restoration is an activity that supports the goal of no-net-loss. After considering the direct loss of habitat and functions at the adversely impacted wetland, restoration can result in a net increase or at least no net change in both wetland function and habitat area. Wetland enhancement does not support the goal of no-net-loss because this activity focuses on improving existing wetland habitat and functions; thus, enhancement does not result in an increase in both wetland area and function and there could be a net loss after accounting for the direct losses at the adversely impacted wetland. All mitigation plans including wetland restoration and enhancement should clearly distinguish between these two activities.

When enhancement activities are proposed as part of a mitigation project it is essential to clearly determine how these activities fit into the overall project, and —more importantly— the amount of mitigation credit enhancement activities receive. This brings in the idea of partial credit, which is defined here as that portion of full compensatory mitigation credit received for an enhancement activity. Although it is beyond the scope of this document to develop a method for determining partial credit, this is a potentially contentious issue that CCC staff must remain aware of in reviewing proposed mitigation projects. The CCC staff's analysis should reflect some objective process for assigning value to a wetland habitat, its functional level, and the resident species both before and after enhancement. For example, what is the difference in value between a saltmarsh dominated by pickleweed and a saltmarsh that contains pickleweed, cord grass, and mudflat. Clearly these sorts of questions are difficult to answer and require input from both a scientific and policy perspective.

4.2.3.2. Mitigation project location

The location of a mitigation project can also affect the chances for success and the degree of direct compensation. A mitigation project located in or adjacent to the adversely impacted wetland (i.e., on-site mitigation) is generally thought to provide a better chance of directly compensating for the habitat and functions identified in the ecological assessment. On-site mitigation can make use of many of the same resources available at the adversely affected wetland (e.g., same water source, same soils, and same seed bank), while providing habitat for the same biological resources. If successful, the complement of wetland habitat remains similar on a local scale, thereby preserving local specificity. In contrast, an off-site mitigation project is located far away from the adversely impacted wetland, for example in a different watershed, and may not provide the same local resource benefits. Creating wetlands off-site can also result in the formation of inappropriate habitat, given the existing resources and surrounding landscape.

As the above discussion suggests, the distinction between on-site and off-site mitigation is most commonly based on distance: at some point, a mitigation project located away from the adversely impacted wetland is considered off-site mitigation. More appropriately, however, the distinction between on-site and off-site mitigation should be based on wetland habitat and function. Thus, the question becomes, what location offers the best chance of successfully providing the appropriate wetland habitat and functions with maximal benefit to the affected organisms and resources? To answer this question properly requires a thorough understanding of the wetland resources within the region (i.e., information from a regional assessment), and in the absence of such regional assessments resource and regulatory agencies continue to show a preference for on-site mitigation. Yet there are situations where the benefits of off-site mitigation could exceed those of on-site mitigation. For example, off-site mitigation may be appropriate in situations where established land uses clearly conflict with on-site mitigation, or where off-site mitigation offers a greater potential for a net-gain in wetland quantity and quality. Although the CCC continues to recommend on-site mitigation, staff must remain open to the idea of off-site mitigation and objectively review all mitigation proposals with the goal of maximizing the natural resource benefits.

4.2.3.3. The mitigation ratio

The mitigation ratio sets the overall size of the mitigation project, and is defined as the ratio of values gained per unit area to values lost per unit area. Although the mitigation ratio is generally expressed in terms of area (e.g., a ratio of 5 to 1 equals five mitigation acres for each acre impacted through development), the ratio calculation should be based on other factors (e.g., appropriate functions and their associated values) in addition to area. Factoring in function and value information is generally a qualitative process that relies on information from the ecological assessment.

The process for determining a final mitigation ratio is influenced by a variety of factors; however, there is no objective process for quantifying many of these factors. The mitigation ratio is affected by the type of project (i.e., creation, restoration, or enhancement), particularly when partial credit is an issue. Project location must also be considered in determining the mitigation ratio. In the absence of a regional understanding of wetland resources, mitigation plans involving off-site mitigation may require higher mitigation ratios. Other factors affect the final mitigation ratio as well. For example, the ratio can also be adjusted to account for the uncertainty of success. Projects involving complex structures or a high degree of management may reduce the chances for complete success, and therefore require higher mitigation ratios to ensure full compensation. The expected length of interim losses of functional habitat (i.e., the losses occurring between the time of adverse impacts and the time of successful mitigation) is also important in determining the appropriate mitigation ratio. A higher mitigation ratio is warranted in cases where the compensatory mitigation occurs well after the wetland losses are sustained.

Currently, the CCC determines the applicable mitigation ratio on a case-by-case basis. In an attempt to account for concerns over project location, interim losses, and reduced chances of success, the CCC has required compensatory mitigation ratios greater than 1 to 1⁷.

4.2.4. Monitoring Program

The monitoring program is another major element that must be considered during the design of a wetland mitigation project. The monitoring program is the means by which appropriate data and information are gathered to evaluate the performance of the mitigation wetland over time. The evaluation of performance, in turn, is used to determine if the project goals are being met or if remediation is necessary. In many respects, the monitoring program should use an approach similar to that of the ecological assessment and the resulting data should be directly comparable. Yet, reviews of numerous mitigation projects show the monitoring program is all too often included as an afterthought or is non-existent, resulting in subjective and uninformed determinations of success (Kentula, et al., 1992; Ischinger and Schneller–McDonald, 1988). Design and implementation of the mitigation project and the monitoring program should occur simultaneously to ensure the proper dedication of the necessary resources and effort (Josselyn and Bucholz, 1982).

A comprehensive monitoring program should include methods for assessing both structural (i.e., habitat) and functional attributes of a wetland. As Kentula, et al. (1992) note, structural features such as water levels or percent plant cover are convenient to measure; however, these features are most useful when related to the functional capabilities of the wetland. Yet many structural measures, such as a single measure of plant diversity, become indicators of wetland function when monitored over time (Kentula, et al., 1992). The monitoring program should include a rationale for the types of data collected and how those data will be used. It should also be clear how the monitoring data will contribute to the evaluation of performance. This process is much more straightforward if the performance standards state in quantifiable terms, the level or extent of the attributes necessary to reach the goals and objectives.

4.2.4.1. Types of monitoring program assessments

The intensity and frequency of post-construction monitoring may vary with the project goals and objectives, the environmental significance of the project, the age of the project, and the probability of successfully achieving targeted wetland functions (Kentula, et al., 1992). In general, however, two types of assessments should be undertaken as part of any monitoring program: 1) an as-built assessment, which is completed after all construction at the mitigation site to determine if the project was built as planned; and 2) periodic assessments, which are repeated on some recurring basis. Information from these assessments is used:

• to determine if the project meets the stated goals, objectives, and performance standards (i.e., project success;

• to determine if project remediation is necessary;

• and to determine the mitigation site's level of ecological function (i.e., the sites functional equivalency relative to historic information or reference wetland sites).

The monitoring program may also include concurrent monitoring (i.e., simultaneous assessment) of both the mitigation wetland and reference wetland sites (Kentula, et al., 1992; Simenstad, et al., 1991).⁸ Concurrent monitoring of reference sites would be required if the performance standards for the mitigation site are defined relative to the level of some resource present at the reference sites. For example, the performance standards under goal one, in Box Two (page 13) state the required fish species number and density as a percentage of the values at the reference sites. In this case, the performance levels (i.e., fish species number and density) are assessed relative to the present day condition of the reference sites; thus, it is not necessary for the absolute values of the performance standards to remain constant, or continually show and increase over time. Identifying suitable reference sites and determining the number of sites required, the attributes monitored, and the monitoring frequency will vary with each case, but all decisions should be objective and rely on the best information available.

4.2.4.2. What to include in a monitoring program

It is difficult to describe a generic monitoring program. On the one hand, the attributes and processes most appropriate to monitor will vary depending on the habitats and functions of interest and the specific wetland in question. On the other hand, a variety of appropriate monitoring methodologies exist, and stating just the few protocols common to all monitoring programs may suggest that relatively little work is actually required. In addition, the size and complexity of the project, and the availability of qualified personnel can all affect the type of protocols considered appropriate. Table 1 lists many of the attributes potentially important in assessing the habitats and functions of a wetland, while Table 2 provides an example of a minimal monitoring program appropriate for a tidal wetland with open-water and marsh habitats. Ultimately, the goal of any monitoring program is to provide ecologically meaningful data for evaluating wetland performance and for early identification of needed remediation. This is not easy. Numerous decisions must be made, and some decisions may require preliminary data from the wetland in question or direct experience from a competent field ecologist. However, a sound monitoring program is vital to determining whether compensatory mitigation is ultimately successful.

Table 1. A List of the Attributes Potentially Important to Assessing Wetland Habitats and Functions⁹

Table 2. Example of a Monitoring Program for a Tidally Influenced Wetland With Open-Water and Marsh Habitats¹¹

4.2.5. Performance Evaluation

Performance evaluation is the process by which information from the monitoring program is used to evaluate the status of the mitigation wetland in relation to the performance standards. In large measure, the performance standards will dictate the type of monitoring data needed and the analyses necessary to determine the mitigation wetland's level of performance. Stating the performance standards in quantifiable terms is crucial to ensuring a comprehensive and objective evaluation process.

4.2.5.1 The evaluation process

One way to track the performance of a mitigation project is through the use of a performance evaluation process designed to answer some important questions about the mitigation site (Figure 3). Information from the monitoring program and the performance standards is used to answer the questions in sequence, and the answer determines what course of action, for example remediation or continued monitoring, is necessary. The performance evaluation is best completed by a neutral party with no vested interest in the project, but with the appropriate technical expertise to complete the required tasks. If the evaluation shows remediation is necessary, then a recommendation for an appropriate response should be included as part of the evaluation. Final authority for requiring any remedial action rests with the relevant resource and regulatory agencies. Ultimately, the aim of the performance evaluation is to ensure a successful mitigation project (see Box Three), and the mitigation plan should provide a mechanism for repeating the evaluation process until success is achieved.

Figure 3. Performance Evaluation Process

4.2.5.2. Determining the basis for evaluating wetland performance

Whether performance of a mitigation wetland is evaluated relative to reference wetlands, some predetermined standard, or a combination of the two is probably best determined on a case-by-case basis. Project-specific attributes such as the functions and habitat being mitigated for, the chances for success, and the environmental consequences of the project all affect how performance is evaluated.

Linking the performance of the mitigation site to that of appropriate reference sites is advantageous because environmental variation due to both natural forces and human activities is more accurately accounted for in the monitoring data. Such information can be used to determine the most appropriate response to changes in the mitigation wetland. For example, many southern California wetlands were subjected to heavy flooding in 1993 and 1995. If subsequent monitoring of the mitigation site showed fish abundances declined after such a flood, similar concurrent information from the reference wetlands could be used to determine how changes at the mitigation wetland compare to other wetlands in the area. This information could then be used to determine if human intervention is necessary, and if so, what type of intervention is most appropriate.

The use of reference wetlands, however, may not be appropriate in all situations. It may be difficult to identify appropriate reference sites for some functions or habitat features, given the existence of widespread and long-standing human impacts to many wetlands. In addition, depending on the function of interest, there may be large variation within a wetland, potentially requiring extensive sampling strategies to obtain the necessary information. Thus, in some situations it may be more appropriate to establish predetermined values for the performance standards. The main advantages of using predetermined values include: 1) a potential reduction in the overall amount of required monitoring, since the monitoring of reference wetlands would not occur; and 2) the expected level of performance is set in advance, potentially reducing future uncertainty and conflict. A predetermined performance standard can be absolute (e.g., 90% cover of native plant species by the fifth year), or vary with time (e.g., native plant cover must be at least 20% in year one, 40% in year two, 60% in year three, etc.). The main disadvantages of using predetermined performance standards include: 1) the expected level of performance may not be accurate. A standard set too low could result in a net loss of wetland habitat and/or resources. A standard set too high may not be achievable, resulting in a failure to reach compliance. And 2) unforeseen future events may alter the mitigation wetland rendering the performance standard inappropriate.

4.2.5.3. Performance curves: a potential tool for evaluating wetland performance

Performance curves may provide a useful analytical tool for evaluating monitoring data to determine the performance level of the mitigation wetland (Kentula, et al., 1992; Simenstad and Thom, in revision). A performance curve documents the change in a function (i.e., the performance level) of the mitigation wetland over time relative to the functional level of one or more reference wetlands (Figure 4), or some predetermined, but not necessarily absolute, level. Such curves can also be used to determine compliance (i.e., when a performance standard is reached) and to estimate functional equivalency with historic conditions or with reference wetlands.

Figure 4. Hypothetical Performance Curves¹³

Performance curves, however, are not a "cookbook" solution. Currently, little information exists on how wetland functions change over time. Thus, it is not known what the performance curves for most wetland functions look like, or the time required for various functions to match those of undisturbed wetlands. Hypothetical curves exist like the ones shown in Figure 4, but in reality, curves using real data will probably look very different. Much more information on the development of wetland functions is needed before we are able to consistently specify accurate performance standards. Nevertheless, performance curves can be an important tool for evaluating the performance level of a wetland, and it is reasonable to expect an increase in the use of performance curves.

ENDNOTES

⁵A more recent process for classifying wetlands, the hydrogeomorphic (HGM) classification is being developed through the Army Corps of Engineers Waterway Experiment Station. HGM is now being field tested in several parts of the United States and is intended to provide a foundation for ongoing efforts to develop methods for assessing the physical, chemical, and biological functions of wetlands. For more information see Brinson, 1993.

⁶Source: FWS, 1988.

⁷For specific examples of Commission required mitigation ratios see coastal development permit number 5-90-913, 5-92-408, 5-93-276, 6-86-2, 6-87-611, 6-87-667, 6-88-277, 6-88-388, 6-89-195, 6-90-219, 6-90-77.

⁸A reference wetland is defined as a wetland that exhibits some or all of the habitat and functional attributes to be mitigated for, and is located in a land use setting similar to the setting of the mitigation site.

⁹Based on information from Kentula, et al., 1992; PERL, 1990; and Zedler, Personal Communication.

¹⁰1= high priority, most needed; 2 = desirable; 3 = worthwhile.

¹¹Adapted from PERL, 1990.

¹²M = sample once during a month; B = sample biweekly through the month; o = monthly samples to omit if funds are insufficient.

¹³This figure illustrates some of the alternative trajectories of functional attributes for a mitigation wetland (lines A, B, D, and E) and a reference wetland (line C). Each data point is a mean value ( one standard error. Attributes of wetland function may: (A) progressively approach and then surpass the mean level for the reference wetland; (B) rapidly (linearly) converge to reference levels and remain stable thereafter; (D) progressively develop but stabilize at a level significantly lower than reference levels; and (E) progress very slowly before approaching reference levels. Another trajectory, in which an attribute of wetland function starts at a higher level but progressively declines to below reference levels, is not shown. Figure courtesy of C. Simenstad.

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