Applied Wetlands Science - Chapter 3 pps

Kent, Donald M. “Evaluating Wetland Functions and Values” Applied Wetlands Science and Technology Editor Donald M. Kent Boca Raton: CRC Press LLC,2001 ©2001 CRC Press LLC CHAPTER 3 Evaluating Wetland Functions and Values Donald M. Kent CONTENTS Functions and Values Aquatic and Wildlife Habitat Educational and Scientific Venue Elemental Transformation and Cycling Flood Flow Alteration Groundwater Recharge Particle Retention Production Export Raw Materials Recreation Soil Stabilization Evaluating Functions and Values Representative Evaluation Techniques Expert Opinion Wetland Evaluation Technique Rapid Assessment of Wetlands (RAW) Wetlands Integrated Monitoring Condition Index (WIMCI) Hydrogeomorphic Assessment (HGM) Habitat Evaluation Procedures (HEP) Virtual Reference Wetlands (VRW) Economic Valuation Economic Valuation Methodologies Direct Economic Valuation Indirect Economic Valuation ©2001 CRC Press LLC The Value of the World’s Ecosystem Services and Natural Capital References As do all ecosystems, wetlands have functions and values. Functions are pro- cesses that are inherent to a wetland. They derive from the wetland’s hydrological, geological, biological, and chemical characteristics. For example, groundwater recharge is a wetland function that occurs when water in the wetland, derived from precipitation, surface runoff, or both, infiltrates downward through permeable soils to the groundwater table. Wetland functions occur regardless of whether there are people present to benefit from these processes. Wetland values are functions that prove useful or are important to people. The aforementioned wetland functioning to recharge groundwater will possess a ground- water recharge value only if the recharged groundwater is used by local or regional populations. Values may be provided within the confines of the wetland, for example, recreation, or beyond the wetland boundaries, for example, flood protection. Another characteristic of wetland values is that they vary with time and circumstances. Again returning to the example of a groundwater recharge wetland, a downstream com- munity drawing drinking water from a surface impoundment does not view the wetland as valuable to its drinking water supply. Should the surface water supply diminish or become contaminated, and groundwater withdrawal become necessary, that wetland now takes on value. Clearly, wetland functions and values are inextricably linked. Values cannot be provided without there first being a function. Conversely, a function has no value until someone exploits that function. Recognizing the confounding nature of the relationship between wetland function and value, many functions and values have been attributed to wetlands (Amman et al., 1986; Mitsch and Gosselink, 1993; Adamus et al., 1987; Reimold, 1994; Brinson, 1995). Some of the commonly recognized functions and values of wetlands are listed in Table 1 and described briefly below. Table 1 Wetland Functions and Values Aquatic and wildlife habitat Educational and scientific venue Elemental transformation and cycling Flood flow alteration Groundwater recharge Particle retention Production export Raw materials Recreation Soil stabilization ©2001 CRC Press LLC FUNCTIONS AND VALUES Aquatic and Wildlife Habitat All wetlands, with the exception of those that have been severely degraded, provide habitat for wildlife. And wetlands with seasonal or permanent surface water support fish and other aquatic vertebrates and invertebrates. Many threatened and endangered species are associated with wetlands. The type and degree to which aquatic and wildlife habitat is provided is dependent upon local and landscape characteristics including water depth and permanence, vegetation type and cover, habitat size, and the nature of the surrounding environment (Forman and Godron, 1986; Kent, 1994). Educational and Scientific Venue Numerous public and private organizations exist for the purpose of educating people about the importance of wetlands. Educational topics include awareness, regulations and legislation, conservation and planning, and science and management (Drake and Vicario, 1994). Wetlands provide an opportunity for studying fundamen- tal biological and ecological principles including energy flow, biogeochemical cycling, population biology, and community structure. As well, wetlands are the focus of more specific studies related directly to inherent functions and values such as pollutant removal, habitat provision, and flood attenuation. Elemental Transformation and Cycling Wetlands serve as sinks, sources, or transformers of many inorganic and organic chemicals, including those of ecological and socioeconomic importance such as nitrogen and phosphorus, carbon, sulfur, iron, and manganese. Chemicals enter the wetland through hydrologic pathways such as precipitation, surface or groundwater, tidal exchange, or alternatively through biotic pathways including photosynthetic fixation of atmospheric carbon and bacterial fixation of nitrogen, respectively. Wet- lands export or lose chemicals by burying in the sediment, outflow in surface or groundwaters, denitrification, atmospheric loss of carbon dioxide, ammonia volatil- ization, or methane and sulfide release. While within the wetland, chemicals may become part of the litter, remineralized, translocated in plants, or transformed by changes in redox potential or biotic components. Flood Flow Alteration Wetlands have the potential for reducing downstream peak flows and delaying the timing of peak flows. Water from precipitation, overbank flow, overland flow, and subsurface flows may be detained in wetlands by depressions, plants, and debris, or as the result of the wetland slope. Alternatively, water may be retained in the wetland, infiltrate, and recharge surficial groundwater. The importance of wetlands ©2001 CRC Press LLC for reducing downstream flooding increases with an increase in wetland area, dis- tance the wetland is downstream, size of the flood, closeness to an upstream wetland, and the lack of other upstream storage areas (Ogawa and Male, 1983, 1986). Coastal wetlands also have the capacity to alter flood flows as well as reduce flood wave severity. In this case, salt marshes and mangrove forests absorb the energy of coastal storms, thereby protecting inland areas. Groundwater Recharge Wetlands with pervious underlying soils recharge underlying materials, ground- water, or aquifers. Recharge is thought to occur primarily around the edge of wetlands, making groundwater recharge relatively more important in smaller wet- lands. As most wetlands are thought to have impervious underlying soils, the majority of wetlands may not exhibit this function and value (Larson, 1982; Carter and Novitzki, 1988). Particle Retention Wetlands trap and retain sediments, nutrients, and toxicants, primarily through physical processes. Reduction in water velocity causes sediments, and chemicals sorbed to sediments, to settle. Dissolved elements and compounds are retained with inorganic and organic particulates after sorption, complexation, precipitation, and chelation. In contrast to chemical transformation and cycling, incoming particles are subject to long-term accumulation or permanent loss from incoming water sources through burial in the sediments or uptake by vegetation. Production Export Some wetlands, especially those with high primary productivity, export dissolved and particulate organic carbon to downslope aquatic ecosystems. Plant material and other organic matter are leached, flushed, displaced, or eroded from the wetland, providing the basis for microbial and detrital food webs. Raw Materials Wetlands are a source of plants and animals that serve as raw materials for various domestic, commercial, and industrial activities. Forested wetlands, for exam- ple, bottomland hardwoods and cypress swamps, are a source of lumber. Lower quality timber and woody shrubs are used for the production of other wood products, paper pulp, or firewood. Marsh vegetation is used for food (e.g., rice), fodder, thatch for roofs, and other commodities. Wetland wildlife, fish, and shellfish are consumed as food, and wildlife skins are used for clothing and related items. Because of the extractive nature of this function and value, the provision of raw materials is likely to have serious impacts on other wetland functions and values. Sustainable practices can minimize these impacts. ©2001 CRC Press LLC Recreation Wetlands provide passive and active recreation including fishing, hunting, bird- watching, hiking, canoeing, photography, and others. The opportunity for recreation is related to access and landscape heterogeneity. Recreation can at times be incom- patible with other functions. Soil Stabilization Vegetated wetlands have the potential for stabilizing underlying soils. Stems, trunks, and branches dissipate water energy through frictional resistance and reduce erosive forces. Roots bind soil. The dissipation of erosional forces and binding of soil affords protection to nonwetlands in coastal and in riverine areas. EVALUATING FUNCTIONS AND VALUES The white and gray literature is replete with methods for evaluating wetland functions and values. Differences among the methods are reflected in the precision, accuracy, and reliability of conclusions. Critical factors to consider when selecting or interpreting evaluation methods are whether functions and values are measured directly or implied through indicators, whether evaluated data are qualitative or quantitative, whether the evaluation was conducted off-site or on-site, and whether assumptions and limitations are clearly stated. In general, a method should be selected based upon the type and level of information desired, available labor and economic resources, and the required time scale. Several representative evaluation methods are described below. In many circum- stances, a combination of two or more of these methods, or development of an original method, may be most appropriate. Representative Evaluation Techniques Expert Opinion Expert opinion is perhaps the simplest, quickest, and least expensive technique for evaluating wetland function and value. The technique is most applicable when a functional assessment is required on short notice, when money is a limiting factor, and a precise or accurate evaluation is not essential. However, when a group of experts is convened and empirical information is available, expert opinion can represent actual function and value with fair accuracy. At its simplest, expert opinion consists of the professional judgment of an individual conversant with wetland ecological processes. Individual professional judgment should not be the entire basis for decision making when the decision can have serious consequences. More commonly, expert opinion consists of a conven- tion of experts that come together with the goal of reaching consensus. The ©2001 CRC Press LLC consensus opinion can be given more weight, and more reasonably be used in critical decision making. The two expert opinion techniques that have enjoyed widespread use are the Nominal Group Technique and the Delphi Technique (Delbecq et al., 1975). The two techniques are similar, except that the Nominal Group Technique requires face- to-face meeting(s) of participating experts, whereas the Delphi Technique is typically conducted through correspondence. The Nominal Group Technique is the quicker and more cost-effective technique if the convening experts are proximally located. Conversely, the Delphi Technique may be less costly and less time consuming for participants that interact poorly or are geographically disjunct. In general, the Delphi Technique will require more time to conduct and complete. The Delphi Technique is described to illustrate the Nominal Group and Delphi Techniques process. Delphi was the meeting site in Greece where Oracles met to discuss matters of the time and issue opinions. In modern times, the Delphi process consists of a discussion among knowledgeable individuals with the goal of reaching an agreeable conclusion (Pill, 1971). There are two assumptions fundamental to the process: 1. Expert opinion is sufficient input to decision making when absolute answers are unknown. 2. The collective decision of a group of experts will be more accurate than the professional judgment of an individual. Involved in a Delphi process are three separate groups: the decision makers, a moderator, and experts (Turoff, 1970). Decision makers initiate the process by posing a question, and then seek an individual or group to moderate the process. The moderator identifies experts, designs the initial and follow-up questionnaires, and summarizes the expert responses. The experts respond to the question posed by the decision makers and transmitted by the moderator. Generally, the experts are polled, responses are tabulated, analyzed, and returned to the experts, and the experts respond again based upon the aggregate responses. The process is repeated until a consensus is reached. The identity of the experts may remain hidden to all parties except the moderator throughout the process. Delbecq et al. (1975) indicated that the quality of Delphi responses is strongly influenced by the interest and commitment of the experts. One area in which the Delphi Technique has been applied with some success is in the development, habitat suitability curves for fish (Crance, 1985, 1987a, 1987b). Habitat suitability curves describe the relationship between a habitat variable (e.g., water temperature or bottom substrate) and the probability that a fish will use a habitat with that particular characteristic. Crance (1987b) has offered guidelines for developing habitat suitability curves, based in part upon general recommendations by Delbecq et al. (1975). The guidelines are believed to be applicable to terrestrial species as well. The number of experts is governed by the number of respondents needed to constitute a representative pooling of judgments, and the information processing capabilities of the monitor. A total of 8 to 10 experts are likely an optimal number, ©2001 CRC Press LLC although more or less may be sufficient. Crance (1987b) develops a list of 15 to 20 experts, and then prioritizes the list based upon best knowledge of the species’ habitat requirements, geographical coverage, and enthusiasm. The experts should represent a diversity of knowledge about the habitat use by the species, and overrepresentation by any single stakeholder group should be avoided. Experts are mailed an information packet that reiterates the purpose of the exercise and provides guidelines for responding. A response time of about 10 days is established. A second information packet is sent after 4 to 6 weeks which sum- marizes the results of the first round and includes the preliminary suitability index curves for each variable and life stage considered to be important, new questions, and instructions for the second round. Experts review the preliminary suitability index curves and indicate their agreement or disagreement. Disagreement with a prelimi- nary curve requires sketching of a new curve and providing explanatory comments. Responses to the second round are summarized by the monitor and returned to the experts for further review and comment. The process continues until an acceptable level of agreement is reached. A final report is generated which includes feedback to the experts, and which summarizes exercise goals, process, and results. Crance (1985) has concluded that Delphi exercises are not a replacement for empirical curve development, but provide a more updated and interactive exchange of scientific information than can be achieved with a literature search. Also, Delphi- derived curves tend to represent average values of habitat quality for a species and, therefore, will be useful only for predicting average suitability indices. Wetland Evaluation Technique The Wetland Evaluation Technique (WET, Adamus et al., 1987) was developed upon recognition that professional expertise may not always be available, and can be difficult to reproduce. WET’s objectives are to assess most recognized wetland functions and values, be applicable to a wide variety of wetland types, be rapid and reproducible, and have a sound technical basis in the scientific literature. There are 11 functions and values assessed by WET (Table 2). In addition, WET assesses the suitability of wetland habitat for 14 waterfowl species groups, 4 freshwater fish species groups, 120 species of wetland-dependent birds, 133 species of saltwater fish and invertebrates, and 90 species of freshwater fish. Adamus et al. (1987) suggest that WET can be used to compare different wet- lands, estimate impacts from wetland modification, prioritize wetlands for acquisi- tion or more detailed study, develop conditions for permits, and compare enhanced, restored, or created wetlands with reference wetlands. Geographically, WET is designed for use in the contiguous United States. Users should, at a minimum, have an undergraduate degree in biology, wildlife management, environmental science or a related discipline, or have several years of experience in one of these areas. Knowledge of the Fish and Wildlife Service classification system (Cowardin et al., 1979, see Chapter 1) and an ability to delineate wetlands are also recommended. WET evaluates functions and values in terms of social significance, effectiveness, and opportunity. Social significance assesses the value of a wetland to society due to its special designations, potential economic value, and strategic location. For ©2001 CRC Press LLC example, a wetland would have a high social significance value for groundwater recharge if it were a sole source aquifer, Class II Groundwater, or had wells, and if it were used as a source of water by a nearby population. Effectiveness assesses the capability of a wetland to perform a function owing to its physical, chemical, or biological characteristics, and opportunity assesses the opportunity for a wetland to perform a function to its level of capability. For example, wetlands with a high effectiveness and opportunity for recharging groundwater would have permeable substrata, a negative discharge differential, and no outlet or a restricted outlet. Functions and values are characterized based upon physical, chemical, or bio- logical processes and attributes. Characterization is accomplished by identifying threshold values for predictors—simple or integrated variables that directly or indi- rectly measure the physical, chemical, or biological processes and attributes of a wetland and its surroundings. Predictors are chosen for ease of measure or evaluation and vary in directness and accuracy. Threshold values for predictors are established by answering questions, and the responses to the questions are analyzed in a series of interpretation keys. The interpretation keys define the relationship between pre- dictors and functions and values based upon information found in the technical literature. Functions and values are assigned a qualitative probability rating of high, moderate, or low. The ratings are not direct estimates of the magnitude of a wetland function or value, but are an estimate of the probability that a function or value will exist or occur. In practice, WET requires three steps: preparation, question response, and inter- pretation (Figure 1). Preparation includes obtaining resources, establishing the con- text, and defining the assessment and surrounding areas. Type and level of evaluation are also determined at this time. The Social Significance Evaluation has two levels: the first level has 31 questions and can be completed in 1 to 2 hr. The second level refines the probability rating for Uniqueness/Heritage function and value, and requires several hours to several weeks to complete depending upon the availability of information. Table 2 Functions and Values Assessed by the Wetland Evaluation Technique (WET, Adams et al., 1987) Groundwater recharge Groundwater discharge Floodflow alteration Sediment stabilization Sediment/toxicant retention Nutrient removal/transformation Production export Wildlife diversity/abundance Aquatic diversity/abundance Recreation Uniqueness/heritage ©2001 CRC Press LLC Figure 1 Evaluation process for the Wetland Evaluation Technique (WET, Adamus et al., 1987). [...]... technical issues regarding the hydrogeomorphic approach to function assessment of wetlands, Wetl Bull., 14 (3) , 23, 1997 Kent, D M., Designing wetlands for wildlife, in Applied Wetlands Science and Technology, Kent, D M., Ed., Lewis Publishers, Boca Raton, FL, 1994, 2 83 Kent, D M., Reimold, R J., And Kelly, J M., Macroscale Wetlands Delineation and Assessment, Technical report to the Connecticut Department... comparison of recent contingent valuation studies, W- 133 Benefits and Cost Transfer in Resource Planning, 6th Interim report, Department of Agricultural and Applied Economics, University of Georgia, Athens, 19 93 Carter, V and Novitzki, R P., Some comments on the relation between ground water and wetlands, in The Ecology and Management of Wetlands, Vol 1, Ecology of Wetlands, Hook, D D., McKee, W H., Jr., Smith,... bibliography, Socio-Econ Plan Sci., 5, 57, 1971 Pimm, S L., The value of everything, Nature, 38 7, 231 , 1997 Reimold, R J., Wetlands functions and values, in Applied Wetlands Science and Technology, Kent, D M., Ed., Lewis Publishers, Boca Raton, FL, 1994 Schroeder, R L., Habitat Suitability Index Models: Yellow Warbler, U.S Department of the Interior, Fish and Wildlife Service FWS/OBS-82/10.27, 1982 Stevens,... wetland complexes, the majority of which were broad-leaved, deciduous forested wetlands Wetlands at the airport were assessed using RAW in the spring of 1990 The majority of the wetlands were assessed as poor value These wetlands were primarily small, isolated wetlands effective only for flood storage and groundwater recharge Two larger, contiguous wetlands were assessed as high value, effective for... year, with an average of US $33 trillion per year Wetlands were estimated to have a value of US$29,571 per hectare per year and a total value of US$4.9 trillion per year This is approximately 15 percent of total global ecosystem services For purposes of the study, the wetland biome consisted of freshwater wetlands (swamps, bogs, riparian wetlands, and floodplains) and coastal wetlands (tidal marshes and... for their opinions about the importance of wetlands and about rules and regulations governing wetland preservation in New England Respondents were also asked to rank four types of wetlands: 1 2 3 4 Wetlands Wetlands Wetlands Wetlands that provide recreation containing rare species of plants that provide food that provide flood protection, water supply, and water pollution control Surveyed individuals... and water pollution control; 38 percent gave top priority to wetlands containing rare species of plants; only 9 and 4 percent gave top priority to wetlands providing recreational opportunities and food, respectively Of the respondents, 64 percent were willing to pay to preserve wetlands The average respondent was willing to pay between US$ 73. 89 and US$80.41 per year for wetlands that provide flood protection,... between US$80.77 and US$96.07 for wetlands containing rare species of plants, and approximately US$114 to preserve all wetland types The aggregate value of New England wetlands was estimated to be between US$242 and US$261 million per year for wetlands providing flood protection, water supply, and water pollution control, and between US$264 and US $31 3 million per year for wetlands containing rare species... Sutton, P., and van den Belt, M., The value of the world’s ecosystem services and natural capital Nature, 38 7, 2 53, 1997 Cowardin, L M., Carter, V., Golet, F C., and LaRoe, E T., Classification of Wetlands and Deepwater Habitats of the United States, U.S Fish and Wildlife Service Publication FWS/OBS-79 /31 , Washington, D.C., 1979 Crance, J H., Delphi Technique Procedures Used to Develop Habitat Suitability... condition index for wetlands monitoring, in Ecological Indicators, McKenzie, D H., Hyatt, D E., and McDonald, V J., Eds., Elsevier Applied Science, London, 1992 ©2001 CRC Press LLC Kent, D M., Schwegler, B R., and Langston, M A., Virtual reference wetlands for assessing wildlife, Fla Sci., 62, 222, 1999 Kusler, J A and Kentula, M E., Eds., Wetland Creation and Restoration: The Status of the Science, U.S Environmental . Wetland Functions and Values” Applied Wetlands Science and Technology Editor Donald M. Kent Boca Raton: CRC Press LLC,2001 ©2001 CRC Press LLC CHAPTER 3 Evaluating Wetland Functions and. which were broad-leaved, deciduous forested wetlands. Wetlands at the airport were assessed using RAW in the spring of 1990. The majority of the wetlands were assessed as poor value. These wetlands. modification, prioritize wetlands for acquisi- tion or more detailed study, develop conditions for permits, and compare enhanced, restored, or created wetlands with reference wetlands. Geographically,