Applied Wetlands Science - Chapter 3 pps

Kent CONTENTS Functions and ValuesAquatic and Wildlife HabitatEducational and Scientific VenueElemental Transformation and CyclingFlood Flow Alteration Groundwater RechargeParticle Retent

Kent, Donald M “Evaluating Wetland Functions and Values”

Applied Wetlands Science and Technology

Editor Donald M Kent

Boca Raton: CRC Press LLC,2001

CHAPTER 3 Evaluating Wetland Functions and Values

Donald M Kent

CONTENTS

Functions and ValuesAquatic and Wildlife HabitatEducational and Scientific VenueElemental Transformation and CyclingFlood Flow Alteration

Groundwater RechargeParticle RetentionProduction ExportRaw MaterialsRecreationSoil StabilizationEvaluating Functions and ValuesRepresentative Evaluation Techniques

Expert OpinionWetland Evaluation TechniqueRapid 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 ValuationIndirect Economic Valuation

The Value of the World’s Ecosystem Services and Natural Capital

References

As do all ecosystems, wetlands have functions and values Functions are cesses that are inherent to a wetland They derive from the wetland’s hydrological,geological, biological, and chemical characteristics For example, groundwaterrecharge is a wetland function that occurs when water in the wetland, derived fromprecipitation, surface runoff, or both, infiltrates downward through permeable soils

pro-to the groundwater table Wetland functions occur regardless of whether there arepeople present to benefit from these processes

Wetland values are functions that prove useful or are important to people Theaforementioned wetland functioning to recharge groundwater will possess a ground-water recharge value only if the recharged groundwater is used by local or regionalpopulations Values may be provided within the confines of the wetland, for example,recreation, or beyond the wetland boundaries, for example, flood protection Anothercharacteristic of wetland values is that they vary with time and circumstances Againreturning to the example of a groundwater recharge wetland, a downstream com-munity drawing drinking water from a surface impoundment does not view thewetland as valuable to its drinking water supply Should the surface water supplydiminish or become contaminated, and groundwater withdrawal become necessary,that wetland now takes on value

Clearly, wetland functions and values are inextricably linked Values cannot beprovided without there first being a function Conversely, a function has no valueuntil someone exploits that function Recognizing the confounding nature of therelationship between wetland function and value, many functions and values havebeen attributed to wetlands (Amman et al., 1986; Mitsch and Gosselink, 1993;Adamus et al., 1987; Reimold, 1994; Brinson, 1995) Some of the commonlyrecognized functions and values of wetlands are listed in Table 1 and describedbriefly 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

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 watersupport fish and other aquatic vertebrates and invertebrates Many threatened andendangered species are associated with wetlands The type and degree to whichaquatic and wildlife habitat is provided is dependent upon local and landscapecharacteristics 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 educatingpeople 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, biogeochemicalcycling, population biology, and community structure As well, wetlands are thefocus 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 organicchemicals, including those of ecological and socioeconomic importance such asnitrogen and phosphorus, carbon, sulfur, iron, and manganese Chemicals enter thewetland through hydrologic pathways such as precipitation, surface or groundwater,tidal exchange, or alternatively through biotic pathways including photosyntheticfixation of atmospheric carbon and bacterial fixation of nitrogen, respectively Wet-lands export or lose chemicals by burying in the sediment, outflow in surface orgroundwaters, denitrification, atmospheric loss of carbon dioxide, ammonia volatil-ization, or methane and sulfide release While within the wetland, chemicals maybecome part of the litter, remineralized, translocated in plants, or transformed bychanges in redox potential or biotic components

Flood Flow Alteration

Wetlands have the potential for reducing downstream peak flows and delayingthe 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 thewetland, infiltrate, and recharge surficial groundwater The importance of wetlands

for reducing downstream flooding increases with an increase in wetland area, 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 reduceflood wave severity In this case, salt marshes and mangrove forests absorb the energy

dis-of coastal storms, thereby protecting inland areas

Groundwater Recharge

Wetlands with pervious underlying soils recharge underlying materials, water, or aquifers Recharge is thought to occur primarily around the edge ofwetlands, making groundwater recharge relatively more important in smaller wet-lands As most wetlands are thought to have impervious underlying soils, the majority

ground-of wetlands may not exhibit this function and value (Larson, 1982; Carter andNovitzki, 1988)

Particle Retention

Wetlands trap and retain sediments, nutrients, and toxicants, primarily throughphysical processes Reduction in water velocity causes sediments, and chemicalssorbed to sediments, to settle Dissolved elements and compounds are retained withinorganic and organic particulates after sorption, complexation, precipitation, andchelation In contrast to chemical transformation and cycling, incoming particles aresubject to long-term accumulation or permanent loss from incoming water sourcesthrough burial in the sediments or uptake by vegetation

Production Export

Some wetlands, especially those with high primary productivity, export dissolvedand particulate organic carbon to downslope aquatic ecosystems Plant material andother 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 forvarious domestic, commercial, and industrial activities Forested wetlands, for exam-ple, bottomland hardwoods and cypress swamps, are a source of lumber Lowerquality 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, thatchfor 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 theextractive nature of this function and value, the provision of raw materials is likely

to have serious impacts on other wetland functions and values Sustainable practicescan minimize these impacts

EVALUATING FUNCTIONS AND VALUES

The white and gray literature is replete with methods for evaluating wetlandfunctions 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 measureddirectly or implied through indicators, whether evaluated data are qualitative orquantitative, whether the evaluation was conducted off-site or on-site, and whetherassumptions and limitations are clearly stated In general, a method should beselected based upon the type and level of information desired, available labor andeconomic resources, and the required time scale

Several representative evaluation methods are described below In many stances, a combination of two or more of these methods, or development of anoriginal method, may be most appropriate

circum-Representative Evaluation Techniques

At its simplest, expert opinion consists of the professional judgment of anindividual conversant with wetland ecological processes Individual professionaljudgment should not be the entire basis for decision making when the decision canhave serious consequences More commonly, expert opinion consists of a conven-tion of experts that come together with the goal of reaching consensus The

consensus opinion can be given more weight, and more reasonably be used incritical decision making.

The two expert opinion techniques that have enjoyed widespread use are theNominal Group Technique and the Delphi Technique (Delbecq et al., 1975) Thetwo techniques are similar, except that the Nominal Group Technique requires face-to-face meeting(s) of participating experts, whereas the Delphi Technique is typicallyconducted through correspondence The Nominal Group Technique is the quickerand more cost-effective technique if the convening experts are proximally located.Conversely, the Delphi Technique may be less costly and less time consuming forparticipants that interact poorly or are geographically disjunct In general, the DelphiTechnique will require more time to conduct and complete

The Delphi Technique is described to illustrate the Nominal Group and DelphiTechniques process Delphi was the meeting site in Greece where Oracles met todiscuss matters of the time and issue opinions In modern times, the Delphi processconsists of a discussion among knowledgeable individuals with the goal of reaching

an agreeable conclusion (Pill, 1971) There are two assumptions fundamental tothe 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, amoderator, and experts (Turoff, 1970) Decision makers initiate the process by posing

a question, and then seek an individual or group to moderate the process Themoderator identifies experts, designs the initial and follow-up questionnaires, andsummarizes the expert responses The experts respond to the question posed by thedecision makers and transmitted by the moderator Generally, the experts are polled,responses are tabulated, analyzed, and returned to the experts, and the expertsrespond again based upon the aggregate responses The process is repeated until aconsensus is reached The identity of the experts may remain hidden to all partiesexcept the moderator throughout the process Delbecq et al (1975) indicated thatthe 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 ahabitat with that particular characteristic Crance (1987b) has offered guidelines fordeveloping habitat suitability curves, based in part upon general recommendations

by Delbecq et al (1975) The guidelines are believed to be applicable to terrestrialspecies as well

The number of experts is governed by the number of respondents needed toconstitute a representative pooling of judgments, and the information processingcapabilities of the monitor A total of 8 to 10 experts are likely an optimal number,

although more or less may be sufficient Crance (1987b) develops a list of 15 to 20experts, and then prioritizes the list based upon best knowledge of the species’ habitatrequirements, 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 theexercise 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 marizes the results of the first round and includes the preliminary suitability indexcurves for each variable and life stage considered to be important, new questions,and instructions for the second round Experts review the preliminary suitability indexcurves 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 theexperts for further review and comment The process continues until an acceptablelevel of agreement is reached A final report is generated which includes feedback

sum-to the experts, and which summarizes exercise goals, process, and results

Crance (1985) has concluded that Delphi exercises are not a replacement forempirical curve development, but provide a more updated and interactive exchange

of scientific information than can be achieved with a literature search Also, derived curves tend to represent average values of habitat quality for a species and,therefore, will be useful only for predicting average suitability indices

Delphi-Wetland Evaluation Technique

The Wetland Evaluation Technique (WET, Adamus et al., 1987) was developedupon recognition that professional expertise may not always be available, and can

be difficult to reproduce WET’s objectives are to assess most recognized wetlandfunctions and values, be applicable to a wide variety of wetland types, be rapid andreproducible, 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 thesuitability of wetland habitat for 14 waterfowl species groups, 4 freshwater fishspecies groups, 120 species of wetland-dependent birds, 133 species of saltwaterfish and invertebrates, and 90 species of freshwater fish

Adamus et al (1987) suggest that WET can be used to compare different 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 isdesigned for use in the contiguous United States Users should, at a minimum, have

wet-an undergraduate degree in biology, wildlife mwet-anagement, 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 (Cowardinet 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

example, a wetland would have a high social significance value for groundwaterrecharge 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 thecapability of a wetland to perform a function owing to its physical, chemical, orbiological characteristics, and opportunity assesses the opportunity for a wetland toperform a function to its level of capability For example, wetlands with a higheffectiveness and opportunity for recharging groundwater would have permeablesubstrata, 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 identifyingthreshold values for predictors—simple or integrated variables that directly or indi-rectly measure the physical, chemical, or biological processes and attributes of awetland and its surroundings Predictors are chosen for ease of measure or evaluationand 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 dictors and functions and values based upon information found in the technicalliterature 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 wetlandfunction or value, but are an estimate of the probability that a function or value willexist or occur

pre-In practice, WET requires three steps: preparation, question response, and pretation (Figure 1) Preparation includes obtaining resources, establishing the con-text, and defining the assessment and surrounding areas Type and level of evaluationare 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 levelrefines the probability rating for Uniqueness/Heritage function and value, andrequires several hours to several weeks to complete depending upon the availability

inter-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

Figure 1 Evaluation process for the Wetland Evaluation Technique (WET, Adamus et al.,

1987).

Effectiveness and opportunity are evaluated concurrently at three levels Eachlevel consists of a series of questions, and successive levels build upon previouslevels to develop an increasingly detailed characterization The level selecteddepends upon available time and information, and the desired confidence in theevaluation results Level 1 can be conducted off-site in 1 to 2 hr Level 2 requires

a site visit and 1 to 3 hr Level 3 requires a site visit and detailed physical, chemical,and biological monitoring data The second level is recommended as an appropriatelevel in most circumstances

Interpretation is accomplished through a series of keys; each key consists of aseries of boxes Within each box are coded references to a question or group ofquestions, and each coded reference is followed by a specified answer of “yes” or

“no.” A “true” or “false” arrow leads from each box to either another box or to aprobability rating The user proceeds through each key until a probability rating hasbeen assigned to each function and value for each type of evaluation There aresocial significance keys for 11 functions and values, effectiveness keys for 10functions and values, and opportunity keys for 3 functions and values The HabitatSuitability Evaluations are accomplished in the same manner using answers toquestions in Effectiveness and Opportunity Evaluations 1, 2, and 3

Dougherty (1989) evaluated the applicability of WET to high elevation wetlands

in Colorado Two subalpine wetland complexes, Cross Creek and Willliams Fork,

at similar elevations but of differing hydrologic regime, size, and geomorphologywere studied in 1985 to evaluate WET’s ability to distinguish between similarwetlands and to compare WET’s evaluations to collected data At both sites, datawere available on groundwater level and surface water stage, groundwater andsurface water quality, vegetation cover and standing crop, and stream gauging Thewetlands were assessed using WET Social Significance Levels 1 and 2, Effectivenessand Opportunity Levels 1, 2, and 3, and Habitat Suitability

The evaluation indicated differences in ratings between the two wetland plexes and differences between the WET probability ratings and empirical data Ofthe 24 WET probability ratings, 13 were considered questionable, 4 were supported

com-by empirical data, and 7 were rated moderate and thus considered neutral com-by erty (1989) The 13 questionable ratings centered on three issues First, WET isinsensitive to the degree of overbank flooding which is a major hydrologic distin-guishing characteristic of montane and subalpine wetlands in Colorado Second,WET does not consider snowmelt which drives high elevation wetland hydrology.Third, WET’s heavy reliance on locality (“a relatively small political or hydrologicarea”) as a predictor of social significance functions and values may have artificiallyapplied different probability ratings for floodflow alteration and nutrientremoval/transformation to the two wetland complexes

Dough-In the opinion of the author, WET was most accurate in instances where moredetailed data were available (e.g., groundwater measurement) to support the Effec-tiveness and Opportunity Level 3 assessment However, the application of WET tothis situation is limited by questions that do not appear to be well suited forassessment of high elevation wetlands In part, this may be attributed to the reliance

of WET on the technical literature which is sparse for this region In closing,

Dougherty (1989) cautions that WET should be considered as a broad-brush toolfor the organization of information and decision making, and not an end in itself.

Rapid Assessment of Wetlands (RAW)

Kent et al (1990) developed a macroscale wetland function and value assessmenttechnique to facilitate preliminary land-use planning efforts The technique wasdesigned to assess widely recognized wetland functions and values, provide expe-ditious field application, apply to a variety of wetland types, and to be reproducible.The function and value assessment incorporates functions and values, and criticalcriteria identified in WET (Adamus et al., 1987) and in the “Method for the Evalu-ation of Inland Wetlands in Connecticut” (Amman et al., 1986)

There are 11 functions and values, identical to those of WET, assessed usingavailable resources (e.g., U.S Geological Survey maps, soil surveys, National Wet-land Inventory maps, etc.) and one or more field visits Each function and value isassessed relative to critical criteria (Table 3), which are used to determine whether

or not a wetland potentially provides a function and value under consideration Awetland is presumed effective for a function and value if the assigned criteria aresatisfied Conversely, a wetland is presumed ineffective for a function and value ifthe assigned criteria are not satisfied The cumulative value of a wetland is deter-mined by summing the number of positive responses, dividing this sum by thenumber of functions and values being assessed (less than or equal to 11), andmultiplying the resultant quotient by 100 Wetland systems with percents rangingfrom 1 to 20 are assigned a poor value, 21 to 40 a below average value, 41 to 60

an average value, 61 to 80 a high value, and 81 to 100 a very high value

The State of Connecticut Department of Transportation, Bureau of Planning,conducted a macroscale delineation and function and value assessment of wetlands

at Bradley International Airport in 1990 The purpose of the delineation and ment was to develop a wetland resource map that would provide guidance to theDepartment in the development of the Bradley Master Plan, and to facilitate futureplanning by identifying areas requiring more detailed investigation at a later date.The area covered by the determination and assessment was approximately 405 ha(1000 acres) Identified were 18 separate wetland complexes, the majority of whichwere broad-leaved, deciduous forested wetlands

assess-Wetlands at the airport were assessed using RAW in the spring of 1990 Themajority of the wetlands were assessed as poor value These wetlands were primarilysmall, isolated wetlands effective only for flood storage and groundwater recharge.Two larger, contiguous wetlands were assessed as high value, effective for all wetlandfunctions and values except for aquatic diversity and abundance, recreation, anduniqueness and heritage Intermediate size wetlands with a hydrological connection

to other wetlands were assessed as below average and average value

RAW adequately satisfied the planning goals of the Connecticut Department ofTransportation, Bureau of Planning The assessment was conducted in a relativelyshort period of time and at low cost Wetland experts with the Bureau of Planningreviewed the assessment and found its conclusions consistent with their opinions ofsite functions and values Nevertheless, the authors caution that this technique is

applicable only to planning efforts, and that there is no scientific basis for assigning

a cumulative wetland value

Wetlands Integrated Monitoring Condition Index (WIMCI)

The Wetlands Integrated Monitoring Condition Index (WIMCI) was intended toprovide a framework for cost effective, scientifically responsive monitoring ofenhanced, restored, and created wetland functions and values, particularly thoseassociated with local, state, and federal permit activities (Kent et al., 1992) Theauthors recognized that the standard for measuring success was based largely onstructural parameters related to vegetation, and that functional approaches for mon-itoring wetland ecosystems or addressing impacts were largely nonexistent (Kuslerand Kentula, 1989) WIMCI was designed to directly assess the majority of wetlandfunctions, to be flexible, simple to use, produce repeatable results, relatively inex-pensive, and to be accomplished in a reasonable period of time

WIMCI assessed eight functions (Table 4) Values, such as uniqueness, heritage,recreation, and education, for which insufficient published literature suitable forobjective assessment was lacking, were excluded So, too, consumptive functionsand values (e.g., agriculture, forestry) inconsistent with the intended use of the indexwere also excluded The eight assessed functions and values are measured directlyand expressed as a fraction of a reference wetland function and value Individual

Table 3 Functions and Values and Assessment Criteria for the Rapid Assessment of

Wetlands (RAW, Kent et al., 1990)

Function and Value Criteria

Aquatic diversity and abundance Permanent open water; open water and vegetation

interspersion, water quality suitable for aquatic organisms

Flood flow alteration or flood storage Regulated outflow, perceived outflow less than

perceived inflow, greater than 200 acres and at least

70 percent vegetation coverage Groundwater discharge Pervious substrate, nonfringe wetlands with outlet

only Groundwater recharge Pervious substrate, permanent inlet and no outlet,

impermanent inundation Nutrient removal and transformation Sediment retention, well-vegetated, low water flow

velocity Production export Permanent outlet, high primary productivity, potential

erosive conditions, permanent or periodic high water flow velocity

Recreation Public use permitted

Sediment stabilization Potential sediment sources, reduced water inflow

velocity, well-vegetated Sediment and toxicant retention Potential sediment and toxicant source, absent or

constricted outlet, well-vegetated Uniqueness and heritage Critical habitat for threatened and endangered

species, historical or archaeological site Wildlife diversity and abundance Large and vegetatively diverse, moderate-sized

oasis, floodplain