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

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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

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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

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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.

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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

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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,

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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


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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

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Figure 1

Evaluation process for the Wetland Evaluation Technique (WET, Adamus et al.,
1987).

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Effectiveness and opportunity are evaluated concurrently at three levels. Each
level consists of a series of questions, and successive levels build upon previous
levels to develop an increasingly detailed characterization. The level selected
depends upon available time and information, and the desired confidence in the
evaluation 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 appropriate
level in most circumstances.
Interpretation is accomplished through a series of keys; each key consists of a
series of boxes. Within each box are coded references to a question or group of
questions, 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 a
probability rating. The user proceeds through each key until a probability rating has
been assigned to each function and value for each type of evaluation. There are
social significance keys for 11 functions and values, effectiveness keys for 10
functions and values, and opportunity keys for 3 functions and values. The Habitat
Suitability Evaluations are accomplished in the same manner using answers to
questions 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 geomorphology
were studied in 1985 to evaluate WET’s ability to distinguish between similar
wetlands and to compare WET’s evaluations to collected data. At both sites, data
were available on groundwater level and surface water stage, groundwater and
surface water quality, vegetation cover and standing crop, and stream gauging. The
wetlands were assessed using WET Social Significance Levels 1 and 2, Effectiveness
and Opportunity Levels 1, 2, and 3, and Habitat Suitability.
The evaluation indicated differences in ratings between the two wetland com-
plexes and differences between the WET probability ratings and empirical data. Of

the 24 WET probability ratings, 13 were considered questionable, 4 were supported
by empirical data, and 7 were rated moderate and thus considered neutral by Dough-
erty (1989). The 13 questionable ratings centered on three issues. First, WET is
insensitive 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 hydrologic
area”) as a predictor of social significance functions and values may have artificially
applied different probability ratings for floodflow alteration and nutrient
removal/transformation to the two wetland complexes.
In the opinion of the author, WET was most accurate in instances where more
detailed data were available (e.g., groundwater measurement) to support the Effec-
tiveness and Opportunity Level 3 assessment. However, the application of WET to
this situation is limited by questions that do not appear to be well suited for
assessment 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,

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Dougherty (1989) cautions that WET should be considered as a broad-brush tool
for 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 assessment
technique to facilitate preliminary land-use planning efforts. The technique was
designed 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 critical
criteria 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 using
available 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 is
assessed relative to critical criteria (Table 3), which are used to determine whether
or not a wetland potentially provides a function and value under consideration. A
wetland is presumed effective for a function and value if the assigned criteria are
satisfied. Conversely, a wetland is presumed ineffective for a function and value if
the 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 the
number of functions and values being assessed (less than or equal to 11), and
multiplying the resultant quotient by 100. Wetland systems with percents ranging
from 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 assess-
ment was to develop a wetland resource map that would provide guidance to the
Department in the development of the Bradley Master Plan, and to facilitate future
planning 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 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 all wetland
functions and values except for aquatic diversity and abundance, recreation, and
uniqueness 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 of
Transportation, Bureau of Planning. The assessment was conducted in a relatively
short period of time and at low cost. Wetland experts with the Bureau of Planning
reviewed the assessment and found its conclusions consistent with their opinions of
site functions and values. Nevertheless, the authors caution that this technique is

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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 to
provide a framework for cost effective, scientifically responsive monitoring of
enhanced, restored, and created wetland functions and values, particularly those
associated with local, state, and federal permit activities (Kent et al., 1992). The
authors recognized that the standard for measuring success was based largely on
structural parameters related to vegetation, and that functional approaches for mon-
itoring wetland ecosystems or addressing impacts were largely nonexistent (Kusler
and Kentula, 1989). WIMCI was designed to directly assess the majority of wetland
functions, 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 for
objective assessment was lacking, were excluded. So, too, consumptive functions
and values (e.g., agriculture, forestry) inconsistent with the intended use of the index
were also excluded. The eight assessed functions and values are measured directly
and 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


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functions and values can then be averaged to produce the WIMCI. Condition index
values range from zero for a monitored wetland that does not provide any functions,
to one for a monitored wetland that functions at a level comparable to the reference
wetland. Instances in which the monitored wetland functions and values exceed that
of the reference wetland are also assigned a value of one.
As the overall WIMCI averages individual functions and values, it is compen-
satory in nature. A high function and value can offset an absent or low individual
function and value. The converse is also true. WIMCI does not allow one function
and value to be an absolute limiting factor to overall wetland condition. The
WIMCI approach is flexible in two ways. First, WIMCI can use more or less
functions than described above. Second, WIMCI can be easily modified to assign
weights to individual functions and values. The authors note that WIMCI has not
been applied in its entirety but is based upon commonly used measurement and
assessment techniques.

Hydrogeomorphic Assessment (HGM)

The HGM assessment was designed to accurately and rapidly measure the net
change in wetland function resulting from degradation and restoration (Brinson,
1995, 1996). Changes in function are measured by comparing an impacted or
degraded wetland with reference wetlands. The assessment differs from many other
evaluation techniques by measuring only functions and not values and by requiring
that functions be sustainable. A number of regional guidebooks presenting examples
of how to assess wetlands are in press, in development and testing, or being planned
(Brinson et al., 1997).
HGM first classifies wetlands into functional categories based upon the position
of the wetland in the landscape, dominant sources of water, and the flow and
fluctuation of the water. A total of seven wetland classes have been recognized:

riverine, depressional, slope, mineral soil flats, organic soil flats, estuarine fringe,
and lacustrine fringe (see Chapter 1). The classification is intended to simplify the
development and conduct of the assessment.

Table 4 Wetlands Integrated Monitoring Condition Index (WIMCI)

Functions, Values, and Measurements (Kent et al., 1992)
Function and Value Measurement

Aquatic habitat Animal species list
Flood attenuation Flood storage capacity
Groundwater recharge Recharge volume
Nutrient metabolism Total nitrogen or total phosphorus
Production export Total suspended organics
Sediment retention Total suspended solids
Toxicant retention Heavy metals, volatile organics, and petroleum
hydrocarbon analysis
Wildlife habitat Animal species list

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For a given wetland class, a series of indicators and variables are developed to
reflect the measurable properties of the wetland’s functions. Variables are either
hydrologic, representing inflow processes, or structural, representing removal pro-
cesses, and are derived from measurements and visual indicators of wetland function
(Table 5). Level of functioning is estimated by combining variables in equations.
Variables scale from zero, indicating no function, to one, indicating function equiv-
alent to a reference standard. Focal wetland functions exceeding the reference stan-
dard are also assigned a value of one. Unlike other evaluation approaches, the user
has the option of reducing the estimated value if the function is determined to be

nonsustainable.
Reference wetlands are the most critical component of the HGM assessment.
Reference standards are established based upon observations and measurements of
wetland sites of the same class. The reference wetlands are intended to be self-
sustaining and representative of the highest levels of overall performance. Reference
wetlands must be established, at a minimum, for regional subclasses in each phys-
iographic province. Because professional judgment and local knowledge are required
to select appropriate reference wetlands, assessment teams comprised of members
with complementary scientific skills are recommended. The assessment concludes
with a calculation of replacement ratios.
To demonstrate its use, Brinson et al. (1995) developed a guidebook for applying
the HGM approach for functional assessment to riverine wetlands. To develop the
guidebook, wetland sites were studied in the glaciated northeast, Gulf coastal plain,
Southwest, Rocky Mountains, Olympic Peninsula, and Puget Sound. The guidebook
is to be used by teams of individuals who adapt the information to riverine wetlands
of their physiographic region. The information in the guidebook must be modified,
calibrated, and tested to determine its effectiveness under local and regional conditions.
The guidebook identified 15 functions of riverine wetlands in 4 major categories:
hydrologic, biogeochemical, plant habitat, and animal habitat (Table 6). A total of
44 variables were identified: 14 for hydrologic functions, 16 for biogeochemical

Table 5 Hydrogeomorphic (HGM) Assessment

Functions (Brinson et al., 1995)

Hydrologic
Short-term surface water storage
Long-term surface water storage
Maintenance of high water table
Biogeochemical

Transformation, cycling of elements
Retention, removal of imported substances
Accumulation of peat
Accumulation of inorganic sediments
Habitat and food web support
Maintenance of characteristic plant communities
Maintenance of characteristic energy flow

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functions, and 27 for habitat functions. From two to nine measurements are required
to determine the value of an individual variable.
HGM limits include an inability to compare wetland functions between wetland
classes. Also, the development of a reference wetland set can require tens of thou-
sands of dollars and several months time, limiting the applicability of HGM to
relatively large or controversial projects (Magee, 1996). Criticisms of the HGM
assessment approach include poorly defined terminology (e.g., self-sustaining eco-
systems, sustainable, ecological stability), and an inability to quantify levels of
functions greater than that of reference wetlands (Hruby, 1997). Additional devel-
opment may be necessary before HGM can be widely used (Opheim, 1996).

Habitat Evaluation Procedures (HEP)

HEP was developed in response to a need to document the nonmonetary value
of fish and wildlife resources and is based upon the assumption that habitat quality
and quantity can be numerically described (U.S. Fish and Wildlife Service, 1980a).
The assessment procedure is a species-habitat approach to impact assessment. Hab-
itat quality for selected evaluation species is documented with the Habitat Suitability
Index (HSI) which is derived from an evaluation of the species’ key habitat com-
ponents. HSI values are multiplied by area and aggregated to obtain a Habitat Unit

(HU). HUs provide the basis for comparison of the relative value of different
wetlands at the same point in time, or the relative value of the same wetland at two
different points in time. The time and costs associated with a HEP analysis are highly
variable, and depend upon size of the study area, number of cover types, number of
evaluation species, and the number and types of proposed actions.

Table 6 Riverine Wetland Functions (Brinson

et al., 1995)

Hydrologic
Dynamic surface water storage
Long-term surface water storage
Energy dissipation
Subsurface storage of water
Moderation of groundwater flow or discharge
Biogeochemical
Nurtient cycling
Removal of imported elements and compounds
Retention of particulates
Organic carbon export
Plant habitat
Maintain characteristic plant communities
Maintain characteristic detrital biomass
Animal habitat
Maintain spatial structure of habitat
Maintain interspersion and connectivity
Maintain distribution and abundance of invertebrates
Maintain distribution and abundance of vertebrates


©2001 CRC Press LLC

The steps required to conduct a HEP analysis are depicted in Figure 2 (U.S. Fish
and Wildlife Service, 1980b). Study limits are defined initially. This includes defining
the study area, delineating cover types, and selecting evaluation wildlife species.
The study area should include areas where direct or indirect biological changes are
expected to occur. The level of delineation of cover types depends upon mapping
constraints and the level of detail required for the analysis. A cover type classification
applicable to the region is recommended. Evaluation wildlife species can be a single
species, a group of species, a species life stage, or a species life requisite. There are
two approaches to the selection of species: selection of species with high public
interest or economic value and selection of species providing a broad ecological
perspective of the assessment area. Examples of the latter include species sensitive
to land-use changes, keystone species, and species that represent guilds.
HUs are determined next. HUs are the product of the total area of available
habitat and the HSI. The total area of available habitat includes all areas that can
be expected to provide some support to the evaluation species. The recommended
method of describing HSI values is through the use of models which may be in
word or mathematical form. Calculating an HSI requires establishing HSI model
requirements, acquiring an HSI model, and determining HSI for available habitat.
Index values are an estimate of habitat conditions in the subject area relative to a
standard of comparison, typically optimal habitat conditions. Values range from 0.0
(no habitat) to 1.0 (optimal habitat). Ideally, HSI models produce an index with a
proven, quantified, positive relationship to carrying capacity. Model development is
described in Habitat Evaluation Procedures (U.S. Fish and Wildlife Service, 1980b).
Figure 3 is an example of an HSI. Schroeder (1982) developed a HSI model for
the yellow warbler (

Dendroica petechia


) to facilitate consideration in HEP evalua-
tions. The model is applicable to the breeding range, season, and habitat of the
species. Breeding habitat was determined to be deciduous shrubland and deciduous
scrub–shrub wetland (U.S. Fish and Wildlife Service, 1981). There are three vari-
ables that describe the suitability of breeding habitat for the yellow warbler: percent
deciduous shrub crown cover (variable 1), average height of deciduous shrub canopy
(variable 2), and percent of deciduous shrub canopy comprised of hydrophytic shrubs
(variable 3). Optimal habitat is considered to exist at shrub densities of 60 to 80
percent, shrub heights of 2 m, and 100 percent hydrophytic vegetation. Other levels
of suitability are described by the equation (variable 1

×

variable 2

×

variable 3)

1/3

.
Baseline HUs describe the existing ecological conditions which facilitate land-
use planning and alternatives analysis. Baseline HUs can be compared among areas
or to predictions of future HUs for a single area following some change in land use.
The latter application constitutes an impact assessment. Application of HEP to
impact assessments requires predictions of changes in physical, vegetative, and
chemical variables. The same HSI models must be used to determine habitat value
at all points in time.
HEP allows the incorporation of value judgments through the use of a Relative

Value Index (RVI). RVIs are applied as weighting values to the HUs calculated for
each evaluation species. Calculation of RVIs requires defining the perceived signif-
icance of RVI criteria, rating each evaluation species against each criterion, and

©2001 CRC Press LLC

transforming the perceived significance of each criterion and each evaluation species’
rating into a RVI. HUs are no longer directly related to carrying capacity after
adjustment by RVIs.
Unavoidable HU losses can be offset by the development of compensation plans
that apply specified management measures to existing habitat to effect a net increase
in HUs. Compensation may be in kind, in which the goal is to offset the HU loss
for each evaluation species. Alternatively, the compensation plan may have a goal
of equal replacement, in which HU losses may be compensated by a gain of an
equal number of total HUs, regardless of individual evaluation species’ HUs.

Figure 2

Habitat Evaluation Procedures (HEP) evaluation process (U.S. Fish and Wildlife
Service, 1980b).

©2001 CRC Press LLC

Virtual Reference Wetlands (VRW)

VRW (Kent et al., 1999) offer an alternative or supplemental approach to assess-
ing wildlife. An idealized standard, the VRW, is established by compiling a list of

Figure 3


Suitability index graphs for the yellow warbler (Schroeder, 1982).

©2001 CRC Press LLC

all wildlife species occurring in regional wetlands. Compilation can be accomplished
using field guides, agency lists, scientific publications, the gray literature, or expert
opinion. The VRW can represent wildlife of all wetland types or can be partitioned
by wetland type. Also, the VRW can represent wildlife of all seasons or any one
season. Wildlife of the focal wetland, determined by direct observation, is compared
to the VRW. The approach is applicable to assessing the success of enhancement,
restoration, and creation efforts, or establishing the relative value of a population of
wetlands as part of an alternative analysis.
The VRW approach is repeatable and, because it is based upon direct observation,
allows for evaluation of actual rather than potential function and value. The use of
an idealized standard eliminates the need to identify an appropriate reference wetland
and facilitates comparison and extrapolation to other wetlands. VRW also provide
for calculation of various metrics including relative richness, similarity, and the
proportion of upland–wetland species and habitat generalists–specialists. The met-
rics can be applied at several temporal and spatial scales. The most serious limitation
of the VRW approach is the inability to compare wildlife abundance.
Kent et al. (1999) applied the VRW approach to evaluation of wildlife in a created
wetland. The created wetland wildlife community was found to be relatively rich,
due in part to the occurrence of upland birds. The wildlife community most closely
resembled that of freshwater marshes of the region consistent with the wetland’s
physical characteristics. Habitat specialists were just as likely to occur in the wetland
as habitat generalists.

ECONOMIC VALUATION

There has been recognition in recent years that wetlands provide ecosystem

services, and that these ecosystem services can be economically valued (e.g., Thi-
bodeau and Ostro, 1981; Danielson and Leitch, 1986; Costanza et al., 1997). The
total economic value of a wetland consists of its use value and its nonuse value (see
Table 7 and Pearce and Moran, 1994). Use value represents the value arising from
the actual use of the wetland and is further divided into direct use, indirect use, and
option values. Direct use values include recreation, fishing, and forest products.
Indirect use values derive from ecosystem functions such as water quality renovation.
Option values represent an individual’s willingness to pay for the option to use a
value at a later date.

Table 7 Categories of Wetland Economic

Values (Pearce and Moran, 1994)

Total Economic Value
Use values Nonuse values

Direct use Bequest values
Indirect use Existence values
Option values

©2001 CRC Press LLC

Nonuse values, by contrast, accrue independent of on-site or off-site use of the
wetland. Somewhat more difficult to estimate, nonuse values are divided between
bequest values and existence values. Bequest values accrue to an individual from
the knowledge that others might benefit from the wetland in the future. Existence
values derive simply from the knowledge that the wetland exists, even if the indi-
vidual never sees the wetland. Nonuse value may be quite large relative to use value
(Brown, 1993) and has become increasingly accepted. For example, nonuse values

have been recognized by the Comprehensive Environmental Response, Compensa-
tion and Liability Act (CERCLA, 26 U.S.C. 4611 et seq.) and the 1990 Oil Pollution
Act (35 U.S.C. 2701 et seq.).
In practice, total economic value is almost impossible to calculate. Unlike finan-
cial analyses, which consider whether a project will be profitable for investors,
economic analyses must consider the value of a project to society as a whole. All
economic analyses rely on the accuracy of costs and an accurate prediction of the
future. In practice, many environmental costs are difficult, if not impossible, to
estimate. Existing valuation techniques can reasonably distinguish use values from
nonuse values but cannot reliably distinguish between option, bequest, and existence
values (Pearce and Moran, 1994). Economic valuation is also unlikely to accurately
account for underlying, holistic, ecosystem functions, and for intrinsic value (Pearce
and Moran, 1994; Pimm, 1997).

Economic Valuation Methodologies

Direct and indirect approaches are used to estimate the economic value of
environmental goods including wetlands (Pearce and Moran, 1994). Direct
approaches establish values directly from individuals through surveys or experiments
and can be used to determine both use and nonuse values. Indirect approaches
establish values from actual, observed market-based information. Nonuse values
cannot be determined from indirect approaches.
All of the valuation techniques have advantages and limitations that should be
understood prior to use. In general, users should select and use techniques that are
institutionally acceptable, that consider the needs of the end user(s), and that balance
costs against the level of information required (Pearce and Moran, 1994).

Direct Economic Valuation

Experiments offer the most reliable method for establishing the economic value

of a wetland. For example, to determine the recreation value of a wetland, the wetland
could be enclosed and an entrance fee charged. In practice, it is difficult to design
and establish experiments to determine the economic value of a wetland.
Individuals may be asked to rank their preferences as in the Contingent Ranking
Method. More commonly the Contingent Valuation Method (CVM) is used and
individuals are asked to state what they are willing to pay for some change in the
provision, or what they are willing to accept to forgo a change in the provision, of
a wetland function or value.

©2001 CRC Press LLC

The CVM has three parts. First, a hypothetical description of the terms under
which the function or value is to be offered is presented to the respondent. Second,
the respondent is asked questions to determine how much they value the function
or value. Respondents may be asked whether or not they want to pay for a function
or value if it costs a specified amount or how much they would be willing to pay
for the function or value. And third, relating responses to socioeconomic and demo-
graphic characteristics tests response validity. CVM willingness to pay responses
are analyzed for the frequency distribution of the responses to the valuation questions
and relationships between willingness to pay and socioeconomic variables.
The CVM is not without its shortcomings (Batie and Shabman, 1982; Diamond
and Hausman, 1994; Pearce and Moran, 1994). The quality and presentation of
information described to the respondent can have a significant effect on results. The
method inherently establishes a hypothetical market which may or may not reflect
the behavior of respondents if they had to make actual payments. Also, respondents
may not be familiar with the commodity being valued, and responses are sensitive
to the described method of payment. Arrow et al. (1993) offer guidelines which
improve the reliability of the Contingent Valuation Method.
Stevens et al. (1995) used the CVM to estimate the total value of preserving
different types of wetlands in New England. A survey was mailed to 2,510 randomly

selected New England residents. Each group was asked for their opinions about the
importance of wetlands and about rules and regulations governing wetland preser-
vation in New England. Respondents were also asked to rank four types of wetlands:

1. Wetlands that provide recreation
2. Wetlands containing rare species of plants
3. Wetlands that provide food
4. Wetlands that provide flood protection, water supply, and water pollution control

Surveyed individuals were asked one of five versions of a contingent valuation
question about the amount of sales tax they were willing to pay to prevent wetland
loss. The first version asked respondents if they would accept a sales tax of $

N

each
year for the next 5 years for their highest priority wetland type. The second version
asked for the respondents’ willingness to pay for all four types of wetland. Version
three asked about the willingness to pay to preserve wetlands containing rare species
of plants. Version four was the same as version two except less information was
provided, and version five asked about willingness to pay for wetland restoration
rather than preservation.
The survey response rate was 34 percent and 90 percent of respondents said that
wetland preservation was very important to them. Of the respondents, 48 percent
gave top priority to wetlands that provide flood protection, water supply, 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, water


©2001 CRC Press LLC

supply, and water pollution; between US$80.77 and US$96.07 for wetlands contain-
ing 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$313 million per year for
wetlands containing rare species of plants. There was no significant difference in
willingness to pay for wetland preservation compared to restoration. The majority
of respondents who would not pay were opposed to the special sales tax.
The authors concluded that a substantial economic value is associated with
wetland preservation and restoration by New England residents. Nevertheless, the
response rate, combined with the tendency for respondents to be better educated
than the average resident, may have influenced the willingness to pay amount.

Indirect Economic Valuation

Indirect valuations elicit values from observed market-based information, that
is, an individual purchases a good to which the wetland function or value can be
related (Pearce and Moran, 1994). Obtained values will be sufficient for cost–benefit
purposes. Indirect valuations can be divided into two categories: surrogate market
and conventional market.
Surrogate market techniques consider markets for private goods and services
that are related to environmental goods and services. Individuals reveal the value
they place on the environmental goods and services by the value they place on the
private goods and services. Surrogate market approaches include household produc-
tion functions and the hedonic pricing method.
Household production functions use expenditures for goods or services that are
substitutes for the environmental goods or services. The travel cost approach is

perhaps the most commonly applied household production function and uses expen-
ditures for travel to recreation sites. Money and time spent by individuals to get to
a site are used to estimate willingness to pay for a site’s functions and values. Data
requirements for the travel cost approach are extensive and include the number of
visitors to a site, the visitor’s place of origin, socioeconomic characteristics, journey
duration, direct travel expenses, and purpose of the visit (Pearce and Moran, 1994).
Nevertheless, the travel cost approach can value the demand for recreation function
and value.
Another surrogate market technique, the hedonic pricing method, estimates an
implicit price for an environmental good or service, that is, a use value, by looking
at real markets in which those goods or services are traded (Pearce and Moran,
1994). For example, house or land values are used to establish a relationship between
property prices and proximal environmental attributes. As with the travel cost
approach, data requirements are substantial and may be difficult to obtain.
Conventional market techniques use market prices, or shadow market prices, to
establish the value of an environmental good or service. Recognized are two
approaches: dose–response and replacement cost (Pearce and Moran, 1994). The
dose–response technique establishes a dose–response function by relating damage
to the environment (the response) to the cause of the damage (the dose). A monetary

©2001 CRC Press LLC

damage function is established by multiplying the dose–response function by the
price or value per unit of damage. The approach is applicable to environmental
changes that have impacts on marketable goods; for example, pollution impacts on
fisheries, forestry, and agriculture. Cost of application ranges from inexpensive to
expensive depending upon the availability of dose–response functions. The approach
is not suited to valuing nonuse benefits.
As the name implies, the replacement cost approach estimates the cost of replac-
ing or restoring a damaged environment to its original condition. Replacement costs

can be determined by observing actual spending on replacement efforts, or estimation
of the cost of replacement. Incomplete assessment of actual damage, and the practical
inability to replace all functions and values, can lead to underestimation. Conversely,
use of replacement cost to assign value may underestimate ancillary benefits of the
replacement.

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

Costanza et al. (1997) estimated the value of the world’s ecological services and
natural capital stocks to make the range of potential values more apparent, to
establish a first approximation of the relative magnitude of global ecosystem services,
to establish a framework for further analysis, and to point out those areas in need
of more research. Ecological services are defined as the “flows of materials, energy,
and information from capital stocks that combine with manufactured and human
capital services to produce human welfare.” Capital stocks are “a stock of materials
or information that exists at a point in time.” Trees, minerals, ecosystems, and the
atmosphere are examples of the latter.
Ecosystem services were grouped into 17 major categories and applied to 16
biomes. Only renewable services were considered. The unit value of ecosystem
services was estimated by synthesizing previous studies which used a variety of
methods including direct observation, contingent valuation, and replacement cost.
The areal extent of the 16 ecosystems was determined and multiplied by the unit
value of the ecosystem services to estimate the total value of the world’s ecosystem
services and natural capital. This value is estimated to be in the range of US$16–54
trillion per 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 mangroves). Assigned to freshwater wetlands

were 10 ecosystem services which had a total value of US$19,580 per hectare per
year and a total global value of US$3.2 trillion per year (Table 8). Water supply and
disturbance regulation (i.e., storm protection) were the most significant ecosystem
services of freshwater wetlands. Assigned to coastal wetlands were 6 ecosystem
services which had a total value of US$9990 per hectare per year and a total global
value of US$1.6 trillion per year. Waste treatment was the most significant ecosystem
service provided by coastal wetlands, accounting for 67 percent of the total value.

©2001 CRC Press LLC

Costanza et al. (1997) consider their estimate of the value of ecosystem services
to be a minimum estimate because of a number of uncertainties, including the
exclusion of the infrastructure value of ecosystems. Pimm (1997) agrees that the
estimate is clearly an underestimate, in part because ecosystems are exceedingly
complex and poorly understood and, therefore, cannot reasonably be replicated.
Pimm (1997) also questions the moral right to place monetary values on sustaining
the environment for future generations. Both Costanza et al. (1997) and Pimm (1997)
recognize that the value of ecosystem services will increase exponentially as they
become scarcer. Constanza et al. (1997) conclude that their (and subsequent) valu-
ation of ecosystem services will help modify systems of national accounting and
provide a basis for project appraisal.

REFERENCES

Adamus, P. R., Clairain, E. J., Smith, R. D., and Young, R. E.,

Wetland Evaluation Technique
(WET)

, Vol. II,


Methodology

, Operational Draft Department of the Army Waterways
Experiment Station, Vicksburg, MS, 1987.
Amman, A. P., Franzen, R. W., and Johnson, J. L., Method for the Evaluation of Inland
Wetlands in Connecticut, Connecticut Department of Environmental Protection, Bulletin
No. 9, 1986.
Arrow, K., Solow, R., Portney, P. R., Leamer, E. E., Radner, R., and Schuman, R., Report of
the NOAA panel on contingent valuations,

Fed. Regist.

, 58(10), 4602, 1993.
Batie, S. and Shabman, L., Estimating the economic value of wetlands: principles, methods,
and limitations,

Coastal Zone Manage. J

, 10, 255, 1982.
Brinson, M., The HGM approach explained,

Nat. Wetl. Newsl.,

November/December, 7, 1995.
Brinson, M., Assessing wetland functions using HGM,

Nat. Wetl. Newsl.,

January/February,

10, 1996.
Brinson, M. M., Hauer, F. R., Lee, L. C., Nutter, W. L., Rheinhardt, R. D., Smith, R. D., and
Whigham, D.,

A Guidebook for Application of Hydrogeomorphic Assessments to Riverine
Wetlands

, Final Report to the U.S. Army Corps of Engineers, Waterways Experiment
Station, Vicksburg, MS, 1995.

Table 8 Average Global Value of Annual Wetland Services

(Costanza et al., 1997)

1994 US$ per Hectare per Year
Services Freshwater Coastal Total

Gas regulation 265 265
Disturbance regulation 7,240 1,839 9,079
Water regulation 30 30
Water supply 7,600 7,600
Waste treatment 1,659 6,696 8,355
Habitat/refuge 439 169 608
Food production 47 466 513
Raw materials 49 162 211
Recreation 491 658 1,149
Cultural 1,761 1,761
Total 19,581 9,990 29,571