United States Environmental

Protection Agency

Office of Water

Washington, DC 20460

EPA-822-R-02-017

March 2002

Methods for evaluating wetland condition

#7 Wetlands Classification
United States Environmental

Protection Agency

Office of Water

Washington, DC 20460

EPA-822-R-02-017

March 2002

Methods for evaluating wetland condition

#7 Wetlands Classification

Principal Contributor

U.S. Environmental Protection Agency

Naomi E. Detenbeck

Prepared jointly by:

The U.S. Environmental Protection Agency

Health and Ecological Criteria Division (Office of Science and Technology)

and

Wetlands Division (Office of Wetlands, Oceans, and Watersheds)
United States Environmental

Protection Agency

Office of Water

Washington, DC 20460

EPA-822-R-02-017

March 2002

Notice

The material in this document has been subjected to U.S. Environmental Protection Agency (EPA)

technical review and has been approved for publication as an EPA document. The information

contained herein is offered to the reader as a review of the “state of the science” concerning wetland

bioassessment and nutrient enrichment and is not intended to be prescriptive guidance or firm advice.

Mention of trade names, products or services does not convey, and should not be interpreted as

conveying official EPA approval, endorsement, or recommendation.

Appropriate Citation

U.S. EPA. 2002. Methods for Evaluating Wetland Condition: Wetlands Classification. Office of

Water, U.S. Environmental Protection Agency, Washington, DC. EPA-822-R-02-017.

This entire document can be downloaded from the following U.S. EPA websites:

http://www.epa.gov/ost/standards

http://www.epa.gov/owow/wetlands/bawwg

ii
iii

Contents

Foreword ...............................................................................................................v

List of “Methods for Evaluating Wetland

Condition” Modules...........................................................................................vi

Summary .................................................................................................................1

Purpose..................................................................................................................1

Introduction.........................................................................................................1

Goals of Classification ...................................................................................2

Existing wetland classification schemes ...................................................4

Sources of Information for Mapping

Wetland Classes ............................................................................................. 17

Empirical Classification Methods ............................................................. 19

State of the Science ....................................................................................... 20

Suggested Readings....................................................................................... 23

References ....................................................................................................... 24

Appendixes......................................................................................................... 28

Glossary ............................................................................................................ 32

List of Tables

Table 1: Comparison of Landscape and Wetland

Classification Schemes................................................................. 18

List of Figures

Figure 1: Map of Omernik Aquatic Ecoregions ........................................... 5

Figure 2: Map of Bailey Ecoregions With Coastal and

Estuarine Provinces .......................................................................... 7
iv

Figure 3: Examples of First Four Hierarchical Levels of

Ecological Units: Domain, Division, Province,

and Section .......................................................................................... 7

Figure 4: Dominant Water Sources to Wetlands ....................................... 8

Figure 5: Dominant Hydrodynamic Regimes for

Wetlands Based on Flow Pattern ................................................ 9

Figure 6: Examples of Hydrogeomorphic Wetland

Classes: A) Depressional Wetland, B) Lacustrine

Fringe, C) Tidal Fringe, D) Riverine Wetland, E)

Mineral Flats Wetland, and F) Organic Flats Wetland ..... 10

Figure 7: Interaction With Break in Slope With

Groundwater Inputs to Slope Wetlands .................................15

Figure 8: A) Cowardin Hierarchy of Habitat Types for

Estuarine Systems, B) Palustrine Systems ...............................16
v

Foreword

In 1999, the U.S. Environmental Protection Agency (EPA) began work on this series of reports entitled

Methods for Evaluating Wetland Condition. The purpose of these reports is to help States and

Tribes develop methods to evaluate (1) the overall ecological condition of wetlands using biological

assessments and (2) nutrient enrichment of wetlands, which is one of the primary stressors damaging

wetlands in many parts of the country. This information is intended to serve as a starting point for States

and Tribes to eventually establish biological and nutrient water quality criteria specifically refined for

wetland waterbodies.

This purpose was to be accomplished by providing a series of “state of the science” modules concerning

wetland bioassessment as well as the nutrient enrichment of wetlands. The individual module format

was used instead of one large publication to facilitate the addition of other reports as wetland science

progresses and wetlands are further incorporated into water quality programs. Also, this modular

approach allows EPA to revise reports without having to reprint them all. A list of the inaugural set of

20 modules can be found at the end of this section.

This series of reports is the product of a collaborative effort between EPA’s Health and Ecological

Criteria Division of the Office of Science and Technology (OST) and the Wetlands Division of the

Office of Wetlands, Oceans and Watersheds (OWOW). The reports were initiated with the support

and oversight of Thomas J. Danielson (OWOW), Amanda K. Parker and Susan K. Jackson (OST),

and seen to completion by Douglas G. Hoskins (OWOW) and Ifeyinwa F. Davis (OST). EPA relied

heavily on the input, recommendations, and energy of three panels of experts, which unfortunately have

too many members to list individually:

n Biological Assessment of Wetlands Workgroup

n New England Biological Assessment of Wetlands Workgroup

n Wetlands Nutrient Criteria Workgroup

More information about biological and nutrient criteria is available at the following EPA website:

http://www.epa.gov/ost/standards

More information about wetland biological assessments is available at the following EPA website:

http://www.epa.gov/owow/wetlands/bawwg
vi

List of “Methods for Evaluating Wetland

Condition” Modules

1 ................. Introduction to Wetland Biological Assessment

2 ................. Introduction to Wetland Nutrient Assessment

3 ................. The State of Wetland Science

4 ................. Study Design for Monitoring Wetlands

5 ................. Administrative Framework for the Implementation of a

Wetland Bioassessment Program

6 ................. Developing Metrics and Indexes of Biological Integrity

7 ................. Wetlands Classification

8 ................. Volunteers and Wetland Biomonitoring

9 ................. Developing an Invertebrate Index of Biological

Integrity for Wetlands

10............... Using Vegetation to Assess Environmental Conditions

in Wetlands

11 ............... Using Algae to Assess Environmental Conditions in

Wetlands

12 ............... Using amphibians in Bioassessments of Wetlands

13 ............... Biological Assessment Methods for Birds

14 ............... Wetland Bioassessment Case Studies

15 ............... Bioassessment Methods for Fish

16 ............... Vegetation-Based Indicators of Wetland Nutrient

Enrichment

17 ............... Land-Use Characterization for Nutrient and Sediment

Risk Assessment

18............... Biogeochemical Indicators

19 ............... Nutrient Load Estimation

20 .............. Sustainable Nutrient Loading

Module # Module Title
1

Summary

T

he ultimate goal of classification is to reduce

variation within classes to enable detection of

differences between reference and impacted condition within classes as cost-effectively as possible,

while minimizing the number of classes for which

reference conditions must be defined. There are

two different approaches to classification of aquatic

resources, one that is geographically based, and one

that is independent of geography but relies on environmental characteristics that determine aquatic

ecosystem status and vulnerability at the region-,

watershed-, or ecosystem-scale. The goal of geographically based classification schemes is to reduce variability based on spatial covariance in climate and geology, and thus topography, climax vegetation, hydrology, and soils. Geographically independent or environmentally based schemes include

those derived using watershed characteristics such

as land use and/or land cover, hydrogeomorphology, vegetation type, or some combination of these.

It is possible to combine geographically based with

hydrogeomorphic and/or habitat-based approaches. If an integrated assessment of aquatic

resources within a watershed or region is desired, it

also may be useful to consider intercomparability

of classification schemes for wetlands, lakes, and

riverine systems to promote cost-effective sampling

and ease of interpretation. In general, very few

definitive tests of alternative classification schemes

for wetlands are available with respect to describing reference condition for either nutrient criteria or

biocriteria. There are no known studies where reference conditions for both nutrient criteria and

biocriteria have been assessed simultaneously.

However, evidence from the literature suggests that

in many cases, both geographic factors (e.g., climate, geologic setting) and landscape setting

(hydrogeomorphic type) are expected to affect both

water quality and biotic communities. Thus, classification should be viewed as an iterative approach,

involving the initial choice of a framework as an

hypothesis, validation with univariate and multivariate statistical techniques, and subsequent modification to create new classes or combine existing

classes.

Purpose

T

he purpose of this module is to introduce the

scientific basis for classifying wetlands,

review some common classification schemes, and

discuss their implications for establishing biological and nutrient criteria for wetlands.

Introduction

U

se of a common scheme across State boundaries should facilitate more efficient collaborative efforts in describing reference condition for

biota or water quality and in developing indices of

biological integrity (IBIs) or other indicators (U.S.

EPA 1993, http://www.epa.gov/emap/html/

remap.html). We describe a series of national classification systems that could be used to provide a

common framework for implementation, and suggest ways in which these classification schemes

could be combined in a hierarchical fashion. Some

regional approaches are also available. Adoption

of any classification scheme must be considered an

iterative process at this point, whereby initial results

of biological or water quality sampling can be used

to test and refine a given system.

Classes that behave similarly can be combined and

apparent outliers examined for additional sources

of variability that need to be considered. At the

extreme, new classification schemes can be derived

empirically through multivariate analysis. The ultimate goal is to reduce variation within classes to

enable detection of differences between reference

and impacted condition within classes as cost-effectively as possible, while minimizing the number

of classes for which reference conditions must be

defined. For example, there might be different ex-
2

pected conditions with respect to water quality or

biological community composition for wetland

classes in the absence of human impacts, and thus

different criteria might be established for those

classes. In assessing impacts to wetlands and determining whether restored or created wetlands

were approaching a natural state, it would be most

appropriate to choose a wetland from the same or

targeted class for comparison.

Goals of

Classification

T

 he overall goal of classification is to

reduce variability within classes caused by differences in natural condition related to factors such

as geology, hydrology, and climate. The type of

classification system chosen depends on the particular scientific, management, or regulatory application of interest. For the purposes of criteria development, classification is important in refining expectations for reference condition, or the state of

wetlands in the absence of anthropogenic impacts.

Definition of Wetlands for

Classification Purposes

Wetlands have been included in the definition of

“waters of the United States” since 1975, based on

an interpretation of the Clean Water Act (CWA)

(Natural Resources Defense Council v. Callaway,

524 F.2d 79 (2nd Cir. 1975)). In order to apply

water quality standards to wetlands, wetlands must

be legally included in the scope of States’ and

Tribes’ water quality standards programs. The U.S.

Environmental Protection Agency (EPA) had requested that States’ and Tribes’ water quality standards be modified to include wetlands in the definition of “State waters” by the end of FY 1993. States

and Tribes could accomplish this by adopting a regulatory definition of “State waters” at least as inclusive as the Federal definition of “waters of the U.S.”

and adopting an appropriate definition for “wetlands” (U.S. EPA 1990a, http://www.epa.gov/

OWOW/wetlands/regs/quality.html). However, the

CWA does not preclude States and Tribes from

adopting a more expansive definition of “waters of

the State” in order to meet the goals of the Act.

Examples of different State approaches can be

found at: http://www.epa.gov/OWOW/wetlands/

partners/links.html#State Agencies.

One of the most widely accepted definitions of

wetlands was adopted by the U.S. Fish and Wildlife Service (U.S. FWS) in 1979 (Cowardin et al.

1979, http://www.nwi.fws.gov/classman. html):

Wetlands are lands transitional between terrestrial and aquatic systems where the water

table is usually at or near the surface or the

land is covered by shallow water... Wetlands

must have one or more of the following three

attributes: (1) at least periodically, the land

supports predominantly hydrophytes, (2) the

substrate is predominantly undrained hydric

soil, and (3) the substrate is nonsoil and is

saturated with water or covered by shallow

water at some time during the growing season of each year.

Reference Concept

Under guidance for biocriteria development, reference conditions “describe the characteristics of

waterbody segments least impaired by human activities and are used to define attainable biological

or habitat conditions” (U.S. EPA 1990b). At least

two general approaches have been defined to establish reference condition: the site-specific approach and the regional approach (U.S. EPA

1990b, http://www.epa.gov/ceisweb1/ceishome/

atlas/bioindicators/). The current approach to developing water quality criteria for nutrients also

emphasizes identification of expected ranges of nutrients by waterbody type and ecoregion for leastimpaired reference conditions (U.S. EPA 1998,

http://www.epa.gov/ost/standards/nutrient.html).
3

Biocriteria-related Issues

Biological criteria are narrative descriptions or numerical values that are used to describe the

reference condition of aquatic biota inhabiting waters of a designated aquatic life use. They are

developed by biologists and other natural resource specialists to directly assess the overall

condition of an aquatic community in surface waters such as streams, rivers, lakes, estuaries,

and wetlands. Biocriteria have traditionally been developed through comparison of community-level indices describing biological integrity for test sites with index ranges derived for relatively unimpacted reference sites (U.S. EPA 1990b, http://www.epa.gov/ceisweb1/ceishome/

atlas/bioindicators/ ). Reference sites are typically stratified by landscape units such as ecoregions

to reduce the variation in expected natural biological condition and to facilitate standardization

of methods. Classification or identification of covariates explaining a significant fraction of

variation at the waterbody scale also may be necessary. Finally, classification or ranking schemes

may be necessary to describe gradients of disturbance against which biocriteria can be calibrated.

Nutrient-related Issues

The Office of Water has established a procedure to implement the Clean Water Action Plan

through development of regionally-applicable nutrient criteria for each aquatic resource type

(U.S. EPA 1998b, http://www.cleanwater.gov/ ) Development of nutrient criteria through comparison to reference conditions requires that the Nation first be stratified to reduce variability in

expected condition to a reasonable range. (U.S. EPA 1998a, http://www.epa.gov/ost/standards/nutrient.html) For example, it would not be appropriate to set expectations for nutrient

levels in peatlands receiving primarily precipitation as a water source based on background

nutrient levels observed in riverine wetlands. Stratification may be necessary both at the landscape level, to take into account natural regional differences in runoff and fertility of soils influencing background levels of nutrient inputs, and at the scale of water-bodies, to take into

account differences in source water characteristics and retention time related to sensitivity of

response. As wetlands water quality criteria are developed for other constituents (e.g., clean

sediments) regionalization of criteria and related classification issues will be important for these

as well.

An alternative definition of the reference concept

has been developed for the hydrogeomorphic assessment (HGM) approach, used to describe expectations for wetland function by wetland

hydrogeomorphic type and region. Under the HGM

approach, “(r)eference wetlands are actual wetland

sites that represent the range of variability exhibited

by a regional wetland subclass as a result of natural

processes and anthropogenic disturbance. In establishing reference standards, the geographic area

from which reference wetlands are selected is the

reference domain.” For practical purposes, HGM

practitioners define reference standard as: “conditions exhibited by a group of reference wetlands

that correspond to the highest level of functioning

(highest, sustainable level of functioning) across the

suite of functions performed by the regional subclass. By definition, the highest level of functional

capacity is assigned a functional capacity index value

of 1.0.” (see Smith et al. 1995, http://

www.wes.army.mil/el/wetlands/pdfs/wrpde9.pdf).
4

Existing Wetland

Classification

Schemes

T

 here are two different approaches to

classification of aquatic resources, one that is

geographically based and one that is independent

of geography, but relies on environmental characteristics that determine aquatic ecosystem status and

vulnerability at the region, watershed, or ecosystem scale (Detenbeck et al. 2000). Ecoregions (including “nutrient ecoregions”) and ecological units

represent geographically based classification

schemes that have been developed and applied nationwide (Omernik 1987, Keys et al. 1995). The

goal of geographically based classification schemes

is to reduce variability based on spatial covariance

in climate and geology, as well as in topography,

climax vegetation, hydrology, and soils. For some

regions of the country, ecoregions have been refined to explain a finer scale of spatial variation (e.g.,

Omernik and Gallant 1988). Geographically independent or environmentally based schemes include

those derived through watershed characteristics

such as land-use and/or land-cover (Detenbeck et

al., 2000), hydrogeomorphology (Brinson 1993),

vegetation type (Grossman et al. 1998, http://

consci.tnc.org/library/pubs/class/toc1.html), or some

combination of these (Cowardin et al. 1979). Both

geographically dependent and environmentally

based schemes have been developed for single

scales, and for a nested hierarchy of scales

(Detenbeck et al. 2000).

Geographically Based

Classification Schemes

Regional classification systems were first developed specifically for the United States by land management agencies. The U.S. Department of Agriculture (USDA) has described a hierarchical system of Land Resource Regions and Major Land

Resource Areas for agricultural management based

mainly on soil characteristics (USDA SCS 1981).

Ecoregions were then refined for USDA and the

U.S. Forest Service based on a hierarchical system

in which each of several environmental variables such

as climate, landform, and potential natural vegetation were applied to define different levels of classification (Bailey 1976). Subsequently, Omernik and

colleagues developed a hierarchical nationwide

ecoregion system to classify streams, using environmental features they expected to influence aquatic

resources as opposed to terrestrial resources

(Hughes and Omernik 1981, Omernik et al. 1982).

The new ecoregion system was based on an overlay of “component maps” for land use, potential

natural vegetation, land-surface form, and soils, and

a subjective evaluation of the spatial congruence of

these factors as compared to the hierarchical approach used by Bailey, which relied only on natural

features (not land use). Omernik has produced a

national map of 76 ecoregions defined at a scale of

1:7,500,000 (Figure 1) (Omernik 1987; http://

water.usgs.gov/GIS/metadata/usgswrd/

ecoregion.html ). More detailed regional maps have

been prepared at a scale of 1:2,500,000 in which

the most “typical” areas within each ecoregion are

defined. Cowardin et al. (1979) have suggested an

amendment to Bailey’s ecoregions to include

coastal and estuarine waters (Figure 2). In practice, Omernik’s scheme has been more widely used

for classification of aquatic resources such as

streams, but few examples of applications are available for wetlands.

Finally, an attempt has been made to integrate

approaches across Federal agencies to produce

regional boundaries termed ecological units (Keys

et al. 1995). Information has been combined on

climate, landform, geomorphology, geology, soils,

hydrology, potential vegetation, and water to produce a nested series of boundaries for the eastern

United States, but different combinations of environmental parameters are emphasized at each hierarchical level of classification. This scheme was

developed to explain variation in both terrestrial and
5

Figure 1: Map of Omernik aquatic ecoregions.
6

aquatic systems and is consistent with a more comprehensive strategy to classify lotic systems down

to the level of stream reaches (Maxwell et al. 1995).

The mapped system for the eastern United States

includes classification at the following levels:

domain (n=2) > divisions (n=5) > provinces

(n=14) > sections (n=78) > subsections,

where sections are roughly equivalent to half of an

ecoregion as defined by Omernik (Figure 3). For

lotic systems, additional spatial detail can be added

by defining watersheds (at the level of landtype

associations), subwatersheds (at the level of

landtypes), valley segments, stream reaches, and

finally channel units (Maxwell et al. 1995). In reality,

all watersheds are not nested neatly within

subsections, and may cross subsection boundaries.

Some States and Tribes have chosen to refine the

spatial resolution of Omernik’s ecoregional boundaries for management of aquatic resources (e.g.,

Region 3 and Florida, http://www.dep.state.fl.us/

water/slerp/bio/sbecoreg.htm). For example, the

State of Florida has defined subecoregions for

streams based on analysis of macroinvertebrate data

from 100 reference sites. Efforts are currently under way to define ecoregions for Florida wetlands

based on variables influencing the water budget (M.

Brown, personal communication). Potential source

geographic information system (GIS) data layers to

support such an effort are described below.

Environmentally Based

Classification Systems

Hydrogeomorphic classification system(s)

Brinson (1993) has defined a hydrogeomorphic

classification system for wetlands, based on geomorphic setting, dominant water source (Figure 4),

and dominant hydrodynamics (Figure 5; http://

www.wes.army.mil/el/wetlands/regdoc.html ).

Seven classes have been described: riverine, depressional, slope, mineral soil flats, organic soil flats,

tidal fringe, and lacustrine fringe (Smith et al. 1995).

Depressional systems, as the name implies, are located in topographic depressions where surface

water can accumulate (Figure 6a). Depression wetlands can be further classified based on presence

of inlets or outlets and primary water source as

closed, open/groundwater, or open/surface water.

Lacustrine fringe wetlands are located along lake

shores where the water elevation of the lake determines the water table of the adjacent wetland. Great

Lakes coastal wetlands represent one important

region of lacustrine fringe wetlands (Figure 6b).

These coastal systems are strongly influenced by

coastal forming processes, and, as such, have been

further classified by geomorphic type through various schemes (Jaworski and Raphael 1979, and others summarized in Michigan Natural Features Inventory 1997). These geomorphic coastal positions will further influence the predominant source

of water and degree and type of energy regime (riverine vs. seiche and wave activity). Tidal fringe

wetlands occupy a similar position relative to marine coasts and estuaries and where the water level

is influenced by sea level (Figure 6c). Tidal fringe

wetlands can be broken down further based on

salinity into euhaline vs. mixohaline subclasses.

Slope wetlands occur on slopes where groundwater discharges to the land surface but typically do

not have the capacity for surface water storage (Figure 7). Riverine wetlands are found in floodplains

and riparian zones associated with stream channels

(Figure 6d). Riverine systems can be broken down

based on watershed position (and thus hydrologic

regime) into tidal, lower perennial, upper perennial,

and nonperennial subclasses. Mineral soil flats are

in areas of low topographic relief (e.g., interfluves,

relic lake bottoms, and large floodplain terraces)

with precipitation as the main source of water (Figure 6e). In contrast, the topography of organic soil

flats (e.g., peatlands) is controlled by the vertical

accretion of organic matter (Figure 6f). The HGM

classification system is being further refined to the

subclass level for different regions or states and

classes (Cole et al. 1997, http://www.wes.army.mil/

el/wetlands/regdoc.html ). In addition to the classi-
7

Figure 2: Map of Bailey ecoregions with coastal and estuarine

provinces, from Cowardin et al., 1979.

Figure 3: Examples of first four hierarchical levels of Ecological

Units: domain, division, province, and section, from US EPA

Environmental Atlas.
8

Figure 4: Dominant water sources to wetlands, from Brinson 1993.
9

Figure 5: Dominant hydrodynamic regimes for wetlands based on

flow pattern, from Brinson 1993.
10

Figure 6: Examples of hydrogeomorphic wetland classes:

a) Depressional wetland, b) Lacustrine fringe, c) Tidal fringe, d)

Riverine wetland, e) Mineral flats wetland, and f) Organic flats

wetland.

a) Depressional wetland

b) Lacustrine fringe
11

Figure 6 (continued) (c) Tidal fringe

fication factors described above, the Army Corps

of Engineers (ACE) suggests using parameters such

as the degree of connection between the wetland

and other surface waters (depressional wetlands),

salinity gradients (tidal), degree of slope or channel

gradient (slope and riverine wetlands), position in

the landscape (riverine, slope), and a scaling factor

(stream order, watershed size or floodplain width

for riverine subclasses). In some cases, existing

regional schemes could be used as the basis for

subclass definition (e.g., Stewart and Kantrud 1971,

Golet and Larson 1974, Wharton et al. 1982,

Weakley and Schafale 1991, Keough et al. 1999).

The ACE is currently defining regions for refinement of HGM classes based on factors such as climate and geology.

The HGM classification system has been applied

primarily for a functional assessment strategy termed

the HGM approach (Smith et al. 1995, http://

www.wes.army.mil/el/wetlands/pdfs/wrpde9.pdf ).

However, the same environmental parameters that

influence wetland functions also determine water

regime and background water quality, which in turn

drive wetland habitat structure and community composition and the timing of biotic events. Thus, the

HGM classification system can serve as a basis for

partitioning variability in reference trophic status and

biological condition, as well as defining temporal

strategies for sampling.

Habitat-based classification systems

Wetland habitat types are described very simply

but coarsely by the Circular 39 definitions, ranging

from temporarily flooded systems to ponds (Shaw

and Fredine 1956) (see Appendix A-2). A more

refined hierarchical classification system is available

based on vegetation associations; one system developed by the Nature Conservancy for terrestrial

vegetation (including some wetland types) has been

adopted as a standard for Federal agencies

(Grossman et al. 1998, http://consci.tnc.org/library/

pubs/class/toc1.html ). Vegetation associations have

been used to classify Great Lakes coastal wetlands

within coastal geomorphic type (Michigan Natural

Features Inventory 1997).

Cowardin classification system

The U.S. Fish and Wildlife Service (FWS) classification system (Cowardin et al. 1979) was developed as a basis for identifying, classifying, and map-
12

Figure 6 (continued) (d) Riverine wetland

ping wetlands, other special aquatic sites, and

deepwater aquatic habitats, and has since been established by both Federal and some State agencies

as the official system for wetland inventory and classification. The Cowardin system combines a number of approaches incorporating position, hydrologic regime and habitat (vegetative) type (Figure

8a,b; http://www.nwi.fws.gov/classman.html).

Wetlands are categorized first by landscape position (tidal, riverine, lacustrine, and palustrine), then

by cover type (e.g., open water, submerged aquatic

bed, persistent emergent vegetation, shrub wetlands,

and forested wetlands), and then by hydrologic regime (ranging from saturated or temporarily-flooded

to permanently flooded). Modifiers can then be

added for different salinity or acidity classes, soil

type (organic vs mineral), or disturbance activities

(impoundment, beaver activity, etc.). Thus, the

Cowardin system includes a mixture of geographically-based factors, proximal forcing functions (hydrologic regime, acidity), anthropogenic disturbance

regimes, and vegetative outcomes. In practice, the

Cowardin system can be aggregated by combination of HGM type and predominant vegetation cover

if digital coverages are available (Ernst et al. 1995).
13

Figure 6 (continued) (e) Mineral flats wetland

Comparison of Environmentally

Based Classification Systems

The Anderson Level 2 land-cover classification

system, used in classifying cover from satellite imagery or aerial photo interpretation, can be described as a combination of Cowardin classes (Appendix A-1) (Anderson et al. 1976). Anderson’s

land-cover classification system has been merged

with a modification of Cowardin’s system for freshwater (Great Lakes) and marine coastal systems as

part of NOAA’s Coastal Change Analysis Program

(C-CAP; NOAA 1995, http://www.csc.noaa.

gov ). Comparisons of Cowardin’s classification system with other earlier methods can be found in

Cowardin et al. (1979; http://www.nwrc.gov/

diglib.html) (see also Appendix A-2).

If an integrated assessment of aquatic resources

within a watershed or region is desired, it also may

be useful to consider intercomparability of classification schemes for wetlands, lakes, and riverine

systems to promote cost-effective sampling and ease

of interpretation. The HGM approach could intergrade readily with a finer level of classification for

lake type because lentic systems are separated out

as lacustrine fringe or depressional wetlands based

on lake or pond size and influence of water level on

the adjacent wetland. Lacustrine classification systems for water quality have included geography (climate + bedrock characteristics, Gorham et al. 1983)

or hydrologic setting (Winter 1977, Eilers et al.

1983) as factors for categorization. For Great

Lakes coastal wetlands, McKee et al. (1992) suggest a modification of Cowardin’s system, incorporating landscape position (system), depth zone

(littoral vs. limnetic subsystems), vegetative or substrate cover (class and subclass), and modifiers of

ecoregions, water level regimes, fish community

structure, geomorphic structure, and human modification. In contrast, the Michigan Natural Features Inventory (1997) categorizes Great Lakes

coastal wetlands by Great Lake, then by nine unique

geomorphic types within lakes, then by vegetative

association.
14

Figure 6 (continued) (f) Organic flats wetland
15

Figure 7: Interaction with break in slope with groundwater inputs

to slope wetlands, from Brinson 1993.
16

Figure 8: b) palustrine systems, from Cowardin et al. 1979.

Figure 8: a) Cowardin hierarchy of habitat types for

estuarine systems.
17

For lotic systems, Brinson et al. (1995) describes

an approach to further classify riverine classes into

subclasses based on watershed position and stream

size/permanence. This strategy is consistent with

current monitoring efforts to develop stream IBIs,

which typically use stream order as a surrogate for

watershed size in explaining additional background

variation in IBI scores (U.S. EPA 1996). A more

detailed classification of stream reach types, based

on hydrogeomorphic character, is described by

Rosgen (1996). This classification scheme has been

predominantly applied to assessments of channel

stability and restoration options, and not to development of criteria. The Bureau of Land Management has described a cross-walk between riparian

and wetland classification and description procedures (Gephardt et al. 1990); see http://

www.rwrp.umt.edu/Montana.html for a regional

application.

Combinations of Geographic and

Environmentally Based

Approaches

It is possible to combine geographically based and

hydrogeomorphic and/or habitat-based approaches. For example, a scheme could be defined that nests Cowardin (Cowardin et al. 1979)

vegetative cover class within HGM class within

ecoregion. Maxwell et al. (1995) have defined a

scheme for linking geographically based units based

on geoclimatic setting (domains => divisions =>

provinces => sections => subsections) to watersheds and subwatersheds (roughly equivalent to

landtype associations), and thus to riverine systems

composed of valley segments, stream reaches, and

channel units, or to lacustrine systems composed of

lakes, lake depth zones, and lake sites/habitat types.

Maxwell et al. (1995) also define a series of fundamental hydrogeomorphic criteria for classifying

wetlands based on Brinson (1993) and Winter

(1992), including physiography (landscape position), water source, hydrodynamics, and climate.

The first three are similar to the HGM classification

system, whereas moisture regimes and soil temperature regimes are generally consistent at the province level (see summary tables in Keys et al. 1995).

Finer scale variation in landforms is captured at the

level of sections and below, which in turn will determine the dominance of different hydrogeomorphic

classes of wetlands and associated surface waters

(lakes and rivers).

Characteristics and relative advantages and disadvantages of the different classification systems are

summarized in Table 1.

Sources of

Information for

Mapping Wetland

Classes

I

n order to select wetlands for sampling,

whether in a targeted, random, or randomstratified design, it is necessary to have a record of

wetland locations to choose from, preferably

categorized by the classification system of interest.

For some but not all portions of the country,

wetlands have been mapped from aerial

photography through the National Wetlands

Inventory (NWI) system maintained by the U.S.

Fish and Wildlife Service. In other cases, individual

States have developed inventories, or researchers

have developed lists of restricted types wetlands

within a given region, e.g., Great Lakes coastal

wetlands (Herdendorf et al. 1981).

In order to sample these mapped wetland areas

in a random fashion such that the results are

representative for all wetlands, all wetland areas,

or wetlands of a specified type within a region, it is

necessary to have a list of the wetland population,
18

preferably with areas attached. A GIS allows one

to automatically produce a list of all wetland

polygons or all wetland polygons by type within a

specified region. Sources of digital information for

mapping and/or classifying wetlands in a GIS are

presented in Appendix B. In areas for which digital

NWI maps do not yet exist, potential wetland areas

can be mapped using GIS tools to predict relative

wetness (e.g., Phillips 1990). It should be noted

that where hydrology has been significantly altered,

e.g., through ditching, tiling, or construction of urban

stormwater systems, areas of potential wetlands will

have been removed already. Similarly, although

there are no current maps of wetlands by

hydrogeomorphic class, these could be derived

through GIS techniques using a combination of

wetland coverages, hydrography (adjacency to large

lakes and rivers), and digital elevation models to

derive landforms (mineral and organic soil flats) and/

or landscape position (slope and depressional

wetlands; see http://www.geog.le.ac.uk/jwo/

research/LandSerf/index.html for free terrain

analysis software, and example applications of terrain

analysis for identifying landforms at: http://

www.undersys.com/caseGW.html , http://

www.ncgia.ucsb.edu/conf/SANTA_FE_CDROM/sf_papers/fels_john/fels_and_matson.html).

Classification

scheme

Scale Hierarchical? Levels of strata Advantages Disadvantages Potential links with other

schemes

Bailey=s ecoregions Nationwide Yes

Domains

Divisions

Provinces

Sections

Only natural attributes

included

Digital maps

Terrestrial basis

Untested for wetlands

No hydrology

Could form first strata for any of the

schemes below ecological units

Omernik ecoregions Nationwide No Ecoregions

Subecoregions Digital maps

Combines land use with natural

attributes

Untested for most wetlands

No hydrology

Could form first strata for any of the

schemes below ecological units

Ecological units

(Maxwell et al. 1995) Nationwide Yes

Domain Divisions

Provinces

Sections

Subsections

Digital maps

Greater number of strata and

units than for ecoregions

Untested for wetlands

Could form first strata for any of the

schemes below ecological units

Ties to classification schemes already

defined within hydrogeomorphic types

U.S. ACE

hydrogeomorphic

Classes

Nationwide at class

level; regionalized

at subclass level

Yes - limited Class

Subclass Specific for wetlands Subclasses not comparable acrossdifferent regions

Intermediate strata between geographic

and habitat-scale

Rosgen channel types Nationwide Yes Level I

Level II

Captures differences in

hydrologic regime for

riverine wetlands

More focused on instream channel

form than riparian characteristics

Riverine only

Not mapped

Intermediate strata between hydrogeomorphic type and habitat-scale

Anderson land-cover

classes Nationwide Yes

Level I

Level II

Level III

Common basis for landuse/land-cover mapping Not functionally based Cross-walk with NWI system possible

Circular 39 classes Nationwide No Class Popular recognition

Mixture of criteria used to

distinguish classes

Not mapped

Strata below geographic but contains

mixture of hydrogeomorphic type and

habitat type

National Wetland

Inventory Nationwide Yes

System

Subsystem

Class

Subclass

Hydrologic modifier

Other modifiers

Digital maps available

for much of Nation

(but smallest wetlands

omitted)

Inconsistencies in mapping water

quality modifiers

Limited consideration of

hydrogeomorphic type

Strata below geographic

Hydrogeomorphic class could be

improved by link with HGM system

Vegetation

associations International Yes

System

Formation class

Formation subclass

Formation group

Formation subgroup

Formation alliance

Association

Consistency across

terrestrial and aquatic

systems

Not functionally based

No digital maps

Taxa specific

Could be used as lowest level within

other schemes

Table 1: Comparison of Landscape and Wetland

Classification Schemes
19

Empirical

Classification

Methods

C

lassification should be viewed as an

iterative approach, involving the initial choice

of a framework as a hypothesis, validation with

univariate and multivariate statistical techniques, and

subsequent modification to create new classes or

combine existing classes. Best professional judgment can be used to generate a hypothetical set of

classes, using techniques such as the Delphi approach to gain consensus (Linstone and Turoff

1975). The Delphi approach is a process to extract the collective intelligence of a group of experts

who may have a wide range of backgrounds, expertise, and opinions. Responses to the Delphi process, either via interviews or questionnaires, are

anonymous, and must be summarized by a third

party and redistributed back to the group of experts for reconsideration until a consensus is reached.

The process can be time-intensive, requiring up to

four rounds of questioning to achieve consensus (or

the closest approximation possible). The process is

appropriate when input is needed from a range of

experts, frequent group meetings are not feasible

because of time or cost, or face-to-face communications may be hindered by the strength of disagreements and/or by the personalities of participants.

To produce a more objective framework, it is

possible to sample a suite of reference wetlands

randomly, and then classify sites based on physical,

chemical, and/or biological characteristics after the

fact through parametric techniques such as cluster

analysis, discriminant function analysis, detrended

canonical correlation analysis (DCCA), and/or nonparametric techniques such as nonmetric dimensional scaling (NMDS). Cluster analysis is an exploratory technique that groups similar entities, e.g.,

by community composition, in a hierarchical structure. Discriminant function analysis can be used to

objectively define those attributes of groups responsible for intergroup differences. Detrended canonical correlation analysis is a parametric multivariate technique for relating multiple explanatory

variables such as site characteristics to multiple response variables such as species abundances, or

metrics within an index of biological integrity. It

corrects for the “arch” effect of regular canonical

correlation analysis (CCA) that results from the

unimodal distribution of species along environmental gradients. NMDS is a nonparametric technique

(i.e., does not rely on the normal distribution of underlying data) that can be used to order sites along

gradients based on species composition differences,

then independently determine which environmental

variables significantly covary with community gradients. Although these techniques can be used in

an exploratory fashion, they can also be applied

with a second set of data to confirm an initial classification scheme:

Option 1:

CHOOSE CLASSES => RANDOMLY

SAMPLE => TEST DATA TO CONFIRM

GROUPINGS

Option 2:

RANDOMLY SAMPLE FULL POPULATION

=> DERIVE CLASSES EMPIRICALLY

FROM SUBSET 1 => TEST VALIDITY OF

CLASSES WITH SUBSET 2.

Numerous examples of the application of empirical classification schemes for other aquatic ecosystem types can be found in the September 2000

issue of the Journal of the North American

Benthological Society (vol. 19, issue 3). Multivariate analysis techniques are available in common

statistical packages such as SAS (SAS Institute

1979), SPSS (Nie et al. 1975), and BMDP (Dixon

1981). In addition, more specialized software exists that is specifically geared towards the analysis

of biological community data, including CANOCO

(ter Braak and Šmilauer 1998), PC-ORD (MJM
20

Software Design 2000), TWIN-SPAN (Mohler

1991), and others (see http://www.okstate.edu/

artsci/botany/ordinate/software.htm for partial

listing).

State of the

Sciences

V

ery few definitive tests of classification

systems for wetlands monitoring have been

completed, although a number of monitoring strategies have been implemented based on preselected

strata. Monitoring efforts to develop or assess biological criteria have generally used a combination

of geographic region and hydrogeomorphic class

or subclass (Appendix C). The ability of geographic

or hydrogeomorphic classes to discriminate among

biological community types can be tested a priori

through multivariate analysis. Cole and colleagues

(1997) have measured significant differences in hydrologic attributes among riparian wetlands of different HGM subclasses in Pennsylvania, which are

expected to control vegetation type. Subsequent

work on macroinvertebrate communities found similarity among sites within the same HGM subclass.

However, there were important microhabitat differences within HGM subclasses, e.g., between soil

and stream habitats in headwater floodplains, Habitats in different HGM subclasses but with similar

hydroperiods (ephemeral pools in riparian depressions and saturated soils in slope wetlands) were

nearly 50% similar in community composition.

Overall, soil organic matter and site wetness showed

strong relationships with invertebrate community

composition and could probably be used as indices

of similarity across sites (Bennett 1999). Researchers with the Michigan Natural Features Inventory

have examined vegetation associations among HGM

subclasses of coastal wetlands within different Great

Lakes using TWINSPAN, a cluster analysis package (Michigan Natural Features Inventory 1997).

Associations were found to differ by climate regime (N vs. S, roughly at the province level), soil

pH (related to bedrock type), connectivity to the

lake, and degree of human disturbance. Apfelbeck

(1999) classified Montana wetlands by

hydrogeomorphic subclass within ecoregion for

development of IBIs based on diatoms and

macroinvertebrate communities. Multivariate analysis of these communities showed good agreement

overall with preselected classes, although some

classes were indistinguishable for diatoms (riparian, open lakes, closed basins), whereas others had

to be further subdivided based on extremes of water chemistry/source water type (saline, closed basin-alkaline, closed basin-recharge vs. closed basin-surface water) or water permanence (ephemeral).

Analysis of vegetative associations has been used

to derive empirical classifications based on factors

such as landscape position, water source, climate,

bedrock, and sediment hydraulic conductivity

(Weakley and Schafale 1991, Nicholson 1995,

Halsey et al. 1997, Michigan Natural Features Inventory 1997). Only one case of classification

based on wetland macroinvertebrate composition

was found. For Australian wetlands, wetland classes

grouped by macroinvertebrate communities were

distinguished by water chemistry extremes (low pH,

high salinity), degree of nutrient enrichment, and

wetland color (Growns et al. 1992).

In some cases, e.g., northern peatlands, the classification criteria that are derived on the basis of

vegetation associations are less powerful in discriminating among nutrient regimes (e.g., Nicholson

1995); this may be particularly true where variation

in vegetation type is related to differences in major

ion chemistry and pH. However, controls may differ regionally. For southern pocosins, short and tall

pocosins differ in seasonal hydrology but not soil

chemistry, whereas pocosins and swamp forest differ strongly in soil nutrients (Bridgham and

Richardson 1993). For some potential indicators

of nutrient status such as vegetation N:P ratios, indicator thresholds will be consistent across species

(Koerselman and Meuleman 1996), whereas oth-
21

ers (tissue nutrient concentrations) vary across functional plant groupings with different life history strategies, indicating potential differences in sensitivity

to eutrophication (McJannet et al. 1995).

Sensitivity to nutrient loading (as evidenced by

differences in nutrient removal efficiency) may also

be related to differences in hydroperiod among

wetlands. Wetland mesocosms exposed to pulse

discharges had higher nutrient removal rates than

those exposed to continuous flow regimes

(Busnardo et al. 1992). Mineralization rates of carbon, nitrogen, and phosphorus differ significantly

among soils from northern Minnesota wetlands, related to an ombrotrophic to minerotrophic gradient

(i.e., degree of groundwater influence) and aeration status. The physical degree of decomposition

of organic matter serves as an integrating variable

that can be used to predict carbon, nitrogen, and

phosphorus mineralization rates (Bridgham et al.

1998).

In general, very few definitive tests of alternative

classification schemes for wetlands are available with

respect to describing reference condition for either

nutrient criteria or biocriteria. There are no known

studies where reference conditions for both nutrient criteria and biocriteria have been assessed simultaneously. However, evidence from the literature suggests that in many cases, both geographic

factors (e.g., climate, geologic setting) and landscape setting (hydrogeomorphic type) are expected

to affect both water quality and biotic communities.

A hypothetical example of how geographic factors,

landscape setting, and habitat type could be taken

into account in establishing a sampling design is presented below for the Prairie Pothole Region.

Hypothetical Case Study:

Prairie Pothole Region

The following example illustrates some of the considerations necessary in designing a classification

strategy for a given region. The resulting classification could be used for a variety of purposes, e.g.,

stratification of populations for describing ecological condition, choice of reference wetlands against

which to compare impacted or restored sites in local assessments, or derivation of nutrient or biological criteria by wetland class. As this example

illustrates, the strategy employed for a given region

could easily incorporate elements of several different classification schemes. For example, a combination of ecoregions, hydrogeomorphic wetland

classes, Rosgen channel types or water permanence

(NWI hydrology modifier), and NWI cover system/class is recommended. In this case, a different

set of strata is recommended for different

hydrogeomorphic types. Finally, behavior of different wetland classes can vary depending on the

period of the wet-dry cycle, so that differences in

reference condition should be described over time.

In the Prairie Pothole Region, the main

hydrogeomorphic wetland types vary by ecoregion

because of the influence of glacial history on the

distribution of landforms. For example, the Glaciated Plains ecoregions contain predominantly depressional wetlands that are differentiated from one

another by hydroperiod related to position in the

landscape and in the groundwater flow path. Wetlands high in the landscape typically are fed by snowmelt or direct precipitation, are groundwater recharge sites, and have hydrology that is temporary

or seasonal in nature. Temporary wetlands will typically have a wet meadow and emergent vegetation

zone, whereas seasonal wetlands may have some

shallow standing water as well as emergent vegetation and wet meadow zones. Wetlands further down

the landscape gradient will have a longer

hydroperiod and receive more groundwater discharge. Semipermanent wetlands will have the three

habitat zones described above, while permanent

wetlands will be saline due to groundwater inputs

and high evapotranspiration rates and have very little

or no emergent vegetation along the shore (with very

low diversity).
22

Macroinvertebrate community structure will be

influenced by both hydroperiod and vegetative structure. Predator taxa (both large-bodied invertebrates

and tiger salamander larvae) will be more dominant

in systems with longer hydroperiods (e.g., semipermanent or permanent wetlands) and should have

an influence on lower trophic level structure as well.

Waterfowl use also differs among wetland basins

with different hydroperiods, although many waterfowl will use a variety of wetland types over the

course of the season.

Nutrients in the water column, particularly phosphorus, will differ between wet and dry years and

between vegetative zones. During the wet cycle

anoxia may develop, but open-water zones will

experience some diurnal fluctuations in dissolved

oxygen, with the net result that phosphorus released

to the water column is tied up with iron that oxidizes as it diffuses from the sediments. Heavily vegetated zones tend to become anoxic throughout the

water column and remain stagnant throughout the

diurnal cycle. Phosphorus could also be more available in shallower systems with abundant vegetation

because dissolved organic carbon is higher and may

serve to keep phosphate-iron-humic complexes in

solution. Thus, wetlands may switch from nitrogen

limitation during low to average rainfall years to

phosphorus limitation during wet years. Thus, reference trophic status will be a combined function of

water permanence and vegetative cover, both of

which influence redox conditions and nutrient cycling.

A reasonable sampling design for wetlands in the

Prairie Pothole Region for both water quality and

biological communities would be to first stratify by

ecoregion into Northwestern Glaciated Plains,

Northern Glaciated Plains, and Red River Valley to

take into account differences in landform (and thus

wetland density) and the east-to-west gradient in

precipitation:evapotranspiration ratio. It is possible

that reference condition would be similar across the

two glaciated plains ecoregions and that the greatest amount of variation would be explained by differences in hydroperiod among wetlands; this could

be assessed after sampling was complete. Within

the Prairie Pothole Region, there are two predominant hydrogeomorphic wetland classes, depressional wetlands and riverine wetlands. Within the

HGM class of depressional wetlands, wetland basins could be stratified according to hydroperiod

(based on NWI hydrologic modifier), e.g., temporary vs. seasonal vs. semipermanent vs. permanent.

This could be done in an automated fashion using

NWI maps by selecting basins based on the polygon within the basin, with a hydrologic modifier

denoting the longest hydroperiod. It is possible that

reference condition might be similar enough between

temporary and seasonal wetlands, or between seasonal and semipermanent wetlands, so that these

hydrologic types could be combined, but it is also

likely that the degree of difference would depend

on the status of the wet-dry cycle, so these differences should be examined empirically over a wetdry cycle before combining types. For depressional

basins, it is likely that variance in reference condition would be minimized if sampling were further

stratified (or restricted) by cover system/class

(palustrine open water vs. palustrine emergent), and

within the palustrine emergent class by the presence or absence of standing water (shallow emergent vegetation zone vs. wet meadow zone). The

latter strategy would allow potentially useful comparisons to be made across hydrologic types within

vegetative class/zone.

Within riverine systems of the Prairie Pothole Region, wetlands can be divided into three NWI subsystems: Lower Perennial (with aquatic bed, emergent vegetation, and unconsolidated shore subclasses), Upper Perennial (aquatic bed and unconsolidated shore), and Intermittent (streambed only).

Reference condition and responses of vegetation in

Lower and Upper Perennial subclasses to hydrologic impacts such as dams and withdrawals for ir-
23

rigation can be expected to differ among channel

types. For example, braided and meandering systems respond differently to climate change and hydrologic disturbance (Johnson 1998); thus main

Rosgen channel type could be used as an intermediate strata between NWI system and NWI subclass.

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hydrotopographic relationships. Wetlands 15: 119-133.

Nie NH, Hull CH, Jenkins JG, Steinbrenner K, Bent DH.

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Omernik JM. 1987. Ecoregions of the conterminous

United States. Ann Assoc Am Geogr 77:118-125.

Omernik JM, Gallant AL. 1988. Ecoregions of the upper

Midwest states. U.S. Environmental Protection

Agency. Environmental Research Laboratory,

Corvallis, OR. EPA/600/3-88/037.

Omernik JM, Shirazi MA, Hughes RM. 1982. A synoptic

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1981. Univ. of Maine, Orono, ME. Society of American

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Phillips JD. 1990. Saturation-based model of relative

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26:333-342.

Rosgen DL. 1996. Applied river morphology. Wildland

Hydrology, Pargosa Springs, CO.

SAS Institute, Inc. 1979. SAS User’s Guide, 1979 Edition.

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States. U.S. Fish and Wildlife Service, Circ. 39.

Smith RD, Ammann A, Bartoldus C, Brinson MM. 1995.

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ponds and lakes in the glaciated prairie region. U.S.

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USDA SCS. 1981. Land resource regions and major land

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assessment program. EPA/625/R-93/012. September

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Canada: 127-148.
28

Type Anderson

et al. 1976

Cowardin

et al. 1979

2. Aquatic Cover

 1. Palustrine 61x P

 1. Open water (< 8ha) POW

 2. Aquatic bed 613 PAB

 3. Emergent 616 PEM

 4. Scrub/Shrub 617 PSS

 1. Mainly Evergreen 6182 PFO2,3,4,7

 2. Mainly Deciduous 6181 PFO1,6

 3. Mixed -- PFO#/#

 5. Forested 618 PFO

 1. Mainly Evergreen 6182 PFO2,3,4,7

 2. Mainly Deciduous 6181 PFO1,6

 3. Mixed -- PFO#/#

2. Lacustrine (> 8ha) 6xx L

 1. Open water LOW

 1. Limnetic 62x L1

 1. Aquatic bed 623 L1AB

 2. Unconsol=d bottom 622 L1UB

 2. Littoral 63x L2

 1. Aquatic bed 633 L2AB

 2. Emergent 636 L2EM

 3. Unconsolidated bottom/shore 632/635 L2UB/US

3. Riverine* 65x, 66x, 67x R

 1. Open water 650/660 ROW

 2. Aquatic bed 6x3 RxAB

 3. Emergent 6x6 RxEM

 4. Unconsolidated bottom 6x2 RxUB/US

* Riverine includes all headwater streams and mainstem rivers, with an associated narrow band of wetland.

4. Estuarine 68x, 69x E

 1. Open water 68x, 69x EOW

 1. Subtidal 68x E1

 2. Intertidal 69x E2

 2. Aquatic bed 683, 691 ExAB

 3. Emergent 696 ExEM

 4. Scrub/shrub 697 ExSS

 5. Unconsolidated bottom 682, 695 ExUB/US

5. Marine 70x M

 1. Open water MOW

 1. Subtidal M1

 2. Intertidal M2

 2. Aquatic bed MxAB

 3. Rocky shore M2RS

 4. Unconsolidated bottom/shore MxUB/US

Appendix A-1. Cross-walk between Anderson and Cowardin

classification schemes per Robert Brooks (Pennsylvania State

University). Coding consistent with Anderson et al. 1976, and

Cowardin et al. 1979.
29

Circular 39

wetland class

Cowardin Classification System

Classes Water Regimes Water

Chemistry

Type l-Seasonally flooded basins

or flats

Emergent Wetland

Forested Wetland

Temporarily Flooded

Intermittently Flooded

Fresh

Mixosaline

Type 2-Inland fresh meadows Emergent Wetland Saturated Fresh

Mixosaline

Type 3-Inland shallow fresh

marshes Emergent Wetland Semipermanently FloodedSeasonally Flooded

Fresh

Mixosaline

Type 4-Inland deep fresh

marshes

Emergent Wetland

Aquatic Bed

Permanently Flooded

Intermittently Exposed

Semipermanently Flooded

Fresh

Mixosaline

Type 5 - Inland open fresh

water

Aquatic Bed

Unconsolidated Bottom

Permanently Flooded

Intermittently exposed

Fresh

Mixosaline

Type 6 - Shrub swamps Scrub-shrub Wetland All Nontidal Regimes except

Permanently Flooded Fresh

Type 7- Wooded swamps Forested Wetland All Nontidal Regimes except

Permanently Flooded Fresh

Type 8 - Bogs

Scrub-shrub

WetlandForested

WetlandMoss-lichen

Wetland

Saturated Fresh (acid only)

Type 9 - Inland saline flats Unconsolidated Shore

Seasonally flooded

Temporarily flooded

Intermittently Flooded

Eusaline

Hypersaline

Type 10 - Inland saline marshes Emergent Wetland Semipermanently Flooded

Seasonally Flooded Eusaline

Type 11 - Inland open saline

water

Unconsolidated Bottom Permanently Flooded

Intermittently Exposed Eusaline

Type 12 - Coastal shallow fresh

marshes Emergent Wetland

Regularly Flooded

Irregularly Flooded

Semipermanently Flooded - tidal

Mixosaline

Fresh

Type 13 - Coastal deep fresh

marshes Emergent Wetland Regularly Flooded

Semipermanently Flooded - tidal

Mixosaline

Fresh

Type 14 -Coastal open fresh

water

Aquatic Bed

Unconsolidated Bottom

Subtidal

Permanently flooded tidal

Mixosaline

Fresh

Type 15 - Coastal salt flats Unconsolidated Shore Regularly Flooded

Irregularly Flooded

Hyperhaline

Euhaline

Type 16 - Coastal salt meadows Emergent Wetland Irregularly Flooded Euhaline

Mixohaline

Type 17 - Irregularly flooded

salt marshes Emergent Wetland Irregularly Flooded EuhalineMixohaline

Type 18 - Regularly flooded salt

marshes Emergent Wetland Regularly Flooded EuhalineMixohaline

Type 19 - Sounds and bays

Unconsolidated

BottomAquatic

BedUnconsolidated Shore

Subtidal

Irregularly Exposed

Regularly Flooded

Irregularly Flooded

Euhaline

Mixohaline

Type 20 - Mangrove swamps Scrub-shrub

WetlandForested Wetland

Irregularly Exposed

Regularly Flooded

Irregularly Flooded

Hyperhaline

Euhaline

MixohalineFresh

Appendix A-2: Cross-walk between Circular 39 wetland types (Shaw

and Fredine 1959) and Cowardin classification system, adapted from

Cowardin et al. 1979
30

Category Source Web site

Wetland and hydrography coverages

Cowardin et al. (1979)

classification National Wetland Inventory http://www.nwi.fws.gov/

Wisconsin Wetland Inventory http://www.dnr.state.wi.us/org/at/et/geo/guide_2e

/app_g/custodia/wwi_1.htm

Minnesota modified NWI

(contains Circ. 39 classes)

http://lucy.lmic.state.mn.us/metadata/nwi.html

Ohio Wetland Inventory http://www.dnr.state.oh.us/odnr/relm/resanalysis/

owidoc.html

S. California Coastal Wetlands

Inventory

http://ceres.ca.gov/wetlands/geo_info/so_cal.html

Ferren et al., 1996

Great Lakes coastal wetlands Herdendorf et al., 1981 N/A

Hydrography (1:100,000) USGS - National Hydrography

Dataset (NHD) http://nhd.usgs.gov/

General land-cover (including wetlands)

Aerial photos SCS county offices

Aerial photos USGS digital orthophotoquads

(DOQs) www.terraserver.com

Satellite imagery MultiResolution Landscape

Characterization (MRLC)

http://edcwww.cr.usgs.gov/programs/lccp/

natllandcover.html

GAP habitat cover types http://www.gap.uidaho.edu/gap/

Natural Heritage programs Individual States

Unclassified satellite imagery USGS http://earthexplorer.usgs.gov

Geographic regions

Ecoregions EPA (Omernik 1987) http://water.usgs.gov/GIS/metadata/usgswrd/

ecoregion.html

Ecological Units USFS (Keys et al 1995)

Hydrologic Units USGS HUCs http://water.usgs.gov/GIS/huc.html

Watershed boundaries Individual States/NRCS http://www.ftw.nrcs.usda.gov/HUC/huc_

download.html

Historic or potential wetland coverage

Soils STATSGO http://water.usgs.gov/lookup/getspatial?muidhttp:/

/water.usgs.gov/lookup/getspatial?ussoils

County soil surveys -

SSURGO http://www.ftw.nrcs.usda.gov/ssur_data.html

Surficial geology USGSState geological surveys http://water.usgs.gov/lookup/getspatial?ofr99-77

_geol75m

Climate NOAA http://water.usgs.gov/lookup/getspatial?climate_

divhttp://www.ocs.orst.edu/prism/prism_new.html

Digital elevation models

(DEMs)

USGS National Elevation

Database (NED) http://edcnts12.cr.usgs.gov/ned

Appendix B. Sources of GIS coverages and imagery for mapping

and classifying wetlands
31

Appendix C. Case studies applying wetland classification schemes for

indicator development or status assessment

a

Headwater wetlands, riparian wetlands, open lake wetlands, closed basin wetlands.

b

Diatom assemblages indistinguishable for riparian, open lakes, and closed basin systems; New classes identified based on water

chemistry and water permanence- ephemeral, saline, closed basin-recharge, closed basin-surface water, closed basin-alkaline.

cMWCP 1997, Ecological Classification System for Minnesota.

d

Defined by combination of landscape position (depression, floodplain, littoral zone, sedge meadows + wet prairies), associated river

size, and associated lake water chemistry (calcareous vs. noncalcareous).

Study (location) Wetland type Classification

Criteria

Success

Cole et al., 1997 (PA) Riparian wetlands in PA HGM subclasses Sign. differences in hydrological attributes

among subclasses

Gernes, 1999 (MN) Riparian wetlands in St.

Croix R. Basin HGM subclasses Not yet validated

Michigan Natural

Features Inventory 1997

(Great Lakes)

Great Lakes coastal

wetlands Great LakeHGM subclasses

Veg. associations distinguished through

TWINSPAN by climate regime (N v. S), soil

pH, connectivity to lake, and human

disturbance

Apfelbeck, 1999 (MT)

All wetland types w

standing water in at least

one season

Ecoregion

Hydrogeomorphic subclassa

TWINSPAN, DCCA on diatoms and

macroinvertebrates showed good agreement

overall

Fennessey et al.

(OH)http://www.epa.gov/owow/wetlands/bawwg/case/oh1.html

Riparian wetlands

Ecoregions

Hydrogeomorphic classes

Watersheds

No definitive comparisons

Galatowitsch et al.,

2000 (MN)

Depressional, riparian,

littoral, and wet

meadows

Ecoregion sections

Geomorphic class

No comparisons made across ecoregions or

classes

Wilcox et al., 2000 (WI,

MI)

Great Lakes coastal

wetlands

Great Lake

Hydrogeomorphic subclass No test of alternate classification schemes

Detenbeck, 1994 (MN) All wetland types Hydrogeomorphic subclass

Sign. differences in nutrient levels

demonstrated by water depth, closed vs.

open basins, confirmed by change following

disturbance

a

b

c

d
32

Glossary

Ecoregion A geographic unit derived through

comparison of climate, climax vegetation, land-use,

and soils maps. Several different classification

schemes have been developed, including those by

Omernik 1997 and Bailey 1976.

Emergent vegetation “Erect, rooted herbaceous

angiosperms that may be temporarily to permanently

flooded at the base but do not tolerate prolonged

inundation of the entire plant; e.g., bulrushes

(Scirpus spp.), saltmarsh cordgrass” (Cowardin et

al. 1979).

Environmentally based classification In this

chapter, an environmentally based classification

scheme does not rely on geographically based similarities, but classifies units based on their attributes

(e.g., watershed land-cover classes) independent

of geographic adjacency.

Estuarine System “Deepwater tidal habitats and

adjacent tidal wetlands that are usually semienclosed

by land but have open, partly obstructed, or sporadic access to the open ocean, and in which ocean

water is at least occasionally diluted by freshwater

runoff from the land.” (Cowardin et al. 1979) The

Coastal Zone Management Act of 1972 includes

estuarine-type coastal wetlands in the Great Lakes

in this definition, but Cowardin’s system of classification does not.

Euhaline Systems with salinity of 30.0-40 ppt,

derived primarily from ocean salts.

Floodplain “The lowland that borders a stream

or river, usually dry but subject to flooding.”

(NDWP Water Words Dictionary, http://

www.state.nv.us/cnr/ndwp/dict-1/waterwds.htm )

Fringe wetlands Wetlands that occur along or

near the edge of a large body of water (oceanic or

large lake) such that the water surface elevation of

the wetland is influenced by tides and seiche activity of the adjacent water body.

Anderson’s classification system A hierarchical classification system for land-use/land-cover

derived from remote sensing imagery developed by

the U.S. Geological Survey (Anderson et al. 1976).

Channel gradient The slope of the main channel

of a stream, typically expressed in change in elevation (feet) per mile.

Channel units “Subdivisions of a stream reach

that represent specific habitat and micro-habitat units

that are quite uniform in their morphologic and hydraulic properties” (Maxwell et al. 1995)

Classification The process of assigning units to

categories by similarity of attributes, generally with

a purpose of reducing variation within classes.

Cluster analysis An exploratory multivariate statistical technique that groups similar entities in an

hierarchical structure.

Delphi approach A means to record best professional judgments through a consensus-building

approach.

Depressional wetland A hydrogeomorphic wetland type located in topographic depressions where

surface water can accumulate.

Detrended canonical correlation analysis A

multivariate technique for relating multiple explanatory variables to multiple response variables (e.g.

species abundances).

Digital elevation models A grid-based geo-referenced representation of relative elevation across

a landscape in electronic form.

Discriminant function analysis A multivariate

statistical technique that allows one to determine

what combination of explanatory variables best predicts the separation among classes of observations.

Ecological units Mapped units that are delineated based on similarity in climate, landform, geomorphology, geology, soils, hydrology, potential vegetation, and water.
33

Functional assessment A process for estimating the functions or processes occurring in a wetland such as nutrient cycling, food chain support,

and water retention.

Geographic information system (GIS) A computerized information system that can input, store,

manipulate, analyze, and display geographically referenced data to support decision-making processes.

(NDWP Water Words Dictionary)

Geographically based classification An approach for delineating units of land based on similarity of adjacent lands with respect to attributes

such as climate, natural potential vegetation, soils,

and landforms.

Geomorphology The origins and changing structure and form of the earth’s land surfaces

Hydraulic conductivity The rate at which water

can move through an aquifer or other permeable

medium (NDWP Water Words Dictionary)

Hydrodynamics Branch of science that deals with

the dynamics of fluids, especially incompressible fluids, in motion (NDWP Water Words Dictionary)

Hydrogeomorphic Land form characterized by

a specific origin, geomorphic setting, water source,

and hydrodynamic (NDWP Water Words Dictionary)

Hydrogeomorphic Assessment Approach A

process of evaluating wetland functions by comparing site profiles with those of reference wetlands

in a similar hydrogeomorphic class.

Hydrography Description and mapping of oceans,

lakes, and rivers. (NDWP Water Words Dictionary)

Interfluve An area of relatively unchannelized

upland between adjacent streams flowing in approximately the same direction.

Lacustrine “Includes wetlands and deepwater

habitats with all of the following characteristics: (1)

situated in a topographic depression or a dammed

river channel; (2) lacking trees, persistent emergents,

emergent mosses or lichens with greater than 30%

areal coverage; and (3) total area exceeds 8 ha (20

acres). Similar wetland and deepwater habitats

totaling less than 8 ha are also included in the Lacustrine System if an active wave-formed or bedrock

shoreline feature makes up all or part of the boundary, or if the water depth in the deepest part of the

basin exceeds 2 m (6.6 feet) at low water...may be

tidal or nontidal, but ocean-derived salinity is always less than 0.5%” (Cowardin et al. 1979).

Landform A discernible natural landscape that

exists as a result of wind, water or geological activity, such as a plateau, plain, basin, mountain, etc.

(NDWP Water Words Dictionary)

Lentic Characterized by standing water, e.g.,

ponds and lakes.

Limnetic The open water of a body of fresh water.

Littoral Region along the shore of a non-flowing

body of water.

Lotic Characterized by flowing water, e.g., streams

and rivers.

Mesosaline Waters with salinity of 5 to 18%,

due to land-derived salts.

Mineral soil flats Level wetland landform with

predominantly mineral soils

Mineralization The process of breaking down

organic matter to its inorganic constituents

Minerotrophic Receiving water inputs from

groundwater, and thus higher in salt content (major

ions) and pH than ombrotrophic systems.

Mixohaline Water with salinity of 0.5 to 30%,

due to ocean salts.

Multivariate Type of statistics that relates one or

more independent (explanatory) variables with multiple dependent (response) variables.

Nonmetric dimensional scaling A nonparametric statistical technique for indirect ordination, e.g.,

ordering a series of observations along a gradient
34

based on similarity/differences in community composition independent of any potential explanatory

variables. Vectors related to potential explanatory

variables can be overlaid on NMDS plots to ascertain potential environmental relationships with

community gradients.

Nonparametric Referring to a type of statistical

approach that does not rely on the assumption that

data are distributed according to a normal distribution.

Nutrient ecoregions Level II ecoregions defined

by Omernik according to expected similarity in attributes affecting nutrient supply ( http://

www.epa.gov/OST/standards/ecomap.html )

Ombrotrophic Receiving water inputs predominantly from precipitation rather than groundwater.

Organic soil flats Wetland landforms that are

level, expansive, and comprised of predominantly

organic soil.

Palustrine “Nontidal wetlands dominated by trees,

shrubs, persistent emergents, emergent mosses or

lichens, and all such wetlands that occur in tidal areas where salinity due to ocean-derived salts is below 0.5%. It also includes wetlands lacking such

vegetation, but with all of the following four characteristics: (1) area less than 8 ha (20 acres); (2) active wave-formed or bedrock shoreline features

lacking; (3) water depth in the deepest part of basin less than 2 m at low water; and (4) salinity due

to ocean-derived salts less than 0.5%” (Cowardin

et al. 1979).

Peatlands “A type of wetland in which organic

matter is produced faster than it is decomposed,

resulting in the accumulation of partially decomposed vegetative material called Peat. In some mires

peat never accumulates to the point where plants

lose contact with water moving through mineral soil.

Such mires, dominated by grasslike sedges, are

called Fens. In other mires peat becomes so thick

that the surface vegetation is insulated from mineral

soil. These plants depend on precipitation for both

water and nutrients. Such mires, dominated by acidforming sphagnum moss, are called Bogs.” (NDWP

Water Words Dictionary)

Persistent emergent vegetation Emergent hydrophytes (water-loving plants) that generally remain standing until the beginning of the next growing season, such as cattails or bulrushes.

Physiography Physical geography

Pocosin Evergreen shrub bog, found on Atlantic

coastal plain.

Random-stratified A type of sampling in which

the population is first subdivided into predefined

classes (strata) based on perceived similarities, and

then subsamples are selected randomly (each with

an equal chance of selection) from within each class.

Reference wetlands Under the Hydrogeomorphic Assessment approach, “(r)eference wetlands are actual wetland sites that represent the range

of variability exhibited by a regional wetland subclass as a result of natural processes and anthropogenic disturbance.” (Smith et al. 1995)

Reference condition Under the EPA’s Biocriteria

program, wetland reference condition is defined as

the status of wetland sites either unaltered or leastimpaired by anthropogenic disturbance.

Reference domain Under the Hydrogeomorphic

Assessment approach, the geographic area from

which reference wetlands are selected (Smith et al.

1995)

Riparian “Pertaining to the banks of a river, stream,

waterway, or other, typically, flowing body of water as well as to plant and animal communities along

such bodies of water. This term is also commonly

used for other bodies of water, e.g., ponds, lakes,

etc., although Littoral is the more precise term for

such stationary bodies of water.” (NDWP Water

Words Dictionary)

Riverine System “Includes all wetlands and

deepwater habitats contained within a channel, with

two exceptions: (1) wetlands dominated by trees,
35

shrubs, persistent emergents, emergent mosses, or

lichens, and (2) habitats with water containing

ocean-derived salts in excess of 0.5%.” (Cowardin

et al. 1979)

Riverine wetland A hydrogeomorphic class of

wetlands found in floodplains and riparian zones

associated with stream or river channels.

Site potential “The highest sustainable functional

capacity that can be achieved in a reasonable period of time by a wetland, given disturbance history, land use, or other ecosystem and landscape

scale factors that influence function.” (See http://

www.wes.army.mil/el/wetlands/pdfs/wrpde9.pdf )

Slope wetland A wetland typically formed at a

break in slope where groundwater discharges to

the surface. Typically there is no standing water.

Stratification The process of separating a population into classes prior to sampling.

Stream reaches A length of channel which is

uniform in its discharge depth, area, and slope

(NDWP Water Words Dictionary)

Stream order A measure of stream size. First

order streams have no tributaries, while secondorder streams can only be formed by the union of

two first order streams and so on.

Submerged aquatic bed “The Class Aquatic Bed

includes wetlands and deepwater habitats dominated by plants that grow principally on or below

the surface of the water for most of the growing

season in most years.” (Cowardin et al. 1979)

Terrace “An old alluvial plain, ordinarily flat or

undulating, bordering a river, lake, or the sea. Stream

terraces are frequently called second bottoms, as

contrasted to flood plains, and are seldom subject

to overflow... Also, a Berm or discontinuous segments of a berm, in a valley at some height above

the Flood Plain, representing a former abandoned

flood plain of the stream.” (NDWP Water Words

Dictionary)

Trophic status Degree of nutrient enrichment of

a water body.

Univariate Type of statistical analysis involving a

single dependent (response) variable.

Valley segments “Valley segments stratify the

stream network into major functional components

that define broad similarities in fluvial processes,

sediment transport regimes, and riparian interactions.” (Maxwell et al. 1995)

Waters of the United States Waters of the United

States include:

a. All waters that are currently used, were used in

the past, or may be susceptible to use in interstate

or foreign commerce, including all waters that are

subject to the ebb and flow of the tide;

b. All interstate waters, including interstate wetlands;

c. All other waters such as interstate lakes, rivers,

streams (including intermittent streams), mudflats,

sandflats, wetlands, sloughs, prairie potholes, wet

meadows, playa lakes, or natural ponds the use,

degradation, or destruction of which would affect

or could affect interstate or foreign commerce including any such waters:

1 That are or could be used by interstate or

foreign travelers for recreational or other

purposes;

2 From which fish or shellfish are or could be

taken and sold in interstate or foreign commerce; or

3 That are used or could be used for industrial

purposes by industries in interstate commerce;

d. All impoundments of waters otherwise defined

as waters of the United States under this definition;

e. Tributaries of waters identified in paragraphs (a)

through (d) of this definition;

f. The territorial sea; and

g. Wetlands adjacent to waters (other than waters

that are themselves wetlands) identified in paragraphs

(a) through (f) of this definition.
36

Wetland(s) (1) Those areas that are inundated or

saturated by surface or groundwater at a frequency

and duration sufficient to support, and that under

normal circumstances do support, a prevalence of

vegetation typically adapted for life in saturated soil

conditions [EPA, 40 C.F.R.§ 230.3 (t) / USACE,

33 C.F.R. § 328.3 (b)]. (2) Wetlands are lands

transitional between terrestrial and aquatic systems

where the water table is usually at or near the surface or the land is covered by shallow water. For

the purposes of this classification, wetlands must

have one or more of the following three attributes:

(a) at least periodically, the land supports predominantly hydrophytes, (b) the substrate is predominantly undrained hydric soil, and (c) the substrate is

nonsoil and is saturated with water or covered by

shallow water at some time during the growing season of each year (Cowardin et al. 1979). (3) The

term “wetland,” except when such term is part of

the term “converted wetland,” means land that (a)

has a predominance of hydric soils, (b) is inundated

or saturated by surface or ground water at a frequency and duration sufficient to support a prevalence of hydrophytic vegetation typically adapted

for life in saturated soil conditions, and (c) under

normal circumstances does support a prevalence

of such vegetation. For purposes of this Act and

any other Act, this term shall not include lands in

Alaska identified as having a high potential for agricultural development which have a predominance

of permafrost soils [Food Security Act, 16 U.S.C.

801(a)(16)].

Wetland functions Physical, chemical, or biological processes inherent to wetlands. Functions may

or may not be related to wetland “services” or benefits to society.