Wetlands Research Program Technical Report WRP-DE-11

A Guidebook for Application of Hydrogeomorphic

Assessments to Riverine Wetlands

by Mark M. Brinson, Richard D. Rheinhardt, F. Richard Hauer,

Lyndon C. Lee, Wade L. Nutter, R. Daniel Smith, Dennis Whigham

December 1995 – Operational Draft

Approved For Public Release; Distribution Is Unlimited

US Army Corps

of Engineers

Waterways Experiment

Station




v

Contents

Preface ........................................................... vii

Conversion Factors, Non-SI to SI Units of Measurement ................... ix

1—Introduction ..................................................... 1

Riverine Wetlands Defined ......................................... 1

Purpose of the Guidebook .......................................... 5

Documentation of Functions for the Riverine Wetland Class ............... 8

Definition of function ........................................... 9

Discussion of function and rationale ............................... 9

Description of variables and functions .............................. 9

Documentation of functions ..................................... 14

Field form ................................................... 14

2—Documentation of Riverine Wetland Functions ........................ 15

Dynamic Surface Water Storage .................................... 15

Long-Term Surface Water Storage .................................. 24

Energy Dissipation ............................................... 28

Subsurface Storage of Water ....................................... 35

Moderation of Groundwater Flow or Discharge ........................ 38

Nutrient Cycling ................................................. 42

Removal of Imported Elements and Compounds ....................... 46

Retention of Particulates .......................................... 55

Organic Carbon Export ........................................... 62

Maintain Characteristic Plant Community ............................. 68

Maintain Characteristic Detrital Biomass ............................. 73

Maintain Spatial Structure of Habitat ................................ 79

Maintain Interspersion and Connectivity .............................. 85

Maintain Distribution and Abundance of Invertebrates .................. 91

Maintain Distribution and Abundance of Vertebrates .................... 96

References ....................................................... 105

Appendix A: Definitions of Variables and Functions for Riverine

 Wetlands ....................................................... A1

Appendix B: Relationship Between Variables and Wetland Functions ....... B1
vi

Appendix C: Field Forms—Tally Sheets and Synopses ................... C1

SF 298
vii

Preface

The work described in this report was authorized by Headquarters, U.S. Army

Corps of Engineers (HQUSACE), as part of the Delineation and Evaluation Task

Area of the Wetlands Research Program (WRP). The work was performed under

Work Unit 32756, “Evaluation of Wetland Functions and Values,” for which

Mr. R. Daniel Smith, Environmental Laboratory (EL), U.S. Army Engineer Waterways Experiment Station (WES), was the Principal Investigator. Mr. John Bellinger

(CECW-PO) was the WRP Technical Monitor for this work. Development funds

were also contributed by the institutions, agencies, and firms with which the authors

are associated (the Environmental Protection Agency (3-BO978NTEX) and the Divisions of Coastal Management (F3078) and Environmental Management (J-3054)

of the North Carolina Department of Environment, Health, and Natural Resources),

as well as other sources of funds and support.

Mr. Dave Mathis (CERD-C) was the WRP Coordinator at the Directorate of

Research and Development, HQUSACE; Dr. William L. Klesch (CECW-PO)

served as the WRP Technical Monitor's Representative; Dr. Russell F. Theriot,

WES, was the Wetlands Program Manager; and Mr. Ellis J. Clairain, WES, was the

Task Area Manager. The work was performed under the direct supervision of

Mr. Smith and under the general supervision of Mr. Clairain, Acting Chief, Wetlands Branch; Dr. Conrad J. Kirby, Chief, Ecological Research Division; and

Dr. John W. Keeley, Director, EL.

This report was prepared by Dr. Mark M. Brinson, professor, Biology

Department, and Dr. Richard D. Rheinhardt, research assistant, East Carolina

University, Greenville, NC; Dr. F. Richard Hauer, professor, Flathead Lake

Biological Station, University of Montana, Polson, MT; Dr. Lyndon C. Lee, L. C.

Lee and Associates, Inc., Seattle, WA; Dr. Wade L. Nutter, hydrologist, School of

Forest Resources, University of Georgia, Athens, GA; Mr. R. Daniel Smith,

ecologist, WES; and Dr. Dennis Whigham, wetland scientist, Crofton, MD.

The authors wish to thank several individuals who were involved in the development of this manuscript. Mr. Richard Novitzki took part in all of the field trips

and many of the discussions. His expertise in hydrology of wetlands, experience

with EMAP-wetland projects, and clarity of thinking were important to the development of concepts. Mr. William Ainslie provided frequent doses of regulatory reality

at critical moments and contributed through his experience in applying early versions of the method to wetlands in Kentucky. Appreciation is also expressed to
viii

Messrs. Garrett Hollands and Dennis Magee for their leadership in the field in New

England and participation in meetings. Dr. Robert Beschta provided leadership in

the early stages on geomorphic processes and hydrology, particularly in the western

and arid regions. Dr. Gregory Auble contributed to early meetings and suggestions

on subsequent drafts, and Dr. James Gosselink participated in work on the Pearl

River. Dr. Ed Maltby provided perspective by keeping the Riverine Working Group

abreast of parallel efforts in Europe as well as co-chairing a session at the Columbus

INTECOL meeting in 1992 on functional assessment. Ms. Marie Sullivan, Dr. Julie

Stromberg, and Dr. Duncan Patten guided the Riverine Working Group through the

arid riparian ecosystem of Arizona. Thanks go also to Dr. Mark LaSalle for his efforts to facilitate funding during the early phase.

At the time of publication of this report, Director of WES was Dr. Robert W.

Whalin. Commander was COL Bruce K. Howard, EN.

This report should be cited as follows:

Brinson, M. M., Hauer, F. R., Lee, L. C., Nutter, W. L.,

Rheinhardt, R. D., Smith, R. D., and Whigham, D. (1995). “A guidebook for application of hydrogeomorphic assessments to riverine wetlands,” Technical Report WRP-DE-11, U.S. Army Engineer Waterways

Experiment Station, Vicksburg, MS.

Note: This Operational Draft will be in effect for 2 years from date of

publication. Comments from users are solicited for 1 year from date of

publication. Mail comments to the U.S. Army Engineer Waterways

Experiment Station, ATTN: CEWES-ER-W, 3909 Halls Ferry Road,

Vicksburg, MS 39180-6199.

The contents of this report are not to be used for advertising, publication,

or promotional purposes. Citation of trade names does not constitute an

official endorsement or approval of the use of such commercial products.
ix

Conversion Factors, Non-SI to

SI Units of Measurement

Non-SI units of measurement used in this report can be converted to SI units as

follows:

Multiply By To Obtain

acres 4,046.873 square meters

square feet 0.09290304 square meters
Chapter 1 Introduction 1

1 Introduction

Riverine Wetlands Defined

This guidebook provides the basis for applying the hydrogeomorphic (HGM)

approach for wetland functional assessment to riverine wetlands. “Riverine” refers

to a class of wetland that has a floodplain or riparian geomorphic setting (Brinson

1993a). The other classes or geomorphic settings are depressional, slope, mineral

soil and organic soil flats, and estuarine and lacustrine fringe (Table 1).

Table 1

Hydrogeomorphic Classes of Wetlands Showing Associated Dominant Water

Sources, Hydrodynamics, and Examples of Subclasses

Examples of Subclasses

Hydrogeomorphic Class Dominant Water Source Dominant Hydrodynamics Eastern USA and Alaska

Western USA

Riverine Overbank flow from Unidirectional, horizontal Bottomland Riparian

channel hardwood forested

forests wetlands

Depressional Return flow from Vertical Prairie pothole California

groundwater and marshes vernal pools

interflow

Slope Return flow from Unidirectional, horizontal Fens Avalanche

groundwater chutes

Mineral soil flats Precipitation Vertical Wet pine Large playas

flatwoods

Organic soil flats Precipitation Vertical Peat bogs; Peat bogs

portions of

Everglades

Estuarine fringe Overbank flow from Bidirectional, horizontal Chesapeake San Francisco

estuary Bay marshes Bay marshes

Lacustrine fringe Overbank flow from lake Bidirectional, horizontal Great Lakes Flathead Lake

marshes marshes
2

Chapter 1 Introduction

Riverine wetlands occur in floodplains and riparian corridors in association with

stream channels (Table 1). Dominant water sources are overbank flow from the

channel or subsurface hydraulic connections between the stream channel and wetlands. Additional water sources may be interflow and return flow from adjacent

uplands, occasional overland flow from adjacent uplands, tributary inflow, and precipitation. When overbank flow occurs, surface flows down the floodplain may

dominate hydrodynamics. At their headwater-most extension, riverine wetlands often are replaced by slope or depressional wetlands where channel (bed) and bank

disappear, or they may intergrade with poorly drained flats or uplands. (Definitions

of other classes are given in Table 2.) Riverine wetlands lose surface water by flow

returning to the channel after flooding and saturation surface flow to the channel

during rainfall events. They lose subsurface water by discharge to the channel,

movement to deeper groundwater (for losing streams), and evapotranspiration. Peat

may accumulate in off-channel depressions (oxbows) that have become isolated

from riverine processes and subjected to long durations of saturation from groundwater sources. Bottomland hardwood floodplains are a common example of riverine

wetlands.

First-order streams, usually designated by solid blue lines on U.S. Geological

Survey (USGS) 7.5-min topographic maps (scale 1:24,000), are normally associated with riverine wetlands. They may also continue farther upstream where broken

blue lines on topographic maps indicate the presence of channels. Perennial flow is

not a requirement for a wetland to be classified as riverine.

The downstream extent of riverine wetlands is where they normally intergrade

with estuarine fringe wetlands. According to the hydrogeomorphic classification,

the riverine class is dominated by unidirectional flows (Brinson 1993a). The interface with the estuarine fringe class occurs where hydrodynamics change to bidirectional flows where freshwater tidal marshes and swamps can be found (Odum

et al. 1984). This is an unstable transition zone for vegetation because freshwater

tidal marshes and freshwater tidal swamps can be found to occur in virtually the

same hydrologic and salinity regime. Plant community physiognomy strongly

influences ecological functions related to habitat. Because riverine wetlands are

usually forested, their vegetation is more similar to freshwater tidal swamps than to

freshwater tidal marshes. Salinity strongly affects plant physiognomy, normally

excluding arboreal vegetation in the range of 1 to 5 parts per thousand and higher

(Brinson, Bradshaw, and Jones 1985; Conner and Askew 1992).

Riverine wetlands normally extend perpendicular from stream channel to the

edge of the stream's floodplain. Large floodplains in landscapes with great

topographic relief and steep hydrostatic gradients may function hydrologically more

like slope wetlands because of dominance by groundwater sources. In headwater

streams where floodplains are lacking or only weakly developed, slope wetlands

may lie adjacent to the stream channel. Large riverine wetlands may themselves

contain sites with affinities to other classes. 
Chapter 1 Introduction 3

Table 2

Definitions of Hydrogeomorphic Wetland Classes Other than

Riverine

Hydrogeomorphic Class Definition

Depressional Depressional wetlands occur in topographic depressions. Dominant

water sources are precipitation, groundwater discharge, and both

interflow and overland flow from adjacent uplands. The direction of flow

is normally from the surrounding uplands toward the center of the

depression. Elevation contours are closed, thus allowing the accumulation of surface water. Depressional wetlands may have any combination

of inlets and outlets or lack them completely. Dominant hydrodynamics

are vertical fluctuations, primarily seasonal. Depressional wetlands may

lose water through intermittent or perennial drainage from an outlet, by

evapotranspiration and, if they are not receiving groundwater discharge,

may slowly contribute to groundwater. Peat deposits may develop in

depressional wetlands. Prairie potholes are a common example of

depressional wetlands.

Slope Slope wetlands normally are found where there is a discharge of

groundwater to the land surface. They normally occur on sloping land;

elevation gradients may range from steep hillsides to slight slopes. 

Slope wetlands are usually incapable of depressional storage because

they lack the necessary closed contours. Principal water sources are

usually groundwater return flow and interflow from surrounding uplands

as well as precipitation. Hydrodynamics are dominated by downslope

unidirectional water flow. Slope wetlands can occur in nearly flat

landscapes if groundwater discharge is a dominant source to the

wetland surface. Slope wetlands lose water primarily by saturation

subsurface and surface flows and by evapotranspiration. Slope

wetlands may develop channels, but the channels serve only to convey

water away from the slope wetland. Fens are a common example of

slope wetlands.

Mineral Soil Flats Mineral soil flats are most common on interfluves, extensive relic lake

bottoms, or large floodplain terraces where the main source of water is

precipitation. They receive no groundwater discharge, which distinguishes them from depressions and slopes. Dominant hydrodynamics

are vertical fluctuations. Mineral soil flats lose water by evapotranspiration, saturation overland flow, and seepage to underlying

groundwater. They are distinguished from flat upland areas by their

poor vertical drainage, often due to spodic horizons and hardpans, and

low lateral drainage, usually due to low hydraulic gradients. Mineral soil

flats that accumulate peat can eventually become the class organic soil

flats. Pine flatwoods with hydric soils are a common example of mineral

soil flat wetlands.

Organic Soil Flats Organic soil flats, or extensive peatlands, differ from mineral soil flats, in

part because their elevation and topography are controlled by vertical

accretion of organic matter. They occur commonly on flat interfluves,

but may also be located where depressions have become filled with peat

to form a relatively large flat surface. Water source is dominated by

precipitation, while water loss is by saturation overland flow and seepage

to underlying groundwater. Raised bogs share many of these characteristics, but may be considered a separate class because of their

convex upward form and distinct edaphic conditions for plants. Portions

of the Everglades and northern Minnesota peatlands are common

examples of organic soil flat wetlands.

(Continued)
4

Chapter 1 Introduction

Table 2 (Concluded)

Hydrogeomorphic Class Definition

Estuarine Fringe Tidal fringe wetlands occur along coasts and estuaries and are under

the influence of sea level. They intergrade landward with riverine wetlands where tidal currents diminish and riverflow becomes the dominant

water source. Additional water sources may be groundwater discharge

and precipitation. The interface between the tidal fringe and riverine

classes is where bidirectional flows from tides dominate over

unidirectional ones controlled by floodplain slope of riverine wetlands. 

Because tidal fringe wetlands frequently flood and water table elevations

are controlled mainly by sea surface elevation, tidal fringe wetlands

seldom dry for significant periods. Tidal fringe wetlands lose water by

tidal exchange, by saturated overland flow to tidal creek channels, and

by evapotranspiration. Organic matter normally accumulates in higher

elevation marsh areas where flooding is less frequent and the wetlands

are isolated from shoreline wave erosion by intervening areas of low

marsh. Spartina alterniflora salt marshes are a common example of

estuarine fringe wetlands.

Lacustrine Fringe Lacustrine fringe wetlands are adjacent to lakes where the water

elevation of the lake maintains the water table in the wetland. In some

cases, these wetlands consist of a floating mat attached to land. 

Additional sources of water are precipitation and groundwater discharge,

the latter dominating where lacustrine fringe wetlands intergrade with

uplands or slope wetlands. Surface water flow is bidirectional, usually

controlled by water-level fluctuations such as seiches in the adjoining

lake. Lacustrine fringe wetlands are indistinguishable from depressional

wetlands where the size of the lake becomes so small relative to fringe

wetlands that the lake is incapable of stabilizing water tables. Lacustrine

wetlands lose water by flow returning to the lake after flooding, by

saturation surface flow, and by evapotranspiration. Organic matter

normally accumulates in areas sufficiently protected from shoreline wave

erosion. Unimpounded marshes bordering the Great Lakes are a

common example of lacustrine fringe wetlands.

For example, oxbow features in floodplains may assume depressional characteristics

for most of the year.

Classification is made difficult not only because of these problems of scale, but

also because of the continuous nature of water sources between extremes in wetland

class (Figure 1).

Riverine wetlands, as applied in the HGM classifications and assessment approach, differ from the riverine class of Cowardin et al. (1979) used for National

Wetland Inventory maps of the U.S. Fish and Wildlife Service (FWS). The FWS

definition includes only the riverbed, bank to bank; most portions of floodplain wetlands are classified as palustrine in the FWS classification. The HGM approach

classifies these areas as riverine. Rivers and floodplains in the HGM approach are

assumed to be integral parts of the riverine wetland ecosystem. For practical

reasons, however, the two may have to be separated for the purpose of functional

assessment.
Chapter 1 Introduction 5

Figure 1. Diagram expressing the relative contribution of three water sources: 

precipitation, groundwater discharge, and surface flow. Location of

major wetland classes (bogs, riverine, etc.) within the triangle shows

the relative importance of water sources. Boundaries drawn between

classes should not be interpreted as distinct; rather, gradients between classes are continuous (Brinson 1993b)

Purpose of the Guidebook

This document is for use by a team of individuals who adapt information in this

guidebook to riverine wetlands in specific physiographic regions. By adapting from

the generalities of the riverine class to specific regional riverine subclasses, such as

high-gradient streams of the glaciated northeastern United States, the procedure can

be made responsive to the specific conditions found in one's region of interest. For

example, it may by necessary to separate wetlands associated with high-gradient

streams from those associated with low-gradient streams in order to reduce the

amount of variation in indicators and to make the assessment more sensitive to

detecting impacts.

This guidebook is not called an assessment manual because “manual” connotes a

procedure that can be taken to the field and immediately applied. The guidebook is

not for direct application by environmental consultants, agency personnel, and

others who assess wetland functions. For the guidebook to be useful, it must first be

modified, calibrated, and tested to determine its effectiveness under local and
6

Chapter 1 Introduction

regional conditions. Reference wetlands serve as the foundation for identifying

functions, and for determining which variables and indicators are appropriate for a

particular region.

The process of adapting this guidebook to regional subclasses of wetlands normally requires a team effort. Ideally, this group should consist of individuals from

relevant disciplines, who are knowledgeable in hydrology, geomorphology, plant

ecology, ecosystem ecology, population ecology, soil science, wildlife biology, and

other related disciplines. For a regionalized procedure to be acceptable to the regulatory community, the team should include federal and state regulators, private consultants, academics, and others. This group may be called the Assessment Procedure Development Team, or simply, “A-team.” Because the work of the A-team is

critical in regionalizing the procedure, the team must also set standards applicable to

the region so there is consistency of use over time.

One of the responsibilities of an A-team is to consistently identify and define the

regional nomenclature of reference (Smith et al., in press). This task requires the

talents of individuals who are very familiar with all wetland subclasses in their region, a number of individual wetland sites in each subclass, and the technical literature pertaining to each class nationally and to each regional subclass. Ultimately,

the A-team must determine two critical issues that relate to the nomenclature. One

is the geographic boundaries of the reference domain for each of the regional subclasses. The other is the reference standards or the level of functioning by wetlands

that have the highest suite of functions (that is, the least degraded) in the reference

domain (defined in Table 3). Such an effort requires a high level of knowledge

about wetlands of a particular region, as well as quantitative data on reference wetlands that can be used to distinguish between wetlands used to establish reference

standards and wetlands that fall short of the highest level of functioning due to alteration and other disturbances (Brinson and Rheinhardt, in press). The assessment

approach document (Smith et al., in press) provides the rationale for the role of reference wetlands in functional assessment, and also provides detailed instructions for

identifying reference wetlands and determining reference standards.

An A-team should keep in mind the various uses of reference in making its decision about reference domain and reference standards. Foremost is the use of reference standards as a basis for comparison with sites proposed for Section 404 projects. Not only is it necessary to distinguish between sites that meet reference standards (that is, fully functional wetlands) and those that function at some lower level,

but one must also be able to measure the amount of function that will be lost following a given project. For projects that completely displace a wetland, losses in functioning are complete also and are not difficult to determine. For projects with minor

impacts, the small changes are more difficult to detect and would require fine calibrations of functions. A-team members should include in their group of reference

wetlands some sites below the reference standard that will help to establish potential

variation for the reference domain.
Chapter 1 Introduction 7

Table 3

Categories and Nomenclature for Reference

Term Definition

Reference domain All wetlands within a defined geographic region that belong to a

single hydrogeomorphic subclass.

Reference wetlands Wetland sites within the reference domain that encompass the

known variation of the subclass. They are used to establish the

range of functioning within the subclass. Reference wetlands

may include former wetland sites for which restoration to wetland

is possible, and characteristics of sites derived from historic records or published data.

Reference standard sites The sites within a reference wetland data set from which reference standards are developed. Among all reference wetlands,

reference standard sites are judged by an interdisciplinary team

to have the highest level of functioning.

Reference standards Conditions exhibited by a group of reference wetlands that correspond to the highest level of functioning (highest sustainable capacity) across the suite of functions of the subclass. By definition, reference standard functions receive an index score of 1.0.

Site potential The highest level of functioning possible given local constraints of

disturbance history, land use, or other factors. Site potential may

be equal to or less than levels of functioning established by reference standards.

Project target The level of functioning identified or negotiated for a restoration or

creation project. The project target must be based on reference

standards and/or site potential and must be consistent with restoration or creation goals. Project targets are used to evaluate

whether a project is developing toward reference standards

and/or site potential.

Project standards Performance criteria and/or specifications used to guide the restoration or creation activities toward the project target. Project

standards should include and specify reasonable contingency

measures if the project target is not being achieved.

If a Section 404 permit is granted, and is conditioned with compensatory mitigation requirements, reference standards represent the standard against which restoration or creation efforts are measured. Creation of riverine wetlands is difficult because rivers are highly integrated into existing landforms. Geomorphic features in

particular may have required millennia to develop. Consequently, compensatory

mitigation for degradation of riverine wetland functions seldom can be accomplished by creating new ones given the scarcity of appropriate sites. Opportunities

for restoration, however, are normally more abundant. There are riverine wetlands

in most regions of the country that exist in a degraded condition from such alterations as channelization, drainage, levees that block overbank flow, grazing, and

other hydrologic alterations. Impediments to restoration, if they exist, may be due

more to the lack of commitment and creative approaches to restoration or the lack of

data required to detect differences in functioning than to a scarcity of sites for restoration. This situation, however, underscores the need for A-teams to construct a

sensitive method for assessing function, comparing alternatives, and designing restoration strategies.
8

Chapter 1 Introduction

Documentation of Functions for the

Riverine Wetland Class

The 15 functions identified for the riverine wetland class arose from workshops

and field trips conducted by the authors and other participants (Table 4). Wetland

sites were studied in the following geographic regions: glaciated New England (several streams in Massachusetts), the Gulf Coastal Plain of Mississippi (Pearl River in

Mississippi), the arid Southwest (Verde, Santa Cruz, Gila, and San Pedro Rivers in

Arizona), northern Rocky Mountains (Flathead River in Montana), and the Olympic

Peninsula (Hoh and Queets Rivers) and Puget Sound lowlands. The process benefited also from personal experiences of the authors and participants in other regions

of the United States.

Table 4

Functions of Riverine Wetland Classes Listed by Four Major

Categories

Hydrologic

 Dynamic Surface Water Storage

 Long-Term Surface Water Storage

 Energy Dissipation

 Subsurface Storage of Water

 Moderation of Groundwater Flow or Discharge

Biogeochemical

 Nutrient 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

Note: Definitions are given in Appendix A.

The remainder of this chapter describes the content and introduces the sequence

that is used in Chapter 2 for each of the 15 functions. The sequence is as follows: 

definition of function, discussion of function and rationale, description of variables

and function, index of function, and documentation of functions. The function

Organic Carbon Export will be used to illustrate the sequence. Upon finishing this

chapter, the reader should be familiar enough with the functions and their derivation

to be able to understand the rationale, assumptions, and limitations of establishing

functions, and how the information on functions might be adapted to specific riverine wetland conditions. This is the material that the A-team modifies and adapts to

its regional or local group of riverine subclasses. The documentation section
Index of Function = [(VFREQ VSURFIN VSUBIN VSURFCON)/4]

× VORGAN

1/2

Chapter 1 Introduction 9

represents the control point for updating and changing the assessment of regional

subclasses.

Definition of function

A succinct definition is provided in one or a few sentences. For the function Organic Carbon Export, the definition is “export of dissolved and particulate organic

carbon from a wetland. Mechanisms include leaching, flushing, displacement, and

erosion.”

Discussion of function and rationale

Each function is described and a brief rationale is provided, including appropriate literature citations, if available. The rationale for the choice of functions is explained in Brinson (1993a), Brinson et al. (1994), and Smith et al. (in press). 

Description of variables and functions

Variables are factors that are necessary for functions to occur. For example, the

Organic Carbon Export function requires a source of organic matter in the wetland

and appropriate water flows to transport the organic matter downstream. The flow

pathway variables for riverine wetlands include the frequency of overbank flow

from the channel (V ), which is assumed to flood the riverine wetland surface, FREQ

flow from subsurface flow (V ) and surface flow (V ), and surface hydraulic SUBIN SURFIN

connections (V ) with the stream channel. The source of organic matter SURFCON

(V ) is defined as the types and amounts of organic matter in the wetland includ- ORGAN

ing leaf litter, coarse woody debris (down and standing), live woody vegetation, live

and dead herbaceous plants, organic-rich mineral soils, and histosols.

To determine an index for the level of functioning (Index of Function or Functional Capacity) (Smith et al., in press), pertinent variables are combined in equations or models. The reference standards represent the highest level of sustainable

functioning in the landscape. These are the conditions used to calibrate the models

so that both variables and the Index of Function are set at 1.0. The equation for

Organic Carbon Export is

If V = 0, the function is absent. ORGAN

The equation that models the Organic Carbon Export function is arranged so the

geometric mean of the last variable and the arithmetic mean of the first four can result in the Index of Function being zero if either all hydrologic variables are absent

or organic matter is missing from the wetland being assessed.
 A table of factors for converting non-SI units of measurement to SI units is presented on page ix. 1

10 Chapter 1 Introduction

Variables cannot always be quantified in absolute units in rapid assessment procedures. At a minimum, they must be measured in units that can be related to those

used for reference standards developed on reference standard sites (that is, the least

degraded conditions for the subclass in the reference domain). Let us assume for

simplicity that biomass of trees was the only component of organic matter, V . ORGAN

A measurement or indicator of that component in forests is basal area. The level of

the variable would be calculated based on the basal area of the forest stand being

assessed relative to reference standards. Thus, a basal area of 120 ft /acre for the 2 1

site being assessed would have an index of 0.60 (120/200) relative to the reference

standard of 200 ft /acre. 2

Often field indicators are not so easy to measure, either because the methods are

costly and time consuming or the accuracy necessary for adequate measurement

would require more effort than is warranted in rapid assessment. The cost to determine Organic Carbon Export, for example, would require monitoring of organic

carbon concentrations and discharges for inflow and outflow pathways over several

seasons to obtain an estimate of the function. This is simply not practical. For such

costly and time-consuming methods, indicators must be used as surrogate measures

for variables. In the Organic Carbon Export function, these surrogates are the presence of organic matter in the wetland and the presence of flows to transport organic

matter. The justification for the use of such indicators may be mere common sense

or a combination of research results and an extension of logic. For example, variable VSURFCON in Organic Carbon Export is “surface hydraulic connections among

main and side channels.” Until such time as this variable is quantified and calibrated to reference standards, only the presence or absence of surface hydraulic connections can suggest the presence or absence of the variable.

Another time-saving approach is to use categorical estimates rather than continuous measures of indices. In the extreme case, the index would be present or absent,

resulting in variables of 1.0 or 0.0, respectively. An alternative with somewhat better resolution, and that chosen herein for illustration purposes, is to establish four

discrete categories: 1.0, 0.5, 0.1, and 0.0. For a variable to have an index of 1.0,

indicators must be judged to be “similar to the reference standard” (see definition of

reference standards in Table 3). When quantified, this level may actually be in the

range of 75 to 125 percent of the mean for the reference standard. Hence, it is important that variability in reference standard sites be reflected in the variables that

are derived from them. For a variable to be in the 0.5 category, indicators are

judged to be “less than reference conditions.” This may fall in the range of 25 to

75 percent of the mean for the reference standard. Finally, a variable that falls in the

range of 1 to 25 percent would receive an index of 0.1, while the lack of the variable

(or indicators of it) would be assigned a zero.

Alternate approaches may be taken to encompass other conditions. For example,

an index of 0.1 may be assigned for the variable if indicators are absent but the wetland has potential for recovery (that is, the impact may be reversible). An index of

0.1 may be chosen also to hedge judgment for indicators that are absent, but
Chapter 1 Introduction 11

presence of the variable cannot be ruled out completely. The 0.1 index can be somewhat analogous to using “trace” as a measure of sparse plant cover. It is neither

completely absent nor is it sufficiently important to warrant a higher index. Of

course, an index of zero rules out the variable altogether. In some cases, alterations

intentionally or inadvertently eliminate variables or perhaps functions completely

from a wetland. For example, construction of artificial flood levees likely eliminates

the “overbank flow” variable, V . FREQ

Another approach having similar effects is the use of negative indicators. These

may be based on some disturbance to the wetland which results in the partial or

complete loss of a variable. For example, stream channelization usually eliminates

overbank flow because channel capacity and conveyance have been increased with

the intention of eliminating this variable. Consequently, functions that have frequency of overbank flow as a variable may be partially or totally lost.

When variables can be measured directly and quickly, or direct measures already

exist for a site, there is no reason to use indicators. There are obvious advantages

for having reference wetlands where indicators have been calibrated against quantitative data. In fact, the USGS has developed models for ungauged streams in many

states to predict their hydrologic characteristics from gauged ones (e.g., Stamey and

Hess 1993 for Georgia). For ungauged streams of riverine wetlands, such models

could be applied to estimate frequency and duration of overbank flow.

Because riverine wetland assessments need to be tailored to specific regions of

the country and their corresponding subclasses, there are no hard and fast rules on

what qualifies as an indicator or how to use them. Indicators must be scaled to regional reference standards where the function is known to exist. This is especially

true for habitat functions that deal with species of plants and animals that have limited biogeographic distribution. Indicators and variables should encompass conditions inherent to the reference domain.

In the HGM approach, levels of certainty (or uncertainty) are not determined for

indicators, variables, or functions. The user is only responsible for applying the

method to riverine wetlands insofar as the method is capable of detecting thresholds

of functioning. The user does not have to ask the question “What is the certainty

that the function exists?” This does not mean that the approach is free of uncertainty. Rather, there are degrees of uncertainty at every level in such assessments,

and it would be extremely cumbersome to use and interpret results from a method

that required both the assessment of function and the certainty that it exists. Certainty should be handled by the A-team in the regional refinement of the procedure. 

The A-team must decide whether enough information and evidence exists to use

specific indicators and variables, and how variables should be combined for calculating functional indices. Certainty should become a property of the method rather

than an additional factor to be assessed. Because this functional assessment procedure is completely open to review and examination, and the documentation explicit,

anyone can judge certainty by applying the logic and becoming familiar with relevant literature. This has a twofold purpose: it allows the method to be scrutinized

and improved by addition or change as new information becomes available on wetlands and their functions, and it allows details to be challenged or defended based on
12 Chapter 1 Introduction

evidence and facts as they currently exist. There is no presumption that this assessment procedure is better or worse than any other approach just because it may have

been adopted for use by a particular agency or firm. However, if parts of this

method are regarded as unreliable, then the challenger must provide evidence to support such a conclusion. The intention of this approach is to improve consistency

and predictability of decision making in wetland regulatory programs by applying

the best science possible. 

If an indicator or variable cannot be observed, yet there is no indication that the

corresponding function is missing, one default option might be to assign scores

of 1.0 to appropriate variables and functions. Other conventions could be developed as long as measures of certainty are not invoked to complicate the assessment

and confound interpretation. If indicators or variables are not the kind that can be

readily observed in a particular regional subclass, the A-team should explain why,

and offer substitutes if appropriate.

The procedure should be field-tested by an A-team that develops regional reference standards. It would be prudent also to spend some time and money on quality

control, including a comparison of the repeatability of the results among users and

the reliability of the indicators, thresholds of indicators to verify a variable, and sensitivity of the equations to detect differences in functioning. Training should be an

integral part of implementing functional assessments.

The scale between zero (no function) and 1.0 (reference standards) is probably

adequate for most projects, especially those that completely displace vegetated wetlands with fill. Finer resolution may be needed where impacts are less acute, for

example, where wetlands are subjected to slightly modified hydroperiods, accelerated nutrient loading, and increases in sediment deposition. Restoration projects

that require measurements of changes over short periods of time may benefit from

using expanded scales to detect significant but subtle changes toward specific project targets. In such cases, small annual changes that occur soon after the planting

of wetlands may require that smaller differences be detected than is possible with a

robust assessment scaled for major impacts. Indicators, equations, and models can

be modified to accommodate specific needs not routinely encountered in regulatory

programs. This does not require sacrificing an HGM approach, but rather refining

and extending it to meet the needs of specific projects.

If the resolution for detecting changes is too coarse for routine assessments, and

further attempts fail to improve indicators and variables, the A-team might consider

developing finer subclasses. This may solve problems that originate from large

amounts of variation in reference standards.

Scaling is done explicitly at the variable level so that absence of a variable receives a zero and its presence at the defined sustainable maximum (reference standards) is 1.0. Scaling is done implicitly at the function level, however, by combining indices of variables in equations in such a manner that wetlands representing the

reference standard receive a score of 1.0. One of the most difficult concepts to

understand is that indices of both variables and functions cannot exceed a level of

1.0. This is because wetland ecosystems are the unit of HGM assessments, not
Chapter 1 Introduction 13

individual functions. Higher scores cannot be given to variables in the assessment

area than are set for reference standards. Such an approach would violate the fundamental tenet that sustainable levels of ecosystem functioning cannot be maximized

at the same time and on the same site. As a simple example, removal of trees from a

wetland may slightly increase long-term surface water storage by providing more

accessible space for water to be stored. This example illustrates two principles: 

such effects on single functions usually are not sustainable (that is, the forest will

grow back on its own if not otherwise managed), and unsustainable increases in one

function generally occur at the expense of other functions (that is, habitat conditions

would be altered).

Any modifications to this method must be documented in order to maintain consistency among users. If this were not the case, there would be no reliable standards

on what constitutes a function, how the function is determined, and what evidence is

used for developing variables and indicators. The Documentation of Functions section is the core of the assessment method. As functions are updated and indicators

are modified, both the documentation and forms used in fieldwork must be revised. 

The method will benefit from the experience of practitioners as they gain more insight into how functions relate to structure and the reference wetland database. 

Consequently, each version of the functions and field forms should carry the date on

which they were approved and adopted so that previously conducted assessments

can always be referenced to the version that was used at the time of assessment. 

Unless changes are substantial and require the measurement of additional indicators

and application of additional variables, modified indices of functions should be easily reconstructed from previous versions and calibrated to those currently in existence. Modification of the “Documentation of Functions” for a regional subclass of

wetlands should be controlled by an oversight committee that has regulatory responsibility, technical expertise, and familiarity with wetlands in the region of interest.

Documentation of functions

The portion of the guidebook on documentation (Chapter 2) is the core information for the 15 functions performed by most riverine wetlands (Table 4). Examples

in the Riverine Guidebook are not specific for any physiographic region of the country, but rather are generic to provide a common point of departure for A-teams. 

First, these generic examples are adapted by A-teams for a particular physiographic

region or subclasses of wetlands. Thereafter, procedures should be established for

modifying the details by an experienced and knowledgeable group of practitioners

according to some prescribed time schedule. This could be done by the A-team or

others directed to update the procedure. Just as standards are developed and

monitored by professionals in other disciplines, so should functional assessments be

reviewed and updated by qualified experts. Summary tables of definitions of functions and variables are listed in Appendixes A and B.
14 Chapter 1 Introduction

Field form

The Documentation of Functions described above is the information that must be

modified for the regional subclasses of riverine wetlands. That level of detail is inappropriate for use in the field while conducting assessments because of the large

volume of material. Rather, a short form of the documentation, called the Field

Form, is closer to what the practitioner might carry to the field. The Field Forms, in

Appendix C, have two parts: (1) a synopsis of each function for reference in the

field and (2) tally sheets for recording site identification and mode of assessment

(i.e., project impact versus restoration), choosing indices of variables, and calculating the index for each function. The synopsis level of documentation is a suggested

level of detail for fieldwork. Without it, there is a greater likelihood that the assessor will misinterpret the intent of the A-team in choosing certain indicators and variables. This is especially important when the assessor must predict functioning for

restored wetland sites.
Chapter 2 Documentation of Riverine Wetland Functions 15

2 Documentation of Riverine

Wetland Functions

Each riverine wetland function is described in the following order: definition,

discussion of function and rationale, description of variables, index of function, and

documentation.

Dynamic Surface Water Storage

Definition

The capacity of a wetland to detain moving water from overbank flow for a short

duration when flow is out of the channel. This function is associated with moving

water from overbank flow and/or upland surface water inputs by overland flow or

tributaries.

Discussion of function and rationale

Detention of floodwaters is an important riverine wetland function. As overbank

flow or upslope surface inputs are detained in the wetland, the timing of passage of

the flood wave (wave celerity) is reduced. Alteration of the flood wave and detention of water may result in reduced downstream peak flows and delayed timing of

the peak flows. 

The movement of surface water through a wetland during an overbank flow

event is controlled by width, slope, and roughness of the area inundated. The longer

water is detained as it moves through the wetland, the greater the potential for the

wetland to perform the function and to support other wetland functions.

Through the performance of this function, the wetland detains water long enough

and reduces velocity sufficiently for particulate organic matter and sediments to settle out of the water column. Movement of water through a wetland redistributes

organic and inorganic particulates and facilitates the import or export of plant propagules. Slow-moving water can also transport fine particulate organic matter away

from the wetland to support food webs in connected aquatic environments. The
16 Chapter 2 Documentation of Riverine Wetland Functions

spreading of water over the wetland and the settling of sediments and other particulates lead to an improvement of water quality. Infiltration of the flooded water

into wetland soils can lead to support of other wetland functions, including nutrient

cycling and removal of elements and compounds. The slower moving surface water

in the wetland, in contrast to the higher velocity water in the stream channel,

provides a refuge for aquatic organisms not well adapted to strong currents as well

as a conduit for organisms to access the wetland for feeding and recruitment.

The frequency and duration of flooding from overbank flow are important

dimensions of this function. If frequencies of overbank flow increase due to

upstream modifications (e.g., urbanization), other functions may be modified even

though the dynamic storage function is still occurring. If an increase in frequency

and/or duration leads to increased sediment transport, the coating of plant leaves

with silt may reduce photosynthesis, seedlings and seeds may become buried in

sediment, and the site may become overloaded with nutrients. Consequently, the

reference standard for this function must be selected carefully to recognize the

principal physical attributes of the function, i.e., detention of surface water flowing

through the wetland. The measurement of this function is critical because other

attributes such as particulate retention and nutrient cycling are dependent on it.

The variables describing this function are related to the frequency and duration

of overbank flow and wetland roughness features. Wetland slope may be a factor

controlling the rate of surface water movement along the floodplain, particularly in

low-order, steep-gradient systems. Major roughness features such as woody debris,

macrotopography, and tree stems often dominate over slope. If major roughness

features are not present in the reference standard sites, a slope variable may be

added to compensate. 

Description of variables

V , Frequency of overbank flow. The annual frequency at which a channel FREQ

overtops its banks (when bank-full discharge is exceeded or water is delivered from

upland sources) is important as a driving force for other wetland functions. 

Williams (1978) discusses methods for measuring bank-full discharge. Many

studies have determined that bank-full discharge frequency for most streams is

between 1.0 and 2.5 years, with 1.5 years being a reasonable average (Leopold

1994). Exceptions to this general conclusion are streams not in equilibrium due to

strong down-cutting (degradation) of their channels into recent alluvial sediments, a

result of past accelerated erosion and deposition. An example is the southeastern

U.S. Piedmont where degrading channels may have a bank-full discharge frequency

in excess of 10 to 25 years (Burke and Nutter, in press). Another example is oak

flats in bottomland hardwoods where the recurrence intervals may be on the order of

2 to 5 years rather than 1.5 years. 

Although the principal focus of this variable is overbank flow, it is recognized

that some wetlands have substantial input from overland flow or tributaries (often

ephemeral or intermittent streams) from adjacent uplands. A wetland may serve in

these circumstances to provide the same moderation of the surface flow as occurs
Chapter 2 Documentation of Riverine Wetland Functions 17

with overbank flow. A common situation in which these upland flows occur is from

agricultural and urban runoff which may represent an altered condition. Comparison to the reference standard must be sensitive to the altered condition.

In the documentation section of this function, values given in parentheses indicate that other recurrence intervals could be used, depending on the reference domain. For example, recurrence intervals for oak flats would be approximately 2 to

5 years. With that as a reference standard, the 2- to 5-year recurrence would have

an index of 1.0, with lower scores for altered conditions, e.g., <2 years or >5 years. 

The reference standard in this case must reflect the longer frequencies and, if annual

flooding occurs in such circumstances, the index for the variable would be less than

1.0.

Contributions by overland flow and tributary input from the upland are also included in this variable. Although these flows are not technically overbank flow

from a channel, the variable should account for them if they represent reference

standards. If these sources are dominant in comparison to overbank flow, it should

be noted whether they represent conditions of the reference standard or if they represent an alteration and should score below 1.0. The score for flooding at greater or

less than recurrence intervals of the reference standard has an index of 0.5, e.g., a

recurrence interval of greater or less than one-half year departure from the reference

standard. Absence of flooding from overbank flow or from upland surface sources

results in a score of zero.

V , Average depth of inundation. Average depth of inundation should be INUND

determined for the overbank discharge event frequency used for V . Of course, FREQ

the surest method of determining the average depth is directly from nearby stage

data extrapolated to the site in question. In the absence of stage data, regional relationships of peak flow discharge for different frequencies to basin area may be

available from agencies such as the USGS. For an example of USGS state-specific

studies for regional peak discharge relationships, see Stamey and Hess (1993) and

for flood-depth frequency see Price (1977). An estimated peak discharge used in

conjunction with calculation of channel and floodplain flow capacity by Manning's

formula can be solved for flow depth at the time of peak discharge. Procedures for

determining flow capacity by Manning's formula are given in many hydrology textbooks. The reader is directed to Chow, Maidment, and Mays (1988) and Dunne and

Leopold (1978) for two levels of discussion on application of the Manning formula. 

Rosgen's (1994) methodology of stream classification is also a helpful tool for comparing channel systems and depth of inundation associated with their floodplain. 

A wetland that has an average depth of inundation for the annual flood (or the

recurrence interval indicated by the appropriate reference standard) equal to about

75 to 125 percent of the average reference standard scores 1.0. Lesser or greater

inundation depths for the annual flood stage would have an index of 0.5 or 0.1, depending on degree of departure. The reasoning for assigning a lower index score to

lesser or greater inundation depths is that the attainment of the function would be

less under both conditions. For example, greater depths of inundation would likely

not have as great an impact on timing of the flood wave, in comparison to the reference standard, than if the depth were within the 75- to 125-percent range. If the
18 Chapter 2 Documentation of Riverine Wetland Functions

reference domain indicates otherwise, the variable can be appropriately scaled. If

overbank flow or upland surface flow does not occur, depth of inundation is zero

and the index score is zero.

VMICRO, Microtopographic complexity. Microtopography is a component of

roughness that influences the tortuosity of flow pathways and reduces average velocity, and hence, detention time of surface water flowing through a wetland. 

Deep flooding may cancel the effects of microtopographic complexity to the

point that it does not have a significant effect on the function during major floods,

especially in large, high-energy river systems. Microtopographic complexity should

not be overlooked, however, because even minor relief may be important in detaining flood flow in low-energy systems. Further, microtopographic complexity is

usually important for long-term surface water storage and vegetation and habitat

functions.

As with depth of inundation, surface roughness between 75 and 125 percent of

the reference standard scores 1.0. Departures from the reference standard are scored

using the same approach as for depth of inundation. Microtopographic surveys are

too costly for most applications. A suggested alternative is to make visual comparisons by recording the number of depressions or hummocks that fall within predetermined size (cross-section area and depth/height dimensions) classes per unit area

(e.g., 10 by 10 m). For example, microdepression size classes might be 0.5, 1.0,

and 1.5 m and depths of 5, 10, and 15 cm. 2

Another empirical measure of roughness is Manning's roughness coefficient (n). 

This measure encompasses not only VMICRO, but also roughness due to vegetation

(e.g., V , V , and V ) and coarse woody debris (V ). A number of ap- SHRUB BTREE DTREE CWD

proaches can be used to estimate the coefficient; whichever method is used, it must

account for floodplain roughness. The user is referred to Arcement and Schneider

(1989) and Barnes (1967) for handbooks of photographs and measurements, and to

local guides often available from the Natural Resources Conservation Service

(NRCS) for suggested field methods to determine the roughness coefficient. Be

sure to use an approach that allows determination of the floodplain roughness coefficient, since it is the floodplain wetland and not the stream channel that is performing the function. Floodplain values of n are given in Dingman (1994) and others. 

Consultation with an experienced, local surface water hydrologist is another

approach to selecting the appropriate coefficient. An assessment site with a Manning's n similar to the reference standard would score a 1.0. Sites with a somewhat

significant positive or negative departure would score a 0.5, and significant departures would score a 0.1 or 0. If the Manning's n is difficult to determine, use the

variables VMICRO, V , V or V , and V without substitution. SHRUB BTREE DTREE CWD

Plant roughness variables. The density and size of woody stems (trees and

shrubs) are major contributors to site roughness. These attributes create surface

roughness that detain water. Stems also may trap organic debris ranging in size

from leaves and twigs to logs. Trapped debris enhances the roughness and serves to

further detain water by slowing water velocity.
Chapter 2 Documentation of Riverine Wetland Functions 19

In the discussion below, the woody vegetation roughness variable is separated

into its components (trees and shrubs) and either an average or a weighted average

is calculated to determine their scores. Energy Dissipation utilizes two vegetation

roughness variables. In low-energy systems, it may be appropriate to consider cover

or density of herbaceous plants in conjunction with woody vegetation roughness.

When assessing this variable with respect to the Dynamic Surface Water Storage

function, keep in mind that the roughness contributed by stems and debris within the

average depth of inundation (V ) is represented by the roughness factors to be INUND

considered. It is for this reason that number of stems and concentration of woody

debris on the ground are the metrics for direct or indirect measurement. The index

of the variable is scored in the same manner as variable VMICRO. 

Direct measures of vegetation roughness are stem density (stems/acre) for trees

and shrubs and basal area for trees. If a Manning's roughness coefficient is used,

variables VMICRO, VSHRUB, VBTREE or VDTREE, and VCWD may be combined, as explained

in VMICRO.

V , Shrub and sapling density, biomass, or cover. Density, biomass, or SHRUB

cover of woody understory plants (shrubs and saplings). Shrubs and saplings contribute to the roughness mainly by clumps and/or number of stems. They tend to be

more effective at higher densities because of their stature and resistance.

V , Tree density. Density of large-diameter canopy trees (V may be DTREE BTREE

used instead). Tree density, although low relative to shrubs and herbaceous plants,

creates roughness that is especially effective at high flows and in deep water. Secondary effects are the entrapment of coarse woody debris, which can further increase

site roughness.

VBTREE, Tree basal area. Basal area or biomass of trees ( VDTREE may be used

instead). Basal area is easy to measure and is somewhat proportional to the surface

area of stems in contact with flowing water, thus contributing to site roughness.

V , Coarse woody debris. Coarse woody debris (CWD) on floodplains con- CWD

tributes to roughness, hence, slowing the movement of water and ameliorating

flooding downstream. CWD includes dead and downed trees and limbs larger in

diameter than some predetermined size (usually greater than 10 cm in diameter and

longer than 1 meter) appropriate to the reference standard of the regional geomorphic class being assessed. The ecological significance of CWD is described in more

detail in the section Maintain Characteristic Detrital Biomass. For example, a much

higher biomass for CWD would be expected for high-energy floodplains of oldgrowth forests in the Pacific Northwest than for an equivalent geomorphic riverine

class in the eastern United States or in urban areas.

Several methods have been developed for measuring CWD (Harmon et al.

1986), but almost all express the variable in volume per unit area. Average

diameters and lengths of stems could be measured or their density estimated in plots

for comparison with reference standards. Overall roughness can be cal- culated
Index of Function [VFREQ × (VINUND VMICRO VSHRUB

VBTREE or VDTREE VCWD)/5]

1/2

Index of Function [VFREQ × (VINUND

VMICRO, SHRUB, BTREE or DTREE, and CWD)/2]

1/2

20 Chapter 2 Documentation of Riverine Wetland Functions

using Manning's roughness coefficient to replace variables VMICRO, V , V or SHRUB BTREE

V , and V . DTREE CWD

Index of function

For Dynamic Surface Water Storage, the variables are frequency of overbank

flow (VFREQ), average depth of inundation (VINUND), microtopographic complexity

(VMICRO), woody vegetation roughness (VSHRUB, VBTREE, or VDTREE), and coarse woody

debris roughness (V ). Overbank flow or upland surface flow is an absolute re- CWD

quirement for this function; if it does not occur, the index score is zero as depicted

in the equation. If depth and roughness variables are all absent, the index score is

also zero. It is assumed that both factors are equally important in the reference standard. A slope variable may be appropriate to add for low-order, steep-gradient

systems.

If the Manning's roughness coefficient is used to aggregate variables VMICRO, V , SHRUB

V , V , and V , the equation becomes BTREE DTREE CWD
Chapter 2 Documentation of Riverine Wetland Functions 21

Documentation

DYNAMIC SURFACE WATER STORAGE

Definition: Capacity of a wetland to detain moving water from overbank flow for a short duration

when flow is out of the channel; associated with moving water from overbank flow and/or upland

surface water inputs by overland flow or tributaries.

Effects Onsite: Replenishes soil moisture; import/export of materials (i.e., sediments, nutrients,

contaminants); import/export of plant propagules; provides conduit for aquatic organisms to access

wetland for feeding, recruitment, etc.

Effects Offsite: Reduces downstream peak discharge; delays downstream delivery of peak discharges; improves water quality.

Model Variables Direct Measure Indirect Measure Index of Variable

VFREQ: Frequency Gauge data (1.5) yr return At least one of the following: aerial pho- 1.0

of overbank flow interval similar to reference tos showing flooding, water marks, silt

standard. (Interval in paren- lines, alternating layers of leaves and

theses must be adjusted to fine sediment, ice scars, drift and/or

the reference standard.) wrack lines, sediment scour, sediment

deposition, directionally bent vegetation

similar to reference standard.

Gauge data (>2 or <1) yr As above, but somewhat greater or less 0.5

return interval. than reference standard. 

Gauge data show extreme Above indicators absent but related indi- 0.1

departure from reference cators suggest overbank flow may

standard. occur.

Gauge data indicate no Indicators absent and/or there is evi- 0.0

flooding from overbank flow. dence of alteration affecting variable.

VINUND: Average Gauge data indicate that Height of water stains and other indica- 1.0

depth of inundation depth is between 75% and tors of water depth (ice scars, bryophyte

125% that of reference lines, drift and/or wrack lines, etc.)

standard. between 75% and 125% of reference

standard.
22 Chapter 2 Documentation of Riverine Wetland Functions

VINUND: Gauge data indicate depth is <75% Height of water stains and other indi- 0.5

(Concluded) or >125% of reference standard. cators of water depth (ice scars,

bryophyte lines, drift and/or wrack

lines, etc.) <75% of reference

standard.

Gauge data indicate infrequent or Above indicators absent but related 0.1

minor overbank flooding relative to indicators suggest variable may be

reference standard. present. 

Gauge data indicate flooding does Indicators absent and/or evidence of 0.0

not occur. alteration affecting the variable.

VMICRO: Microtopo- Microtopographic complexity (MC) Visual estimate indicates that micr- 1.0

graphic

complexity

measured (surveyed) shows MC otopographic complexity (MC) is

>75% to <125% of reference >75% and <125% of reference

standard. standard.

Measured MC is between 25% and Visual assessment confirms MC is 0.5

75% that of reference standard. present, but somewhat less than

reference standard.

Measured MC between 0% and Visual assessment indicates MC is 0.1

25% that of reference standard; much less than reference standard;

restoration possible. restoration possible.

No MC at assessed site or natural Visual assessment indicates MC is 0.0

substrate replaced by artificial virtually absent or natural substrate

surface. replaced by artificial surface; restoration not possible.

VSHRUB: Shrub Shrub abundance >75% that of ref- Visual estimate of shrubs and sap- 1.0

and sapling density, biomass, or

cover

erence standard. lings indicates site is similar (>75%)

to reference standard.

Shrub abundance between 25% and Visual estimate of shrubs and sap- 0.5

75% that of reference standard. lings indicates site is between 25%

and 75% that of reference standard. 

Shrub abundance between 0% and Shrubs and saplings are sparse or 0.1

25% that of reference standard. absent relative to reference standard;

restoration possible.

Shrubs absent; restoration not Shrubs absent; restoration not 0

possible. possible.

VBTREE: Tree Basal area or biomass is greater Stage of succession similar to refer- 1.0

basal area (VDTREE

may be used

instead)

than 75% of reference standard. ence standard.

Basal area or biomass between Stage of succession departs 0.5

25% and 75% of reference significantly from reference

standard. standard.

Basal area or biomass between 0% Stage of succession at extreme de- 0.1

and 25% of reference standard; res- parture from reference standard.

toration possible. 

No trees present; restoration not Stand cleared without potential for 0.0

possible. recovery.
Index of Function [VFREQ × (VINUND VMICRO VSHRUB

VBTREE or VDTREE VCWD)/5]

1/2

Index of Function [VFREQ × (VINUND

VMICRO, SHRUB, BTREE or DTREE and CWD)/2]

1/2

Chapter 2 Documentation of Riverine Wetland Functions 23

VDTREE: Tree Measured or estimated tree Stage of succession similar to reference 1.0

density (VBTREE

may be used

instead)

density between 75% and standard.

125% of reference standard.

Tree density between 25% Stage of succession departs significantly 0.5

and 75%, or between 125% from reference standard.

and 200% of reference

standard.

Tree density between 0% and Stage of succession at extreme 0.1

25% or greater than 200% of departure from references standard; resreference standard; restora- toration possible.

tion possible.

No trees are present; Stand cleared; no restoration possible. 0.0

restoration not possible.

VCWD: Coarse Biomass of CWD is >75% Average diameters and lengths of CWD 1.0

woody debris and <125% of reference is >75% and <125% of reference

standard. standard.

Biomass of CWD is between Average diameters and lengths of CWD 0.5

25% and 75% that of refer- is between 25% and 75% that of reference standard. ence standard.

Biomass of CWD is between Average diameters and lengths of CWD 0.1

0% and 25% that of refer- is between 0% and 25% that of reference

ence standard; restoration standard; restoration possible.

possible.

No CWD present; restoration No CWD present; restoration not 0.0

not possible. possible.

Option 1:

If the Manning's roughness coefficient is used to aggregate variables VMICRO, V , SHRUB

V or V , and V , the equation becomes BTREE DTREE CWD

Option 2:
24 Chapter 2 Documentation of Riverine Wetland Functions

Long-Term Surface Water Storage

Definition

Long-term surface water storage is the capacity of a wetland to store (retain) surface water for long durations. The source of water may be overbank flow, overland

flow, tributary flow, subsurface flow from uplands, or direct precipitation. Longterm surface water storage is associated with standing water in the wetland that is

not moving over the surface. Durations vary with region, but long-term storage may

be considered to begin when overbank flow retreats into the channel and is present

in the wetland for more than 7 days. When the source of water is direct precipitation or from upland sources, long-term storage is water ponded until lost by evapotranspiration and drainage.

Discussion of function and rationale

As with the dynamic surface water storage function, long-term surface water

storage has both hydrologic and ecological importance (Gosselink and Turner

1978). Many river systems possess wetlands that cover broad, flat floodplains. 

Therefore, water may pond over the surface of these wetlands for long periods of

time in backswamp areas, behind natural levels, in old meander scars, in depressions

and pits, etc. Ponding is considered long term if it lasts for a week or longer, because shorter durations in most cases are not long enough to be critical to other variables associated with soil anaerobiosis, biogeochemical processes, and invertebrate

habitat. An increase in duration of long-term storage, such as occurs from backwater (channel restrictions) and impoundments, can have an adverse impact on

hydrologic and ecologic functions (Conner and Day 1989).

If the source of water is overbank flow, retention of floodwater in the wetland

will decrease the volume of floodwater transported downstream. The portion of the

retained water that infiltrates and recharges surficial ground- water may become

base flow at a later time, thus contributing to higher base flows and moderated

distribution of seasonal flows. Ponding may also diminish gaseous exchange

between the atmosphere and soil, prohibit the germination of seeds, lead to

prolonged soil saturation (quite often longer than the period of ponding), provide

support for aquatic vertebrates and invertebrates, and contribute to other ecological

processes. Colloidal inorganic and organic sediments with sorbed nutrients and

contaminants will settle during the prolonged ponding and contribute to other

functions.

If the principal source of water is other than overbank flow, this function is still

important to the overall functioning of a wetland. The same onsite effects are likely

to occur when other sources dominate, except there will be no moderation of a flood

hydrograph because water did not enter the wetland by overbank flow.
Chapter 2 Documentation of Riverine Wetland Functions 25

Description of variables

V , Indications of surface water presence. For the Long-Term Surface SURWAT

Water Storage function to occur, a wetland must be inundated by ponded or retained

water for a continuous period of not less than 1 week. Site assessments are not always possible when there is the presence of surface water for the requisite continuous duration. Use of this variable assumes that if surface water is present, it is present for the required duration. Therefore, local indicators must usually be developed

as indirect measures of presence and duration. It is suggested that a hierarchy of

decision points be used to determine if ponded water has or is expected to occur; if

the ponding is continuous; and if continuous, the duration of ponding. 

Indicators of presence of ponding (such as drift lines) may not indicate much

about continuity and duration. Other indicators such as the absence of regeneration

of annual plants or water-stained leaves may imply continuity and duration of

ponded water. It is recommended that, during the establishment of the reference

standard for this variable, observation of local indicators as tied to direct measures

be noted to aid in the interpretation of assessment sites. 

Other indicators of ponded water include direct observation, appearance on aerial photographs, inference from NRCS soil series descriptions, water balance calculations using local rainfall and evapotranspiration data, or calculations of streamflow or staff gauge data indicating the occurrence of overbank flow that would fill

depressions, backswamps, or trap water behind natural levees. 

Indirect indicators of the presence of water ponded over the long term are the

absence of herbaceous vegetation (indicating that soil surfaces are not exposed

during normal germination and emergence periods), organic matter accumulation in

the soil, and low permeability or infiltration rates of the soil. 

Low infiltration capacity can be inferred from NRCS hydrologic soil groups C or

D (if soil series is known). The NRCS hydrologic soil groups are used in the runoff

curve number approach to predict stormflow volumes. The hydrologic soil group

for all soil series are published in modern Soil Surveys and in soil series

interpretations. Groups C and D have the lowest infiltration capacity and therefore

the highest stormflow production potential. Because of soil variability, particularly

in alluvial riverine settings, the published hydrologic soil group may not be the best

indicator of infiltration capacity and ponding ability. If used as an indicator, the soil

groups should be verified in the field and used in conjunction with other indicators. 

However, if soils with low infiltration are not part of reference standards, other

indicators should be used for this variable.

If surface water is present more often than not, and the principal water source for

maintenance of ponding condition is other than overbank flow, it may be advisable

to place the wetland in a depressional class. Slow losses of ponded water through a

constricted outlet (e.g., oxbow depression) would indicate its connection with a

riverine system.
26 Chapter 2 Documentation of Riverine Wetland Functions

Sites equivalent to the reference standard based on the presence of either direct

or indirect indicators score 1.0. Less strong indications of long-term storage in

comparison with the reference standard are scored lower. The highest score of 1.0 is

generally associated with strong indications that water is ponded for long periods of

time at least once each year during the growing season. Lack of conditions to pond

water or presence of an altered condition scores zero. 

VMACRO, Macrotopographic relief. For long-term storage to occur, particularly

when a stream has retreated to within its banks, there must be topographic relief on

the floodplain that consists of restricted outlets thus allowing surface water to be

trapped for the requisite duration. Relief features on a sloping landscape that will

not serve to trap water for long periods do not contribute to the expression of this

variable. 

Macrotopographic relief features include oxbows, meander scrolls, abandoned

channels, and backswamps. Each of these features in a riverine setting is often associated with a particular landform or landscape setting and stream order. Such

macrotopographic features are usually found in higher order streams or streams with

steep gradients. Low-energy systems and small stream floodplains with low gradients usually lack such distinctive macrotopographic features. Therefore, this variable should not be used in modeling the Long-Term Surface Water Storage function

if it is not present in reference standard sites.

When the macrotopographic relief features are similar to reference standards,

such as being well formed on a wetland with little or no surface gradient, the variable index is 1.0. Where relief features have been altered so that they do not serve

to trap water for long periods, the site should be scored lower (0.5 or 0.1), depending on the rate at which surface drainage might occur relative to the reference standard. If macrotopographic relief is not significant and the surface gradient is moderate to steep, indicating a rapid loss of water or that no ponding occurs relative to

reference standards, the variable index is zero. Altered wetlands may have their

macrotopographic features reduced or made ineffective through filling, leveling, and

drainage.

Index of function

Presence of water (V ) and macrotopographic relief (V ) are variables SURWAT MACRO

associated with the Long-Term Surface Water Storage function. There is no variable directly related to the actual length of time that water is present on the surface;

rather, time of ponding (inferred by vegetation and soil indicators of processes) is

compared with the reference standard. Longer times of ponding are not critically

important to offsite effects of this function since the main effect is the reduction of

flow peaks. In some wetland ecosystems, the length of time may be critical to some

onsite ecological processes and wetland functions. When this is the case, a time of

ponding variable should be added to the model (consider using V ). The same DURAT

index must be used for the assessed wetland as for reference standard sites.
Index of Function (VSURWAT VMACRO)/2

Chapter 2 Documentation of Riverine Wetland Functions 27

Documentation

LONG-TERM SURFACE WATER STORAGE

Definition: Capacity of a wetland to temporarily store (detain) surface water for long durations;

associated with standing water not moving over the surface. Sources of water may be overbank flow,

direct precipitation, or upland sources such as overland flow, channel flow, and subsurface flow.

Effects Onsite: Replenishes soil moisture; removes sediments, nutrients, and contaminants; detains

water for chemical transformations; maintains vegetative composition; maintains habitat for feeding,

spawning, recruitment, etc., for pool species; influences soil characteristics.

Effects Offsite: Improves water quality; maintains base flow; maintains seasonal flow distribution;

lowers the annual water yield; recharges surficial groundwater.

Model Variables Direct Measure Indirect Measure Index of Variable

VSURWAT: Indicators 1. Gauge data indicate overbank Compared to regional reference 1.0

of surface water

presence

flow sufficient to pond water or standard: 

2. Direct observation of ponded 1. Annual understory (grass and

water or woody reproduction, etc., absent)

3. Aerial photo evidence con- or

firms flooding similar to reference 2. High organic matter accumulastandard. tion at soil surface or

3. Massive soil structure with low

permeability and general lack of

small roots in the surface soil horizon or

4. NRCS Hydrologic Soil Group C

or D when soil series known.
Index of Function (VSURWAT VMACRO)/2

28 Chapter 2 Documentation of Riverine Wetland Functions

VSURWAT: As above, but below reference 0.5

(Concluded) standard.

Above indicators absent but related 0.1

indicators suggest variable may be

present.

Gauge data indicate no overbank Indicators absent and/or there is 0.0

flow; ponding minor or not evi- evidence of alteration affecting

dent; no evidence of flooding on variable.

aerial photos.

VMACRO: 1. Contour maps indicate gross Oxbows, meander scrolls, aban- 1.0

Macrotopographic

relief 

relief and/or closed contours sim- doned channels, backswamps,

ilar to reference standard or etc., similar in magnitude to refer2. Topographic survey shows ence standard. 

relief similar to reference

standard. 

Indicators above much less devel- 0.5

oped than reference standard and

area has a low surface gradient.

Maps and/or topographic survey All above indicators absent and 0.0

indicate relief very dissimilar to area has a moderate to steep

reference standard. gradient.

Energy Dissipation

Definition

Allocation of the energy of water to other forms as it moves through, into, or out

of the wetland as a result of roughness associated with large woody debris, vegetation structure, micro- and macrotopography, and other obstructions.

Discussion of function and rationale

This function not only pertains to rate of flow through the wetland, partially accounted for by Dynamic Surface Water Storage, but is related more to how energy is

expressed in the water flowing into, through, and out of a wetland. In high-energy

streams, common in the Pacific Northwest and other mountainous regions, large

woody debris and boulders are moved in the channel and onto wetlands. As a result

of energy dissipation within wetlands, pressure on channel beds and banks is lower

so the system is more stable. For example, a recently clear-cut forested riparian area

will have few trees in place for large woody debris to lodge against. Energy that

would otherwise be dissipated in the floodplain will be transferred to channel scour,

channel clogging by debris, and movement/ deposition of sediment. Similar
Chapter 2 Documentation of Riverine Wetland Functions 29

hydrologic processes occur in lower energy systems with less obvious expressions,

but no less important to the functioning of wetlands.

Energy dissipation has secondary effects as well. Deposition of large woody

debris within a wetland not only enhances the function but also is important to

biogeochemical functions (Lisle 1995). Dissipated energy expressed as scour holes

and sediment deposition may also enhance dynamic and long-term surface water

storage by creating more topographic relief and surface roughness. An offsite hydrologic expression of the energy dissipation function is the reduction in flood peak,

flood wave celerity, and improved water quality (i.e., less sediment). Channelized

streams are designed to increase channel velocity and minimize overbank flow. The

resultant channel flow (unless artificially stabilized) will undercut banks, and the

channel will begin a meandering process to dissipate the energy.

Description of variables

V , Reduction in flow velocity. Critical to dissipation of energy is reduc- REDVEL

tion in water velocity as it passes through the wetland. Velocity is reduced by surface roughness and obstructions, and by spreading of water over a larger area (the

wetland). In using the general relationship of discharge (Q) equals mean velocity

(V) times cross section of flow area (A), an increase of A results in a proportional

reduction in V.

Direct measures of velocity reduction are difficult; rarely is one at the site at the

time of a flood event. Velocity of flow within the wetland may be estimated by use

of Manning's formula, but careful selection of the roughness coefficient for the

floodplain must be made. (See discussion for the Dynamic Surface Water Storage

function, V , for a discussion of the roughness coefficient.) A local table of INUND

roughness coefficients could be developed to estimate relative differences between

wetland conditions that could be related to expected velocity reductions.

The stronger the expression of velocity reduction in a wetland, the greater its

index score relative to the reference standard. Sediment deposits, scour, buried root

collars, and large woody debris deposited or moved about indicate a wetland's capacity to reduce velocity. When velocity reduction is not clearly evident at the reference wetland sites by the above indicators, the site roughness variables identified

below should be used instead. The rationale is that velocities are not great or site

roughness has contributed to a marked reduction in velocity as overbank flow occurs. The observer must make the distinction based on local knowledge and best

professional judgment.

In systems where gradient (none to steep) is a dominant factor in reducing velocity and is exhibited by the indicators, a slope variable may be added to the regional

model. Slope combined with the roughness and overbank flow variables may be an

appropriate model in low-order, steep-gradient riverine systems.

An alternative to direct measures of velocity are estimates, perhaps by Manning's

equation, of the ratio of expected velocities in the channel at bank-full stage and
30 Chapter 2 Documentation of Riverine Wetland Functions

expected velocity at V . A velocity reduction ratio within 75 percent of the ref- INUND

erence standard would score 1.0, and lesser reductions would score 0.5 or 0.1. No

reduction would score a zero.

V , Frequency of overbank flow. For flow energy to be dissipated, water FREQ

must enter a wetland. Therefore, the frequency and occurrence of overbank flow to

a riverine wetland is critical to this function. Flooding recurrence intervals used for

assessment of this function must be tied to the reference standard. Absence of overbank flow negates the function for the frequent events and the variable scores zero. 

Riverine wetlands that do not experience frequent (annual) overbank flows are usually not high-energy systems, and so energy dissipation on short recurrence intervals

by such wetlands may not be critical. Rather, it may be during long recurrence-interval events (e.g., 50- and 100-year events) that incised wetlands may play a critical

role in dissipation of these high-energy overbank flows. Such high-energy, infrequent flows often reset riverine wetlands by creating scour holes, depositing sandbars, and importing or moving about large woody debris and other similar features.

The use of parentheses in the documentation of this variable indicates that other

recurrence intervals could be used relative to the reference domain. For example,

recurrence interval for oak flats would be approximately 2 to 5 years. In this case, a

2- to 5-year recurrence would have an index of 1.0, with lower scores for altered

conditions, e.g., less than 2 years or greater than 5 years.

Overbank flow is best quantified by hydrographic data that can be used as a direct measure of this variable. Such data may be obtained from either federal or state

agencies that maintain hydrogeographic databases. The reference standard is the

frequency of overbank flow found in reference standard sites. If the frequency of

overbank flow of the assessment site has a frequency of 75 to 125 percent, a score

of 1.0 is given. If the frequency is 25 to 75 percent or >125 percent, compared to

reference standards, an index score of 0.5 is given. If the assessment area rarely

floods (>0 to <25 percent), 0.1 is recorded. If there is no flooding of the wetland by

overland flow, the variable receives a zero.

VMACRO, VMICRO, V , V , Site roughness. If indicators of velocity reduc- DTREE CWD

tion are not readily interpreted, a site roughness complex variable may be used instead. As size and number of obstacles to surface flow increase, the potential for

energy dissipation increases. As water flows over surfaces, friction and shear forces

create turbulent flow and reduce velocities. These critical gross features of site

roughness are characterized by macrotopographic relief (VMACRO), microtopographic

complexity (VMICRO), numbers of trees (V ), and the size, distribution, or volume DTREE

of coarse woody debris (V ). CWD

The more complex the roughness and the more stable its structure (large- diameter stems, large woody debris lodged against tree stems), the greater the potential for

energy dissipation. As with the Long-Term Surface Water Storage function, the

microtopographic complexity variable (VMICRO) may not be appropriate for high-energy riverine systems. The four variables are scaled independently. However, Manning's coefficients have been developed for site-specific data to attempt to provide

quantitative relationships between roughness and wetland structure (Arcement and
Index of Function (VFREQ × VREDVEL)

1/2

Index of Function {VFREQ × [(VMACRO VMICRO VDTREE

VCWD)/4]}

1/2

Index of Function [VFREQ × (VMACRO, MICRO, DTREE, CWD)]

1/2

Chapter 2 Documentation of Riverine Wetland Functions 31

Schneider 1989). This coefficient integrates all variables of roughness which, if

information were available, would allow the collapsing of VMACRO through VCWD into

one variable (see Dynamic Surface Water Storage function as an example). However, care must be exercised if Manning's roughness coefficient is used for making

field comparisons, because many tables of values do not include large features that

may occur in some wetlands, particularly large woody debris found in the Pacific

Northwest.

Each of the roughness components should be evaluated separately unless there

are available guidelines for Manning's n. A complex and stable roughness system

comparable to the reference standard scores a 1.0, and as complexity decreases, the

score decreases to 0.1. Estimates below reference standard score 0.5 unless roughness is virtually absent. Smoothed, graded surfaces receive 0.1 or zero depending

on the potential for recovery.

Index of function

Reduction in flow velocity (VREDVEL), frequency of overbank flow (VFREQ), and

site roughness (VMACRO, VMICRO, V , V ) are the variables describing the func- DTREE CWD

tion. These variables must be scaled to reference standards appropriate to the hydrologic regime. The variables are combined to express the function index as follows:

or

or

if Manning's n is used as a surrogate for the site roughness factors, 

It is assumed that each of the combined roughness variables, frequency of overbank

flow, and reduction of flow velocity are equally important in maintaining the function in reference standards.
32 Chapter 2 Documentation of Riverine Wetland Functions

Documentation

ENERGY DISSIPATION

Definition: Allocation of the energy of water to other forms as it moves through, into, or out of the

wetland as a result of roughness associated with large woody debris, vegetation structure, micro- and

macrotopography, and other obstructions.

Effects Onsite: Increases deposition of suspended material; increases chemical transformations and

processing due to longer residence time.

Effects Offsite: Reduces downstream peak discharge; delays delivery of peak discharges; improves

water quality; reduces erosion of shorelines and floodplains.

Model Variables Direct Measure Indirect Measure Index of Variable

VREDVEL: Reduc- Velocity in wetland >75% Sediment deposits, silt deposits on vege- 1.0

tion in flow

velocity

of that expected in reference tation, buried root collars, stacked wracks

standard sites. of debris, etc., similar to reference

standard.

Less than 75% reduction in Sediment scour, scoured root collars, 0.5

velocity relative to standard. large woody debris moved about; erosion

of soil surface, etc., indicating less than

reference standard.

Directionally bent vegetation, bare soil 0.1

exposed (not sediment deposits), strongly

departing from reference standard.
Chapter 2 Documentation of Riverine Wetland Functions 33

VREDVEL: No reduction in velocity by di- Strong evidence of severe site degrada- 0.0

(Concluded) rect measurement. tion by channel scour, exposed root

masses, suggesting variable is absent.

VFREQ: Frequency Gauge data At least one of the following: aerial pho- 1.0

of overbank flow (1.5) yr return interval; within tos showing flooding, water marks, silt

75% and 125% of reference lines, alternating layers of leaves and fine

standard. (Intervals in paren- sediment, ice scars, drift and/or wrack

theses must be adjusted to the lines, sediment scour, sediment deposireference standard.) tion, directionally bent vegetation similar to

reference standard.

Gauge data As above, but somewhat greater or less 0.5

(>2 or <1) yr return interval; than reference standard.

25% to 75% or >125% of reference standard.

Gauge data show extreme Above indicators absent, but related indi- 0.1

departure from reference stan- cators suggest overbank flow may occur.

dard, e.g., 0% to 25%.

Gauge data indicate no flood- Indicators absent and/or there is evidence 0.0

ing from overbank flow. of alteration affecting variable; restoration

not possible.

VMACRO: Macro- 1. Contour maps indicate gross Oxbows, meander scrolls, abandoned 1.0

topographic relief relief and/or closed contours channels, backswamps, etc., similar in

similar to reference standard or magnitude to reference standard.

2. Topographic survey shows

relief similar to reference

standard.

Indicators above much less developed 0.5

than reference standard, and area has a

low surface gradient.

Maps and/or topographic sur- All above indicators absent and area has 0.0

vey indicates relief very dissimi- a moderate to steep gradient.

lar to reference standard.

VMICRO: Micro- Microtopographic complexity Visual estimate indicates that micro- 1.0

topographic

complexity

(MC) measured (surveyed) topographic complexity (MC) is >75% and

shows MC > 75% to < 125% of <125% of reference standard.

reference standard.

Measured MC is between 25% Visual assessment confirms MC is 0.5

and 75% that of reference present, but somewhat less than

standard. reference standard.

Measured MC between 0% and Visual assessment indicates MC is much 0.1

25% that of reference stan- less than reference standard; restoration

dard; restoration possible. possible.

No MC at assessed site of Visual assessemnt indicates MC is 0.0

natural substrate replaced by virtually absent or natural substrate

artificial surface. replaced by artificial surface; restoration

not possible.
Index of Function (VFREQ × VREDVEL)

1/2

Index of Function {VFREQ × [(VMACRO VMICRO VDTREE VCWD)/4]}

1/2

Index of Function [VFREQ × (VMACRO, MICRO, DTREE, CWD)]

1/2

34 Chapter 2 Documentation of Riverine Wetland Functions

VDTREE: Tree density Measured or estimated tree density Stage of succession similar to 1.0

between 75% and 125% of refer- reference standards.

ence standard.

Tree density between 25% and Stage of succession departs 0.5

75%, or between 125% and 200% significantly from reference

of reference standard. standards.

Tree density between 0% and Stage of succession at 0.1

25%, or greater than 200%, of ref- extreme departure from refererence standard; restoration ence standards; restoration

possible. possible.

No trees are present; restoration Stand cleared; no restoration 0.0

not possible. possible.

VCWD: Coarse woody Biomass of CWD >75% and Average diameters and 1.0

debris <125% that of reference standard. lengths of CWD is >75% and

<125% that of reference

standard. 

Biomass of CWD between 25% Average diameters and 0.5

and 75% that of reference lengths of CWD is between

standard. 25% and 75% that of reference standard.

Biomass of CWD is between 0% Average diameters and 0.1

 and 25% that of reference stan- lengths of CWD is between

dard; restoration possible. 0% and 25% that of reference

standard; restoration possible.

No CWD present; restoration not No CWD present; restoration 0.0

possible. not possible.

or

or

If Manning's n is used as a surrogate for the site roughness factors, 

It is assumed that each of the combined roughness variables, frequency of overbank

flow, and reduction of flow velocity are equally important in maintaining the function in reference standards.
Chapter 2 Documentation of Riverine Wetland Functions 35

Subsurface Storage of Water

Definition

Availability of storage for water beneath the wetland surface. Storage capacity

becomes available as periodic drawdown of the water table or reduction in soil

saturation occurs, making drained pores available for storage of water. Drawdown

may be the result of vertical and lateral drainage and/or evapotranspiration.

Discussion of function and rationale

Evacuated pores provide available volume for storing water entering a wetland. 

The absorption and storage of water below-ground can reduce the depth of wetland

inundation and slow the release of water to the stream (in contrast to surface flow

directly to the channel). Below-ground storage also helps to maintain base flows. 

The ability of soils with small pores to absorb and hold water for long periods favors the survival of plant species that can most tolerate long periods of saturation

(obligate and facultative wet hydrophytes).

A soil's potential for subsurface storage is a function of the size and abundance

of the soil pore spaces and antecedent degree of saturation. Although clay soils possess more pore space than sandy soils, the smaller size of pores in clay retards the

rate of both absorption and release of water. For this reason, clay soils usually possess a lower capacity to store water than sandy soils.

The degree of saturation of a soil is affected by prior flooding events, precipitation and other inputs, and rate and extent of water table drawdown. This determines

actual storage capacity at a particular point in time. Frequent floods (a seasonal

phenomenon in some areas) or a constant input of water (either ground or surface

water) may render a wetland soil incapable of additional storage of water. Alterations of hydrology that create inundation (e.g., beaver activity) or saturation to the

surface also alter this function.

Storage of water beneath the wetland surface supports ecological processes and

maintains hydrologic processes. As water is evacuated from porous media (mineral

or organic soils) as a result of drainage or evapotranspiration, gaseous exchange

readily occurs and empty pores are filled with air. This fluctuation between aerobic

and anaerobic conditions benefits the recruitment, survival, and competitiveness of

wetland plant species and sustains environmental conditions necessary for microbially mediated biogeochemical cycling.

Description of variables

V , Soil pore space available for storage. Soil texture and drawdown of the PORE

water table or reduction in soil saturation (creating air-filled pores) are factors that

must be considered in scaling this variable. Coarse soil textures (sandy loams and

coarser) and water tables that fluctuate within 15 to 30 cm of the surface, yet
36 Chapter 2 Documentation of Riverine Wetland Functions

maintain wetland soil wetness conditions, would have a high potential for providing

volume of empty pore space for subsurface water storage. Finer texture soils that

have a capillary fringe extending to near the surface would have a low potential for

subsurface storage. Sites saturated to the surface or ponded for long periods of time

have little or no potential for subsurface storage.

Caution must be exercised in specifying a reference standard for this function's

variables because the “wetter” a wetland is, the lower its index score. So it is important that the reference standard be correctly identified both in terms of degree of

soil wetness, rate of drainage or water table drawdown, and soil texture. The time

of year that this function should be defined is when the riverine wetland is subject to

the most frequent flooding (i.e., the annual flood). It is during this period of time

that the variables are most critical to the function. The variables are less important

for less frequent floods that are preceded by high rainfall, thereby saturating the soil

and reducing the potential for subsurface storage. Frequent flooding that leads to

long-term soil saturation or inundation also reduces the capacity for subsurface

storage.

For comparative purposes the available water storage capacity for soil series horizons (NRCS Soil Surveys) can be used to determine the potential pore space available for storage if the soil were drained. The degree of saturation and position of

the water table must then be considered to determine how much of the pore space

will be available for subsurface storage.

Comparisons must be made to similar conditions defined by the reference standard. Sites similar to the reference standard for soil textures and fluctuating water

table or degree of soil saturation score an index of 1.0. Sites that do not meet the

reference standard score zero when no subsurface storage is available.

VWTF, Fluctuation of water table. The water tables of most riverine wetlands

undergo drawdowns due to evapotranspiration and drainage, and rises due to precipitation and flood events. Drawdowns combine with pore space to provide potential

volume for storage of water below the wetland surface.

Fluctuations in the water table can be directly measured as depth to water table

from the surface in wells screened throughout the depth interval of fluctuation. 

High frequency measurements (>1/day) can be made in association with data loggers; alternatively, less frequent measurements would approximate the range in fluctuations on a seasonal basis. During a period of high evapotranspiration rates, water tables may fluctuate several inches per day. Thus, frequent measurements are

sometimes needed during the growing season. Redoximorphic features such as mottling and formation of concretions may also serve as an indicator for water table

fluctuation. However, such indirect measures need to be calibrated with seasonal

water table dynamics over more than one growing season. Water balance models

may also be applied to estimate water table drawdown under prevailing climatic

conditions.

If water tables fluctuate between 75 and 125 percent of the reference standard,

the variable should receive a score of 1.0. For fluctuations between 25 and
Index of Function (VPORE VWTF)/2

Chapter 2 Documentation of Riverine Wetland Functions 37

75 percent or greater than 125 percent, a variable score of 0.5 should be assigned. 

Fluctuations between zero and 25 percent should receive a score of 0.1. Static water

tables and water tables that remain much too deep for comparison with reference

standards are scored zero.

Index of function

The subsurface storage model is simply the variable soil pore space available for

storage. The index is

Documentation

SUBSURFACE WATER STORAGE

Definition: Availability of water storage beneath the wetland surface. Storage capacity becomes

available as periodic drawdown of water table or reduction in soil saturation occurs.

Effects Onsite: Short- and long-term water storage; influences biogeochemical processes in the soil;

retains water for establishment and maintenance of biotic communities.

Effects Offsite: Surficial groundwater recharge; maintains base flow; maintains seasonal flow

distribution.
Index of Function (VPORE VWTF)/2

38 Chapter 2 Documentation of Riverine Wetland Functions

Model Variables Direct Measure Indirect Measure Index of Variable

VPORE: Soil pore Example: The reference stan- Use direct measure. 1.0

space available

for storage

dard is sandy loam to coarser

texture soil with good structure

(abundant macropores).

Soil textures finer than sandy Use direct measure. 0.5

loam.

Soil saturated to surface or 1. Algae in pore spaces, 0.1

ponded for long durations dur- 2. Films on ped faces, or

ing the growing season. 3. Soil compacted or replaced by substrate with negligible pore space.

Soil saturated to surface or Soil compacted or replaced by sub- 0.0

ponded throughout the year. strate with negligible pore space.

VWTF: Fluctuation Range of water table fluctua- Example: Water table falls rapidly to 1.0

of water table tion between 75% and 125% 15-30 cm of surface

of reference standard.

Range of water table fluctua- Water table falls slowly and/or to a 0.5

tion between 25% and 75% or depth of 15 cm.

>125% of reference standard.

Range of water table fluctua- Soils stay nearly saturated or fluctuate 0.1

tion between 0% and 25% of within a few cm of the surface over

reference standard. several days to a week.

Static water tables or water Soil saturated to surface throughout the 0.0

tables much deeper than year or water table at 30 cm or greater

reference standard. for long periods.

Moderation of Groundwater Flow or Discharge

Definition

Capacity of a wetland to moderate the rate of groundwater flow or discharge

from upgradient sources.

Discussion of function and rationale

Riverine wetlands usually form along low-gradient reaches of streams, resulting

in relatively low rates of subsurface flow through the wetland. Subsurface flows,

both unsaturated and saturated (groundwater), are important linkages between

uplands, wetlands, and streams (see for example Roulet 1990 and O'Brian 1980). 

This is best illustrated by considering Darcy's Law, which states that velocity (V) is

equal to the conductivity (K) times the hydraulic gradient (dH/dL). For a saturated

K, a reduction in gradient results in a proportional reduction in V. Subsurface water
Chapter 2 Documentation of Riverine Wetland Functions 39

flowing into the wetland from upland, riparian sources, and upgradient in the

riverine system (floodplain) encounters a lower gradient and, often, a reduced

conductivity as well. The combination of these physical characteristics moderates

the flow of water into, through, and out of the wetland. This moderation of flow is

usually manifested in prolonged soil wetness in the wetland, more uniform

discharges to base flow, and maintenance of seasonal low flows. This function is

also manifested in the same way by moderating discharge of groundwater from the

wetland resulting from direct precipitation or overbank flows.

Moderation of subsurface flow into the wetland is also important to other

functions as well. Studies have shown how wetland/riparian systems serve as sinks

for nutrients and contaminants from upland sources (Lowrance et al. 1984). This

process results in removal of imported elements and compounds and improved

water quality downstream.

Reductions in gradient and/or conductivity are often apparent at the riparian edge

of many wetlands where subsurface seepage discharges to the surface at the break in

slope. This source area flow often is a major source of stormflow (Dunne and Black

1970, Nutter 1973), and wetlands serve to moderate both timing and volume of

storm discharge to the stream. In many riverine wetland systems, the source area

flow sustains wetland functions later in the growing season when evapotranspiration

rates are high and water from early growing season precipitation and/or overbank

flows has been depleted. 

Warmer subsurface water feeding the wetland in late fall or early spring sustains

or creates warmer soil temperatures which result in a longer season for biological

activity and other wetland functions.

Description of variables

VSUBIN, Subsurface flow into wetland. Subsurface flow into a riverine wetland

is often revealed by soil saturation maintained by seeps along the break in slope at

the wetland edge. Other evidence is the slow drainage of water from the wetland

after a precipitation or flooding event and the positive upward flow indicated by

springs or piezometers installed in the wetland. Extreme low-conductivity clays and

coarse sands have little impact on flow of groundwater for opposite reasons. Tight

clays with very low conductivities do not transmit water readily, particularly under

the conditions of low hydraulic head common in many riverine wetlands. Conversely, coarse sands with very high conductivities do not moderate flow significantly because of their high flow-through rates.

The relationship between channel depth and distance to edge of wetland defines

the slope of hydraulic gradient from wetland to channel. This gradient will

determine the rate of discharge from a riverine floodplain wetland to its stream. 

Different fractional distances may be appropriate for specific subclasses and

combinations of soil permeability, gradients, and stratigraphy.
40 Chapter 2 Documentation of Riverine Wetland Functions

The determination of subsurface flow conditions is difficult because they cannot

be seen directly. Scaling the index of the variable in comparison with the reference

standard requires careful selection of the reference domain and placement of the

wetland class in the proper hydrogeomorphic subclass.

A reference standard determined by indirect methods is presented here as an example. Careful selection of the indicators directly related to site conditions is necessary to establish the reference standard. It may be necessary to establish a monitoring network of piezometers in a representative reference wetland to understand the

nature of these variables. Decreasing evidence or diminishing of the variable requires a reduction in the index.

V , Subsurface flow from wetland to aquifer or to base flow. Rate of SUBOUT

discharge of groundwater from the wetland is controlled by, among other things, the

supply of water into the wetland (V ) and hydraulic head gradients to the point of SUBIN

discharge. Other than losses to evapotranspiration, most riverine wetlands lose

water as base flow to the stream, as subsurface stormflow, or as recharge to an

underlying aquifer. The presence of underlying impeding layers may shunt more

flow to the stream. Absence of such a layer may promote a greater portion of

discharge to an underlying aquifer, particularly if the soils are of moderate to high

permeability.

The average base flow stage in an adjacent stream influences the water table

gradient in a floodplain wetland, much like a drainage ditch dug in an agricultural

field. Incised streams with a low base flow stage would result in a higher gradient

on the water table next to the stream and a higher rate of discharge than a stream not

deeply incised or with average base flow stage near the wetland surface.

Flow from the wetland groundwater system is characterized by a negative

downward gradient. Direct observation of this must be by piezometer or by

comparing groundwater and streamflow measurements during base flow periods. 

Both methods are difficult, costly, and time consuming. Ruddy (1989) describes

one possible approach to measuring groundwater gradients. Indirect observations

are usually necessary to make comparisons to the reference standard of the same

hydrogeomorphic subclass. Permeable soils underlain by somewhat permeable

underlying layers should score 1.0. Where underlying horizons or strata are less

permeable and/or gradients become less steep due to alterations of water tables, the

score should be scaled downward. A zero score should be assigned if there is no

direct connection to a stream or aquifer due to extreme water table alteration. 
Index of Function (VSUBIN VSUBOUT)/2

Chapter 2 Documentation of Riverine Wetland Functions 41

Index of function

The model is the sum of the variables that describe the input of subsurface water

(V ) and the discharge of subsurface water (V ). The model is SUBIN SUBOUT

It is assumed that these two variables are of equal importance in the reference

standard.

Documentation

MODERATION OF GROUNDWATER FLOW OR DISCHARGE

Definition: Capacity for wetland to moderate the rate of groundwater flow or discharge from upgradient sources.

Effects Onsite: Prolonged wetness/saturated soil conditions; extended growing season; moderate

soil temperatures.

Effects Offsite: Maintains upgradient or upslope groundwater storage, base flow, seasonal flow

regimes, surface water temperature.

Model Variables Direct Measure Indirect Measure Index of Variable

VSUBIN: Subsurface 1. Groundwater discharge mea- Example of the reference standard 1.0

flow into wetland sured in seeps or springs and determined by regional standards:

discharge from wetland or 1. Seeps present at edge of wetland

2. Positive (upward) ground- or

water gradient measured by 2. Vegetation growing during dormant

piezometers; scored relative to season or drought (i.e., wet soils supreference standard. port vegetation) or

3. Wetland occurs at toe of slope or

4. Artesian flow (upwelling) on wetland surface.

Regional standards greatly reduced. 0.5

Regional standards absent with 0.1

potential for recovery.

Regional standards absent with no 0.0

potential for recovery.

VSUBOUT: Subsur- Negative (downward) ground- Example of the reference standard 1.0

face flow from

wetland to aquifer

or to base flow 

water gradient measured by determined by regional standards:

piezometers; score relative to 1. Sandy soils without underlying

reference standard. impeding layer or

2. Permeable underlying stratigraphy.
Index of Function (VSUBIN VSUBOUT)/2

42 Chapter 2 Documentation of Riverine Wetland Functions

VSUBOUT: Regional standards greatly reduced. 0.5

(Concluded)

Regional standards absent with po- 0.1

tential for recovery.

Regional standards absent with no 0.0

potential for recovery. 

Nutrient Cycling

Definition

Abiotic and biotic processes that convert nutrients and other elements from one

form to another; primarily recycling processes.

Discussion of function and rationale

Cycling of nutrients (including nonessential elements) is a fundamental ecosystem process. Nutrient cycling is mediated by two variables: net primary productivity, in which nutrients are taken up by plants, and detritus turnover, in which nutrients are released for renewed uptake by plants, thus completing a cycle. In performing this function, wetlands can maintain standing stocks of nutrients sufficient to

support a level of net primary production and detrital turnover typical of ambient

climatic and edaphic conditions. In general, fertile sites (i.e., those that are nutrientrich) have higher levels of annual net primary production and nutrient uptake than

infertile ones. Controls on detritus turnover, especially of large woody components

and humus, have not been as well established or as widely recognized (Boddy

1983).

Because this function involves some of the most conspicuous components of

ecosystems (living plants and dead plant material), its variables have been well studied and documented. There is a rich literature in ecology and forestry that reports

estimates of biomass and aerial net primary productivity (ANPP) for mature and

successional stages of many forested wetlands (reviewed in Brinson 1990). Detrital

turnover of large woody components is less frequently measured, but decay rates of

annual leaf-fall are well documented. It is well established that most recycling occurs through the breakdown of organic matter in detrital pathways, not grazing ones

(Brinson, Lugo, and Brown 1981).
Chapter 2 Documentation of Riverine Wetland Functions 43

The full suite of elements that becomes transformed between oxidized and reduced conditions is the essence of this function. Further, the recycling of nutrients

in a wetland ecosystem does more to maintain a favorable biogeochemistry (i.e.,

good water quality) than relatively permanent removal of inflowing nutrients and

other elements by wetlands. While the foregoing sentence may overstate the case in

some wetlands, imagine the capacity of a wetland to remove nutrients that has neither ANPP nor detrital turnover. Further, without the return of nutrients from detritus, ecosystems would quickly become depleted of nutrients and their primary production would decrease. In short, the function is responsible for maintaining living

biomass and detrital stocks. Without a rough balance between uptake and turnover,

a much lower rate for one of the two processes could limit the other.

Nutrient cycling can be contrasted with the Removal of Imported Elements and

Compounds function which evaluates wetlands as elemental sinks. Most relatively

intact and unpolluted riverine wetlands, however, do not substantially reduce the

concentration of inorganic nitrogen, phosphorus, or other constituents downstream

unless loading rates are well above background. This is because considerable recycling occurs such that uptake and release are in relatively close balance (Finn 1980). 

This recycling is critical to maintaining low concentrations of elements and nutrients

in flowing water (Elder 1985). The concept is similar to nutrient spiraling in

streams (Elwood et al. 1983). Specific nutrients or elements are not singled out for

this function. In situations where more detailed assessment of nutrient-related functions is desirable, the cycles of elements such as nitrogen and phosphorus could be

assessed separately.

Description of variables

Nutrient Cycling can be estimated in several ways. One way would be to directly

measure litterfall, stemflow, canopy throughflow, and net biomass production, multiply each of the flows by the concentration of a particular nutrient, and appropriately aggregate the flows over time, usually 1 year. A similar approach could be

taken for nutrient release from detritus. These would all be direct measures requiring considerable effort and time.

The function can be approached logically. If living and detrital biomass are distributed in a wetland being assessed in the same proportions and quantities as occur

at reference standard sites, it is unlikely that the cycling of nutrients could differ significantly between the two conditions. One way of estimating living and dead biomass is to estimate biomass or cover of vegetation, and the volume or cover of detritus. Each of these components is related as variables to reference standards and

appropriately aggregated into the variables used for the index of function. This is

the approach used for wet pine flats in North Carolina (Brinson and Rheinhardt, in

press). The variables discussed below are only aerial net primary productivity and

annual turnover of detritus rather than the more detailed measurements described in

Brinson and Rheinhardt (in press).

VPROD, Aerial net primary productivity. Aerial net primary productivity

(ANPP) is one of two variables for the function that can be directly measured. The
44 Chapter 2 Documentation of Riverine Wetland Functions

great amount of effort required to do this is impractical for rapid assessment. Instead, ANPP can be indirectly estimated from estimates of leaf area, or leaf area

index (as determined from interception of incoming solar radiation). Other components of ANPP have been estimated in some forested wetlands from the relationships between age, basal area, and biomass for developing stands (Mengel and Lea

1990). We assume that the presence of living biomass is an indicator that nutrient

uptake processes are occurring. Standing stocks of trees, density or cover of shrubs,

and herbaceous plant cover could be measured or estimated as a substitute for primary production (e.g., V , V , V ). BTREE SHRUB HERB

The ANPP can be estimated from regressions between growth and age-dependent stand characteristics, and measures of annual litterfall. If one can assume that

these indices and measures are proportional to the V , a continuous scale may be PROD

used to estimate the variable relative to the reference standard score of 1.0, and 0.0

as the endpoint in the absence of living biomass. Otherwise, categorical variables

may be assigned using 1.0 for 75 to 125 percent of reference standard, 0.5 for 25 to

75 percent or >125 percent of reference standard, 0.1 for 0 to 25 percent of reference standard, or zero for the absence of variables and indicators. If the forest has

recently been cleared, but has potential for recovery, it may be scored 0.1. This recognizes that root stock and seed banks may be viable, so the distinction can be made

between a site that has potential for recovery and one that has received an irreversible alteration. If the area is essentially barren and is not being managed for recovery, no credit is given. Open patches due to canopy gap dynamics (Pickett and

White 1985) should not be construed as a lack of ANPP, but rather a common condition of relatively mature forest stands (see VPATCH and VGAPS in section Maintain

Spatial Structure of Habitat).

V , Annual turnover of detritus. Detritus turnover is “the other half” of TURNOV

nutrient cycling. Detrital stocks are represented by snags, down and dead woody

debris, organic debris on the forest floor (leaf litter, fermentation, and humus layers), and organic components of mineral soil. It is assumed that detritus standing

stocks are proportional to detritus turnover. Standing stocks of detrital biomass

(V , V , V ) can be substituted for turnover. SNAG CWD FWD

Most detrital components can be observed directly and compared with reference

standards. Additional indicators could include fungi and mycorrhizae, as well as

arthropods and other invertebrates, for assessments conducted in more detail.

Sites within 75 to 125 percent of reference standards in detrital stocks score 1.0. 

Where detrital stocks are significantly reduced (25 to 75 percent) or overabundant

(>125 percent), the variable should score 0.5; if major disturbance has depleted the

site of most soil and detrital organic matter (1 to 25 percent), the function should

receive a 0.1. If there are no detrital stocks and the potential for recovery is absent,

the score should be zero.
Index of Function If VPROD > VTURNOV, then index is VTURNOV;

otherwise, VPROD

Chapter 2 Documentation of Riverine Wetland Functions 45

Index of function

Aerial net primary productivity (V ) and annual detritus turnover (V ) PROD TURNOV

are the variables that model the Nutrient Cycling function. Because of the interdependency of the two processes, the level of functioning is determined by the lesser

of the two in comparison with reference standards. The reference standard for this

function is a level of ANPP and decomposition, roughly in balance with one another,

that is required to sustain living biomass and detrital stocks.

If one of the variables is lacking, the function does not occur in a sustainable fashion

in the sense described here.

Documentation

NUTRIENT CYCLING

Definition: Abiotic and biotic processes that convert nutrients and other elements from one form to

another; primarily recycling processes. 

Effects Onsite: Net effects of recycling are elemental balances between gains through import processes and losses through hydraulic export, efflux to the atmosphere, and long-term retention in

persistent biomass and sediments.

Effects Offsite: To the extent that nutrients are held onsite by recycling, they will be less susceptible

to export downstream. This reduces the level of nutrient loading offsite.
Index of Function If VPROD > VTURNOV, then index is VTURNOV;

otherwise, VPROD

46 Chapter 2 Documentation of Riverine Wetland Functions

Model Variables Direct Measure Indirect Measure Index of Variable

VPROD: Aerial net pri- Annual litterfall or living bio- Percent cover of all strata 1.0

mary productivity mass accumulation esti- (canopy, subcanopy, shrub,

mated from stand metrics as ground cover) between 75% and

a linear relationship between 125% of reference standard. 

reference standard (1.0) and

absent (0.0). Percent cover as above, but 0.5

between 25% and 75% or >125%

of reference standard.

Leaf area or living biomass 0.1

between 0% and 25% of reference standard or the site lacks

living biomass due to clearing with

potential for recovery.

No leaf area due to clearing; no 0.0

potential for recovery.

VTURNOV: Annual Turnover of detritus as a Stocks of detrital and soil organic 1.0

turnover of detritus linear relationship between matter between 75% and 125% of

reference standard and zero. reference standard in terms of: 

snags, down dead woody debris,

leaf litter, fermentation and humus

layers, and fungal fruiting bodies. 

As above, but between 25% and 0.5

75% or >125% of reference

standard. 

Stocks of detrital and soil organic 0.1

matter between 0% and 25% of

reference standard, or stocks of

detrital and soil organic matter

absent with potential for recovery.

Area barren; no potential for 0.0

recovery.

Removal of Imported Elements and Compounds

Definition

The removal of imported nutrients, contaminants, and other elements and

compounds.
Chapter 2 Documentation of Riverine Wetland Functions 47

Discussion of function and rationale

The functioning of wetlands as interceptors of nonpoint source pollution is well

documented (reviewed by Johnston 1991). Riverine wetlands, particularly those in

headwater positions, are strategically located to intercept nutrients and contaminants

before they reach streams (Brinson 1988). We use the term “removal” to imply the

relatively long-term accumulation or permanent loss of elements and compounds

from incoming water sources. This can be contrasted with the Nutrient Cycling

function in which a portion of the elements is recycled on a time frame of one year

or less.

This method takes a very broad approach to both the elements and compounds of

interest and the mechanisms by which they are removed. This is in contrast to most

research on the topic, which is conducted on one element or mechanism at a time. 

Elements include macronutrients essential to plant growth (nitrogen, phosphorus,

potassium, etc.) and other elements such as heavy metals (zinc, chromium, etc.) that

can be toxic at high concentrations. Compounds include herbicides, pesticides, and

other imported materials. Mechanisms of removal include sorption, sedimentation,

denitrification, burial, decomposition to inactive forms, uptake and incorporation

into long-lasting woody and long-lived perennial herbaceous biomass, and similar

processes.

Within a physiographic region, it may be important to focus on particular elements. For example, one might focus on nitrogen and phosphorus, because of their

importance in eutrophication of lakes and streams (Gunterspergen and Stearns

1985; Johnston, Detenbeck, and Niemi 1990). Nitrogen and phosphorus are removed in very different ways because the former is part of a gaseous biogeochemical cycle and the latter a sedimentary cycle (Schlesinger 1991). Both elements

may be more or less permanently buried in deeper sediments. However, nitrogen

removal occurs primarily by denitrification, which releases nitrogen gases to the

atmosphere. Phosphorus, however, is not truly removed. The soluble

orthophosphate ion (PO ) may become sorbed to clay and iron particles in the soil. 4

3-

The capacity of soils to sorb phosphorus from solution is largely a function of iron

and aluminum content (Richardson 1985), both of which are generally found in

abundance in riverine wetlands. Normally most phosphorus is associated with

particulate materials that are removed from the water column as sediments settle on

the floodplain during flooding. Annual net uptake of phosphorus by growing

vegetation, although significant, usually represents a small quantity relative to other

soil/sediment sinks of phosphorus (Brinson 1985).

Reviews on nutrient removal by wetlands include those by Faulkner and

Richardson (1989) and Johnston (1991). From the mid-1970s to the mid-1980s,

much research and development effort was invested in utilizing wetlands as sites for

tertiary treatment of wastewaters. Much of the nutrient uptake work is summarized

in U.S. Environmental Protection Agency (1983), Godfrey et al. (1985), and Ewel

and Odum (1984).
48 Chapter 2 Documentation of Riverine Wetland Functions

Description of variables

V , Frequency of overbank flow. In order for riverine wetlands to remove FREQ

imported elements and compounds, they must first be transported to a wetland. In

riverine wetlands, one of the most common transport mechanisms is overbank flow. 

Without it, there would be little opportunity for waterborne materials in streams to

be removed by biogeochemical processes operating on floodplain wetlands.

Data from stream-gauging stations are reliable for estimating this variable. Few

streams have gauges, however, or few have them in locations that would be useful

for determining frequency of overbank flow. Other applicable indicators are water

marks, silt lines, ice scars, bryophytes and lichens on trunks, drift and wrack lines,

sediment scour, and sediment deposition. Many of these simply indicate recent

flooding (silt lines) or infrequent events (ice scour) and, therefore, may not be particularly helpful in establishing the flood return interval (inverse of flood frequency)

of a particular site.

Indices correspond to flood return intervals, with the maximum condition being

1.0 for the reference standard. If the reference standard is flooding at the 2- to

5-year return interval, a score of 1.0 should be assigned. An annual flood regime

would be inappropriate for that site and should score 0.5. Likewise, a return

interval longer than 5 years should receive a 0.5. A score of 0.1 could be used for

extreme departures of flooding above and below the appropriate return interval. A

score of 0.0 should be used to indicate lack of overbank flow.

V , Surface inflow. When precipitation rates exceed soil infiltration rates, SURFIN

overland flow in uplands adjacent to riverine wetlands may become a water source. 

Indicators include the presence of rills and rearranged litter on an upland leading to

a floodplain. Saturated surface flow may also occur as partial area contributions

(Dunne and Black 1970). Tributaries leading to the riverine upland and not

connected to the main channel contribute channelized surface inflow to the wetland.

VSURFIN can be measured directly, but this is impractical for rapid assessment and

methods are fraught with problems. Indirect measures can be made visually. Rills

on adjacent slopes and lateral tributaries not connected to the main channel of the

wetland can be quantified. Seeps at the toe of upland slopes are indicative of

saturated surface inflow from partial area contributions.

The variable score is 1.0 if either of the following indicators is similar to

reference standards: rills on adjacent upland slopes, or lateral tributaries entering

the floodplain and not connected to the channel. If neither of these indicators is

similar to reference standards, and either is less than reference standards, the

variable is 0.5. Absence of both indicators scores 0.1, while the presence of ditches

at the toe of the slope (which would intercept surface flows) would warrant a score

of zero.

V , Subsurface inflow. Another common transport mechanism is SUBIN

subsurface flow, which includes unsaturated flow and groundwater discharge from

upslope. If soils of adjacent uplands are porous (sandy), high infiltration rates will
Chapter 2 Documentation of Riverine Wetland Functions 49

minimize overland flow except during extreme precipitation or frozen soil

conditions. Groundwater discharge can occur where the base of an upland slope

intersects with a floodplain surface. Groundwater may also discharge from below

into a floodplain alluvium itself. In either case, a floodplain wetland will have an

opportunity to influence water chemistry unless its stream channel has cut into adjacent upland and directly intercepts subsurface inflows. Several studies have documented this process (Peterjohn and Correll 1984, Roulet 1990). For headwater

streams lacking well-developed floodplains, this transport mechanism is particularly

relevant where there is insufficient channel discharge to cause overbank flow.

Groundwater discharge to a wetland seldom can be observed directly, but base

flow in stream channels, saturation to the surface, and seeps at the foot of slopes are

indicators that discharge is occurring. Confirmation from piezometer or well data in

concert with stream hydrographs are direct measures. 

Because of the difficulty in measuring unsaturated lateral flow and groundwater

discharge, one normally must rely on indirect methods rather than direct hydrologic

measurements. The suggestion for scores of 1.0, 0.5, 0.1, and 0.0 is an attempt to

scale along a gradient of decreasing levels of indicators.

VMICRO, Microtopographic complexity. Many of the nutrient removal and sorption processes are dependent on the water table creating specific soil moisture conditions that facilitate the removal of nutrients (e.g., anoxic or oxidized conditions). 

No soil condition is conducive for all processes. In fact some conditions promote

opposite results (e.g., phosphorus precipitation and removal from the water column

under oxic conditions and phosphorus release from sediments and diffusion to the

water column under anoxic conditions). For example, phosphate precipitation occurs most readily where conditions are oxic, and iron and aluminum are abundant. 

Denitrification requires anoxia, but nitrification is carried out by bacteria metabolizing aerobically. Consequently, a varied and complex microtopography will expose water simultaneously to a variety of conditions at any one time.

Measurement of microtopographic complexity is discussed under Dynamic Surface Water Storage. Microtopographic complexity similar to the reference standard

scores 1.0. Estimates below reference standard should score 0.5 unless they are virtually absent. Smoothed, graded surfaces should receive 0.1 or 0.0 depending on

their potential for recovery.

VMICROB, Surfaces for microbial activity. Microbial activity removes or renders

inactive many chemicals and compounds. Microbes tend to be associated with complex surfaces such as leaf litter, humus and soil particles, and plant surfaces. Complex surfaces provide a platform for growth and reproduction, but the material itself

may also be a source of organic matter for metabolism.

These surfaces can be estimated from the litter layer (as percent cover, depth, or

biomass), organic matter content of soil, stems and leaves of herbaceous plants, peat

layers, and so forth.
50 Chapter 2 Documentation of Riverine Wetland Functions

Surfaces for microbial activity similar to the reference standard should score 1.0. 

Estimates below score 0.5 unless they are virtually absent. Absence of such

surfaces should receive 0.1 or 0.0 depending on a site's potential for recovery.

V , Sorptive properties of soils. Physical and chemical removal of dis- SORPT

solved elements and compounds occurs through complexation, precipitation, and

other mechanisms of removal (Kadlec 1985). Phosphorus is the most thoroughly

studied element. It has been demonstrated that the extractable aluminum of soils,

which tends to be inversely proportional to organic carbon content, correlates

strongly with potential for phosphorus removal (Richardson 1985). Actual

measurement of extractable aluminum concentrations is beyond the scope of most

assessments. Various metals also undergo complexation with soil particles, and

ions may be temporarily removed from water by cation and anion exchange sites.

Generally, soils that have fine texture (clays, silts) have greater sorption

capacities than those with coarse textures. Organic matter also has sorptive

properties, particularly in the chelation of heavy metals. Regardless of the

mechanisms involved, a comparison of an assessed site with reference standards is

the basis for assigning index scores.

County soils surveys, if field verified, can be used to determine in general and

describe specifically soil types found in reference standard sites. This same approach can be used in an assessment process.

Soils with physical properties similar to their reference standard should score

1.0. Those that depart in texture, organic carbon content, and other properties

should score 0.5. Major departures (e.g., sand to cobbles, clay to sand) should

receive 0.1, while 0.0 should be assigned to surfaces lacking soil or natural substrate

(e.g., asphalt, concrete).

V , Tree basal area. The capacity of herbaceous plants to remove elements BTREE

for longer than 1 year is limited to long-lived rhizomes, rootstocks, etc. Woody

plants, however, may detain elements for longer than 1 year because they are

perennial, and woody parts tend to decompose slowly. Elements that have

accumulated in tree trunks may become buried in wetlands after falling. The high

organic matter content of many wetland sediments is an indication that recycling

through decomposition is slow (often a reflection of anoxic conditions) while low

organic matter content in other wetlands generally indicates high recycling rates.

The presence of woody basal area (or biomass) measured directly or indirectly

can be used as an indicator of the function. If the plants, as in marshes, are all

herbaceous and relatively short lived, this variable should not be used in the

equation for this function.

If a forested wetland is considered to be midsuccessional, it could be assigned an

index score of 1.0. Alternatively, in the unlikely event that the reference standard's

condition is truly at a steady state (e.g., an old-growth forest), earlier successional

stages represent a departure from the reference standard and should legitimately
Index of Function {[(VFREQ VSURFIN VSUBIN)/3] [(VMICRO

VMICROB VSORPT)/3] VBTREE}/3

Index of Function {[(VFREQ VSURFIN VSUBIN)/3] [(VMICRO

VMICROB VSORPT)/3]}/2

Chapter 2 Documentation of Riverine Wetland Functions 51

score less than 1.0. Only barren sites without potential for recovery should be given

a 0.0 score.

Index of function

Variables for the Removal of Imported Elements and Compounds function fall

into two categories. The first category consists of hydrologic transport mechanisms

that bring nutrients to a wetland. The variables are frequency of overbank flow

(V ), and sources from adjacent uplands (V and V ). FREQ SURFIN SUBIN

In the other category are factors contributing to the removal of elements and

compounds. These include transformation by exposure to a variety of microenvironments, microbes, sorption to soil, and uptake by vegetation. Microtopography

indicates the extent of vertically stratified microsites (VMICRO). The more that microsites are stratified, the greater are the number of soil conditions to which water will

be exposed at any one time, resulting in the simultaneous processes of transformation by microbes (VMICROB) and sorption to soil (VSORPT). Uptake by perennial woody

vegetation (V ) is more a property of net biomass accumulation and may be re- BTREE

lated to the successional status of vegetation.

The variables are combined to depict the function in the following manner:

If the vegetation is normally dominated by short-lived herbaceous species

(marshes), then V should not be used. Therefore, BTREE

It is assumed that the three groups of variables, water sources, soil properties, and

uptake by vegetation, are equally important in maintaining the function at this reference standard condition.
52 Chapter 2 Documentation of Riverine Wetland Functions

Documentation

REMOVAL OF IMPORTED ELEMENTS AND COMPOUNDS

Definition: The removal of imported nutrients, contaminants, and other elements and compounds.

Effects Onsite: Nutrients and contaminants in surface or ground water that come in contact with

sediments are either removed from a site or rendered “noncontaminating” because they are broken

down into innocuous and biogeochemically inactive forms.

Effects Offsite: Chemical constituents removed and concentrated in wetlands, regardless of source,

reduce downstream loading.

Model Variables Direct Measure Indirect Measure Index of Variable

VFREQ: Frequency Gauge data (1.5) yr return At least one of the following: aerial 1.0

of overbank flow interval similar to reference photos showing flooding, water marks,

standard. (Interval in paren- silt lines, alternating layers of leaves

theses must be adjusted to and fine sediment, ice scars, drift

reference standard.) and/or wrack lines, sediment scour,

sediment deposition, directionally bent

vegetation similar to reference standard.

Gauge data As above, but somewhat greater or 0.5

(>2 or <1) yr return interval. less than that of reference standard.

Gauge data show extreme Above indicators absent but related 0.1

departure from reference indicators suggest overbank flow may

standard. occur.

Gauge data indicate no flood- Indicators absent and/or there is evi- 0.0

ing from overbank flow. dence of alteration affecting variable.

VSURFIN: Surface Use of data from runoff col- Any of the following indicators similar 1.0

inflow to the

wetland

lectors as a continuous vari- to reference standard:

able from reference standard 1. Rills on adjacent upland slopes. 

(1.0) to absent (0.0). 2. Lateral tributaries entering floodplain and not connected to the

channel.
Chapter 2 Documentation of Riverine Wetland Functions 53

VSURFIN: Neither of the above indicators similar 0.5

(Concluded) to reference standards, and either of

the above indicators less than the

reference standard.

Absence of both of the above 0.1

indicators.

Absence of both of the above indica- 0.0

tors and hydraulic gradient reversed

by regional cone of depression or

channelization across wetland and

ditches at toe of slope.

VSUBIN: Subsur- 1. Groundwater discharge Example of the reference standard 1.0

face flow into

wetland

measured in seeps or springs determined by regional standards:

and discharge from wetland or 1. Seeps present at edge of wetland

2. Positive (upward) or

groundwater gradient mea- 2. Vegetation growing during dormant

sured by piezometers and season or drought (i.e., wet soils supscored relative to reference port vegetation) or

standard. 3. Wetland occurs at toe of slope or

4. Artesian flow (upwelling) on wetland surface.

Regional standards greatly reduced. 0.5

Regional standards absent with poten- 0.1

tial for recovery.

Regional standards absent with no 0.0

potential for recovery.

VMICRO: Microtopographic complexity Visual estimate indicates that 1.0

Microtopographic

complexity

(MC) measured (surveyed) microtopographic complexity (MC) is

shows MC >75% to <125% of >75% to <125% of reference

reference standard. standard.

Measured MC is between Visual assessment confirms MC is 0.5

25% and 75% that of refer- somewhat less than reference

ence standard. standard.

Measured MC is between Visual assessment indicates MC is 0.1

0% and 25% that of reference much less than reference standard;

standard; restoration possible. restoration possible.

No MC at assessed site or Visual assessment indicates MC is 0.0

natural substrate replaced by virtually absent or natural substrate

artificial surface. replaced by artificial surface; restoration not possible.

VMICROB: Surfaces Mass of litter layer measured Indicators similar to reference stan- 1.0

for microbial

activity

as a continuous variable be- dard, i.e., litter layer, humus stratum,

tween reference standard woody debris, and floating, sub-

(1.0) and absent (0.0). merged, and herbaceous emergents. 

As above, but indicators less than 0.5

reference standards.
Index of Function {[(VFREQ VSURFIN VSUBIN)/3]

[(VMICRO VMICROB VSORPT)/3]

VBTREE}/3

Index of Function {[(VFREQ VSURFIN VSUBIN)/3]

[(VMICRO VMICROB VSORPT)/3]}/2

54 Chapter 2 Documentation of Riverine Wetland Functions

VMICROB: Indicators absent, with potential for 0.1

(Concluded) recovery. 

Indicators absent, without potential for 0.0

recovery. 

VSORPT: Sorptive Cation exchange capacity and Physical properties of soils similar to 1.0

properties of soils percent base saturation simi- the reference standard.

lar to reference standard. 

As above, but less than refer- Soil departs in texture, organic carbon 0.5

ence standard. content, and other properties.

As above, but greatly reduced Major departures (e.g., sand to cob- 0.1

from reference standard. bles, clay to sand). 

Soil absent; replaced by Surfaces lacking soil or natural 0.0

nonsoil surfaces. substrate (e.g., asphalt, concrete).

VBTREE: Tree Basal area is greater than Stage of succession similar to 1.0

basal area 75% of reference standard. reference standard.

Basal area between 25% and Stage of succession departs sig- 0.5

75% of reference standard. nificantly from reference standard.

Basal area between 0% and Stage of succession at extreme 0.1

25% of reference standard; departure from reference standard.

restoration possible. 

No trees present; restoration Stand cleared without potential for 0.0

not possible recovery.

If the vegetation is normally dominated by short-lived herbaceous species

(marshes), then V should not be used. Therefore, BTREE

It is assumed that the three groups of variables, water sources, soil properties, and

uptake by vegetation, are equally important in maintaining the Removal of Imported

Elements and Compounds function at the reference standard.
Chapter 2 Documentation of Riverine Wetland Functions 55

Retention of Particulates

Definition

Deposition and retention of inorganic and organic particulates (>0.45 m) from

the water column, primarily through physical processes.

Discussion of function and rationale

Flooding from overbank flow of alluvial streams is a major source of inorganic

particulates for floodplain wetlands. Floodplains of smaller streams also receive

sediments due to overland flow from adjacent uplands. Once waterborne sediment

has been transported to a floodplain, velocity reduction normally occurs due to surface roughness and increasing cross-sectional area of discharge (Nutter and Gaskin

1989). This leads to a reduction in the capacity of water to transport suspended sediments, so particulates settle. The best evidence of this function is the presence of

retained sediments in depositional layers. This evidence is particularly diagnostic

when deposition is recent and can be related to a specific flood event.

Retention applies to particulates arising from both onsite and offsite sources, but

excludes in situ production of peat. The Retention of Particulates function contrasts

with Nutrient Cycling and Removal of Imported Elements and Compounds because

the emphasis is more dependent on physical processes (e.g., sedimentation and particulate removal). Sediment retention occurs through burial and chemical precipitation (e.g., removal of phosphorus by Fe ). Dissolved forms may be transported as 3+

particles after undergoing sorption and chelation (i.e., heavy metals mobilized with

humic and fulvic compounds). Imported sediment can undergo renewed pedogenesis on site, which potentially involves weathering and release of elements that were

previously inaccessible to mineral cycling.

The same hydrodynamics that facilitate sedimentation may also capture and retain existing organic particulates. For example, deposition of silt by winter floods

following autumn litterfall appears to reduce the potential for leaves to become suspended by currents and exported (Brinson 1977). 

Because sources of water and depth of flooding vary greatly among stream orders (Brinson 1993b), there may be a need to stratify subclasses by stream order to

reduce this natural source of variation. Headwater streams that accumulate large

amounts of sediments may represent a disturbed condition incapable of sustaining

the function. Excessive retention of particulates, as in reservoirs, may create a

“sediment shadow” downstream from the dam (Rood and Mahoney 1990). Consequently, unusually high or low depositional rates in such areas should not receive the

highest functional index score. In addition, such sites should not be used to determine reference standards. 
56 Chapter 2 Documentation of Riverine Wetland Functions

Description of variables

V , Frequency of overbank flow. Sediments must be transported to the wet- FREQ

land surface in order for them to be removed. In riverine wetlands, one of the most

common transport mechanisms is overbank flow. Without it, there would be little

opportunity for fine suspended sediments in streams to be removed by floodplain

wetlands. 

Data from stream-gauging stations are reliable for estimating this variable, but

not all streams have gauges. Other applicable indicators are water marks, silt lines,

ice scars, bryophytes and lichens on trunks, drift and wrack lines, sediment scour,

and sediment deposition. Many of these simply indicate recent flooding (silt lines)

or an infrequent event (ice scour), and therefore may not be particularly helpful in

establishing the flood return interval (inverse of flood frequency) of a particular site.

Indices correspond to flood return intervals, with the maximum condition being

1.0 for the reference standard. If reference standard sites flood at a 2- to 5-year return interval, an unaltered condition in an assessed wetland site with a 2- to 5-year

return interval would score 1.0. In contrast, if the site were altered to have an annual flood regime or a return interval of >5 years, a score of 1.0 would be inappropriate for such a site and it should score less than 1.0. A score of 0.1 would be used

for large departures above and below the return interval for the reference standard. 

A score of zero should be used to indicate lack of overbank flow.

VSURFIN, Surface inflow. Overland flow from uplands to the wetland surface can

transport sediments to the wetland surface. If soils of adjacent uplands are porous

(sandy), high infiltration rates will probably eliminate overland flow except during

extreme precipitation or frozen soil conditions. 

Surface inflow may be indicated by rills along the upland slope leading to a

floodplain. If wetlands are relatively undisturbed, there should be little surface inflow. Lateral tributaries entering a floodplain and not connected to the main channel

would also qualify as a surface inflow. The variable score is 1.0 if either of the following indicators is similar to reference standards: rills on adjacent upland slopes,

or lateral tributaries entering the floodplain and not connected to the channel. If neither of the above indicators is similar to reference standards, and either is less than

reference standards, the variable is 0.5. Absence of both indicators scores 0.1, while

the presence of ditches at the toe of the slope (which would intercept surface flows)

would warrant a score of zero.

VHERB, VSHRUB, VBTREE, VDTREE, VMICRO, VCWD, Roughness factors. The six

roughness factors are roughness due to herbaceous plants (VHERB), roughness due to

shrubs (V ), roughness due to tree basal area (V ), roughness due to tree SHRUB BTREE

density (VDTREE), roughness due to microtopographic complexity (VMICRO), and

roughness due to coarse woody debris (VCWD). As water flows over surfaces, friction

and shear forces create turbulent flow and reduce velocities, both of which are conducive to sediment deposition. The four variables are scaled independently. However, Manning's coefficients have been developed for site-specific data to attempt to

provide quantitative relationships between roughness and wetland structure
Chapter 2 Documentation of Riverine Wetland Functions 57

(Arcement and Schneider 1989). This coefficient integrates all variables of roughness which, if information were available, would allow the collapsing of VHERB

through V into one variable. CWD

Each of the roughness components should be evaluated separately unless there

are available guidelines for Manning's n. Roughness similar to the reference standard should receive a score of 1.0. Estimates below reference standard should score

0.5 unless roughness is virtually absent. Smoothed, graded surfaces should receive

0.1 or zero depending on a site's potential for recovery.

V , Retained sediments. Sophisticated techniques are available for deter- SEDIM

mining quantitative rates of sedimentation (i.e., cesium-137 mass balances; Cooper

and Gilliam 1987). These techniques are too time consuming for the rapid assessment used in the HGM approach.

Qualitative evidence of retained sediments may be indicated by layers of leaves

buried under sediment layers, but such rates of deposition are infrequent in most

undisturbed and small watersheds. Another indicator of sediment deposition in

riverine wetlands is the presence of natural levees formed by overbank flow. Coarse

sediments settle on streambanks during floods, thus contributing to levee formation,

while finer sediments escape sedimentation until they are carried into more quiescent parts of the floodplain. 

Deposition similar to the reference standard scores 1.0. Deposition below the

reference standard should receive a score of 0.5 unless deposition is virtually absent. 

Deposits that greatly exceed the reference standard or absence of sediments should

receive 0.1. If hydrologic alterations eliminate this variable, a score of zero should

be assigned.

Index of function

The variables used in the Retention of Particulates function are frequency of

overbank flow (V ), surface inflow (V ), roughness of wetland surfaces FREQ SURFIN

(V , V , V , V , V , V ), and evidence of retained sediments HERB SHRUB BTREE DTREE MICRO CWD

(V ). In small streams where overbank flow seldom occurs due to the headwater SEDIM

position, a potential source of sediments would be from uplands as particulates

transported in overland flow. Most headwater streams are erosional, however, and

relatively undisturbed uplands do not serve as a substantial source of sediments. 

When uplands are disturbed and begin to release sediments, headwater streams may

become depositional (Cooper and Gilliam 1987). This is possibly a function of an

altered landscape and must be dealt with in the context of a specific reference

domain. 
Index of Function {[(VFREQ VSURFIN)/2] × [(VHERB VSHRUB

VBTREE VDTREE VMICRO VCWD)/6]}

1/2

Index VSEDIM

58 Chapter 2 Documentation of Riverine Wetland Functions

The variables depict the function in the following manner:

First option: 

Second option if data or indicators are available:

It is assumed that the transport group of variables and roughness factors are equally

important in maintaining the function under reference standards condition. 

Documentation

RETENTION OF PARTICULATES

Definition: Deposition and retention of inorganic and organic particulates (>0.45 m) from the

water column, primarily through physical processes.

Effects Onsite: Sediment accumulation contributes to the nutrient capital of an ecosystem. Deposition increases surface elevation and changes topographic complexity. Organic matter may also be

retained for decomposition, nutrient recycling, and detrital food web support.

Effects Offsite: Reduces stream sediment load and entrained woody debris that would otherwise be

transported downstream.
Chapter 2 Documentation of Riverine Wetland Functions 59

Model Variables Direct Measure Indirect Measure Index of Variable

VFREQ: Frequency of Gauge data At least one of the following: 1.0

overbank flow (1.5) yr return interval; simi- aerial photos showing flooding,

lar to reference standard. water marks, silt lines, alternat-

(Intervals in parentheses ing layers of leaves and fine

must be adjusted to the sediment, ice scars, drift and/or

reference standard.) wrack lines, sediment scour,

sediment deposition, directionally bent vegetation similar to

reference standard.

Gauge data As above, but somewhat 0.5

(>2 or <1) yr return interval; greater or less than that of 

departure from reference reference standard.

standard.

Gauge data show extreme Above indicators absent but 0.1

departure from reference related indicators suggest overstandard. bank flow may occur.

Gauge data indicate no Indicators absent and/or there 0.0

flooding from overbank is evidence of alteration affectflow. ing variable.

VSURFIN: Surface Inflow Use of data from runoff Any of the following indicators 1.0

to the wetland collectors as a continuous similar to reference standard:

variable from reference 1. Rills on adjacent upland

standard (1.0) to absent slopes. 

(0.0). 2. Lateral tributaries entering

floodplain and not connected to

the channel.

Both of the above indicators 0.5

similar to reference standards,

and any of the above indicators

less than the reference

standard.

Absence of both of the above 0.1

indicators.

Absence of both of the above 0.0

indicators, and channelization

across wetland prevents sedimentation on wetland surface.

VHERB: Herbaceous Herbaceous density, bio- Herbaceous plant cover be- 1.0

plant density, biomass,

or cover

mass or cover scaled as a tween 75% and 125% that of

linear function of reference reference standard.

standard ranging from 1.0

to 0.0 

Herbaceous plant cover be- 0.5

tween 25% and 75%, or more

than 125% that of reference

standard.

Herbaceous plant cover be- 0.1

tween 0% and 25% that of

reference standard.
60 Chapter 2 Documentation of Riverine Wetland Functions

VHERB: (Concluded) Herbaceous plant cover absent; 0.0

restoration not possible.

VSHRUB: Shrub and sap- Shrub abundance >75% Visual estimate of shrubs and 1.0

ling density, biomass, or

cover

that of reference standard. saplings indicates site is similar

(>75%) to reference standard.

Shrub abundance between Visual estimate of shrubs and 0.5

25% and 75% that of refer- saplings indicates site is beence standard. tween 25% and 75% that of

reference standard.

Shrub abundance between Shrubs and saplings sparse or 0.1

0% and 25% that of refer- absent relative to reference

ence standard. standard; restoration possible.

Shrubs absent; restoration Shrubs and saplings absent; 0

not possible. restoration not possible.

VBTREE: Tree basal area Basal area or biomass is Stage of succession similar to 1.0

greater than 75% of refer- reference standard.

ence standard.

Basal area or biomass be- Stage of succession departs 0.5

tween 25% and 75% of significantly from reference

reference standard. standard.

Basal area or biomass be- Stage of succession at extreme 0.1

tween 0% and 25% of ref- departure from reference stanerence standard; restora- dard; restoration possible.

tion possible.

No trees are present; resto- Stand cleared; no restoration 0

ration not possible. possible.

VDTREE: Tree density Measured or estimated tree Stage of succession similar to 1.0

density is between 75% reference standard.

and 125% of reference

standard.

Tree density is between Stage of succession departs 0.5

25% and 75%, or between significantly from reference

125% and 200%, of refer- standard.

ence standard.

Tree density is between Stage of succession at extreme 0.1

0% and 25%, or greater departure from reference stanthan 200%, of reference dard; restoration possible.

standard; restoration

possible.

No trees are present; resto- Stand cleared; no restoration 0.0

ration not possible. possible.

VMICRO: Microtopo- Microtopographic com- Visual estimate indicates that 1.0

graphic complexity plexity (MC) measured microtopographic complexity

(surveyed) shows MC (MC) is >75% and <125% of

>75% and <125% of reference standard. 

reference standard. 
Index of Function {[(VFREQ VSURFIN)/2] × [(VHERB VSHRUB

VBTREE VDTREE VMICRO VCWD)/6]}

1/2

Chapter 2 Documentation of Riverine Wetland Functions 61

VMICRO: (Concluded) Measured MC is between Visual assessment confirms 0.5

25% and 75% that of refer- MC is somewhat less than refence standard. erence standard.

Measured MC between 0% Visual assessment indicates 0.1

and 25% that of reference MC is much less than reference

standard; restoration standard; restoration possible.

possible. 

No MC at assessed site or Visual assessment indicates 0.0

natural substrate replaced MC is virtually absent or natural

by artificial surface; resto- substrate replaced by artificial

ration not possible. surface; restoration not

possible.

VCWD: Coarse woody Biomass of CWD >75% Volume of CWD is >75% and 1.0

debris (CWD) and <125% that of refer- <125% that of reference

ence standard. standard.

Biomass of CWD between Volume of CWD is between 0.5

25% and 75% that of refer- 25% and 75% that of reference

ence standard. standard.

Biomass of CWD between Volume of CWD is between 0% 0.1

0% and 25% that of refer- and 25% that of reference stanence standard; restoration dard; restoration possible.

possible.

No CWD present; resto- No CWD present; restoration 0.0

ration not possible. not possible.

VSEDIM: Retained sedi- Accumulation rates using Silt or sediment layering on sur- 1.0

ments cesium-137, lead-210, feld- faces or buried root collars or

spar clay layer, scaled as a natural levees between 75%

linear function from refer- and 125% of reference

ence standard (1.0) to ab- standard. 

sent (0.0).

As above, but between 25% 0.5

and 75%, or >125%, of reference standard. 

As above, but between 0% and 0.1

25%, of reference standard.

Hydrologic alterations eliminate 0.0

variable; restoration not

possible.

Option 1:
Index VSEDIM

62 Chapter 2 Documentation of Riverine Wetland Functions

Option 2: 

Organic Carbon Export

Definition

Export of dissolved and particulate organic carbon from a wetland. Mechanisms

include leaching, flushing, displacement, and erosion.

Discussion of function and rationale

Wetlands export organic carbon at higher rates per unit area than terrestrial ecosystems (Mulholland and Kuenzler 1979) in part because surface water has greater

contact time with organic matter in litter and surface soil. While the molecular

structure of most of organic matter is not well known because of its chemical complexity (Stumm and Morgan 1981), organic matter nevertheless plays important

roles in geochemical and food web dynamics. For example, organic carbon complexes with a number of relatively immobile metallic ions which facilitates transport

in soil (Schiff et al. 1990). Organic carbon is a primary source of energy for microbial food webs (Dahm 1981; Edwards 1987; Edwards and Meyer 1986) which form

the base of the detrital food web in aquatic ecosystems. These factors, in combination with the proximity of wetlands to aquatic ecosystems, make wetlands critical

sites for supplying both dissolved and particulate organic carbon.

Description of variables

V , Frequency of overbank flow. Overbank flow supplies water to flood- FREQ

plain surfaces. Long contact times of shallow water over large surface areas of organic rich sediments allow organic matter to accumulate in surface waters. However, organic carbon can be exported from floodplains that do not receive overbank

flow. Precipitation on riverine wetlands and overland flow from uplands to wetlands can transport water to stream channels for delivery downstream. However,

wetlands receiving overbank flow would normally have several orders of magnitude

greater water turnover than a wetland without such a water source.

Data from stream-gauging stations are reliable in estimating this variable but not

all streams have gauges. Other applicable variables that could be used include

water marks, silt lines, ice scars, bryophyte and lichen levels, drift and wrack lines,

sediment scour, and sediment deposition. Many of these variables simply indicate

that recent flooding (silt lines) may have occurred during an infrequent event (ice

scour), and therefore not be particularly helpful in establishing the flood return

interval of a particular site.
Chapter 2 Documentation of Riverine Wetland Functions 63

Indices are related to flood frequencies and a maximum of 1.0 should be given to

a site that receives the same flood frequency as its reference standard. Indices for

other frequencies are lower and lack of overbank flow should receive a zero.

V , Surface inflow. When precipitation rates exceed soil infiltration rates, SURFIN

overland flow in uplands adjacent to riverine wetlands can transport organic carbon,

both dissolved (DOC) and particulate (POC), to a wetland surface. Indicators include the presence or rills and rearranged litter on upland slopes leading to the

floodplain. Saturated surface flow may also occur as partial area contributions

(Dunne and Black 1970). Tributaries leading to a riverine wetland and not connected to the main channel may also transport organic carbon to the wetland being

assessed. Even if these sources do not contribute excess organic carbon to a

wetland being assessed, these sources would likely displace surface water ponded in

the wetland so that export occurs. V can be measured directly, but this is SURFIN

impractical for rapid assessment.

Indirect measures are made visually and compared with reference standards. 

Seeps at the toe of upland slope are indicative of saturated surface inflow from the

partial area contributions. Both DOC and POC may be transported from these sites

to the wetland.

The variable should score 1.0 if either of the following indicators is similar to

reference standards: rills on adjacent upland slopes, or lateral tributaries entering a

floodplain and not connected to its channel. If neither of the above indicators is

similar to the reference standard, and either is less than its reference standard, the

variable should score 0.5. Absence of both indicators should score 0.1, while the

presence of ditches at the toe of the slope (which would intercept surface flows)

would warrant a score of zero.

VSUBIN, Subsurface inflow. Subsurface flow into a riverine wetland is often

revealed by soil saturation maintained by seeps along the break in slope at the

wetland edge. Other evidence includes the slow drainage of water from the wetland

after precipitation or a flooding event, and a positive upward flow indicated by

springs or piezometers. The conductivity of the alluvium relative to the conductivity

of recharge areas in the upland will modify rates of transport.

Subsurface inflow contributes to organic carbon export. Displacement of

existing soil water within alluvium may create outflow through surface and

subsurface pathways to downstream localities. 

Direct measures of groundwater movement are time consuming and impractical

for rapid assessment. Indirect methods will depend on regional conditions: 

Examples are the same as provided for V in the function Moderation of SURFIN

Groundwater Flow or Discharge.

V , Surface hydraulic connections with channel. Internal networks of SURFCON

channels are common features on large riverine floodplains. These channels are

conduits for overbank flow during periods of high upriver discharge, but also
64 Chapter 2 Documentation of Riverine Wetland Functions

provide pathways for drainage as upriver discharge is reduced. Where natural

levees are prominent, as in alluvial river systems, breaks in levees indicate the

potential for overbank flow through channels during high upriver discharge. These

breaks are normally connected to the channel network in such a manner that drainage continues to occur long after stage height has fallen below bank-full levels.

Aerial photographs taken during the leafless dormant season may provide evidence of channel patterns. If a wetland is large enough, some of these features are

apparent on 7.5-minute topographic maps. Otherwise, onsite visual estimates must

be made.

Scaling of surface hydraulic connections is absolutely dependent on calibration

established by a reference domain. If the quantity of internal channels is similar to

the reference standard, the assessment site should receive a score of 1.0. Estimates

below the reference standard should score 0.5 unless connections are virtually absent. Apparent absence of connections should receive a 0.1. Known alterations to

sever or block connections should receive a score of zero.

V , Organic matter in wetland. Both live and dead plant materials are ca- ORGAN

pable of contributing to the organic carbon concentration of exported water

(Cuffney 1988). Leaf litter, especially soon after the autumn litterfall peak, contributes large amounts of leachable dissolved organic carbon (DOC) to floodwaters

(Brinson 1977). Other detrital sources include woody debris (both coarse and fine)

and organic matter in soil. Leaching of plant material during precipitation events

results in high concentrations of DOC in throughfall and stemflow (Brinson et al.

1980, Hauer 1989). Surface accumulations of leaves and twigs into debris piles

normally represent material redistributed by overland flow. These litter piles then

provide a source for transport downstream (Cummins 1974, Dahm 1981). Wintertime flooding may remove surface litter, and transport material to streams or offsite. 

The importance of woody debris in food web support on floodplains is not as well

documented in the Southeast (Hauer and Benke 1991) as it is in the Pacific

Northwest.

Indicators of the presence of organic carbon include estimates of living biomass

(V , V , V ), litter and fine woody debris (V ), coarse woody debris BTREE SHRUB HERB FWD

(V ), and soil organic carbon (not an established variable). Thus, the various CWD

components of organic matter could and probably should be determined separately. 

Measurements of these various organic matter components are discussed in the Nutrient Cycling function. 

A score of 1.0 is earned if indicators are equivalent to the reference standard. A

zero should be assigned for a site barren of both detritus and living plants with no

potential for recovery. Higher resolution of intermediate values could be established

based on direct measurements on reference standard sites.
Index {[(VFREQ VSURFIN VSUBIN VSURFCON)/4] × VORGAN}

1/2

Chapter 2 Documentation of Riverine Wetland Functions 65

Index of function

Two factors are required for a wetland to be a source of organic carbon for export: a source of organic matter and water flow (a transport mechanism). Water

flow has two components - water sources and surface hydraulic connections. The

variables used are frequency of overbank flow (V ), and overland flow (V ) FREQ SURFIN

or groundwater discharge (V ) from adjacent uplands. Surface connections be- SUBIN

tween the wetlands and stream channel (V ) are essential for providing a path- SURFCON

way for return flows to channels, thus assuring that export actually occurs. Normally, if overbank flow occurs, surface connections are present. The fourth variable

used is the source of organic matter in a wetland (VORGAN). One approach is to

substitute for V all variables that potentially contribute organic carbon for ORGAN

export. These include, in addition to soil organic matter and leaf litter, V , BTREE

V , V , and V (these variables include both living and dead organic SHRUB HERB CWD

matter). If either organic carbon is absent or surface hydraulic connections are

lacking (i.e., the wetland is diked or otherwise isolated), the function is lacking:

If V = 0, the function is absent. ORGAN

It is assumed that in order for the reference standard condition to be sustained,

mechanisms of transport and a source of organic carbon are equally important and

essential.
66 Chapter 2 Documentation of Riverine Wetland Functions

Documentation

ORGANIC CARBON EXPORT

Definition: Export of dissolved and particulate organic carbon from a wetland. Mechanisms include

leaching, flushing, displacement, and erosion.

Effects Onsite: The removal of organic matter from living biomass, detritus, and soil organic matter

contributes to decomposition. Metals may be mobilized by chelation to dissolved and particulate

forms of organic carbon.

Effects Offsite: Provides support for aquatic food webs and biogeochemical processing downstream

from the wetland.

Model Variables Direct Measure Indirect Measure Index of Variable

VFREQ: Frequency Gauge data (1.5) yr return At least one of the following: aerial photos 1.0

of overbank flow interval similar to reference showing flooding, water marks, silt lines, alstandard. (Interval in paren- ternating layers of leaves and fine seditheses must be adjusted to ment, ice scars, drift and/or wrack lines,

reference standard.) sediment scour, sediment deposition, directionally bent vegetation similar to reference

standard.

Gauge data (>2 or <1) yr As above, but somewhat greater or less 0.5

return interval. than reference standard.

Gauge data show extreme Above indicators absent, but related indica- 0.1

departure from reference tors suggest overbank flow may occur.

standard.

Gauge data indicate no Indicators absent and/or there is evidence 0.0

flooding from overbank flow. of alteration affecting variable; restoration

not possible.

VSURFIN: Surface Use of data from runoff Any of the following indicators similar to 1.0

Inflow to a

wetland

collectors as a continuous reference standard:

variable from reference 1. Rills on adjacent upland slopes. 

standard (1.0) to absent 2. Lateral tributaries entering floodplain

(0.0). and not connected to the channel.

Neither of the above indicators similar to 0.5

reference standards, and either of the

above indicators less than reference

standard.

Absence of both of the above indicators. 0.1

Absence of both of the above indicators, 0.0

and hydraulic gradient reversed by regional

cone of depression, or channelization

across wetland prevents inflow.
Index of Function {[(VFREQ VSURFIN VSUBIN VSURFCON)/4]

× VORGAN}

1/2

Chapter 2 Documentation of Riverine Wetland Functions 67

VSUBIN: Subsur- 1. Groundwater discharge Example of the reference standard deter- 1.0

face flow into measured in seeps or mined by regional standards:

wetland springs and discharge from 1. Seeps present at edge of wetland or

wetland or 2. Vegetation growing during dormant sea2. Positive (upward) son or drought (i.e., wet soils support vegegroundwater gradient mea- tation) or

sured by piezometers and 3. Wetland occurs at toe of slope or

scored relative to reference 4. Artesian flow (upwelling) on wetland

standards. surface.

Regional standards greatly reduced. 0.5

Regional standards absent with potential 0.1

for recovery.

Regional standards absent with no potential 0.0

for recovery.

VSURFCON: Surface No direct measures. Visual estimates of internal drainage chan- 1.0

hydraulic

connections

nels present and connected to main channel between 75% and 125% that of reference standard.

As above but between 25% and 75% or 0.5

>125% that of reference standard.

As above, but between 0% and 25% that of 0.1

reference standard.

Internal drainage channels absent or pres- 0.0

ent and blocked from main channel. 

VORGAN: Organic Measured standing stocks Visual estimates of litter, coarse woody de- 1.0

matter in wetland of live and dead biomass bris, live woody vegetation, live or dead herand soil organic matter be- baceous plants, organic rich mineral soils,

tween 75% and 125% of or histosols at levels between 75% and

reference standard. 125% that of reference standard. 

As above but between 25% As above but between 25% to 75% or 0.5

and 75% or >125% of refer- >125% of reference standard

ence standard.

As above, but between 0% As above, but between 0% and 25% of ref- 0.1

and 25% of reference erence standard.

standard.`

Standing stocks of live and No organic matter; no potential for recovery. 0.0

dead biomass and soil organic matter absent.
68 Chapter 2 Documentation of Riverine Wetland Functions

Maintain Characteristic Plant Community

Definition

Species composition and physical characteristics of living plant biomass. The

emphasis is on the dynamics and structure of the plant com- munity as revealed by

the dominant species of trees, shrubs, seedlings, saplings, and ground cover, and by

the physical characteristics of vegetation.

Discussion of function and rationale

Vegetation accounts for most of the biomass of riverine wetlands, and the physical characteristics of living and dead plants are closely related to ecosystem functions associated with hydrology, nutrient cycling, and the abundance and diversity of

animal species (Gregory et al. 1991). Vegetation is not static, however, and species

composition and physical characteristics can change in space and time in response

to natural and anthropogenic influences (Shugart 1987).

The importance of plant communities to riverine ecosystems can be understood

by considering what happens when vegetation is removed or highly disturbed (Harris and Gosselink 1990). Removal or severe disturbance of riparian vegetation can

lead to a change in the structure of macroinvertebrate communities (Hawkins,

Murray, and Anderson 1982), a decrease in the species diversity of stream ecosystems, a decline in the local and/or regional diversity of animals associated with

riverine corridors, a deterioration of downstream water quality, and a significant

change in river/stream hydrology (Gosselink et al. 1990).

The goal of assessing this function is to evaluate species composition and structure of wetland plant communities to determine their successional status relative to

their reference standard. If a site being evaluated contains species in various life

history stages and in densities that are similar to those found in a mature riparian

forest in the same area (i.e., the same wetland hydrogeomorphic class), its plant

community is likely to be stable. If a site is dominated by species other than those

that are characteristic of mature stands within the area, it is likely that the site has

been disturbed by natural or anthropogenic events. If the site has been disturbed,

the goal of an assessment is to use species that are present and physical characteristics of the vegetation to determine whether or not the plant community is progressing toward the reference standard.

Description of variables

V , Species composition for tree, sapling, shrub, and ground cover strata. COMP

Species composition is one of five variables used to assess the plant community

function. Species identifications are relatively easy for most plants, and species lists

can be used to compare an assessment site with its reference standard. The highest

priority should be given to compilation of a complete species list for each
Chapter 2 Documentation of Riverine Wetland Functions 69

assessment site. A complete species list provides a direct measure of plant species

richness of a site and is also valuable in determining whether a site contains any species that are rare, threatened, or endangered. When it is not possible to obtain a

complete species list, the most common species in the tree, sapling, shrub, and

ground-cover layers should be identified from surveys of the assessment site (direct

measure) or from species lists previously compiled for the site (indirect measure). 

If three of the dominant species in each of the four strata (tree, sapling, shrub,

and ground cover) match three of the four dominants in equivalent strata of reference standard, then the variable should be assigned a 1.0. If only the ground cover

does not meet this condition, the site should receive 0.75 for the variable score. The

score decreases to 0.5 if neither ground cover nor saplings match three of the four

dominants of reference standards. If only the tree stratum shares its three dominants

with reference standards, a 0.25 should be assigned to the variable. Finally, if none

of the strata meet reference standards, then a score of zero should be assigned. If

information is only a variable from an indirect measure (e.g., a species list that has

been published or a source of unpublished data), an index score of 1.0 is given only

if the species information is verified.

V , Regeneration from seedlings/saplings and/or clonal shoots. Death is REGEN

a natural process in ecosystems (Shugart 1987), and the maintenance of plant communities requires replacement of individuals that die. The understory of a stable

plant community typically contains small individuals (saplings/seedlings) of species

that occur in the forest canopy. Saplings and seedlings of understory species

(shrubs, herbs, and vines) in stable communities will also be present. Species composition of the understory vegetation is, therefore, useful in predicting what a plant

community will be like in the future, especially for sites that have been disturbed

and are undergoing secondary succession (Sharitz, Schneider, and Lee 1990). 

If a direct measure shows that the ratio of sapling and seedling species to canopy

species is between 50 and 75 percent of its reference standard (a mature forest), an

assessment site has a high probability of being stable and an index of 1.0 should be

given for the variable. A score of 0.5 should be given if the measure is 25 to 50 percent of the reference standard; a score of 0.1 should be given if the measure is 0 to

25 percent of the reference standard. If species composition of seedlings or saplings

has no similarities with the reference standard sites, or if a site is devoid of vegetation, an index of 0.0 should be given. If information is available only from an indirect measure such as a species list that has been published or obtained from an unpublished source, a score of 1.0 should be given only if such lists are verified. The

plant communities of marshes can also be assessed, but without the need to specify

strata.

V , Canopy cover. Canopy cover is an estimate of spatial continuity in the CANOPY

upper layers of a forest canopy. Many riverine forests possess a relatively continuous canopy, but considerable variation can be expected due to impacts of disturbances from windstorms, floods, and various human activities. Canopy gaps are

also present in most mature forests, but these gaps are created by normal mortality

processes and should not be considered as a sign of disturbance.
70 Chapter 2 Documentation of Riverine Wetland Functions

The measurement of canopy cover can be done most simply by making a visual

estimate of how much of the sky is covered by leaves when one looks into the

canopy. A bottomless cup or cone could be used as a sighting device by pointing it

toward the canopy for an estimate of cover. More quantitative methods (analysis of

fisheye photographs, measurements of percent light transmission to the forest

understory, densitometer measurements) are available, but in most instances they

would not be necessary.

If the percent cover in an assessment site is >75 percent of the value established

from reference standard sites, a score of 1.0 should given. Index scores of 0.5 and

0.1 should be given when an assessment site and reference standards show 25 to

75 percent and 0 to 25 percent similarity, respectively. A zero is given when there is

no tree layer. Indirect measures of percent cover should not be used unless it is impossible to make a direct measure. Recent aerial photographs, taken during the

growing season, can be used to provide an indirect measure, but these should be

used with great caution as changes may have occurred at the assessment site between the time the evaluation is made and the time the photographs were taken. If

data from the indirect measure are verified during a visit to an assessment site,

scores should be given using the same ranges as used for direct measures of

variables.

V , Tree density. Density (V ) and basal area (V , below) of trees DTREE DTREE BTREE

can be used to evaluate the successional status and stability of plant communities. 

As forests mature, tree density decreases and basal area increases until both reach a

sustainable level. Tree density and basal area are among the most easily measured

variables for forested wetlands, and a large number of publications are available that

describe appropriate methods (e.g., Mitsch and Gosselink 1993; Golet et al. 1993;

Lugo, Brinson, and Brown 1990). The tree density variable should be used in

combination with basal area to provide a robust estimate of forest structure.

If tree density at an assessment site is between 75 and 125 percent of reference

standards, it may be assumed that the site is stable and a score of 1.0 should be

given. A score of 0.5 should be assigned if the range is either 25 to 75 percent or

>125 to 200 percent. Densities beyond the foregoing ranges (i.e., higher or lower)

should be assigned 0.1. The absence of tree species receives a zero. Indirect

measures of density and basal area should not be used unless it is impossible to

obtain a direct measure. The only acceptable indirect measure should be published

data or unpublished data that are verified. The same intervals may be used for

published or verified data.

VBTREE, Tree basal area. Basal area of trees ( VBTREE) is proportional to

aboveground plant biomass of trees and is a dependable indication of forest

maturity. In bottomland hardwood forests, for example, basal area and stem density

both increase early in succession. Thereafter, tree density decreases, and, as the

forest reaches maturity, the rate of increase of basal area diminishes to steady-state

conditions (Brinson 1990).

Because basal area of trees can be estimated accurately with angle gauges and

prisms, indirect measures do not offer any advantage over direct ones. Therefore,
Index of Function [(VCOMP VREGEN VCANOPY)

(VDTREE VBTREE)/2]/4

Chapter 2 Documentation of Riverine Wetland Functions 71

measurements at and above the reference standard should receive a 1.0, while all

other measures below that level should be assigned an index value proportional to

the reference standard.

Index of function

Species composition of the tree, sapling, shrub, and ground cover strata (V ), COMP

species composition of seedlings, saplings, and regeneration from clonal shoots of

plants in the understory (VREGEN), percent canopy cover (VCANOPY), and the combined

variables of tree density (V ) and basal area (V ) are used to assess the DTREE BTREE

Maintain Characteristic Plant Community function. The variables must be scaled to

existing reference standards appropriate for the physiographic region of interest and

wetland class.

Documentation

MAINTAIN CHARACTERISTIC PLANT COMMUNITY

Definition: Species composition and physical characteristics of living plant biomass. The emphasis

is on the dynamics and structure of the plant community as revealed by the dominant species of trees,

shrubs, seedlings, saplings, and ground cover, and by the physical characteristics of vegetation.

Effects Onsite: Converts solar radiation and carbon dioxide into complex organic compounds that

provide energy to drive food webs. Provides seeds for regeneration. Provides habitat for nesting,

resting, refuge, and escape cover for animals. Creates microclimatic conditions that support completion of life histories of plants and animals. Creates roughness that reduces velocity of floodwaters. Provides organic matter for soil development and soil-related nutrient cycling processes. 

Creates both long- and short-term habitat for resident or migratory animals.
72 Chapter 2 Documentation of Riverine Wetland Functions

Effects Offsite: Provides a source of propagules to maintain species composition and/or structure of

adjacent wetlands and supplies propagules for colonization of nearby degraded systems. Provides

food and cover for animals from adjacent ecosystems. Provides corridors (migratory pathways) between habitats, enhances species diversity and ecosystem stability, and provides habitat and food for

migratory and resident animals. Supports primary and secondary production in associated aquatic

habitats. Contributes leaf litter and coarse woody debris habitat for animals in associated aquatic

habitats (Bilby 1981).

Model Variables Direct Measure Indirect Measure Index of Variable

VCOMP: Species com- Three of the dominant species in Published lists of dominant spe- 1.0

position for tree, sapling, shrub and

ground cover strata

each of the four vegetation strata cies of each stratum show presmatch three of the four dominants ence of same species as referin equivalent strata of reference ence standard.

standard.

As above, but ground cover does 0.75

not meet reference standard.

As above, but ground cover and 0.5

saplings don't meet reference

standard.

As above, but only tree stratum 0.25

meets reference standard.

None of the strata meets refer- Site devoid of vegetation or no 0.0

ence standard. species shared with reference

standard.

VREGEN: Seedlings/ Ratio of seedling/sapling species Published lists or unpublished lists 1.0

saplings and/or clonal

shoots

to canopy species is within 75% that are verified and show same

of the ratio for reference species composition as reference

standard. standard.

As above, but between 25% and 0.5

75% of the ratio of reference

standard.

As above, but between 0% and 0.1

25% of the ratio of reference

standard.

Seedlings/saplings and/or clonal Site devoid of vegetation or no 0.0

shoots are absent or share no species shared.

species with reference standard

sites.

VCANOPY: Canopy Measure of canopy cover is Remote or other indirect methods 1.0

cover >75% of reference standard. not recommended.

As above, but between 25% and 0.5

75% of reference standard.

As above, but between 0% and 0.1

25% of reference standard.

Canopy cover is absent. 0.0
Index of Function [(VCOMP VREGEN VCANOPY (VDTREE

VBTREE)/2]/4

Chapter 2 Documentation of Riverine Wetland Functions 73

VDTREE: Tree density Measured or estimated tree den- Stage of succession similar to 1.0

sity is between 75% and 125% of reference standard.

reference standard.

Tree density is between 25% and Stage of succession departs sig- 0.5

75%, or between 125% and nificantly from reference standard.

200%, of reference standard.

Tree density is between 0% and Stage of succession at extreme 0.1

25%, or greater than 200%, of departure from reference stanreference standard; restoration dard; restoration possible.

possible.

No trees are present; restoration Stand cleared; no restoration 0.0

not possible. possible.

VBTREE: Tree basal Basal area or biomass is greater Stage of succession similar to 1.0

area than 75% of reference standard. reference standard.

Basal area or biomass between Stage of succession departs 0.5

25% and 75% of reference significantly from reference

standard. standard.

Basal area or biomass between Stage of succession at extreme 0.1

0% and 25% of reference departure from reference stanstandard; restoration possible. dard; restoration possible.

No trees are present; restoration Stand cleared; no restoration 0.0

not possible. possible.

Maintain Characteristic Detrital Biomass

Definition

The production, accumulation, and dispersal of dead plant biomass of all sizes. 

Sources may be onsite or upslope and upgradient. Emphasis is on the amount and

distribution of standing and fallen woody debris.

Discussion of function and rationale

This function refers primarily to categories of detritus known as fine woody

detritus (wood <10 cm in diameter) and coarse woody debris (wood >10 cm

diameter). Fine and coarse woody debris (Harmon et al. 1986) are part of the

detritus pools of ecosystems. Woody debris contributes to the functioning of

ecosystems by reducing erosion and helping build soils (McFee and Stone 1966). 

Decomposing detritus also provides wildlife habitat and serves as a store of

nutrients and water (Franklin, Shugart, and Harmon 1987; Harmon et al. 1986;

Thorp et al. 1985). Woody debris is a major source of energy, and a major habitat

for decomposers and other heterotrophs (Harmon et al. 1986; Seastedt, Reddy, and

Cline 1989). Coarse woody debris and debris dams (Smock, Metzler, and Gladden
74 Chapter 2 Documentation of Riverine Wetland Functions

1989) also play an important role in the dynamics of floodplain-stream ecosystems

(Bilby 1981).

Fine woody detritus normally is associated with the forest floor while coarse

woody debris has both vertical and horizontal components. Standing dead trees

(snags), for example, may account for a large amount of coarse woody debris in forests and provide key habitat for many species (Harmon and Hua 1991). Fallen trees

and tree branches that come into contact with the soil surface undergo decomposition at a faster rate than standing trees. It is the decomposition process that ultimately converts wood into material that becomes incorporated into soil and recycles

nutrients between living and dead biomass (Harmon et al. 1986).

One way of assessing this function is to evaluate the amount and distribution of

woody debris relative to reference standards developed from sites that are mature

and are likely to have stable accumulations of detritus. The amount of both fine and

coarse woody debris can vary greatly as a result of storms, e.g., Hurricane Hugo’s

effect on the Congaree Swamp National Monument, a riverine floodplain forest in

South Carolina (Putz and Sharitz 1991).

Description of variables

V , Density of standing dead trees (snags). Standing dead trees (snags) are SNAGS

a normal component of floodplain and riparian wetlands dominated by trees. The

density of standing dead trees provides information on the suitability of a site as

animal habitat and whether or not a site is mature. A forested wetland may also

contain more standing dead trees than the reference standard as a result of

modifications to its hydrologic regime. For example, a restriction in the flow of a

stream caused by the construction of a road crossing would lead to a die-off of less

flood-tolerant trees on the affected floodplain. Beaver dams built along a lowgradient reach of a stream can lead to a similar density or biomass of standing dead

trees. Because the two sites would probably receive similar variable index scores

for this variable, it might be useful to recognize beaver-dominated wetlands as a

separate subclass, so that the more temporary and natural influence of beaver can be

distinguished from the more permanent drainage constriction caused by road

construction. In some cases, the natural beaver-influenced system might be the

subclass upon which reference standards are developed. When establishing a

reference domain or comparing assessment areas, one should also be aware of

alternative explanations for site characteristics. For example, diseases (e.g., Dutch

elm disease) can be responsible for high mortality rates of trees in floodplain

forests. 

The number of standing dead trees at an assessment site should be counted or

estimated (categorical data) and compared to its reference standard. If the density is

>75 percent of the reference standard, an index score of 1.0 should be assigned. 

Comparisons that are between 25 and 75 percent of the reference standard should be

scored as 0.5, while those falling below 25 percent should be assigned 0.1. If an

assessment site has no standing dead trees, a score of 0.0 should be given. There is

no suitable indirect measure for this variable at the 1.0 level. However, if leaf-off
Chapter 2 Documentation of Riverine Wetland Functions 75

aerial photography at a suitable scale is available, indirect indices can be obtained

for sites that cannot be sampled. A variable score of 0.5 should be given if the

aerial photographs show an assessment site has >75 percent of the density of the

standing dead trees relative to its reference standard. Values less than 75 percent

are scored 0.1, and a score of zero is given when no standing dead trees are visible

on aerial photographs.

V , Coarse woody debris. Down and dead trees, branches, etc., on the forest CWD

floor represent coarse woody debris (CWD). CWD provides important wildlife

habitat and can serve as a refuge for animals during floods. The volume of fallen

logs can be measured at an assessment site (indirect measure of biomass) and compared to its reference standard. 

If the volume of fallen logs is >75 percent of its reference standard, then a score

of 1.0 should be given. Comparisons that place the assessed site at 25 to 75 percent

of reference standard should be scored as 0.5, while those from 0 to <25 percent are

scored as 0.1. If an assessment site has no coarse woody debris on the soil surface,

the variable should be scored 0.0. It would be very difficult to obtain an indirect

measure of this variable. The only other suitable way to determine the indicator for

this variable would be to examine high-quality aerial photographs taken during the

leafless season. Aerial photographs should be used only if they are recent and it is

known that the site has not been altered since the photographs were taken. There is

no appropriate indirect measure if the site is dominated by evergreen trees. A variable score of 0.5 should be given if the aerial photography shows that an assessment

site has >50 percent of the density of fallen logs relative to its reference standard. 

Values <50 percent are scored as 0.1, and an index score of 0.0 is given when no

fallen logs are visible on aerial photographs.

V , Logs in several stages of decomposition. Decomposing logs contribute LOGS

nutrients and organic matter to soils. Logs also provide habitat for animals that use

them as resting sites, feeding platforms, and as sources of food (Harmon et al.

1986). Mature riparian forests contain logs in various stages of decomposition, indicating steady recruitment of coarse woody debris to a forest floor as a result of

tree death. A standard protocol is available for assessing stages of decomposition

of coarse woody debris (Harmon et al. 1986), but for purposes of this functional

assessment method, it is only necessary to compare the range of conditions found

among decomposing logs at the assessment site with information from reference

standard sites.

The volume of fallen logs is assessed to estimate the biomass of coarse woody

debris (V ). These same logs can be assessed to determine their stage of decom- CWD

position. For “logs in several stages of decomposition” variable (V ), a direct LOGS

measure could be used to determine the number of the abundance (e.g., common,

rare, absent) of decomposition stages of logs present, based on the following

categories:

Class 1: Logs recently fallen and show little decay; bark still present; and leaves

and fine twigs are often still present.
76 Chapter 2 Documentation of Riverine Wetland Functions

Class 2: Logs relatively undecayed but no leaves and fine twigs present; bark starting to fall off; fungal sporocarps (mushrooms) start to appear at this stage.

Class 3: Logs with no bark and only a few branch stubs remaining.

Class 4: Logs with no branches or bark cover; outer parts of the log may be gone

leaving some heartwood that is still undergoing decomposition.

Class 5: Logs elliptical in cross section (indicative of advanced decay) and wood

often scattered across the soil surface.

If the assessment site has more than 75 percent of the range of log decay classes,

a score of 1.0 should be given. If an assessment site has 25 to 50 percent of the log

decay classes, 0.5 should be given. If an assessment site contains 0 to 25 percent of

the possible decay classes, a score of 0.1 should be given. If the assessment site

contains no logs, a score of 0.0 should be given. There is no suitable indirect measure for this variable even if published or unpublished data exist for an assessment

site because a site visit would be necessary to verify such information. A direct

measure is the only appropriate measurement for this variable.

V , Fine woody debris (accumulating in active channels and side chan- FWD

nels). This variable refers to woody components smaller than coarse woody debris

and includes both fine wood detritus and leaf litter. Hydrologic interactions between

streams and riparian/floodplain areas are dynamic. Water redistributes materials

within a floodplain, and woody debris often accumulates on wetland surfaces or in

channels that are filled with water when the stream floods. The accumulation of

woody debris in piles of various sizes is one of the most obvious signs that a riparian/floodplain zone actively interacts with its associated stream. Piles of woody

debris serve to retain dissolved and particulate nutrients, provide habitat for decomposers and organisms that shred leaf litter, and provide temporary habitat for stream

vertebrates and invertebrates (Gregory et al. 1991).

This variable is assessed by comparing the abundance of accumulated woody

debris in an assessment site with information from its reference standard. When the

amount and distribution of accumulated organic matter in the assessment site is approximately similar to the amount found in the reference standard sites, a score of

1.0 should be given. If the amount and distribution of accumulated debris is between 25 and 75 percent of the reference standard, a score of 0.5 should be given. 

When the assessment site contains little accumulated organic matter (between 0 and

<25 percent) relative to the reference standard, it should score 0.1. When there is

very little or no accumulated organic matter compared to the reference standard, the

variable should score zero. There is no suitable indirect measure for this variable.

Index of function

The abundance of standing (V ) and downed (V ) logs, the decay stages of SNAGS CWD

the logs (V ), and the abundance of piles of accumulated organic matter (V ) LOGS FWD

are variables used to assess the detritus function. All variables must be scaled to
Index of Function {VSNAGS [(VCWD VLOGS)/2)] VFWD}/3

Chapter 2 Documentation of Riverine Wetland Functions 77

existing reference standards appropriate for the physiographic region and the

wetland class.

The standing dead tree variable is assumed to be as important as the average of the

variables for decay stages and abundance of downed logs, and to fine woody debris.

Documentation

MAINTAIN CHARACTERISTIC DETRITAL BIOMASS

Definition: The production, accumulation and dispersal of dead plant biomass of all sizes. Sources

may be onsite or upslope and upgradient. Emphasis is on the amount and distribution of standing

and fallen woody debris.

Effects Onsite: Provides primary resources for supporting detrital-based food chains, which support

the major nutrient-related processes (cycling, export, import) within wetlands. Provides important

resting, feeding, hiding, and nesting sites for animals of higher trophic levels. Provides surface

roughness that decreases velocity of floodwaters. Retains, detains, and provides opportunities for

in situ processing of particulates. Primarily responsible for organic composition of soil.

Effects Offsite: Provides sources of dissolved and particulate organic matter and nutrients for downstream ecosystems. Contributes to reduction in downstream peak discharges and delayed downstream delivery of peak discharges. Contributes to downstream water quality through particulate

retention and detention.
78 Chapter 2 Documentation of Riverine Wetland Functions

Variables Direct Measure Indirect Measure Index of Variable

VSNAGS: Density of Density >75% of reference No suitable measure available. 1.0

standing dead trees standard. 

Density between 25% and 75% 0.5

that of reference standard.

Density between 0% and 25% 0.1

of reference standard.

No standing dead trees; resto- 0.0

ration not possible. 

VCWD: Coarse Biomass of CWD is >75% and Average diameters and lengths 1.0

woody debris <125% that of reference stan- of CWD >75% and <125% that

(CWD) dard. of reference standard.

Biomass of CWD between Average diameters and lengths 0.5

25% and 75% that of reference of CWD between 25% and 75%

standard. that of reference standard.

Biomass of CWD between 0% Average diameters and lengths 0.1

and 25% that of reference stan- of CWD between 0% and 25%

dard; restoration possible. that of reference standard; restoration possible.

No CWD present; restoration No CWD present; restoration not 0.0

not possible. possible.

VLOGS: Logs in sev- Greater than 75% of the range No suitable indirect measure 1.0

eral stages of of log decay classes relative to

decomposition reference standard.

Between 25% and 75% of log 0.5

decay classes relative to reference standard.

Logs are only one decay class 0.1

regardless of average diameter

and length.

Site contains no logs. 0.0

VFWD: Fine woody Cover of fine woody debris No suitable indirect measure. 1.0

debris (accumulat- >75% of reference standard.

ing in active channels, side channels,

and/or microtopographic

depressions)

Cover of fine woody debris 0.5

between 25% and 75% of

reference standard.

Cover of fine woody debris 0.1

between 0% and 25% of

reference standard.

No surface woody debris 0.0

present.
Index of Function {VSNAGS [(VCWD VLOGS)/2] VFWD}/3

Chapter 2 Documentation of Riverine Wetland Functions 79

Maintain Spatial Structure of Habitat

Definition

The capacity of a wetland to support animal populations and guilds by providing

heterogeneous habitats.

Discussion of function and rationale

This function is designed to compare the suitability of vegetation structure for

sustaining animal populations. Vegetation structure refers to dimensional complexity (cavities, canopy gaps, vertical partitioning of vegetative strata, etc.) and not to

species composition. Because structure is an important habitat component for resident and nonresident animals, communities possessing greater structural complexity

often are more diverse and species rich. If intensive studies of wildlife and animal

communities are needed and justified, the more time-consuming “Habitat Evaluation

Procedure” should be used (U.S. Fish and Wildlife Service 1980).

Vegetation of mature, intact riverine ecosystems reflects the constraints imposed

by environmental parameters (climate, hydrologic regime, edaphic factors, geomorphology, etc.) and the competitive interactions of its plants. Wetland vegetation

patterns of altered riverine systems are affected by current and past disturbances, in

addition to the constraints previously listed.

Most large river systems and many smaller ones in the continental United States

have been dramatically altered by dams, levees, diversions, and abstractions (Stanford and Ward 1979). Therefore, present vegetation patterns in riverine wetlands

often reflect past and ongoing anthropogenic alterations in hydrogeomorphic conditions.

Plant communities provide complex, three-dimensional structure in riparian

zones for both vertebrates and invertebrates. Food, shelter (cover), nesting, breeding, and foraging depend, in part, on the complexity and composition of this vegetation. Forested wetlands, particularly mature systems with a full complement of age

classes, are vertically stratified into canopy (overstory tree species), subcanopy

(understory trees and younger overstory species), shrub, and ground cover (both

herbaceous and woody vegetation layers). As vertical complexity of forests increases due to the number of strata, both the abundance of individuals and species

richness increases.

Habitat patchiness is another factor that controls animal species richness and

diversity. The types and distribution of ecotones (sharp boundaries in vegetation

types) and canopy gaps affect ecosystem processes and species composition. The
80 Chapter 2 Documentation of Riverine Wetland Functions

scale at which patchiness is evaluated determines the reliability and usefulness of

the measurements.

The goal of assessing the habitat structure function is to evaluate the structural

and spatial complexity of a wetland plant community, particularly those components

that affect animal populations. This function must be examined in the context of

reference standards for a hydrogeomorphic subclass (i.e., one must be cognizant that

reference standards may vary regionally, among rivers of the same region, and between different reaches of the same river).

Description of variables

V , Density of standing dead trees (snags). Standing dead trees are impor- SNAGS

tant in contributing to habitat structure. Mature forests (in which tree senescence is

common) and forests subjected to periodic disturbances on the order of decades or

longer (outbreaks of insect infestations and disease, hurricanes, etc.) usually possess

standing dead trees (snags). The importance of snags to woodpecker foraging is

well established (they feed on insects in decomposing snags). In addition, limbs of

large snags provide resting, perching, feeding, and nesting sites for large birds, particularly raptors (eagles, osprey, etc.). Other avian predators (kingfishers, cormorants, owls, etc.) use snags for resting, feeding, searching for prey, and drying-out

(cormorants). Neotropical songbirds, waterfowl, and woodpeckers nest within snag

cavities. Mammals (bears, squirrels, mice, etc.) and reptiles (snakes, lizards, etc.)

use snags for feeding, nesting, and hunting. Amphibians (frogs, salamanders, etc.)

use coarse woody debris (CWD), and thus are ultimately dependent on a supply of

CWD from snags. Snags are an extremely important habitat for animal populations

that exploit forested wetlands.

Density determinations should focus on the larger size classes of snags (with

respect to reference standards), because large snags provide the widest range of potential habitats for use by animals. While an analysis of canopy species composition is not necessary to determine the condition of this variable (VSNAGS), such an

analysis could be beneficial in estimating the time required for an assessment site to

approach a project target via succession.

The density of snags is most appropriately determined through direct measurements. However, if measuring is not possible, aerial photographs may be used if

dead and living trees can be discriminated and counted. Discrimination may be possible in some evergreen coniferous forests. Great caution must be exercised when

using remotely sensed data in deciduous forests because it is difficult during leafless

periods to distinguish living from dead trees; during the growing season, leaves of

neighboring trees may obscure observation of snags.

If the frequency of snags is >75 percent of its reference standard, an index variable score of 1.0 should be given. If snag density has been altered through timber

management, or some other disturbance that lowers snag density to between 75 and

25 percent, a variable index score of 0.5 should be given. If snag density is between

25 and 0 percent or there is potential to create snags, a score of 0.1 is given. If there
Chapter 2 Documentation of Riverine Wetland Functions 81

are no snags present, and there is no potential for creating snags, a score of zero

should be given.

VMATUR, Abundance of very mature trees. Standing mature or dying trees provide nesting habitat for a variety of animal species, including invertebrates, birds,

reptiles, amphibians, and mammals. The direct measure of habitat, that of counting

potential cavities, is difficult because cavities are often obscured from sight by an

observer on the ground. Consequently, accuracy is greatly sacrificed in rapid assessments (Tom Roberts 1995, personal communication). Other measures or surrogates for cavities, such as determining the density or species richness of cavitynesting birds, are too time consuming and logistically limiting.

Reference wetlands provide data upon which to establish the tree size considered

as very mature, and thus appropriate, habitat for cavity-nesting animals. Very mature trees may be determined by recording densities of trees greater than some predefined diameter appropriate to the forest community being assessed. Index scores

may be determined as in V above. SNAGS

V , Number and attributes of vertical strata of vegetation. Mature for- STRATA

ested wetlands are usually vertically stratified in temperate North America. Riverine

forests generally possess more than three strata. Because forest organisms exhibit a

remarkable fidelity to a particular stratum, differences in structure between sites

likely represent differences in animal composition between sites as well. In fact,

more spatially stratified communities often contain more species.

Vertical stratification must be measured directly and compared with the reference standard when assessing a site. No indirect measure is available. The number

of strata, density, or cover of plants in each stratum, or some composite index,

should be developed that is appropriate to the reference domain. A condition

>75 percent of reference standards should receive a variable index score of 1.0. 

Conditions between 75 and 25 percent of the reference standard should score 0.5. 

Assessment sites that possess between 0 and 25 percent of the reference standard

(with potential for restoration) should be scored 0.1. Sites that have no potential to

recover vertical stratification similar to that of the reference standard should score a

zero.

V , Vegetation patchiness. Heterogeneity in distribution and abundance PATCH

(patchiness) of organisms is inherent at all scales in every natural ecosystem. Any

measure of ecosystem attributes must consider the appropriate scale and sample size

in which to measure those attributes in order to understand ecosystem processes

(competition, trophic interactions, energy flow, habitat structure). Wetlands are no

exception. Habitat heterogeneity occurs across different spatial scales for different

plant life forms (canopy, shrub, herbaceous, etc.) and across different hydrogeomorphic classes. Patchiness of vegetation affects the types and abundances of trophic

interactions, energy flow, and competition among animals. These processes in turn

affect animal populations. Plants are rarely uniformly distributed in wetlands, and

observed patterns can often be quite complex, ranging from clonal species that are

clumped to species that are not very abundant and appear to occur randomly. The
82 Chapter 2 Documentation of Riverine Wetland Functions

level of this variable should be evaluated by detailed sampling and analysis with

comparison to the reference standard.

The scale at which patchiness is measured and evaluated determines the reliability and usefulness of measurements. For example, shrubs and trees may not be uniformly distributed across a forested wetland landscape. A closed canopy may give

way to a shrub/scrub thicket near a tributary. Each habitat type supports a different

assemblage of animal species, and so the combined species richness of several habitats is greater than the richness of any area evaluated separately. Hence, areas with

a more diverse array of habitat types would support more species than those with

less diverse internal patchiness. Using the appropriate scale and reference domain is

critical to determining the variable condition of an assessment site. Transects laid

perpendicular to the length of the stream channel can be used to determine discontinuities in vegetation and their frequency per unit distance. Indirect measures (for

example, examining aerial photos) can be used, but methods depend upon the scale

at which patchiness is to be assessed and the types of organisms that rely on parameters associated with the habitat patchiness. For example, insects, small mammals,

and large wide-ranging mammals each rely on different scales of patchiness.

Patchiness between 75 and 125 percent of its reference standard should receive a

variable index score of 1.0. Patchiness between 75 and 25 percent or >125 percent

of its reference standard should score 0.5. Assessment sites that are between 0 and

25 percent of this reference standard for patchiness (and in which patchiness can be

restored) should be scored 0.1. Sites that have no potential for restoring patchiness

to the reference standard should receive a zero score.

V , Canopy gaps. Death of canopy trees is a normal process that has impor- GAPS

tant implications for the dynamics of ecosystems. Openings in the canopy allow

more light to reach the ground, and consequently they play an important role in reproduction of plants and creating patchiness in the understory. Canopy gaps create

microclimate variation within forests and serve as focal points for foraging animal

feeding.

The nature of canopy gaps is distinct from the variable of vegetation patchiness. 

Canopy gaps are created by windfall, while patchiness of vegetation may occur in

other strata. Canopy gaps are often indicative of forest maturity, particularly in assessing unaltered sites. Mature sites are normally used to represent the reference

standard because they generally support the highest biodiversity and overall functioning across the suite of functions. However, canopy gaps may reflect anthropogenic disturbances and in such cases should be used with caution.

Aerial photographs may be interpreted to obtain an indirect measure during period of leaf-out. Direct measures may be made by determining percent of linear

transects intercepting gaps or area of gaps per unit area of landscape. Gaps can also

be expressed as density per unit area.

Gap area or density that is between 75 and 125 percent of reference standards

should receive a variable index score of 1.0. Conditions between 75 and 25 percent

or >125 percent of the reference standard should score 0.5. Assessment sites that
Index of Function = (VSNAGS VMATUR VSTRATA

VGAPS )/5

Chapter 2 Documentation of Riverine Wetland Functions 83

are between 0 and 25 percent of the reference standard (with potential for recovery

given sufficient time) should be scored 0.1. Immature forests normally lack canopy

gaps but should develop them as they mature; such sites should be scored 0.1. Sites

than have no potential for recovery to the reference standard (development of gaps

not possible) should receive a zero score.

Index of function

The variables density of standing dead trees (V ), abundance of mature trees SNAGS

(VMATUR), number and attributes of vertical strata (V ), vegetation patchiness STRATA

(V ), and canopy gaps (V ) are used to assess the function Maintain Spatial PATCH GAPS

Structure of Habitat. Each indicator, whether determined via direct or indirect measure, must be scaled to a suite of reference wetlands and conditions appropriate for

the physiographic region and wetland subclass.

Each variable is assumed to be of equal importance.

Documentation

MAINTAIN SPATIAL STRUCTURE OF HABITAT

Definition: The capacity of a wetland to support animal populations and guilds by providing heterogeneous habitats.

Effects Onsite: Provides potential feeding, resting, and nesting sites for vertebrates and invertebrates. Regulates and moderates fluctuations in temperature. Provides habitat heterogeneity to support a diverse assemblage of organisms. Affects all ecosystem processes. 

Effects Offsite: Provides habitat heterogeneity to landscape, provides habitat for wide-ranging and

migratory animals, provides a corridor for gene flow between separated populations, and allows

progeny to exploit new areas.
84 Chapter 2 Documentation of Riverine Wetland Functions

Variables Direct Measure Indirect Measure Index of Variable

VSNAGS: Density of Density >75% of reference In selected forest types, aerial 1.0

standing dead trees standard. photos may be used to estimate density.

Density between 25% and 75% 0.5

of reference standard.

Density between 0% and 25% 0.1

of reference standard.

No standing dead trees. 0.0

VMATUR: Abundance Density of very mature trees No suitable measures 1.0

of very mature trees >75% of reference standard. available.

Density of very mature trees 0.5

between 25% and 75% of reference standard.

Density of very mature trees 0.1

between 0% and 25% of reference standard; restoration

possible.

No very mature trees; no poten- 0.0

tial for restoration.

VSTRATA: Number 1. Number of vertical strata, or Complexity of canopy (number 1.0

and attributes of vertical strata of

vegetation

2. Density or cover of plants in of strata) shown on recent aeeach stratum, or rial photographs taken in leaf

3. Some composite index of season, with field calibration,

above is >75% of reference similar to reference standard.

standard.

As above, but between 25% As above, but less than refer- 0.5

and 75% of reference ence standard.

standard.

As above, but between 0% and No canopy; restoration 0.1

25% of reference standard. possible.

Vertical strata missing. No canopy; restoration not 0.0

possible.

VPATCH: Vegetation Appropriate measure of patchi- Texture of canopy shown on 1.0

patchiness ness >75% and <125% of recent aerial photographs taken

reference standard. in leaf season, field calibrated,

similar to reference standard.

As above, but between 25% As above, but less than refer- 0.5

and 75% or >125% of refer- ence standard.

ence standard.

As above, but between 0% and 0.1

25% of reference standard.
Index of Function = (VSNAGS VMATUR VSTRATA

VGAPS )/5

Chapter 2 Documentation of Riverine Wetland Functions 85

VPATCH: (Concluded) No canopy present. Recent aerial photographs 0.0

show no tree canopy.

VGAPS: Gaps in Number, distribution, or size Recent aerial photographs 1.0

forest frequency of gaps in the forest taken during leaf-out season

canopy 75% to 125% of refer- show gaps in the tree canopy

ence standard. similar in number, size, and

abundance to reference

standard.

As above, but between 25% As above, but less than refer- 0.5

and 75% or >125% of refer- ence standard.

ence standard.

As above, but between 0% and 0.1

25% of reference standard.

No canopy gaps present. Methods above indicate no 0.0

gaps in the tree canopy.

Maintain Interspersion and Connectivity

Definition

The capacity of a wetland to permit aquatic organisms to enter and leave the wetland via permanent or ephemeral surface channels, overbank flow, or unconfined

hyporheic gravel aquifers. The capacity of wetland to permit access of terrestrial or

aerial organisms to contiguous areas of food and cover.

Discussion of function and rationale

Riverine floodplains and the wetlands associated with them are used extensively

by both terrestrial and aquatic animals to complete portions of their life histories

(i.e., spawning by fish, nesting by waterfowl) (Minshall, Jensen, and Platts 1989;

Welcomme 1979, Wharton et al. 1982). Adequate habitat corridors are required for

connecting wetlands to other ecosystems. Aquatic vertebrates enter floodplain wetlands during flooding, most often via small connections from side or main channels. 

Natural or man-made levees may restrict surface connections to wetlands during low

flood years. In contrast, large areas of a river corridor may be flooded during large

events, permitting unrestricted access across a floodplain surface.

Riverine wetlands in floodplains containing coarse gravel sediments are often

directly connected via subsurface paleo-channels to the main flow of the river (Stanford and Ward 1993). This permits a rapid exchange between channel surface water

and subsurface flow. Such hyporheic waters, particularly those in gravel bed rivers,

permit the development of complex, underground food webs that sustain exchanges
86 Chapter 2 Documentation of Riverine Wetland Functions

of nutrients, microbes, and aquatic insects between a channel and the wetland (Stanford and Ward 1988, 1992).

Wetlands of riverine floodplains often support a heterogeneous mosaic of habitat

types at a variety of temporal and spatial scales. For example, depressions on a

floodplain surface may hold water for long periods between floods, thus supporting

aquatic organisms and more flood-intolerant plants than nearby, less wet sites. 

Likewise, channels connecting a floodplain to the main river are important conduits

of seed dispersal to and from wetlands. 

Wetlands also provide water and other life requirements for motile species that

primarily exploit upland habitats. In addition, all vegetational strata in wetlands,

from herbaceous layer to tree canopy, provide wildlife corridors (connections) between different wetland types, between uplands and wetlands, and between uplands

(Sedell et al. 1990). Such connections between habitats help maintain higher animal

and plant diversity across the landscape than would be the case if habitats were

more isolated from one another.

Description of variables

V , Frequency of overbank flow. The frequency of overbank flow is a criti- FREQ

cal component of the character of riverine wetland. Overbank flow is often necessary in affording access to riverine wetlands by anadromous or adfluvial fishes that

use floodplain habitats to complete portions of their life histories, such as spawning

and rearing (Ward 1989). The temporal periodicity and magnitude of flooding may

have direct bearing on strengths of year classes among vertebrates. Likewise, overbank flow and connectivity between the main channels and floodplain wetlands facilitate the dispersal of plant seeds and other propagules. Thus, flooding and connectivity are critical components of site-specific structure and function.

Overbank flow is best quantified by hydrographic data which can be used as a

direct measure of this variable. Such data may be obtained from either federal or

state agencies that maintain hydrogeographic databases. The reference standard is

the frequency of overbank flow found in wetlands used for reference standards. If

the frequency of overbank flow of assessment site is similar to the reference standard, an index score of 1.0 is given. If frequencies are greater than or less than the

reference standard, lower scores are assigned. If there is no flooding by overbank

flow, the variable should receive a zero score.

V , Duration of overbank flow. The duration of overbank flow is deter- DURAT

mined by both discharge upriver and the volume of water that is dissipated across

and temporarily stored on adjacent floodplains during floods. Thus, the duration of

overbank flow is affected by the size of the floodplain and the hydraulic connectivity

between the main channel and associated floodplain wetlands (Stanford and Ward

1993).

Duration of flooding is important in permitting organisms sufficient time to access floodplain wetlands for spawning and feeding, and in allowing some species to
Chapter 2 Documentation of Riverine Wetland Functions 87

complete important life-history developmental stages. Longer periods of flooding

may also aid in the dispersal of some plants. However, it should be kept in mind

that what benefits one set of organisms may be detrimental to others. Therefore, an

assessment site must be compared with the appropriate reference standard to determine its index score. If the duration of overbank flow at the assessment site has a

temporal magnitude of between 75 and 125 percent that of its reference standard, an

index score of 1.0 should be given. If overbank flow occurs within a temporal magnitude between 25 and 75 percent or >125 percent compared to the reference standard, an index score of 0.5 should be given. If the assessment area rarely floods or

flooding occurs for a very short time period (between 0 and 25 percent), 0.1 should

be recorded. If no flooding occurs, a zero should be scored for the variable.

VMICRO, Microtopographic complexity. Microtopographic complexity is an important factor contributing to the interspersion of habitat types and connections between river and floodplain wetlands. Elevated structures (for example, hummocks)

and low areas (channels and small depressions) direct the flow of water through

wetlands, and affect the direction and duration of flows. Wetlands with a mosaic of

interspersed habitat types provide conditions suitable for a higher diversity of plant

and animal species than do wetlands with uniform topography.

A direct measure of microtopographic complexity is acquired by performing a

survey of microtopography (using an auto-level, laser-total survey, etc.) within a

well-designed suite of transects intersecting the wetland. The indirect measure is a

visual assessment of the wetland surface. The reference standard for this variable

must be based on data obtained from reference standard sites. If an assessment site

contains between 75 and 125 percent of the frequency and depth of microtopographic depressions in comparison to its reference standard, an index score of 1.0

should be given. Lower scores are given (0.5 or 0.1) as microtopographic

depressions decrease in frequency and magnitude. If an assessment site has no

microtopographic depressions or its natural substrate has been replaced by an

artificial surface, a score of zero should be given.

V , Surface hydraulic connections. Multiple hydraulic connections SURFCON

between a river and wetlands on its floodplain strongly indicate a high heterogeneity

of habitats (and hence, relatively high species diversity), interspersion among

habitat types, and potential for complex trophic interactions (Foreman and Godron

1981, Gregory et al. 1991). Reference wetlands provide examples, such as lateral

or secondary channels and gaps in levees. If the frequency of surface hydraulic

connections between the wetland and the river channel is >75 percent that of its

reference standard, an index score of 1.0 should be given. Lower scores are given

(0.5 or 0.1) as the number of connections decrease. If an assessment site has no

hydraulic connectivity to the main channel or side channels, a score of zero should

be given.

V , Subsurface hydraulic connections. High-energy streams and flood- SUBCON

plains with coarse gravels usually have subsurface hydraulic connections that

provide a conduit for small aquatic organisms to move back and forth between

habitats without leaving their aquatic environment. Aquatic insects are particularly

well adapted to exploiting this connection. Reference wetlands provide examples
Index of Function = (VFREQ VDURAT VMICRO V

VSUBCON VCONTIG )/6

88 Chapter 2 Documentation of Riverine Wetland Functions

(such as springs, seeps, and upwellings) that illustrate both lateral and longitudinal

connections through hyporheic flow. Local conditions need to be examined in order

to find indicators to quantify this variable, and to scale this variable according the

conditions found at reference standard sites. This variable may not be applicable for

floodplains and streams dominated by silt and clay alluvium, a condition which minimizes the availability of effective connections.

VCONTIG, Contiguous vegetation cover and/or corridors between wetland and

upland, between channels, and between upstream-downstream areas. Continuity of vegetation, connectivity of specific vegetation types, the presence and scope of

corridors between upland/wetland habitats, and corridors among wetlands all have

direct bearing on the movement and behavior of animals that use wetlands (Pautou

and Décamps 1985). Assessment of this variable is region-specific, and must be

placed in the context of the animal species that are known to utilize such connections. For example, both whitetail deer and passerines are known to use vegetative

corridors for cover in bottomland hardwoods, but the cover required by the two

groups differs. If an assessment site is equivalent to its reference standard, a score

of 1.0 should given. Lower scores are given (0.5 or 0.1) as the density of vegetation

mosaics and the connectivity via vegetation or channel corridors decrease. If an assessment site has no connectivity to upland vegetation or riverine channels, a score

of zero should be given for the variable.

While the foregoing provides rough guidelines, the contiguity variable will have

to be scaled both to the organisms of interest and the size of the stream- floodplain

complex being assessed.

Index of function

The variables—frequency of overbank flow (VFREQ), duration of overbank flow

(V ), microtopographic complexity (V ), surface hydraulic connections DURAT MICRO

(VSURFCON), subsurface hydraulic connections (VSUBCON), and contiguous vegetation

cover and/or corridors between wetland and upland, between channels, and between

upstream-downstream areas (V )—are used to assess the function in maintain- CONTIG

ing habitat interspersion and connectivity. Each indicator, whether determined via

direct or indirect measures, must be scaled to a suite of reference wetlands and conditions appropriate for the physiographic region of the wetland's functional class.
Chapter 2 Documentation of Riverine Wetland Functions 89

Documentation

MAINTAIN HABITAT INTERSPERSION AND CONNECTIVITY

Definition: The capacity of a wetland to permit aquatic organisms to enter and leave the wetland via

permanent or ephemeral surface channels, overbank flow, or unconfined hyporheic gravel aquifers. 

The capacity of a wetland to permit access of terrestrial or aerial organisms to contiguous areas of

food and cover.

Effects Onsite: Provides habitat diversity. Contributes to secondary production and complex trophic interactions. Provides access to and from wetland for reproduction, feeding, rearing, and cover. 

Contributes to completion of life cycles and dispersal between habitats.

Effects Offsite: Provides corridors for wide-ranging or migratory species. Provides refugia for

plants and animals. Provides conduits for dispersal of plants and animals to other areas.

Model Variables Direct Measure Indirect Measure Index of Variable

VFREQ: Frequency of Gauge data (1.5) yr return inter- At least one of the following: 1.0

overbank flow val similar to reference standard. aerial photos showing flooding,

(Interval in parentheses must be water marks, silt lines, alternatadjusted to the reference ing layers of leaves and fine

standard.) sediment, ice scars, drift and/or

wrack lines, sediment scour,

sediment deposition, directionally bent vegetation similar to

reference standard.

Gauge data (>2 or <1) yr return As above, but somewhat greater 0.5

interval. or less than reference standard.

Gauge data show extreme Above indicators absent but 0.1

departure from reference stand- related indicators suggest overard. bank flow may occur.

Gauge data indicate no flooding Indicators absent and/or alter- 0.0

from overbank flow. ation has eliminated variable.

VDURAT: Duration of Gauge data (x-y) yr show dura- Duration of connection related 1.0

overbank flow tion between 75% and 125% of indicators only, and similar to

reference standard. (Duration in reference standard.

parentheses must be adjusted to

the reference standard.)
90 Chapter 2 Documentation of Riverine Wetland Functions

VDURAT: (Concluded) As above, but between 25% and Any indicators, i.e., aerial pho- 0.5

75% or >125% of reference tos showing continuity of durastandard. tion, flooding tolerance of tree

species, etc., showing continuity of flooding as less than reference standard.

As above, but between 0% and Any indicators showing greatly 0.1

25% of reference standard. reduced duration relative to

reference standard.

Gauge data indicate no over- Flooding is absent. 0.0

bank flow.

VMICRO: Microtopo- Microtopographic complexity Visual estimate indicates that 1.0

graphic complexity (MC) measured (surveyed) at microtopographic complexity

site shows MC between 75% (MC) of site is between 75%

and 125% of reference and 125% of reference

standard. standard.

As above, but MC of site is Visual assessment confirms 0.5

between 25% and 75% that of MC is present, but somewhat

reference standard. less than reference standard.

Measured MC between 0% and Visual assessment indicates 0.1

25% of reference standard; MC is much less than reference

restoration possible. standard; restoration possible.

VMICRO: (Concluded) No MC at assessed site or natu- Visual assessment indicates 0.0

ral substrate replaced by artifi- MC is virtually absent or natural

cial surface; restoration not substrate replaced by artificial

possible. surface; restoration not

possible.

VSURFCON: Surface Use of data from runoff collec- Number of surface connections 1.0

hydraulic connections tors as a continuous variable 75% to 125% of reference

from reference standard (1.0) to standard.

absent (0.0).

Surface connections 25% to 0.5

75% of reference standard.

As above, but 0% to 25% of 0.1

reference standard.

No surface connections due to 0.0

obstructions or alterations.

VSUBCON: Subsurface Direct measures not practical. Seeps, springs, upwellings 1.0

hydraulic connections Tracer and dye methods are similar to reference standard.

required.

Excessive fine sediment supply 0.5

sufficient to block subsurface

connections.

Stream channel and floodplain 0.1

highly altered with minimal

connections.
Index of Function = (VFREQ VDURAT VMICRO V

VSUBCON VCONTIG )/6

Chapter 2 Documentation of Riverine Wetland Functions 91

VSUBCON: (Concluded) No possible subsurface con- 0.0

nections exist because of

alterations.

VCONTIG: Contiguous Continuity among vegetation Recent aerial photographs 1.0

vegetation cover connections between channels, taken during leaf season show

uplands, and upstream-down- abundant vegetation and

stream wetland areas >75% of vegetated corridors connecting

reference standard. mosaics of habitat types similar

to reference standard.

As above, but continuity be- Recent aerial photographs 0.5

tween 25% and 75% of refer- taken during leaf season show

ence standard. lower abundance of vegetative

connections than reference

standard.

As above, but continuity Lack of continuous vegetation 0.1

between 0% and 25% of connections with potential for

reference standard. recovery.

Assessment site fragmented Lack of continuous vegetation 0.0

and isolated from channels and connections with no potential for

adjacent uplands and upstream- recovery.

downstream wetland areas.

Maintain Distribution and Abundance of

Invertebrates

Definition

The capacity of a wetland to maintain characteristic density and spatial distribution of invertebrates (aquatic, semi-aquatic, and terrestrial).

Discussion of function and rationale

Invertebrate fauna (insects, nematodes, molluscs, etc.) is extremely rich in

species and modes of existence in most wetlands. Invertebrates exploit almost every

microhabitat available in wetlands. Because invertebrates are so pervasive and

partition habitats so finely, they are excellent indicators of ecosystem function. In

fact, without invertebrates, wetland ecosystems would fail to function.

Coarse particulate organic matter (CPOM) enters a riverine-wetland ecosystem

as allochthonous material from its riparian overstory or from upstream locations. 

CPOM is generally retained either in the stream or on the riparian floodplain surface

where it is used and/or processed through a multitude of consumer pathways. A
92 Chapter 2 Documentation of Riverine Wetland Functions

significant portion of these pathways is mediated by invertebrates that shred leaf

litter and burrow into woody material. Emergent and submersed macrophytes also

contribute organic matter. Aquatic macrophytes are frequently grazed by invertebrates, or may enter the detrital pool where microbial activity and detritivory by

both terrestrial and aquatic invertebrates play important roles in decomposition

processes.

Riverine wetlands are often subject to alternating conditions between wet and dry

(terrestrial and aquatic) environments. Meander scrolls, for example, may be wet or

flooded for extended time periods (e.g., several months) during annual or more frequent inundation intervals (depending on local climatic and hydrologic regimes), but

lose surface moisture as dryer conditions return. When surficial standing water is

absent, terrestrial invertebrates are important to soil development. These include

worms, snails, and small arthropods (e.g., mites, millipedes, centipedes, insects). 

These organisms are important processors of organic material that add significantly

to organic soil development. In breaking down organic matter, these organisms enable soil microbes to transform nutrients from unavailable to available forms. They

are also import sources of animal material to higher level consumers (e.g., amphibians, reptiles, birds, and mammals).

Description of variables

V , Distribution and abundance of invertebrates in soil. Species composi- SINVT

tion and abundance of soil invertebrates are important determinants of soil condition

and confirm that decomposition is occurring. Although identification to the species

level is often difficult, familiarity with dominant taxa is fairly easily grasped. Measurements of invertebrate density and species richness must be compared with a reference standard. A direct measure of invertebrate species richness and abundance at

an assessment site is best obtained by any of several standard sampling techniques. 

Rapid assessment is possible in the field by people familiar with dominant invertebrate taxa. Similarity can be determined by comparing density, species richness, or

some index of similarity (see ecology textbooks for a discussion of such measures). 

Invertebrate species using wetlands may be aquatic, semi-aquatic, or terrestrial. 

Many immature stages of aquatic forms exploit terrestrial or aerial environments as

adults; species listed must be scrutinized for aquatic and semi-aquatic life forms

(Merritt and Cummins 1995).

If soil invertebrate density and taxa richness (or similarity) is >75 percent of the

reference standard, an index value of 1.0 should be given. If an assessment site condition is between 75 and 25 percent of the reference standard, an index value of 0.5

should be recorded. If an assessment site condition is 0 to 25 percent of its reference standard, an index value of 0.1 should be assigned. If there is no evidence of

invertebrates in the soil, a value of zero should be given.

Indirect measures may also be used to compare similarities in invertebrate communities between assessment wetlands and reference sites. Indirect indicators include measures of the presence and activity of soil invertebrates, insects, or some

other invertebrate category that would reasonably be expected to indicate wetland
Chapter 2 Documentation of Riverine Wetland Functions 93

functions. The type of indirect measurements and the categories to be measured

should be those that can be reliably used to compare assessment sites to its reference

standard. For a level of invertebrate activity and density at an assessment site that is

similar to its reference standard should be given an index score of 1.0. If these indirect measures are reduced in frequency from that of its reference standard, a score

of 0.5 is given. If there is no evidence of invertebrate activity in the soil, but there is

potential for recovery to reference standard levels, a score of 0.1 should be given. If

there is no evidence of soil invertebrates and no potential for recovery, a score of

zero should be given.

V , Distribution and abundance of invertebrates in leaf litter and coarse LINVT

woody debris. Invertebrates are an essential part of the decomposition of leaf litter

and coarse woody debris (CWD) on the forest floor. Organic material in wetland

ecosystems is processed through the detrital or grazing food webs. Invertebrates,

both terrestrial and aquatic, play important roles in the processing of organic matter,

particularly leaf litter (Benfield, Jones, and Patterson 1977; Benke and Meyer 1988;

Benke et al. 1984, 1992). By shredding leaves and burrowing into woody material,

invertebrates (and soil microbes associated with this process) break down cellulose

and lignin of coarse material; this activity is essential to soil development in wetlands. Insects, crustaceans, and oligochaetes are important detritivores in rivers and

riverine wetlands, and indicate efficient organic matter processing (Hauer, Poff, and

Firth 1986; Reice 1977). Determining invertebrate activity in coarse woody debris

is best determined measured directly. Similarity can be determined by comparing

density, species richness, or some index of similarity (see any ecology text for a

discussion of such measures) at an assessment site with its reference standard.

For direct measures, a variable index score of 1.0 is assigned to assessment sites

that show >75 percent similarity to their reference standard. Similarity can be

determined by comparing density, species richness, or some index of similarity (see

any ecology text for a discussion of such measures). A variable condition in which

between 25 and 75 percent of the reference standard is met should score 0.5. 

Assessment sites that show between 0 and 25 percent of their reference standard

should be scored 0.1. Assessment sites devoid of invertebrates associated with the

breakdown of leaf litter and coarse woody debris should receive a zero.

Indirect measures of this variable can be made by looking for evidence of

invertebrate activity (leaf skeletonization, galleries in logs, etc.). If a site is similar

to its reference standard, an index score of 1.0 should be given. An assessment that

shows a close similarity between the assessment site and the reference standard

should score a 0.5. A comparison that shows a large dissimilarity between the two,

but with potential for recovery of the variable at the assessed site, should receive

a 0.1 variable index score. Assessment sites devoid of litter invertebrates with no

potential for their restoration should receive a zero.

V , Distribution and abundance of invertebrates in aquatic habitats AQINVT

(e.g., microdepressions, seeps, side channels). Aquatic invertebrates are

exceptionally diverse taxonomically and often very abundant. Benthic macroinvertebrates may reach densities of thousands of individuals per square meter. 

During flooding conditions, ephemeral channels and permanent wetlands exchange
Index of Function = (VSINVT VLINVT VAQINVT)/3

94 Chapter 2 Documentation of Riverine Wetland Functions

organic materials with their main channel and are an integral part of upstreamdownstream processes that characterize the lotic environment. Habitat diversity in

floodplain wetlands is very high; likewise, species richness of aquatic invertebrates

is high and density can vary considerably between habitats. Direct measures of

aquatic invertebrates should be made using standard sampling techniques. Rapid

assessment procedures for aquatic invertebrate sampling, identification, and

enumeration are fairly well established, but these methods require specialized

training and expertise. All sampling must be done at a time of year that will allow

useful comparison with sampling done on reference standard sites.

For direct measures, a variable index score of 1.0 is assigned to assessment sites

that show >75 percent similarity to their reference standard. Similarity can be

determined by comparing density, species richness, or some index of similarity (see

any ecology text for a discussion of such measures). A variable condition in which

between 25 and 75 percent of the reference standard for a site is met should

score 0.5. Assessment sites that show 0 to 25 percent similarity to their reference

standard should be scored 0.1. Assessment sites devoid of aquatic invertebrates

should receive a zero.

Indirect measurements of the presence and activity of aquatic invertebrates may

be based upon visual estimates of suitable aquatic habitats and the presence of

aquatic invertebrate activity (for example, exudates, egg cases, and shell fragments). 

Not much work has been done to quantify the relationship between such indirect

indicators and population estimates, so care must be taken. However, any indirect

measures chosen should be suitable for comparing sites in a given reference domain. 

Index scores should be determined as above.

Index of function

The variables species richness and density (or some similarity index) of

invertebrates in soil (V ), species richness and density (or similarity measure) of SINVT

invertebrates in leaf litter and coarse woody debris (VLINVT), and species richness and

density (or a similarity measure) of invertebrates in aquatic habitats (e.g., microdepressions, seeps, and side channels) (VAQINVT) are used to assess the function

Maintaining Distribution and Abundance of Invertebrates. Each indicator, whether

determined by direct or indirect measures, must be scaled to a suite of reference wetlands and conditions appropriate for the physiographic region and wetland class.

Each variable is assumed to be of equal importance in contributing to this function.
Chapter 2 Documentation of Riverine Wetland Functions 95

Documentation

MAINTAIN DISTRIBUTION AND ABUNDANCE OF INVERTEBRATES

Definition: The capacity of a wetland to maintain characteristic density and spatial distribution of

invertebrates (aquatic, semi-aquatic, and terrestrial).

Effects Onsite: Provides food (energy) to predators, aerates soil and coarse woody debris by building tunnels, breaks down (decomposes) coarse woody debris, increases availability of organic matter

for nutrient cycling microbes, and disperses seeds within site.

Effects Offsite: Provides food (energy) for wide-ranging carnivores/insectivores, etc. Transports

seeds and propagules for germination elsewhere.

Model Variables Direct Measure Indirect Measure Index of Variable

VSINVT: Distribution Similarity index for species Tunnels, shells, casts, holes, etc., 1.0

and abundance of

invertebrates in soil

composition and abundance in soil similar to reference standard

75% of reference standard. (indirect measures may be developed that can be quantified).

Similarity index for species As above, but much less than ref- 0.5

composition and abundance erence standard.

between 25% and 75% of reference standard.

Similarity index for species No evidence of items above, but 0.1

composition and abundance with potential for habitat recovery.

0% to 25% of reference

standard.

No soil invertebrates or evi- No evidence of items above and no 0.0

dence of soil invertebrates potential for recovery of habitat.

found.

VLINVT: Distribution Similarity index for species Visual assessment of galleries in 1.0

and abundance of

invertebrates in leaf

litter and in coarse

woody debris

composition and abundance logs and twigs, tunnels in wood,

75% of reference standard. shells, casts, trails, holes, etc.,

similar to reference standard (measures may be developed that can

be quantified).
Index of Function = (VSINVT VLINVT VAQINVT)/3

96 Chapter 2 Documentation of Riverine Wetland Functions

VLINVT: (Concluded) Similarity index for species As above, but much less than ref- 0.5

composition and abundance erence standard.

between 25% and 75% of reference standard.

Similarity index for species Absence of above conditions, but 0.1

composition and abundance with potential for habitat recovery.

0% to 25% of reference

standard.

No invertebrates or evidence of Absence of above conditions but 0.0

invertebrates found in leaf litter no potential for habitat recovery.

or coarse woody debris. 

VAQINVT: Distribution Similarity index for species Presence of suitable aquatic habi- 1.0

and abundance of

invertebrates in

aquatic habitats

(microdepressions,

side channels,

seeps)

composition and abundance tats (microdepressions, seeps,

75% of reference standard or etc.) and evidence of shell fragregional indicator/keystone ments, exudate, etc., similar to refspecies. erence standard. Measures may

be developed that can be

quantified.

Similarity index for species As above, but indicators much less 0.5

composition and abundance than reference standard.

between 25% and 75% of reference standard.

Similarity index for species No evidence of items above, but 0.1

composition and abundance with potential for habitat recovery.

0% to 25% of reference

standard.

No invertebrates or evidence of No evidence of suitable aquatic 0.0

invertebrates found in aquatic habitats and no potential for habitat

habitats. recovery.

Maintain Distribution and Abundance of

Vertebrates

Definition

The capacity of a wetland to maintain characteristic density and spatial distribution of vertebrates (aquatic, semi-aquatic, and terrestrial) that use wetlands for food,

cover, rest, and reproduction.

Discussion of function and rationale

Riverine wetlands depend upon physical, chemical, and biological connections to

their river channels for a number of processes. These processes support resident,

seasonal, and migratory vertebrate species (Blake and Hoppes 1986; Décamps,

Joachim, and Lauga 1987). Vertebrate distribution and abundance in any given

river and wetland system is not static, but rather is highly dynamic and can change

rapidly in both space and time (Matthews 1988). For example, several species of
Chapter 2 Documentation of Riverine Wetland Functions 97

fishes use wetlands as spawning and rearing areas; however, fish are limited in their

access to wetlands due to the hydrographic regime of the river and the temporal sequence of flooding events. Thus, maintenance of a particular fish species in a drainage basin may depend on a suitable frequency of flooding and duration of overbank

flow.

Vertebrates are usually conspicuous users of wetland habitats and resources and

some may even influence riverine dynamics (Naiman et al. 1988). For example,

beavers profoundly affect hydrologic regimes, nutrient dynamics, and vegetation

characteristics of low order streams, and deer can negatively impact recruitment success of plants. Wetlands are also generally considered to support a richer fauna than

adjacent upland communities, and many species that exploit mainly upland habitats

require wetlands for some important life requisite. Waterfowl control the density of

aquatic macrophytes and invertebrate assemblages. Fish feed on invertebrates and

other fishes. Small rodents and birds play an important role in seed dispersal and

interactions between vegetation and mycorrhizal dynamics.

The landscape-level diversity of riverine wetlands is developed and maintained

largely through main channel hydrologic processes. Natural disturbances are often

significant in maintaining high vertebrate diversity, particularly in high-energy riverine systems. Natural or anthropogenic factors that decrease wetland heterogeneity

in either time or space often negatively affect animal species.

The goal in assessing this function is to compare reference and assessment site

functions with respect to species composition and structure of vertebrate species

associated with a wetland and the presence of necessary habitats to support wetland

vertebrate fauna. Some vertebrate species (deer, game fishes, etc.) are managed for

recreational extraction; others supply commercial fisheries. However, most vertebrates that depend upon wetlands provide no direct economic utility to man, but

have great importance to overall ecosystem processes and to the maintenance of

global biodiversity.

Description of variables

V , Distribution and abundance of resident and migratory fish. Riverine FISH

wetlands are important as spawning and rearing habitat for many fish species. 

Thus, fish are particularly sensitive to severed connections between a river and its

floodplain wetlands. Migratory fish are also sensitive to alterations of seasonal hydrologic regimes because many migratory species have evolved to exploit an annual

flooding pattern that allows them access to adjoining wetlands for spawning.

Fish are relatively well studied in North America, and the scientific literature

contains much information on how to measure relative abundance, determine species

richness, and calculate similarity indices. The fish density/ richness variable must

be examined in the context of reference standards and hydrogeomorphic class (that

is, one must be aware that reference standards usually vary regionally, among rivers

of the same region and between different reaches of the same river).
98 Chapter 2 Documentation of Riverine Wetland Functions

For direct measures, a variable index score of 1.0 is assigned to assessment sites

that show >75 percent similarity with their reference standard. Similarity can be

determined by comparing density, species richness, or some index of similarity (see

any ecology text for a discussion of such measures). A variable condition in which

between 25 and 75 percent of its reference standard is met should score 0.5. Assessment sites that show 0 to 25 percent of their reference standard should be

scored 0.1. Assessment sites devoid of fishes should receive a zero.

A direct measure of adult or juvenile fish population levels or species richness

(number of species) can be expensive and logistically difficult to gather. However,

many state game agencies have data on fish species abundances for river basins and

for particular reaches of a river. This information can be used as an indirect measure of fish density or species richness if the data are current. An assessment that

shows a close similarity between the assessment site and its reference standard

should score a 1.0. A comparison that shows a moderate dissimilarity between the

two should be given an index score of 0.5. If a comparison that shows that the

assessment site and its reference standard are dissimilar, but suggests that there is

potential for recovery of fish to the reference standard, a variable index score of 0.1

should be given. Assessment sites devoid of fish with no potential for recovery

should receive a zero.

VHERP, Distribution and abundance of herptiles. Wetlands provide important

habitat for some or all life stages of many herptile species (amphibians and reptiles). 

Amphibians are particularly sensitive to a loss of wetland habitat and changes in

water chemistry or hydrologic regime, primarily because most amphibians require

water to breed. Reptiles such as turtles, snakes, and alligators also depend upon a

particular suite of factors (provided by wetlands) to maintain their populations.

Although herptiles are not as well studied as some other vertebrate groups

(particularly birds and fishes), there are still many direct measurement (quantitative)

techniques for estimating population size or comparing sites, including direct

counts, tag/recapture methods, and encounters per unit time. The same technique

should be used to compare assessment sites with reference standard, and all

assessments should be calibrated against appropriate reference standard sites.

For direct measures, a variable index score of 1.0 is assigned to assessment sites

that show >75 percent similarity with their reference standard. Similarity can be

determined by comparing density, species richness, or some index of similarity (see

any ecology text for a discussion of such measures). A variable condition in which

between 25 and 75 percent of its reference standard is met should score 0.5. 

Assessment sites that show 0 to 25 percent of their reference standard should be

scored 0.1. Assessment sites devoid of herptiles should receive a zero.

The collection of direct measurements may be costly and time consuming. However, one could use surrogate (indirect) measures to compare sites, such as presence

of egg masses, tracks, calls, etc., or refer to reliable inventories collected recently at

assessment and reference standard sites. For indirect measures, comparisons of

recent species lists or abundance data can be used to derive similarity comparisons. 

An assessment using indirect measures that shows a close similarity between an
Chapter 2 Documentation of Riverine Wetland Functions 99

assessment site and reference standards should score a 1.0. A comparison that

shows a moderate dissimilarity between the two should be given an index score

of 0.5. If a comparison shows that an assessment site and the reference standard

have few similarities, but suggests that there is potential for recovery of herptiles to

reference standard, a variable index score of 0.1 should be given. Assessment sites

devoid of the herptiles with no potential for recovery should receive a zero.

V , Distribution and abundance of resident and migratory birds. The BIRD

abundance and species richness of birds is closely related to habitat complexity because birds have evolved to fill most available terrestrial niches. They partition

habitats temporally (day versus night feeders), spatially (ground feeders, mid- and

top-canopy feeders, etc.), and trophically (frugivores, insectivores, piscivores, etc.). 

Thus, birds are sensitive to alterations in the structure and function of wetland ecosystems. In addition, because birds are a well-studied group of vertebrate organisms, scientific literature is replete with information on how to measure relative

abundance, determine species richness, and calculate similarity indices.

For direct measures, a variable index score of 1.0 is assigned to assessment sites

that show >75 percent similarity with their reference standard. Similarity can be

determined by comparing density, species richness, or some index of similarity (see

ecology textbooks for a discussion of such measures). A variable condition in

which between 25 and 75 percent of its reference standards is met should score 0.5. 

Assessment sites that show between 0 and 25 percent of their reference standard

should be scored 0.1. Assessment sites devoid of birds should receive a zero.

Because direct measurements can be costly and time consuming, indirect measures may also be used to compare similarities in bird communities between assessment wetlands and their reference standard. Results from recent and reliable surveys can be used as indirect indicators of presence. Comparisons of recent species

lists or abundance data can be used to derive similarity comparisons. A comparison

that shows a large dissimilarity between the two, but with potential for recovery of

the variable at an assessed site, should receive a 0.1 variable index score. Assessment sites devoid of birds with no potential for recovery should receive a zero.

VMAMM, Distribution and abundance of permanent and seasonally resident

mammals. Riverine wetlands provide habitat important to large and small mammals. Mammals are relatively well studied, and so there is abundant scientific literature on appropriate censusing techniques (mark/recapture, visual counts, etc.). 

Wide- ranging mammals (e.g., deer and bear) use wetlands as riparian corridors for

foraging, cover, rest, and water. In arid regions, riparian zones are several degrees

cooler during the day than surrounding uplands, and mammals often cool off and

rest in such areas during midday.

Many small mammals are permanent residents of riverine wetlands, and in many

hydrogeomorphic settings, more small mammals (in numbers and species) inhabit

wetlands than surrounding upland areas. As is true for birds, mammals partition

temporally, spatially, and trophically. Thus, mammals are sensitive to alterations in

the structure and function of wetland ecosystems. In addition, because mammals are
100 Chapter 2 Documentation of Riverine Wetland Functions

a well studied group, there is ample scientific literature on how to measure relative

abundances, determine species richness, and calculate similarity indices.

For direct measures, a variable index score of 1.0 is assigned to assessment sites

that show >75 percent similarity to the reference standard. Similarity can be determined by comparing density, species richness, or some index of similarity (see ecology textbooks for a discussion of such measures). A variable condition in which

between 25 and 75 percent of its reference standards is met should score 0.5. Assessment sites that show between 0 and 25 percent of their reference standard

should be scored 0.1. Assessment sites devoid of mammals should receive a zero.

Because direct measurement can be costly and time consuming, indirect measures may also be used to compare similarities in mammal communities at

assessment wetlands and reference sites. Results from recent and reliable surveys or

indirect indicators of presence and activity (burrows, scat, tracks, kills, browsed

plants, etc.) can be used. Comparisons of recent species lists or abundance data can

be used to derive similarity comparisons. If an assessment using indirect measures

shows a close similarity between an assessment site and its reference standard, a

score of 1.0 should be assigned. A comparison that shows a moderate dissimilarity

between the two should given an index score of 0.5. If a comparison that shows that

an assessment site and reference standard have few similarities, but suggests that

there is potential for recovery of mammals to its reference standard, a variable index

score of 0.1 should be given. Assessment sites devoid of mammals with no

potential for their recovery should receive a zero.

V , Abundance of beaver. Beaver have profound effects upon riverine wet- BEAV

lands, and thus are treated here separately from the other mammals. Beaver effects

are manifest through virtually all of the other wetland functions, from dynamics of

surface water storage to nutrient cycling to characteristics of the plant community. 

Beaver activity can be measured in various ways, but direct observation and

individual counts provide the best empirical basis for assessment.

This variable should not be used if beaver are not locally available in the

reference domain and if streams with beaver ponds are separated as a distinct

subclass for assessment.

If direct measure of beaver abundance is >75 percent of its reference standard,

an index value of 1.0 is given. If an assessment site condition is between 75 and

25 percent of its reference standard, an index value of 0.5 should be recorded. If an

assessment site condition is between 0 and 25 percent of its reference standard, an

index value of 0.1 should be given. If there is no evidence of beaver in the wetland

area, a value of zero should be given.

Indirect measures of the presence and activity of beavers can be made. Evidence

based on aerial photographs of beaver dams and lodges, or direct observation of

these indicators along with cut plants, scat, or trails provides strong inference that

beaver activity is occurring in a wetland. If the strength of those indicators is

similar to that observed in reference standard wetlands, an index score of 1.0 should

be given. If these indirect measures are reduced in frequency from that of their
Index of Function = (VFISH VHERP VBIRD VMAMM VBEAV)/5

Index of Function = (VFISH VHERP VBIRD VMAMM)/4

Chapter 2 Documentation of Riverine Wetland Functions 101

reference standard, a score of 0.5 should be given. If there is no evidence of beaver

activity in a wetland, but there is potential for recovery to reference standard levels,

a score of 0.1 should be given. If, however, there is no evidence of beaver activity

and no potential for recovery, a score of zero is given.

Care must be taken in dealing with the assessment of wetlands modified by beaver because of their capacity to greatly alter hydrology, biogeochemistry, and habitat

conditions of free-flowing streams and adjacent wetlands and uplands. If reference

standards are to include beaver, provisions must be made to accommodate the condition in one of at least two possible ways. One option is to develop reference sets

for beaver ponds separate from riverine wetland reaches not directly affected by the

dams. Another is to try to encompass ponded and unimpounded reaches with the

reference set, although this violates the goal of homogeneous conditions in assessment areas. 

Index of function

The variables diversity and density of permanent and seasonally resident fishes

(V ), distribution and abundance of permanent and seasonally resident herptiles FISH

(V ), distribution and abundance of resident and migratory avifauna (V ), di- HERP BIRD

versity and abundance of permanent and seasonally resident mammals (VMAMM), and

abundance of beaver (V ) are used to assess the function Maintaining Distribu- BEAV

tion and Abundance of Vertebrates. Each indicator, whether determined via direct

or indirect measures, must be scaled to a suite of reference wetlands and conditions

appropriate for the physiographic region wetland class.

With beaver ponds:

Without beaver ponds:

Each variable is assumed to be of equal importance in contributing to the function

under reference standard conditions.
102 Chapter 2 Documentation of Riverine Wetland Functions

Documentation

MAINTAIN DISTRIBUTION AND ABUNDANCE OF VERTEBRATES

Definition: The capacity of a wetland to maintain characteristic density and spatial distribution of

vertebrates (aquatic, semi-aquatic, and terrestrial) that utilize wetlands for food, cover, rest, and

reproduction.

Effects Onsite: Disperses seeds throughout a site, pollinates flowers (bats), aerates the soil and

coarse woody debris with tunnels, and alters hydroperiod and light regime (beavers, muskrats).

Effects Offsite: Disperses seeds between sites, pollinates flowers (bats), provides food (energy) for

predators, alters hydroperiod and light regime (beavers, muskrats), and alters downstream flows.

Model Variables Direct Measure Indirect Measure Index of Variable

VFISH: Distribution and Similarity index for species Surrogate measurements (e.g., egg 1.0

abundance of resident

and migratory fish

composition and abundance masses, larval and fry stages, and

75% of reference standard. adults) similar to reference standard.

Similarity index for species Above indicators much less than 0.5

composition and abundance reference standard.

between 25% and 75% of

reference standard.

Similarity index for species No evidence of indicators above, but 0.1

composition and abundance potential for habitat recovery.

between 0% and 25% of

reference standard.

No fish or evidence of fish No evidence of indicators above, and 0.0

found. no potential for habitat recovery.
Chapter 2 Documentation of Riverine Wetland Functions 103

VHERP: Distribution and Similarity index for species Surrogate measurements (e.g., egg 1.0

abundance of herptiles composition and abundance masses, tracks, calls, larval stages,

75% of reference standard. skins, skeletons) similar to reference

standard.

Similarity index for species Evidence of indicators as above, but 0.5

composition and abundance less than reference standard.

between 25% and 75% of

reference standard.

Similarity index for species No evidence of above indicators, but 0.1

composition and abundance potential for habitat recovery.

between 0% and 25% of reference standard.

No herptiles or evidence of No visual evidence of above indica- 0.0

herptiles found. tors and no potential for habitat

recovery.

VBIRD: Distribution and Similarity index for species Surrogate measure (e.g., nests, 1.0

abundance of resident

and migratory birds

composition and abundance tracks, calls, feathers, skeletons)

75% of reference standard. similar to reference standard.

Similarity index for species Evidence of above indicators, but 0.5

composition and abundance less than reference standard.

between 25% and 75% of

reference standard.

Similarity index for species No evidence of above indicators, but 0.1

composition and abundance potential for recovery of habitat to

between 0% and 25% of reference standard.

reference standard.

No birds or evidence of birds No evidence of above indicators, and 0.0

found. no potential for recovery of habitat.

VMAMM: Distribution Similarity index for species Visual evidence of mammals (e.g., 1.0

and abundance of permanent and seasonally

resident mammals

composition and abundance trails, scats, kills, presence of prey

75% of reference standard. species, burrows, browsed plants)

similar to reference standard.

Similarity index for species As above, but less than reference 0.5

composition and abundance standard.

between 25% and 75% of

reference standard.

Similarity index for species No visual evidence of mammal indi- 0.1

composition and abundance cators, but potential for recovery of

between 0% and 25% of mammal habitat.

reference standard.

No mammals or evidence of No visual evidence of mammal indi- 0.0

mammals found and no po- cators, but no potential for recovery

tential for recovery of habitat of mammal habitat.

to reference standard.

VBEAV: Beaver Abundance 75% of refer- Surrogate measure (e.g., recent ae- 1.0

abundance ence standard. rial photographs, presence of active

and abandoned lodges and dams,

cut and chewed plants, scat, trails)

similar to reference standard.
Index of Function = (VFISH VHERP VBIRD VMAMM VBEAV)/5

Index of Function = (VFISH VHERP VBIRD VMAMM)/4

104 Chapter 2 Documentation of Riverine Wetland Functions

VBEAV: (Concluded) Abundance between 25% and As above, but indicators less than 0.5

75% of reference standard. reference standard.

Abundance between 0% and No evidence of above indicators, but 0.1

25% of reference standard. potential for recovery of habitat

exists.

No beaver or evidence of bea- No evidence of above indicators and 0.0

ver found. no potential for recovery of beaver

habitat.

With beaver ponds:

Without beaver ponds:
References 105

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Appendix A Definitions of Variables and Functions for Riverine Wetlands A1

Appendix A

Definitions of Variables and

Functions for Riverine

Wetlands

Variables

V Aquatic invertebrates: Composition and abundance of invertebrates AQINVT

that live in aquatic habitats.

V Beaver: Abundance of beaver. BEAV

V Birds: Distribution and abundance of resident and migratory birds. BIRD

V Tree basal area: Basal area or biomass of trees. BTREE

V Canopy cover: Measure of the percent closure of the canopy. CANOPY

VCOMP Species composition: Dominant species for tree, shrub, and herb

strata. 

VCONTIG Contiguous vegetation cover: Contiguous cover and corridors between

wetland and upland, between channels, and between upstreamdownstream areas.

V Coarse woody debris: Volume of dead and down trees and limbs larger CWD

than an appropriately defined diameter.

V Tree density: Density of large-diameter canopy trees. DTREE

V Duration of overbank flow: Duration of connection between channel DURAT

and floodplain.

V Fish: Distribution and abundance of resident and migratory fishes. FISH
A2 Appendix A Definitions of Variables and Functions for Riverine Wetlands

VFREQ Frequency of overbank flow: Frequency or recurrence interval at which

bank-full discharge is exceeded.

V Fine woody debris: Small limbs, twigs, and leaves. FWD

V Canopy gaps: Density or percent cover of openings (gaps) in forest GAPS

canopy resulting from tree fall.

V Herbaceous density, biomass, or cover: The density, biomass, or per- HERB

centage cover of herbaceous plants.

V Herptiles: Distribution and abundance of herptiles. HERP

V Depth of inundation: Average flooding depth during overbank flood- INUND

ing events.

V Litter invertebrates: Composition and abundance of invertebrates that LINVT

live in litter.

V Logs in several stages of decomposition: Biomass of logs in each of LOGS

several decay classes. 

VMACRO Macrotopographic relief: Large-scale relief in the form of oxbows,

meander scrolls, abandoned channels, and backswamps.

VMAMM Mammals: Distribution and abundance of permanent and seasonally

resident mammals.

VMATUR Abundance of very mature trees. Density of very mature and dying

trees. 

VMICRO Microtopographic complexity: Small-scale topographic relief in the

form of pit-and-mound or hummock-and-hollow patterns.

VMICROB Surfaces available for microbial activity: Measure of organic surfaces

(litter, plant material, other organic matter) available as platforms for

microbial growth.

V Organic matter in wetland: Dissolved and particulate organic matter ORGAN

(live and dead).

V Vegetation patchiness: Spatial heterogeneity of vegetation-types. PATCH

V Soil pore space: Pore space available for storing water. PORE

V Aerial net primary production: Aerial net primary production, mea- PROD

sured as leaf area index, aboveground biomass, etc. 
Appendix A Definitions of Variables and Functions for Riverine Wetlands A3

V Reduction in flow velocity: Reduction in flow through a wetland dur- REDVEL

ing an overbank flooding event.

V Regeneration from seedlings, saplings, clonal shoots: Comparison of REGEN

dominant species list between reproductive stages of assessment site

and mature stages of reference standard.

V Retained sediments: Presence of natural levees of coarse sediments SEDIM

near stream and fine sediments on floodplain.

VSHRUB Shrub density, biomass, or cover: Density, biomass, or cover of woody

understory plants (shrubs and saplings).

V Soil invertebrates: Composition and abundance of invertebrates that SINVT

live in soil.

V Snags: Density or biomass of standing dead trees. SNAGS

VSORPT Sorptive properties of soils: Similarity of soils to reference standard

with respect to texture, organic carbon content, and other properties.

V Number and attributes of vertical strata: Direct count of the number of STRATA

vegetation strata.

V Subsurface hydraulic connections: Subsurface pathways that connect SUBCON

portions of the wetland with the stream channel.

V Subsurface flow into wetland: Subsurface flow into a wetland via SUBIN

interflow and return flow.

VSUBOUT Subsurface flow out of wetland: Subsurface flow from a wetland to

aquifer or to base flow.

VSURFCON Surface hydraulic connections: Hydraulic connections between stream

channel and floodplain (usually large-scale features on high-energy

rivers).

VSURFIN Surface inflow to the wetland: Overland flow from upland to wetland

as indicated by rills and rearranged litter on upland slopes leading to

wetland.

V Indications of surface water presence: Presence or indication that sur- SURWAT

face is inundated for at least 1 week. 

V Annual turnover of detritus: Standing stocks of detritus (snags, coarse TURNOV

woody debris, and humus).
A4 Appendix A Definitions of Variables and Functions for Riverine Wetlands

VWTF Fluctuation of water table: Change in water table elevation with rises

usually caused by precipitation or flooding events and falls due to

evapotranspiration and drainage.

Hydrologic Functions

Dynamic surface water storage. Capacity of a wetland to detain moving water

from overbank flow for a short duration when flow is out of the channel; associated

with moving water from overbank flow and/or upland surface water inputs by overland flow or tributaries.

Long-term surface water storage. The capability of a wetland to temporarily

store (retain) surface water for long durations; associated with standing water not

moving over the surface. Water sources may be overbank flow, overland flow

and/or channelized flow from uplands, or direct precipitation.

Energy dissipation. Allocation of the energy of water to other forms as it

moves through, into, or out of the wetland as a result of roughness associated with

large woody debris, vegetation structure, micro- and macrotopography, and other

obstructions.

Subsurface water storage. Availability of water storage beneath the wetland

surface; storage capacity becomes available due to periodic drawdown of water

table.

Moderation of groundwater flow or discharge. Capacity of a wetland to

moderate rate of groundwater flow or discharge from upgradient sources or from

groundwater discharge within a wetland.

Biogeochemical Functions

Nutrient cycling. Abiotic and biotic processes that convert elements from one

form to another; primarily recycling processes.

Removal of imported elements and compounds. The removal of imported

nutrients, contaminants, and other elements or compounds.

Retention of particulates. Deposition and retention of inorganic and organic

particulates (>0.45 μm) from the water column, primarily through physical

processes.

Organic carbon export. Export of dissolved and particulate organic carbon

from the wetland. Mechanisms include leaching, flushing, displacement, and

erosion.
Appendix A Definitions of Variables and Functions for Riverine Wetlands A5

Habitat Functions

Maintain characteristic plant community. Species composition and physical

characteristics of living plant biomass. The emphasis is on the dynamics and structure of the plant community as revealed by the species of trees, shrubs, seedlings,

saplings, and herbs and by the physical characteristics of the vegetation.

Maintain characteristic detrital biomass. The process of production, accumulation, and dispersal of dead plant biomass of all sizes. Sources may be onsite or

upslope and upgradient.

Maintain spatial structure of habitat. The capacity of a wetland to support

animal populations and guilds by providing heterogeneous habitats.

Maintain interspersion and connectivity. The capacity of a wetland to permit

aquatic organisms to enter and leave the wetland via permanent or ephemeral surface channels, overbank flow, or unconfined hyporheic gravel aquifers. The capacity of the wetland to permit access of terrestrial or aerial organisms to contiguous

areas of food and cover.

Maintain distribution and abundance of invertebrates. The capacity of the

wetland to maintain the density and spatial distribution of invertebrates (aquatic,

semi-aquatic, and terrestrial).

Maintain distribution and abundance of vertebrates. The capacity of the

wetland to maintain the density and spatial distribution of vertebrates (aquatic,

semi-aquatic, and terrestrial).
Appendix B Relationship Between Variables and Wetland Functions B1

Appendix B

Relationship Between Variables and Wetland Functions
B2

Appendix B Relationship Between Variables and Wetland Functions

Hydrologic Functions

Variables Dynamic Long-Term Dissipation Subsurface Moderation

 1. VBTREE X O O O O

 2. VCWD X O X O O

 3. VDTREE X O X O O

 4. VFREQ X O X O O

 5. VINUND X O O O O

 6. VMACRO O X X O O

 7. VMICRO X O X O O

 8. VPORE O O O X O

 9. VREDVEL O O X O O

10. VSHRUB X O O O O

11. VSUBIN O O O O X

12. VSUBOUT O O O O X

13. VSURWAT O X O O O

14. VWTF O O O X O

Note: Dynamic = Dynamic Surface Water Storage, Long-term = Long-Term Surface Water Storage,

Dissipation = Energy Dissipation, Subsurface = Subsurface Water Storage,

Moderation = Moderation of Groundwater Flow or Discharge.

Variables

 1. V = Tree basal area BTREE

 2. V = Coarse woody debris CWD

 3. VDTREE = Tree density

 4. V = Frequency of overbank flow FREQ

 5. VINUND = Average depth of inundation

 6. VMACRO = Macrotopographic relief

 7. VMICRO = Microtopographic complexity

 8. V = Soil pore space PORE

 9. VREDVEL = Reduction in flow velocity

10. V = Shrub density, biomass, or cover SHRUB

11. VSUBIN = Subsurface flow into wetland

12. VSUBOUT = Subsurface flow out of wetland

13. V = Indications of surface water presence SURWAT

14. VWTF = Fluctuation of water table
Appendix B Relationship Between Variables and Wetland Functions B3

Biogeochemical Functions

Variables Nutrient Removal Particulate Organic

 1. VBTREE O X X O

 2. VCWD O O X O

 3. VDTREE O O X O

 4. VFREQ O X X X

 5. VHERB O O X O

 6. VMICRO O X X O

 7. VMICROB O X O O

 8. VORGAN O O O X

 9. VPROD X O O O

10. VSEDIM O O X O

11. VSHRUB O O X O

12. VSORPT O X O O

13. VSUBIN O X O X

14. VSURCON O O O X

15. VSURFIN O X X X

16. VTURNOV X O O O

Note: Nutrient = Nutrient cycling, Removal = Removal of imported elements and compounds,

Particulates = Retention of particulates, Organic = Organic carbon export.

Variables

 1. V = Tree basal area BTREE

 2. V = Coarse woody debris CWD

 3. VDTREE = Tree density

 4. VFREQ = Frequency of overbank flow

 5. V = Herbaceous density, biomass, or cover HERB

 6. VMICRO = Microtopographic complexity

 7. VMICROB = Surfaces available for microbial activity

 8. VORGAN = Organic matter in wetland

 9. VPROD = Aerial net primary production

10. V = Retained sediments SEDIM

11. V = Shrub density, biomass, or cover SHRUB

12. V = Sorptive properties of soils SORPT

13. VSUBIN = Subsurface inflow into wetland

14. V = Surface hydraulic connections SURFCON

15. VSURFIN = Surface inflow to wetland

16. V = Annual turnover of detritus TURNOV
B4

Appendix B Relationship Between Variables and Wetland Functions

Habitat Functions

Variables Plant Detrital Habitat Interspersion Invertebrates Vertebrates

 1. VAQINVT O O O O X O

 2. VBEAV O O O O O X

 3. VBIRD O O O O O X

 4. VBTREE X O O O O O

 5. VCANOPY X O O O O O

 6. VCOMP X O O O O O

 7. VCONTIG O O O X O O

 8. VCWD O X O O O O

 9. VDURAT O O O X O O

10. VDTREE X O O O O O

11. VFISH O O O O O X

12. VFREQ O O O X O O

13. VFWD O X O O O O

14. VGAPS O O X O O O

15. VHERP O O O O O X

16. VLINVT O O O O X O

17. VLOGS O X O O O O

18. VMAMM O O O O O X

19. VMATUR O O X O O O

20. VMICRO O O O X O O

21. VPATCH O O X O O O

22. VREGEN X O O O O O

23. VSINVT O O O O X O

24. VSNAGS O X X O O O

25. VSTRATA O O X O O O

26. VSUBCON O O O X O O

27. VSURFCON O O O X O O

Note: Plant = Maintain Characteristic Plant Community, Detrital = Maintain Characteristic Detrital Biomass,

Habitat = Maintain Spatial Structure of Habitat, Interspersion = Maintain Habitat Interspersion and Connectivity, 

Invertebrates = Maintain Distribution and Abundance of Invertebrates, Vertebrates = Maintain Distribution and Abundance

of Vertebrates.
Appendix B Relationship Between Variables and Wetland Functions B5

Variables

 1. V = Aquatic invertebrates AQINVT

 2. V = Beaver BEAV

 3. V = Birds BIRD

 4. V = Tree basal area BTREE

 5. V = Canopy cover CANOPY

 6. V = Species composition COMP

 7. V = Contiguous vegetation cover CONTIG

 8. V = Coarse woody debris CWD

 9. VDTREE = Tree density

10. VDURAT = Duration of overbank flow

11. VFISH = Fish

12. VFREQ = Frequency of overbank flow

13. V = Fine woody debris FWD

14. V = Canopy gaps GAPS

15. V = Herptiles HERP

16. V = Litter invertebrates LINVT

17. VLOGS = Logs in several stages of decomposition

18. VMAMM = Mammals

19. VMATUR = Abundance of very mature trees

20. VMICRO = Microtopographic complexity

21. V = Vegetation patchiness PATCH

22. V = Regeneration from seedlings, saplings, clonal shoots REGEN

23. V = Soil invertebrates SINVT

24. V = Snags SNAGS

25. V = Number of attributes of vertical strata STRATA

26. V = Subsurface hydraulic connections SUBCON

27. V = Surface hydraulic connections SURFCON
Appendix C Field Forms—Tally Sheets and Synopses C1

Appendix C

Field Forms—Tally

Sheets and Synopses
C2 Appendix C Field Forms—Tally Sheets and Synopses

Tally Sheet for Dynamic Surface Water Storage

Site Location ________________________________________________

Reference Domain ____________________________________________

Team _______________________________________________________

Date ________________________________________________________

VFREQ: Frequency of Overbank Flow

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect At least one of the following: aerial photos show- 1.0 1.0

ing flooding, water marks, silt lines, alternating

layers of leaves and fine sediment, ice scars, drift

and/or wrack lines, sediment scour, sediment

deposition, directionally bent vegetation similar to

reference standard.

As above, but somewhat greater or less than ref- 0.5 0.5 

erence standard. 

Above indicators absent but related indicators 0.1 0.1

suggest overbank flow may occur.

Indicators absent and/or there is evidence of al- 0.0 0.0

teration affecting variable.

Direct Gauge data (1.5) yr return interval similar to ref- 1.0 1.0

erence standard.

Gauge data (>2 or <1) yr return interval; slight 0.5 0.5

departure from reference standard.

Gauge data show extreme departure from refer- 0.1 0.1

ence standard.

Gauge data indicate no flooding from overbank 0.0 0.0

flow.

 Index of V = FREQ
Appendix C Field Forms—Tally Sheets and Synopses C3

VINUND: Average Depth of Inundation

Method Pre Post

(choose one) Measure Relative to the Reference Standard Project Project Comments and Notes

Indirect Height of water stains and other indicators of water 1.0 1.0

depth (ice scars, bryophyte lines, drift and/or wrack

lines, etc.) between 75% and 125% of reference

standard.

Height of water stains and other indicators of water 0.5 0.5

depth (ice scars, bryophyte lines, drift and/or wrack

lines, etc.) <75% of reference standard.

Above indicators absent but related indicators sug- 0.1 0.1

gest variable may be present. 

Indicators absent and/or evidence of alteration af- 0.0 0.0

fecting the variable.

Direct Gauge data indicate that depth is between 75% 1.0 1.0

and 125% that of reference standard.

Gauge data indicate depth is <75% or >125% of 0.5 0.5

reference standard. 

Gauge data indicate infrequent or minor overbank 0.1 0.1

flooding relative to reference standard.

Gauge data indicate flooding does not occur. 0.0 0.0

 Index of V = INUND
C4 Appendix C Field Forms—Tally Sheets and Synopses

VMICRO: Microtopographic Complexity

Method Pre Post

(choose one) Measure Relative to the Reference Standard Project Project Comments and Notes

Indirect Visual estimate indicates that microtopographic 1.0 1.0

complexity (MC) is >75% and <125% of reference

standard.

Visual assessment confirms MC is present, but 0.5 0.5

somewhat less than reference standard.

Visual assessment indicates MC is much less 0.1 0.1

than reference standard; restoration possible.

Visual assessment indicates MC is virtually ab- 0.0 0.0

sent or natural substrate replaced by artificial surface; restoration not possible.

Direct Microtopographic complexity (MC) measured (sur- 1.0 1.0

veyed) shows MC >75% to <125% of reference

standard.

Measured MC is between 25% and 75% that of 0.5 0.5

reference standard.

Measured MC between 0% and 25% that of refer- 0.1 0.1

ence standard; restoration possible.

No MC at assessed site or natural substrate re- 0.0 0.0

placed by artificial surface; no restoration possible.

 Index of VMICRO = 
Appendix C Field Forms—Tally Sheets and Synopses C5

VSHRUB: Shrub Density

Method Pre Post

(choose one) Measure Relative to the Reference Standard Project Project Comments and Notes

Indirect Visual estimate of shrubs indicates site is similar 1.0 1.0

(>75%) to reference standard.

Visual estimate of shrubs indicates site is between 0.5 0.5

25% and 75% that of reference standard.

Shrubs sparse or absent relative to reference standard; 0.1 0.1

restoration possible.

Shrubs absent; restoration not possible. 0.0 0.0

Direct Shrub abundance >75% that of reference standard. 1.0 1.0

Shrub abundance between 25% and 75% that of refer- 0.5 0.5

ence standard.

Shrub abundance between 0% and 25% that or refer- 0.1 0.1

ence standard.

Shrubs absent; restoration not possible. 0.0 0.0

 Index of V = SHRUB

VBTREE: Tree Basal Area

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Stage of succession similar to reference standard. 1.0 1.0

Stage of succession departs significantly from ref- 0.5 0.5

erence standard.

Stage of succession at extreme departure from 0.1 0.1

reference standard.

Stand cleared without potential for recovery. 0.0 0.0

Direct Basal area or biomass is greater than 75% of refer- 1.0 1.0

ence standard.

Basal area or biomass between 25% and 75% of 0.5 0.5

reference standard.

Basal area or biomass between 0% and 25% of 0.1 0.1

reference standard; restoration possible.

No trees present; restoration not possible. 0.0 0.0

 Index of V = BTREE
C6 Appendix C Field Forms—Tally Sheets and Synopses

VDTREE: Tree Density

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Stage of succession similar to reference standard. 1.0 1.0

Stage of succession departs significantly from ref- 0.5 0.5

erence standard.

Stage of succession at extreme departure from 0.1 0.1

reference standard; restoration possible.

Stand cleared; no restoration possible. 0.0 0.0

Direct Measured or estimated tree density between 75% 1.0 1.0

and 125% of reference standard.

Tree density is between 25% and 75%, or between 0.5 0.5

125% and 200% of reference standard.

Tree density is between 0% and 25% or greater 0.1 0.1

than 200% of reference standard; restoration

possible.

No trees are present; restoration not possible. 0.0 0.0

 Index of V = DTREE
Appendix C Field Forms—Tally Sheets and Synopses C7

VCWD: Coarse Woody Debris

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Average diameters and lengths of CWD is >75% 1.0 1.0

and <125% of reference standard.

Average diameters and lengths of CWD is be- 0.5 0.5

tween 25% and 75% that of reference standard.

Average diameters and lengths of CWD is be- 0.1 0.1

tween 0% and 25% that of reference standard;

restoration possible.

No CWD present; restoration not possible. 0.0 0.0

Direct Biomass of CWD is >75% and <125% of refer- 1.0 1.0

ence standard.

Biomass of CWD is between 25% and 75% that 0.5 0.5

of reference standard.

Biomass of CWD is between 0% and 25% that of 0.1 0.1

reference standard; restoration possible.

No CWD present; restoration not possible. 0.0 0.0

 Index of V = CWD

Calculate Change in Function (Transfer indices of variables to this table)

Indices of Variables

Condition VFREQ VINUND VMICRO VSHRUB VBTREE VDTREE VCWD

Index of Function = [VFREQ

× (VINUND + VMICRO + VSHRUB

+ V or V + V )/5] BTREE DTREE CWD

1/2

a) Pre-Project/

Mitigation

b) Post-Project/

Mitigation

 Change Due to Project (subtract b from a)
C8 Appendix C Field Forms—Tally Sheets and Synopses

Synopsis of Dynamic Surface Water Storage

Definition. Capacity of a wetland to detain moving water from overbank flow

for a short duration when flow is out of the channel; associated with moving water

from overbank flow and/or upland surface water inputs by overland flow or

tributaries.

Effects onsite. Replenish soil moisture; import/export of materials (i.e., sediments, nutrients, contaminants); import/export of plant propagules; conduit for

aquatic organisms to access wetland for feeding, recruitment, etc.

Effects offsite. Reduce downstream peak discharge and streamflow volume;

delay downstream delivery of peak discharges; and improve water quality.

Description of indicators and variables.

VFREQ , Frequency of overbank flow. Without a supply of water via overbank

flow, a riverine wetland cannot store flood water. If appropriate to the reference

domain, a wetland that is flooded annually scores 1.0; a greater or lesser frequency

would score less than 1.0. If overbank flow does not occur, the score is zero. Other

sources, such as overland flow or tributary flow from upland areas, must be treated

separately, in a manner that is appropriate to the reference standard.

V , Average depth of inundation. Any increase in flooding depth at a INUND

given site leads to a greater volume of stored water. However, a greater depth of

inundation may result in shorter detention times per unit volume because

flow-through rates increase.

VMICRO , Microtopographic complexity. Microtopographic complexity is an

expression of the tortuosity of flow pathways. The greater the complexity (roughness), the more the resistance to flow and water will be detained for longer periods

of time.

V , V or V , Roughness of vegetation surfaces. Frictional of SHRUB BTREE DTREE

water passes over surfaces creates turbulent flow and reduced velocities, both of

which are conducive to sediment deposition. Here, three variables are scaled independently. However, Manning's coefficients have been developed for site-specific

data in order to attempt to provide quantitative relationships between roughness and

wetland structure.

If available or if it can be estimated reliably, Manning's roughness coefficient

may be substituted as an aggregate of variables VMICRO, , or , and . SHRUB BTREE DTREE CWD

VCWD , Coarse woody debris. Coarse woody debris creates resistance to flow

during flooding; resistance extends detention times, reduces flow velocity, and increases short-term water storage.
Index of Function = [VFREQ × (VINUND VMICRO VSHRUB

VBTREE or VDTREE VCWD)/5]

1/2

Index of Function = [VFREQ × (VINUND

VMICRO, SHRUB, BTREE or DETREE and CWD)/2]

1/2

Appendix C Field Forms—Tally Sheets and Synopses C9

*Option 2: If Manning's roughness coefficient is used to aggregate variables

VMICRO, VSHRUB, VBTREE or VDTREE, and VCWD
C10 Appendix C Field Forms—Tally Sheets and Synopses

Tally Sheet for Long-Term Surface Water Storage

Site Location ________________________________________________

Reference Domain ____________________________________________

Team _______________________________________________________

Date _______________________________________________________

VSURWAT: Indicators of Surface Water Presence

Method Pre Post

(choose Measure Relative to the Reference Standard Project Project Comments and Notes

one)

Indirect Compared to regional reference standard: 1.0 1.0

1. Annual understory (grass and woody reproduction, etc., absent) or

2. High organic matter accumulation at soil surface

or

3. Massive soil structure with low permeability and

general lack of small roots in the surface soil horizon

or

4. NRCS Hydrologic Soil Group C or D when soil

series known.

As above, but below reference standard. 0.5 0.5

Above indicators absent but related indicators sug- 0.1 0.1

gest variable may be present.

Indicators absent and/or there is evidence of alter- 0.0 0.0

ation affecting variable.

Direct 1. Gauge data indicate overbank flow sufficient to 1.0 1.0

pond water or

2. Direct observation of ponded water or

3. Aerial photo evidence confirms flooding similar to

reference standard.

Gauge data indicate no overbank flow; ponding 0.0 0.0

minor or not evident; no evidence of flooding on

aerial photos.

 Index of V = SURWAT
Appendix C Field Forms—Tally Sheets and Synopses C11

VMACRO: Macrotopographic Relief

Method Pre Post

(choose one) Measure Relative to the Reference Standard Project Project Comments and Notes

Indirect Oxbows, meander scrolls, abandoned channels, 1.0 1.0

backswamps, etc., similar in magnitude to reference standard.

Indicators above much less developed than refer- 0.5 0.5

ence standard and area has a low surface gradient.

All above indicators absent and area has a moder- 0.0 0.0

ate to steep gradient.

Direct 1. Contour maps indicate gross relief and/or 1.0 1.0

closed contours similar to reference standard or

2. Topographic survey shows relief similar to reference standard.

Maps and/or topographic survey indicate relief very 0.0 0.0

dissimilar to reference standard.

 Index of VMACRO = 

Calculation of Change in Function (Transfer indices of variables to this table)

Condition Index of Function = (V + V )/2

Indices of Variables

SURWAT MACRO

VSURWAT VMACRO

a) Pre-Project/

Mitigation

b) Post-Project/ Mitigation

 Change Due to Project (subtract b from a)
Index of Function = (VSURWAT VMACRO)/2

C12 Appendix C Field Forms—Tally Sheets and Synopses

Synopsis of Long-Term Surface Water Storage

Definition. The capability of a wetland to temporarily store (retain) surface water for long durations; associated with standing water not moving over the surface. 

Water sources may be overbank flow, overland flow and/or channelized flow from

uplands, or direct precipitation.

Effects onsite. Replenishes soil moisture; removes sediments, nutrients, and

contaminants; detains water for chemical transformations; maintains vegetative

composition; maintains habitat for feeding, spawning, recruitment, etc., for pool

species; and influences soil characteristics.

Effects offsite. Improves water quality; maintains base flow; maintains seasonal

flow distribution; lowers the annual water yield; recharges surficial groundwater.

Description of indicators and variables.

V , Indicators of surface water presence. For long-term storage (consid- SURWAT

ered to be longer than 1 week) to occur, water must be ponded in the wetland. This

can be directly observed or determined from interpretation of site features that indicate water was ponded on the surface for long periods of time. Overbank flow is

important to this variable, but ponding can occur and/or be sustained by precipitation, subsurface discharge, and surface discharge from riparian uplands.

VMACRO , Macrotopographic relief. There must be sufficient macrotopographic

relief, particularly when the stream has retreated to within its banks, to retain water

for long periods of time. These features may be in the form of oxbows, meander

scrolls, abandoned channels, pits and mounds, etc., with restricted outlets.

Index of function.
Appendix C Field Forms—Tally Sheets and Synopses C13

Tally Sheet for Energy Dissipation

Site Location ________________________________________________

Reference Domain ____________________________________________

Team _______________________________________________________

Date _______________________________________________________

VREDVEL: Reduction in Flow Velocity

Method Project/ Project/

(choose one) Measure Relative to the Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Sediment deposits, silt deposits on vegetation, bur- 1.0 1.0

ied root collars, stacked wracks of debris, etc., similar to reference standard.

Sediment scour, scoured root collars, large woody 0.5 0.5

debris moved about; erosion of soil surface, etc.,

indicating less than reference standard.

Directionally bent vegetation, bare soil exposed (not 0.1 0.1

sediment deposits), strongly departing from reference standard.

Strong evidence of severe site degradation by chan- 0.0 0.0

nel scour, exposed root masses, suggesting variable is absent.

Direct Velocity in wetland >75% of that expected in refer- 1.0 1.0

ence standard sites. 

Less than 75% reduction in velocity relative to 0.5 0.5

standard.

No reduction in velocity by direct measurement. 0.0 0.0

 Index of V = REDVEL
C14 Appendix C Field Forms—Tally Sheets and Synopses

VFREQ: Frequency of Overbank Flow

Method Project/ Project/

(choose one) Measure Relative to the Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect At least one of the following: aerial photos showing 1.0 1.0

flooding, water marks, silt lines, alternating layers

of leaves and fine sediment, ice scars, drift and/or

wrack lines, sediment scour, sediment deposition,

directionally bent vegetation similar to reference

standard.

As above, but somewhat greater or less than refer- 0.5 0.5

ence standard.

Above indicators absent, but related indicators 0.1 0.1

suggest overbank flow may occur.

Indicators absent and/or there is evidence of alter- 0.0 0.0

ation affecting variable; restoration not possible.

Direct Gauge data (1.5) yr return interval within 75% and 1.0 1.0

125% of reference standard.

Gauge data (>2 or <1) yr return interval 25% to 0.5 0.5

75% or >125% of reference standard.

Gauge data show extreme departure from refer- 0.1 0.1

ence standard, e.g., 0% to 25%.

Gauge data indicate no flooding from overbank 0.0 0.0

flow. 

 Index of V = FREQ

VMACRO: Macrotopographic Relief

Method Pre Post

(choose one) Measure Relative to the Reference Standard Project Project Comments and Notes

Indirect Oxbows, meander scrolls, abandoned channels, 1.0 1.0

backswamps, etc., similar in magnitude to reference standard.

Indicators above much less developed than refer- 0.5 0.5

ence standard, and area has a low surface

gradient.

All above indicators absent and area has a moder- 0.0 0.0

ate to steep gradient.

Direct 1. Contour maps indicate gross relief and/or 1.0 1.0

closed contours similar to reference standard or

2. Topographic survey shows relief similar to reference standard.

Maps and/or topographic survey indicate relief very 0.0 0.0

dissimilar to reference standard.

 Index of VMACRO = 
Appendix C Field Forms—Tally Sheets and Synopses C15

VMICRO: Microtopographic Complexity

Method Project/ Project/

(choose one) Measure Relative to the Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Visual estimate indicates that microtopographic 1.0 1.0

complexity (MC) is >75% and <125% of reference

standard.

Visual assessment confirms MC is present, but 0.5 0.5

somewhat less than reference standard.

Visual assessment indicates MC is much less 0.1 0.1

than reference standard; restoration possible.

Visual assessment indicates MC is virtually ab- 0.0 0.0

sent or natural substrate replaced by artificial surface; restoration not possible.

Direct Microtopographic complexity (MC) measured (sur- 1.0 1.0

veyed) shows MC >75% to <125% of reference

standard.

Measured MC is between 25% and 75% that of 0.5 0.5

reference standard.

Measured MC between 0% and 25% that of refer- 0.1 0.1

ence standard; restoration possible.

No MC at assessed site or natural substrate re- 0.0 0.0

placed by artificial surface.

 Index of VMICRO = 

VDTREE: Tree Density

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Stage of succession similar to reference standard. 1.0 1.0

Stage of succession departs significantly from 0.5 0.5

reference standard.

Stage of succession at extreme departure from 0.1 0.1

reference standard; restoration possible.

Stand cleared; no restoration possible. 0.0 0.0

Direct Measured or estimated tree density is between 1.0 1.0

75% and 125% of reference standard.

Tree density is between 25% and 75% or between 0.5 0.5

125% and 200% of reference standard.

Tree density is between 0% and 25% or >200% of 0.1 0.1

reference standard; restoration possible.

No trees are present; restoration not possible. 0.0 0.0

 Index of V = DTREE
C16 Appendix C Field Forms—Tally Sheets and Synopses

VCWD: Coarse Woody Debris

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Average diameter and lengths of CWD is >75% 1.0 1.0

and <125% that of reference standard.

Average diameter and lengths of CWD is be- 0.5 0.5

tween 25% and 75% that of reference standard.

Average diameter and lengths of CWD is be- 0.1 0.1

tween 0% and 25% that of reference standard;

restoration possible.

No CWD present; restoration not possible. 0.0 0.0

Direct Biomass of CWD >75% and <125% that of 1.0 1.0

reference standard.

Biomass of CWD between 25% and 75% that of 0.5 0.5

reference standard.

Biomass of CWD is between 0% and 25% that of 0.1 0.1

reference standard; restoration possible.

No CWD present; restoration not possible. 0.0 0.0

 Index of V = CWD

Calculation of Change in Function (Transfer indices of variables to this table)

Conditions + V + V + V )/4]}

Indices of Variables

Index of Function = (V × V ) FREQ REDVEL

1/2

or

Index of Function = {VFREQ × [(VMACRO

MICRO DTREE CWD

1/2

VFREQ VREDVEL VMACRO VMICRO VDTREE VCWD

a) Pre-Project/

Mitigation

b) Post-Project/

Mitigation

 Change Due to Project (subtract b from a)
Appendix C Field Forms—Tally Sheets and Synopses C17

Synopsis of Energy Dissipation

Definition. Allocation of the energy of water to other forms as it moves through,

into, or out of the wetland as a result of roughness associated with large woody

debris, vegetation structure, micro- and macrotopography, and other obstructions.

Effects onsite. Increases deposition of suspended material; increases chemical

transformations and processing due to longer residence time.

Effects offsite. Reduces downstream peak discharge; delays delivery of peak

discharges; improves water quality; reduces erosion of shorelines and floodplains.

Description of indicators and variables.

V , Frequency of overbank flow. For energy to be dissipated by the FREQ

wetland, water must enter the wetland. Overbank flow and dissipation of energy can

result in better distribution of large woody debris and improved channel stability.

V , Reduction in flow velocity. A critical variable in energy dissipation of REDVEL

flowing water energy. As depth of inundation increases, velocity decreases. Further

decreases result from sinuosity of channels and other shape factors of the wetland. 

Indications of velocity reduction are best made through “cause and effect”

relationships, such as scour holes around trees, sediment deposits in the form of

small bars, buried root collars, development of wrack lines, etc.

VMICRO , Microtopographic complexity. Microtopographic complexity is an

expression of the tortuosity of flow pathways. The greater the complexity

(roughness), the more the resistance to flow, and the higher the dissipation of

energy.

VMACRO , Macrotopographic relief. There must be sufficient macrotopographic

relief, particularly when the stream has retreated to within its banks, to retain water

for long periods of time. These features may be in the form of oxbows, meander

scrolls, abandoned channels, pits and mounds, etc., with restricted outlets.

VDTREE , Tree density. If both tree density at the assessment site is 75 to

125 percent of reference standards, it may be assumed that the site is stable and a

score of 1.0 is given. A score of 0.5 is assigned if the range is either 25 to 75 percent or 125 to 200 percent. Densities beyond the foregoing ranges (i.e., higher or

lower) are assigned 0.1. The absence of tree species receives a 0.0. Indirect

measures of density and basal area should not be used unless it is impossible to

obtain a direct measure. The only acceptable indirect measure should be published

data or data that have not been published but can be verified.

V , Coarse woody debris. If the density of fallen logs at the assessment site CWD

is >75 percent of the reference standard, a score of 1.0 is given. Comparisons that

are <75 percent are scored as 0.5 or 0.1 depending on whether the assessment site

has >25 to <75 percent or >1 to <25 percent of the density relative to the reference
Index of Function = [VFREQ × VREDVEL]

1/2 or

Index of Function = VFREQ × [(VMACRO VMICRO

VDTREE VCWD)/4)]

1/2

Index of Function = [VFREQ × (VMACRO, MICR, DTREE, CWD)]

1/2

C18 Appendix C Field Forms—Tally Sheets and Synopses

standard, respectively. If the assessment site has no coarse woody debris on the soil

surface, a variable score of 0.0 is given. The only appropriate indirect measure

would be information compiled from recent aerial photographs, taken during the

leafless season. There is no appropriate indirect measure if the site is dominated by

evergreen trees.

If Manning's n is used as a surrogate for the site roughness factors,

It is assumed that each of the combined roughness variables, frequency of overbank flow, and reduction of flow velocity are equally important in maintaining the

function in reference standards.
Appendix C Field Forms—Tally Sheets and Synopses C19

Tally Sheet for Subsurface Water Storage

Site Location ________________________________________________

Reference Domain ____________________________________________

Team _______________________________________________________

Date _______________________________________________________

VPORE: Soil Pore Space Available for Storage

Method Project/ Project/

(choose one) Measure Relative to the Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Use direct measure. 1.0 1.0

Use direct measure. 0.5 0.5

1. Algae in pore spaces, 0.1 0.1

2. Films on ped faces, or

3. Soil compacted or replaced by substrate with

negligible pore space.

Soil compacted or replaced by substrate with 0.0 0.0

negligible pore space.

Direct Example: The reference standard is sandy loam to 1.0 1.0

coarser texture soil with good structure.

Soil textures finer than sandy loam. 0.5 0.5

Soil saturated to surface or ponded for long 0.1 0.1

durations during the growing season.

Soil saturated to surface or ponded throughout the 0.0 0.0

year.

 Index of V = PORE
C20 Appendix C Field Forms—Tally Sheets and Synopses

VWFT: Fluctuation of Water Table

Method Project/ Project/

(choose one) Measure Relative to the Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Example: Water table falls rapidly to 15-30 cm of 1.0 1.0

surface.

Water table falls slowly and/or to a depth of 15 cm. 0.5 0.5

Soils stay nearly saturated or fluctuate within a few 0.1 0.1

cm of the surface over several days to a week.

Soil saturated to surface throughout the year. 0.0 0.0

Direct Range of water table fluctuation between 75% and 1.0 1.0

125% of reference standard.

Range of water table fluctuation between 25% and 0.5 0.5

75% or >125% of reference standard.

Range of water table fluctuation between 0% and 0.1 0.1

25% of reference standard.

Static water tables or water tables much deeper 0.0 0.0

than reference standard.

 Index of VWFT = 

Calculation of Change in Function (Transfer index of variable to this table)

Conditions Index of Function: (V + V )/2

Index of Variable

PORE WTF

VPORE VWTF

a) Pre-Project/Mitigation

b) Post-Project/ Mitigation

 Change Due to Project (subtract b from a)
Index of Function = (VPORE VWTF)/2

Appendix C Field Forms—Tally Sheets and Synopses C21

Synopsis of Subsurface Storage of Water

Definition. Availability of water storage beneath the wetland surface. Storage

capacity becomes available as periodic drawdown of the water table or reduction in

soil saturation occurs making drained pores available for storage of water.

Effects onsite. Short- and long-term water storage; influences biogeochemical

processes in the soil; retains water for establishment and maintenance of biotic

communities.

Effects offsite. Surficial groundwater recharge; maintains base flow; maintains

seasonal flow distribution.

Description of indicators and variables.

V , Soil pore space available for storage. Soil texture and drawdown of the PORE

water table (creating air-filled pores) are factors that must be considered in scaling

this variable. Coarser soil textures (sandy loams and coarser) and water tables that

fluctuate within 15 to 30 cm of the surface, yet maintain wetland soil wetness

conditions, would have a high potential for subsurface water storage. Comparisons

must be made to similar conditions defined by the reference standard.

VWTF , Functional water table. The water tables of most riverine wetlands

undergo drawdowns due to evapotranspiration and drainage, and rises due to

precipitation and flood events. Drawdowns combine with pore space to provide

potential volume for storage of water below the wetland surface.
C22 Appendix C Field Forms—Tally Sheets and Synopses

Tally Sheet for Moderation of Groundwater Flow or

Discharge

Site Location ________________________________________________

Reference Domain ____________________________________________

Team _______________________________________________________

Date _______________________________________________________

VSUBIN: Subsurface Flow Into Wetland

Method Project/ Project/

(choose one) Measure Relative to the Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Example of the reference standard determined by 1.0 1.0

regional standard:

1. Seeps present at edge of wetland or

2. Vegetation growing during dormant season or

drought (i.e., wet soils support vegetation) or

3. Wetland occurs at toe of slope or

4. Artesian flow (upwelling) on wetland surface.

Regional standard greatly reduced. 0.5 0.5

Regional standard absent with potential for 0.1 0.1

recovery.

Regional standard absent with no potential for 0.0 0.0

recovery.

Direct 1. Groundwater discharge measured in seeps of 0.0 - 1.0 0.0 - 1.0

springs and discharge from wetland or

2. Positive (upward) groundwater gradient

measured by piezometers.

 Index of V = SUBIN
Appendix C Field Forms—Tally Sheets and Synopses C23

VSUBOUT: Subsurface Flow From Wetland to Aquifer or Base Flow

Method Project/ Project/

(choose one) Measure Relative to the Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Example of the reference standard determined by 1.0 1.0

regional standard:

1. Sandy soils without underlying impeding layer

or

2. Permeable underlying stratigraphy.

Regional standard greatly reduced. 0.5 0.5

Regional standard absent with potential for 0.1 0.1

recovery.

Regional standard absent with no potential for 0.0 0.0

recovery.

Direct Negative (downward) groundwater gradient 0.0 - 1.0 0.0 - 1.0

measured by piezometers; score relative to

reference standard.

 Index of V = SUBOUT

Calculation of Change in Function (Transfer indices of variables to this table)

Indices of Variables

Condition VSUBIN VSUBOUT (V + V )/2

Index of Function:

SUBIN SUBOUT

a) Pre-Project/Mitigation

b) Post-Project/Mitigation

 Change Due to Project (subtract b from a)
Index of Function = (VSUBIN VSUBOUT )/2

C24 Appendix C Field Forms—Tally Sheets and Synopses

Synopsis of Moderation of Groundwater Flow or

Discharge

Definition. Capacity for wetland to moderate the rate of groundwater flow or

discharge from upgradient sources.

Effects onsite. Prolong wetness/saturated soil conditions; extended growing

season; moderate soil temperatures.

Effects offsite. Maintains upgradient or upslope groundwater storage, base

flow, seasonal flow regimes, surface water temperature.

Description of indicators and variables.

V , Subsurface flow into the wetland. May be indicated by the presence of SUBIN

seeps, springs, or early and/or late season vegetation growth (indication of warmer

groundwater seepage to root zone). As inflow to the wetland encounters either low

gradients or zones of reduced permeability, hydrodynamics of flow are moderated.

V , Subsurface flow from wetland to aquifer or to base flow. Presence SUBOUT

or absence of underlying horizons or strata that may restrict flow due to lower

permeability indicates whether subsurface discharge occurs in the wetland. Strata or

horizons of reduced permeability indicate principal flow vectors to lateral discharge

points, usually in the stream channel. The absence of restricting permeability

horizons indicates that flow may occur unrestricted to the underlying aquifer. Flow

may also occur to the stream.
Appendix C Field Forms—Tally Sheets and Synopses C25

Tally Sheet for Nutrient Cycling

Site Location ________________________________________________

Reference Domain ____________________________________________

Team _______________________________________________________

Date _______________________________________________________

VPROD: Aerial Net Primary Productivity

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Percent cover of all strata (canopy, etc.) between 1.0 1.0

75% and 125% of reference standard.

Percent cover as above, but between 25% and 0.5 0.5

75% or >125% of reference standard.

Leaf area or living biomass between 0% and 25% 0.1 0.1

of reference standard or the site lacks living

biomass due to clearing with potential for recovery.

No leaf area due to clearing; no potential for 0.0 0.0

recovery.

Direct Annual litterfall or living biomass accumulation 0.0 - 1.0 0.0 - 1.0

estimated from stand metrics as a linear

relationship between reference standard (1.0) and

absent (0.0).

 Index of V = PROD
C26 Appendix C Field Forms—Tally Sheets and Synopses

VTURNOV: Annual Turnover of Detritus

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Stocks of detrital and soil organic matter between 1.0 1.0

75% and 125% of reference standards in terms of

snags, down dead woody debris, leaf litter,

fermentation and humus layers, and fungal

fruiting bodies.

As above, but between 25% and 75%, or >125% 0.5 0.5

of reference standards.

As above, but between 0% and 25% of reference 0.1 0.1

standards or stocks of detrital and soil organic

matter absent with potential for recovery.

Area barren; no potential for recovery. 0.0 0.0

Direct Turnover of detritus and soil organic matter a 0.0 - 1.0 0.0 - 1.0

linear function between reference standard (1.0)

and absent (0.0).

 Index of V = TURNOV

Calculate Change in Function (Transfer indices of variables to this table)

Condition (the lesser of the two)

Indices of Variables

Index of Function:

VPROD VTURNOV

a) Pre-Project/Mitigation

b) Post-Project/Mitigation

 Change Due to Project/Mitigation (subtract b from a)
Index of Function = If VPROD > VTURNOV, then VTURNOV;

otherwise VPROD

Appendix C Field Forms—Tally Sheets and Synopses C27

Synopsis of Nutrient Cycling

Definition. Abiotic and biotic processes that convert nutrients and other elements from one form to another; primarily recycling processes.

Effects onsite. Net effects of recycling are elemental balances between gains

through import processes and losses through hydraulic export, efflux to the

atmosphere, and long-term retention in persistent biomass and sediments.

Effects offsite. To the extent that nutrients are held onsite by recycling, they

will be less susceptible to export downstream. This reduces the level of nutrient

loading offsite.

Index of function. Aerial net primary productivity (V ) and annual turnover PROD

of detritus (V ) are the variables. These must be scaled to existing reference TURNOV

conditions appropriate for the physiographic region and the wetland's functional

class. Index of Function is V or V , whichever is lower relative to reference PROD TURNOV

standards.

Description of indicators and variables.

VPROD , Aerial net primary productivity. Aerial net primary productivity

(ANPP) is one of two variables for the function. Aerial net primary productivity is

dependent on the development of leaf area, and estimates of leaf are assumed to be

roughly indicative of primary productivity. Other components of ANPP have been

estimated in some forested wetlands from the relationship between basal area and

age for developing stands. It is assumed that biomass is a rough approximation of

whether uptake processes are in place. If biomass is absent or reduced relative to

the reference standard, the causes may be due to natural or man-made disturbance. 

Annual litterfall and leaf area index (as determined from interception of incoming

solar radiation) are possible indices of ANPP. Litterfall is only one component of

ANPP, however, and may be less responsive to stressors than stem growth. Leaf

area index is another indicator that ANPP is taking place. It may be estimated by

light interception by the canopy relative to the reference standard.

VTURNOV , Annual turnover of detritus. Standing stocks of detritus are assumed

to be proportional to annual turnover. Stocks include snags, down and dead woody

debris, the forest floor or “O” horizons of soil (leaf litter, fermentation, and humus

layers), and the organic component of mineral soil. Sites equivalent to the reference

standard in detrital stocks and soil organic component score 1.0. Detrital stocks that

are noticeably reduced score 0.5; if major disturbance has depleted the site of most

soil and detrital organic matter, the function receives a 0.1 or zero depending on

potential for recovery.
C28 Appendix C Field Forms—Tally Sheets and Synopses

Tally Sheet for Removal of Imported Elements and

Compounds

Site Location ________________________________________________

Reference Domain ____________________________________________

Team _______________________________________________________

Date _______________________________________________________

VFREQ: Frequency of Overbank Flow

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect At least one of the following: aerial photos 1.0 1.0

showing flooding, water marks, silt lines,

alternating layers of leaves and fine sediment,

ice scars, drift and/or wrack lines, sediment

scour, sediment deposition, directionally bent

vegetation similar to reference standard.

As above, but somewhat greater or less than 0.5 0.5

that of reference standard.

Above indicators absent, but related indicators 0.1 0.1

suggest overbank flow may occur.

Indicators absent and/or there is evidence of 0.0 0.0

alteration affecting variable.

Direct Gauge data (1.5) yr return interval similar to 1.0 1.0

reference standard.

Gauge data (>2 or <1) yr return interval. 0.5 0.5

Gauge data show extreme departure from 0.1 0.1

reference standard.

Gauge data indicate no flooding from overbank 0.0 0.0

flow. 

 Index of V = FREQ
Appendix C Field Forms—Tally Sheets and Synopses C29

VSURFIN: Surface Inflow to the Wetland

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Any of the following indicators similar to refer- 1.0 1.0

ence standard:

1. Rills on adjacent upland slopes. 

2. Lateral tributaries entering floodplain and not

connected to the channel.

Neither of the above indicators similar to refer- 0.5 0.5

ence standards, and either of the above indicators less the reference standard.

Absence of both of the above indicators. 0.1 0.1

Absence of both of the above indicators and 0.0 0.0

hydraulic gradient reversed by regional cone of

depression or channelization across wetland and

ditches present at toe of slope.

Direct Use of data from runoff collectors as a continuous variable from reference standard (1.0) to 0.0-1.0 0.0-1.0

absent (0.0).

 Index of V = SURFIN
C30 Appendix C Field Forms—Tally Sheets and Synopses

VSUBIN: Subsurface Flow Into Wetland

Method Project/ Project/

(choose one) Measure Relative to the Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Example of the reference standard determined by 1.0 1.0

regional standards:

1. Seeps present at edge of wetland or

2. Vegetation growing during dormant season or

drought (i.e., wet soils support vegetation) or

3. Wetland occurs at toe of slope or

4. Artesian flow (upwelling) on wetland surface.

Regional standards greatly reduced. 0.5 0.5

Regional standards absent with potential for 0.1 0.1

recovery.

Regional standards absent with no potential for 0.0 0.0

recovery.

Direct 1. Groundwater discharge measured in seeps or 0.0-1.0 0.0-1.0

springs and discharge from wetland or

2. Positive (upward) groundwater gradient

measured by piezometers and scored relative to

reference standard.

 Index of V = SUBIN
Appendix C Field Forms—Tally Sheets and Synopses C31

VMICRO: Microtopographic Complexity

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Visual estimate indicates that microtopo- 1.0 1.0

graphic complexity (MC) is >75% and <125%

of reference standard.

Visual assessment confirms MC is somewhat 0.5 0.5

less than reference standard.

Visual assessment indicates MC is much less 0.1 0.1

than reference standard; restoration possible.

Visual assessment indicates MC is virtually 0.0 0.0

absent or natural substrate replaced by

artificial surface; restoration not possible.

Direct Microtopographic complexity (MC) measured 1.0 1.0

(surveyed) shows MC >75% to 125% of

reference standard.

Measured MC is between 25% and 75% of 0.5 0.5

reference standard.

Measured MC between 0% and 25% of 0.1 0.1

reference standard; restoration possible.

No MC at assessed site or natural substrate 0.0 0.0

replaced by artificial surface; no restoration

possible.

 Index of VMICRO = 
C32 Appendix C Field Forms—Tally Sheets and Synopses

VMICROB: Surfaces for Microbial Activity

Method Project/ Project/

(choose one) Measure Relative to the Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Indicators similar to reference standard, i.e., litter 1.0 1.0

layer, humus stratum, woody debris, and floating,

submersed, and herbaceous emergents.

As above, but indicators less than reference 0.5 0.5

standards.

Indicators absent, with potential for recovery. 0.1 0.1

Indicators absent, without potential for recovery. 0.0 0.0

Direct Mass of litter layer measured as a continuous 0.0-1.0 0.0-1.0

variable from reference standard (1.0) to absent

(0.0).

 Index of VMICROB = 

VSORPT: Sorptive Properties of Soils

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Physical properties of soil similar to the reference 1.0 1.0

standard.

Soil departs in texture, organic carbon content, 0.5 0.5

and other properties.

Major departures (e.g., sand to cobbles, clay to 0.1 0.1

sand).

Surfaces lacking soil or natural substrate (e.g., 0.0 0.0

asphalt, concrete).

Direct Cation exchange capacity and percent base 1.0 1.0

saturation similar to reference standard.

As above, but less than reference standards. 0.5 0.5

As above, but greatly reduced from reference 0.1 0.1

standards.

Soil absent; replaced by nonsoil surfaces. 0.0 0.0

 Index of V = SORPT
Appendix C Field Forms—Tally Sheets and Synopses C33

VBTREE: Tree Basal Area

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Stage of succession similar to reference 1.0 1.0

standard.

Stage of succession significantly departs from 0.5 0.5

reference standard.

Stage of successional at extreme departure from 0.1 0.1

reference standard.

Stand cleared without potential for recovery. 0.0 0.0

Direct Basal area is greater than 75% of reference 1.0 1.0

standard.

Basal area between 25% and 75% of reference 0.5 0.5

standard.

Basal area between 0% and 25% of reference 0.1 0.1

standard; restoration possible.

No trees present; restoration not possible. 0.0 0.0

 Index of V = BTREE

Calculation of Change in Function (Transfer indices of variables to this table)

Condition V V V V V V V + V }/3

Indices of Variables Index of Function = {[(VFREQ +

VSURFIN + VSUBIN)/3] + [(VMICRO

+ VMICROB + V )/3] SORPT

FREQ SURFIN SUBIN MICRO MICROB SORPT BTREE BTREE)

a) Pre-Project/

Mitigation

b) Post-Project/

Mitigation

 Change Due to Project (subtract b from a)
C34 Appendix C Field Forms—Tally Sheets and Synopses

Synopsis of Removal of Elements and Compounds

Definition. The removal of imported nutrients, contaminants, and other elements or compounds.

Effects onsite. Nutrients and contaminants in surface or ground water that come

in contact with sediments are either removed from the site or rendered “noncontaminating” because they are broken down into innocuous and biogeochemically inactive

forms.

Effects offsite. Chemical constituents removed and concentrated in wetlands,

regardless of source, reduce downstream loading.

Description of indicators and variables.

V , Frequency of overbank flow. Without flooding from overbank flow, FREQ

there would be little opportunity for waterborne materials in streams to be removed

by biogeochemical processes operating on floodplain wetlands. For an unaltered

site that receives flooding at a 2- to 5-year interval, the 2- to 5-year interval would

score a 1.0; an annual flooding regime would be inappropriate for that site and

would score less than 1.0.

V , Surface inflow to the wetland. When precipitation rates exceed soil SURFIN

infiltration rates, overland flow in uplands adjacent to riverine wetland may be a

water source. Indicators include the presence of rill and rearranged litter on the

upland leading to the floodplain.

V , Subsurface flow into the wetland. May be indicated by the presence of SUBIN

seeps, springs, or early and/or late-season vegetation growth (indication of warmer

groundwater seepage to root zone). As inflow to the wetland encounters either low

gradients or zones of reduced permeability, hydrodynamics of flow are moderated.

VMICRO , Microtopographic complexity. Microtopographic complexity is an

expression of the tortuosity of flow pathways. The greater the complexity

(roughness), the more the resistance to flow and water will be detained for longer

periods of time.

VMICROB , Surfaces for microbial activity. The primary reason that many

chemicals and compounds are removed by wetlands is due to microbial activity. 

Microbes in aquatic ecosystems tend to be associated with complex surfaces such as

leaf litter, humus and soil particles, and plant surfaces.

V , Sorptive properties of soils. Physical and chemical removal of dis- SORPT

solved elements and compounds occurs through complexation, precipitation, and

other mechanisms of removal. Phosphorus is the best studied.

VBTREE , Tree basal area. If the plant community of a wetland is accumulating

biomass over the long term, through forest development, the capacity to detain
Index of Function = [(VFREQ VSURFIN VSUBIN)/3]

[(VMICRO VMICROB VSORPT)/3] VBTREE /3

Index of Function = [(VFREQ VSURFIN VSUBIN)/3]

[(VMICRO VMICROB VSORPT)/3] /2

Appendix C Field Forms—Tally Sheets and Synopses C35

elements for longer than 1 year is enhanced because woody parts are recycled (turn

over) more slowly than nonwoody parts. Fallen logs and roots that occasionally

become buried in wetlands require much longer to recycle than those that

decompose above-ground.

If the vegetation is dominated by short-lived herbaceous species, then V can be BTREE

removed without penalty, such that:

It is assumed that the three groups of variables, water sources, soil properties, and

uptake by vegetation, are equally important in maintaining the function at the

reference standard.
C36 Appendix C Field Forms—Tally Sheets and Synopses

Tally Sheet for Retention of Particulates

Site Location ________________________________________________

Reference Domain ____________________________________________

Team _______________________________________________________

Date _______________________________________________________

VFREQ: Frequency of Overbank Flow

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect At least one of the following: aerial photos 1.0 1.0

showing flooding, water marks, silt lines,

alternating layers of leaves and fine sediment, ice

scars, drift and/or wrack lines, sediment scour,

sediment deposition, directionally bent vegetation

similar to reference standard.

As above, but somewhat greater or less than 0.5 0.5

reference standard.

Above indicators absent but related indicators 0.1 0.1

suggest overbank flow may occur.

Above indicators absent and/or there is evidence 0.0 0.0

of alteration affecting variable. 

Direct Gauge data (1.5) yr return interval; similar to ref- 1.0 1.0

erence standard.

Gauge data (>2 or <1) yr return interval; 0.5 0.5

departure from reference standard.

Gauge data show extreme departure from 0.1 0.1

reference standard.

Gauge data indicate no flooding from overbank 0.0 0.0

flow. 

 Index of V = FREQ
Appendix C Field Forms—Tally Sheets and Synopses C37

VSURFIN: Surface Inflow to the Wetland

Method Project/ Project/

(choose one) Measure Relative to the Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Any of the following indicators similar to reference 1.0 1.0

standard:

1. Rills on adjacent upland slopes. 

2. Lateral tributaries entering floodplain and not

connected to the channel.

Both of the above indicators similar to reference 0.5 0.5

standards, and any of the above indicators less

than reference standard.

Absence of both of the above indicators. 0.1 0.1

Absence of both of the above indicators, and 0.0 0.0

channelization across wetland prevents sedimentation on wetland surface.

Direct Use of data from runoff collectors as a continuous 0.0-1.0 0.0-1.0

variable from reference standard (1.0) to absent

(0.0).

 Index of V = SURFIN

VHERB: Herbaceous Plant Density

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Herbaceous plant cover between 75% and 125% 1.0 1.0

that of reference standard.

Herbaceous plant cover between 25% and 75%, 0.5 0.5

or more than 125% that of reference standard.

Herbaceous plant cover between 0% and 25% 0.1 0.1

that of reference standard.

Herbaceous plant cover absent; restoration not 0.0 0.0

possible.

Direct Herbaceous density, biomass, or cover scaled as 1.0 1.0

a linear function of reference standard ranging

from 1.0 to 0.0

 Index of V = HERB
C38 Appendix C Field Forms—Tally Sheets and Synopses

VSHRUB: Shrub Density

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Visual estimate of shrubs and saplings indicates 1.0 1.0

site is similar (>75%) to reference standard.

Visual estimate of shrubs and saplings indicates 0.5 0.5

site is between 25% and 75% that of reference

standard.

Shrubs and saplings sparse or absent relative to 0.1 0.1

reference standard; restoration possible.

Shrubs and saplings absent; restoration not 0.0 0.0

possible.

Direct Shrub abundance >75% that of reference

standard. 1.0 1.0

Shrub abundance between 25% and 75% that of 0.5 0.5

reference standard.

Shrub abundance between 0% and 25% that of 0.1 0.1

reference standard.

Shrubs absent; restoration not possible. 0.0 0.0

 Index of V = SHRUB
Appendix C Field Forms—Tally Sheets and Synopses C39

VBTREE: Tree Basal Area

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigatio Comments and Notes

Pre Post

n

Indirect Stage of succession similar to reference standard. 1.0 1.0

Stage of succession departs significantly from 0.5 0.5

reference standard.

Stage of succession at extreme departure from 0.1 0.1

reference standard; restoration possible.

Stand cleared; no restoration possible. 0.0 0.0

Direct Basal area or biomass is greater than 75% of 1.0 1.0

reference standard.

Basal area or biomass between 25% and 75% of 0.5 0.5

reference standard.

Basal area or biomass between 0% and 25% of 0.1 0.1

reference standard; restoration possible.

No trees are present; restoration not possible. 0.0 0.0 

 Index of V = BTREE
C40 Appendix C Field Forms—Tally Sheets and Synopses

VDTREE: Tree Density

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigatio Mitigatio Comments and Notes

Pre Post

n n

Indirect Stage of succession similar to reference 1.0 1.0

standard.

Stage of succession departs significantly 0.5 0.5

from reference standard.

Stage of succession at extreme departure 0.1 0.1

from reference standard; restoration possible.

Stand cleared; no restoration possible. 0.0 0.0

Direct Measured or estimated tree density is be- 1.0 1.0

tween 75% and 125% of reference standard.

Tree density is between 25% and 75%, or 0.5 0.5

between 125% and 200% of reference

standard.

Tree density is between 0% and 25%, or 0.1 0.1

greater than 200% of reference standard;

restoration possible.

No trees are present; restoration not possible. 0.0 0.0 

 Index of V = DTREE
Appendix C Field Forms—Tally Sheets and Synopses C41

VMICRO: Microtopographic Complexity

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Visual estimate indicates that microtopographic 1.0 1.0

complexity (MC) is >75% and <125% of reference

standard.

Visual assessment confirms MC is somewhat less 0.5 0.5

than reference standard.

Visual assessment indicates MC is much less 0.1 0.1

than reference standard; restoration possible.

Visual assessment indicates MC is virtually 0.0 0.0

absent or natural substrate replaced by artificial

surface; restoration not possible.

Direct Microtopographic complexity (MC) measured 1.0 1.0

(surveyed) shows MC >75% to <125% of

reference standard.

Measured MC is not between 25% and 75% that 0.5 0.5

of reference standard.

Measured MC is between 0% and 25% of 0.1 0.1

reference standard; restoration possible.

No MC at assessed site or natural substrate 0.0 0.0

replaced by artificial surface; no restoration

possible.

 Index of VMICRO = 
C42 Appendix C Field Forms—Tally Sheets and Synopses

VCWD: Coarse Woody Debris

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Volume of CWD is >75% and <125% of reference 1.0 1.0

standard.

Volume of CWD is between 25% and 75% that of 0.5 0.5

reference standard.

Volume of CWD is between 0% and 25% that of 0.1 0.1

reference standard; restoration possible.

No CWD present; restoration not possible. 0.0 0.0

Direct Biomass of CWD is >75% and <125% of 1.0 1.0

reference standards.

Biomass of CWD is between 25% and 75% that 0.5 0.5

of reference standard.

Biomass of CWD is between 0% and 25% of 0.1 0.1

reference standard; restoration possible.

No CWD present; restoration not possible. 0.0 0.0

 Index of V = CWD

VSEDIM: Retained Sediments

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Silt or sediment layering on surfaces or buried 1.0 1.0

root collars or natural levees between 75% and

125% of reference standard.

As above, but between 25% and 75% of 0.5 0.5

reference standard.

As above, but between 0% and 25% or >125% 0.1 0.1

of reference standard.

Hydrologic alterations eliminate variable; 0.0 0.0

restoration not possible.

Direct Accumulation rates using cesium-137, lead-210, 0.0-1.0 0.0-1.0

feldspar clay layer, scaled as a linear function

from reference standard (1.0) to absent (0.0).

 Index of V = SEDIM
Appendix C Field Forms—Tally Sheets and Synopses C43

Calculation of Change in Function (Transfer indices of variables to this table)

Conditions V V V V V V V V V Option 2: Index = V

Indices of Variables Index of Function = {[(VFREQ

+ VSURFIN)/2] × [(VHERB + VSHRUB

+ VBTREE + VDTREE + VMICRO

+ V )/6]} CWD

1/2

FREQ SURFIN HERB SHRUB BTREE DTREE MICRO CWD SEDIM SEDIM

a) Pre-Project/

Mitigation

b) Post-Project/

Mitigation

 Change Due to Project (subtract b from a)
Index of Function = [(VFREQ VSURFIN)/2]

× [(VHERB VSHRUB VBTREE VDTREE

VMICRO VCWD)/6]

1/2

Option 2: Index = VSEDIM

C44 Appendix C Field Forms—Tally Sheets and Synopses

Synopsis of Retention of Particulates

Definition. Deposition and retention of inorganic and organic particulates

(>0.45 μm) from the water column, primarily through physical processes.

Effects onsite. Sediment accumulation contributes to the nutrient capital of the

ecosystem. Deposition increases surface elevation and changes topographic

complexity. Organic matter may also be retained for decomposition, nutrient

recycling, and detrital food web support.

Effects offsite. Reduces stream sediment load and entrained woody debris that

would otherwise be transported downstream.

Description of indicators and variables.

V , Frequency of overbank flow. Flooding from overbank flow is the FREQ

transport mechanism by which sediments from streams enter floodplains. Many of

these are simply indicative of recent flooding (silt lines) or may have occurred

during an infrequent event (ice scour), and therefore not be particularly helpful in

establishing the flooding return interval of a particular site.

V , Surface inflow to the wetland. When precipitation rates exceed soil SURFIN

infiltration rates, overland flow in uplands adjacent to riverine wetland may be a

water source. Indicators include the presence of rill and rearranged litter on the

upland leading to the floodplain.

VHERB , V , V , V , V , V , Roughness of surfaces. SHRUB BTREE DTREE MICRO CWD

Frictional force of water passes over surfaces and creates turbulent flow and reduced

velocities, both of which are conducive to sediment deposition. Here, three variables are scaled independently. However, Manning's coefficients have been

developed for site-specific data to attempt to provide quantitative relationships

between roughness and wetland structure.

V , Retained sediments. Direct evidence of retained sediments is the best SEDIM

qualitative indicator. Occasionally, layers of leaves will be buried under sediment

layers, but such rates of deposition are infrequent in most undisturbed and small

watersheds.
Appendix C Field Forms—Tally Sheets and Synopses C45

Tally Sheet for Organic Carbon Export

Site Location ________________________________________________

Reference Domain ____________________________________________

Team _______________________________________________________

Date _______________________________________________________

VFREQ: Frequency of Overbank Flow

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect At least one of the following: aerial photos showing 1.0 1.0

flooding, water marks, silt lines, alternating layers

of leaves and fine sediment, ice scars, drift and/or

wrack lines, sediment scour, sediment deposition,

directionally bent vegetation similar to reference

standard.

As above, but somewhat greater or less than 0.5 0.5

reference standard.

Above indicators absent, but related indicators 0.1 0.1

suggest overbank flow may occur.

Indicators absent and/or there is evidence of 0.0 0.0

alteration affecting variable; restoration not

possible.

Direct Gauge data (1.5) yr return interval similar to the ref- 1.0 1.0

erence standard.

Gauge data (>2 or <1) yr return interval. 0.5 0.5

Gauge data show extreme departure from refer- 0.1 0.1

ence standard.

Gauge data indicate no flooding from overbank 0.0 0.0

flow.

 Index of V = FREQ
C46 Appendix C Field Forms—Tally Sheets and Synopses

VSURFIN: Surface Inflow to the Wetland

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Any of the following indicators similar to reference 1.0 1.0

standard:

1. Rills on adjacent upland slopes.

2. Lateral tributaries entering floodplain and not

connected to the channel.

Neither of the above indicators similar to reference 0.5 0.5

standards, and either of the above indicators less

than reference standard.

Absence of both of the above indicators. 0.1 0.1

Absence of both of the above indicators, and 0.0 0.0

hydraulic gradient reversed by regional cone of

depression, or channelization across wetland prevents inflow.

Direct Use of data from runoff collectors as a continuous 0.0-1.0 0.0-1.0

variable from reference standard (1.0) to absent

(0.0).

 Index of V = SURFIN

VSUBIN: Subsurface Flow into Wetland

Method Project/ Project/

(choose one) Measure Relative to the Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Example of the reference standard determined by 1.0 1.0

regional standards:

1. Seeps present at edge of wetland or

2. Vegetation growing during dormant season or

drought (i.e., wet soils support vegetation) or

3. Wetland occurs at toe of slope or

4. Artesian flow (upwelling) on wetland surface.

Regional standards greatly reduced. 0.5 0.5

Regional standards absent with potential for 0.1 0.1

recovery.

Regional standards absent with no potential for 0.0 0.0

recovery.

Direct 1. Groundwater discharge measured in seeps of 0.0-1.0 0.0-1.0

springs and discharge from wetland or

2. Positive (upward) groundwater gradient measured by piezometers and scored relative to

reference standards.

 Index of V = SUBIN
Appendix C Field Forms—Tally Sheets and Synopses C47

V : Surface Hydraulic Connections with Channel SURFCON

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Visual estimates of internal drainage channels 1.0 1.0

present and connected to main channel between

75% and 125% of reference standard.

As above but between 25% and 75% or >125% 0.5 0.5

of reference standard.

As above, but between 0% and 25% of reference 0.1 0.1

standard.

Internal drainage channels absent or present and 0.0 0.0

blocked from main channel.

Direct No direct measures.

 Index of V = SURFCON

VORGAN: Organic Matter in Wetland

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigatio Mitigation Comments and Notes

Pre Post

n

Indirect Visual estimates of litter, coarse woody debris, live 1.0 1.0

woody vegetation, live or dead herbaceous plants,

organic-rich mineral soils, or histosols at levels

between 75% and 125% that of reference

standard.

As above, but between 25% and 75% or >125% of 0.5 0.5

reference standard.

As above, but between 0% and 25% of reference 0.1 0.1

standard.

No organic matter; no potential for recovery. 0.0 0.0

Direct Measured standing stocks of live and dead 1.0 1.0

biomass and soil organic matter between 75% and

125% of reference standard.

As above but between 25% and 75% or >125% of 0.5 0.5

reference standard.

As above, but between 0% and 25% of reference 0.1 0.1

standard.

Standing stocks of live and dead biomass and soil 0.0 0.0

organic matter absent.

 Index of VORGAN = 
C48 Appendix C Field Forms—Tally Sheets and Synopses

Calculation of Change in Function (Transfer indices of variables to this table)

Condition + V + V )/4] × V }

Indices of Variables

Index of Function = {[(VFREQ + VSURFIN

SUBIN SURFCON ORGAN

V V V V V 1/2 FREQ SURFIN SUBIN SURFCON ORGAN

a) Pre-Project/

Mitigation

b) Post-Project/

Mitigation

 Change Due to Project (subtract b from a)
Appendix C Field Forms—Tally Sheets and Synopses C49

Synopsis of Organic Carbon Export

Definition. Export of dissolved and particulate organic carbon from the

wetland. Mechanisms include leaching, flushing, displacement, and erosion.

Effects onsite. The removal of organic matter from living biomass, detritus, and

soil organic matter contributes to decomposition. Metals may be mobilized by

chelation.

Effects offsite. Provides support for aquatic food webs and biogeochemical

processing downstream from the wetland.

Description of indicators and variables.

V , Frequency of overbank flow. Flooding from overbank flow supplies FREQ

water to the floodplain surface where long contact times over large surface areas of

organic-rich sediments allow organic matter to accumulate in surface waters. 

Indices are related to flooding frequencies, with the maximum of 1.0 for a site that

receives annual flooding because the reference domain falls into that return interval. 

Indices for other frequencies are lower, and lack of overbank flow receives a zero.

V , Surface inflow to the wetland. When precipitation rates exceed soil SURFIN

infiltration rates, overland flow in uplands adjacent to riverine wetland may be a

water source. Indicators include the presence of rill and rearranged litter on the

upland leading to the floodplain.

V , Subsurface flow into the wetland. May be indicated by the presence of SUBIN

seeps, springs, or early and/or late-season vegetation growth (indication of warmer

groundwater seepage to root zone). As inflow to the wetland encounters either low

gradients or zones of reduced permeability, hydrodynamics of flow are moderated.

V , Surface hydraulic connections with channel. Internal networks of SURFCON

channels are common features on large riverine floodplains. These channels are

conduits for overbank flow during increasing flows, but also act as drainages during

the descending limb of the hydrograph. Where natural levees are prominent, as in

alluvial river systems, breaks in the levee also indicate this type of flow.

V , Organic matter in wetland. Both live and dead plant materials are ORGAN

capable of contributing to the organic carbon concentration of exported water. A

subindex of 1.0 is earned if there is a mix of leaf material, woody debris, and organic carbon content equivalent to the reference standard. A zero would be assigned

for a site barren of both detritus and living plants with no potential for recovery.
Index of Function = [(VFREQ VSURFIN VSUBIN VSURFCON)/4]

× VORGAN

1/2

C50 Appendix C Field Forms—Tally Sheets and Synopses
Appendix C Field Forms—Tally Sheets and Synopses C51

Tally Sheet for Maintain Characteristic Plant

Community

Site Location ________________________________________________

Reference Domain ____________________________________________

Team _______________________________________________________

Date _______________________________________________________

VCOMP: Species Composition for Tree, Shrub, and Ground Cover Strata

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Published lists of dominant species in each 1.0 1.0

stratum that show presence of same species

as reference standard.

Site devoid of vegetation or no species 0.0 0.0

shared with reference standard.

Direct Three of the dominant species in each of the 1.0 1.0

4 vegetation strata match 3 of the

4 dominants in equivalent strata of reference

standard.

As above, but ground cover does not meet 0.75 0.75

reference standard.

As above, but ground cover and saplings do 0.5 0.5

not meet reference standard.

As above, but only tree stratum meets refer- 0.25 0.25

ence standard.

None of the strata meets reference standard. 0.0 0.0

 Index of V = COMP
C52 Appendix C Field Forms—Tally Sheets and Synopses

VREGEN: Seedlings/Saplings and/or Clonal Shoots

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Published lists or unpublished lists that are 1.0 1.0

verified and show same species composition

as reference standard.

Site devoid of vegetation or no species 0.0 0.0

shared.

Direct Ratio of seedling/sapling species to canopy 1.0 1.0

species is within 75% of the ratio for the reference standard.

As above, but between 25% and 75% of the 0.5 0.5

ratio of the reference standard.

As above, but between 0% and 25% of the 0.1 0.1

ratio of the reference standard.

Seedlings/saplings and/or clonal shoots are 0.0 0.0

absent or share no species with reference

standard sites.

 Index of V = REGEN

V : Canopy Cover CANOPY

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Remote or other indirect methods not

recommended.

Direct Measure of canopy cover is >75% of refer- 1.0 1.0

ence standard.

As above, but between 25% and 75% of 0.5 0.5

reference standard.

As above, but between 0% and 25% of 0.1 0.1

reference standard.

Canopy cover is absent. 0.0 0.0

 Index of V = CANOPY
Appendix C Field Forms—Tally Sheets and Synopses C53

VDTREE: Tree Density

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Stage of succession similar to reference 1.0 1.0

standard.

Stage of succession departs significantly from 0.5 0.5

reference standard.

Stage of succession at extreme departure from 0.1 0.1

reference standard; restoration possible.

Stand cleared; no restoration possible. 0.0 0.0

Direct Measured or estimated tree density is between 1.0 1.0

75% and 125% of reference standard.

Tree density is between 25% and 75%, or 0.5 0.5

between 125% and 200%, of reference

standard.

Tree density is between 0% and 25%, or 0.1 0.1

greater than 200%, of reference standard;

restoration possible.

No trees are present; restoration not possible. 0.0 0.0

 Index of V = DTREE

VBTREE: Tree Basal Area

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Stage of succession similar to reference 1.0 1.0

standard.

Stage of succession departs significantly 0.5 0.5

from reference standard.

Stage of successional at extreme departure 0.1 0.1

from reference standard; restoration possible.

Stand cleared; no restoration possible. 0.0 0.0

Direct Basal area or biomass is greater than 75% of 1.0 1.0

reference standard.

Basal area or biomass between 25% and 0.5 0.5

75% that of reference standard.

Basal area or biomass between 0% and 25% 0.1 0.1

of reference standard; restoration possible.

No trees present; restoration not possible. 0.0 0.0

 Index of V = BTREE
C54 Appendix C Field Forms—Tally Sheets and Synopses

Calculate Change in Function (Transfer indices of variables to this table)

Conditions

Indices of Variables V +

Index of Function = [V + COMP REGEN

VCOMP VREGEN VCANOPY VDTREE VBTREE VCANOPY + (VDTREE + VBTREE)/2]/4

a) Pre-Project/Mitigation

b) Post-Project/Mitigation

Change Due to Project (subtract b from a)
Appendix C Field Forms—Tally Sheets and Synopses C55

Synopsis of Maintain Characteristic Plant

Community

Definition. Species composition and physical characteristics of living plant

biomass. The emphasis is on the dynamics and structure of the plant community as

revealed by the dominant species of trees, shrubs, seedlings, saplings, and ground

cover, and by the physical characteristics of vegetation.

Effects onsite. Converts solar radiation and carbon dioxide into complex

organic compounds that provide energy to drive food webs. Provides seeds for

regeneration. Provides habitat for nesting, resting, refuge, and escape cover for

animals. Creates microclimatic conditions that support completion of life histories

of plants and animals. Creates roughness that reduces velocity of floodwaters. 

Provides organic matter for soil development and soil-related nutrient cycling

processes. Creates both long- and short-term habitat for resident or migratory

animals.

Effects offsite. Source of propagules to maintain species composition and/or

structure of adjacent areas and to supply propagules for colonization of nearby

degraded systems. Provides food and cover for animals from adjacent ecosystems. 

Provides corridors (migratory pathways) between habitats, enhances species

diversity and ecosystem stability, and provides habitat and food for migratory and

resident animals. Supports primary and secondary production in associated aquatic

habitats. Contributes leaf litter and coarse woody debris habitat for animals in

associated aquatic habitats (Bilby 1981).

Description of indicators and variables.

V , Species composition for tree, sapling, shrub, and ground cover COMP

strata. The reference standard is a complete species list for the appropriate

reference site. If the assessment site contains >75 percent of the species in the reference site, a score of 1.0 is given. Similarities of >25 and <75 percent score 0.5, and

values between 0 and 25 percent score a 0.1. If there are no species in common, 0.0

is given. Indirect measures should not be used unless the data source can be verified

and the data are recent. For all of the variables used to evaluate this function,

indirect measures yield scores that are similar to those given for direct measures

only if the data are verified.

V , Seedlings/saplings and/or clonal shoots. If a direct measure shows REGEN

that the ratio of sapling and seedling species to the canopy species is within 75 percent of the reference standard (a mature forest), the assessment site has a high

probability of being stable and an index of 1.0 is given for the variable. Scores of

0.5 and 0.1, respectively, are given if the measure shows 25 to 75 percent and 1 to

25 percent similarity in proportion to the ratio of species found in reference standard

sites. If the species composition of seedlings or saplings has no similarities with the

reference site, or if the site is devoid of vegetation, an index of 0.0 is given. If

information is available only from an indirect measure such as a species list that has

been published or obtained from an unpublished source, a score of 1.0 is given only
Index of Function [VCOMP VREGEN VCANOPY (VDTREE VBTREE)/2]/4

C56 Appendix C Field Forms—Tally Sheets and Synopses

if it is possible to verify the information. Plant communities of marshes can be

compared also, but without the need to specify strata.

V , Canopy cover. If the percent cover in the assessment site is >75 per- CANOPY

cent of the value established from the reference standard sites, a score of 1.0 is

given. Index scores of 0.5 and 0.1 are given when the assessment site and reference

standards show 25 to 75 percent and 0 to 25 percent similarity, respectively. A 0.0

is given when there is no tree layer. Indirect measures of percent cover should not

be used unless it is impossible to make a direct measure. Recent aerial photographs,

taken during the growing season, can be used to provide an indirect measure but

they should be used with great caution as changes may have occurred at the assessment site between the time the evaluation is made and the time that the photographs

were taken. If data from the indirect measure are verified during a visit to the

assessment site, scores can be given using the same ranges as used for direct

measures.

V , Tree density. If tree density at the assessment site is 75 to 125 percent DTREE

of reference standard, it may be assumed that the site is stable, and a score of 1.0 is

given. A score of 0.5 is assigned if the range is either 25 to 75 percent or 125 to

200 percent. Densities beyond the foregoing ranges (i.e., higher or lower) are

assigned 0.1. The absence of tree species receives a 0.0. Indirect measures of density and basal area should not be used unless it is impossible to obtain a direct

measure. The only acceptable indirect measure should be published data or data

that have not been published but can be verified. The same intervals may be used

for published or verified data.

V , Tree basal area. Because basal area of trees can be estimated accur- BTREE

ately with angle gauges and prisms, indirect measures do not offer any advantage

over direct ones. Therefore, measurements above the reference standard receive a

1.0, while all other measures below that level are assigned an index value

proportional to the reference standard.
Appendix C Field Forms—Tally Sheets and Synopses C57

Tally Sheet For Characteristic Detrital Biomass

Site Location _________________________________________________

Reference Domain ____________________________________________

Team ______________________________________________________

Date _______________________________________________________

V : Density of Standing Dead Trees (Snags) SNAGS

Method Project/ Mitigatio

(choose one) Measure Relative to Reference Standard Mitigation n Comments and Notes

Pre Project/

Post

Indirect No suitable measure available.

Direct Density >75% of reference standard. 1.0 1.0

Density between 25% and 75% of reference 0.5 0.5

standard.

Density between 0% and 25% of reference 0.1 0.1

standard.

No standing dead trees; restoration not possible. 0.0 0.0

 Index of V = SNAGS
C58 Appendix C Field Forms—Tally Sheets and Synopses

VCWD: Coarse Woody Debris

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Volume of CWD is >75% and <125% of 1.0 1.0

reference standard.

Volume of CWD is between 25% and 75% 0.5 0.5

that of reference standard.

Volume of CWD is between 0% and 25% that 0.1 0.1

of reference standard; restoration possible.

No CWD present; restoration not possible. 0.0 0.0

Direct Biomass of CWD is >75% and <125% of 1.0 1.0

reference standard.

Biomass of CWD is between 25% and 75% 0.5 0.5

that of reference standard.

Biomass of CWD is between 0% and 25% 0.1 0.1

that of reference standard; restoration

possible.

No CWD present; restoration not possible. 0.0 0.0

 Index of V = CWD

VLOGS: Logs in Several Stages of Decomposition

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect No suitable indirect measure.

Direct Greater than 75% of the range of log decay 1.0 1.0

classes relative to reference standard.

Between 25% and 75% of log decay classes 0.5 0.5

relative to reference standard.

Logs are only one decay class regardless of 0.1 0.1

average diameter and length.

Site contains no logs. 0.0 0.0

 Index of VLOGS =
Appendix C Field Forms—Tally Sheets and Synopses C59

V : Fine Woody Debris (Accumulating in Active Channels, and/or FWD

Microtopographic Depressions) 

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect No suitable indirect measure.

Direct Cover of fine woody debris >75% of reference 1.0 1.0

standard.

Cover of fine woody debris between 25% and 0.5 0.5

75% of reference standard.

Cover of fine woody debris between 0% and 25% 0.1 0.1

of reference standard.

No fine woody debris present. 0.0 0.0

 Index of V = FWD

Calculate Change in Function (Transfer Indices of Variables to This Table)

Conditions

Indices of Variables

Index of Function = {V + SNAGS

VSNAGS VCWD VLOGS VFWD [(VCWD + VLOGS)/2] + VFWD}/3

a) Pre-Project/Mitigation

b) Post-Project/Mitigation

Change Due to Project (subtract b from a)
C60 Appendix C Field Forms—Tally Sheets and Synopses

Synopsis of Maintain Characteristic Detrital

Biomass

Definition. The processes of production, accumulation, and dispersal of dead

plant biomass of all sizes. Sources may be onsite or upslope and upgradient. 

Emphasis is on the amount and distribution of standing and fallen woody debris.

Effects onsite. Provides primary resources for supporting detrital-based food

chains, which support the major nutrient-related processes (cycling, export, import)

within the wetland. Provides important resting, feeding, hiding, and nesting sites for

animals of higher trophic levels. Provides surface roughness that decreases velocity

of floodwaters. Retains, detains, and provides opportunities for in situ processing

of particulates. Primarily responsible for organic composition of soil.

Effects offsite. Provides sources of dissolved and particulate organic matter and

nutrients for downstream ecosystems. Contributes to reduction in downstream peak

discharges and delayed downstream delivery of peak discharges. Contributes to

downstream water quality through particulate retention and detention.

Description of indicators and variables.

V , Density of standing dead trees (snags). A direct measure of the SNAGS

number (density) of standing dead trees at the assessment site is compared to the

reference standard. If the density is >75 percent of the reference standard, the

variable score is 1.0. If the density is <75 percent but >25 percent, the index score

is 0.5. A score of 0.1 is given when the density of standing dead trees at the assessment site is between 1 and 25 percent of the reference standard. A score of 0.0 is

given when there are no standing dead trees at the assessment site. For an indirect

measure, a variable score of 0.5 is given when recent and verified aerial photography, taken during the growing season, shows that the assessment site has

>75 percent of the density of standing dead trees found under reference standards. 

An indirect measure between 0 and 75 percent of the reference standard is 0.1, and

0.0 is given when no standing dead trees are shown on the aerial photographs.

V , Coarse woody debris. If the density of fallen logs at the assessment site CWD

is >75 percent of the reference standard a score of 1.0 is given. Comparisons that

are <75 percent are scored as 0.5 or 0.1 depending on whether the assessment site

has >25 to <75 percent or >0 to <25 percent of the density relative to the reference

standard, respectively. If the assessment site has no coarse woody debris on the soil

surface, a variable score of 0.0 is given. The only appropriate indirect measure

would be information compiled from recent aerial photographs, taken during the

leafless season. There is no appropriate indirect measure if the site is dominated by

evergreen trees. A variable score of 0.5 is given if the aerial photographs show that

the assessment site has >75 percent of the density of fallen logs compared to

reference standards. Values <75 percent are scored 0.1 and a score of 0.0 is given

when no fallen logs are shown on aerial photographs.
Index of Function VSNAGS [(VCWD VLOGS)/2] VFWD /3

Appendix C Field Forms—Tally Sheets and Synopses C61

V , Logs in several stages of decomposition. A direct measure is the LOGS

abundance (e.g., common, rare, absent) of logs in five classes of decomposition. If

the assessment site has approximately the same number (>75 percent) of log decay

classes and relative abundance of logs in each class, a variable score of 1.0 is given. 

If the assessment site has fewer log decay classes and as little as 25 percent of the

reference standard, a score of 0.5 is given. If the assessment site contains logs in

only one of the decay classes and if the reference standard has logs in four or more

of the classes, a score of 0.1 is given. If the assessment site contains no logs, a

score of zero is given. There is no suitable indirect measure for this variable.

V , Fine woody debris (accumulating in active channels and side chan- FWD

nels). When the amount of organic matter accumulated in channels in the

assessment site is approximately similar to the amount found in the reference site(s),

a score of 1.0 is given. If the amount and distribution of accumulated debris is

medium compared to the reference site(s), an index score of 0.5 is given. When the

assessment site contains little accumulated organic matter (a low amount) relative to

reference standards, a score of 0.1 is given. When there is very little or no

accumulated organic matter compared to reference standard, the variable score is

0.0. There is no suitable indirect measure for this variable.

Index of function. The abundance of standing (V ) and downed (V ) SNAGS LOGS

logs, the decay stages of the logs (VCWD), and the abundance of piles of accumulated

organic matter (V ) are the variables used to assess the detritus function. All FWD

variables must be scaled to existing reference standards appropriate for the physiographic region and the wetland's functional class.
C62 Appendix C Field Forms—Tally Sheets and Synopses

Tally Sheet for Maintain Spatial Structure of

Habitat

Site Location _________________________________________________

Reference Domain ____________________________________________

Team ______________________________________________________

Date _______________________________________________________

V : Density of Standing Dead Trees (Snags) SNAGS

Method Project/ Miti-

(choose one) Measure Relative to Reference Standard Mitigation gation Comments and Notes

Pre Project/

Post

Indirect In selected forest types, aerial photos may be

used to estimate density.

Direct Density >75% of reference standard. 1.0 1.0

Density between 25% and 75% of reference 0.5 0.5

standard.

Density between 0% and 25% of reference 0.1 0.1

standard.

No standing dead trees. 0.0 0.0

 Index of VSNAGS =

VMATUR: Abundance of Very Mature Trees

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect No suitable measures available.

Direct Density of very mature trees >75% of refer- 1.0 1.0

ence standard.

Density of very mature trees between 25% 0.5 0.5

and 75% of reference standard.

Density of very mature trees between 0% and 0.1 0.1

25% of reference standard; restoration

possible.

No very mature trees present; no potential for 0.0 0.0

restoration.

 Index of VMATUR = 
Appendix C Field Forms—Tally Sheets and Synopses C63

VSTRATA: Number and Attributes of Vertical Strata of Vegetation

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Complexity of canopy (number of strata) shown 1.0 1.0

on recent aerial photos taken in leaf season, with

field calibration, similar to reference standard.

As above, but less than reference standard. 0.5 0.5

No canopy; restoration possible. 0.1 0.1

No canopy; restoration not possible. 0.0 0.0

Direct 1. Number of vertical strata, 1.0 1.0

2. Density or cover of plants in each stratum,

 or

3. Some composite index of above: Is >75% of

reference standard.

As above, but between 25% and 75% of refer- 0.5 0.5

ence standard.

As above, but between 0% and 25% of reference 0.1 0.1

standard.

Vertical strata missing. 0.0 0.0

 Index of V = STRATA

VPATCH: Vegetation Patchiness

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Texture of canopy shown on recent aerial photos 1.0 1.0

taken in leaf season, field calibrated, similar to

reference standard.

As above, but less than reference standard. 0.5 0.5

Recent aerial photos show no tree canopy. 0.0 0.0

Direct Appropriate measure of patchiness >75% and 1.0 1.0

<125% of reference standard. 

As above, but between 25% and 75% or >125% 0.5 0.5

of reference standard.

As above, but between 0% and 25% of reference 0.1 0.1

standard.

No canopy present. 0.0 0.0

 Index of V = PATCH
C64 Appendix C Field Forms—Tally Sheets and Synopses

VGAPS: Gaps in Forest

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Recent aerial photographs taken during leaf- 1.0 1.0

out season show gaps in the tree canopy

similar in number, size, and abundance to

reference standard.

As above, but less than reference standard. 0.5 0.5

Methods above indicate no gaps in tree 0.0 0.0

canopy.

Direct Number, distribution, or size frequency of 1.0 1.0

gaps in the forest canopy 75% to 125% of

reference standard. 

As above, but between 25% and 75% or 0.5 0.5

>125% of reference standard.

As above, but between 0% and 25% of 0.1 0.1

reference standard. 

No canopy gaps present. 0.0 0.0

 Index of VGAPS = 

Calculate Change in Function (Transfer Indices of Variables to This Table)

Conditions

Indices of Variables V V

Index of Function = (V + + SNAGS MATUR STRATA

VSNAGS VMATUR VSTRATA VPATCH VGAPS + VPATCH + VGAPS)/5

a) Pre

Project/Mitigation

b) Post

Project/Mitigation

Change Due to Project (subtract b from a)
Appendix C Field Forms—Tally Sheets and Synopses C65

Synopsis of Maintain Spatial Structure of Habitat

Definition. The capacity of a wetland to support animal populations and guilds

by providing heterogeneous habitats.

Effects onsite. Provides potential feeding, resting, and nesting sites for

vertebrates and invertebrates. Regulates and moderates fluctuations in temperature. 

Provides habitat heterogeneity to support a diverse assemblage of organisms. 

Affects all ecosystem processes. 

Effects offsite. Provides habitat heterogeneity to landscape, provides habitat for

wide-ranging and migratory animals, provides a corridor for gene flow between

separated populations, and allows excess progeny to exploit new areas.

Description of indicators and variables.

V , Density of standing dead trees (snags). Mature forests and forests SNAGS

subjected to periodic disturbances on the order of decades or longer usually possess

standing dead trees (snags). The importance of snags to woodpecker foraging is

well established (they feed on insects that are decomposing the snag). In addition,

limbs of large snags provide resting, perching, feeding, and nesting sites for large

birds, particularly raptors. Other avian predators use snags for resting, feeding,

searching for prey, and drying-out. Neotropical songbirds, waterfowl, and

woodpeckers nest within snag cavities. Mammals and reptiles use snags for

feeding, nesting, and hunting. Density determinations should focus on the larger

size classes of snags (with respect to reference standards), because large snags

provide the widest range of potential habitats for use by animals. 

VMATUR , Abundance of very mature trees. Standing and mature or dying trees

provide nesting habitat for a variety of animal species, including invertebrates,

birds, reptiles, amphibians, and mammals. The density of very mature tress must be

calibrated to some old-growth reference standard sites. Other indirect measures, for

example determining the density or species richness of cavity nesting birds, are too

time consuming and more logistically limited than making a direct count of cavities. 

Index scores are determined as in V above. SNAGS

V , Number and attributes of vertical strata of vegetation. Mature STRATA

forested wetlands are usually vertically stratified. The number of strata in mature

riverine forests generally ranges between three and seven in temperate North

America. Because forest organisms exhibit a remarkable fidelity to a particular

stratum, differences in structure between sites likely represent differences in animal

composition between sites as well. In fact, more spatially stratified communities

often contain more species. Vertical stratification must be measured directly and

compared with the reference standard when assessing a site.

V , Vegetation patchiness. Heterogeneity in distribution and abundance PATCH

(patchiness) of organisms is inherent at all scales in every natural ecosystem. Any

measure of ecosystem attributes must consider the appropriate scale and sample size
Index of Function (VSNAGS VMATUR VSTRATA VPATCH VGAPS)/5

C66 Appendix C Field Forms—Tally Sheets and Synopses

in which to measure those attributes in order to understand ecosystem processes

(competition, trophic interactions, energy flow, habitat structure). Wetlands are no

exception. Habitat heterogeneity occurs across different spatial scales for different

plant life forms (canopy, shrub, herbaceous, etc.) and across different hydrogeomorphic classes. Patchiness of vegetation affects the types and abundances of

trophic interactions, energy flow, and competitive interactions of animals. These

processes in turn affect animal populations. The scale at which patchiness is

measured and evaluated determines the reliability and usefulness of measurements. 

For example, shrubs and trees may not be uniformly distributed across a forested

wetland landscape. Each habitat type supports a different assemblage of bird

species, and the combined species richness (for birds) of both habitats is greater

than the richness of either area evaluated separately.

VGAPS , Canopy gaps. Canopy gaps often indicate forest maturity, particularly in

assessing unaltered sites. Mature sites are normally used to represent the best

reference standard because they generally support the highest biodiversity. 

However, canopy gaps may reflect both natural and anthropogenic disturbances and

should be used with caution when applying the variable to the Maintain Spatial

Structure of Habitat Function. As with all variables, using the appropriate reference

domain is critical in determining the variable condition of an assessment site.
Appendix C Field Forms—Tally Sheets and Synopses C67

Tally Sheet for Maintain Interspersion and

Connectivity

Site Location _________________________________________________

Reference Domain ____________________________________________

Team ______________________________________________________

Date ______________________________________________________

VFREQ: Frequency of Overbank Flow

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect At least one of the following: aerial photos show- 1.0 1.0

ing flooding, water marks, silt lines, alternating

layers of leaves and fine sediment, ice scars, drift

and/or wrack lines, sediment scour, sediment

deposition, directionally bent vegetation similar to

reference standard. 

As above, but somewhat greater or less than 0.5 0.5

reference standard.

Above indicators absent but related indicators 0.1 0.1

suggest overbank flow may occur.

Indicators absent and/or alteration has eliminated 0.0 0.0

variable.

Direct Gauge data (1.5) yr return interval similar to ref- 1.0 1.0

erence standard. 

Gauge data show (>2 or <1) yr return interval. 0.5 0.5

Gauge data show extreme departure from refer- 0.1 0.1

ence standard.

Gauge data indicate no flooding from overbank 0.0 0.0

flow.

 Index of V = FREQ
C68 Appendix C Field Forms—Tally Sheets and Synopses

VDURAT: Duration of Overbank Flow

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Duration of connection-related indicators only, 1.0 1.0

and similar to reference standard.

Any indicators, i.e., aerial photos showing 0.5 0.5

continuity of duration, flooding tolerance of

tree species, etc., showing continuity of flooding as less than reference standard.

Any indicators showing greatly reduced dura- 0.1 0.1

tion relative to reference standard.

Flooding is absent. 0.0 0.0

Direct Gauge data (x-y) yr show duration of connec- 1.0 1.0

tion between 75% and 125% of reference

standard.

As above, but between 25% and 75%, or 0.5 0.5

>125% of reference standard.

As above, but between 0% and 25% of refer- 0.1 0.1

ence standard. 

Gauge data indicate no overbank flow. 0.0 0.0

 Index of V = DURAT
Appendix C Field Forms—Tally Sheets and Synopses C69

VMICRO: Microtopographic Complexity

Method Project/ Mitiga-

(choose one) Measure Relative to Reference Standard Mitigation tion Comments and Notes

Pre Project/

Post

Indirect Visual estimate indicates that microtopographic 1.0 1.0

complexity (MC) is between 75% and 125% of

reference standard.

Visual assessment confirms MC is present, but 0.5 0.5

somewhat less than reference standard.

Visual assessment indicates MC is much less than 0.1 0.1

reference standard; restoration possible. 

Visual assessment indicates MC is virtually absent 0.0 0.0

or natural substrate replaced by artificial surface;

restoration not possible.

Direct Microtopographic complexity (MC) measured (sur- 1.0 1.0

veyed) shows MC >75% to <125% of reference

standard.

As above, but MC of site is between 25% and 75% 0.5 0.5

that of reference standard.

Measured MC between 0% and 25% of reference 0.1 0.1

standard; restoration possible.

No MC at assessed site or natural substrate 0.0 0.0

replaced by artificial surface; restoration not

possible. 

 Index of VMICRO = 

V : Surface Hydraulic Connections with Channel SURFCON

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Number of surface connections 75% to 125% of 1.0 1.0

reference standard.

Number of surface connections 25% to 50% of 0.5 0.5

reference standard.

Number of surface connections 0% to 25% of 0.1 0.1

reference standard.

No surface connections due to obstructions or 0.0 0.0

alterations.

Direct Use of data from runoff collectors as a continuous variable from reference standard (1.0) to

absent (0.0).

 Index of V = SURFCON
C70 Appendix C Field Forms—Tally Sheets and Synopses

V : Subsurface Hydraulic Connections with Channel SUBCON

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Seeps, springs, upwellings similar to reference 1.0 1.0

standard.

Excessive fine sediment supply sufficient to block 0.5 0.5

subsurface connections.

Stream channel and floodplain highly altered with 0.1 0.1

minimal connections.

No possible subsurface connections exist because 0.0 0.0

of alterations.

Direct Direct measures not practical. Tracer and dye

methods are required.

 Index of V = SUBCON
Appendix C Field Forms—Tally Sheets and Synopses C71

VCONTIG: Contiguous Vegetation Cover and/or Corridors Between Wetland and

Upland, Between Channels, and Between Upstream and Downstream Areas

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Recent aerial photographs taken during leaf 1.0 1.0

season show abundant vegetation and vegetated corridors connecting mosaics of habitat

types similar to reference standard.

Recent aerial photographs taken during the 0.5 0.5

leaf season show lower abundance of

vegetative connections than reference

standard.

Lack of continuous vegetation connections with 0.1 0.1

potential for recovery.

Lack of continuous vegetation connections with 0.0 0.0

no potential for recovery.

Direct Continuity >75% of reference standard. 1.0 1.0

As above, but between 25% and 75% of 0.5 0.5

reference standard.

As above, but between 0% and 25% of 0.1 0.1

reference standard. 

Assessment site fragmented and isolated from 0.0 0.0

channels and adjacent uplands and upstreamdownstream wetland areas.

 Index of V = CONTIG

Calculate Change in Function (Transfer indices of variables to this table)

Conditions V V V V V V + V )/6

Indices of Variables Index of Function = (VFREQ +

VDURAT + VMICRO + VSURFCON + VSUBCON

FREQ DURAT MICRO SURFCON SUBCON CONTIG CONTIG

a) Pre

Project/Mitigation

b) Post

Project/Mitigation

Change Due to Project/Mitigation (subtract b from a)
C72 Appendix C Field Forms—Tally Sheets and Synopses

Synopsis of Maintain Interspersion and

Connectivity

Definition. The capacity of the wetland to permit aquatic organisms to enter and

leave the wetland via permanent or ephemeral surface channels, overbank flow, or

unconfined hyporheic gravel aquifers. The capacity of a wetland to permit access of

terrestrial or aerial organisms to contiguous areas of food and cover.

Effects onsite. Provides habitat diversity. Contributes to secondary production

and complex trophic interactions. Provides access to and from wetland for

reproduction, feeding, rearing, and cover. Contributes to completion of life cycles

and dispersal between habitats.

Effects offsite. Provides corridors for wide-ranging or migratory species. 

Provides refugia for plants and animals. Provides conduits for dispersal of plants

and animals to other areas.

Description of indicators and variables.

V , Frequency of overbank flow. The frequency of overbank flow is a FREQ

critical component of the character of a particular riverine wetland. Such flooding is

often an integral part of affording access to the wetland by anadromous or adfluvial

fishes that use floodplain habitats, especially wetlands, to complete portions of their

life histories (e.g., spawning and rearing). The temporal periodicity and magnitude

of flooding may have direct bearing on year-class strengths among vertebrates. 

Likewise, overbank flow and connectivity between the main channel and floodplain

wetlands affect the dispersal of plant propagules or plant parts. Thus, flooding and

connectivity are critical components of site-specific structure and function. Overbank flow is best quantified by hydrographic data.

V , Duration of overbank flow. The duration of overbank flow is DURAT

determined by both the discharge upriver and the volume of water that gets

dissipated across and temporarily stored on adjacent floodplains during floods. 

Thus, the duration of overbank flow is affected by the size of the floodplain and the

hydraulic connectivity between the main channel and floodplain wetlands. The

duration of flooding is important in permitting organisms sufficient time to access

wetlands for spawning and feeding, and in allowing some species to complete

important lifehistory developmental stages. Longer periods of flooding may also

aid in the dispersal of some plants. However, it should be kept in mind that what

benefits one set of organisms may be a detriment to others. Every species of plants

and animals requires some restricted range of flooding duration to maintain an

optimal population size. 

VMICRO , Microtopographic complexity. Microtopographic relief is an important factor contributing to the interspersion of habitat types and connections between river and floodplain wetlands. Elevated structures (for example, hummocks)

and low areas (for example, channels and small depressions) direct the flow of water

through wetlands and affect direction and duration of flows. Wetlands with a
Index of Function = (VFREQ VDURAT VMICRO VSURFCON

VSUBCON VCONTIG)/6

Appendix C Field Forms—Tally Sheets and Synopses C73

mosaic of interspersed habitat types provide conditions suitable for a higher

diversity of plant and animal species than do wetlands with uniform topography. A

direct measure of surface roughness is acquired by performing a survey of microtopography (using an auto-level, laser-total survey, etc.) within a well-designed suite

of transects intersecting the wetland.

V and V , Hydraulic connections among main and side SURFCON SUBCON

channels, surface, and subsurface. Multiple hydraulic connections between a

river and the wetlands on its floodplain strongly indicate a high heterogeneity of

habitats (and hence relatively high species diversity), interspersion among habitat

types, and the potential for complex trophic interactions.

VCONTIG , Contiguous vegetation cover and/or corridors between wetland and

upland, between channels, and between upstream-downstream areas. 

Continuity of vegetation, connectivity of specific vegetation types, the presence and

scope of corridors between upland and wetland habitats, and corridors between

wetlands all have direct bearing on the movement and behavior of animals that use

wetlands. Assessment of this variable is region-specific, and must be placed in the

context of the animal species that are known to utilize these connections.
C74 Appendix C Field Forms—Tally Sheets and Synopses

Tally Sheet for Maintain Distribution and

Abundance of Invertebrates

Site Location _________________________________________________

Reference Domain ____________________________________________

Team ______________________________________________________

Date _______________________________________________________

V : Distribution and Abundance of Invertebrates in Soil SINVT

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Tunnels, shells, casts, holes, etc., in soil similar to 1.0 1.0

reference standard. 

As above, but much less than reference standard. 0.5 0.5

No evidence of items above, but with potential for 0.1 0.1

habitat recovery. 

No evidence of items above and no potential for 0.0 0.0

recovery of habitat. 

Direct Similarity index for species composition and abun- 1.0 1.0

dance of soil invertebrates >75% of reference

standard.

Similarity index between 25% and 75% of refer- 0.5 0.5

ence standard.

Similarity index 0% to 25% of reference standard. 0.1 0.1

No soil invertebrates or evidence of soil inverte- 0.0 0.0

brates found.

 Index of V = SINVT
Appendix C Field Forms—Tally Sheets and Synopses C75

VLINVT: Distribution and Abundance of Invertebrates in Leaf Litter and Coarse Woody

Debris

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Visual assessment of galleries in logs and 1.0 1.0

twigs, tunnels in wood, shells, casts, trails,

holes, etc., similar to reference standard.

As above, but much less than reference 0.5 0.5

standard. 

Absence of above conditions, but with poten- 0.1 0.1

tial for recovery.

Absence of above conditions, but potential for 0.0 0.0

recovery. 

Direct Similarity index for species composition and 1.0 1.0

abundance of invertebrates 75% of reference standard. 

Similarity index between 25% and 75% of 0.5 0.5

reference standard.

Similarity index between 0% to 25% of refer- 0.1 0.1

ence standard.

No invertebrates or evidence of invertebrates 0.0 0.0

found in leaf litter or coarse woody debris.

 Index of V = LINVT
C76 Appendix C Field Forms—Tally Sheets and Synopses

VAQINVT: Distribution and Abundance of Invertebrates in Aquatic Habitats

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Presence of suitable aquatic habitats (micro- 1.0 1.0

depressions, seeps, etc.) and evidence of shell

fragments, exudate, etc., similar to reference

standard. Measures may be developed that can be

quantified. 

As above, but indicators much less than reference 0.5 0.5

standard. 

No evidence of items above, but with potential for 0.1 0.1

habitat recovery.

No evidence of suitable aquatic habitats present 0.0 0.0

and no potential for habitat recovery.

Direct Similarity index for species composition and abun- 1.0 1.0

dance or regional indicator or keystone species

75% of reference standard. 

Similarity index for species composition and abun- 0.5 0.5

dance between 25% and 75% of reference

standard. 

Similarity index for species composition and abun- 0.1 0.1

dance 0% to 25% of reference standard.

No invertebrates or evidence of invertebrates found 0.0 0.0

in aquatic habitats.

 Index of V = AQINVT

Calculate Change in Function (Transfer indices of variables to this table)

Conditions

Indices of Variables

VSINVT VLINVT VAQINVT Index of Function = (VSINVT + VLINVT + VAQINVT)/3

a) Pre

Project/Mitigation

b) Post

Project/Mitigation

Change Due to Project/Mitigation (subtract b from a)
Index of Function (VSINVT VLINVT VAQINVT)/3

Appendix C Field Forms—Tally Sheets and Synopses C77

Synopsis of Maintain Distribution and Abundance

of Invertebrates

Definition. The capacity of the wetland to maintain the density and spatial

distribution of invertebrates (aquatic, semi-aquatic, and terrestrial).

Effects onsite. Provides food (energy) to predators, aerates soil and coarse

woody debris by building tunnels, in breaking down coarse woody debris increases

availability of organic matter for nutrient cycling microbes, and disperses seeds

within site.

Effects offsite. Provides food (energy) for wide-ranging carnivores/

insectivores, etc. Transports seeds and propagules for germination elsewhere.

Description of indicators and variables.

V , Distribution and abundance invertebrates in soil. Measurements of SINVT

invertebrate density and species richness must be compared with the reference

standard. A direct measure of invertebrate species richness and abundance at the

assessment site is best obtained by any of several standard sampling techniques. 

Rapid assessment is possible in the field by people familiar with the dominant taxa. 

Similarity can be determined by comparing density, species richness, or some index

of similarity (see any ecology text for a discussion of such measures).

V , Distribution and abundance of invertebrates in leaf litter and coarse LINVT

woody debris. Determining invertebrate activity in coarse woody debris is best

determined by direct measurements. Similarity can be determined by comparing

density, species richness, or some index of similarity (see any ecology text for a

discussion of such measures). The reference standard is a species richness and

abundance (or some similarity measure) commensurate with the reference standard.

V , Distribution and abundance of invertebrates in aquatic habitats AQINT

(e.g., microdepressions, seeps, side channels). Direct measures of aquatic

invertebrates should be made using standard sampling techniques. Rapid

assessment procedures for sampling aquatic invertebrate, identification, and

enumeration are fairly well established, but these methods require specialized

training and expertise.
C78 Appendix C Field Forms—Tally Sheets and Synopses

Tally Sheet for Maintain Distribution and Abundance of Vertebrates

Site Location _________________________________________________

Reference Domain ____________________________________________

Team ______________________________________________________

Date _______________________________________________________

VFISH: Distribution and Abundance of Resident and Migratory Fish

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Surrogate measurements (e.g., egg masses, 1.0 1.0

larval and fry stages, and adults) similar to reference standard.

Above indicators much less than reference 0.5 0.5 

standard.

No evidence of indicators above, but potential for 0.1 0.1

habitat recovery.

No evidence of indicators above and no potential 0.0 0.0

for habitat recovery.

Direct Similarity index for species composition and abun- 1.0 1.0

dance 75% of reference standard.

Similarity index for species composition and abun- 0.5 0.5

dance between 25% and 75% of reference

standard.

Similarity index for species composition and abun- 0.1 0.1

dance between 0% and 25% of reference

standard.

No fish or evidence of fish found. 0.0 0.0

 Index of V = FISH
Appendix C Field Forms—Tally Sheets and Synopses C79

VHERP: Distribution and Abundance of Herptiles

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Surrogate measures (e.g., egg masses, tracks, 1.0 1.0

calls, larval stages, skins, skeletons) similar to

reference standard.

Evidence of above indicators, but less than 0.5 0.5

reference standard.

No evidence of above indicators, but potential for 0.1 0.1

habitat recovery.

No evidence of above indicators and no potential 0.0 0.0

for habitat recovery.

Direct Similarity index for species composition and 1.0 1.0

abundance >75% of reference standard.

Similarity index for species composition and 0.5 0.5

abundance between 25% and 75% of reference

standard.

Similarity index for species composition and 0.1 0.1

abundance between 0% and 25% of reference

standard.

No herptiles or evidence of herptiles found. 0.0 0.0

 Index of V = HERP
C80 Appendix C Field Forms—Tally Sheets and Synopses

VBIRD: Distribution and Abundance of Resident and Migratory Birds

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Surrogate measurements (e.g., nests, tracks, 1.0 1.0

calls, feathers, skeletons) similar to reference

standard.

Evidence of above indicators, but less than refer- 0.5 0.5

ence standard.

No evidence of above indicators, but potential for 0.1 0.1

recovery of habitat.

No visual evidence of above indicators and no 0.0 0.0

potential for recovery of habitat.

Direct Similarity index for species composition and abun- 1.0 1.0

dance 75% of reference standard.

Similarity index for species composition and abun- 0.5 0.5

dance between 25% and 75% of reference

standard.

Similarity index for species composition and abun- 0.1 0.1

dance between 0% and 25% of reference

standard.

No birds or evidence of birds found. 0.0 0.0

 Index of V = BIRD
Appendix C Field Forms—Tally Sheets and Synopses C81

VMAMM: Distribution and Abundance of Permanent and Seasonally Resident

Mammals

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Visual evidence of mammals (e.g., trails, scat, kills, 1.0 1.0

presence of prey species, burrows, browsed

plants) similar to reference standard. 

As above, but less than reference standard. 0.5 0.5

No visual evidence of mammal indicators, but 0.1 0.1

potential for recovery of mammal habitat.

No visual evidence of mammal indicators, but no 0.0 0.0

potential for recovery of mammal habitat.

Direct Similarity index for species composition and abun- 1.0 1.0

dance 75% of reference standard.

Similarity index for species composition and abun- 0.5 0.5

dance between 25% and 75% of reference

standard.

Similarity index for species composition and abun- 0.1 0.1

dance between 0% and 25% of reference standard.

No mammals or evidence of mammals found and 0.0 0.0

no potential for recovery of habitat to reference

standard.

 Index of VMAMM = 
C82 Appendix C Field Forms—Tally Sheets and Synopses

VBEAV: Beaver Abundance

Method Project/ Project/

(choose one) Measure Relative to Reference Standard Mitigation Mitigation Comments and Notes

Pre Post

Indirect Surrogate measurements (e.g., recent aerial 1.0 1.0

photographs, presence of active and abandoned

lodges and dams, cut and chewed plants, scat,

trails) similar to reference standard.

As above, but indicators less than reference 0.5 0.5

standard.

No evidence of above indicators, but potential for 0.1 0.1

recovery of habitat exists.

No evidence of above indicators and no potential 0.0 0.0

for recovery of beaver habitat.

Direct Abundance 75% of reference standard. 1.0 1.0

Abundance between 25% and 75% of reference 0.5 0.5

standard.

Abundance between 0% and 25% of reference 0.1 0.1

standard.

No beaver or evidence of beaver found. 0.0 0.0

 Index of V = BEAV

Calculate Change in Function (Transfer indices of variables to this table)

Conditions

Indices of Variables V V +

Index of Function = (V + + FISH HERP BIRD

VMAMM + V )/5* VFISH VHERP VBIRD VMAMM VBEAV BEAV

a) Pre

Project/Mitigation

b) Post

Project/Mitigation

Change Due to Project/Mitigation (subtract b from a)

* V is omitted without penalty if beaver ponds are not considered part of the reference domain. BEAV
Appendix C Field Forms—Tally Sheets and Synopses C83

Synopsis of Maintain Distribution and Abundance

of Vertebrates

Definition. The capacity of the wetland to maintain the density and spatial

distribution of vertebrates-aquatic, semi-aquatic, and terrestrial. Vertebrates utilize

wetlands for food, cover, resting, reproduction, etc.

Effects onsite. Disperse seeds throughout the site, pollinate flowers (bats),

aerate the soil and coarse woody debris with tunnels, and alter hydroperiod and light

regime (beavers, muskrats).

Effects offsite. Disperse seeds between sites, pollinate flowers (bats), provide

food (energy) for predators, and alter hydroperiod and light regime (beavers,

muskrats).

Description of indicators and variables.

V , Distribution and abundance of resident and migratory resident fish. FISH

Fish are particularly sensitive to severed connections between a river and its

floodplain wetlands. Migratory fish are also sensitive to alterations of in-seasonal

hydrologic regimes because many migratory species have evolved to exploit an

annual flooding pattern that allows them access to adjoining wetlands for spawning. 

Fish are relatively well studied in North America, and the scientific literature

contains much information on how to measure relative abundance, determine species

richness, and calculate similarity indices. The fish density/richness function must be

examined in context of reference standards, hydrogeomorphic class, and regional

variation.

VHERP , Distribution and abundance of herptiles. Although herptiles are not as

well studied as some other vertebrate groups (particularly birds and fishes), there

are still many direct measurement (quantitative) techniques available in the

scientific literature for estimating population size or comparing sites, including

direct counts, tag/recapture methods, and encounters per unit time.

V , Distribution and abundance of resident and migratory birds. The BIRD

abundance and species richness of birds is closely related to habitat complexity

because birds have evolved to fill most available terrestrial niches. In addition, because birds are the best studied group of vertebrates, the scientific literature is

replete with information on how to measure relative abundance, determine species

richness, and calculate similarity indices.

VMAMM , Diversity and abundance of permanent and seasonally resident

mammals. Mammals are relatively well studied, and there is abundant scientific

literature on appropriate censusing techniques (mark/recapture, visual counts, etc.). 

Wide-ranging mammals (e.g., deer and bear) use wetlands as riparian corridors for

foraging, cover, rest, and water. In arid regions, riparian zones are several degrees

cooler than surrounding uplands, and mammals often cool off and rest in such areas

during midday.
Index of Function (VFISH VHERP VBIRD VMAMM VBEAV)/5

Index of Function (VFISH VHERP VBIRD BMAMM)/4

C84 Appendix C Field Forms—Tally Sheets and Synopses

V , Abundance of beaver. Beaver effects are manifest through virtually all BEAV

of the other wetland functions, from dynamics of surface water storage to nutrient

cycling to characteristics of the plant community. Beaver activity can be measured

in various ways, but direct observation and individual counts provide the best

empirical basis for assessment.

Index of Function

With beaver ponds.

Without beaver ponds.

7. (Concluded).

East Carolina University, Greenville, NC 27858-4353;

University of Montana, Polson, MT 59860;

L. C. Lee and Associates, Inc., 221 1st Avenue W.

Seattle, WA 98119;

University of Georgia, Athens, GA 30602;

U.S. Army Engineer Waterways Experiment Station

3909 Halls Ferry Road, Vicksburg, MS 39180-6199;

1456 Harwell Avenue, Crofton, MD 21114

11. (Concluded).

solicited for 1 year from date of publication. Mail comments to the U.S. Army Engineer Waterways Experiment Station,

ATTN: CEWES-ER-W, 3909 Halls Ferry Road, Vicksburg, MS 39180-6199.

13. (Concluded).

avoid and minimize impacts, determine mitigation requirements or success, as well as other applications requiring the

assessment of wetland functions.

 This document is for use by a team of individuals who adapt information in this guidebook to riverine wetlands in

specific physiographic regions. By adapting from the generalities of the riverine class to specific regional riverine subclasses, such as high-gradient streams of the glaciated northeastern United States, the procedure can be made responsive

to the specific conditions found there. For example, separation of high-gradient from low-gradient streams may be necessary to reduce the amount of variation indicators to make the assessment more sensitive to detecting impacts.

14. (Concluded).

Classification

Clean Water Act

Ecosystem

Functional assessment

Hydrogeomorphic

Impact analysis

Mitigation

Reference wetlands

Restoration

Section 404 Regulatory Program

Wetland