United States

Department of

Agriculture Guidelines for Evaluating Air

Forest Service Pollution Impacts on Class I

Pacific Southwest

General Technical

Research Station Wilderness Areas in California

Report PSW-GTR-136

David L. Peterson Daniel L. Schmoldt Joseph M. Eilers Richard W. Fisher

Robert D. Doty
Peterson, David L.; Schmoldt, Daniel L.; Eilers, Joseph M.: Fisher, Richard W.; Doty, Robert D. 1992. Guidelines

for evaluating air pollution impacts on class I wilderness areas in California. Gen. Tech. Rep. PSW-GTR136. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 34 p.

The 1977 Clean Air Act legally mandated the prevention of significant deterioration (PSD) of air quality related

values (AQRVs) on wilderness lands. Federal land managers are assigned the task of protecting these wilderness

values. This report contains guidelines for determining the potential effects of incremental increases in air pollutants

on natural resources in wilderness areas of the National Forests of California. These guidelines are based on current

information about the effects of ozone, sulfur, and nitrogen on AQRVs. Knowledge-based methods were used to

elicit these guidelines from scientists and resource managers in a workshop setting. Linkages were made between air

pollutant deposition and level of deterioration of specific features (sensitive receptors) of AQRVs known to be

sensitive to pollutants. Terrestrial AQRVs include a wide number of ecosystem types as well as geological and

cultural values. Ozone is already high enough to injure conifers in large areas of California and is a major threat to

terrestrial AQRVs. Aquatic AQRVs include lakes and streams, mostly in high elevation locations. Current sulfur and

nitrogen deposition is probably too low to warrant immediate concern in most areas (with the exception of nitrogen

deposition at some locations in southern California), although the low buffer capacity of many aquatic systems in

California makes them sensitive to potential future increases in acidity. Visibility is considered as a discrete AQRV.

Guidelines are presented for determining degradation of visibility based on sensitive views in wilderness areas.

Estimates of current deposition of ozone, sulfur, and nitrogen are compiled for all California wilderness areas.

Recommendations are included for resource monitoring, data collection, and decision criteria with respect to the

disposition of permit applications.

Retrieval Terms: acidic deposition, air pollution, air quality related values, ozone, wilderness, visibility

The Authors:

David L. Peterson is an Associate Professor of Forest Biology, National Park Service, Cooperative Park Studies

Unit, University of Washington, AR-10, Seattle, WA 98195. Daniel L. Schmoldt is a Research Forest Products

Technologist with the Southeastern Forest Experiment Station, USDA Forest Service, Blacksburg, VA 24061-0503.

Joseph M. Eilers is a Limnologist with E&S Environmental Chemistry, Inc., P.O. Box 609, Corvallis, OR 97339.

Richard W. Fisher is an Air Resource Specialist, USDA Forest Service, Washington, D. C., and stationed at the

Rocky Mountain Station, USDA Forest Service, 240 Prospect St., Fort Collins, CO 80526. Robert D. Doty is an Air

Resource Program Leader with the Pacific Southwest Region, USDA Forest Service, 630 Sansome St., San

Francisco, CA 94111.

Acknowledgments:

We thank the scientists and resource managers who participated in the South Lake Tahoe (California) workshop

(May 1-4, 1990) for sharing their data, concerns, and ideas. This publication is the result of their workshop

contributions, subsequent discussions, and review comments. Tom Nash of Arizona State University was particularly helpful in compiling information used in the section on lichens. June Rugh assisted with editing of the

manuscript.

Publiser:

Pacific Southwest Research Station

Albany, California

(Mailing address: P.O. Box 245, Berkeley, CA 94701-0245

Telephone: 510-559-6300)

November 1992
Guidelines for Evaluating Air Pollution Impacts on

Class 1 Wilderness Areas

in California

David L. Peterson Daniel L. Schmoldt Joseph M. Eilers Richard W. Fisher Robert D. Doty

Contents

In Brief ............................................................................................................................................. ii

Glossary of Acronyms ..................................................................................................................... ii

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

Legal Background of Managing Air Quality in Class I Wilderness ................................................. 2

WildernessAct ............................................................................................................................ 2

The Clean Air Act and the PSD Program ....................................................................................... 2

Atmospheric Deposition in California Class I Wilderness ................................................................ 3

Effects on Terrestrial Resources ....................................................................................................... 5

Vegetation .................................................................................................................................. 6

Ecosystems, AQRVs, and Sensitive Receptors ........................................................................ 6

Trees and Herbaceous Plants .................................................................................................. 6

Ozone ........................................................................................................................................ 6

Sulfur ......................................................................................................................................... 9

Nitrogen ................................................................................................................................... 10

Lichens .................................................................................................................................... 10

Interactions ............................................................................................................................... 11

Monitoring, Data Collection, and Criteria for Decisions on PSD Applications ............................... 12

Other Terrestrial Resources ........................................................................................................ 14

Prehistoric Rock Art ............................................................................................................ 14

Geological Features ............................................................................................................ 14

Threatened and Endangered Animals .................................................................................... l4

Human Response Relative to Wilderness Perceptions ............................................................ 14

Natural Odors ..................................................................................................................... 15

Pollutant odors ................................................................................................................... 15

Effects on Aquatic Resources ........................................................................................................ 15

Pollutant Interactions ................................................................................................................ 21

Monitoring, Data Collection, and Criteria for Decisions on PSD Applications .............................. 22

Effects on visibility ........................................................................................................................ 23

A Process to Manage Visibility in Class I Areas ........................................................................... 23

Example Application: Visibility AQRV for Desolation Wilderness ............................................. 27

Nighttime Visibility as an AQRV ............................................................................................... 27

Establishing Baseline Conditions ........................................................................................ 28

Determining Source Impacts ............................................................................................... 28

References .................................................................................................................................... 32
In Brief . . .

Peterson, David L.; Schmoldt, Daniel L.; Eilers, Joseph M.;

Fisher, Richard W.; Doty, Robert D. 1992. Guidelines for

evaluating air pollution impacts on class I wilderness

areas in California. Gen. Tech. Rep. PSW-GTR-136.

Albany, CA: Pacific Southwest Research Station, Forest

Service, U.S. Department of Agriculture; 34 p.

Retrieval Terms: acidic deposition, air pollution, air quality

related values, ozone, wilderness, visibility

Wilderness areas within National Forests are some of the last

remaining lands in the United States with minimal disturbance

by humans. Legislative mandates provide special protection for

wilderness in order to preserve ecosystems in perpetuity. Although wilderness lands are often thought of as pristine, they are

subject to potential impacts from various types of air pollutants.

The 1977 Clean Air Act (CAA) is a critical piece of legislation

that ensures the prevention of significant deterioration (PSD) of

air quality related values (AQRVs) in wilderness. Although

federal land managers (FLMs) are responsible for protecting

wilderness from damage caused by air pollution and other threats,

they have few tools for evaluating potential or actual air pollution effects.

This report contains guidelines to assist FLMs in determining

the potential effects of future increases in air pollutants on

terrestrial resources, aquatic resources, and visibility in wilderness areas of National Forests in California. The guidelines are

based on current information on the effects of ozone, sulfur, and

nitrogen on AQRVs. Guidelines were developed during a threeday workshop in South Lake Tahoe, California conducted by the

Pacific Southwest Region of the USDA Forest Service. The

workshop was an interdisciplinary effort between scientists and

resource managers, who worked cooperatively to develop guidelines that are technically rigorous and address management

concerns.

Linkages were made between air pollutant deposition levels

and the amount of deterioration of AQRV features with known

sensitivity to pollutants (sensitive receptors). AQRVs for terrestrial resources include abroad range of ecosystem types as well

as certain types of geological and cultural features. There is

particular concern about the potential impact of ambient ozone

on terrestrial resources. Ozone concentrations are already high

enough in some parts of California to cause reduced vigor in

sensitive conifer species. Increasing human population and use

of fossil fuels could exacerbate this problem. Sulfur and nitrogen deposition is too low in most of the state (with the exception

of nitrogen in parts of southern California) to cause much concern about effects on terrestrial resources. Aquatic resources are

probably not endangered by current levels of sulfur and nitrogen

deposition, although the low buffer capacity of some lakes and

streams makes them potentially sensitive to future increases in

acidic deposition. Visibility is an AQRV that is highly valued

by most visitors to wilderness. Guidelines are presented for

determining how visibility might be degraded for vistas in each

wilderness.

There are many other topics relevant to determining pollution

impacts in wilderness. An important first step is simply knowing

current deposition levels. These data are summarized for each

wilderness area in California. In some cases, additional information must be obtained in order to make a decision on whether

an additional increment of air pollution will cause a significant

effect on a resource. Recommendations are therefore included

for resource monitoring and data collection that will assist in

quantifying the relationship between pollutants and potential

impacts. Guidelines and associated information in this document will assist Forest Service managers in reviewing applications for permits that would increase pollution levels.

Glossary of Acronyms

ANC:

AQRV:

CAA:

DOC:

EPA:

FLM:

ILWAS:

IMPROVE:

JND:

LAC:

MAGIC:

NADP:

NAPAP:

NESCAUM:

NFS:

NPS:

NTN:

PM:

PSD:

QA:

QC:

TSP:

UTM:

VIT:

WLS:

Acid neutralizing capacity (alkalinity)

Air quality related value

Clean Air Act

Dissolved organic carbon

Environmental Protection Agency

Federal land manager

Integrated Lake and Watershed Acidification

Study

Integrated Monitoring of Protected Visual

Environments

Just noticeable difference

Limits of acceptable change

Model of Acidification of Groundwater in

Catchments

National Atmospheric Deposition Program

National Acid Precipitation Assessment

Program

Northeast States for Coordinated Air Use

Management

National Forest System

National Park Service

NationaI Trends Network

Particle rnass

Prevention of significant deterioration

Quality assurance

Quality control

Total suspended particulate

Universal Transverse Mercator

Visibility impairment table

Western Lake Survey

ii USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
Introduction

T

he development of guidelines to evaluate the effects of

air pollution on wilderness resources is an ambitious

task. It requires the assessment of a wide range of physical, chemical, and biological data as well as knowledge about

individual wilderness areas. It requires information on technical

scientific issues as well as input from resource managers. Furthermore, guidelines must be developed in the absence of all the

data that would be desirable for decision-making (Sigal and

Suter 1987).

In order to develop a screening procedure in an efficient and

cost-effective manner, a workshop was convened by the Pacific

Southwest Region (California and Hawaii) of the Forest Service

in South Lake Tahoe, California, May 1-4, 1990. This forum

was used to collect information, elicit expert knowledge from

participants, and summarize recommendations for wilderness

protection (Schmoldt and Peterson 1991).

There were approximately 50 workshop participants, including both scientists and resource managers (table 1). Participants

were organized into working groups to review and discuss air

quality related values (AQRVs), sensitive receptors, pollutant

loadings, and resource impacts. Each of the working groups

specialized in one of the following areas:

• Terrestrial effects (northern California wilderness Caribou, Marble Mountain, South Warner, Thousand Lakes, Yolla

Belly-Middle Eel)

• Terrestrial effects (Sierra Nevada wilderness: Ansel Adams,

Desolation, Domeland, Emigrant, Hoover, John Muir,

Mokelumne, Kaiser)

• Terrestrial effects (southern California wilderness: Agua

Tibia, Cucamonga, San Gabriel, San Gorgonio, San Jacinto, San

Rafael, Ventana)

• Aquatic effects (water quality)

• Aquatic effects (biota)

• Visibility

Forest Service land managers were responsible for: (1)

identifying and describing AQRVs in each class I wilderness,

and (2) defining the limits of acceptable change (LAC) in the

AQRVs that were identified as sensitive receptors. Scientists

helped to (1) identify sensitive receptors among the AQRVs

listed for class I wilderness areas, (2) describe their relative

susceptibility to air pollutant impacts, and (3) determine the

quantity of various pollutants expected to cause LAC to be

exceeded. Information was gathered on the sensitivity of AQRVs

to the effects of sulfur (S) and nitrogen (N) deposition, ozone

exposure, and particulate (with respect to visibility impairment). This report summarizes the results of the workshop.

Details on the workshop procedures and knowledge elicitation

techniques used to compile information were reported by

Schmoldt and Peterson (1991).

Table 1 —Participants in the workshop are listed by subgroup.

VEGETATION EFFECTS (Northern California Forests)

Suraj Ahuja Don Haskins

Tom Cahill Bill Hogsett

Cal Conklin Bob Musselman

Beth Corbin

VEGETATION EFFECTS (Sierra Nevada Forests)

Mike Arbaugh John Pronos

Diane Ewell Jim Shiro

Earl Franks Geroge Taylor

Luci McKee Susan Ustin

VEGETATION EFFECTS (Southern California Forests)

Andrzej Bytnerowicz Paul Miller

Carl Fox Tom Nash

Kathy Jordan Linda Riddle

Craig Mahaffey Judy Rocchio

AQUATIC EFFECTS (Water Quality)

Aaron Brown Andrea Holland

Jim Frazier George Ice

Bob Goldstein Dale Johnson

Bob Harris Mike McCorrison

AQUATIC EFFECTS (Biota)

Scott Conroy Matt Lechner

Malcolm Gordon Bruce McGurk

Maryanne Hackett Deborah Potter

Rick Jameson John Stoddard

VISIBILITY

Bob Bachman Dennis Inman

Cliff Benoit John O'Gara

Alan Ewert Joan Reynolds

Rich Fisher Will Richards

Francis Fujioka Tony Van Curen

Ron Henry

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 1
Table 2 —Examples of AQRVs sensitive receptors, and factors potentially

changed by air pollution.

Legal Background of Managing

Air Quality in Class I Wilderness

Class I wilderness areas1 managed by the USDA Forest

Service contain ecosystems and esthetic values that have the

potential to be degraded by existing or future air pollutant

emissions. The Clean Air Act (CAA) as amended in 1977

(Public Law 95-95)2 gives Federal land managers (FLMs),

including the Forest Service, ”... an affirmative responsibility y

to protect the air quality related values . . . within a class I

area.” Forest Service land managers need information to help

prevent unacceptable changes from new or increased pollutant

sources to AQRVS

3 within lands they are mandated to protect

(table 2). Information required by the Forest Service to protect

AQRVs in class I areas includes

• Components, or sensitive receptors (table 2), of the AQRVs

within class I areas most vulnerable to degradation from air

pollution.

• Acceptable limits of air pollution-caused changes (LAC)

for these sensitive receptors.

• The amount of various pollutants that could be expected to

cause more than the acceptable change in sensitive receptors.

• Legal mechanisms that empower Forest Service managers

in air resource management decision-making.

Wilderness Act

The Wilderness Act (Public Law 88-557) gives the Forest

Service the responsibility to manage designated wilderness to

preserve and protect wilderness integrity. The Wilderness Act

defines wilderness as “an area untrammeled by man” and “an

area of undeveloped Federal land retaining its primeval character and influence.” It is to be “protected and managed so as to

preserve its natural conditions.” “Untrammeled” means not

subject to human controls or manipulations that hamper the free

operation of natural forces. The regulations for managing wilderness and primitive areas state, “National Forest Wilderness

resources shall be managed to promote, perpetuate, and where

necessary, restore the wilderness character of the land.” The

National Forest Management Act (Public Law 94-558) gives the

Forest Service the authority to determine the management goals

and objectives for wilderness, including the protection of wilderness from external threats.

1Class I wildernesses are those wilderness areas more than 5000 acres (204 1

ha) that were in existence as of August 7, 1977, or any later expansions made to

these wildernesses. At other National Forest lands are class II, including new

wilderness.

2Legislation was passed by the US Congress in 1990 amending the Clean

Air Act. Protection is extended to land areas that are extensions of existing

wilderness, although other implications on the discussion presented here are not

clear at the present time.

3

42 U.S.C. 7475 (d)(2)(C)(ii) and (iii).

AQRV

Flora

Water

Soil

Visibility

Cultural/archaeological

values

Odor

Sensitive receptors Factors changed by air

pollution

Ponderosa pine, Growth, mortality,

lichens reproduction, visible

injury

Alpine lakes Total alkalinity, pH,

metal concentration,

dissolved oxygen

Alpine soils pH, cation exchange

capacity, base saturation

High usage vista Contrast, visual range,

coloration

Pictographs Decomposition rate

Popular hiking trail Ozone odor

The Wilderness Act and regulations developed to implement

it do not directly address air quality or air pollution impacts to

wilderness. However, they do provide guidance to the Forest

Service in determining what should be protected in wilderness

and to what degree. Although it may not be possible to manage

every wilderness in a natural state, each wilderness should be

maintained in as pristine a condition as possible within legal and

political constraints.

The Clean AirAct and the PSD

Program

The CAA Amendments of 1977 include a program for prevention of significant deterioration (PSD) of air quality. The

basic objective of the PSD program is to prevent substantial

degradation of air quality in areas that comply with national

ambient air quality standards, while maintaining a margin for

future industrial growth. Certain new or modified air pollution

sources must apply for a PSD permit from the appropriate air

regulatory agency before construction. In California some air

pollution control districts and counties have the authority to

manage the PSD permitting program; U.S. Environmental Protection Agency has authority for others.

A permit applicant is required to demonstrate that the proposed polluting facility will: (1) not violate national or state

ambient air quality standards, (2) use the best available control

technology to limit emissions, (3) not violate either class I or

class II PSD increments for sulfur dioxide, nitrogen dioxide, and

particulate, and (4) not cause or contribute to adverse impacts to

AQRVs in any class I area.

The PSD increments are allowable pollutant concentrations

that can be added to existing concentrations over a given time

period. The values chosen as PSD increments by Congress were

2 USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992
not selected on the basis of any existing information on concentration limits relative to specific resource values. Therefore, it

may be possible to exceed the legal class I increments without

causing any damage to a class I wilderness. It is also possible

that a class I wilderness could be impacted without exceeding

the increments. The role of the Forest Service manager is to

determine whether there is potential for additional air pollution

to cause more than the LAC in a sensitive receptor whether or

not the PSD increments have been exceeded. If a proposed

facility will not violate any class I increments, the Forest Service

can still recommend denial of a permit by demonstrating that

there will be adverse impacts in an AQRV in a wilderness.

Provisions for mitigation can be recommended by the Forest

Service or the agency that regulates permits.

The following questions must be answered in response to

PSD permit applications:

• What are the identified sensitive receptors within AQRVs in

each class I wilderness that could be affected by the new source?

• What are the LAC for the identified sensitive receptors?

• Will the proposed facility result in pollutant concentrations

or atmospheric deposition that will cause the identified LAC to

be exceeded?

The first two are land management questions that should be

answered on the basis of management goals and objectives for

wilderness areas. The third is a technical question that must be

answered on the basis of modeled analysis of emissions from the

proposed facility and available scientific data.

The permit application decision is the responsibility of the air

regulatory agency if PSD increments are not exceeded. The

Forest Service may determine that the proposed facility will

result in a change in a sensitive receptor within a wilderness

beyond an identified LAC, but the regulatory agency has the

authority to make the final decision.

If the proposed facility will cause a violation of the class I

increments, the PSD permit can still be issued if the applicant

demonstrates to the satisfaction of the Forest Service and air

regulatory agency that the facility will not create an adverse

impact on a class I area. The permit can be issued even if the

proposed facility will cause a violation of a class I increment and

the applicant cannot demonstrate that the facility will not create

an adverse impact. In this case, the governor of the state containing the proposed facility must recommend approval and transmit

this recommendation to the President of the United States. The

President is able to approve or deny the permit application after

reviewing the recommendations.

The exceedance or non-exceedance of class I increments

determines which party has the burden of proof in demonstrating

whether a particular new pollutant source would compromise

identified wilderness management goals and objectives. The

burden of proof is with the applicant if the PSD increments are

predicted to be exceeded. The burden of proof rests with the

Forest Service air resource manager if the increments are predicted to not be exceeded.

Coordination between the Forest Service and the air regulatory agency is required in decisions on PSD permits. In nearly all

cases, the air regulatory agency makes the final determination to

grant or deny a PSD permit. However, the Forest Service, not the

air regulatory agency, is authorized to define LAC to sensitive

receptors of AQRVs in class I wilderness. The Forest Service

must be able to provide timely, credible, and effective recommendations to state air regulatory agencies in order to protect

wilderness from potential air pollution effects.

Forest Service air resource managers clearly have legal

mechanisms available to help them protect class I wilderness

from air pollution impacts. The CAA is a tool that can be

implemented to meet the management goals and objectives of

the Wilderness Act and the National Forest Management Act.

Forest Service managers facilitate the PSD process by: (1)

making management decisions on which components of the

wilderness should be protected from air pollution impacts, (2)

providing high-quality information on the existing condition

of AQRVs, atmospheric deposition, and air chemistry in wilderness, and (3) understanding the state PSD permitting process. The development and implementation of air resource

monitoring programs by the Forest Service can help to ensure

the protection of wilderness resources from the impacts of air

pollution and other human activities.

Atmospheric Deposition in

California Class I Wilderness

California covers a large land area that ranges from coastal

environments along the Pacific Ocean to high peaks in the Sierra

Nevada and other mountain ranges. Class I wilderness areas are

located throughout the state (fig. 1). Climate and atmospheric

circulation patterns vary considerably, although the state generally has a Mediterranean climate regime, with most of the annual

precipitation falling between October and March.

The pollution climate of an area is influenced by: (1) regional

and local emissions of air pollutants and (2) regional and local

meteorology. The physical and chemical states of the atmosphere determine the dispersion, transport, chemical transformation, and deposition of air pollutants. In many cases, meteorology is more important than atmospheric chemistry in determining the place at which, and the form in which, pollutants are

deposited (e.g., Cape and Unsworth 1987).

Atmospheric conditions in California tend to be relatively

stable with dominant high pressure systems and strong inversions in valley locations. These conditions are conducive to the

accumulation of pollutants (nitrogen [N] and sulfur [S] compounds, hydrocarbons). Nitrogen oxides and hydrocarbons from

fossil fuel combustion are photochemically oxidized and transported from metropolitan and industrial areas to adjacent mountain locations (Carroll and Baskett 1979, Ewell and others 1989,

Seinfeld 1989). Ozone, a product of this oxidation, is generally

considered the most phytotoxic component of air pollution in

California.

Estimates of pollutant loadings to an area usually require a

detailed analysis of (1) emissions, (2) transport, dispersion, and

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 3
FOREST SERVICE

R5 Californi a

Mandatory Class I

Designation

31. Aqua Tibia Wilderness

32. Caribou

33. Cucamonga

34. Desolation

35. Domeland

36. Emigrant

37. Hoover

39. John Muir

40. Kaiser

44. Marble Mountain

45. Ansel Adams

46. Mokelumne

50. San Gabriel

51. San Gorgonia

52. San Jacinto

53. San Rafael

54. South Warner

55. Thousand Lakes

56. Ventana

57. Yolla Bolly-Middle Eel

Forest(s)

Cleveland

Laasen

San Bernardino

LTBMU/Eldorado

Sequoia

Stanislaus

Inyo/Toiyabe (R4)

Inyo/Sierra

Sierra

Klamath

Inyo/Sierra

Eldorado/Stanislaus

Angeles

San Bernardino

San Bernardino

Las Padres

Modoc

Lassen

Los Padres

S-T

MANDATORY CLASS I WILDERNESS

AREAS ON NATIONAL FOREST LANDS

Figure 1 —Location of class I wilderness on Forest Service lands in California. (LTBMU=Lake Tahoe Basin Management Unit; R4=Region 4;

S-T=Shasta-Trinity)

4

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
chemical transformation of the pollutants in the atmosphere, and

(3) deposition processes and the relative roles played by each

process in the total deposition of pollutants. Such an analysis can

be based on statistical techniques of extrapolation or on atmospheric modeling.

The California Air Resources Board maintains a network of

air pollution monitoring stations in metropolitan and valley

locations that can be used to infer air pollution exposure in

adjacent wildland areas. These data are summarized in the annual publication California Air Quality Data (California Air

Resources Board 1989). A limited amount of air quality data

collected by the USDA Forest Service and National Park Service from mountain locations can be used to verify these inferences. Pollutant exposure is generally considered severe in the

Los Angeles Basin area of southern California where high

emissions are confined topographically, and ozone concentrations and N deposition are especially high. Pollutant concentrations are moderate in the southern Sierra Nevada, where ozone is

the major problem. The northern half of the state has relatively

low pollutant levels because of lower emissions, less restrictive

topography, and more active atmospheric mixing.

There are few data on air pollution exposure from montane

locations or class I wilderness in California. There are large

differences in climate and deposition processes (e.g., snow vs.

rain, cloud frequency) between monitoring sites and wilderness

areas, because of differences in elevation. Air quality data from

one site or a large region are therefore not necessarily representative of specific sites in wilderness. Statistical extrapolation of

monitoring data is compromised by lack of information on

pollutant concentrations at high elevations and little information

on the different mechanisms influencing deposition at high rather

than low elevations.

Even with these constraints, it is necessary to have some

estimate of current deposition levels in class I areas in order to

evaluate the current and future condition of natural resources.

Pollution loadings in class I areas of California were estimated

by a workshop subgroup (Bob Bachman, Tom Cahill, Diane

Ewell, Paul Miller, Tony Van Curen) that used the best existing

data to infer exposure to ozone, N, and S. The analysis integrated

monitoring data and information from local experience and the

literature. The following sources were used to compile air pollution loadings: Ashbaugh and others (1989), Böhm (1989, in

press), Böhm and Vandetta (1990), Cahill (1989), Cahill and

others (1990), California Air Resources Board (1989), Fenn and

Bytnerowicz (1991).

Annual N deposition is based on ammonium and nitrate

concentrations, including both wet and dry deposition. Annual S

deposition is based on sulfate concentrations, including both wet

and dry deposition. Ozone data are given as a 24-hour average

concentration for the period May through October. Air pollutant

loadings are summarized in table 3. Most values in table 3 are

not direct measurements, but inferences from various data sources,

most of which are from lower elevation locations. Interpolation

of isopleths of pollutant concentrations was used in many cases,

in addition to professional judgment and knowledge about specific areas. Dry deposition for high-elevation class I areas is

estimated as 50 percent of low-elevation measurements, because

of a known reduction in particle transport of approximately this

magnitude. Dry deposition of N for class I areas in the Los

Angeles Basin is much higher than for other areas in California

because of high nitric acid inputs (as high as 80 percent of total N

input). Nitrogen deposition for the San Gabriel, San Gorgonio,

and San Jacinto Wildernesses are estimates based primarily on

data in Fenn and Bytnerowicz (1991), adjusted for the location

of each wilderness. Values in table 3 are appropriately listed as

ranges; they should be considered estimates only, not exact

measurements.

Effects on Terrestrial Resources

The effects of air pollutants on natural resources have been

studied for at least 50 years. The sensitivity of plant species to

abnormally high exposures of ozone, N, S, and other pollutants has been the focus of many of these studies. Sulfur

concentrations are relatively low in California compared to

the eastern United States, and N deposition is high only at

some locations adjacent to the Los Angeles Basin. However,

ozone concentrations are high enough to cause plant injury

over large areas of the state.

Table 3 —Estimates of pollutant deposition for each class I wilderness in

California are listed for total annual nitrogen (N), total annual sulfur (S), and

mean ozone concentration (24-hour mean, May through October)1

Wilderness

Agua Tibia

Ansel Adams

Caribou

Cucamonga

Desolation

Domeland

Emigrant

Hoover

John Muir

Kaiser

Marble Mountain

Mokelumne

San Gabriel

San Gorgonio

San Jacinto

San Rafael

South Warner Mountain

Thousand Lakes

Ventana

Yolla Bolly-Middle Eel

N S Ozone

kg/ha/yr

2.9 - 4.8

2.0 - 2.7

1.3 - 1.7

3.8 - 5.2

2.0 - 2.7

2.4 - 2.9

2.0 - 2.7

2.0 - 2.7

2.4 - 2.9

2.4 - 2.9

0.3 - 0.9

2.0 - 2.7

20-30

20 - 30

5 - 15

1.4 - 2.1

0.5 - 1.1

1.3 - 1.7

1.4 - 2.0

0.9 - 1.4

kg/ha/yr

0.9 - 1.1

0.6 - 0.9

0.4 - 1.2

1.0 - 1.2

0.6 - 1.4

0.8 - 0.9

0.6 - 0.9

0.6 - 0.9

0.8 - 0.9

0.8 - 0.9

0.1 - 0.4

0.6 - 0.9

1.0 - 1.2

1.0 - 1.2

1.0 - 1.2

0.5 - 1.1

0.2 - 1.0

0.1 - 0.4

0.6 - 0.9

0.5 - 0.7

ppb

40 - 70

22 - 50

9 - 36

70 - 100

22 - 50

50 - 60

22 - 50

22 - 50

22 - 50

20 - 60

9 - 36

22 - 50

70 - 100

70 - 100

60 - 90

40 - 60

22 - 50

22 - 50

20 - 40

22 - 50

1Ranges are used to quantify estimates, because data are generally not based

on measurements in specific wilderness areas. See section on atmospheric

deposition for methods used to calculate deposition.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 5
During the 1980's there was a major research effort in North

America and Europe to evaluate forest health and vigor. The

motivation for this research effort was increased awareness of

the concept of “forest decline,” and of how stress in forest

ecosystems might be affected by atmospheric deposition, including acidic precipitation and ozone (Smith 1984). Much of

this work focused on documenting the physiological and growth

status of forest stands, and on establishing dose-response relationships under experimental conditions for economically important tree species. There has been less emphasis on the effect

of pollutants on organisms such as lichens and mosses. Relatively few taxa of higher plants were evaluated in these studies,

and the difficulty of identifying physiological stress in the field

has made it difficult to quantify the relationship between pollutants and specific organisms or processes.

The terrestrial subgroup of the workshop initially determined that they would address two different classes of AQRVs.

One class consists of vegetation; the other class consists of all

other terrestrial resources, including geological and cultural

features. These classes were evaluated separately with respect

to pollutant effects and guidelines. Generic guidelines were

developed that apply to all class I areas in California, because

there is insufficient information to justify guidelines for specific wilderness areas.

Vegetation

Ecosystems, AQRVs, and Sensitive Receptors

It was determined that ecosystems are the most appropriate

representative of AQRVs in California wilderness. A limited

number of systems are identified across different wilderness

locations, despite minor differences in structure and species

composition. Some of the “ecosystem” designations more closely

approximate plant “communities” or “associations,” but these

distinctions are not critical for this application. The main objective is to use a designation that can be readily used to identify

discrete AQRVs.

Fifteen ecosystem types arc used to represent specific AQRVs

in California. These types are intended to encompass the range

of terrestrial communities that might be found at any location,

including areas such as intermittent riparian zones. These ecosystem types are:

Alpine ---------------------------------- AL

Bigcone Douglas-fir ------------------ BD

Buckwheat / lichen / grass ----------- BL

Chaparral ------------------------------ CH

Desert ---------------------------------- DE

Digger pine / oak ---------------------- DP

Juniper shrubland --------------------- JS

Mixed conifer ------------------------- MC

Montane forest ------------------------ MF

Oak woodland ------------------------- OW

Pinyon pine / juniper ----------------- PJ

Redwood ------------------------------- RE

Riparian -------------------------------- RI

Sagebrush ------------------------------ SA

Subalpine forest ----------------------- SF

6

These ecosystems are distributed among the class I wilderness

areas as shown in table 4. The higher elevation systems such

as alpine, subalpine forest, and mixed conifer forest are the

most common types, and most others have relatively low

representation.

Sensitive receptors identified within each of the AQRV ecosystems (table 5) represent species or groups of species. Only

those species for which some information was available on

sensitivity to pollutants, or whose sensitivity could be inferred

from studies of related species, were identified. Some of the

groups, such as lichens and herbaceous species, include a large

number of species. They are included as sensitive receptors,

because at least some species within these general categories are

known to be sensitive to pollutants.

Trees and Herbaceous Plants

More information is available on ozone effects on plants than

on N and S effects. In fact, much of the research on ozone effects

has been conducted in the mixed conifer forest and other vegetation types of California, and studies have tended to focus on

dominant species in those areas (e.g., Miller and others 1989;

D.L. Peterson and others 1987, 1991). There are few data that

relate pollutant exposure to growth or other characteristics of

mature trees, and almost no data for herbaceous species. As a

result, guidelines were established to be general enough to apply

to all species with respect to potential stress from air pollutants.

Ozone

Exposure of plants to elevated levels of ozone can produce

several quantifiable effects, including visible injury, reduced

photosynthetic capacity, increased respiration, premature leaf

senescence, and reduced growth (Miller and others 1989, Patterson

and Rundel 1989; D.L. Peterson and others 1987, 1991; Pronos

and Vogler 1981; Reich and Amundson 1985). The seventy of

effects depends on pollutant concentration, duration of exposure, and other environmental factors. Sensitivity to ozone and

other stresses varies within and among species because of differences in uptake (Reich 1987) and genetic factors (Karnosky and

Steiner 1981).

The immediate effects of elevated ozone levels in wilderness

areas are expected to be one or more of the following: foliar

injury, decreased leaf longevity, reduced carbon gain of foliage,

and reduced plant growth. Other effects could include alteration

of carbon allocation, greater susceptibly to environmental stress

(such as low soil moisture, insects, and fungi), changes in plant

community composition, and loss of sensitive genotypes from a

population (Fox and others 1989, Treshow 1984).

Although a change in histological and physiological processes (for example, photosynthesis) is probably the earliest

detectable evidence of pollutant stress, visible signs of damage

(for example, chlorosis, leaf senescence) are easier and more

practical to detect in class I areas. Much of the existing data on

ozone stress in conifers has been compiled for ponderosa pine

and Jeffrey pine, which are sensitive to elevated ozone concentrations. Injury levels have been established for these species

with respect to chlorotic injury and needle longevity based on

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
Table 4 —Air quality related values (AQRVs) for regeneration are listed by ecosystem type for each class I wilderness in California.

1AL, alpine; BD, bigcone Douglas-fir; BL, buckwheat/lichen/grass; CH, chaparral; DE, desert; DP, digger pine; JS, juniper

shrubland; MC, mixed conifer; MF, montane forest; OW, oak woodland; PJ, pinyon pine/juniper; RE, redwood; RI, riparian; SA,

sagebrush; SF, subalpine forest

studies conducted in the Sierra Nevada and San Bernardino

Mountains of California (Duriscoe and Stolte 1989, Miller and

others 1989, Pronos and others 1978). These and other data

collected by these authors are the best information available on

field level analysis of pollutant stress. Additional experimental

data on the effects of ozone on seedlings are available for some

conifers found in California (Hogsett and others 1989).4 These

data sources were used to develop condition classes for all

conifers considered sensitive receptors, even though data are not

available for all species. Limited experimental data for conifer

seedlings indicate differences in sensitivity among species (table

6). For example, ponderosa pine is more sensitive to ozone than

is incense-cedar.

4Unpublished data from P.R. Miller, Pacific Southwest Research Station,

Riverside, California.

Four condition classes were established with respect to ozone

effects on trees: no injury, slight injury, moderate injury, and

severe injury. These condition classes are based on a per tree

evaluation. A given stand can have trees in multiple condition

classes, so overall stand condition can be stated as percentages

of each condition class. Acceptable distributions of condition

classes can be set; or, alternatively, the condition of a stand can

be defined conservatively as being synonymous with the tree

with the most severe condition class. The same condition classes

are used for different species because (1) there is insufficient

information to confidently infer sensitivity in mature trees, and

(2) generic condition classes based on sensitive species are

conservative enough to provide maximum protection for all

species. Condition classes and ozone concentrations associated

with those classes (Miller and others 1983)4 are as follows:

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 7
Table 5 —Sensitive receptors are indicated for each of the air quality related value (AQRV) ecosystems.

8

1AL, alpine; BD, bigcone Douglas-fir; BL, buckwheat/lichen/grass; CH, chaparral; DE, desert; DP, digger pine; JS, juniper

shrubland; MC, mixed conifer; MF, mountain forest; OW, oak woodland; PJ, pinyon pine/juniper; RE, redwood; RI, riparian; SA,

sagebrush; SF, subalpine forest.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136, 1992.
Table 6 —Sensitivity of tree species to ozone, S, and N pollution1

.

Sensitive receptor

Ponderosa pine

Jeffrey pine

White fir

Incense cedar

Calif. black oak

Douglas-fir

Bigcone Douglas-fir

W. white pine

LodgePole pine

Limber pine

Huckleberry oak

Aspen

Alders

Sugar pine

Whitebark pine

Foxtail pine

Pacific silver fir

Mountain hemlock

Red fir

Digger pine

Cottonwoods

Junipers

Coast redwood

Pinyon pine

Santa Lucia fir

Sensitivity

Ozone Sulfur Nitrogen

H H H

H H H

M H H

L

M

M H H

L

L-M

M H H

M

L

H

M

1Ratings are based on Davis and Wilhour (1976), Miller and others (1983),

Hogsett and others (1989)2

, and personal knowledge of workshop participants.

Sensitivity to S and N are based primarily on experimental exposures to acidic

fog, SO2 and NO2

. Sensitivity ratings are: high (H), moderate (M), and low (L).

Blanks indicate that there is insufficient information to rate sensitivity.

2Unpublished data from P.R. Miller, Pacific Southwest Research Station,

Riverside, California.

Condition Needle age class Needle retention Ozone concentration

class with chlorotic as percent of (7-hr growing

mottle normal season mean)

years pct ppb

No injury None >80 <60

Slight injury ≥ 5 71-80 61-70

Moderate injury 3-4 41-70 71-90

Severe injury 1-2 <40 >90

This table has been developed with data from pine species

and is therefore more accurate for pines than for other species.

The table can be applied cautiously to other conifers as well.

However, the needle age class should not be used because some

species retain marry years of needles (up to 18 years in white fro).

The condition classes listed above are based on visible injury

characteristics that can be observed in the field. The relationship

of these condition classes to tree growth is unknown, although it

has been shown for Jeffrey pine that photosynthesis is reduced

50 percent when 30 percent of needles show chlorotic mottle

(Patterson and Rundel 1989). Only detailed long-term monitoring of many mature trees would establish the relationship between growth and ozone exposure (Peterson and Arbaugh 1988;

D.L. Peterson and others 1987, 1991).

Some areas of the Sierra Nevada and southern California are

subject to episodes of high ozone concentration during periods

of atmospheric stability. The effect of these occasional pulses of

pollutants on conifers is poorly quantified, but may produce

substantial stress and affect the condition class of trees (Hogsett

and others 1989). No guidelines are offered here with respect to

these ozone episodes because there are no data on which to base

them. The potential effects of these episodes on plants should be

considered, however, when considering the impacts of ozone

exposure on wilderness. Probability y of effects will likely be

greater downwind from large metropolitan areas.

Hardwood tree species have different leaf injury symptoms

than conifers, and there are few data available on the effects of

ozone on hardwoods (Jensen and Masters 1975). The condition

classes for hardwoods are similar to those for conifers, and an

additional class has been added:

Condition Percent of leaf area Ozone concentration

class with chlorotic mottle (7-hr growing season mean)

pct ppb

No injury 0 <45

Very slight injury 1-20 45-70

Slight injury 21-40 71-90

Moderate injury 41-60 91-120

Severe injury 60-100 >120

Because there are few data on which to base ozone effects on

hardwoods, the condition classes and associated ozone levels are

less reliable than for conifers. The higher ozone concentrations

for hardwood condition classes reflect somewhat less sensitivity

than in conifers, although injury should be considered on a

species-by-species basis if data are available.

There are so few data on the effects of ozone on herbaceous

and grass species in California that it is difficult to define condition classes. Native species for which there is some information

about ozone sensitivity include sweet-cicely (Osmorhiza

brachypoda) (high sensitivity), squawbush (Rhus trilobata) (high),

and perennial ryegrass (Lolium perenne) (moderate).4 Cultivated grasses with known sensitivity include timothy (Phleum

pratense) (high), orchardgrass (Dactylis glomerata) (high), and

fescue (Festuca sp.) (low).5 These data are insufficient to make

generalizations about all herbaceous species and grasses. The

condition classes for hardwood species can be applied cautiously to herbaceous species until additional data are available.

Sulfur

There are very few data on the effects of S compounds on

mature trees or other native plants, and there is a wide range of

sensitivities to ambient S compounds (Davis and Wilhour 1976,

Westman and others 1985). Limited data on tree seedlings (Hogsett

and others 1989)5 indicate that SO2 concentrations below 20 ppb

(24-hour mean) do not produce visible injury symptoms. Slight

injury is found in ponderosa pine and lodgepole pine above 40

ppb and moderate injury above 65 ppb. Slight injury is found for

Douglas-fir above 65 ppb. It is difficult to set condition classes

for California plant species on the basis of these data, so only

general guidelines are suggested. In order to maximize protection of all plant species, maximum SO2 concentrations should

5Unpublished data from W. Hogsett, U.S. Environmental Protection Agency,

Corvallis, Oregon.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 9
not exceed 40-50 ppb, and annual average SO2 concentrations

should not exceed 8-12 ppb.

Despite the lack of good quantitative information, the relative

sensitivity of some California tree species to SO2 can be ranked

(Davis and Wilhour 1976). This list can be referred to if a greater

level of resolution is needed. Sensitivity to SO2 is as follows,

listed from most to least sensitive: Douglas-fir, lodgepole pine,

ponderosa pine, Western white pine, Pacific silver fir, white fir,

juniper (several species), limber pine, pinyon pine.

Total S loadings are relatively low in most of California,

although there are some areas adjacent to smelters and power

plants where total S deposition is locally high. The effects of S

deposition, especially sulfates, are often mediated through soil

processes such as cation exchange. Deposition must be high to

produce potentially toxic effects. Fox and others (1989) determined that 20 kg S/ha/yr is the maximum long-term deposition

that can be tolerated without impacts in most terrestrial ecosystems, on the basis of several assumptions about cation exchange

capacity and mineral weathering rates. Effects are very unlikely

below 5 kg/ha/yr. In the absence of additional data, these general

guidelines can be used for California as a first approximation.

However, soil properties vary among locations, and it is important to consider soil effects with respect to specific wilderness

areas.

Nitrogen

There are few data on the effects of nitrogen dioxide (NO2) on

plant species in California; however, scattered data from scientific studies in the United States and Europe can be used to

establish some general guidelines for injury and exposure (Davis

and Wilhour 1976, J. Peterson and others 1992, Smith 1990,

Treshow 1984):

Condition class NO2 concentration

(24-hr annual mean)

ppb

No injury <15

Potential injury 15-50

Severe injury >50

These values were defined for all plant species in California and

should be used only as general guidelines. Individual plant

species have a wide range of sensitivities.

Nitrogen is a critical nutrient for many plant metabolic

processes. Nitrogen deposition in the form of nitrate or ammonium can increase plant growth in some cases. Long-term

deposition of elevated levels of nitrogen compounds may

affect soil microbiological processes, resistance to insect and

pathogens, winter injury in conifers, and foliar leaching. Perhaps more important are the potential effects of long-term N

deposition on ecosystem structure and diversity. Nitrogen is a

potential fertilizer that can be assimilated preferentially by

some plant species. For example, plant species in a N-poor

system such as a bog may be replaced by species with higher

N requirements. Based on limited data on ecosystem effects

(Fox and others 1989), generic condition classes can be set for

different vegetation types as follows:

Vegetation type Total N deposition (kg/ha/yr)

No injury Potential injury Severe injury

Coniferous forest <3 3-15 >15

Hardwood forest <5 5-20 >20

Shrubs <3 3-5 >5

Herbaceous plants <3 3-10 >10

These general guidelines do not account for variation in plant

sensitivity. It is also known that acidic fog, which contains S

and N compounds, has the potential to alter the growth of

seedlings of some California tree species (Hogsett and others

1989, P.R. Miller unpublished data4

). These effects do not

generally occur under experimental conditions unless pH is

below 3.5. Fog acidity less than 3.5 has been measured in the

San Gabriel Mountains of southern California (Hoffman and

others 1989). Unfortunately there are too few data on cloud

chemistry and the effects of acidic fog on plants to set guidelines for acidity at this time.

Lichens6

Lichens are known to be sensitive receptors for air pollution, as determined by a variety of studies (Ferry and others

1973, Galun and Rohnen 1988, Nash and Wirth 1988, Ross

1982, Ryan and Rhoades 1991, Sigal and Nash 1983). Water

and gas exchange proceed uninhibited over the entire surface

of a lichen because there are no stomata or cuticles to exclude

gases. Lichens grow slowly and can live for centuries, and are

therefore exposed to pollution for a long period of time. In

addition, lichens tend to concentrate heavy metals and other

elements, and are not capable of shedding parts of the thallus

injured by toxic gases. Lichens reflect the cumulative effects

of air pollution over time, not just the acute effect of a given

concentration.

Lichens are often the most sensitive component of the vegetation within a given ecosystem, and can have predictive value in

assessing future effects on vascular plants. Reduced vigor of

lichens may have direct impacts on an ecosystem, because of

their importance for N-fixation, soil stabilization, rock weathering, and food for animals.

There is a wide range of sensitivity of lichens to various types

of air pollutants, although sensitivity is poorly quantified with

respect to dose-response relationships. There is more information on sensitivity to SO2 and ozone than sensitivity to nitrogen

oxides (NOX) or fluoride. Four classes of lichen sensitivity to air

pollution can be defined: very sensitive, sensitive, tolerant, and

very tolerant. These classes can be associated with pollutant

exposure as follows:

6The information in this section was compiled with the assistance of Tom

Nash, professor, Arizona State University, Tempe, Arizona.

10 USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
Pollutant Sensitivity class

Very sensitive Sensitive Tolerant Very tolerant

Ozone (ppb)1 ≤ 20 21-40 41-70 >70

Sulfur (kg/ha/yr) ≤ 1.5 1.5-2.5 2.6-3.5 >3.5

Nitrogen (kg/ha/yr) ≤ 2.5 2.6-5.0 5.1-7.0 >7.0

1Ozone concentration is the 7-hour mean for May-October.

These sensitivity classes are based on pollutant effects on

Hypogymnia enteromorpha, which commonly grows on trees in

the mixed conifer forest of California. Morphological and reproductive changes have been measured in this species under field

and experimental conditions (Nash 1988, Nash and Sigal 1979,

Nash and Sigal 1980, Sigal and Nash 1983). The classes with

respect to ozone exposure can be characterized in some detail for

H. enteromorpha and for other species in somewhat less detail

(table 7). Ozone exposures at the highest level (> 70 ppb) have

caused the loss of up to 50 percent of all lichen species present in

some areas of mixed conifer forest in southern California (Sigal

and Nash 1983). It is assumed that morphological changes observed in the field in southern California are, in fact, caused by

ozone rather than by N or S pollution.

A comprehensive list of lichens in California wilderness is

beyond the scope of this document. However, the more common

species, their sensitivity class with respect to ozone sensitivity,

and location are summarized here in order to aid assessments of

potential impacts (tables 8-10). Morphological criteria associated with condition classes for ozone exposure can also be

applied cautiously to effects of exposure to S and N in the

absence of other criteria, although the species’ sensitivities may

be completely different. Limited experimental and field data on

the effects of S pollution on lichens indicate a range of sensitivities for the following species found in California (from most to

least sensitive): Evernia prunastri, Hypogymnia sp., Usnea sp.,

Bryoria sp., Parmelia sp.) (Nash 1988). There is considerable

variation among studies with respect to species’ sensitivities.

More experimental work is necessary to clearly differentiate the

effects of small amounts of S pollution. There are insufficient

data on the effects of N pollution to compile even a relative

ranking of sensitivity.

Interactions

The potential for interactions between pollutants should be

considered when evaluating effects of pollutants on natural resources. Three general types of interactions are (1) pollutantPollutant, (2) pollutant-natural stress, (3) and pollutant-genotype. An interaction occurs when the presence of one stress

modifies the response to a second stress such that the effect is not

additive. The interaction can be antagonistic (less than additive)

or synergistic (greater than additive). This can occur as the

interactive effects of two gases, such as ozone and SO2

, on

photosynthesis and growth. It can also occur as the interaction of

a pollutant and natural factors, such as ozone stress, drought, and

bark beetles; this interaction has been documented for conifers

in southern California. It is probably beyond the scope of the

PSD process to identify pollutant-genotype interactions, but it is

important to recognize that there is differential sensitivity within

and between populations. There are very few data on stress

interactions for pollutants and plant species in California. Limited data on lichens suggest that there are likely synergistic

interactions for ozone/SO2 (DeWit 1976) and ozone/NOx (Sigal

and Nash 1983). Although it is difficult to make generalizations,

situations can be identified for which interactions are likely

(table 11).

Table 7 —Sensitivity classes for lichens with respect to ozone exposure are defined in terms of (1)

morphological changes in Hypogymnia enteromorpha, and (2) relative presence of other species.

Sensitivity Ozone Description

class conc.

1

Hypogymnia Other species

ppb

Very sensitive <20 - Generally not bleached or - Very sensitive species

convoluted common

- Fertility >75 pct

Sensitive

Tolerant

Very tolerant

21-40 - Majority not bleached, but large - A few very sensitive species

percentage bleached absent

- Most thalli slightly convoluted - Sensitive species common

- Fertility 65-85 pct

41-70 - Majority slightly bleached -Some very sensitive species

- Unconvoluted to moderately absent

convoluted - A few sensitive species

- Fertility 40-65 pct present (Usnea sp.)

- Tolerant and sensitive

species more common

>70 - Moderately to highly bleached - A few very tolerant species

- Moderately to highly convoluted common (Parmelia subolivacea,

- Fertility <40 pct P. multispora)

-50 pct of all species absent

1 Ozone concentration is the 7-hour mean for May-October.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 11
Table 8 —Sensitivity classes for lichen species found in mixed conifer forest in

southern California wilderness.

Table 9 —Sensitivity classes for lichen species found on oaks in oak woodland

in southern California wilderness.

Sensitivitv class

Conifers

Very sensitive1

Sensitive 2

Tolerant

Very tolerant

Oaks (primarily

California black oak)

Very sensitive1

Sensitive 2

Tolerant

Very tolerant

Lichen species

Alectoria sarmentosa

Bryoria abbreviate

Bryoria fremontii

Bryoria oregana

Calcium virile

Cetraria canadensis

Evernia prunastri

Platismatia glauca

Cetraria merrillii

Cladonia sp.

Parmelia quercina

Ramalina farinacea

Usnea sp.

Hypogymnia enteromorpha

Letharia vulpina

Evernia prunastri

Pseudocyphellaria anthraspis

Collema nigrescens

Parmelia sulcata

Parmelia quercina

Phaeophyscia ciliata

Usnea sp.

Parmelia (Melanelia) glabra

Parmelia (Melanelia) subolivacea

Parmelia (Melanelia) multispora

Parmelia (Melanelia) elegantula

Physconia grisea

Xanthoria fallax

1 Species in the very sensitive class are no longer found in the mountains

adjacent to the Los Angeles Basin.

2 Species in the sensitive class are found only in small amounts in the

mountains adjacent to the LOS Angeles Basin.

Monitoring, Data Collection, and

Criteria for Decisions on PSD

Applications

As indicated above, there are few data on which to base

current guidelines for evaluating PSD applications. More data

are needed to improve the quantitative rigor of these guidelines.

Constraints on time and money will always limit scientific efforts in this area so it is important to set priorities for data needs

with respect to estimating pollution impacts and evaluating PSD

applications.

It is extremely difficult and costly to determine the effects of

air pollutants on entire AQRVs or ecosystems. It is therefore

appropriate to focus on specific components, such as sensitive

receptors, that have the greatest potential sensitivity to air pollution. For example, an applicant whose pollution source may

contribute to elevated levels of ozone should survey the existing

and future condition of ponderosa pine, which is known to be

sensitive to this gas. Several lichen species are known to be

sensitive to elevated concentrations of ozone, so lichens maybe

another sensitive indicator of pollutant effects.

Sensitivity class

Very sensitive1

Sensitive2

Tolerant

Very tolerant

Lichen species

Evernia prunastri

Peltigera collina

Pseudocyphellaria anthraspis

Ramalina farinacea

Ramalina menziesii

Collema nigrescens

Leptogium californicum

Parmelia quercina

Parmelia sulcata

Parmelia (Melanelia) glabra

Xanthoria polycarpa

Physcia biziana

Physcia tenella

Physconia grisea

Xanthroia fallax

1 Species in the very sensitive class are no longer found in the mountains

adjacent to the Los Angeles Basin.

2 Species in the sensitive class arc found only in small amounts in the

mountains adjacent to the Los Angeles Basin.

The recent effort by scientists and policy makers to understand effects of acidic deposition on ecosystems has produced

several models of plant and ecosystem response (for example,

Gay 1989). In the future, these or other models maybe appropriate for predicting ecosystem-specific effects of new sources.

One of the goals of protecting wilderness should be to apply

appropriate models to identify the sensitivity of various features

of AQRVs to air pollutants. This could greatly expedite decisions about potential effects if large amounts of data from a

specific wilderness are not available.

In general, there are few air quality monitoring data for

wilderness areas in California. The monitoring network is located mostly in and near metropolitan areas, with few measure_

ments in mountain locations near class I areas. Improving this

network in wildland areas would have a large immediate impact

on our knowledge of atmospheric deposition in class I areas in

California. For example, the few data that exist on cloud chemistry suggest that cloudwater at high elevations can be highly

acidic in some cases, although the level of exposure and potential for biological impacts are unknown. A research and monitoring effort in this area would be an important contribution. The

placement of additional monitors should be optimized to provide

data that will be applicable over relatively broad geographic

areas. Protocols should be established for data collection and

analysis to ensure high-quality data.

It is necessary to know natural rates of change in the absence

of pollutant stress, in order to detect changes that might be

associated with increased levels of air pollution. It is also important to recognize that for long-lived organisms such as trees,

community organization may reflect stochastic events related to

disturbances, rather than a common tolerance to environmental

conditions. In any case, a better understanding of basic ecological relationships is needed at the population, community, and

ecosystem level. A carefully designed inventory and monitoring

program can determine the current condition of natural resources

12 USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
Table 10 —Sensitivity classes for lichen species found in mixed conifer forest /

oak woodland and subalpine forest in Sierra Nevada and northern California

wilderness.

Sensitivity class

Mixed conifer forest

oak woodland:

conifers and oaks

Very sensitive

Sensitive

Tolerant

Very tolerant

Subalpine forest:

conifers

Very sensitive

Sensitive

Tolerant

Very tolerant

Lichen species

Alectorio sarmentosa

Bryoria SP.

Evernia prunastri

Peltigera canina

Peltigera collina

Pseudocyphellaria anthraspis

Collema nigrescens

Parmelia sulcata

Parmelia quercina

Usnea sp.

Melanelia glabra

Melanelia subolivacea

Xanthoria polycarpa

Letharia colurnbiana

Letharia vulpina

Xanthoria fallax

Bryoria sp.

Pseudephebe minuscula

Pseudephebe pubescens

Cladonia sp.

Tuckermannopsis merrillii

Usnea sp.

Hypogymnia enteromorpha

(may not be found at higher

elevations)

Letharia columbiana

Letharia vulpina

as well as potential future changes (Silsbee and Peterson 1991).

Simply conducting an inventory of lichen species is art important

first step in describing resource condition. Monitoring programs

must maintain strict protocols for sampling and measurement in

order to detect subtle changes in resource condition (for example, Fox and others 1987). Standardized guides would greatly

assist monitoring efforts in wilderness. For example, a pictorial atlas with examples of foliar injury in conifers and evaluation criteria would assist in measuring potential ozone effects.

Managers and permit applicants should be made aware of

plant species that are valued because of their sensitivity to air

pollution (sensitive receptors) or scarcity (threatened or endangered species).

There are currently few experimental data on plant species

found in California wilderness, and very few field data. Research on basic ecological relationships is clearly needed to

quantify air pollution effects that can be observed in the field.

Typical symptoms of air pollutant injury and sensitivities to air

pollutants are unknown for most plant species in California

wilderness. Additional data on dose-response relationships for

pollutants and various plant species will help make the critical

link between pollutant exposure and plant effects.

Several subjects must be addressed as part of the decisionmaking process for PSD permit applications. At the least, class I

areas should have a complete inventory of sensitive receptors

within each AQRV. These inventories can be updated as new

information becomes available (for example, scientific data may

indicate that a sensitive receptor should be added that was not

previously thought to be sensitive to a pollutant). In addition,

sensitive receptors should be monitored for a minimum of three

consecutive years in order to evaluate natural temporal changes

in the condition of natural resources. Scientific literature and

unpublished data relevant to pollutant effects in each AQRV

should be compiled and updated as necessary; site- and specieslevel information should be obtained whenever possible. Monitoring requirements, data needs, and decision criteria for PSD

applications should be summarized and made available, so that

Table 11 —of probable interactions among pollutants and other environmental factors with

respect to effects on plants1.

Ozone Sulfur Cloud Total Total Drought Cold Insects/

dioxide acidity nitrogen sulfur pathogens

(SO2) (N) (S)

Ozone X X - + X

SO2 X X

Cloud acidity +

Total N X X X

Total S

1 Interactions are greater than additive (+), less than additive (-), or likely but of unknown direction or

magnitude (X); blanks indicate that there is no known or suspected interaction.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 13
potential applicants and regulatory agencies will be aware of

Forest Service concerns for wilderness protection.

Maintenance of the vigor and health of wilderness ecosystems and values (AQRVs) is a primary management objective in

protecting class I areas from degradation by air pollution. The

condition of sensitive receptors within AQRVs is used to measure potential changes. Deterioration of sensitive receptor condition beyond the current condition class exceeds the LAC in class

I areas. The challenge for resource managers and permit applicants is to identify these potential changes and to distinguish the

effects of pollutants from other environmental factors.

Other Terrestrial Resources

Many other terrestrial resources could be potential AQRVs in

California wilderness. Defining and describing some of these

resources was a difficult component of the workshop, despite

general agreement that they were important AQRVs. The

workgroup responsible for this topic concluded that six AQRVs

could be defined generically across all wilderness: prehistoric

rock art, geological features, threatened and endangered animals, human response relative to wilderness perceptions, natural

odors, and pollutant odors.

Prehistoric Rock Art

Various forms of rock art by Native Americans, including

pictographs and petroglyphs, are found in some of the wilderness areas of California. Rock art is considered an important

resource and AQRV in the Agua Tibia, San Rafael, and Ventana

Wildernesses. Air pollutants can degrade these features through

degradation of pigments and dissolution of rock. Oxidants are

known to degrade some organic compounds, and the effect of

acidic deposition on statues, buildings, and other mineral-based

structures is well known. Although there are no methods of

monitoring the condition of rock art overtime, it may be possible

to draw some inferences from the literature on the effects of

acidic compounds on structural materials. Because cultural artifacts are irreplaceable, it was determined that no degradation

beyond baseline (“normal”) deterioration would be acceptable

in wilderness. A monitoring program to evaluate the condition

of prehistoric art features over time should be established in

order to evaluate potential degradation of the resource.

Geological Features

This AQRV includes prominent geological features and

deposits that are unique because of their beauty or scientific

value. For example, cliff marble formations are an important

AQRV in the Marble Mountain Wilderness. Other wildernesses have large deposits of fossils that contain information

on prehistoric plants and animals. The minerals that comprise

these features are subject to degradation from acidic deposition. It is difficult to establish condition classes for these

AQRVs because there are few data on deterioration of natural

geological features. The deterioration of massive features would

no doubt be less observable than that of prehistoric art. It may

again be possible to draw some inferences from the literature

on the effects of acidic deposition on structural materials. A

monitoring program to evaluate the condition of geologic

materials over time could include photographic and spectroscopic techniques. Such a monitoring program would require

relatively infrequent sampling, and could be augmented by the

use of standard reference materials.

Threatened and Endangered Animals

Many animals found in California wilderness are rare because that is their natural condition or because their populations

have been affected by humans. Some of these species have

federal or state protection or both by having been designated as

threatened or endangered. This status makes protection of a

species from all threats, including air pollution, a high priority.

Unfortunately, almost nothing is known about the effects of air

pollutants on animals. Clinical data on humans and laboratory

animals might be used to draw inferences about the response of

other animals to exposure to ozone, S, and N pollutants. Perhaps

the most well-known effect of pollutants on animals is impaired

respiratory capacity in humans and other mammals, which is

caused by elevated ozone exposure. An indirect effect of air

pollutants on animals is alteration of habitat as a result of pathological effects on plants or aquatic systems. It was determined

that no reduction in population viability due to air pollution

should be allowed in wilderness, although this maybe difficult

to quantify. The condition of populations cart be monitored over

time, but caution must be used to differentiate the effects of air

pollutants from those of other environmental factors.

Human Response Relative to Wilderness Perceptions

People often use wilderness in order to enjoy a relatively

pristine environment. Clean air is clearly one component of that

experience. Humans have different sensitivities to air pollutants

with respect to both physiological and psychological effects.

Ozone can affect respiratory capacity in relatively small concentrations, reduce overall physiological well-being, and restrict

hiking or other strenuous activity at high elevations. A range of

condition classes defines the possible effects:

Condition class Class description

No effect No human-perceived discomfort or physiological

impairment

Slight effect Slight discomfort or short-term physiological

impairment

Moderate effect Moderate discomfort or moderately long-term

physiological impairment

Severe effect Severe discomfort or long-term physiological

impairment

These categories are quite general in order to reflect the subjectivity of human response as well as the variation in human

sensitivity. It may be possible to quantify these descriptions

through inferences from the medical literature on human respiratory function and vision with respect to pollutants. It may

also be possible to conduct a survey of National Forest users to

determine levels of discomfort and physiological impacts. In

any case, it was determined that any deleterious effect of air

pollutants on humans (respiratory impairment, eye irritation,

etc.) is unacceptable in wilderness.

14 USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
Natural Odors

Air pollutants such as ozone and SO2 can mask the wide

variety of natural fragrances perceived by humans and other

animals. Masking of volatile organic chemicals, secondary plant

compounds, and pheromones can reduce enjoyment of wilderness by humans and block important chemical cues sensed by

animals. Disruption of normal odor detection can therefore affect human perceptions as well as ecosystem function. The

following condition classes are defined for natural odors:

Condition class Class description

No effect No interference with natural odors

Moderate deterioration Masking of natural odors observed by 10-30

percent of observers

Severe deterioration Masking of natural odors observed by >30

percent of observers

It may be possible to monitor the effect of air pollutants on

natural odors by comparing exposure data with the concentration of volatile organic compounds.

Pollutant Odors

Some pollutants are readily identified by smell. Ozone has a

distinctive metallic odor; SO2, an acrid odor and hydrogen

sulfide (H2S), a “rotten egg” odor. These odors, as well as the

masking of natural odors, are generally perceived as negative

impacts by wilderness users. The following condition classes

were defined for pollutant odors:

Condition class Class description

No effect No chemical or sensory interference with

human smell

Moderate deterioration Air pollutant odor is detectable

Severe deterioration Air pollutant odor is the only detectable odor

Effects on Aquatic Resources

Lakes, streams, and their associated biota represent important

AQRVs in most class I wilderness areas and national parks in

California (table 12). The aquatic resources can be conveniently

divided into three primary subpopulations, located in the Klamath Mountains, Southern Cascade Mountains, and Sierra Nevada/southern California (table 13). Of these, the Sierra Nevada

contains the greatest number of wilderness areas and the most

intensively studied aquatic resources.

The most extensive study to date of the aquatic resources in

this region is the Western Lake Survey (WLS) conducted by the

U.S. Environmental Protection Agency (EPA) in 1985 (Landers

and others 1987). The purpose of the survey was to quantify,

with known uncertainty, the chemical status of lakes in areas of

the western United States that contain the majority of lakes

having acid neutralizing capacity (ANC) less than 400 μeq/L.

Although the western United States currently receives a small

fraction of the atmospheric acid loading received in the East

(Young and others 1988), an acceptable atmospheric deposition

loading to prevent acidification of western aquatic resources is

unknown. Of particular concern is the degree of protection

necessary to maintain the chemical and biological integrity of

lakes and streams in the designated USDA Forest Service wilderness areas and national parks.

The WLS sampled a statistically representative group of

lakes in California, including 13 lakes in each of the Klamath

Mountains and Southern Cascades and 71 lakes in wilderness

areas (not all class I) of the Sierra Nevada. Although no lakes

were sampled in southern California wilderness areas, watersheds in this region are similar to those of the Sierra Nevada

with predominantly granitic geology and thin, poorly developed soils. Potential effects of pollutants on aquatic resources

in southern California wilderness can be estimated reasonably

well from data collected at Sierra Nevada lakes, until additional data are available.

Table 12 —Aquatic air quality values (AQRVs) for California wilderness.

AQRV

Wilderness Lake Stream

Agua Tibia

Ansel Adams X X

Caribou X X

Cucamonga X

Desolation X X

Domeland X

Emigrant X X

Hoover X X

John Muir X X

Kaiser X X

Marble Mountain X X

Mokelumne X X

San Gabriel X

San Gorgonio X X

San Jacinto X

San Rafael X

South Warner Mountain X X

Thousand Lakes X X

Ventana X

Yolla Bolly-Middle Eel X X

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 15
Table 13 —USDA Forest Service wilderness areas (not all class I) and national

parks in California containing lakes sampled during the Western lake Survey

by the U.S. Environmental Protection Agency (Landers and others 1987).

Subpopulation

Klamath Mountains

Siskiyou Wilderness

Marble Mountain Wilderness

Trinity Alps Wilderness

Southern Cascades

Thousand Lakes Wilderness

Lassen Volcanic National Park

Caribou Wilderness

Bucks Lake Wilderness

Sierra Nevada

Desolation Wilderness

Mokelumne Wilderness

Hoover Wilderness

Emigrant Wilderness

Yosemite National Park

Minarets Wilderness

John Muir Wilderness

Kaiser Wilderness

Dinkey Lakes Wilderness

Kings Canyon National Park

Sequoia National Park

Number of lakes

sampled

13

2

4

7

13

2

7

3

1

71

11

3

1

4

9

5

16

1

1

11

9

Aquatic resources in this region are vulnerable to potential

effects from acidic deposition because of the predominance of

slowly weatherable igneous rocks, thin acidic soils, and generally large volumes of winter precipitation (Melack and others

1985, Melack and Stoddard 1991). These aquatic resources

provide water for agriculture, and for municipal and industrial

use in metropolitan areas such as Los Angeles and San Francisco. They also provide the focus for many wilderness recreational activities in the region. Although important aquatic resources include rivers and streams, as well as lakes, few of the

former have been chemically or biologically characterized in a

systematic fashion. Consequently, this section on aquatic resources focuses primarily on lakes.

Climate in the mountainous areas of California is characterized by warm, dry summers and cool, wet winters. Altitude

and topography strongly influence climatic factors in the region. Meteorological stations and data are scarce at the higher

elevations. Available data, however, suggest the following

climatological conditions (Melack and Stoddard 199 1). Mean

annual precipitation on the western side of the crest of the

mountains increases from less than 40 cm below 250 m elevation in the foothills to about 140 cm above 2000 m elevation.

The eastern side receives about two-thirds as much precipitation as the western side. Most precipitation falls as snow at the

higher elevations, especially above about 3000 m. Runoff

from mid- to high-elevations comes predominantly during

snowmelt from April through July. Prevailing winds are from

the west. On a local scale, winds are channeled by valleys,

with generally up-valley flow during warm months and downvalley flow during cool months.

The initial concern regarding potential impacts to the aquatic

resources in this region has focused on potential acidification

from anthropogenic emissions of S and N (Eilers and others

1989; Landers and others 1987; Melack and others 1983, 1985;

Melack and Stoddard 199 1; Stoddard 1986). Sulfate, nitrate, and

ammonium all have the potential to acidify surface waters (Stumm

and Morgan 198 1). Increased sulfate is typically associated with

chronic acidification of surface waters (L.A. Baker and others

1990), although nitrate (NO3

-

) (Henriksen and others 1988) and

ammonium (NH4

+

) (Schuurekes and others 1988) are important

in some cases. Episodic acidification, however, is typically associated with rapid release of accumulated NO3

- during snowmelt

runoff (Eshleman 1988, Schnoor and Nikolaidis 1989, Wigington

and others 1990). Episodic acidification may be of particular

concern in California because of the relative importance of N, as

compared with S, deposition in the West. Many of the workshop

participants believed that aquatic resources in the Sierra Nevada

are not likely to experience chronic acidification in the near

future. This belief was based on various model applications in

the literature and on empirical studies suggesting that increased

acidic inputs to the Sierra Nevada would likely increase weathering rates rather than cause chronic acidification. For this reason, empirical modeling efforts that employ F-factor calculations (for example, Henriksen 1984) were not considerd appropriate for AQRV guidelines in this region. Rather, most workshop participants favored an approach based on episodic chemistry, and this preference is reflected in the condition classes

selected during the workshop.

Acidification of soils and surface waters contributes to increased mobilization and availability of aluminum (Al), which

can be highly toxic to aquatic life, especially if the Al is in the

inorganic monomeric form (J.P. Baker and others 1990). The

toxic effects of surface water acidification have been attributed

to the combined increases in hydrogen ion and Al (J.P. Baker

and others 1990). Calcium (Ca) concentration is also important;

biota generally tolerate lower pH and higher Al concentrations

in the presence of higher calcium ion (Ca2+) concentration.

Organic acids can also play an important role in affecting the

acid-base status of surface waters and their sensitivity to acidification. However, only waters low in concentrations of both base

cations and organic acids are highly susceptible to acidification

(Sullivan 1990). Waters high in base cations (and therefore

alkalinity) receive substantial neutralization potential from their

watersheds, and therefore typically have the capacity to completely neutralize acidic deposition inputs, largely through increased weathering and exchange of base cations (Brakke and

others 1990, Henriksen 1984). Similarly, waters high in organic

acids have a strong buffering capability that resists further acidification (Kramer and Davies 1988). Nearly all surface waters in

this region have low dissolved organic carbon (an indication of

organic acid concentrations); consequent y, the issue of sensitivity in these systems is determined primarily by their base cation

concentrations.

16 USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
Other potential consequences of atmospheric pollutants in

the deposition include eutrophication7 of N-limited lakes and

damage associated with trace contaminants such as metals (for

example, mercury, cadmium) and organic compounds (polynuclear aromatic hydrocarbons, pesticides). Cases of N limitation in oligotrophic Western lakes are becoming more widely

documented (Axler and others 1981, Goldman 1981, Larson

1988, Morris and Lewis 1988), suggesting that increases in N

deposition could be a concern with respect to both episodic

acidification and increases in lake productivity. Trace contaminants are typically not addressed in the PSD process and will not

be discussed here.

Although concern for damage associated with atmospheric

deposition of pollutants is primarily associated with the possible

loss of sensitive biota, most studies of atmospheric impacts on

aquatic ecosystems have focused on measuring changes in surface water chemistry. Therefore, most of the criteria for evaluating sensitive waters are based on water chemistry, reflecting the

relative ease and precision of collecting and measuring water

chemistry as compared to quantitative sampling of aquatic organisms. The need to base the criteria on water chemistry also

reflects the poor state of knowledge of aquatic communities.

The only statistical sampling of aquatic resources in the

region is the WLS. Other limited data sets have also been

collected in the Sierra Nevada and provide more detailed

information, especially regarding seasonality, for a nonstatistical

subset of lakes. Wilson and Wood (1984) sampled 85 lakes in

northern California, including 22 lakes sampled during both

summer and fall. Melack and others (1985) sampled 73 lakes

along the Sierra Nevada crest. Stoddard (1986) and Holmes

(1986) sampled 29 lakes to relate lakewater pH to diatom

distributions, including mostly lakes previously sampled by

Melack and others (1985). Melack and Setaro (1986) sampled

17 lakes during the ice-free seasons and during ice cover.

McCleneghan and others (1985, 1987) sampled 34 lakes as

part of a statewide survey of lakes vulnerable to acidic deposition. Data collected in these studies have been summarized by

Melack and Stoddard (1991). Characteristics exhibited by

lakes included in these surveys are presented in table 14, from

Melack and Stoddard (1991).

The majority of the lakes in the Sierra Nevada are small and

shallow, and drain relatively large watersheds. About 70 percent of the lakes are less than 10 ha in area and 10 m deep.

Most have pH between 6.5 and 7.5 and ANC < 100 μeq/L.

Sulfate concentrations tend to be extremely low (< 7 μeq/L),

as are concentrations of dissolved organic carbon (DOC) (<

160 μmol/L). As a whole, the region is characterized by a large

number of small, extremely dilute lakes (Melack and Stoddard

1991). They constitute the most dilute group of lakes sampled

in the United States (Landers and others 1987). Thus, although

no acidic lakes were sampled, they are undoubtedly among the

most sensitive aquatic resources to acidic deposition effects in

the country. The median ANC of lakes in the Sierra Nevada is

7

The process of increasing lake productivity is usually associated with

increasing nutrient loads at the lake. Increasing nutrient loads stimulate growth

of algae and aquatic plants. This usually results in decreased lake transparency.

60 μeq/L (table 14). Perhaps of greater interest with respect to

the PSD process is the large number of lakes in this region

with alkalinity values less than 25 μeq/L. Local variations in

geology and hydrologic flow paths can greatly modify lake

alkalinity expected on the basis of generalized geology. Assessment of lake alkalinity in relatively small areas such as

wilderness areas may require more detailed information than

is available from surveys such as Landers and others (1987).

Fortunately, the lakes in California are primarily bicarbonate

systems (Landers and others 1987),8 and one can estimate

surface water alkalinity simply by measuring conductivity.

Regressions of base cation sum and alkalinity versus conductivity for low-conductivity (≤ 15 μSiemens/cm) lakes in the

Sierra Nevada yield the following (fig. 2):

Basic cation sum (μeq/L) = 9.52 C + 0.09

n = 34, r2 = 0.96, SE = 0.36

Alkalinity (μeq/L) = 9.42 C - 8.59

n = 34, r2 = 0.93, SE = 0.45

where C is conductivity (μS/cm). Both base cation sum and

alkalinity have been used widely to estimate surface water sensitivity to acidification, and conductivity is a suitable surrogate for

quickly estimating either of these parameters to identify lowconductivity lakes. The high percent variance in alkalinity explained by conductivity shows that this inexpensive measurement can be used to conduct rapid assessments of surface water

alkalinity throughout the region. This regression equation will

have poor predictive capability for lakes receiving substantial

marine aerosols or those with watershed sources of sulfate, but

for most lakes conductivity can be used to accurately estimate

alkalinity. With the additional measurements of SO4

2- and pH,

the process can be further refined to screen for acidic waters

from either watershed or atmospheric sources of S. Although

conductivity screening would not provide direct information

on the prevalence or likelihood of episodic acidification, it is

the low alkalinity/conductivity systems that are most sensitive

to episodic acidification. A conductivity screening provides a

rapid and inexpensive procedure for identifying waters of

highest interest.

Low-alkalinity lakes are found throughout the region. Weathering of base cations is extremely low in many of these watersheds. Background SO4

2- values are also extremely low; sea-saltcorrected SO4

2- values are typically near 0. This is in general

agreement with estimates of background sulfate concentrations

for areas not receiving acidic deposition (Brakke and others

1988). It is generally accepted that surface waters with chemical

8A small number of lakes in the West have substantial sulfate concentrations (Landers and others 1987) that have been attributed to watershed sources of

sulfur (Loranger and Brakke 1988, Stauffer 1990).When the sulfate concentrations are sufficiently great, the lakes can be acidic. For example, West Twin Lake

in the Oregon Cascades has an alkalinity of-5 μeq/L and a sulfate concentration

of 307 μeq/L (Eilers and Bernert 1990). There arc two known acidic lakes from

watershed sources of sulfate in rise Sierra Nevada, located in Kings Canyon

National Park and the John Muir Wilderness Area (J. Stoddard personal communication).

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 17
Table 14 —Median values, With first and third quartiles in parentheses, for elevation and major ion chemistry in five Sierra Nevada lake chemistry data sets1 (from

Melack and Stoddard 1991)

Data set

Western Lake Survey

(population)

Western Lake Survey

(sample)

Melack and others

(1985)

Holmes (1986)

Melack and Setaro

(1986)

McCleneghan and others

(1985, 1987)

n pH ANC SO4

2- DOC NO3- Cl- Ca2+ Mg2+ Na+

SBC Elevation

2119

114

82

29

17

34

6.93

(6.65-7.30)

6.95

(6.71-7.29)

6.95

(6.51-7.26)

6.93

(6.44-7.42)

6.64

(6.50-6.72)

6.56

(6.19-6.73)

μeq/L

60

(37-130)

71

(45-137)

48

(25-98)

67

(27-258)

57

(53-101)

66

(30-97)

μeq/L

7

(4-7)

6

(4-11)

15

(9-3 1)

12

(5-83)

10

(8-14)

3

22

(16-39

μmol/L

67

(42-158)

106

(58-183)

μeq/L

0.4

(0.1-1.7)

0.3

(0.1-1.2)

0.4

(0.1-1.5)

0.7

(0-3.3)

2.6

(1.3-3.9)

0.4

(0.1-1.2)

μeq/L μeq/L

2 43

(1-3) (29-104)

3 45

(2-6) (29-91)

6 37

(4-10) (24-83)

2 58

(2-4) (42-345)

46

(2-4) (40-92)

3 47

(2-4) (22-79)

μeq/L

6

(3-9)

10

(4-20)

5

(3-l0)

9

(4-18)

6

(4-9)

11

(6-19)

μeq/L

19

(11-21)

23

(14-40)

19

(11-31)

12

(9-29)

17

(10-19)

12

(18-26)

ueq/L

76

(51-120)

86

(58-164)

73

(44-137)

88

(60-413)

74

(64-113)

88

(52-121)

m

3008

(2150-3140)

2626

(2131-3159)

3255

(2999-3424)

3194

(2999-3365)

3170

(2899-3365)

2664

(2195-3146)

1ANC = acid neutralizing capacity, DOC = dissolved organic carbon, SBC = sum of base cations. Western Lake Survey pH values are closed system; others are partially

air-equilibrated.

characteristics typical of this region are extremely sensitive, but

the lakes do not currently exhibit any signs of acidification from

atmospheric deposition (L.A. Baker and others 1990, Sullivan

1990). The WLS provided a quantitative assessment of the

chemical status of lakes in the region, although the sampling

intensity was generally insufficient to adequately characterize

the lake populations within individual wilderness areas. Furthermore, the samples for each lake were taken on a single day and

all sampling was done in the autumn. The number of WLS

sample lakes is not sufficient to develop an acceptable characterization of the lakes within individual wilderness areas, with the

possible exception of the John Muir Wilderness (table 13).

The primary concern for maintaining high water quality in

wilderness areas is the desire to prevent the loss of indigenous

(and intentionally stocked) aquatic organisms. Other nonbiotic

concerns, however, such as water clarity, are also thought to be

important to the wilderness experience. There are two problems

with the use of aquatic organisms to serve as indicators of air

pollution stress. First, very little is known about the species of

aquatic organisms present in these wilderness areas. Only isolated studies of a small number of aquatic habitats have been

conducted. Second, little is known about the potential response

of these species to changes in water quality. Most studies of

species response to acidification have been conducted outside

California.

Although the workshop participants favored including organisms in a monitoring strategy, the paucity of high-quality, biological data precludes their effective use at this time. Chemical

criteria are easier to implement as indicators of atmospheric

degradation. It is hoped that subsequent research will provide

support for use of specific values linking the changes in water

chemistry with undesirable biological impacts. Suggested water

quality parameters that can be used to indicate air quality related

impacts in wilderness areas are shown in table 15. Most of these

parameters can be applied to both lakes and streams, with the

exceptions of Secchi disk transparency and dissolved oxygen

concentrations. The latter two parameters reflect potential changes

in lake trophic status caused by either increased deposition of

nutrients, or by effects on the watershed that might affect nutrient export to aquatic systems.

Aquatic organisms were also recognized as potentially valuable indicators of air pollution effects on wilderness areas. Selected taxonomic groups are thought to include sensitive species

(table 16), based on use of these taxa in studies on biological

impacts of acidic deposition in North America and Europe (see

J.P. Baker and others 1990).

Several concerns were identified in the use of biota to

monitor effects in California. The faunistic diversity of wilderness lakes in the region is low; therefore, locating enough

organisms for effective biological monitoring might be a problem. For example, molluscs and other benthic invertebrates

were used to measure biological damage in Norwegian lakes

(Økland and Økland 1986), but the low Ca2+ concentrations in

many Western lakes may restrict the distribution of these

organisms to lower elevations.

Table 17 is a preliminary list of sensitive receptors for the

aquatic resources in California. Although uncertainties and ambiguities are substantial in the use of these sensitive receptors for

assessing the onset of AQRV deterioration, they represent a first

step in the process of identifying AQRV monitoring needs. The

proposed preliminary sensitive receptors for lakes are pH, ANC,

water clarity, and fish populations. For streams they are pH,

ANC, fish populations, and macroinvertebrates.

Once the sensitive receptors have been defined, it is necessary to determine which changes in the sensitive receptors

warrant management response. All measures of water quality

18 USDA Forest Service Gen. Tech. Rep. PSW-GTR- 136. 1992.
Figure 2 —Alkalinity versus conductivity for low-conductivity (≤ 15 μSiemens/cm) Western Lake Survey lakes in California (from

Landers and others 1987).

and biota are associated with uncertainty. Measurement uncertainty arises from sampling error, analytical error, and natural

variability y associated with hydrologic processes. Selection of

LAC requires incorporation of some element of uncertainty.

However, if the level of uncertainty is too great, then it would

be possible for the resource to be degraded yet still within the

LAC. Thus, in developing some initial LAC, the aquatics

group followed the guidance of the Forest Service legal mandate, which is to err on the side of protecting the resource (as

stated in the Wilderness Act 1964).

Three condition classes were defined for each water quality

indicator to reflect classes of impacts associated with changes in

the indicator values: (1) no significant deterioration, (2) significant deterioration, and (3) severe deterioration. The values assigned to each of these classes are intended to reflect realistic

changes based on mechanisms of acidifying (or eutrophying)

processes, observations in areas already acidified (or eutrophied),

and the reliability of data on aquatic resources in these wildernesses (table 17). These values represent changes in addition to

those imposed by natural processes such as dilution, and should

be used only as an interim guide until subsequent monitoring

and research results are available to revise them. The rationale

for selecting each receptor is briefly summarized below:

ANC: Acid neutralizing capacity (alkalinity) is the most

direct measure of surface water sensitivity to acidification

for surface waters that have not been previously affected

by acid deposition. Reductions in ANC to values near O, as

observed during some hydrologic events (summer thunderstorms, snowmelt), can reduce the quality of aquatic habitat. California lakes have the lowest average ANC values

of any region in the United States (Landers and others

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 19
Table 15 —Potential water quality parameters and their descriptions identified for surface water chemistry.

Parameter

Acid neutralizing capacity

Conductivity

pH

Al1

SO4

2-

NO3

-

NH4

+

Total P

DO

Secchi disk transparency

Description Indicates

Alkalinity (μeq/L)

Specific conductance

(μSiemens/cm)

Hydrogen ion (-log [H+

])

Inorganic monomeric

aluminum (μg/L)

Sulfate (μeq/L)

Nitrate (μeq/L)

Ammonium (μeq/L)

Total phosphorus (μg/L)

Dissolved oxygen (mg/L)

Water clarity (m)

Decrease is a direct measure

of acidification

Can be related to alkalinity;

use as a screening tool

Decrease is a direct measure

of acidification

Present in measurable amounts

only in acidified waters

Acid anion most often associated

with chronic acidification

Acid anion most often associated

with episodic acidification

Seldom present in wilderness lakes;

increase suggests elevated nitrogen

deposition

Often a limiting nutrient; changes

affect trophic status

Reduction in winter or

increased diurnal fluctuations may

represent increased productivity of waters

Decrease indicates loss of transparency,

possibly from increase in phytoplankton

or organic acids. Increased transparency

may indicate acidification.

1987). Condition classes are set to reflect both chronic and

episodic reductions in ANC. Overlapping class descriptions for the first two condition classes reflect a range of

values, because of the uncertainty in specifying deterioration thresholds.

pH: Organisms respond to changes in H+ ion, not ANC.

Although it is often difficult to obtain reliable measures of

pH in dilute waters, it is important that every effort be

made to do so. It is difficult to detect any negative biological response associated with H+ concentration above pH

6.0 (J. P. Baker and others 1990, Eilers and others 1984,

Schindler 1988). Ninety-nine percent of the lakes in the

WLS Western region had pH > 6.0 (Landers and others

1987). There can be changes in community composition

for sensitive taxonomic groups below pH 6.0. ANC is

typically near or ≤ 0 at pH values < 5.3, and detrimental

biological impacts become quite apparent. The impacts

become increasingly severe at pH < 5.0 as inorganic monomeric aluminum (Ali

) is mobilized into solution. Lake pH

can vary considerably during the year because of normal

variation in chemical parameters, such as the concentration

of dissolved gases. Changes can be relatively large at

times, particularly in small bodies of water. The dynamic

nature of lake pH dictates periodic sampling to establish

temporal trends, rather than annual sampling. Reductions

in pH < 5.5 during hydrologic events (storms, snowmelt)

were considered by the workshop participants to be an

indication of severe deterioration with respect to habitat

quality for aquatic organisms. However, natural processes

of dilution and organic enrichment can in some cases lower

episodic surface water pH < 5.5 in the absence of acidic

deposition (Wigington and others 1990). Chronic reductions of 0.3 to 0.5 pH units can also cause significant

deterioration of aquatic habitat. Overlapping class descriptions for the first two pH condition classes (table 17) reflect

a range of values because of the uncertainty in specifying

deterioration thresholds. Monitoring of pH should be done

at least three times a year at standard seasonal times in

order to characterize temporal variation.

Water Clarity: Measurement of transparency (for example, by lowering a Secchi disk into a lake or measuring

optical density) provides art inexpensive indication of phytoplankton production. Transparency in some cases may

increase in acidified lakes. If nutrient deposition (NO3

-

,

NH4

+

, total phosphorus [P]) to the lakes increases, it is

conceivable that the lakes would become less oligotrophic

and therefore less transparent. Workshop participants noted

that although measurement of transparency with a Secchi

disk is easily measured, the majority of the lakes in the

Sierra Nevada are too shallow and too clear to allow sufficient Secchi disk depth to provide any useful information.

The recommended condition classes were therefore based

on optical density rather than Secchi disk transparency.

20 USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
Table 16 —Suggested taxonomic groups of aquatic organisms that could be investigated for sensitivity to stress from

atmospheric pollutants.

Taxonomic group

Macroinvertebrates

Mollusca (snails, clams)

Ephemeroptera (mayflies)

Plecoptera (stoneflies)

Trichoptera (caddisflies)

Plankton

Phytoplankton

Zooplankton

Amphibians

Fish

Bryophytes (mosses)

Macrophytes (aquatic plants)

Primary habitat Notes

Lakes, streams

Lakes, streams

Lakes, streams

Lakes, streams, ponds

Lakes

Lakes

Lakes, streams, ponds,

wetlands

Lakes, streams

Wetlands, lakes,

streams

Wetlands, lakes

Check for loss of species; may be

limited by availability of calcium

Cheek for loss of species; larval (aquatic)

forms are the sensitive life stage

Check for loss of species; larval (aquatic)

forms are the sensitive life stage

Cheek for loss of species larval (aquatic)

forms are the sensitive life stage

Check for changes in species composition,

especially loss of diatoms and increase

in blue-greens

Check for changes in species composition,

including a change to larger species associated

with a reduction in predators (fish)

Possible confounding effects from fish stocking

Also can he sampled for accumulation of trace

contaminants; cheek for loss of year classes

Accumulators of some trace metals

Leaf chlorosis on emergent species

The clarity of water in mountain lakes is a valuable

resource for many wilderness users. It can also serve as a

sensitive receptor for air pollutants, especially elevated

levels of N deposition. Most Sierra Nevada lakes have low

to moderate productivity levels. Additional N deposition

could act as a fertilizer, increasing the productivity of algae

and other organisms, although some Sierra Nevada lakes

may be P-limited (or quickly become P-limited with increased N inputs). An increase in plankton biomass generally reduces the clarity of surface water.

Fish Populations: Fish develop more slowly in acidified water and are generally less physiologically resistant

to environmental stress. Detecting significant changes in

fish populations is difficult because of the high natural

variability inmost lakes. Fish populations vary in response

to changes in food supply, climate, removal by humans,

and other factors. Because of this variation, it is suggested

that young-of-the-year (0-age class) fish be examined to

detect deterioration in habitat quality of lakes. The condition class for “significant deterioration” was not defined

because it was thought that it would not be possible to

distinguish interannual variation in fish populations from

changes due to pollutants. The nonfunctional category indicates art extremely severe situation in which acidity is so

great that it contributes to adult fish mortality. The species

monitored in lakes will vary among locations; in the absence of knowledge about species sensitivity to acidity, a

common species should probably be monitored in order to

better characterize variation. Difficulties in the use of fish

populations as sensitive receptors include the absence of

fish from many waters (especially at high elevation) and

the confounding influence of stocking practices.

Macroinvertebrates: Some species of macroinvertebrates

commonly found in streams are known to be sensitive to

increases in acidity. In fact, changes in their populations

may precede and be detected earlier than those in fish

populations. Natural population variations can obscure

changes that might be related to increased acidity, so condition classes for macroinvertebrates are quite general.

Pollutant Interactions

Because of the acidifying impact of N and S deposition on

aquatic systems, the addition of N or S to a sensitive system may

result in an additive impact due to an increase in acidity. In

addition, some interaction effects between ozone, SO2

, and N

deposition may occur (see section on terrestrial resources above)

in riparian/wetland areas where terrestrial flora are sensitive

receptors (for example, mosses, lichens). It is currently unclear

whether interaction effects among these three pollutants will be

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 21
Table 17 —Sensitive receptors and associated condition classes for aquatic resources proposed at the workshop.

Sensitive receptor

Lake/stream pH

Lake/stream ANC2

Lake clarity

Lake/stream fish populations

Stream macroinvertebrates

Condition class Class Description

No change

Significant deterioration

Severe deterioration1

No change

Significant deterioration

Severe deterioration

No change

Significant deterioration

Severe deterioration

No change

Significant deterioration

Severe deterioration

Non-functional

No change

Significant deterioration

Severe deterioration

— Long-term reduction of pH <0.5 pH units

— Long-term reduction of pH >0.3 pH units

— pH < 5.5 during and immediately following

hydrologic events

— Long-term reduction of ANC < 10 μeq/L

— Long-term reduction of ANC between 5

and 10 μeq/L

— Reduction of ANC ≤ 0 during and

immediately following hydrologic events

— Reduction in optical density of < 0.003

optical density units (ODU)

— Reduction in optical density of 0.003 to

0.01 ODU

— Reduction in optical density of > 0.01 ODU

— Young-of-the-year present each year in

which reproducing populations and

suitable habitat exist

— Not specified

— Long-term loss in reproductive capacity—

ranging from 3 years to no reproduction

— Abnormal adult mortality observed

— No loss of sensitive species

— Loss of some sensitive species

— Loss of all sensitive species

1

There was some concern expressed subsequent to the workshop that episodic reductions in pH and/or ANC

contribute the first warning signals of acidification damage, rather than “severe deterioration.” This discrepancy

illustrates the generally poor knowledge base regarding episodic acidification in these systems.

2ANC = acid neutralizing capacity.

synergistic or antagonistic. Nevertheless, Federal Land Managers should be aware of potential interactions and be prepared to

monitor their effects.

Monitoring, Data Collection, and Criteria for Decisions on PSD Applications

Although survey data for lakes in California are available to

qualitatively document the high sensitivity of these systems to

possible effects of acidic deposition, major uncertainties regarding the quantitative aspects of this sensitivity for lakes, streams,

and wetlands hamper the FLM’s ability to assess impacts associated with the PSD process. The major research/monitoring needs

to reduce these uncertainties include the following:

Lakes: The major ion chemistry of lakes in the region

was characterized in the WLS and other local surveys.

However, data areas are generally insufficient to characterize these resources for individual wilderness (see table 13 ).

Research and monitoring needs for lakes include: (1) characterization of lake chemistry in individual wilderness areas, (2) establishment of long-term monitoring of one to

several lakes/watersheds in selected wilderness areas for

the purpose of detecting trends, and (3) improving our

understanding of the processes controlling chronic, and

especially episodic, lake chemistry.

Streams: Little research has been conducted on streams

in California. There is a need to investigate stream chemistry, especially in the higher mountain sites. No stream

chemistry in the region has been compiled to provide an

overall assessment of the sensitivity of streams to acidification. There is a need for both baseline (for example, current

export of N from undisturbed watersheds) and episodic

stream chemistry data.

Wetlands/Ponds: No data were available to evaluate the

potential sensitivity of wetlands, riparian corridors, or vernal pools (spring ponds) to damage from acidic deposition.

Deposition: Estimates of wet deposition in the region

are based on National Atmospheric Deposition Program/

National Trends Network (NADP/NTN) sites that are generally located at much lower elevations than the aquatic

resources of interest. Deposition data from high elevation

sites dominated by snow inputs are needed. Snow cores

could be considered as an alternative to establishing additional NADP sites (Laird and others 1986).

22 USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
Biota: No species-specific biological data were available to make assessments of either the distribution of sensitive species in the region or their dose-response to pollutant

exposure. A plan should be developed to begin collecting

this basic information.

Snowmelt: Most of the data on aquatic resources in

California have been collected in summer and autumn.

Collecting hydrologic and chemical data for lakes, streams,

and ponds needs greater emphasis during the snowmelt

period. Dilution of base cations will greatly increase the

sensitivity of those systems to acidic deposition.

The condition of sensitive receptors should be monitored at

specific times: (1) in summer, when primary productivity is

highest in lakes and streams, (2) in autumn, when lake turnover

and mixing within the water column occurs, and (3) during

hydrologic event conditions, when there is dynamic change in

physical and chemical parameters. It maybe logistically difficult

to collect data for short-term events, but some effort is necessary

in this area because of its importance in determining the condition of surface water.

Although the areas listed above identify some of the major

research/monitoring needs for aquatic resources in California,

there are several important related issues. First, the FLM needs

to anticipate data requirements for quantitatively evaluating lake

and stream response to atmospheric deposition via processbased model projections. In addition to the information described above, ancillary information on watershed characteristics for selected sensitive resources is needed. The two models

used extensively in forecasting lake and stream response to

acidification in the National Acid Precipitation Assessment Program (NAPAP) program were MAGIC (Model of Acidification

of Groundwater in Catchments) and ILWAS (Integrated Lake

and Watershed Acidification Study). MAGIC model requirements include detailed information on soil properties (for example, depth, bulk density, cation exchange capacity, S-absorption, base cations, extent of soil cover), vegetative cover, exposed bedrock (extent and composition), deposition, and hydrologic flowpaths (Cosby and others 1985a,b,c). More intensive

data collection is required to fully calibrate the ILWAS watershed simulation model (Chen and others 1983, 1984), and it is

therefore not as generally applicable as is MAGIC.

One of the difficulties in obtaining the needed input data for

modeling efforts has been the problem of conducting research in

wilderness areas. The difficulty of gathering data in mountainous areas is compounded by administrative restrictions of the

1964 Wilderness Act. Relaxing management guidelines that

impede data collection may be appropriate in some cases, because one of the purposes of establishing wilderness areas was

for their scientific use (See 2(c)(4) of the 1964 Wilderness Act).

Relatively little is known about the effects of long-term

acidic deposition on aquatic systems. Loadings of S and N in

California are currently low (except for high N deposition in

parts of southern California) and well below previously cited

levels associated with damage. However, the potential sensitivity of California watersheds to small changes in acidity

dictates a conservative approach to resource protection. Dramatic changes in chemical parameters are observed during

hydrologic events in some aquatic systems, even with low

deposition values. Monitoring episodic changes in the most

sensitive lakes and streams will provide the earliest signal of

potential changes caused by air pollutants. Research that can

link S and N inputs to changes in aquatic systems in California

should be a high priority. Studies are also needed that can

determine the effect of episodic changes in chemical parameters on the biotic communities of lakes and streams.

Effects on Visibility

The CAA, as amended in 1977, declared as a national goal

the “prevention of any future, and the remedying of any existing

impairment of visibility in mandatory Class I Federal areas in

which impairment results from man-made air pollution.” The

CAA further states that visibility will be an AQRV for class I

areas. Visibility is equal in importance to other AQRVs, such as

ecosystems and lakes, although it is usually not homogeneously

affected by air pollution throughout a given area. It is a sitespecific value affected by meteorology, topography, the position

of the viewer and the sun, and a number of other variables.

Assessments of visibility rely heavily on human perceptions of

resource condition.

The majority of the visibility workgroup agreed to the premise

that visibility within class I areas (not “integral vistas,” that is,

not including views from or to targets outside the class I area) is

the AQRV, because of the administrative problems associated

with managing air quality over lands outside federal jurisdiction.

This premise was not a unanimous viewpoint because workshop

participants felt that the value of views from class I areas reached

well beyond their boundaries.

The visibility workgroup further concluded that specific vistas or views are the sensitive receptors. Although good visibility

is an important resource throughout class I areas in California

sensitive receptor vistas selected and monitored by FLMs are a

practical way to determine the effects of air pollution on the

visibility resource.

The workgroup concluded that the protection of visibility

should not depend on the number of visitors, and that one visitor

is as important as many visitors.

A Process to Manage Visibility in

Class I Areas

Visibility is a site-dependent value for which guidelines can

be assigned only on a case-by-case basis. That is, each view or

vista holds values of coloration, texture, and pattern, as well as

potential to see distant targets that must be viewed and rated

individually. No procedures have been established to accomplish this task in a standard way. Consequently, the workgroup

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 23
developed a process to identify sensitive views, as well as to

characterize, evaluate, and eventually manage those views. The

following process was the result:

Step 1- Select sensitive vistas.

Step 2- Describe elements of the vistas that are of interest.

Step 3- Discuss the sensitivity of the vista to air pollution.

Step 4- Monitor to establish baseline levels, trends, and

changes.

Step 5- Predict the effect of projected additional loadings.

In order to implement this process, the workgroup suggested

developing a notebook for the FLM that contains two pages for

each identified vista. The first page will summarize the reasoning behind selection of the view and provide information necessary for modeling visibility impacts. It will include a photograph

of the vista, a description of the vista’s features, current visibility

condition (if available), and a brief discussion of how the feature

would be affected by air pollution. The second page will be a

visibility impairment table (VIT) computed specifically for that

vista. The table will give an estimated conservative (larger than

actual) contrast change for a range of increased particle loadings,

expressed as a percentage of the PSD class I increment. Guidance in the form of a photo and a table will be provided to help

the FLM interpret projected contrast changes in terms of human

perception of the vista.

Step l-Select Sensitive Vistas.

Sensitive vistas are indicators that will be used to define

impairment in class I areas. There are three main target areas for

consideration, including:

1. Unique physical features important to the class I area (fossil

bed, limestone layer, natural arch, high pinnacle, glacial

feature),

2. Visually dominant features acting as focal points in a view.

Features so physically dominant that the eye is drawn to

them immediately (a set of arêtes, a waterfall, a highcontrast feature).

3. Frequency and duration of a person’s exposure to a view.

The higher the exposure time, the more important the visual

quality.

The Visual Quality Index (in the Forest Service landscape architect or land management planning handbooks) maybe helpful in

evaluating vistas.

Step 2-Describe Elements of Interest in the Vistas.

The distances and objects of interest in each vista determine

its sensitivity to a given input of additional aerosols. In order to

apply appropriate criteria to judge potential impairment, the

views in each class I area need to be described in terms of the

following sensitivity-enhancing properties:

Distance: Greater viewing distances require cleaner

air. List all the important or representative views in

the class I area, including their viewer-to-target distance and direction.

Coloration: If color of features, such as rock

formations, unusual vegetation, etc., is an important

element of a vista, it is more sensitive than a view of

undifferentiated forest or other “monochromatic”

scenes. Describe colorful elements of the vista.

Contrast: Vistas with low internal contrast between scenic elements, or which have light-colored

materials with low contrast to the sky are more

sensitive than a “typical” forest scene. Describe

both internal scene contrast and contrast with the

bright Sky.

Texture: Texture or fine detail in a scene is lost

before the grand features are rendered invisible. If the

interest of a vista depends on detail, describe it.

Dominant Forms: The shape of objects in a scene

can influence how the human eye perceives them.

Note unusual shapes, such as long straight lines, multiple ridge lines, etc.

The purpose of collecting this descriptive information is to

address the relative sensitivity of different views. It should be

presented in quantitative terms as much as possible. It maybe

useful to employ existing “systems,” such as those developed by

landscape architects, to describe some elements. Relate visual

elements to significant wilderness resources, and note their sensitivity to visibility degradation.

Step 3-Discuss the Sensitivity of the Vista to Air Pollution.

The sensitivity of each identified physical feature of a vista to

air pollution effects varies in relation to its attributes. These

impairments can be quantified through monitoring and baseline

data analysis. They are characterized as the obscuring of distant

targets, color, texture, contrast, and form. The most sensitive of

these (with distance as a constant) is texture, closely followed by

color. The least sensitive indicator is form.

Step 4-Monitor to Establish Baseline Levels, Trends, and

Changes.

The following step-by-step procedure can be used:

A. Identify threats to visibility: Monitoring visibility in class I

areas can be directed by first considering the actual or

perceived threat. This can be judged by using the following initial information.

1. Location of the class I area with regard to known sources

of air pollution. If the area is in the vicinity of, or a few

hundred kilometers downwind from, existing or proposed

large point or area sources, the area could be threatened. If

the area is relatively remote, the threat could be low.

2. Nearby data and data that can be interpolated for the site

from existing National Park Service (NPS) and Integrated

Monitoring of Protected Visual Environments (IMPROVE),

Forest Service, or other data.

3. Observations from Forest Service staff and records located

24

at fire lookouts, wilderness ranger stations, and other

visits. These data might include notes on layered hazes,

plumes, sources of pollutants, duration of impact, time of

year, coloration, and frequency of occurrence.

4. Visitor comments about their experiences within the wilderness, with comments put in terms similar to those in

A.3. above. In addition, expectations and desired conditions can be recorded.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
5. Comparing historical photos with current conditions. This

is largely anecdotal information.

6. Proposed new sources of pollution.

B. Establish baseline: If no existing or perceived threat exists,

monitoring should be directed at establishing current (background) condition. Such monitoring should be sufficient

to confirm lack of&gradation while establishing a baseline

for future threats.

1. Establish a monitoring site near the class I area at a similar

elevation and predominant wind direction comparable to

that in the class I area. The need for line power is not

essential but desirable. Data should be collected over at

least a 3-year period and be continuous for at least 1 year.

Decisions to extend the monitoring period beyond 3 years

or into more winter periods should be based on logistics,

cost, and the potential threat to visibility.

a. Photographic analysis should be performed on at

least two photos per day at 9 a.m. and 3 p.m. These

data should be sensitized and qualitatively evaluated

as is currently done in the Forest Service Visibility

Monitoring Program. An additional photograph at

noon is desirable. Only one photograph per day is

not recommended because of the known changes in

visibility during a day; significant events may well

be missed. Multiple pictures per day offer the opportunity to record diurnal changes that occur in many

locations.

b. Personnel who work in the wilderness (such as

wilderness rangers and fire lookouts) and provide

“airways” type observations (as is done by the National Weather Service and Federal Aviation Administration) should be trained to make visibility

observations in order to provide information about

visibility and causes of any impairment to visibilty

outside the camera’s field of view, and at times other

than the moment the picture is taken.

2. During the third year, or sooner if a threat to visibility is

observed, a 1- to 3-month intensive effort to collect data

should be designed similar to the following configuration.

a. Continuous optical measurements should be made

with either a transmissometer or nephelometer.

b. Aerosol measurements should be made with a sampler capable of providing haze-causing as well as

source-attributing constituents. (The University of

California, Davis SMART sampler is recommended,

pending the outcome of a current evaluation of this

instrument).

c. Meteorology at the monitoring site at 1-hour intervals to include wind speed and direction, temperature, relative humidity, and precipitation. The length

and time of year of the intensive study are sitedependent based on the prior record.

C. Identify imminent threats: If the initial assessment of visibility reveals a current or imminent threat, then the following

protocol should be followed. It is aimed at identifying the

kinds of sources contributing to establishing a baseline

condition, as well as aerosol loading. This monitoring

scheme should be in place long enough to take mitigating

action. Establish a monitoring site at a location that, on the

basis of topographical and meteorological analysis, is

most likely to capture both views of impairment and also

be within the area most affected. Monitoring should be

conducted as follows:

1. Analysis of three photos per day plus human observation,

as described above.

2. Additional optical measurements as described above.

3. Aerosol sampling should be performed, but the type will

depend on the availability of line power and funding.

D. Aerosol sampling methods (table 18): Particle sampling

should be designed to allow resolution of the observed

visibility degradation to causal factors, and trace aerosols

to gas/particulate sources. The period of validation would

be based on the prior record and reflect FLMs’ concerns.

Extension of the monitoring beyond 3 years, or into winter periods, should be evaluated on the basis of logistics,

costs, and level of threats. Monitoring degraded and/or

threatened sites should be adequate to allow separation of

anthropogenic from natural sources.

E. Validate data: Aerosol sampling focuses on identifying

species most responsible for scattering and absorbing light.

Intensive aerosol and optical studies of limited duration

should be scheduled every two years to: (1) extend the

data set unless it is very complete, and (2) satisfy quality

assurance requirements.

F. Optical monitoring methods: Inventory and trend analysis

should include human, qualitative, semi-quantitative, and

quantitative techniques. These include: (1) photographs

(two or three times per day), (2) human observer (events

not in camera range, clouds, etc.), and (3) battery- or

solar- powered transmissometer (first choice), or nephelometer (second choice).

G. Other considerations: A number of other factors should be

considered, including the following points:

1. Quality assurance (QA) and control (QC). The Forest

Service should utilize EPA-reviewed QA/QC procedures.

QC procedures have been prepared for camera monitoring; no QA procedures are known to exist.

2. Nighttime visibility is recognized as a valuable wilderness

experience to be protected in some class I areas. Recommendations for monitoring at night do not include photography. A photometer and lens may be used at the camera

site for vertical measurements of the darkness of the sky.

Further investigation of this issue is warranted.

3. Permanent storage. It is recommended that selected baseline

photographs be digitized. The data will probably be least

perishable on optical discs. Such data should represent a

range of the baseline condition.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 25
Table 18 —Potential aerosol sampling systems (annual operating costs are based on 102 samples).1

System

SMART

IMPROVE

(full)

IMPROVE

(fines only)

IMPROVE

(NESCAUM)

PM10

Features Capital cost / operating cost Power source

2 size ranges (0.3-2.5 μm, $4500 / $65 for 24-hr sample B/S

2.5-10 μm); continuous

sampling of S, trace elements

and soot; 1-4 weeks unattended

2 size ranges (<2.5 μm, $ 16,000 / $12,000 annually LP

<10 μm); flexible sampling period;

sulfate, nitrate, organic C, trace

elements; 4 channels

Same as full IMPROVE except $11,000 / $8500 annually LP

no PM10; 3 channels

Same as full IMPROVE except $2000 / $3500 annually LP

no PM10, nitrate or C; only fine

mass, including trace elements

Mass < 10 μm; elemental $1500 / $3500 annually LP

analysis (influenced by soil)

1LP = line power

B/S = battery/ solar

S = sulfur

C = carbon

IMPROVE = Integrated Monitoring of Protected Visual Environments

NESCAUM = Northeast States for Coordinated Air Use Management

PM10 = Particle mass < 10 μm

4. A nephelometer capable of operating without line power

and in a remote setting unattended for days at a time is

now available. The workshop participants recommended

that the Forest Service evaluate the usefulness of this

device. Nephelometers are lower cost, continuous sampling instruments that avoid some of the problems of

transmissometers and cameras. For example, clouds do

not obscure the data, although techniques for accounting

for moisture and internal instrument heating are necessary. Alignment on targets is also not an issue, although

some operator experience is helpful.

H. Individual site chatacterstics: Finally, although substitute

techniques for camera monitoring have been addressed

here, a monitoring program should be tailored for each

site to account for differing topography, resource and

logistic issues, and real or perceived threats. Visibility

measurements should be designed for their usefulness in

addressing management problems at the class I area in

question rather than to fit in spatially or temporally with a

network of monitoring sites.

Step 5–Predict the Effect of Projected Additional Loadings.

This step provides a process for the manager to quickly

screen the potential visibility impacts of an increase in suspended particle levels, expressed as a percentage of the allowable PSD increment. Given the detailed, vista-specific information developed as described above, a series of calculations are

performed for each vista and line-of-sight that gives the estimated contrast change for several levels of increased particulate

pollution. These calculations are performed beforehand and are

summarized in a visibility impairment table (VIT) (see figure 4).

An explanation of the use of the VIT and an outline of calculation procedures are provided in the example below.

A. Visibility impairment table (VIT): When confronted with a

PSD permit, the FLM will consult a notebook that contains the description of the vistas and views and a VIT for

each one. The PSD permit will usually include an estimate

of the increment in total suspended particulate (TSP) in

the class I area. Expressing TSP as a fraction of the total

PSD increment, the FLM will look up the expected contrast change for each vista. Guidance is provided below on

how to interpret these numbers in terms of changes perceptible to humans. The manager will then use personal

judgment and knowledge of the area to determine whether

the reduction in contrast is significant. The next section

describes how the VIT calculations are made.

B. Estimating visibility “loading”: The PSD “increments” address particles as TSP. Unfortunately, TSP is a very poor

index of visual air quality. Correlations between TSP and

visibility are inherently weak because the larger particles

dominate TSP mass measurements, and the smaller particles dominate the optical effects. In addition, the small

mass increments of fine particles needed to degrade visibility in “clean” wilderness locations are not likely to

be noticed within the inherently large variability of TSP

measurements. The following analysis addresses primarily the particles less than 2.5 μm in diameter (PM 2.5).

1. Estimating baseline light extinction.

a. Use direct optical measurements if they are available. If photographic records are available, use cal26 USDA Forest Service Gen. Tech. Rep. PSW-GTR- 136. 1992.
culated extinction derived from contrast measurements, but be cautious that these calculations do not

violate the assumptions on which they are based.

b. Use particle data, if no optical data are available.

These will generally need to be interpolated from the

regional data from the IMPROVE network. Calculate the extinction from the PM 2.5 estimated mass

by applying either known values for each chemical

component or the generic extinction efficiency (εΕ

)

value of 3 m2/g. Total extinction is the particle value

plus the light scattering due to air at the altitude of

the class I area. If baseline aerosol composition is

likely to include an unusually large amount of coarse

particles, apply the extinction efficiency of 0.7 m2

/g

to correct for the effect of coarse particles.

2. Light extinction due to the predicted pollutant increment. This should be calculated either by using known

properties of its constituent chemicals, or by applying

the generic urban industrial fine aerosol extinction efficiency of 5 m2

/g. Total extinction under the predicted

increment is the sum of the total baseline plus the increment extinction.

3. Atmospherical optical calculations of the VIT (Henry 1977).

Given the extinction efficiency εΕ (see above) and an

ambient concentration of particulate χ (mg/m3

), the extinction coefficient β (m-1) can be calculated as:

β = εΕ χ .

Assuming that absorption is the principal cause of

signal attenuation (visibility reduction), the contrast of

details in a vista (Cd) can be calculated as:

Cd = Che 

β R

where Ch is the measured contrast of a dark target against

the background sky, and R is the distance from the viewer

to the target.

C. Interpretation of the VIT: The contrast changes from the VIT

must be understood in terms of human perception of

changes in the vista. Depending on the vista and the

feature of interest, there are two ways of interpreting the

contrast change numbers from the WT. In the one case, an

FLM may wish to know whether there is a noticeable

change in the scene. In the other case, one would wish to

know whether a feature will be visible or not. Each of

these cases is discussed below.

1. Just noticeable differences (JNDs). As particles are added

to the atmosphere, at some point the observer will notice a

change in the clarity of the scene. This level is one JND

(Carl son and Cohen 1978). As particles continue to be

added, a level will be reached at which another change is

just noticeable. This is two JNDs, and so on. Figure 3 is

the result of applying a rather complex model of the

human visual system, and presents a relationship between

contrast change and the number of JNDs in the scene

(Henry 1979). Also included in the figure is a suggested

interpretation of the meaning of the JNDs. The three

different lines in fig. 3 are the result of using three different values for a technical parameter in the model which is

not easily estimated at this time. This figure will be updated as research into human perception of visibility degradation progresses.

2. Visibility of landscape features. Table 19 gives the threshold contrast of various sizes of features. The VIT can be

used to estimate whether the contrast threshold has been

reached. The contrast change is subtracted from the baseline

contrast. The FLM then refers to the table to estimate the

contrast threshold for the particular feature of interest.

Example Application: Visibility AQRV

for Desolation Wilderness

The five-step process described above is illustrated in fig.4

with an example for Desolation Wilderness.

Nighttime Visibility as an AQRV

The process for managing visibility in class I areas (fig.4)

deals implicitly with daytime visibility. The visibility workgroup

reasoned, however, that nighttime visibility is sufficiently different and valuable that it should be treated as a separate AQRV.

Views for nighttime visibility are defined as vertical and panoramic sights of the night sky. Several potential impacts of air

pollutants are: (1) loss of light or extinction that would reduce

the number of, or obscure, visible stars and planets, (2) source

light diffusion that would decrease the intensity of light visible

from stars and planets, (3) increased night sky brightness due to

increased light sources in and around the viewing area, and (4)

increased diffusion of light through the air mass that would

reduce both light intensity and number of stars and planets

visible in the dark night sky.

Figure 3 —Predicted number of just noticeable differences vs. contrast

reduction for three values of the equivalent sine-wave contrast of visual

detail in a scenic vista (from Henry 1979).

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 27
Table 19 —Visual range of contrast detail, indicating threshold contrast for various sizes of landscape features (from Carlson and

Cohen 1978).

Visual range

Detail of Characteristics Examples for a West East Contrast

level size at 10 km hillside at 10 km (VR=100 km)1

(VR=20 km)1

threshold

m --------------------km--------------------

Very coarse > 100 Hills, valleys, 79 16 -0.046

(form) (>0.57O arc) ridgelines

Coarse 50-100 Cliff faces, smaller 76 15 -0.052

(line) (0.29 O

-0.57 O arc) valleys

Medium 25-50 Clumps of large 62 12 -0.089

(texture) (0.14 O

-0.29 O arc) vegetation, clearings

on forested slopes

Fine < 25 Individual large 22 4 -0.424

(texture) (<0.14O arc) trees, clumps of

small vegetation

1VR is the assumed background visual range.

Principal viewers include professional astronomers at observatories, amateur astronomers, campers and hikers, professional

and amateur photographers, and personnel at military installations. Viewers’ objectives for nighttime observations differ, and

perceptions of night visibility may vary.

The first three steps of the five-step process described above

for day visibility can also be applied to night visibility. Steps 4

and 5, monitoring and prediction, need to be handled differently

because of inherent differences in nighttime viewing.

Establishing Baseline Conditions

Collection of primary data to determine existing conditions

should include viewer observations and photographs. These are

necessary to establish extent and value of the dark sky view. Still

or video photographs of horizontal and vertical views of the

night sky should also be collected. Light scattering can be estimated from the photographs.

Viewer observations can be acquired by oral interviews or

from written observations of personnel who work in the wilderness. Documentation can include interview sheets, visibility

logs, and photographs. The visibility log should include date,

time, location of viewer, and subjective observations of the

visibility conditions of the night sky. Some viewing areas will be

less sensitive because of differences in elevation, slope, or accessibility. Photographs should be correlated with oral interview

results.

Observation of selected stars that can be recognized in the

field can be repeated to track visibility over time. This information should be recorded on visibility log sheets. Extinction of

visible stars in the Milky Way should be evaluated by observers

and recorded in the visibility log. At least one calendar year of

observations is needed to establish baseline nighttime visibility

of the Milky Way because of the rotation of the earth and

variation in weather conditions. Observers need adequate training to assure consistency in observations. Photographs can track

both visibility of the stars and increases in light diffusion in the

night sky. Stars that are part of or near constellations are more

desirable for field observations. Local astronomers can be consulted to assess photographs and verify observations.

In areas where sensitivity and concern for existing conditions

are high, correlation of systematic particle sampling, optical

characterization, and paired horizontal-vertical photographs from

established monitoring sites can be used to establish the existing

condition and to provide sufficient data for modeling pristine

and baseline night-sky conditions. After baseline conditions are

established, periodic monitoring should be continued and data

stored for long-term comparison.

Determining Source Impacts

Stars are the most distinguishing feature of the night sky, and

their visibility extinction can be used to measure impacts on

visibility from air pollutants. A decrease in star magnitude from

6 to 7 should be evaluated both by observation of selected

magnitude 6 stars and by photographic record. Magnitude 6 stars

are a sensitive receptor because they are barely visible with the

naked eye, and source light diffusion could cause them to be

invisible in the night sky. The following guidelines can be used

to verify impacts:

(1) A decrease in star magnitude from 6 to 7 as the indicator

of source light diffusion effects.

(2) Visibility extinction of 50 percent of the visible stars in

the Milky Way as the indicator of loss of light in a dark

night sky.

(3) Inability to capture magnitude 6 stars on photographs

with enough clarity to identify the star with the naked

eye as the indicator of increased night sky brightness.

28 USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
Figure 4 —Application of the five-step visibility process is illustrated with an example for Desolation Wilderness.

STEP 1 SENSITIVE VISTAS

Include a photo of receptor from the proposed monitoring site (with date on back).

Date: 06/19/92

Time: 10:05 a.m.

Photographer / observer: Jane Sharpeyes

Location of photo site (by Universal Transverse Mercator [UTM] coordinates,

elevation [m]): 4314500 m North, 738800 m East; 2767 m

Location of receptor (by UTM coordinates, elevation [m]): 4314500 m North,

728700 m East; 2757 m

Line of sight distance: 10.1 km

Weather: wind speed 7 m/sec, temperature 15°C, relative humidity 30 percent,

high cirrus clouds, no haze

RECEPTOR ATTRIBUTES: Give a brief description.

Unique Feature

A Focal Point

Long Exposure Time

continues

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 29
Figure 4, continued

STEP 2 ELEMENTS OF INTEREST IN THE SCENE

Color:

Contrast:

Texture:

Form:

Describe hues by color chart against background color. (For example, “top

portion dark gray with red bands 100 m wide, low portion uniform light

gray”).

Select either a bright area or a dark area. (For example, “contrast of dark

metamorphic rocks over light granitic rocks”).

Select fine, medium, or coarse.

Select conical, pyramid, dome, or jagged ridge. (For example, “rough,

jagged upper surface and smooth, rounded lower surface”).

STEP 3 HOW THE VISTA CAN BE AFFECTED BY AIR POLUTION

Give a brief description of the effect of air pollution on the scene. For example:

1. Additional path radiance will remove the vividness of the red bands on the side

of Mt. McConnell, making them more gray.

2. Additional particulate pollutant loading will reduce the contrast within the scene

as presented in the visual impairment table (Step 5).

STEP 4 ESTABLISH A MONITORING STRATEGY

No new-source applications are pending, but there is concern about the effect of the

Sacramento Valley area source of pollution. In addition, growth in the Tahoe Basin poses

a threat because Basin aerometric samplers show high ambient concentrations of ozone.

Particulate loadings will also probably increase.

Vista A is a point outside the Wilderness looking across much of the Wilderness that is

at the average elevation and downwind. There is power at a site about 1 km away and 150

m lower. The site is readily accessible 9 months out of the year. Budget= $10,000/yr.

The following strategy is therefore suggested:

Year 1 (1) Purchase one camera and take three photos per day for the 9-month

accessible period and one photo per day at noon during the remaining

period. Hire a temporary employee to change film and filter in years 2 and

3. Capital cost = $2500. Operating Cost= $4500. Labor cost = $1000.

(2) Train Wilderness Rangers to record one routine observation per day

from a prominent or frequently visited part of the Wilderness and to make

30 USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
Figure 4, continued

a “special” observation if they notice a visibility impairment. Camera site

operators should also be trained to make such an observation at the time

the film is changed. Training cost = $100.

(3) Purchase and begin operating, but do not analyze data from, one

SMART particle sampler. Capital cost = $2000.

Year 2,3 (1) Continue with camera schedule. Operating cost = $4500. Labor cost =

$1OOO.

(2) Continue observation by trained personnel. No extra cost.

(3) Continue to operate particle sampler. Analyze data for 1.5 years.

Analysis cost = $3000 x 1.5 yr = $4500.

(4) At end of year 3, analyze data to determine actual impacts (compared

to those predicted at project start). Based on results, assess strategy for

future monitoring and mitigation.

STEP 5 EFFECT OF PROJECTED ADDITIONAL LOADINGS

The Forest Supervisor has determined from reviewing the data collected in Step 4 that a

2 percent change in the baseline contrast measurement (one JND from fig. 3) is unacceptable. The contrast threshold for coarse features (-0.052 from table 19) is exceeded by a

substantial amount at all percentages of this increment (see visual impairment table

below), so the target should be easily visible to the viewer. A new source is predicted to

contribute 25 percent of the TSP class I annual increment (5 μg/m3

) to both sensitive

views. McConnell Peak would experience a 5 percent contrast change against the background sky, while “Red Bands” along the escarpment would experience a 1.7 percent

contrast change (see visual impairment table below). Thus, the criterion value of 2 percent is exceeded for one case. With no additional information, the FLM would probably

recommend denial of the application.

A sample visual impairment table for McConnell Peak (Desolation Wilderness),

Percent

of PSD

increment 1

0

10

25

50

75

100

showing the effect of aditional particulate loading on contrast reduction.

McConnell Peak McConnell Peak (Red Bands)

Contrast Contrast Contrast Contrast

change change

-0.444 0.000 -0.148 0.000

-0.423 0.022 -0.141 0.007

-0.392 0.052 -0.131 0.017

-0.346 0.098 -0.115 0.033

-0.307 0.137 -0.102 0.046

-0.267 0.175 -0.090 0.058

1

PSD = prevention of significant deterioration.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992. 31
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34 USDA Forest Service Gen. Tech. Rep. PSW-GTR-136. 1992.
The Forest Service, U.S. Department of Agriculture, is responsible for Federal leadership in forestry.

It carries out this role through four main activities:

● Protection and management of resources on 191 million acres of National Forest System lands

● Cooperation with State and local governments, forest industries, and private landowners to help

protect and manage non-Federal forest and associated range and watershed lands

● Participation with other agencies in human resource and community assistance programs to

improve living conditions in rural areas

● Research on all aspects of forestry, rangeland management, and forest resources utilization.

The Pacific Southwest Research Station

● Represents the research branch of the Forest Service in California, Hawaii, American Samoa

and the western Pacific.

Persons of any race, color, national origin, sex, age, religion, or

with any handicapping conditions are welcome to use and enjoy

all facilities, programs, and services of the U.S. Department of

Agriculture. Discrimination in any form is strictly against agency

policy, and should be reported to the Secretary of Agriculture,

Washington, DC 20250.