United States

Department of

Agriculture

Forest Service

Rocky Mountain

Research Station

Fort Collins,

Colorado 80526

General Technical

Report RMRS–GTR–4

Guidelines for Evaluating Air Pollution

Impacts on Wilderness Within the

Rocky Mountain Region:

Report of a Workshop, 1990
Abstract

Haddow, Dennis; Musselman, Robert; Blett, Tamara; Fisher, Richard, tech. coords. 1998. Guidelines

for evaluating air pollution impacts on wilderness within the Rocky Mountain Region: Report

of a workshop, 1990. Gen. Tech. Rep. RMRS-GTR-4. Fort Collins, CO: U.S. Department of

Agriculture, Forest Service, Rocky Mountain Research Station. 31 p.

This document is the product of an ongoing effort begun at a 4-day workshop sponsored by the Rocky

Mountain Region of the USDA Forest Service, held in December 1990 in Estes Park, Colorado.

Workshop participants gathered in groups to work on pollution impacts in three specific areas: aquatic

ecosystems; terrestrial ecosystems; and visibility. Because the groups met separately and subsequently worked independently, the reports they generated differ considerably in format and style.

They all focus, however, on providing the Forest Service with information that may be used to identify

and develop sensitive receptors and limits of acceptable change for assessing air pollution impacts

on air quality-related values in wildernesses within the Rocky Mountain Region of the Forest Service.

The reports also address needs and recommendations relating to modeling or predictive techniques,

monitoring, and research.

Keywords: air quality, air pollution, wilderness, aquatics, visibility

Technical Coordinators

Dennis Haddow is an air quality specialist with the USDA Forest Service, Rocky Mountain Region.

Robert Musselman is a plant physiologist with the USDA Forest Service, Rocky Mountain Research

Station.

Tamara Blett is an air quality specialist with the Rocky Mountain Region.

Richard Fisher is an air specialist with the USDA Forest Service, Washington Office.

Publisher

Rocky Mountain Research Station

Fort Collins, Colorado

April 1998

Cover photo of Continental Divide across Forest Canyon in Rocky Mountain National Park by Lane Eskew

You may order additional copies of this publication by sending your

mailing information in label form through one of the following media.

Please send the publication title and number.

Telephone (970) 498-1719

E-mail rschneider/rmrs@fs.fed.us

FAX (970) 498-1660

Mailing Address Publications Distribution

Rocky Mountain Research Station

3825 E. Mulberry Street

Fort Collins, CO 80524-8597
Contents

Acronyms and Symbols ................................................................................ iv

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

The Role of the Forest Service ............................................................ 1

Wilderness Management Premises ................................................. 1

Workshop Format............................................................................. 2

2. Aquatic Ecosystems ............................................................................... 4

By Jill Baron and John Turk

Perspective........................................................................................... 4

Sensitive Receptors and Limits of Acceptable Change ....................... 4

Acidic Deposition.............................................................................. 4

Air Toxic Compounds ....................................................................... 6

Airborne Nutrients ............................................................................ 7

Mercury ............................................................................................ 8

Analyzing and Predicting Adverse Impact............................................ 9

Dynamic Models............................................................................... 9

Empirical Models .............................................................................. 11

Monitoring ............................................................................................. 12

Long-Term Monitoring ...................................................................... 14

Data Base Management .................................................................. 15

Monitoring Priorities ......................................................................... 15

Research Needs and Recommendations ............................................ 16

Priorities ............................................................................................... 16

Literature Cited ..................................................................................... 16

Aquatic Workshop Participants ............................................................ 18

3. Terrestrial Ecosystems .......................................................................... 19

By Anna Schoettle and William Moir

Perspective........................................................................................... 19

Sensitive Receptors and Limits of Acceptable Change ....................... 19

Predictive Techniques .......................................................................... 20

Direct Impact Projections ................................................................. 20

Gaseous Pollutant Uptake ............................................................... 20

Recommendations ........................................................................... 23

Guidelines for Evaluating Air Pollution Impacts

on Wilderness Within the Rocky Mountain

Region: Report of a Workshop, 1990

Dennis Haddow, Robert Musselman, Tamara Blett, and

Richard Fisher, Technical Coordinators
Monitoring ............................................................................................. 23

What to Monitor ................................................................................ 24

A Recommended Monitoring Approach ........................................... 24

Research Recommendations ............................................................... 25

Literature Cited ..................................................................................... 25

Terrestrial Ecosystems Workshop Participants ................................... 26

4. Visibility ................................................................................................... 27

By Douglas Latimer

Perspective........................................................................................... 27

Sensitive Receptors and Limits of Acceptable Change ....................... 28

Modeling Recommendations ................................................................ 29

Monitoring Recommendations ............................................................. 29

Research Recommendations ............................................................... 30

Visibility Workshop Participants ........................................................... 31
Acronyms

ANC Acid neutralizing capacity

AQRV Air quality-related value

BACT Best available control technology

BART Best available retrofit technology

BLM Bureau of Land Management

EPA Environmental Protection Agency

FLM Federal land manager

GIS Geographical information systems

ILWAS Integrated Lake Watershed Acidification Study Model

IMPROVE Interagency Monitoring of Protected Visual Environments

jnc Just noticeable change

LAC Limit of acceptable change

LD50 Lethal concentration for 50% of individuals; standard measure of toxicity

MAGIC Model of Acidification of Groundwater Catchments

NADP National Atmospheric Deposition Program

NAPAP National Acid Precipitation Assessment Program

NPS National Park Service

PAH Polycyclic aromatic hydrocarbons

PCB Polychlorinated biphenyls

PLUVUE Plume visibility model

PM2.5 Particles smaller than 2.5 m in diameter

ppm Parts per million

PREVENT Pacific Northwest Regional Visibility Evaluation Using Natural Tracers

PSD Prevention of Significant Deterioration

QA/QC Quality assurance/quality control

RAIN Reversing Acidification in Norway

TOPMODEL A variable source area import hydrologic model

USDA U.S. Department of Agriculture

USFS USDA Forest Service

USFWS U.S. Fish and Wildlife Service

USGS U.S. Geological Survey

VISCREEN Visibility Screening Model

VOC Volatile organic compound

WHITEX Winter Haze Intensive Tracer Experiment

WLS Western lake survey

DE Plume perceptibility - color contrast change between a plume and its background

iii
Chemicals and Associated Terms

Al Aluminum

Al+n Positively charged aluminum ion

Alm Monomeric aluminum species

As Arsenic

C Carbon

CA Sum of base anions

Ca Calcium

Ca2+ Calcium ion

CB Sum of the base cations

Cd Cadmium

CH3Hg Methyl mercury

Cl- Chloride

CO2 Carbon dioxide

Cu Copper

D D euterium

DO Dissolved oxygen

F Fluoride

H+ Hydrogen ion

HF Hydrogen fluoride

Hg Mercury

HgS Mercuric sulfide, cinnabar

HNO3 Nitric acid

H2SO4 Sulfuric acid

K Potassium

Mg Magnesium

mg milligrams

Mn2+ Divalent manganese ion

N Nitrogen

Na Sodium

ng Nanograms

NH3 Ammonia

NH4

+ Ammonium ion

NO2 Nitrogen dioxide

NO3

- Nitrate ion

NOx Nitrogen oxides

O2 Oxygen

O3 Ozone

18O Isotopic oxygen

P Phosphorus

Pb Lead

PCO2 Partial pressure of CO2

pH Negative log (base 10) of the hydrogen

ion concentration, a measure of acidity

or alkalinity in water

PO4

3- Phosphate ion

S Sulfur

Se Selenium

SO2 Sulfur dioxide

SO4

2- Sulfate ion

Zn Zinc

iv
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 1

1. INTRODUCTION

In December 1990, the Rocky Mountain Region of the

USDA Forest Service conducted a workshop in Estes Park,

Colorado, to exchange facts and information for consideration by the Forest Service in evaluating air pollution

impacts to wilderness areas within the Region. The information and opinions contained in this report along with

any other relevant information obtained since the workshop was conducted will be used on a case-by-case basis

by the Region to determine the acceptability or nonacceptability of air pollution impacts to the Region’s wildernesses.

The goal of the workshop was for National Forest

Managers, other federal land managers, air regulatory

agencies, research scientists, and interested publics to

conduct a workshop to exchange facts and information for

consideration by the USDA Forest Service in identifying

evaluation procedures for air pollution impacts to Wilderness within the Rocky Mountain Region.

The objectives of the workshop were as follows:

1. Compile a workshop report that represents a survey of facts and information that the Forest Service

can consider along with subsequently obtained

information to identify evaluation procedures and

modeling techniques appropriate to predict, on a

case-by-case basis, if existing or proposed air

pollution sources will result in adverse impacts to

wilderness. (Although consensus among participants was not discouraged it was not an objective

of this workshop because the report was to represent a range of facts and information provided by

the participants.)

2. Identify and prioritize any additional monitoring

of air quality related values that should be conducted by the Forest Service within the Rocky

Mountain Region to meet the following needs:

• Develop information about which wildernesses

within the Rocky Mountain Region have the

greatest potential for air pollution impacts.

• Add to the current base of information about

sensitive receptors having potential for air pollution impacts. Identify additional sensitive

receptors as needed, determine the current condition of these sensitive receptors, and determine change in these sensitive receptors attributable to existing air pollution in selected wildernesses.

• Identify or refine evaluation procedures identifying change to sensitive receptors.

• Develop a more complete information base

about sensitive receptors in wilderness, to be

able to better meet the needs of the air regulatory process.

3. Identify research needed within the Rocky Mountain Region to help meet the monitoring needs of

Objective 2, above.

It must be noted that this report is not a binding document and leaves the Forest Service and its decisions makers free to exercise discretion and formulate policy on a

case-by-case basis with respect to air quality related values, sensitive receptors, and limits of acceptable change.

Since the 1990 Workshop, new information not included in this report has become available that is used in

the identification and protection of AQRVs and in the

determination of LACs. This document is presented as a

resource of background information available at the time

of the 1990 Workshop.

The Role of the Forest Service

The USDA Forest Service, as a federal land manager of

88 Class I wilderness areas, is directly involved in implementation of the Prevention of Significant Deterioration

(PSD) program. The Clean Air Act gives “... an affirmative

responsibility to protect the air quality-related values

(including visibility) of any such lands within a Class I

area and to consider, in consultation with the Administrator, whether a proposed major emitting facility will have

an adverse impact on such values.” Examples of AQRVs

in wilderness areas are listed in table 1.

Wilderness management premises

Workshop participants were provided with the following principles related to air quality and wilderness:

1. Wilderness is not merely a commodity for human

use and consumption. Wilderness ecosystems

have intrinsic values other than user/public concerns.

2. The objective of wilderness management is to

offer a natural experience, rather than an enjoyable one. The amount of enjoyment is purely a

personal matter for the individual user to decide.

3. All wilderness components are equally important; none is of lesser value than any other.

4. A wilderness component is important even if

users of the wilderness are unaware of its existence.

5. All life forms are equally important. For example,

microorganisms are as essential as elk or grizzly

bears.
2 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

6. The goal of wilderness management is to protect

not only resources with immediate aesthetic appeal (i.e., sparkling clean streams) but also unseen

ecological processes (such as natural biodiversity

and gene pools).

7. The most sensitive wilderness components are to

be emphasized more than those of average or

normal sensitivity. Sensitivity is generally determined by inertia (resistance to change), elasticity

(how far the component can be “stretched” from

its natural condition without being permanently

modified), and resiliency (the number of times it

can revert to its natural condition after experiencing human-caused change).

8. Each wilderness component is important in itself,

as well as in terms of how it interacts with other

components of the ecosystem. That is, the individual parts of the wilderness ecosystem are as

significant as the sum of the parts.

9. The physical components of the ecosystem (for

instance, lake chemistry) are as essential as its

biological constituents (i.e., salamanders).

10. Wilderness components are to be protected from

“human-caused change” rather than from “damage.” Terms such as “damage” and “harm” are

prejudicial, whereas “human-caused change” is

value-neutral. (For example, deposits of nitrogen

in a lake from nitrogen oxide, a common air

pollutant, might result in more plant growth and

bigger fish. This would, however, be an unnatural—and therefore unacceptable—change in the

aquatic ecosystem.)

11. The goal of wilderness management is to protect

natural conditions, rather than the conditions

when first monitored. That is, if initial monitoring

in a wilderness identifies human-caused changes,

appropriate actions should be taken to remedy

them to restore natural conditions.

12. The designation of a wilderness as Class I or II

does not dictate the management goals for it;

these are identified in the Wilderness Act. The

designation only determines which options are

available to meet the goals. Class I wildernesses,

for instance, can be protected through the specific

AQRV analysis provided for in PSD permitting

regulations, whereas the protection of Class II

wildernesses can be achieved using BACT requirements.

13. While it may not be possible to manage every

wilderness in a natural or near-natural state, each

should be managed in as pristine a condition as

the specific (local) biophysical, legal, scientific,

and social/political situation will allow. That is,

the Region will do the best job possible of wilderness management, based on local constraints and

opportunities. The extent of actual wilderness

protection, therefore, may vary.

14. Although monitoring is critical to any PSD decision, it must not interfere needlessly with wilderness. For example, in mountain ranges or other

geomorphic units of which only part is wilderness, much of the most intrusive monitoring and

instrumentation should be conducted in the adjacent nonwilderness—if such areas adequately represent the wilderness of concern. Often, however,

western wilderness occupies an entire highelevation area for which there is no truly representative nonwilderness subjected to the same

atmospheric deposition from a proposed source.

15. Limits of acceptable change (LACs) should be

conservative. For use in this document, LACs are

defined as those changes in the physical, chemical, biological, or social condition of an air quality

related value that can occur without a loss of

wilderness character. In the case of uncertainty,

LACs should be identified to be over-protective

rather than under-protective of wilderness. However, if for a specific wilderness any party can

provide clear and convincing information which

demonstrates that the selected LAC is either too

restrictive or too lax, the LAC will be modified.

Workshop format

It was the intent of the Estes Park workshop to develop

guidelines for use by Region 2 Forest Service managers in

fulfilling their responsibilities to protect AQRVs related to

aquatic and terrestrial ecosystems and visibility. The participants at the workshop were divided into three groups

to address these three areas. The mission given the

workgroups was to:

1. Develop a document that represents a survey of

facts and information which the Forest Service

can use to identify evaluation criteria and modeling techniques appropriate to predict if existing

or proposed air pollution sources will result in

adverse impacts on wilderness.

2. Identify and prioritize any additional monitoring

of air quality-related values that should be conducted by the Forest Service within the Rocky

Mountain Region to meet the following needs:

• Develop information about which wildernesses

within the Region are the most vulnerable to

air pollution impacts.
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 3

• Add to the current base of information about

sensitive receptors having potential for air pollution impacts. Identify additional sensitive

receptors as needed, determine the current condition of these sensitive receptors, and determine change in these sensitive receptors attributable to existing air pollution in selected wildernesses.

3. Identify research needed within the Rocky Mountain Region to help meet the monitoring needs in

item 2, above.

Within the context of the PSD process and legislated

programs authorizing protection, AQRVs are defined as

any wilderness component that can be modified by human-caused air pollution. Examples include flora, fauna,

soil, water, visibility, and cultural objects. Practically speaking, this concept of AQRVs is sufficiently broad as to

encompass virtually any aspect of wilderness.

To determine whether AQRVs may be adversely impacted, it is necessary to identify sensitive receptors that

can provide a measure of change related to air pollution

impacts. Sensitive receptors may be specific objects, processes, attributes, or species within the broader categories

of AQRVs. It is important that sensitive receptors have the

following characteristics:

• They must be able to be detected, monitored, and

measured;

• They must be sensitive and directly responsive to

change; and

• Changes in receptor behavior and response can be

modeled and predicted.

Limits of acceptable change are identified relative to

certain attributes of sensitive receptors. They are the criteria the Region will use to determine if existing or potential

air pollution impacts on wilderness are acceptable or not.

LACs are not air pollution or atmospheric deposition

standards. LACs are numbers that represent an anthropogenic change in a physical, chemical, or biological

component of the ecosystem or the visibility within wilderness. The acceptable change needs to be small enough

to prevent deterioration of the wilderness resource, but

large enough so as not to unnecessarily hinder development within the range in which wilderness resources

can easily coexist. It must be noted that this document

represents only one source of information that the Region

will use to identify LACs and that any recommendations, definitions, or opinions contained in individual

work group reports are not binding on the Forest Service.

Table 1 provides a general identification of AQRVs

with examples of sensitive receptors and pollution-caused

changes for which acceptable limits of change could be

defined.

The individual work group reports present the perspectives of each group and their efforts to identify sensitive receptors and limits of acceptable change. Each report

further addresses needs and recommendations relating to

modeling or predictive techniques, monitoring, and research.

Table 1. Examples of air quality-related values, sensitive receptors, and potential air pollution-caused changes.

Air quality-related values Sensitive receptor examples Potential air pollution-caused changes

Flora and fauna lichens, zooplankton, rate of growth, mortality, reproduction;

subalpine fir, mosses, raspberry direction of succession; amount of visible

injury, genetic diversity, productivity, and

abundance

Soil alpine soils cation exchange capacity, base saturation,

pH, structure, metals concentration

Water vernal pools, alpine lakes, total alkalinity; pH; concentration of

deposition of rain/snow anions, cations, metals, and dissolved

oxygen

Visibility high-use vista contrast, visual range, coloration

Biological diversity diatoms loss or depletion of a species

Cultural-archaeological and paleontological cave drawings decomposition rate

Odor wilderness user anthropogenic odors
4 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

2. AQUATIC ECOSYSTEMS

By Jill Baron and John Turk

Perspective

This section presents recommendations of the Aquatic

Ecosystems Group. We discussed the state of our understanding of processes by which ecosystems respond to air

pollutants, the possibility for future threats, and the monitoring and research needs for Region 2 wilderness areas.

The group felt fortunate in being able to take advantage

of the results of the 10-year National Acid Precipitation

Assessment Program (NAPAP). As a result of NAPAP,

there has been a large increase in understanding of aquatic

ecosystem processes and organismal response to pollutants. Several members of the group have been active

participants in NAPAP-funded research and were able to

bring their expertise to bear on the questions of maintaining aquatic resource integrity in wilderness areas.

Aquatic ecosystems in wilderness areas include watersheds, lakes, streams, springs and groundwater, riparian

areas and wetlands, ephemeral surface water (such as

vernal pools), wet cave environments, and glaciers.

There was consensus that the chemical composition of

different types of precipitation (snow, rain, fog, clouds,

rime ice) can provide early and sensitive detection of the

presence of many airborne pollutants. The chemical composition of lakes and streams was thought to be a good

indicator of air pollutants, although the effective use of

surface water chemistry requires a good understanding of

annual biogeochemical variation. This is not common

knowledge for most wilderness areas. Organisms or whole

communities in lakes and streams can be good indicators

of change due to airborne pollutants, although these again

require foreknowledge of the natural variation inherent in

Rocky Mountain aquatic populations, the sensitivity of

individual species to each pollutant type, and possibly the

sensitivity of communities (inferred by pollutant-specific

indices). Bioaccumulation of mercury (Hg) in fish and

possibly other aquatic species make organisms especially

appropriate indicators of mercury contamination. Other

possible sensitive receptors mentioned included aquatic

habitat attributes and soil chemical composition.

Acceptable change is change in chemical concentrations, biological populations, or physical attributes of

aquatic ecosystems from natural variability. Natural variability can be caused by seasonal cycles of temperature,

precipitation, solar radiation, and hydrology. It can also

result from natural disturbances such as wildfires, pest

outbreaks, avalanches, drought, floods, debris falls, or

erosional processes. The limits of acceptable change, then,

define the boundary conditions beyond which impacts

would be considered adverse or unacceptable. The Aquatics Group tried to choose limits that could accurately and

precisely indicate a pollutant-caused trend, but would be

below a critical threshold of damage to aquatic organisms.

In all cases, LACs were interpreted to represent the cumulative effect of all emission sources, and not only the effect

caused by each individual PSD permit applicant.

To protect wilderness areas in a cost-effective way, the

Aquatics Group recommended that categories of pollutants be ranked according to their likelihood of occurrence

and severity of impact. This will aid in prioritizing appropriate monitoring and research in wilderness areas. The

Aquatics Group focused on what were thought to be the

most critical threats, based on current knowledge, to

Rocky Mountain wilderness aquatic resources. These

threats include:

• acidic deposition, including wet, dry, and occult

deposition of sulfuric acid (H2

SO4) and nitric acid

(HNO3);

• air toxic compounds, including pesticides, herbicides, volatile organic compounds (VOCs), and

fugitive organic compounds from industrial processes;

• nitrate (NO3

-

) or other nutrients such as phosphate (PO4

3-) or ammonium (NH4+); and

• mercury (Hg).

Sensitive Receptors and

Limits of Acceptable Change

This section suggests appropriate receptors and limits

of acceptable change relating to the priority threats identified above.

Acidic deposition

Whether acidic atmospheric deposition will cause adverse effects on aquatic ecosystems is a complex function

of depositional loading of strong acid anions in rain,

snow, or other precipitation, and the sensitivity of the

ecosystems receiving the deposition. Sensitivity itself is

complex, and depends upon the bedrock and overlying

material (including soil) composition, residence time of

water within the basin (related to topographic relief, hydrologic cycle, and annual precipitation distribution), and

vegetation types and cover. A summary of sensitive receptors and LACs relating to acidic deposition is presented in table 2.
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 5

Sensitive receptor: Chemical composition of wet deposition, including rain and snow. The first evidence of an

increase in acid deposition pollutants will be changes in

the composition of precipitation. Deposition (both wet

and dry) is the necessary link between pollutant emissions

and aquatic ecological effects, so detection of change in

deposition is required before any causal relationship can

be established. More than half of the annual precipitation

to Rocky Mountain wildernesses falls as snow. Wet deposition is monitored throughout the Rocky Mountain region at both high- and low-elevation sites through the

National Atmospheric Deposition Program network

(NADP 1991). Title IX of the 1990 Clean Air Act

Amendments requires monitoring of inputs to western

high-elevation watersheds, so additional deposition monitoring sites may be established.

There is interannual variability in deposition. Deposition also exhibits seasonal trends; summer precipitation is

slightly more acidic than winter precipitation (Baron and

Denning 1993). Individual weeks can have very acidic

precipitation. Limits of acceptable change established for

wet precipitation will have to reflect the potential for

acidic deposition to cause both chronic loss of acid neutralizing capacity (ANC) and episodic acidification, such

as may occur during snowmelt. Time series will need to be

carefully screened to remove confounding seasonality,

skewness, and serial correlation for long-term trend analysis. Short-term acidification needs to be considered in

light of the potential for coincidence of acidic “pulses”

with exposure of sensitive organisms (Corn and Vertucci

1992).

LAC: Where current snowpack pH is <6.0, acidic

deposition should not be more than double current snowpack H+ concentration. Before this is adopted, the possible

effects of this scenario on most sensitive aquatic ecosystems should be explored through research and model

simulations.

Sensitive receptor: Acid neutralizing capacity of surface waters.

The acid neutralizing capacity (ANC) of a specific

aquatic ecosystem can be an indicator of acidic atmospheric deposition. For the purpose of determining appropriate LACs, aquatic ecosystems were considered in three

separate categories based upon whether their open water

period ANC was >100μeq L-1

, 25-100 μeq L-1, or<25μeq L-1.

LAC: Where ANC >100 meq L-1, 10% change from

established baseline (determined by long-term trend analyses or through simulation).

Aquatic ecosystems in areas where the bedrock or

overlying material is easily weathered (such as limestone,

dolomite, and many shale types) generally will not be

sensitive to increased acidic deposition. These areas should

have ANC of >100 μeq L-1 during the ice-free season. The

LAC recommended by the group was considered the

maximum acceptable change, based on the premise that

this amount of change is detectable but is not sufficient to

lead to significant changes in the solubility of H+ or metals

such as Al+n or Hg that would affect biological populations.

LAC: Where ANC = 25-100 μeq L-1, 10% change from

established baseline.

In areas underlain by silicate or other minerals that

resist to weathering or are low in base cations (such as

granite, basalts, highly metamorphosed sedimentary rocks,

sandstones), surface waters may have ANC <100 μeq L-1.

Where ANC is between 25 and 100 μeq L-1, Forest Service

managers need to be aware of both the potential for longterm (chronic) loss of ANC leading to acidification and for

episodic acidification. Episodic acidification, or temporary consumption of ANC, results from titration of ANC

by strong acid anions in snowmelt of storms (Baker et al.

1991). Snow represents 60-80% of total annual precipitation in the Rocky Mountains, and snowpacks do not melt

throughout the winter (Denning et al. 1991, Turk and

Spahr 1991). Snowmelt could potentially cause acidic

episodes in Rocky Mountain wilderness areas. Even though

this loss of ANC is temporary, it can be detrimental to

aquatic organisms. The Aquatics Group recommended

Table 2. Sensitive receptors and limits of acceptable change related to acidic deposition.

Sensitive receptor Ambient condition Limits of acceptable change

Chemical composition of current snow pack pH < 6.0 not more than double current snowpack

 wet deposition H+ concentration

ANC of lake or stream ANC > 100 μeq L-1 10% change from established baseline

surface waters ANC = 25-100 μeq L-1 10% change from established baseline

ANC < 25 μeq L-1 no further decrease is acceptable

Aquatic organisms none recommended
6 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

that the LAC should be split between chronic and episodic

losses. Chronic losses can be determined through longterm monitoring and also through simulation.

Note that the recommended LAC is the same for lakes

with ANC >100 μeq L-1 and for those with ANC between

25 and 100 μeq L-1. This allowable variance becomes more

restrictive as ANC decreases; thus for lakes with ice-free

ANC values of 100 μeq L-1, ANC can range from 90 to 100

eq L-1, but if the ice-free value is 25 μeq L-1, ANC can only

range from 22.5 to 27.5 μeq L-1. In order to protect against

the possibility for episodic acidification, the Forest

Service manager must have information specifically on

surface water responses to snowmelt. A deviation of 10%

from the baseline springtime surface water minimum

ANC (determined from long-term snowmelt monitoring

and from simulation) was thought to be an appropriate

LAC.

LAC: Where ANC <25 μeq L-1, no change.

Surface waters in the Rocky Mountain Region with

ANC <25 μeq L-1

 are considered to already be at critically

low ANC levels. These bodies have a high probability of

episodic acidification. In this case, the LAC has already

been exceeded, and further degradation should be avoided.

Remedies for existing conditions should be sought.

An alternative to the three categories of LAC based

upon ice-free or snowmelt period ANC was voiced by

some members of the Aquatics Group. This alternative

required a minimum ANC of 200 μeq L-1 at any time of

observation. However, there are lakes throughout the

Rocky Mountains with naturally ice-free ANC <200 μeq L-1

(Baron 1992, Eilers et al. 1987, Turk and Spahr 1991).

Dilution during snowmelt also causes large natural declines in ANC that are unrelated to anthropogenic acidification (Baron and Bricker 1987, Denning et al. 1991,

Stoddard 1987). For these two reasons, it was felt that an

arbitrary region-wide ANC value was unrealistic and

unduly restrictive.

Sensitive receptor: Aquatic organisms.

Information is available on the effects of acidification

on biological communities in aquatic ecosystems from

whole lake acidification experiments, mesocosm experiments, and field surveys (Baker and Christensen 1991).

This research indicates many aquatic species are acidsensitive. The number of species present in an aquatic

ecosystem declines with increasing acidity although net

primary production and biomass may stay the same or

even increase (Schindler et al. 1985).

There is some documentation of stream and lake benthic

macroinvertebrate species in Rocky Mountain alpine and

subalpine ecosystems. Arthropod taxa that are known to

be acid-sensitive, including the mayflies Baetis and

Drunella, are common to abundant in Loch Vale watershed and other Front Range systems (Bushnell et al. 1987,

Radar and Ward 1989, Short and Ward 1980, Spaulding et

al. 1992, Ward 1986). A freshwater clam, Pisidium, has

been observed in The Loch and in the Green Lakes Valley

(Bushnell et al. 1987, Spaulding et al. 1992).

Previous experimental work on alpine lakes in the

Sierra Nevada mountains indicates that the effects of

acidification on phytoplankton and zooplankton were

dramatic at pH 5.6 and below, but little change was

observed above pH 5.6 in lakes with ice-free natural pH

values above 6.3 (Melack and Stoddard 1991). Short-term

in situ acidification experiments at The Loch, Rocky

Mountain National Park, did not show any response of the

dominant spring diatom, Asterionella formosa, to pH values of 3.2, although when the experiment was repeated

with the dominant fall alga, Oscillatoria limnetica, populations dramatically declined (McKnight et al. 1990).

Many Rocky Mountain wilderness lakes and streams

support trout populations. Most high-elevation lakes were

originally fishless, and were stocked with rainbow, cutthroat, or brook trout early in the 20th century. All three

species are sensitive to acidification (Farag et al. 1993;

Woodward et al. 1989, 1991; Booth et al. 1988).

Some species of salamanders have been shown experimentally to be sensitive to acidification and associated

loss of Ca2+ and increase in Al+n (Freda and Dunson 1985).

Dose-response experiments on Rocky Mountain tiger salamanders showed that egg survivorship was inversely

related to acidity, and an LD50 (50% mortality) of salamander embryos was pH = 5.6 (Harte and Hoffman 1989).

However, there may be too little known about salamander

life histories and sensitivity to other stresses to make them

good indicators of acidic deposition effects (Corn and

Vertucci 1992).

LAC: None recommended.

While the preservation of natural aquatic communities

may be the major reason for protecting Rocky Mountain

wilderness lakes and streams from acidic deposition, it is

not recommended that fluctuation in organismal populations be used to set LACs. Limits are being established to

determine trends which will lead to ecological damage,

but by the time a species response is observed, ecological

damage will have already occurred. It is recommended

that monitoring of biological populations be initiated so

that information will be available to support chemical

evidence of acidification, should LACs be exceeded in

future years.

Air toxic compounds

Some evidence exists for atmospheric transport and

deposition of toxic organic trace substances to highelevation Rocky Mountain lakes. The occurrence of polychlorinated biphenyls (PCBs) in lake sediments of

Rocky Mountain National Park provides unequivocal

evidence of atmospheric transport, since PCBs are solely

produced by commercial industrial processes (Heit et al.

1983). These authors suggest that possible sources for
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 7

PCBs should include Denver, Salt Lake City, and/or fallout from globally mixed sources. Polycyclic aromatic

hydrocarbons (PAHs) may originate through both natural

(such as forest fires) and industrial processes. While the

PAH fluoranthene was found in the surface sediments of

four Rocky Mountain lakes, it is difficult to evaluate its

source. Sediments taken at depth had lower concentrations of fluoranthene than those from the surface, implying inputs have increased recently. Concentrations of both

PCBs and PAHs of Rocky Mountain lakes were found to

be typical of values reported from other remote lakes, and

were found to be far lower in concentration than the levels

found in severely polluted ecosystems (Heit et al. 1983).

LAC: EPA standards (1986).

LACs for air toxic compounds are based upon EPA

standard values. Exposure to levels of air toxic compounds exceeding EPA standard values is not acceptable.

While the PSD permit process may not provide the Forest

Service manager control over sources of these compounds,

he or she must be alert for the possibility that exceedances

could occur. A partial list of air toxic compounds is found

in table 3.

Airborne nutrients

Most wilderness ecosystems are strongly nutrient-limited, and inadvertent fertilization via atmospheric deposition could alter AQRVs. However, old growth forests,

unvegetated areas such as talus slopes, and areas with

alder represent exceptions to this condition.

Sensitive receptor: NO3

-

 concentrations in late summer.

LAC: None now recommended.

Among the consequences of increased industrial activity is increased NOx

 emissions. These can be transported

and converted to NO3

-

, and deposited via deposition to

Rocky Mountain wilderness areas as either HNO3 or as

nitrogen salts. The Aquatics Group thought that late summer NO3

-

 concentrations greater than 1 μeq L-1 indicated

that the LAC has been exceeded. However, Wetzel (1983)

states “Oligotrophic lakes are often limited by phosphorous and contain an excess of nitrogen.” Phosphorous is

nearly always below detection limits in high-elevation

Rocky Mountain lakes (Baron 1992, Eilers et al. 1987).

Because the source for these high NO3

-

 concentrations is

not known, and may not necessarily be related to air

pollution, no LAC is recommended at this time. Further

research is necessary to determine the source of NO3

-

concentrations.

Sensitive receptor: Ammonium NH4

+, concentrations

during ice-free period.

LAC: NH4

+ = 2 μeq L-1

.

Ammonia from feedlots, agricultural fertilization, or

oil-shale retorting can be atmospherically transported

and deposited in high-elevation watersheds as NH4

+ salts.

Ammonium ion is a more energy efficient and easily

assimilated source of N by organisms than NO3

-

. Because

of this, NH4

+ is preferentially consumed over NO3-

 in

aquatic ecosystems (Wetzel 1983). In Rocky Mountain

high elevation lakes NH4

+ is present only in very low

Table 3. Selected air toxic compounds and water quality thresholds1 (EPA 1986)

Priority Freshwater, Freshwater, Water and fish

pollutant acute2 chronic2 ingestion

Arsenic (pent) no 850 48 -

Cadmium yes 39 11 10

Copper yes 18 12 170 ng

Cyanide yes 22 5.2 200

DDE yes 1,050 - -

DDT yes 11 0.001 0.024 ng

Dieldrin yes 2.5 0.0019 0.071 ng

Fluoranthene yes 3,980 - 42

Lead yes 82 32 50

Nickel yes 1,800 96 13.4

PCBs yes 2 0.014 0.079 ng

PAHs yes - - 2.8 ng

Selenium yes 260 35 10

Silver yes 4.1 0.12 50

Toxaphene yes 1.6 0.013 0.71 ng

Zinc yes 320 47 5 mg

1 Values are in mg L-1 unless otherwise noted.

2 Lowest observed effect level.
8 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

amounts through most of the year (Baron 1992, Eilers et al.

1987). A temporary rise in NH4

+ concentrations occurs

during spring snowmelt in the Loch Vale watershed,

and this has also been reported from eastern North

America, where NH4

+ is elevated in precipitation (Dillon

and Molot 1990, NADP 1991). Detection of NH4

+ in

aquatic ecosystems is indicative of either a gross increase

in emissions or ecosystem malfunction (van Breeman et al.

1982).

Sensitive receptor: Lake dissolved oxygen, DO.

LAC: DO = 5.0 ppm O2 under ice cover for 2/3 of the

lake; or where DO is already <5.0 ppm in 1/3 or more of

the lake, 10% change.

A concern raised by the Aquatics Group was that

nutrient enrichment could lead to summer algal blooms.

Microbial decomposition of these blooms under lake ice

the following winter could deplete lake dissolved oxygen

(DO), causing fish kills from anoxia.

Sensitive receptor: Winter lake O2

 concentrations.

LAC: None recommended

There are several problems with establishing strict

LAC values for winter lake O2 concentrations. The first is

that it constitutes an indirect effect of airborne pollutants,

and thus violates the condition that sensitive receptors

must be sensitive and directly responsive to change. Another problem is that high-quality winter measurements

of wilderness lake conditions are logistically difficult to

obtain and hard to monitor; it is, therefore, difficult to

track the spatial variability of dissolved oxygen. In the

absence of more synoptic and experimental information

on annual DO variability, it is recommended that no limit

be established at this time.

A summary of sensitive receptors and LACs relating to

airborne nutrients and mercury (as discussed in the following section) is provided in table 4.

Mercury

Sensitive receptors: Hg concentrations in water, sediments, and fish tissue.

LAC: None recommended.

Mercury is a toxic metal that has been found in elevated

concentrations in fish from some remote temperate lakes.

As collection and analytical techniques for mercury have

improved over the past 15 years, concentrations of Hg in

temperate lake bodies have been shown to be two orders

of magnitude lower than previously reported values,

making the high tissue concentrations found in game fish

of remote lakes all the more intriguing (Fitzgerald and

Watras 1989). Mercury is concentrated in fish tissue by

about a factor of 10,000 over aqueous concentrations (Pat

Davies, pers. comm.).

There is a negative correlation between the level of Hg

bioaccumulation and both pH and ANC, and a positive

correlation between the body Hg concentrations and total

fish length (Lathrop et al., 1991). Studies and experiments

in Wisconsin lakes showed highest body Hg concentrations in the longest fish in the most acidic lakes with the

lowest ANC (Lathrop et al. 1991). The acute and chronic

toxicity standards that have been recommended as Colorado state standards are orders of magnitude greater than

expected concentrations: 2.4 μg L-1 in water, acute instantaneous 24-hour maximum; 0.1 μg L-1

 in water, acute

instantaneous 24-hour maximum; 0.1 μg L-1 in water,

Table 4. Sensitive receptors and limits of acceptable change related to airborne nutrients and mercury.

Sensitive receptor Limits of acceptable change

Relating to airborne nutrients

NO3

-

 concentrations in late summer now: None recommended

NH4

+ concentrations during ice-free period 2 μeq L-1

DO 5.0 ppm O2 under ice cover for 2/3 of lake; or

where DO < 5.0 ppm O2 in 1/3 or more of lake: 10% change

O2

 winter lake concentrations none recommended

Relating to mercury

Hg concentration in water none recommended

Hg concentration in sediments none recommended

Hg concentration in fish tissue none recommended
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 9

chronic 30-day-average concentration (these are also EPA

standard values). The fish tissue residual for acute and

chronic toxicity are 0.12 μg L-1 and 1.3 μg L-1, respectively.

Methyl mercury (CH3Hg+) is the form most readily

accumulated in fish, comprising 95% or more of the Hg in

fish in northern temperate lakes (Grieb et al. 1990). The

microbial methylation of Hg in lakes and sediments is an

important process affecting Hg bioavailability to fish (Rudd

et al. 1983, Wiener et al. 1990).

Mercury inputs occur via wet and dry deposition, and

many lakes have a large sedimentary reservoir from which

remobilization can occur (Fitzgerald and Watras 1989,

Wiener et al. 1990). Using ultra-clean techniques, Bloom

and Watras found concentrations of total Hg from rain

and snow (from both the Olympic Peninsula of Washington and northern Wisconsin) to range about 2-15 ng L-1

(Bloom and Watras 1989). Methyl mercury comprised 2-

10% of the total Hg, with reactive Hg making up most of

the rest. This suggests atmospherically deposited methyl

mercury is sufficient to account for much of the tissue

concentrations found in game fish in remote inland waters

(Bloom and Watras 1989).

Mercury in the atmosphere comes from natural and

industrial sources. An estimated one-third of atmospheric

mercury is derived from oceans, while another one-third

comes from natural terrestrial sources (such as deposits of

cinnabar, HgS, and other sulfur minerals). The remaining

atmospheric mercury is thought to originate from industrial activity: 50% from coal-fired electricity generation,

25% from chlor-alkali plants, and the remainder from

mining, volatilization from old paint (federal law now

prohibits the occurrence of mercury in paint), dentistry,

manufacturing, and weapon production and testing

(Nriagu 1989, Nriagu and Pacyna 1988).

The concentrations of mercury in high Rocky Mountain

lakes, sediments, and fish are unknown. Because of the

occurrence of mineral ores in Colorado, there is some

possibility of natural and mining-related mercury leaching into some wilderness lakes. Atmospheric deposition

undoubtedly contributes additional mercury. Because

ambient concentrations are not known, no limits of acceptable change can be recommended.

The recent research into mercury biogeochemistry

strongly suggests monitoring cannot be casually undertaken. Trace-metal-free techniques must be employed to

detect pico to nanogram concentrations (Bloom 1989).

Preliminary results from the research conducted in Wisconsin suggest monitoring temporal trends in the ratio of

methyl mercury to total mercury may be a sensitive indicator of adverse impact (Watras and Bloom 1992). Watras

suggests unimpacted lakes may have ratios of 10-30%

methyl mercury; this ratio may change to 70-90% methyl

mercury in an impacted system. The impact is not increased deposition of mercury, since total Hg appears to

be ubiquitous in the atmosphere and lake sediments, but

rather a decrease in lake pH, which affects the availability

of methyl mercury. It is not clear yet whether pH acts

directly to partition the mercury, or whether pH affects

the biogeochemical pathways by which CH3

Hg is produced. These may include microbial methylation, the

bioavailability of substrate mercury to organisms that

methylate mercury, or some other process (Bloom and

Hurley 1991).

The Aquatics Group recommended that current Hg

levels in wilderness lake water, sediments, and fish be

determined for a few Rocky Mountain lakes. Because of

the extreme difficulty in obtaining high quality results, it

is further recommended that Region 2 contract this work

out to a laboratory with proven expertise in the area of

mercury sampling and analysis.

Analyzing and Predicting Adverse Impact

The PSD permit process for evaluating potential threats

to wilderness aquatic ecosystems is a game of futures by

which the Forest Service manager must predict the effects

of potential development in advance of their occurrence.

Dynamic models of watershed and aquatic processes provide a reasonable approach to prediction. Models, however, differ greatly in their assumptions, their predictive

capability, and their input data requirements, so they

should not be used carelessly. Since the quality of model

output is only as good as the quality of data input, there is

a strong need for long-term, high-quality data sets. As

some data are required to parameterize models, and thus

cannot be used to test model performance, other longterm data sets will need to be made available for model

validation. This is critically important, since the actual use

of models to predict the effects of new pollution sources

cannot be rigorously validated. The Aquatics Group discussed the relative merits and disadvantages of several

models that are currently used to assess lake and watershed acidification. This discussion, augmented with statements from the literature (primarily Munson and Gherini

1991), is presented below. A table comparing the resolution and processes of the three most widely applied models was put together by Malanchuk and Turner (1987);

other models have been added to it (table 5).

Dynamic models

The three models most commonly applied in the United

States include MAGIC, (Model of Acidification of Groundwater In Catchments; Cosby et al. 1985), ILWAS (Integrated Lake Watershed Acidification Study Model; Chen

et al. 1983) and Enhanced Trickle Down (Schnoor et al.

1984). The models have been used to identify processes

operating in watersheds, and also for prediction given

different atmospheric deposition scenarios (Munson and
10 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

Gherini 1991). The models differ in their input requirements, assumptions, and complexity; but all three have

been used successfully to recreate existing data sets and

can deliver assessments of surface water acid neutralizing

capacity (Rose et al. 1991).

MAGIC: Model of Acidification of Groundwater

Catchments: The MAGIC model runs on a monthly or

yearly time step. It predicts or postdicts average soil and

stream response to long-term acidic deposition or cessation of acidic deposition. Each model run can cover 140

years, starting from background conditions 140 years ago

and continuing up to the present, or establishing some

future scenario and exploring watershed response. Runs

beginning in the 1850s are particularly useful for estimating how well the model recreates conditions present in the

1990s. This provides a means of testing the fit of the model

to watershed processes in different ecosystems. Scenarios

of current and potential atmospheric deposition have

been built into the model for different regions of the

United States based upon EPA-estimated regional emissions, or the user has an option of building another deposition scenario. The model uses lumped parameters based

Table 5. Comparison of processes and resolution in dynamic and empirical models (after Malanchuk and Turner 1987).

TRICKLE HENRIKSEN RED/GREEN/ TWO BOX

ILWAS MAGIC DOWN BIRKENES -WRIGHT YELLOW MIXING

Atmospheric input E,A A,M,LT A,LT A,D LT LT variable

Hydrology E,A A,M,LT A,LT E,D N/A A E

Weathering A,LT LT LT LT variable N/A LT

Anion retention

SO4

2- + + - + - --

Nitrification + -(+) - - - - -

Denitrification + -(+) - - - - -

Base cation buffering

% base saturation + + + + + --

Al kinetics + + - + + - -

Biological

Uptake + - - - - -+

Excretion, decomposition + - - - - --

Transformation + - - - - -+

Respiration + - - + - - -

SO4

2- + - -(+) + - - +

Spatial resolution V,H, V,H, V, lake V, regional lake, V,

watershed regional, catchment regional catchment

watershed

Temporal Resolution D M D D N/A N/A variable

Key: A = annual

M = monthly

LT = long-term

D = daily

E = episodic

V = vertical

H = horizontal

N/A = not applicable

+ = the model specifically addresses these processes

- = the model does not address these processes

-(+) = the model provides the option of addressing or ignoring these processes
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 11

on watershed basin physical and chemical characteristics.

These parameters are aggregated horizontally over a watershed and broken out vertically into two soil layers and

one completely mixed stream or lake. The hydrologic

portion of the model is calculated using TOPMODEL, a

variable source area input hydrologic model.

Inputs to the model (the empirical field data needed to

run the model) include atmospheric deposition (including dry sulfate deposition estimates) and weathering rates

for base cations and strong acid anions, expressed as

fluxes. Physical data required are mean annual or monthly

hydrologic flux (precipitation in and stream discharge

out), soil and streamwater temperatures, the partial pressure of soil carbon dioxide (soil PCO2), depth, and porosity.

Soil chemical parameters required are cation exchange

capacity, percent base saturation or selectivity coefficients

for Ca-Na, Mg-Na, K-Na, Al-Ca, the aluminum hydroxide

solubility constant, sulfate adsorption capacities, and half

saturation constants of the particular soils. The model

calculates changes in soil and surface water chemical

properties.

The MAGIC model has been calibrated and tested for

watersheds throughout the world (including Loch Vale

watershed in Rocky Mountain National Park and the

Glacier Lakes in the Snowy Range in southeast Wyoming). Among its test sites were two manipulated watersheds in Norway where acid deposition has been experimentally changed as part of the RAIN project (Reversing

Acidification in Norway). The Sogndal watershed, originally pristine, has been acidified via acid deposition, and

the Risdalsheia watershed, which had been acidified, has

been covered over to exclude acid rain (Wright et al. 1990).

A modified, monthly version of MAGIC was developed

for the RAIN project in which snowpack accumulates

during the winter and melts during the spring. MAGIC

successfully reproduced the past four years of stream and

soil chemistry in these manipulated systems. This model

has been recommended.

ILWAS: Integrated Lake Watershed Acidification

Study Model: The ILWAS model is the most spatially

explicit and process-intensive of the three models, and

thus has extreme data input requirements. There are 37

types of input coefficients needed in order to run ILWAS,

compared with 13 needed for MAGIC. Within individual

hydrologic subcatchments, there are model compartments

to represent forest canopy processes, snowpack, and up to

five separate soil layers. A lake can be thermally stratified

to calculate temperature and water quality profiles. Physical and chemical processes that change the acid-base

characteristics of water are simulated by rate and equilibrium expressions, and include mass transfers between

gas, liquid, and solid phases. The model produces time

trends of all major ions, aluminum dynamics, dissolved

organic carbon, and inorganic carbon. The Aquatics Group

felt that ILWAS could best be applied in research watersheds but is generally not suitable for Rocky Mountain

wilderness lakes because of limited data availability.

Enhanced Trickle Down Model: The Enhanced Trickle

Down model is a lumped parameter model that formulates all processes in terms of their direct effects on ANC.

The model runs on a direct time step, and predicts seasonal fluctuations in lake acid-base characteristics, as

interpreted via ANC. Parameters are lumped spatially

over a watershed. Water can be routed through three soil

horizons and a completely mixed lake. All chemical processes of the model are rate-limited except for sulfate

adsorption and CO2

-carbonic acid equilibria. Mass balances are calculated for ANC, SO4

2-, and Cl-

 (as a check of

hydrologic balance). The Enhanced Trickle Down model

has been tested in seepage lakes of the midwest and

drainage lakes of the eastern United States. The Aquatics

Group did not feel confident that western weathering

processes were adequately represented and recommended

that this model not be used for PSD permit applications.

Birkenes Model: The Birkenes model is very similar in

theoretical construct to the MAGIC model. Chemistry is

based on SO4

2- flux of wet and dry deposition passing

through soils. As it moves, SO4

2- can either be adsorbed,

desorbed, mineralized from organic forms, or leached.

Charge balance is maintained with soil cations, and cations are required to meet equilibrium constraints of their

controlling minerals. A hydrologic submodel consists of

two soil reservoirs, a snow reservoir, and a stream. This

model has been applied to Scandinavian and Canadian

catchments, and may be modified for Rocky Mountain

systems.

Empirical models

Henriksen-Wright Model: The Henriksen-Wright

model is an empirical model that has been used in

Scandinavia, eastern North America, and the Rocky Mountains to estimate historical loss of ANC from increased

deposition of sulfate (Henricksen 1982, Wright 1983). In

this model, alkalinity is defined as the sum of the base

cations (CB), total monomeric aluminum species (Alm),

and divalent manganese (Mn2+), less the sum of the strong

acid anions CA, (SO4

2-, NO3-

, Cl-, F) (Henriksen 1979):

ANC = [CB] - [CA] + 2[Alm] + 2[Mn2+].

Increased non-sea-salt sulfate (SO4

2-) deposition affects

ANC two ways: by increasing the release of base cations

from the watershed and by direct replacement of bicarbonate alkalinity with SO4

2- (Wright and Henriksen 1983).

The proportional change in the base cations relative to

SO4

2- is referred to as the F-factor.

The Henriksen-Wright model gives a static view of

surface water chemical composition, and H+ could be used

in a simple predictive model to estimate the loss of ANC
12 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

due to some projected increase in strong acid anion deposition. The model, however, is not dynamic and does not

take any biological, hydrologic, or specific mineralogic

processes into account, so its capacity is limited. For this

model to be rigorously applied to Rocky Mountain lakes,

F-factors will have to be determined for each bedrock

type; but once completed, the model could be used to

provide a screen for most sensitive waters.

Green/Yellow/Red Model: Similar to the HenriksenWright model, the Green/Yellow/Red model is not so

much a simulation of processes as it is a classification

scheme. Developers of the model attempted to provide a

“critical load” guide for managers confronted with a PSD

permit application. Lakes are located on a nomograph

according to their surface water base cation composition,

their total deposition of S and in some areas N, and the

estimated percentage of total annual precipitation that

effluxes as runoff. Depending on where they fall relative

to lines of demarcation, surface water bodies are at risk of

acidification (red line), not at risk (green line), or in an

uncertain category (yellow zone) where further information is required. Crude predictions of the effect of a new

emission source can be made with the nomograph by

varying the amount of total S and N deposition.

This approach provides a good screening technique for

determining possible sensitivity to acidic deposition. Several critical points were raised by members of the Aquatics

Group. Notably, they are also stated as cautions in the

Green/Yellow/Red documentation itself (Fox et al. 1989).

The model is only applicable to lakes without a watershed

S source. Episodic acidification events such as brought on

by snowmelt fall beyond the context of this model. The

biggest problem raised with this model is that most western lakes fall in the yellow zone, where clear management

guidance on how to address a new source permit is

lacking. This, unfortunately, makes the Green/Yellow/

Red model insensitive to Rocky Mountain wilderness

areas unless steps are taken to correct this problem. As

with all other models, extensive testing is required before

it can be used as a screening tool.

Two Box Mixing Model: The Aquatics Group briefly

discussed the possibility of using a Two Box Mixing

model for determining the proportion of water in a water

body attributable to either precipitation or groundwater.

This technique has been applied to Canadian watersheds

to determine sources of hydrologic flowpaths and the

possibility for episodic acidification due to snowmelt

(Bottomley et al. 1986, Maule and Stein 1990). The model

requires that the species that are mixed act conservatively,

that is, their sources can be traced by their chemical or

isotopic signatures even after mixing. Distribution between precipitation and groundwater sources of water

can be determined using naturally occurring isotopes 18O

and deuterium as hydrologic tracers. Isotopic separation

increases with decreasing temperature, thus allowing the

18O and D values of snow to be distinguished from rain

and groundwater. The waters from the different sources

are then mixed proportionally according to the equation

QP = QT[(δTδE)/(δP-δE)]

to derive the amount of water supplied from each source.

This has been used to infer the contribution of accompanying acidic solutes to water bodies (Bottomley et al. 1986).

This method of evaluating sources and flowpaths of

water has potential, but there are several problems with

trying to use it in a predictive mode. Isotopes are expensive, nonroutine analytes requiring a mass spectrometer.

The only place in the Rocky Mountains we know of where

this technique has been applied is Rocky Mountain National Park, and preliminary results suggest the presence

of glaciers, late melting snowbanks, and rock glaciers

confounds the temperature-based technique for determining sources of water during snowmelt (Back 1994.).

While the inference of precipitation-derived acid solutes

from this mixing model is no less robust than other simulation methods that calculate sources of solutes from

equilibrium and kinetic equations, other models (particularly MAGIC) have been tested in many aquatic ecosystems. Finally, it is not possible to use the mixing model in

a predictive mode because the water isotopes do not shed

light on processes affecting ANC.

The Two Box Mixing model can also be applied to

solutes. One example is sulfur, which has distinctly different isotopic signatures depending on source. Distribution

between precipitation and mineral sources of sulfur is the

subject of current research (Turk et al. 1993). The technique has been successfully applied in Loch Vale watershed to detect mineral sulfur sources that had not been

detected by more conventional techniques. In watersheds

without sulfur-bearing minerals, however, the model does

not contribute to understanding the effects of increased S

deposition on ANC, nor can it be used for trend analysis.

Monitoring

Monitoring of aquatic systems is necessary to provide

data with which to make sound PSD recommendations to

protect wilderness areas. Such monitoring needs to be

undertaken well before a PSD permit application is received to assure that sufficient information will be available to allow a timely response. The filing of a PSD

application may necessitate higher frequency sample collections or additional parameters to be collected from an

ongoing monitoring program. Because our present level

of knowledge is limited with respect to prediction of the

effects of emissions on wilderness, monitoring after an

emission source is permitted may also be necessary to

calibrate empirical or numerical models. This will advance our general ability to protect wilderness areas and
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 13

to determine if the new permitted source has caused

unforeseen effects.

Although monitoring is critical to any PSD decision,

such monitoring needs to be conducted in such a way as

to not interfere with the wilderness. For example, in

mountain ranges or other geomorphic units of which only

part is designated wilderness, instrumentation can be

located in adjacent nonwilderness, if these areas adequately

represent the areas of concern. Often, however, western

wilderness areas occupy entire high-elevation areas for

which there is truly no representative nonwilderness area

subjected to the same atmospheric deposition from a

proposed source.

Prior to initiation of a monitoring program, the Forest

Service manager is advised to consider data already available. These include:

1. The Western Lake Survey, conducted by the Environmental Protection Agency (EPA) (Eilers et al.

1987). In some areas there may be sufficient information to define the prevalence of sensitive aquatic

systems. However, the Western Lake Survey

(WLS) was a stratified systematic sample of a list

frame that did not specifically search for the most

sensitive aquatic systems.

2. The Environmental Monitoring and Assessment

Program, initiated by the EPA. Approximately

800 lakes will be sampled nationally per year,

with a sample repetition rate of every 5 years. As

with the WLS, sampling is probability-based rather

than targeted for sensitive systems.

3. The Hydrologic Benchmark Program of the USGS,

operating since about 1966. Several Hydrological

Benchmark watersheds drain western wilderness

areas.

4. Long- and short-term research and monitoring

programs conducted by universities and state

and federal agencies including USGS, NPS, USFS,

BLM, and USFWS.

Before designing a monitoring program, the appropriate maps, journal articles, and books that may describe the

geologic, hydrologic, biotic, or other characteristics of the

wilderness area should be assembled. For example, aquatic

chemistry is very dependent on geology; thus, knowledge

of what parts of a wilderness have a particular bedrock

composition aid the search for the most sensitive aquatic

system. If possible, each wilderness manager should project

the most likely future sources of emissions, assemble a

map of present sources, and gather any other type of

information, such as prevailing wind direction, that can

help describe the most likely areas of greatest deposition

and sensitivity.

The design of a monitoring program requires two major efforts:

1. A synoptic survey to identify sensitive aquatic

systems and relate these to geologic, hydrologic,

and other characteristics that are associated with

the sensitive systems. Such a survey may also

help to identify sensitive organisms associated

with aquatic systems. These data are used to

select the most sensitive systems to be used in

predicting, modeling, and monitoring PSD effects.

2. A long-term monitoring program to define the

natural and pollution-related fluctuations and

trends within these most sensitive systems.

Work related to acid deposition has provided knowledge on how to effectively conduct synoptic sampling in

wilderness areas. However, this knowledge is directed at

finding aquatic systems sensitive to acid deposition. These

systems are not necessarily the most sensitive to other

possible threats, such as air toxic compounds. Maps and

models of lake ANC indicate ANC is a function of bedrock

geology and hydrology. Bedrock geology can affect lake

ANC through control of weathering rates per unit area

and volume of watershed minerals. To have the least ANC

and to be the most sensitive to acidification, a lake needs

to be on any one of the slow-weathering bedrock types

common to the Rocky Mountain region, such as quartzite,

quartz monzonite, granite, or basalt. These slow-weathering bedrock types result in minimal lake ANC because of

slow rates of weathering per unit area of mineral. Within

each of these bedrock types, the most sensitive lakes will

have minimal amounts of material that can form the

matrix of an aquifer, e.g., glacial till or alluvium. These

materials not only provide a large surface area per unit

volume for mineral dissolution and ANC production, but

they also provide a continuous flow of ANC into a lake or

stream.

Hydrology can also affect lake ANC. The most sensitive lakes and pools will occur at the beginning of hydrologic flowpaths, rather than farther downstream. Longer

flowpaths provide additional time for reaction between

groundwater and the minerals that dissolve to produce

ANC. Thus, sensitive lakes are likely to be on or near

topographic highs, such as saddles, cirques, and mesa

tops. These water bodies are in groundwater recharge

areas dominated by precipitation inputs rather than in

groundwater discharge areas, such as stream valleys.

Temporal variations in hydrologic processes, such as

snowmelt, may cause changes in flowpaths that can

decrease ANC by minimizing mineral surface area exposed to reaction and contact time of water and mineral

surface. For example, saturation of soils during snowmelt

may cause a large fraction of flow to a water body to occur

as overland flow. As the zone of saturation thins during

the summer, most of the flow might come from groundwater.
14 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

Given that we know the geologic and hydrologic conditions that are likely to result in a sensitive lake, how do

we select which lakes to sample? If the number of potential lakes is small enough that there is sufficient money

and labor, all lakes can be sampled (a census). This is the

ideal goal of all resource inventory and monitoring programs. In some cases, however, this may require a phased

sampling over several years. In other cases it may not be

possible to sample all lakes. The best approach in this case

is to either sample the lakes thought to be the most

sensitive, or collect a representative subsample of the

sensitive systems. The most sensitive lakes based on geology would be on quartzite followed by granite, gneiss,

monzonite, rhyolite, and basalt. Similarly, the highest

elevation lakes within the local topography are likely to be

the most sensitive. Such information can help reinforce

the idea that there are sensitive aquatic ecosystems and

that, perhaps, more money and manpower are needed to

adequately sample the rest of the lakes.

A stratified random survey can also be collected by

assigning water bodies to some common characteristic

and collecting a random sample from within these groups

of characteristics. This was the approach taken to stratify

lakes for sampling in the Western Lake Survey (Eilers et al.

1987). Lakes and other aquatic systems can be grouped

according to bedrock and surficial geology, as mapped on

readily available USGS geologic maps. Within each of

these groups, further subgroups can be determined by

delineating altitudinal ranges. Each water body within

each subgroup is assigned a number. A random number

approach is then used to select which lakes within each

subgroup should be sampled. This is a statistically desirable approach, but does not take into account problems of

access or efficiency in moving from one selected lake to

another.

The initial synoptic sampling for lakes sensitive to acid

rain can be used to thoroughly address a full suite of

chemistry, or it can utilize several levels of analysis. An

example of a two-stage sampling design might start with

specific conductance and ANC analyzed for all samples;

whereas the full suite of major ions and other constituents

of interest, such as organisms, might be determined for a

10% subsample. Thus, the wilderness area could be

sampled completely at little analytical cost for the most

direct measure of sensitivity to acid deposition ANC,

while still having sufficient detail in some samples to

more adequately determine the causes and effects of high

or low ANC.

To assure the quality of data collected and to enhance

comparability of results among wilderness areas within a

region, it is recommended that a team of experts be selected to advise the USFS manager for each wilderness

area on how best to initiate monitoring. Each USFS manager must operate under the assumption that these data

may have to be defensible in a court of law. It is critical that

generally accepted methods be used and that all steps of

data collection and analysis be documented. In this regard, the Aquatics Group noted that the screening procedure of Fox et al. (1989) is not sufficiently detailed or

defensible enough to be used as a guideline. With proper

expert guidance, synoptic sampling need not be prohibitively expensive, and much of it might be accomplished by

volunteer labor.

Long-term monitoring

After the initial sampling, great care needs to be taken

in selection of aquatic systems for long-term monitoring.

Long-term monitoring must be considered as an indefinite commitment, with explicit institutional support.

Breaks in the monitoring record seriously limit the ability

to detect trends. Systems selected for long-term monitoring should include the most sensitive aquatic ecosystems,

but access to these sites must be taken into consideration.

Some sites may require mechanized access during the

critical period of snowmelt. A combination of most sensitive sites supplemented (but not replaced) with less sensitive but more accessible locations might be established.

Long-term monitoring sites are necessary to detect

trends from human-caused disturbance. They also serve

an important function in defining the limits of natural

variability in the chemical and biotic characteristics of the

aquatic system. Such variation is a function of season,

climate, natural succession, and natural disturbance in

addition to the emissions effects we would like to detect.

Long-term monitoring in advance of new emissions sources

is necessary to define how large a change is needed to

qualify as statistically significant within the context of

natural background variations.

It is difficult to specify the minimum number of samples

necessary to develop a good long-term record. The number varies with the natural controls that cause changes in

lake chemistry or biota, and it will also vary based on the

chemical constituent or organism being monitored. We

recommend seasonal and annual sources of variation be

determined before finalizing a long-term monitoring plan.

That is, enough samples need to be taken at each site in the

first few years to determine whether there is a significant difference among seasons and years. These initial findings can then be used to guide the number of

samples taken in subsequent years. Initial data are also

required to determine how many samples may be needed

to detect a violation of an established limit of acceptable

change.

In addition to monitoring the chemistry and biology of

sensitive aquatic ecosystems, additional information will

be necessary. For example, a direct measure of atmospheric inputs is required in order to identify airborne
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 15

pollutants as a cause of adverse impact. This can include

measurement of snowpack amount and chemistry. If a

model has been chosen, the watershed characteristics

needed as input parameters must be obtained. Samples

for some aspects of biology or chemistry can be collected

and archived for later analysis if funds are not available

for immediate analysis. Changes over the last century or

longer can be evaluated using paleolimnological methods.

Data base management

It is critically important that an appropriate data base

management system be established Region-wide for access to information, quality assurance procedures, and

analyses of data collected. The US Forest Service Air

Resources Program is developing a system-node database. Many USFS offices do not yet have access to personal

computer technology. This should be remedied by supplying field offices with personal computers linked by

modem to a central office and data repository. Each wilderness area office should store and back up their data

bases regularly. In addition, Region 2 data should be

stored and backed up at a central location (perhaps at the

analytical laboratory). Analytical results need to be reviewed as soon after completion as possible in order to

check quality of analyses and possible need for re-analysis. This task may best be accomplished for all sites at one

central locale, so as not to burden each individual field

office with excessive detail. The National Atmospheric

Deposition Program network provides a good model to

follow.

Monitoring priorities

The following monitoring priorities are recommended:

1. The USFS must commit to long-term monitoring

of sensitive aquatic ecosystems. This commitment

should be incorporated into each Wilderness Area

Forest Plan.

2. The USFS Regional Office and individual area

managers together must develop a common sampling and analysis strategy in order to develop a

scientifically sound data base. It is strongly suggested that a central analytical laboratory be established, perhaps at the Rocky Mountain Research

Station, with adequate staff and budget to prepare sample bottles, conduct analyses, impose a

strict quality control program, tabulate data, take

responsibility for shipping of samples and results, and answer questions from field personnel.

3. The USFS Regional Office, in conjunction with the

central analytical laboratory, must adopt and staff

a central, logical, computer-based system for data

archiving, analysis, summary, and retrieval in

response to user needs. While individual field

offices will receive data from their own studies, a

central archive is necessary for rapid regionalscale analyses. A central data archive may also

provide a permanent home for all data and limit

potential lapses in data management caused by

staff turnover at field offices.

4. Synoptic sampling is recommended for each wilderness area to define the presence and distribution of sensitive receptors. This sampling should

be guided and coordinated by a regional team of

experts to assure quality and comparability.

5. The seasonal and yearly variability of sensitive

receptors, and especially episodic changes such

as occur during snowmelt, should be defined for

wilderness areas. These data should then be used

to estimate the sampling frequency required to

identify changes caused by emissions that exceed

LACs.

6. Periodic sampling of snowpack for amount and

chemistry of water should be initiated for wilderness areas. If existing NADP sites are not located

near enough to the wilderness areas, each area

should consider joining the NADP network. Additional western high-elevation monitoring sites

are proposed by NADP/EPA to fulfill obligations

of the 1990 Clean Air Act Amendments; Region 2

managers should work closely with NADP/EPA

personnel to ensure that these sites are located

where they can provide deposition data for wilderness areas of concern.

7. The MAGIC model is recommended to predict

emissions effects on aquatic systems. Data required to parameterize the model will need to be

collected for each long-term monitoring site.

8. Wilderness area managers might begin an archive

collection of organisms and other items that will

be used in the future to define pre-source conditions of the wilderness area. Standabout protocols

should be used for collecting, steering, and

archiving these samples. Suggestions include diatoms (for later community analyses) and animal

tissues (such as feathers, hair, body organs, etc.,

for later determination of toxic element concentrations).

9. Each wilderness area should contract for

paleolimnological sampling to determine how

present conditions differ from background conditions. This research should be coordinated through

the regional office.
16 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

Research Needs and Recommendations

The goals of monitoring can be thought of as defining

the status of and trends in a system. For example, the goal

may be to define how sensitive the lakes of a wilderness

area are to acidification and whether these lakes are becoming acidic. In this context, the goal of research is to

provide the understanding necessary to determine why

sensitive lakes are so sensitive and the cause for change in

acidification status. Thus, research is needed to help design effective monitoring programs and to correctly predict or evaluate the effect of one source among a great

number of complexities, both natural and humanmade,

that can also influence the behavior of an aquatic system.

As an aid in monitoring we need to improve our ability

to relate a given level of pollutant or nutrient emissions to

a chemical or biological response. In particular, our understanding of the dose/response relationship of western

fish, macroinvertebrates, and plankton is minimal. Vernal

pools are a common western aquatic system, but little is

known of their chemistry or the sensitivity of their biota.

Virtually no data exist on the effects of hormonal analogues on biotic growth and reproduction. It is even

difficult to recommend the best way to conduct some

types of sampling, such as for macroinvertebrates in very

rocky littoral areas. Prevention of Significant Deterioration applications often deal with the major pollutant from

one source; however, many sources may also generate

small amounts of toxic substances or nutrients not addressed by the PSD permit.

Priorities

The following research priorities are recommended

(without regard to cost or time in assigning priority):

1. The USFS, in conjunction with other land management agencies, needs to initiate a program to

develop appropriate instrumentation and sampling techniques for wilderness areas. Techniques

are needed for both biological and chemical sampling.

2. Techniques need to be improved for defining

background and natural fluctuations for sensitive

receptors. These, in turn, will need to be incorporated into models so that additional disturbance

from industrial emissions can be detected with

confidence that adverse impacts are not confused

with natural fluxes.

3. Experimental dose-response research, both laboratory and in situ, must be conducted to determine the potential of toxics and limiting nutrients

to affect biotic sensitive receptors.

4. At selected research sites we need to define the

importance of processes and patterns of spatial

variability that affect atmospheric pollutants.

5. Toxicity models need to be developed for nonfish

biotic sensitive receptors.

6. Target loading of pollutants must be developed,

perhaps from European mountainous areas where

damage is detectable.

7. Study is needed of the transport and transformation of pollutants to, within, and from the snowpack.

8. Much more linkage, validation, and testing of

atmospheric transport models with ecological and

biogeochemical process models are necessary

before we can confidently address any air-transported pollutant through the PSD permit process.

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Aquatic Workshop Participants

John Turk, U.S. Geological Survey

Jill Baron, National Park Service

David Brakke, University of Wisconsin, Eau Clair

Steve Corn, U.S. Fish & Wildlife Service

John Crow, Wyoming Environmental Quality Council

Les Dobson, Rio Grande National Forest

Joe Eilers, E&S Environmental Chemistry, Inc.

John Fooks, Platte River Power Authority

Alan Galbraith, Bridger-Teton National Forest

James Gibson, Colorado State University

Steve Gloss, Wyoming Water Research Center

Chuck Harnish, White River National Forest

Cheryl Harrelson, Bridger-Teton National Forest

Gary Holt, Shoshone and Arapahoe Tribes

Wes Kinney, U.S. Environmental Protection Agency

Fred Mangum, Aquatic Ecosystem Analysis Lab

Tonnie Maniero, National Park Service

Larry Meshew, Grand Mesa, Uncompahgre & Gunnison

National Forests

Deborah Potter, U.S. Forest Service, Region 3

Al Riebau, National Biological Survey

Kent Schreiber, U.S. Fish & Wildlife Service

David Skates, U.S. Fish & Wildlife Service

Dennie Sohocki, National Park Service

Mark Story, Gallatin National Forest

Jack Turner, San Juan National Forest

Catherine Vandermoer, Shoshone & Arapahoe Tribes

Frank Vertucci, EG&G, Rocky Flats

Ruth Willey, University of Illinois, Chicago
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 19

3. TERRESTRIAL ECOSYSTEMS

By Anna Schoettle and William Moir

Perspective

The majority of Class I wilderness areas in Region 2 is

high-elevation wilderness. Management of these areas is

also regulated by the Wilderness Act of 1964, which states

that these areas should be managed such that humans

cause little if any impact. When considered in concert with

the Clean Air Act, this implies that an adverse impact in a

wilderness area is any unnatural change, regardless of

whether it may be perceived by humans as positive or

negative. With this in mind, the Terrestrial Ecosystems

Group proceeded to identify sensitive receptors and LACs

in support of our efforts to protect AQRVs.

The consensus of the Terrestrial Group was that everything—all wilderness components, from fungi and soil

microorganisms to trees and mammals, regardless of their

known or unknown ecosystem role—should be protected

from adverse impacts from air pollution. There was considerable discussion of whether AQRVs should be limited

to ecosystem functions rather than components; it was

concluded that not enough is known about what controls

ecosystem functions and therefore all components should

be protected. The Terrestrial Group determined AQRVs to

be any wilderness component that has the potential to be

modified by human-caused air pollution; and sensitive

receptors to be objects or processes, biological or otherwise, that can be identified as having low thresholds of

tolerance to air pollutants. This is consistent with the

perspective of the National Park Service, which considers

all components of ecosystems as AQRVs needing protection. It was also acknowledged that humans are part of the

“natural” processes in wilderness, and therefore some

human effects upon wilderness ecosystems and biota are

inevitable and not incompatible with the Wilderness Act.

However, anthropogenic air pollutant impacts were not

considered to be compatible with wilderness.

It is important to realize that the PSD process provides

a means for the Forest Service manager to protect AQRVs

in Class I areas only by recommending that the state deny

a permit based on predictions of potential impacts prior to

the start-up of a new source. As a result, it is critical that

predictive techniques be applied during the permit review process and that they be scientifically sound and

defensible. Increased control devices can be required after

the source has begun operation, provided deleterious

effects in Class I areas have been detected. Our goal,

however, is to prevent impacts in Class I areas in the first

place—not after a pollution source has started operating.

It was also agreed that if the techniques were biased, the

recommendations should be made toward over-protection of the Class I area, until better projections can be

made. An attempt has been made to limit the list of

sensitive receptors and LACs to those for which information is available that allows predicting impacts from a

given change in air quality. This was not always possible

since there are few predictive techniques available for

components of terrestrial ecosystems.

The monitoring required to implement predictive techniques was discussed. The Terrestrial Group also discussed what information appears to be lacking from our

scientific understanding of the sensitivity of Class I areas

in Region 2, which potentially restricts Forest Service

managers from effectively exercising the Clean Air Act

mandate. The group has suggested research needs that

could be pursued to provide for more effective review of

PSD permits and protection of Class I areas from air

pollution impacts.

Sensitive Receptors and

Limits of Acceptable Change

There was a consensus that only the most sensitive

components of the terrestrial ecosystem should be emphasized in the PSD review process to predict potential pollutant impacts. The Terrestrial Group considered the following attributes of ecosystem condition and function to

be indicative of potential adverse impacts that should be

addressed in defining LACs:

• loss of any species (over and beyond a natural

extinction rate), even if general ecosystem function appears to be little affected;

• unnatural changes in species composition

(floristics and faunistics) of communities or ecosystems;

• fertilizer effects that lead to accelerated or diminished productivity within ecosystems;

• landscape changes in the proportions of species

or ecosystem mosaics as a result of air pollution;

• interruption or breaks in ecosystem function (e.g.,

air pollution-induced changes in the “hidden

diversity” of ecosystem food webs such as mycorrhizal fungi or litter cryptozoans); and

• unnatural deterioration of archaeological or cultural objects.
20 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

Several review papers on effects of air pollutants upon

ecosystems and specific plant or animal species were

prepared for this workshop (Mangis et al. 1990, Bunin

1990). This information proved to be useful in the group

discussions. However, there was a consensus that a more

thorough literature review is necessary for the most suitable LACs to be identified. With this caveat in mind, the

specific sensitive receptors and LACs which this group

recommends for consideration are summarized in table 6.

In the construction of table 6, the group focused on identifying sensitive receptors likely to be impacted by the

most probable pollutants. The pollutants addressed were

SO2, ozone, acidic precipitation (SO4

2-, NO3-

, NOx), and

metals. Consideration was given to CO2, but we did not

specify LAC guidelines. Threatened and endangered species require special attention in relation to all pollutants.

The tolerance limits, or LACs, for those species should be

0% change from population levels in an unpolluted environment. This recommended LAC might change when

direct sensitivity testing data become available.

Predictive Techniques

In the PSD review process, the Forest Service manager

must predict whether a change in air quality (supplied

from the atmospheric transport models and the stack

emissions of the proposed source) will cause a change in

the sensitive receptor which will exceed the LAC. The

group considered that the review of potential vegetation

impacts would be accomplished with projected air quality

information and any sensitive receptor monitoring information that was available (figure 1).

The relationship between atmospheric concentrations

of pollutants and sensitive receptors is seldom known.

Our techniques must be able to predict when an LAC will

be exceeded in a given atmospheric chemistry and what

critical pollution concentration will cause the LAC to be

exceeded. This aspect of the application of terrestrial

sensitivity to pollutants for use in the PSD permit process

is the weakest. Pollutants have little effect on biological

processes until deposition or uptake occurs. The calculation of pollutant uptake is difficult. Several studies on

pollutant uptake have been completed, yet few studies

have been conducted that assess the effects of long-term,

low-exposure pollutant regimes. Two predictive techniques were discussed by the Terrestrial Group.

Direct impact projections

Direct impact projections may be obtained from controlled exposure/impact (dose-response) studies. This

approach eliminates the need to know the uptake levels

(figure 1), yet must be conducted for each species of

concern. The relationships are established on a speciesby-species basis and are usually conducted under controlled environmental conditions that rarely incorporate

the natural stresses of the species. In addition, most of

these studies are conducted over only 1-3 seasons with

seedlings and at relatively high dosages. It is still uncertain if the sensitivity of a species is constant throughout its

life. Regardless of these shortcomings, this type of data,

coupled with field observations of impacts from elevated

pollutant exposure, would be the most defensible for the

PSD review process. However, these data are sparse and

expensive to collect, especially in high-elevation ecosystems. In situ dose/response studies with wet deposition

(e.g., McKenna 1991, Funk and Bonde 1989) are needed

and are much more feasible than those with gaseous

pollutants (see recommended research topics below).

Gaseous pollutant uptake

Another predictive technique is presently being developed (Schoettle 1995) that takes advantage of the fact that

the relationship between pollutant uptake and impact are

much more consistent among species than the relationships between pollutant exposure and impacts (Reich and

Amundson 1985, Reich 1987). This technique will use

Figure 1. Scheme of information needed to predict terrestrial

impacts caused by air pollution.
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 21

Table 6. Sensitive receptors and limits of acceptable change (LACs) relating to probable

pollutants for terrestrial ecosystems in Class I wilderness areas of USDA Forest Service

Region 2. LACs are suggested for impacts due to SO2

, O3, SO4

2-, NOX, metals and VOCs,

fluoride, and all pollutants.

Sensitive receptor Limits of acceptable change

Indicator (comments) (change from baseline)

RELATING TO SO2

Lichens (especially foliose-fruticose forms and epiphytes)

Loss of species 0%

Species composition change 0%

Mosses, loss of species 0%

Vascular plants (fast growing species and riparian species may

be the most sensitive due to high stomatal conductance)

Species change 0%

Photosynthesis <10% decrease

Conifers, foliar lesion <5%

Conifers, leaf tissue S <10% increase

Deciduous, foliar injury <5%

Deciduous, leaf tissue S <10% increase

Insects (especially pollinators)

Species composition 0%

Fecundity 0%

Tissue content 0%

RELATING TO OZONE

Vascular plants (fast growing species and riparian species may

be the most sensitive due to high stomatal conductance)

Species composition 0%

Phenology 0%

Tissue respiration <10% increase

Photosynthesis <10% change

Seedling mortality 0%

Conifers, foliar lesions <5%

Conifers, leaf retention <10% decrease

Conifers, foliated shoot length <10% decrease

Deciduous, foliar injury <5%

RELATING TO SO4

2-, NOX

Vascular plants

Growth (radial or shoot) ±5%

Species cover ±5%

Species composition ±5%

Tissue nutrient ratios (trees on poor soils, e.g.,

Dystric Cryochrepts, may be most sensitive)

N/P (low N/P may be most sensitive) LIT1

C/N (high C/N may be most sensitive) LIT1

Bud break or set ±0 days

Continued
22 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

RELATING TO SO4

2-, NOX (Continued)

Vascular plants (Continued)

Seedling mortality 0%

Leaf tissue S <10% increase

Soils

Base saturation (should be about 20 meq/l)

Low elevation <15% decrease

High elevation 0%

pH ±.5 unit

Deposition (NOX) <5kg/ha/yr

Soil flora and fauna

Decomposition rate LIT1

Earthworm abundance 0%

Cultural resources, petroglyphs

(especially on basic rock) 0%

Lichens (same as above for SO2

)

RELATING TO METALS AND VOCS

Lichens, tissue concentration (lichens may contain high

levels of metals without injury, values represent pristine

conditions; consult vast literature for details)

Pb 200 ppm <10% increase

Zn 400 ppm <10% increase

Hg 2 ppm <10% increase

As 1 ppm <10% increase

Cd 1 ppm <10% increase

Se 1 ppm <10% increase

Cu 100 ppm <10% increase

Mosses

Species composition 0%

Tissue composition LIT1

Soils (sensitive soils will be those with low base saturation,

i.e., Dystric Cryochrepts, Pergelic subgroups, and

many Histosols)

Concentration in inorganic soils 0%

Concentration in organic soils (peat) <10% increase

Cu 100 ppm <10% increase

Zn 400 ppm <10% increase

Pb 200 ppm <10% increase

Cd 1 ppm <10% increase

Hg 2 ppm <10% increase

Se 1 ppm <10% increase

As 1 ppm <10% increase

F 3 ppm <10% increase

Table 6. (Continued)

Sensitive receptor Limits of acceptable change

Indicator (comments) (change from baseline)

Continued
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 23

gaseous pollutant uptake and flux as a predictor of impact; it is based on the fact that stomatal conductance, a

relatively easily measured value, is the primary determinant of gaseous uptake in plants. As a result, plants with

higher stomatal conductance during pollutant exposure

are more likely to be impacted than those with low stomatal conductance (Reich 1987). Knowledge of the average stomatal conductance to gases and the ambient pollutant concentration enables an estimate of pollutant assimilation from which impacts can be estimated.

This approach will reduce the need to study the pollutant response of each species, yet is limited to gaseous

pollutants. There are biochemical factors that can increase

the tolerance of some species to pollutant impacts, yet the

current understanding of these factors and their roles in

tolerance is not sufficient to incorporate them into predictions at this time. This is, of course, a source of error in the

technique. This technique is founded on firm empirical

data that supports its application (Reich 1987), but verification with native, field-grown plants is required before

it can be implemented (and be defensible) in the PSD

permit evaluation process. If this technique proves robust, it will enable predictions of impact to be made for

many more species than could technically and economically be assessed using exposure/impact studies.

Recommendations

The Terrestrial Group recommended that more doseresponse work be conducted for determining wet deposition sensitivity, and that the stomatal conductance modeling approach be further explored for predicting gaseous

pollutant sensitivity.

Monitoring

As the Terrestrial Group developed sensitive receptors

and LACs, it became apparent that baseline measurements are essential. The LACs identified represent

unnatural changes from the baseline condition. Two imRELATING TO METALS AND VOCS (Continued)

Soil Fungi (same as above for SO4

2- and NOX)

Vascular plants (cushion plants in exposed alpine areas may

be most likely to accumulate due to year-round exposure)

Tissue concentration (metals and values

same as those given for lichens above) <10% increase

Bees (domestic bees may be surrogate)

Brood size <10%

Tissue concentration <0-10%

Loss of queen 0%

Bats

Guano concentration LIT1

Tissue concentration LIT1

Birds

Tissue concentration LIT1

Nesting success LIT1

RELATING TO ALL POLLUTANTS

Threatened and endangered species

Population levels 0% change from

unpolluted environment

1 The Terrestrial Group recommended a thorough review of the literature for these LAC values.

The group was confident that the information is available but did not have the expertise to

identify the appropriate limits with any level of confidence.

Table 6. (Continued)

Sensitive receptor Limits of acceptable change

Indicator (comments) (change from baseline)
24 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

portant information needs are implicit in the context of

considering change from a baseline condition: (1) baseline

data for potentially threatened Class I wildernesses and

(2) an understanding of the variation in that baseline that

is a result of natural (nonhuman-caused) environmental

changes (this might be called a natural baseline). This

latter requirement is most difficult if pollutants are already present at the time baseline measurements are

taken. Baseline levels are sometimes determined in the

initial monitoring effort (this might be called a monitoring

baseline), but need not be limited to this. Indeed, the

current condition may be inappropriate if pollution levels

are already high, yet this information will also be useful in

the review process. Baselines can also be determined from

archived collections, previous studies, or from similar,

but more pristine (or at least less polluted) environments

elsewhere. Baseline quantities should include means, seasonal and year-to-year variations, skewness, and other

descriptive statistics against which comparisons of

nonbaseline data can be made. Since effects of pollutants

on populations of sensitive receptors are likely to be subtle

(Gough 1991), good sample design is necessary. Of course,

lack of baseline measurements precludes any implementation of the LACs (i.e., change from what?).

The purpose statement for developing and continuing

a wilderness monitoring program can include additional

benefits other than the factual basis for reviewing PSD

permit applications. Most importantly, perhaps, managers

and their public will have a data base with which an

important aspect of wilderness “condition” can be assessed. While the purpose of the monitoring program will

be to gather information on the current condition of the

resource, the continuation and long-term data base will be

valuable for evaluating and revising the predictive techniques, in the event that the new source is constructed.

Such information will be valuable in future permit application reviews and should feed back into the review

process to improve the management and protection of

Class I areas.

A clear and concise monitoring manual of field locations and methods used is strongly recommended. The

manual should be written, looking to the future, for people

who will be responsible for updating and maintaining the

records if the purpose continues to be persuasive. Managers in Region 2 are advised to consider the methods and

design strategies of this monitoring program for use with

National Forest System wilderness lands.

Another essential feature of monitoring is to build the

decision-maker (the land manager who is responsible for

making the recommendation to the state regulatory

agency) into a monitoring feedback loop. Experience has

shown that if this person is not part of the monitoring

system, it will falter and eventually be abandoned.

What to monitor

The Terrestrial Group recommended that baseline

measurements of the sensitive receptor attributes begin

immediately in each Class I area. Priority sensitive receptors for monitoring should include those that are most at

risk, in light of projected changes in air quality in the

Region.

In addition to monitoring air quality related values, the

Terrestrial Group recommends that the current air quality

near Class I areas be monitored. Specifically, the Group

recommends continuous monitoring of ozone (O3) during

the growing season or, if possible, year-round. Measurements of sulfur dioxide (SO2

) and nitrogen oxides (NOX)

would also be useful when reviewing a permit application.

Table 6 is not exhaustive, but suggests AQRV monitoring opportunities. Monitoring techniques are available

for lichens, perhaps one of the easiest subjects to measure

(but requiring a specialist at first) (see Stolte et al., 1993).

Conifers, too, may be sensitive to several pollutants (O3,

SO2

, HF, NOX, acid rain). Conifers at high elevations, such

as species of Abies, Picea, and Pinus, may be quite sensitive.

Alpine plant communities often grow in N-deficient environments and thus might be responsive to increased loadings of N-based pollutants. Some plants are exposed to

pollutants during most of the year (including pollutant

burdens discharged from melting snow) and tend to be

accumulators (e.g., of heavy metals and S-based pollutants). Mosses, similarly, are accumulators, amenable to

easy measurement and collection (again by a specialist),

and are found in sensitive environments such as snowmelt areas where pollutants may build up. Top carnivores, both vertebrates and invertebrates, may accumulate toxins as part of the food web. Some, such as earthworms, have high exposure to soil contaminants or aluminum toxicity, and readily show toxic symptoms (Root

1990).

The Terrestrial Group often noted how little is known

by scientists outside their immediate field of specialization. It is therefore recommended that literature searches

be conducted on life histories or physiological tolerances

to pollutants of the numerous organisms that might serve

as biological monitors of wilderness pollution. Some literature searches have already been completed but may

need updating (e.g., for animals see Newman and Schreiber

1984; for vascular plants, see Bunin 1990; for lichens, see

Jackson et al. 1992, Stolte et al. 1993; for forests, see Olson

et al. 1992, NAPAP 1991, Nuorteva 1990).

A recommended monitoring approach

At present, with some exceptions, air pollution in Region

2 is at low levels. Projected emission estimates, however,

show both SO2 and NOx substantially increasing to levels
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 25

potentially detrimental to nearby wilderness areas. Levels

of nonlocal pollutants will also probably increase. Because the window of opportunity is both immediate and

likely to be short-lived, the Terrestrial Group make the

following recommendations:

1. Keep monitoring as simple as possible, but don’t

degrade monitoring to avoid more complicated

or expensive techniques. Remember, monitoring

is a service to future managers and publics.

2. Acquire current condition and air quality baseline

information immediately. Baseline needs given in

table 6 are not necessarily exhaustive, but include

measurements of community composition (both

plants and animals); tissue chemistry; distribution and abundance of threatened, endangered,

or sensitive species; soil properties such as cation

exchange capacity; elemental content of organic

matter; condition of important cultural features;

and other properties likely to be adversely affected by pollutants. (This recommendation parallels information needs given by Fox et al. 1989.)

3. Use established field and laboratory techniques,

including updated QA/QC methods. Employ experts or specialists where needed (for example,

lichenologists).

4. Design the monitoring system regionally; implement the system locally.

5. Incorporate into the design as many replicate

samples as necessary to permit some degree of

statistical interpretation in the future. Document

field plots and samples thoroughly. Keep in mind

that some plots will invariably be lost or otherwise rendered useless in the future, so there is a

need to build redundancy into the system.

6. Make use of photographic reference points as

often as possible, making sure the reference points

are well documented and relocatable.

7. Leave room in the plans so that additions can be

made as new information and technologies become available. Ensure that monitoring methods

are not changed over time without complete documentation and cross-comparison to former methods.

Research Recommendations

The Terrestrial Group suggested a number of research

topics. The group further recommends a high degree of

integration and communication with other land managers

responsible for Class I areas within Region 2 to make best

use of research dollars and information. The following list

of research recommendations is not prioritized at this

time:

• Conduct comprehensive literature reviews periodically to evaluate new information and technologies for the revision and completion of table 6.

• Expand the data base of direct dose-response

relationships for native species common to Class I

areas in Region 2. Comparative studies with other

more well-known species sensitivities would be

useful. Sensitivity testing should ideally be conducted in the field, yet controlled environment

studies would also be useful.

• Expand research to develop and test predictive

techniques.

• Improve estimates of pollutant deposition to the

terrestrial ecosystem.

• Expand the understanding of sensitive species’

life cycles. Related to the above, research here

would focus on critical aspects of life histories (for

example, seed germination, pollination) affected

by exposure to, or uptake of, specific pollutants.

• Expand the understanding of the food chain on

which threatened and endangered species are

dependent. Specifically concentrate on links that

may accumulate pollutants and the determination of critical tissue concentrations for animals.

• Expand the understanding of pollutant/impact

relationships of natural communities in already

impacted regions with special attention to monitoring along pollution gradients. Research is

needed on the efficacy of applying direct and

indirect gradient analysis to determine pollutant

effects upon plant communities or plant population attributes.

• Efficiency monitoring. Can monitoring systems

be reduced to some minimum sampling level, in

both space and time, and retain their power of

detection? Closely associated is research into the

manner in which sampling efficiency can be evaluated when determining baseline levels of tissues,

population structure, and community composition.

Literature Cited

Bunin, J. 1990. Sensitivities of Colorado and Wyoming wilderness area

vascular plants to sulfur dioxide, nitrogen dioxide, and ozone: an

overview. Lakewood, CO: U.S. Department of Agriculture, Rocky

Mountain Region, unpublished report. 14 p.
26 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

Fox, D.G.; Bartuska, A.M.; Byrne, J.G.; Cowling, E.; Fisher, R.; Likens,

G.E.; Lindberg, S.E.; Linthurst, R.A; Messer, J.; Nichols, D.S. 1989. A

screening procedure to evaluate air pollution effects on Class I

wilderness areas. Gen. Tech. Rep. RM-168. Fort Collins, CO: U.S.

Department of Agriculture, Rocky Mountain Forest and Range

Experiment Station. 36 p.

Funk, D.; Bonde, R. 1989. Fertilizing effects of artificial sulfuric-acid

mists on Bistorta vivipara plants in alpine tundra. Arctic and Alpine

Research. 21: 169-174.

Gough, L. 1991. USGS/NPS air quality biomonitoring, Florida and

California. Environmental Forum 1990: Geoscience investigations

that emphasize chemical, physical, and biological ecosystem processes. Open-file Rep. 90-288. U.S. Geological Survey. 18 p.

Jackson, L.L.; Ford, J.; Schwartzman, D. 1992. Chemical analysis of

lichens for biomonitoring. In: Huckaby, L.H. ed. Lichens as

Bioindicators for Air Quality. Gen. Tech. Rep. RM-224. Fort Collins,

CO: U.S. Department of Agriculture, Rocky Mountain Forest and

Range Experiment Station. 96-115.

Mangis, D.; Stolte, K.W.; Maniero, T. 1990. Impacts of air pollutant to

terrestrial ecosystems. Lakewood, CO: U.S. Department of Agriculture, Rocky Mountain Region, Air, Aviation, and Fire Management,

unpublished report. 16 p. + 8 p. addendum.

McKenna, M. 1991. Effects of atmospheric processes on natural ecosystems. Final Report; FS contract 28-C8-490. 18 p. Available from:

Rocky Mountain Forest and Range Experiment Station. Fort Collins,

CO.

National Acid Precipitation Assessment Program. 1991. Final Assessment Reports 16, 17, 18. Washington, DC.

Newman, J.R.; Schreiber, R.K. 1984. Animals as indicators of ecosystem

responses to air emissions. Environmental Management. 8: 309-324.

Nuorteva, P. 1990. Metal distribution patterns and forest decline. Seeking Achilles’ heels for metals in Finnish Forest biocoenoses. No. 11.

Helsinki. Publication of Environmental Conservation, University of

Helsinki: 77 p.

Olson, R.K.; Binkley, D.; Bohm, M.; Arbaugh, M. eds. 1992. The response

of western forests to air pollution. Ecological Studies. Vol 97. New

York, NY: Springer Verlag: 532 p.

Reich, P.B. 1987. Quantifying plant response to ozone: a unifying theory.

Tree Physiology. 3: 63-92.

Reich, P.B.; Amundson, R.M. 1985. Ambient levels of ozone reduce net

photosynthesis in tree and crop species. Science. 230: 566-570.

Root, M. 1990. Biological monitors of pollution. BioScience. 40: 83-86.

Schoettle, A.W. 1995. Predicting the potential sensitivity of high elevation wilderness vegetation to changes in atmospheric chemistry - A

strategy. In Tinus, R.W. (ed.) Interior West Global Change Workshop. Gen. Tech. Rep. RM-262. Fort Collins, CO: U.S. Department of

Agriculture. Rocky Mountain Forest and Range Experiment Station.

63-67.

Stolte, K.; Mangis, D.; Doty, R.; Tonnessen, T. Technical Coordinators.

1993. Lichens as bioindicators of air quality. Gen. Tech. Rep. RM-224.

Fort Collins, CO: U.S. Department of Agriculture, Rocky Mountain

Forest and Range Experimental Forest. 131 p.

Terrestrial Ecosystems Workshop

Participants

Will Moir (Chair), USDA Forest Service, Rocky

Mountain Station

Clif Benoit, USDA Forest Service, Region 4

Dan Binkley, Colorado State University

Susan Caplan, USDA Forest Service

Lee Carr, USDA Forest Service, Region 2

Malcolm Edwards, Medicine Bow National Forest

Kathy Foster, San Juan National Forest

Larry Gough, USDA Geological Survey

Meg Lindsey, White River National Forest

Deborah Mangis, National Park Service

Jerry Mastel, Big Horn National Forest

John McCarthy, White River National Forest

Robert Missen, Pacific Power & Light

Robert Musselman, USDA Forest Service, Rocky

Mountain Station

Anna Schoettle, USDA Forest Service, Rocky Mountain

Station

Mike Sestak, National Biological Survey

Mike Sharon, USDA Forest Service, Region 2

Ken Stolte, National Park Service

William Weber, University of Colorado

Robert Willmot, Arapaho & Roosevelt National Forests
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 27

4. VISIBILITY

By Douglas Latimer

This report summarizes the discussion and major conclusions and recommendations of the Visibility Group.

Although the group did not reach consensus on the precise definition of criteria for identifying adverse visibility

impairment, general consensus was reached on the objectives of visibility protection; guidelines for future development of criteria for judging impacts of new and existing

emission sources on visibility; and modeling, monitoring,

and research needs related to visibility protection. These

areas of discussion are summarized below.

Perspective

Certainly, the 1977 and 1990 Clean Air Act Amendments and EPA and state visibility regulations provide a

useful starting point in terms of what the specific objectives of visibility protection need to be. The visibility

provisions of the Clean Air Act (section 169A) direct EPA,

the states, and federal land managers (including the Forest Service) to remedy existing and prevent future visibility impairment, resulting from humanmade air pollution,

in Class I wilderness areas.

Section 165 relating to Prevention of Significant Deterioration provisions gives the USDA Forest Service “...an

affirmative responsibility to protect the air quality-related

values (including visibility) ... and to consider ... whether

a proposed major emitting facility will have an adverse

impact on such values” (42 USC 7475).

The Forest Service needs to take an affirmative responsibility to prevent future degradation of visibility and to

continually improve visibility in wilderness areas, with

the ultimate goal being as close to natural, pristine conditions as possible. An imperceptible amount, perhaps 15%

above natural baseline, could be considered acceptable.

Both the currently existing visibility baseline and the

pristine baseline should be used in visibility regulation.

The air resource should be managed such that future

conditions never deteriorate beyond current conditions

and that future conditions continually move toward natural visibility conditions.

The Visibility Group concurred with the dual federal

visibility strategy: both to prevent additional visibility

impairment and to continually improve existing visibility. The metaphor that the group developed was as

follows: we (our wilderness areas) are currently carrying a heavy backpack (visibility impairment). We want

to take action to start reducing the backpack’s load at

the same time we prevent perceptible additions to the

load.

Considerable discussion was devoted to whether the

ultimate aim of visibility regulation should be to return to

a natural, pristine condition (i.e., one that would exist

without human population impacts) or to prevent any

degradation from a stated baseline visibility. Several alternate baselines were proposed, including 1) current

conditions, 2) estimated natural conditions, 3) conditions

in some recent year, but not the current year, and 4) the

cleanest year in the past 10 years. Use of current conditions

as a baseline drew objections because many felt that

current conditions were unacceptable. It was also pointed

out that unless ”current conditions“ were carefully defined, there could be gradual degradation of visibility

caused by cumulative impact of several small emission

sources, although each one independently might contribute only insignificant levels of pollution. Problems were

identified with using the year with the cleanest measured

visibility because the good visibility might have resulted

from unique meteorological conditions that would be

unlikely to occur again.

Two baseline visibilities should be considered in visibility protection policy. The current visibility would be

used as one baseline from which to measure progress and

the estimated natural visibility; the pristine baseline would

be the long-term goal toward which visibility management activities would continually strive.

The Visibility Group suggested that visibility protection should be provided to all wilderness areas, and some

vistas outside wilderness—not just to Class I areas. For

example, certain views should be protected: from outside

to inside a wilderness, from inside to outside, and from

inside one wilderness area to the outside to inside another

wilderness (the view from one mountain to another).

Potential fire-related visibility policy was discussed.

Fire is natural, to some extent, and therefore should not be

eliminated; however, consideration of the visibility impacts of burning should be factored into the timing of

prescribed fires. Although prescribed fire is a tool used by

humans in forest and range management, it should be

considered a part of natural visibility impairment and

thus should be exempt from visibility regulation. This

conclusion was derived from the fact that wild fire, in the

absence of humankind’s influence, would occur in natural

ecosystems and thus is a part of natural visibility impairment.

Linkages were discussed between emissions, particles,

atmospheric optical conditions, and visual effects. Changes

in all four categories are important. If visibility is to be

improved, reductions are required in:

• emissions of particles and gaseous precursors of

particles, e.g., SO2

, NOx, NH3, and VOCs;
28 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

• ambient concentrations of NO2 gas and particles,

especially the most optically active particles such

as sulfate, nitrate, light-absorbing carbon, and

other PM2.5 (particles small than 2.5 m in diameter);

• light scattering, absorption, and extinction coefficients; and

• perceptible plume or haze layer parameters such

as just noticeable change (jnc), plume contrast,

plume perceptibility (∆E), and uniform haze parameters such as terrain or viewing object contrast, jnc, or visual range.

It is important to stress the interrelationships among

these four categories of parameters and to emphasize that

visibility protection requires limitations and reductions in

emissions.

Sensitive Receptors and

Limits of Acceptable Change

In order to implement the two-fold visibility goals of

preventing future visibility impairment and restoring

natural visibility conditions, alternative criteria for judging whether an existing or proposed emission source

might cause adverse visibility impairment were considered. The two-fold visibility goal requires that visibility

not be degraded beyond currently (admittedly unacceptable) conditions; thus, it was generally agreed that a

stringent test should be given to any new emission source

that might cause potential degradation. The Visibility

Group felt that any perceptible degradation from existing

conditions could not be tolerated. The criterion for judging future emission sources should therefore be defined at

the marginally perceptible level.

The entire frequency distribution of visibility conditions should be used when evaluating visibility impacts.

Various statistical measures such as percentiles could be

used to characterize distribution. Problems were identified with this approach, however. Definition of the just

noticeable change (jnc) for plumes, haze layers, and uniform haze could take years of research. A number of

alternate quantitative parameters descriptive of jnc could

be used as surrogates in regulation; however, jnc might be

difficult to identify. For example, current estimates of a jnc

for plumes and haze layers range from less than 2 percent

contrast to 5 percent, depending on the viewing conditions and the observer. There currently is no research that

would allow one to objectively define a jnc for uniform

haze when visibility varies naturally from day to day and

when the observer is comparing current visibility conditions to memories of previous conditions. Observers have

been able to detect changes in uniform haze between two

photographs viewed simultaneously. However, such viewing conditions are not at all representative of typical

viewing conditions.

Significant or adverse visibility impairment due to

plumes, layered haze, or uniform haze should be defined

as 1 jnc from the pristine baseline, if it occurred more than

1 daylight hour per year. The measurement of jnc would

be refined over time with recommended perception research; however, to start, changes in contrast, light extinction coefficient, or visual range greater than 5% would be

judged adverse or significant. (Table 7 summarizes this

recommendation.)

One member of the group felt strongly that defining

significant or adverse visibility impairment at 1 jnc would

be too restrictive and impractical to implement. Even

small emission sources quite distant from wilderness

areas might be expected to cause impacts of 1 jnc or more

for at least a few hours per year.

The recommended definition of adverse visibility impairment would deal very strictly with each new increment of emissions. However, if this were the only policy

followed to prevent significant deterioration, there would

not be movement toward the second goal of restoring

natural conditions. Thus, each allowed increment in new

emissions should be offset by a decrease in emissions,

greater than the proposed increase, from other sources.

This would result in a net decrease in total regional emissions with each new source addition. An offset policy of

this type would be difficult to structure equitably, but it

must be pursued.

Aggressive movement toward natural visibility conditions will require more than regional emission offsets. The

Forest Service should encourage the states and EPA to

control existing sources of pollution. Controls should not

be sought just for major industrial sources, but also for

minor sources such as wood stoves and motor vehicles

generally associated with more urbanized areas. Existing

power plants or other point sources that are not controlled

with state-of-the-art technology could be required to install retrofit technology. The Forest Service should work

with federal, state, and local governments to reduce emisTable 7. Sensitive receptors and limits of acceptable change

relating to visibility.

Sensitive receptor Limits of acceptable change

Contrast now: <5% change from

baseline

Light extinction coefficient future: <1 jnc from pristine

baseline for 1 daylight hour

per year

Visual range <5% change from baseline
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 29

sions associated with currently uncontrolled major and

minor sources.

Modeling Recommendations

Existing visibility screening and modeling techniques

for plume visual impact (the EPA Visibility Workbook,

VISCREEN, and PLUVUE) were generally considered to

be adequate, but continuing refinement and testing were

recommended.

For uniform and layered haze resulting from multiple

sources of particles, SO2, NOx, and VOCs, the Forest

Service needs to support and encourage the development,

documentation, refinement, evaluation, and application

of screening models and sophisticated deterministic and

receptor models. These models need to be able to address

existing emissions, new emissions, new emission offsets,

and controls on existing sources. And, further, these models need to address the common worst-case meteorological condition in the Rocky Mountain Region—namely,

stagnation in valleys and basins.

Existing tools are not adequate to calculate the impact

of proposed new sources and to evaluate the impacts of

existing sources on uniform haze, especially in rugged

terrain. The types of visibility impacts that were identified

at the Grand Canyon that led to the recent EPA proposal

to retrofit the Navajo Generating Station were not related

to whether the plume itself was identifiable as a coherent

plume. The major impacts of Navajo (and most other

sources) are believed to be increases in haze caused by

emissions once the plume is uniformly mixed with background air. The plume itself is not visible but the plume

contributes to increased haze that is perceptible. These

impacts are largely due to sulfate particles and associated

water formed in the atmosphere from sulfur dioxide (SO2

)

emissions. In other cases, nitrate particles and associated

water converted from NOx emissions may be important.

Visibility models must be able to predict the effect of a

given spatial and temporal distribution of light scattering

and absorbing chemical species on the appearance of

various landscape features and on observer perceptions.

Different vistas have different sensitivities to increase in

haze. For example, the sensitivity of a vista may depend

on the distance and apparent size of various terrain features in the landscape, as well as their form, line, color, and

texture.

Most analyses of proposed future changes—either increases in emissions from new sources or decreases in

emissions from existing sources—require deterministic

model capability. Deterministic models utilize quantitative knowledge of emissions, meteorology, diffusion, deposition, and chemical conversion to project future conditions. However, analysis of the impacts of existing sources

can also be studied using receptor models. Receptor models use measurements of source and ambient concentrations and chemical composition to deduce the impact of a

given source. Further development and refinement of

receptor models is necessary to support activities to encourage the retrofit of existing pollution sources.

Monitoring Recommendations

The Forest Service should design, implement, and coordinate a comprehensive, long-term (in perpetuity) monitoring program to document visibility baselines and trends

in areas representative of both high and low elevations of

all wilderness areas. In addition, special monitoring should

be carried out at existing sources suspected of causing

visibility impairment in wilderness areas and in areas

where future emission growth is anticipated.

Monitoring is required for a number of reasons. First,

through photographic documentation, it may be possible

to qualitatively demonstrate the existence of a visibility

problem deserving additional monitoring, analysis, and

remediation. Second, monitoring is needed to document

existing conditions and trends in conditions over time.

Monitoring of meteorological and ambient conditions is

necessary to provide input for deterministic and receptor

modeling of existing and new emission sources. Finally,

monitoring of existing sources is needed to document

their impact on wilderness areas and provide the necessary technical information to support implementation of

emission retrofitting and other cleanup activities.

Trend and baseline visibility monitoring is needed in

each wilderness area or in an area that is representative of

a given wilderness area. Monitors in the mountainous

wilderness areas of the Rocky Mountain Region need to be

located at both high and low elevations. At high elevations, ambient concentrations tend to be lower and reflect

regional contributions. At low elevations, concentrations

are higher and reflect more local influences. Monitoring at

low elevations is also necessary because layered haze,

especially in winter, is trapped at the low elevations; thus,

high-elevation monitoring would not be representative.

The type of monitoring equipment depends on the

specific monitoring objectives. For example, if one needs

to document qualitatively an existing visibility problem,

photographs taken with an automated system over at

least one year might suffice. However, to document the

current baseline and trends, one needs to measure atmospheric optical parameters and particle concentrations,

size, and chemical composition as well. Further, trend

monitoring requires continuous monitoring over many

years. It may require more than 10 years of data to identify

trends because of year-to-year variability in meteorological conditions. Monitoring should be a perpetual, on-
30 USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998

going activity; it should not be started only to be stopped

later.

Trend monitoring should use the technology and monitoring, data analysis, and quality assurance and control

protocols of IMPROVE (the existing EPA and FLM monitoring network) in areas where electrical power is available. In more remote areas, solar-powered technologies

should be developed, tested, and applied. It is likely that

many low-elevation areas can be monitored with IMPROVE technology, while most high-elevation sites will

require solar powered technology.

Trend monitoring needs to consist of three elements:

1. View monitoring - Photographs of given vistas

with automated cameras, taken at least three times

per day (at 0900, 1200, and 1500).

2. Atmospheric optical monitoring - Measurements

of light extinction and the scattering and absorption components of light extinction. (Transmissometers, nephelometers, filters for light absorbing carbon.)

3. Particle monitoring - Mass, size distribution, and

chemical composition. Important size categories:

0-2.5 μm and 2.5-10 μm. Important chemical species: sulfate, nitrate, organic carbon, elemental

carbon, soil and trace elements with atomic numbers from sodium to strontium.

Specific monitoring strategies, siting policies, data

analysis, and archival and quality assurance protocols

need to be developed and coordinated with other monitoring agencies. These strategies and protocols should be

designed to fit with the specific needs of Forest Service

field personnel.

In areas where future emission growth is anticipated

(e.g., the Piceance Basin), visibility baseline and trend

monitoring, as well as meteorological and ambient concentration monitoring, should be started as soon as possible. In such areas financial support might be obtained

from developers. In other areas, use of volunteers for

photographic monitoring may be useful.

Research Recommendations

Research is needed to support the policy objectives and

the modeling and monitoring recommendations presented

earlier. The Forest Service visibility protection program

must be flexible to allow evolution of our understanding

of visibility and its relationship to atmospheric optics,

ambient concentrations, and regional emissions. Conversely, our visibility research must be designed to support the specific needs of the visibility regulator.

The Forest Service needs to become a major player in

visibility research and needs to coordinate such research

with other agencies and industry. Research and development should be directed to continually improving and

testing modeling and monitoring technology. Research

should be performed in areas directly related to the specific needs of visibility policy, namely to protect and

continuously improve visibility. To understand visibility,

the ”soft“ sciences of psychology, perception, and economics are just as important as the ”hard“ sciences of

physics and chemistry.

The following research topics were recommended by

the Visibility Group:

1. Modeling and monitoring development: Since

modeling and monitoring are major technical tools

required in visibility regulatory activities, it is

imperative that these technologies be continually

refined and tested prior to application. Models

need to incorporate new understanding and new

algorithms as they are developed. Models need to

be evaluated by comparing model calculations

with field measurements. Monitoring technology

needs to be refined and tested also. Considerably

more work is needed to develop monitoring techniques that can operate unattended in remote

wilderness locations without electrical power.

2. Source attribution: To aggressively strive for

natural visibility conditions, special studies of

suspected source contributions to impairment in

wilderness areas need to start. Such studies are

necessary to develop sufficient technical information so that regulatory agencies can pursue Best

Available Retrofit Technology (BART) on currently uncontrolled sources. For example, the

WHITEX, PREVENT, and Mohave studies could

be used as models for such source attribution

studies. Areas where such studies should commence immediately are wildernesses close to currently uncontrolled power plants in Colorado

and Wyoming (e.g., Mt. Zirkel near the Hayden

Power Plant).

3. Remote sensing and geographical information

systems (GIS): Research should be devoted to the

remote monitoring of ambient concentrations

important to visibility and to the use of satellite

imagery in GIS. Technology transfer in many

different areas, such as remote sensing, should be

explored.

4. Data analysis: With extensive monitoring networks employed, large quantities of data need to

be routinely analyzed, interpreted, and visualized. New techniques, including scientific visualization and other computer hardware and software approaches, should be explored.
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–4. 1998 31

5. Socio-economic and psychological research:

Further research needs to be performed to understand user preferences for wilderness areas, willingness to pay for improvements in visibility,

psychological attributes of observers important

in evaluating visibility, perceptual cues and parameters for use in impairment documentation,

and better definition of the just noticeable change

(jnc).

6. Policy research: Policy and implementation alternatives need to be studied to determine which

are most efficient, cost-effective, and acceptable.

Visibility Workshop Participants

William Malm (Chair), Colorado State University

Ann Acheson, USDA Forest Service, Region 1

Tina Arapkiles, Sierra Club, Boulder

Ken Bowers, University of California

Elizabeth Close, USDA Forest Service, Region 1

Charles Collins, Wyoming Air Quality Division

Dennis Crumpler, USDA Environmental Protection

Agency

David Dietrich, Air Resource Specialists

Dan Ely, Colorado Air Pollution Control Division

Richard Fisher, USDA Forest Service

Glen Haas, Colorado State University

Rick Jewell, San Juan National Forest

Gary Kenniston, Colorado Air Pollution Control

Division

Darrell Knuffke, Wilderness Society

Doug Latimer, Latimer and Associates

John Leary, Colorado Air Pollution Control Division

Terri Lorenzon, Wyoming Environmental Quality

Council

Ross Loomis, Colorado State University

Mike Manfredo, Colorado State University

Bob Miller, White River National Forest

David Pavlich, Parachute, Colorado

Robert Pearson, Public Service Company of Colorado

Mark Pitchford, USDA Environmental Protection

Agency

Ken Pitt, USDA Forest Service, Region 2

Steve Posey, Grand Mesa, Uncompahgre & Gunnison

National Forests

Sherry Randall, Colorado Mountain Club

Sherry Reed, Routt National Forest

Chris Risbrudt, USDA Forest Service, Region 1

David Ross, Colorado State University

Paul Schultz, Platte River Power Authority

Dick Vnuk, Arapaho & Roosevelt National Forests

George Wallace, Colorado State University

The Rocky Mountain Research Station develops scientific information

and technology to improve management, protection, and use of forests

and rangelands. Research is designed to meet the needs of National

Forest managers, federal and state agencies, public and private

organizations, academic institutions, industry, and individuals.

Studies accelerate solutions to problems involving ecosystems,

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Research Locations

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Moscow, Idaho

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Missoula, Montana

Lincoln, Nebraska

* Station Headquarters, 240 West Prospect Road, Fort Collins, CO 80526

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