The Role of Lichens in
Air Quality Monitoring
on Federal Lands
What information can lichen monitoring
provide to air resource managers?
Linda Geiser, US Dept. of Agriculture-Forest Service, Pacific Northwest
Region Air Resource Management, PO Box 1148, Corvallis OR 97330
What are lichens?
British soldiers
Button lichen
Lichens are symbiotic
organisms consisting
of a fungus and an
alga and/or a
cyanobacterium.
Lung lichen
What physiological properties make lichens
useful indicators of air quality?
 Range of air pollution sensitivities across species. Lichens exhibit a range
of sensitivities to S- & N compounds in acid rain, sulfur dioxide, ammonia,
and fluoride. Changes in distribution or populations of the most sensitive
lichens provide an early warning that air pollution is beginning to adversely
affect the ecosystem. The mix of species and abundances at any one site
can be used to position the site along an air quality gradient.
 High surface area and no roots. Lichens on trees and shrubs obtain
nutrients from the air, precipitation, and substrate run-off. Tissue levels of
many pollutants are correlated with ambient atmospheric levels.
 Readily absorb water and lack specialized barriers to prevent vapor loss.
Daily cycles of wetting and drying produce a dynamic equilibrium between
concentration and leaching of pollutants. As pollution concentrations
change, so do concentrations in lichens. Mobile elements: S, N, K, Ca,
Mg, Na. – can change significantly over a few months. Less mobile
elements: Pb, Cd, Ni—change more slowly.
What kinds of data are
collected?
Lichen communities and floristics
Tissue analyses
Transplants
Laboratory
#1. Documenting deposition of pollutants in
a Class 1 Area and tracing their source.
Mt. Zirkel
Wilderness,
Routt NF,
Colorado
Yellow lines circle lichen
monitoring plots (black triangles)
REFERENCE: Jackson, LL, L
Geiser, T Blett, C Gries, D
Haddow. 1996: Biogeochemistry of
lichens and mosses in and near Mt.
Zirkel wilderness, Routt National
Forest, Colorado: influences of
coal-fired power plant emissions. Open-File Report, 96-295, U.S.
Department of the Interior, U.S.
Geological Survey. 162 pp.
Mt. Zirkel Wilderness, Routt NF, Colorado
Stable S isotope ratios in lichens were significantly heavier in the MZW and Routt NF
than at regional sites. This was consistent with a local sulfur source with a heavy
isotopic signature resulting from the combustion of marine-influenced coals from the
Yampa Valley.
#2. Check a site within an
area with established
background ranges.
Lichen monitoring
sites indicated by
yellow triangles
Klondike Gold Rush
National Historic Park,
Skagway, Alaska
REFERENCE: Furbish, C.E., L.H. Geiser and C. Rector. 2000. Lichen-air quality pilot study
for Klondike Gold Rush National Historical Park and the City of Skqaway, Alaska. Klondike
Gold Rush National Historical Park Natural Resources Management Program. Report released
December 2000.
Klondike Gold Rush National Historic Park, Skagway, Alaska
Mean concentrations of Al, Cd, Cr, Cu, Fe, Pb, Ni, P, K, S, Zn in the
lichen, Hypogymnia enteromorpha, were higher in Klondike Gold
Rush NHP samples than Tongass National Forest samples.
Lichen tissue was collected
along a transect from the APC
mill, through the town of Sitka
to the Ferry Terminal (red dots).
#3. Mapping
deposition patterns
from a point source.
Tongass National
Forest, Sitka, Alaska
REFERENCE: Geiser, LH/ Derr, CC/ Dillman, KL
1994: Air Quality Monitoring on the Tongass
National Forest. Methods and Baselines Using
Lichens. - USDA-Forest Service, Alaska Region
Technical Bulletin 46. 85 pp.
Tongass National Forest, Sitka, Alaska
Typical cover of lichens on
alder in the Sitka area
Lichens were absent from alder
<0 .25 mi from the pulp mill, an
SO2 source.
Tongass National Forest, Sitka, Alaska
3-D view of lichen tissue concentrations in # of sd from Tongass clean sites mean
(vertical axis) vs sampling site location (horizontal axes). Far right is < 1km from the
pulp mill, center is Sitka city center, far left is the ferry terminal, 14 mi distant.
#4. Estimating deposition from calibrated
lichen data.
Pacific Northwest National Forests
Lichen tissue collections were made within 1 km of 8 NADP monitors
in Oregon and Washington (black dots on national map above).
Pacific Northwest National Forests
Lichen sulfur concentrations, weighted by precipitation,
accurately predicted wet deposition of sulfur to within about 0.3
kg/ha/yr.
8
Hoh RS
SO4 deposition (kg/ha/yr)
6
Alsea
Bull Run
NC
Pack For
HJA
4
Hyslop
2
Starkey
Silver L
0
0
5
10
Lichen % S (pptn weighted)
15
20
Pacific Northwest
National Forests
A map of wet deposition of
sulfur in Pacific NW
national forests constructed
using calibrated lichen data.
Values ranged from < 0.7
(dark blue) to > 4.0 (red)
kg/ha/year.
A map of wet deposition of
nitrogen was similar.
#5. Combining lichen community and tissue data to
indicate patterns of anthropogenic influence and its
effects on vegetation.
Alaska and Pacific Northwest Regions
Red dots indicate monitoring locations where lichen community surveys and tissue
analysis have been completed by the USFS Air program. In PNW forests, monitoring is
co-located with the CVS (= USFS national Forest Inventory Assessment) 3.4 mi grid.
Sensitive, ecologically important lichens, many endemic, are sparse to
absent in areas where acid rain is high.
Growth of pollution-loving, weedy species is enhanced where nitrogen
pollution is high.
Lichen
NMS3Dcommunities indicate a pollution gradient
Area
Willamette N.F.
Siuslaw N.F.
Gifford Pinchot N.F.
Mt. Hood N.F.
Willamette Valley
CRGNSA
Urban Parks
Lichen communities
80
Axis 2
DECMINT
SMRTMP
AirQual
40
Elev
Easting
KMocean
0
0
40
Axis 1
Ordination of sites by lichen communities. Plots (represented by
triangles) with smiliar communities are close together in space.
Environmental variables are overlaid on the ordination Axis 1 is
correlated with increasing sulfur and nitrogen pollution. Axis 2 is
correlated with80decreasing distance from the coast and warmer winter
temperatures. In this analysis, urban parks and the Columbia River
Gorge National Scenic plots receive the highest pollution scores.
#7. Determining whether instrumented
monitoring is warranted
Hell’s Canyon National Recreation Area
Could ancient rock art be threatened by air pollution?
Hell’s Canyon National
Recreation
Area
% N (dw) By Distance
(km)
2.0
1.9
1.8
% N (dw)
1.7
1.6
1.5
1.4
1.3
1.2
1.1
0
0.4
1.6
Wi th Con trol
Dunn ett's
0 .05
>1 .6
Xanthoria Cover (% ) By Distance (km)
Distance (km)
70
60
Means Comparisons
Xan thori a Cover (%)
Dif=Mea50
n[i]-Mean[j]
0
0.4
40
>1 .6
1.6
30
Al pha=
0.05
0
0.0000 00
-0.3280 7
-0.3311 9
-0.3411 9
0.4
0.3280 68
0.0000 00
-0.0031 2
-0.0131 2
>1 .6
0.3311 93
0.0031 25
0.0000 00
-0.0 1
1.6
0.3411 93
0.0131 25
0.0100 00
0.0000 00
Comparisons
with a control using Dunnett's Method
20
|d|
2 .484 75
10
Abs (Dif)-LSD
0
0.4
0
>1 .6
1.6
0
-0.1661 9
0.1469 65
0.1500 0.4
90
0.1600 90
Wi th Con trol
Dunn ett's
0 .05
Pos itive va lues sho w pairs ofDistance
mean s th(km)
at a re si gnifica ntly d iffe rent.
0
1.6
> 1.6
Nitrogen concentrations in lichen tissue and abundance of the nitrogen-loving lichen,
Xanthoria, were highest at sites closestMeans
to the
Snake River.
Comparisons
Hell’s Canyon National Recreation Area
log (% N in Xanthoparmelia) By Comparison Areas
0.35
0.30
log (% N in Xanthoparmelia)
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
-0.10
CRGNSA
HCNRA: 0 k m
HCNRA:>.3 k m
Comp arison Areas
R2 Elev a
R2/6 Back g
With Control
Dunnett's
0.05
Average tissue concentrations of nitrogen at all sites in Hell’s Canyon
were elevated relative to background sites in the western US
Means and Std Deviations
Le vel
Num ber
Mean
Std Dev
Std
Err Mea n
Conclusion:
Instrumented
monitoring
is warranted.
Summary: Advantages of lichen monitoring
 Good indicators of deposition containing sulfur, nitrogen, metals, other
elements, radionuclides and some hydrocarbons/organochlorines.
 Demonstrates presence of contaminants in the ecosystem.
 Lichen communities are good summarizers of air quality—respond to
the synergistic mix of pollutants in the air.
 Lichen communities (species richness, composition and abundance) can
be used to indicate whether anthropogenic activities are affecting the
ecosystem
 Relatively fast and inexpensive—many measuring points can be made in
a short time that summarizing air quality over past months or years.
 Useful in areas of rugged topography where modeling is inadequate.
 Useful in remote areas—does not require electric power.
 Can be used to map relative differences in air quality over a
geographical area of interest and to track changes over time. If air
pollution tolerant species are used, can map polluted areas.
 Source apportionment is possible using multi-element analysis and
isotope ratios.
Summary: Advantages of lichen monitoring
 Compliments instrument measurements and other monitoring
information. Element analyses, community analyses used in combination
with direct measurements or other bioindicatorscan corroborate each other,
making a more convincing argument for decision-makers.
 Plentiful existing data for the PNW and Alaska and Canada for metals, and
in arctic for POPs, some data for radionuclides from Canada. Preliminary
thresholds for metals.
 Can link to existing programs: FHM (lichen communities) and USFSPNW (communities and tissue analysis).
 Not mobile, concentrations reflect local conditions.
 Easy to collect, lichens are widespread and easy to recognize.
 Deposition can be estimated from lichen tissue levels if instrumented sites
are available for calibration.
 Multi-element analysis can evaluate multiple stressors simultaneously,
good idea to measure effects of sulfur and nitrogen deposition together with
other pollutants.
Summary: Limitations of lichen monitoring
 Lichens are relatively insensitive to many air toxics (metals,
radionuclides, organics)– lichen communities affected more by acid
rain, SO2, N deposition and fluorine. I.e. may be able to show presence
of enhanced tissue levels but not adverse effects to ecosystem.
 Cannot separate wet from dry deposition or different forms of sulfur
or nitrogen containing pollutants using lichens—measure total N, total
S and total deposition.
 Some metals are not easily leached from lichen thalli and may remain
concentrated for 10+ years. Can use transplants, select species with
annual growth (Hylacomium splendens) or collect from substrate of
known age (last five terminal bud scars). Or, because epiphytic lichens
grow rather quickly, can monitor changes over time of the population
mean.
 Interference from local dust: use enrichment factor from local soils
(Al).
 Tissue analysis cannot differentiate wet from dry deposition. May
not be able to distinguish different forms of a single element.
Summary: Limitations of lichen monitoring
 Multivariate analysis is often required to separate the pollution
signal from other environmental variables (elevation, precip, forest
continuity, relative humidity, available substrates) OR restrict the range
of these variables within the study area.
 To obtain accurate and repeatable readings of metals, tissue
concentrations of metals should be in the 0.1 ppm range or higher.
Check detection limits of laboratory before analysis.
 Lichen analysis for POPs is analytically challenging because
concentrations are usually low and natural lichen substance interfere with
analyses. But much base work has been completed for the arctic.
 Must have sufficient material– lichens may be difficult to find where
acid rain, SO2 or N deposition is a problem. Can use transplants. Must
compare different sites using the same species.
 Regulatory personnel are often unfamiliar with lichen monitoring
methods. Can establish LACs, develop an MOU, or calibrate data to
units used by regulatory agencies.