Provisional Air Quality Ratings
Table of Contents
- Air Pollution Scores
- What are they?
- What are they?
- How are they calculated?
- What do they mean?
- Air Quality Lichen Sensitivity Ratings
- What are they?
- How were they calculated?
- How are they calculated?
- What do they mean?
- Nitrogen and Sulfur in Platismatia Glauca
- How are they calculated?
- What do they mean?
- Wet Deposition of Nitrogen and Sulfur
- What is this?
- How is deposition estimated using lichens?
- NADP data
- Lichen data?
- Calibration
- What does it mean?
Air Pollution Scores
What are they?
The air pollution score is an assessment of air pollution at a specific location. Values range from 0 (low) to 10 (high). Lichen species diversity and composition is considered to be adversely affected by air pollution at sites with scores > 7.
How are they calculated?
Air pollution scores are based on predictable changes in lichen communities with increasing availability of atmospheric nitrogen (N) and sulfur (S). S and N accumulation in lichens were strongly correlated in our study area, that is, western Oregon and Washington south of Mt. Rainier National Park.
Scores were obtained by:
1) Correlating average N and S concentrations in the lichen, Platismatia glauca, to a three dimensional NMS ordination (McM Software Design Pcord version 4, 12/30/99) of lichen communities in plots west of the crest of the Cascade Range,
2) Rotating the bi-plot to make average N parallel to the x-axis, then saving the axis scores
3) Scaling the resulting plot distances along the x-axis from 0 (lowest nitrogen) to 10 (highest nitrogen).
What do they mean?
Air pollution scores between 7 and 10 indicate sites that are nutrient enhanced. Estimates of nitrogen and sulfur wet deposition at these sites range up to 2.8 and 3.4 kg/ha/yr, respectively. Concentrations of nitrogen and sulfur in the lichen, Platismatia glauca average 0.84 and 0.1, maximum values are 1.2 and 0.16 % dry weight, respectively. Sites with these scores have relatively high abundances of pollution-tolerant and nitrophilous (responding positively to enhanced nitrogen), weedy, urban lichens, decreasing total species diversity, and decreasing abundance to absence of air pollution-sensitive lichens. Typical species at sites with scores in this range include: Candelaria concolor, Candelariella vitellina, Chrysothrix candelaris, Evernia prunastri, Hypogymnia physodes , H. tubulosa, Melanelia exasperatula, Parmelia sulcata, Phaeophyscia orbata, Physcia adscendens, P. aipolia, Physconia perisidiosa, Platismatia glauca, Punctelia subrudecta, Ramalina farinacea, and Xanthoria polycarpa. Some of the coastal or oceanic influenced sites with species such as Cetrelia cetrariodes and Parmotrema arnoldii also score in this range. Most sites scoring in this range were located in the Columbia River Gorge National Scenic Area, urban areas, and the Willamette Valley.
Sites with air pollution scores between 4 and 6 have provided the majority of records for air pollution-sensitive lichens. At nearly all sites, concentrations of nitrogen and sulfur in the lichen, Platismatia glauca, are under 0.74 and 0.10% dry weight and estimates of annual wet deposition of nitrogen and sulfur are under 2.0 and 2.4 kg/ha/yr, respectively. Examples of species very sensitive to sulfur and nitrogen-containing air pollutants are: Alectoria sarmentosa, A. vancouverensis, Hypogymnia occidentalis, Leptogium corniculatum, L. gelatinosum, Lobaria oregana, Nephroma bellum, N. helveticum, N. laevigatum, N. resupinatum, Pseudocyphellaria anomola, P. anthraspis, P. crocata, Ramalina thrausta, Usnea longissima, U. scabrata.
Air pollution scores of 3 or lower indicate lowest atmospheric nutrient and pollutant concentrations. At nearly all of these sites, concentrations of nitrogen and sulfur in the lichen, P. glauca, are under 0.5 and 0.07% dry weight, respectively, and estimates of annual wet deposition of nitrogen and sulfur are under 1.5 kg/ha/yr. These are usually high elevation and drier sites in the Cascade Range and species diversity is low. Typical species at sites with these scores include Alectoria sarmentosa, Bryoria fremontii, Letharia columbiana, L. vulpina Nodobryoria abbreviata, and Parmeliopsis hyperopta.
Table 1. Interpreting Air Pollution Scores summary.
| Air Pollution Score | Air Quality Description and Effects |
|---|---|
0-2 |
Levels of atmospheric nitrogen and sulfur pollution are very low at these sites. Although total lichen species diversity is generally low, air pollution-sensitive species are present, and their biomass is often high. |
3-6 |
Levels of atmospheric nitrogen and sulfur pollution are low. The greatest diversity and biomass of air pollution-sensitive lichens is observed within this score range. |
7-10 |
Levels of atmospheric nitrogen and sulfur-containing pollutants are comparatively high. As scores increase, diversity and biomass of air pollution-sensitive lichens decreases, total lichen species diversity declines, and the proportion of nitrogen-loving and pollution-tolerant weedy species increases. |
Table 2. Comparison of lichen community-derived pollution scores to measurements of nitrogen and sulfur accumulation by lichens and estimates of wet deposition at the same sites.
| Air Pollution Score | Count of Sites | Air Pollution Parameter | Mean | Mean+ 2 SD |
|---|---|---|---|---|
|
0-2 |
26 |
Nitrogen in Platismatia glauca Sulfur in Platismatia glauca Nitrogen wet deposition Sulfur wet deposition |
0.42 % 0.05 % 1.0 kg/ha/yr 0.9 kg/ha/yr |
0.50 % 0.07 % 1.4 kg/ha/yr 1.5 kg/ha/yr |
|
3-6 |
661 |
Nitrogen in Platismatia glauca Sulfur in Platismatia glauca Nitrogen wet deposition Sulfur wet deposition |
0.47 % 0.06 % 1.3 kg/ha/yr 1.4 kg/ha/yr |
0.74 % 0.10 % 2.0 kg/ha/yr 2.4 kg/ha/yr |
|
7-10 |
59 |
Nitrogen in Platismatia glauca Sulfur in Platismatia glauca Nitrogen wet deposition Sulfur wet deposition |
0.84 % 0.10 % 1.8 kg/ha/yr 2.0 kg/ha/yr |
1.2 % 0.16 % 2.9 kg/ha/yr 3.6 kg/ha/yr |
Table 3.Comparison of air pollution scores among national forests, urban and agricultural areas of the Pacific Northwest.
| Area (# of plots) | Mean | Range |
|---|---|---|
|
Willamette N. F. (213) |
4.1 |
1.4-5.8 |
|
Gifford Pinchot N. F. (162) |
4.1 |
0-7.8 |
|
Mt. Hood N. F. (100) |
4.5 |
2.2-6.4 |
|
Siuslaw N. F. (92) |
5.6 |
1.9-10 |
|
Willamette Valley (12) |
6.3 |
5.3-8.8 |
|
Urban Parks (29) |
6.6 |
5.3-9.1 |
|
Columbia River Gorge N. S. A. (31) |
7.3 |
5.4-9.2 |
Air Quality Lichen Sensitivity Ratings
What are they?
Air quality sensitivity ratings are ratings of the pollution sensitivity of individual lichen species in Oregon and Washington. Lichens are known to be most sensitive to sulfur and nitrogen-based gaseous and acidic compounds. The air quality sensitivity rating indicates the sensitivity of an individual lichen species to the regional mixture of these and other air pollutants occurring in western Oregon and Washington. Some species are very sensitive while others can tolerate comparatively high pollution levels.
How were they calculated?
Air quality sensitivity ratings were calculated from field studies of lichen communities in Oregon and Washington, including the urban areas of Portland, Salem, Corvallis, Albany, Eugene, Vancouver, Tacoma and Olympia, public lands in the Willamette Valley, interstate-5 highway corridor in Washington, the Gifford-Pinchot, Siuslaw, Willamette, and Mt. Hood National Forests and the Columbia River Gorge National Scenic Area. These ratings are presented, supplemented with a literature review, photographs and habitat notes in a guide to the sensitivity of Pacific Northwest lichens.
We have used a general rating system (sensitive, intermediate, or tolerant) to provide a wide margin of error for variability of a species' response to pollution under variable climates, substrates, or topographic and microhabitat exposures within the Pacific Northwest region. In general, pendant and nitrogen-fixing epiphytic lichens are most sensitive; medium to large foliose epiphytic macrolichens are intermediate in tolerance; and ground-dwelling lichens and species with comparatively small surface areas, such as crustose and small foliose lichens, are most tolerant to pollution.
Table 4. Interpreting Air Quality Sensitivity ratings.
| Air quality sensitivity rating | Species count | Estimated SO2 tolerance (ppb)1 | Max N deposition kg/ha/yr2 | Max S deposition kg/ha/yr3 | Max Sulfur levels tolerated (% dw)4 | Max Nitrogen levels tolerated (% dw)5 |
|---|---|---|---|---|---|---|
| most sensitive | 12 | 5 to 10 | 1.5 | 2.1 | 0.06 | 0.4 |
| sensitive | 66 | 5 to 15 | 2.0 | 2.8 | 0.11 | 0.8 |
| intermediate | 25 | 10 to 35 | 2.3 | 2.8 | 0.12 | 1.0 |
| tolerant | 37 | >30 | 2.8 | 3.4 | 0.14 | 1.1 |
| most tolerant | 8 | >30 | >2.8 | >3.4 | 0.15 | 1.15 |
1 From Peterson et al. 1992. Guidelines for evaluating air pollution impacts on Class I Wilderness Areas in the Pacific Northwest. USDA-FS PNW Research Station, PNW-GTR-299.
2 Maximum annual nitrogen deposition (wet) in kg/ha/yr for sites where population size of the rated species is >40 individuals/acre.
3 Maximum annual sulfur deposition (wet) in kg/ha/yr for sites where population size of the rated species is >40 individuals/acre.
4 Maximum concentration of sulfur (% dry weight) observed in the lichen, Platismatia glauca, where population size of the rated species >40 individuals/acre.
5 Maximum concentration of nitrogen (% dry weight) observed in the lichen, Platismatia glauca, where population size of the rated species is >40 individuals/acre.
Nitrogen and Sulfur in Platismatia glauca (% dw)
What are they?
Values for nitrogen and sulfur in Platismatia glauca (% dry weight) allow comparison of sulfur and nitrogen pollution levels at different plots within the study area through comparison of their concentrations in the lichen P. glauca.
How were values calculated?
For most plots, the values are simply the total concentrations of nitrogen or sulfur in 10 grams of P. glauca collected from (or within 1 km of) the plot, recorded by the analytical laboratory in units of percent dry weight. P. glauca, was the species most frequently collected for element analysis. It has the broadest ecological amplitude and greatest tolerance to air pollution of the target species and is found in all national forests in the study region and many urban areas.
However P. glauca was not present in sufficient quantities for element analysis at all sites. Through the entire study area, a total of fourteen species were targeted for element analysis. The other species, in order of importance, were Alectoria sarmentosa, Hypogymnia inactiva, Letharia vulpina, Sphaerophorus globosus, Bryoria fremontii, Lobaria oregana, Hypogymnia enteromorpha, Hypogymnia imshaugii, Evernia prunastri, shrubby Usnea species, Isothecium myosuroides (moss), Neckera douglasii (moss) and Xanthoparmelia cumberlandia.
Two target species were collected at each plot. Using linear regression, S and N concentrations in P. glauca were related to S and N concentrations in other target species at plots where they co-occurred (Fig. 1). Linear equations derived from the best fit of the data were then used to estimate the concentration of S and N in P. glauca at sites where the target species did not include P. glauca. For example if E. prunastri and H. inactiva were collected, but not P. glauca, the linear equations below would be used to estimate the concentration of S that would be in P. glauca. The resulting two values would then be averaged to obtain a value for %S in P.glauca at that site.
%S in P. glauca = 0.02 + 0.61 * % S in Hypogymnia inactiva
%S in P. glauca = 0.04 + 0.62 * %S in Evernia prunastri
Figure 1. The relationship between %S in Platismatia glauca and %S in Hypogymnia inactiva
or Evernia prunastri can be described by linear equations.
What do they mean?
Values of %N and %S in P. glauca are used in conjunction with air pollution scores, sensitivity ratings for individual species and estimates of deposition to predict or assess air quality in a geographical area or location. (See Tables 1, 2, 4 above and the following section.) Values of %N and %S in P. glauca greater than 0.8 and 0.1, respectively are associated with absence or paucity of sensitive species and enhancement of pollution-tolerant species that require eutrophied or nutrient-enriched environments.
Wet Deposition of Nitrogen and Sulfur (kg/ha/yr)
What is this?
Deposition is the amount of a pollutant that is deposited on the soil and vegetation per unit area and time. Values for wet deposition of nitrogen (N) and sulfur (S) in our database are estimates of the amount (in kg) of these pollutants that are annually deposited per hectare by precipitation.
How is deposition estimated using lichens?
Deposition values for a site are estimated from lichen content (i.e. %N and %S in Platismatia glauca) and precipitation. To develop a crosswalk between lichen content, precipitation and deposition, we calibrated measurements %N and %S in P. glauca collected at nine sites monitored by the National Acid Deposition Program (NADP) in Oregon and Washington to the measured wet deposition at those sites. NADP and lichen data were obtained as follows:
NADP data
NADP measures the concentration of sulfur and nitrogen in precipitation at each monitor in mg/liter then calculates total deposition by multiplying by the amount of precipitation. (This means that, where pollutant concentrations in precipitation are similar, wet regions will have higher deposition than dry regions.) NADP data from the following nine monitors was downloaded from http://nadp.sws.uiuc.edu.:
Western Washington
Hoh Ranger Station, Olympic National Park
Marblemount Ranger Station, North Cascades National Park
C. L. Pack Experimental Forest, University of Washington
Western Oregon
Oregon State University's Hyslop Farm in the Willamette Valley
Bull Run Watershed, Mt. Hood National Forest
H. J. Andrews Experimental Forest, Willamette National Forest
Alsea Ranger Station, Siuslaw National Forest
Eastern Oregon
Silver Lake Ranger Station, Fremont National Forest
Starkey Experimental Forest, Wallowa Whitman National Forest
Lichen data
During a four-week period in 1998, we established 6 lichen plots around each of the above nine monitors and collected two target species for element analysis at each plot. These collections were analyzed for total sulfur and nitrogen. Values for %S and %N in Platismatia glauca (see above section) were calculated and averaged to obtain single values for %S and %N in P. glauca at each of the 54 plots.
Calibration
We used linear regression (Fig. 2) to develop a predictive model. Now we can estimate S and N deposition at any site using % S and % N in P. glauca and estimates of precipitation. Deposition estimates at all 54 plots in the calibration study were within + 1 kg/ha/yr for nitrogen and + 0.8 kg/ha/yr for sulfur of the NADP measured values.
N kg/ha/yr = 0.33 + 0.03 * (% N in P. glauca * precipitation)
S kg/ha/yr = 0.10 +0.31 * (%S in P. glauca * precipitation)
Figure 2. The relationship between % nitrogen and % sulfur in Platismatia glauca, weighted by precipitation,
to annual deposition of nitrogen and sulfur, in kg/ha, between 1993 and 1998.
What does it mean? How does deposition affect ecosystems?
Seemingly small increments in nitrogen and sulfur deposition can have important and adverse effects on sensitive ecosystem components, such as lichen communities. We find that by the time nitrogen and sulfur deposition reaches 2 and 2.8 kg/ha/yr, respectively, sensitive lichens are absent or sparse. Absence of these sensitive organisms and proliferation of pollution-loving lichens signals the onset of deteriorating air quality and initial adverse effects to ecological function and integrity.
In the case of loss of the air pollution-sensitive lichens, loss of biological diversity is compounded by the loss of the ecological functions fulfilled by these species. Ironically, among the lichens, the sensitive species appear to play the most important ecological roles in Pacific Northwest forests. Specifically, the pendant lichens (e.g. Alectoria, Bryoria, Usnea) and the cyanolichens (e.g. Lobaria, Pseudocyphellaria, Nephroma, Sticta) are important sources of forage or nesting material for small and large mammals, birds and insects. Loss of lichens can contribute to the decline of other species that depend on them. For example, populations of insect-eating birds may decline when the lichens that the insects the feed on became scarce due to air pollution or short tree-harvest rotations. In parts of Oregon, the northern flying squirrel relies almost exclusively on air pollution-sensitive lichens during winter months. The flying squirrel in turn is an important dispersal agent for mycorrhizal fungi, essential to the phosphorus nutrition of trees, and is a primary prey species of the northern spotted owl. Finally, nitrogen-fixing, air pollution sensitive cyanolichens are an important link in the nitrogen cycle of old-growth forests.
Nitrogen and sulfur deposition is much higher than 2 or 3 kg/ha/yr over much of the United States, particularly east of the Mississippi River. In these places, the losses of lichen species and their ecological functions are overshadowed by more serious air pollution and acid rain effects on visibility, water and soil chemistry, aquatic and terrestrial biodiversity and forest health. Currently, growth of trees in many eastern forests is reduced, or even halted, by aluminum toxicity and loss of calcium from acidified soils, by high sulfates and nitrates in soils, by ozone, and by increased vulnerability to insects, disease and storm damage. The maps below show national deposition rates (3 kg/ha S = 9 kg/ha sulfate).
Air quality in most national forests of Oregon and Washington is still adequate to sustain the most sensitive of lichens - an indication that air pollution-sensitive components of our forest ecosystems are intact. Maintaining the integrity, function, and biological diversity of our forests is an essential role of sustainable ecosystem management. Maintaining sustainable forest ecosystems despite increasing human population pressures is essential to insure a sustainable resource base for human needs, including clean air, clean water, forest products and recreation.