Klamath Network: Assessing The Risk of Foliar Injury From Ozone on Vegetation in Parks in the Klamath Network, October 2004
Complete PDF file klamath-network-climate
Objective
This assessment employs a biologically-based method to evaluate the risk of foliar injury from ozone at parks within the 32 Vital Signs Networks. The assessment allows resource managers at each park to better understand the risk of ozone injury to vegetation within their park and permits them to make a better informed decision regarding the need to monitor the impacts of ozone on plants.
This introduction provides an overview of the risk assessment process and the data used. It also provides a summary of the results of risk assessments for sites within the network.
Risk Assessment Methodology
The risk assessment is based on a Triad model that holds that the response of a plant to ozone is the result of the interaction of the plant, the level of exposure and the exposure environment. While interactions among the three variables determine the response, the state of any one of them can serve to accentuate or preclude the production of foliar injury. The response is greatest when all three variables and their interactions are optimized relative to the conditions that foster injury. The optimized states are: the species of plants are highly sensitive to ozone, the exposure levels of ozone significantly exceed the thresholds for foliar injury, and the environmental conditions foster gas exchange and the uptake of ozone by plants.
To conduct a risk assessment for a specific site, information was obtained on the ozone sensitive plant species found there, the levels of ozone exposure that occur over a number of years, and, since soil moisture is a critical variable controlling gas exchange, the levels of soil moisture that exist during the periods of ozone exposure. The information was evaluated to determine the degree to which the levels of ozone exposure and soil moisture conditions integrate to create an environment that leads to the production of foliar injury on sensitive species at the site.
Ozone-Sensitive Plant Species
In 2003 a workshop was convened by the National Park Service to review the ozone research literature and apply the field experience of the attendees to develop a comprehensive list of ozone-sensitive plant species for the eastern and western United States. Because of the emphasis of previous field studies and research, information on the ozone-sensitivity of tropical, arctic and rare species is limited. The workshop identified both sensitive and bioindicator species for ozone, and published its determinations in a National Park Service Report (U.S. National Park Service 2003). An ozone bioindicator species is one whose high level of sensitivity and characteristic pattern of foliar injury allow it to be confidently used to ascertain the occurrence of injurious levels of ozone exposure in the field. With regard to the Triad model, a bioindicator species integrates the effects of exposure and environment while optimizing plant sensitivity. A bioindicator serves as an early-warning agent for the plant community with respect to the potential impacts of ozone. Ozone-sensitive and bioindicator plant species at each site were identified by comparing the site’s floral list from NPSpecies with the list of sensitive species developed at the workshop.
Levels of Ozone Exposure
Ozone exposure data for 1995 through 1999 for each site were obtained either from onsite monitoring or by kriging. Both monitored and kriged data have limitations. Ozone monitoring was conducted at relatively few sites, but provides the most accurate assessment of ozone exposure. However, data from a single monitor may not accurately represent exposures throughout a large park, or a park with significant elevation differences. For sites without monitoring, ozone data were statistically estimated using a technique known as kriging. This technique uses ozone data from near-by monitoring sites to estimate data for the point of interest. Most of the sites in the risk assessment have kriged data. The accuracy of the kriged data depends on the number of near-by monitoring sites, their distance and their spatial arrangement. The accuracy with which the kriged data represents the actual exposure conditions is likely to vary among the sites.
All ozone data, both monitored and kriged, were analyzed by the Air Resources Division of the National Park Service to produce annual indices of exposure for 1995 through 1999 for each site. Since the ozone research community has not completely accepted one index of exposure as fully characterizing the threshold for foliar injury to vegetation, the assessment employed three indices to assure a comprehensive approach was taken in the assessment.
One index is the Sum06 and its attendant thresholds for injury (Heck and Cowling 1997). This index is comprised of the 90-day maximum sum of the 0800 through 1959 hourly concentrations of ozone ? 60 ppb (0.60 ppm). The index is calculated over running 90-day periods and the maximum sum can occur over any period of the year, although the chemistry of ozone generation usually results in it occurring over the summer months. For risk assessment purposes, it is also necessary to know the three-month period over which each year’s maximum index occurs.
Another index is the W126 and its associated thresholds (Lefohn et al. 1997). The W126 index is the weighted sum of the 24 one-hour ozone concentrations daily from April through October, and the number of hours of exposure to concentrations ? 100 ppb (0.10 ppm) during that period. The W126 index uses a sigmoidal weighting function in producing the sum: the lower concentrations are given less weight than are the higher concentrations since the higher exposures play a greater role in producing injury. The significance of the higher concentrations is also reflected in the requirement that there be a specified minimum number of hours of exposure to concentrations ? 100 ppb. Thus, the W126 index has two criteria that must be realized to satisfy its thresholds: a minimum sum of weighted concentrations and a minimum number of hours ? 100 ppb.
The last indicator of ozone exposure, designated N-value, consists of the numbers of hours of exposure each year that exceeded 60, 80 and 100 ppb. While there are no formal thresholds associated with these values, they provide insight to the distribution of exposures among these concentrations, and to the numbers of hours at and above 80 and 100 ppb, levels of exposure that are associated with the production of foliar injury.
Soil Moisture Status
Although gas exchange in plants is influenced by many environmental variables, soil moisture status is a critical factor since stomatal closure during periods of low soil moisture can severely limit gas exchange. Since site-specific soil moisture data are not available for the sites, the USDA’s Palmer Z Index was selected to represent soil moisture conditions. The Palmer Z Index is a measure of the short-term departure of soil moisture from the long-term mean for the area. Consequently, the index automatically takes into account the diversity in precipitation among the parks, and emphasizes the difference that exists between the monthly soil moisture norm for the site and its actual state. The index is calculated monthly for up to ten regions in each of the 48 contiguous states, and measures drought on a scale from 0.0 to –4.0, a range representing normal to severe conditions. The regions are considered to be relatively homogeneous by USDA, but contain a diversity of soil, elevation and site variables that influence the soil moisture conditions at any specific location. The Palmer Z Index is not site specific and may not fully represent the soil moisture conditions at a park during a specific month.
The objective of this aspect of the risk assessment was to determine whether there is a consistent relationship between the level of ozone exposure and soil moisture status for the site by using the five years of data available. Atmospheric conditions that foster the production of ozone, such as clear sky, high UV levels and higher temperatures, are ones associated with the presence of few clouds and reduced precipitation. Consequently, years with high levels of atmospheric ozone may also experience low levels of soil moisture. This inverse relationship can constrain the uptake of ozone by plants in years with high levels of ozone and significantly reduce the likelihood that foliar injury will be produced. Knowing whether this relationship exists at a site is essential in determining whether certain levels of ozone exposure pose a risk to vegetation.
Palmer Z data were obtained from the USDA web site for 1995 through 1999 and tabulated for the three-month period over which the Sum06 exposure indices were compiled, and for the May to October period associated with the W126 exposure indices. Visual analysis of the exposure and soil moisture data was undertaken to determine whether there was an association between the two factors at each site.
Site-Specific Assessment
After information on the presence of sensitive species, levels of ozone exposure and relationships between exposure and soil moisture was compiled, it was synthesized into an assessment of risk of foliar injury for the site. Risk was classified as high, medium or low. Most sites had ozone-sensitive species on them and some of species were bioindicators that could be used in field surveys for ozone injury. If a site did not have any sensitive species, the risk assessment was completed and considered to be potential until sensitive species are identified.
The Sum06 and W126 exposure indices were examined to determine whether they exceeded their respective thresholds for injury, and the frequency with which the thresholds were exceeded over the five-year assessment period. The N-value data were examined to assess the distribution of exposures in a given year, and the consistency of exposure over the five years.
Evaluation of the relationship between ozone exposure and soil moisture might indicate they are inversely related, or they are not related and months of drought occur independent of the level of ozone exposure. At a site where exposure and drought are inversely related, the uptake of ozone is constrained by drought stress in the highest exposure years. In this instance, the risk of foliar ozone injury is likely greatest in years with lower levels of exposure that still exceed the injury thresholds and with soil moisture conditions that are more favorable for the uptake of ozone. In these cases, the greatest risk of foliar injury does not necessarily occur in the year with the highest level of ozone exposure. At sites where exposure and soil moisture are not related, the risk of foliar injury in a given year is a function of the random co-occurrence of high exposure and favorable moisture conditions.
The risk of foliar ozone injury at a site was determined by analyzing the plant, exposure and moisture data. The process was not quantitative, but based upon three primary evaluations: the extent and consistency by which the ozone injury thresholds were exceeded by the Sum06 and W126 exposure indices, the nature of the relationship between exposure and soil moisture, and the extent to which soil moisture conditions constrained the uptake of ozone in high exposure years. The evaluation of these factors and the assessment of their interactions with ozone-sensitive plant species is consistent with the Triad model of risk assessment, and comprises the framework for determining whether the risk of foliar ozone injury was high, moderate or low at each site. The accuracy of a site’s risk assessment is dependent upon the quality of the plant list, the accuracy of the ozone exposure data and the degree to which the regional soil moisture data represent conditions at the site.
Sites receiving a risk rating of high have a probability of experiencing foliar injury in most years, while those rated low are not likely to experience injury in any year. A rating of moderate was assigned to sites where analysis indicated injury was likely to occur at some point in the five-year period, but the chance of injury occurring consistently was low. In other words, foliar injury will probably occur at sites rated moderate, but it is not anticipated it will occur regularly or frequently. Sites rated moderate are likely to experience a wide temporal variation in the occurrence of injury, and over a period of time may experience injury for one or more years while also experiencing several years without injury.
Literature Cited
Heck, W.W. and E.B. Cowling. 1997. The Need for a Long-term Cumulative Secondary Ozone Standard – An Ecological Perspective. Environmental Management. January
Lefohn, AS, W Jackson, D. Shadwick, and HP Knudsen. 1997. Effect of surface ozone exposures on vegetation grown in the Southern Appalachian Mountains: identification of possible areas of concern. Atmospheric Environment 31(11):1695-1708.
U.S. National Park Service. 2003. Ozone Sensitive Plant Species on National Park Service and US Fish and Wildlife Service Lands. NPS D1522. Natural Resource Report NPS/NRARD/NRR-2003/01. Air Resources Division. Denver, CO. 21 pp. (Available at www2.nature.nps.gov/ard/pubs/index.htm)
Summary of Risk Assessments For Parks in the Klamath Network
| Park | Code | State | Risk | O3 Data |
| Crater Lake NP | CRLA | OR | moderate | kriged |
| Lassen Volcanic NP | LAVO | CA | low | monitored |
| Lava Beds NM | LABE | CA | moderate | kriged |
| Oregon Caves NM | ORCA | OR | moderate | kriged |
| Redwood NP | REDW | CA | moderate | kriged |
| Whiskeytown-Shasta-Trinity NRA | WHIS | CA | high | kriged |
Crater Lake National Park (CRLA)
Plant Species Sensitive to Ozone
| Latin Name | Common Name | Family |
| Amelanchier alnifolia | Saskatoon serviceberry | Rosaceae |
| Apocynum androsaemifolium | Spreading dogbane | Apocynaceae |
| Pinus ponderosa | Ponderosa pine | Pinaceae |
| Populus tremuloides | Quaking aspen | Salicaceae |
| Salix scouleriana | Scouler’s willow | Saliaceae |
| Symphoricarpos albus | Common snowberry | Caprifoliaceae |
Representative Ozone Injury Thresholds
Sum06 — The running 90-day maximum sum of the 0800-2000 hourly ozone concentrations of ozone equal to or greater than 0.06 ppm. Index is in cumulative ppm hr.
| Natural Ecosystems | 8 – 12 ppm-hr | (foliar injury) |
| Tree Seedlings | 10 – 16 ppm-hr | (1-2% reduction in growth) |
| Crops | 15 – 20 ppm-hr | (10% reduction in 25-35% of crops) |
W126 — A cumulative index of exposure that uses a sigmoidal weighting function to give added significance to higher concentrations of ozone while retaining and giving less weight to mid and lower concentrations. The number of hours over 100 ppb (N100) is also considered in assessing the possible impact of the exposure. The W126 index is in cumulative ppm-hr.
| W126 | N100 | |
| Highly Sensitive Species | 5.9 ppm-hr | 6 |
| Moderately Sensitive Species | 23.8 ppm-hr | 51 |
| Low Sensitivity | 66.6 ppm-hr | 135 |
Ozone Exposure Data
Ambient concentrations of ozone were not monitored on-site, but were estimated by kriging, a statistical interpolation process. The estimated hourly concentrations of ozone were then used to generate annual exposure values for the site. The exposure values include the Sum06 and W126 exposure indices in ppm-hr and the annual number of hours above 60, 80 and 100 ppb (N60, N80 and N100, respectively).
| Ozone air quality data for CRLA | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| Sum06 | 6 | 13 | 7 | 13 | 11 |
| W126 | 8.2 | 16.8 | 8.4 | 15.6 | 14.9 |
| N60 | 122 | 276 | 132 | 245 | 272 |
| N80 | 14 | 76 | 7 | 65 | 35 |
| N100 | 1 | 13 | 0 | 12 | 3 |
Soil Moisture Status
The uptake of ambient ozone by a plant is highly dependent upon the environmental conditions under which the exposure takes place, and the level of soil moisture is an important environmental variable controlling the process. Understanding the soil moisture status can provide insight to how effective an exposure may be in leading to foliar injury. The Palmer Z Index was selected to indicate soil moisture status since it represents the short-term departure of soil moisture from the average for each month for the site. The objectives of the assessment were to examine the relationship between high annual levels of ozone and soil moisture status, and to consider the impact reduced soil moisture status would have on the effectiveness of exposure.
The Palmer Z Index is calculated for up to 10 regions within a state and therefore is not a site-specific index. Without site-specific data, ozone/soil moisture relationships can only be estimated. Site-specific criteria such as aspect, elevation, and soil type can alter soil moisture conditions such that they depart from those determined for the region. However, in lieu of site-specific data, the Palmer Z Index is the best estimate of short-term soil moisture status and its change throughout the growing season.
Palmer Z data were compiled for the site for both the three months used to calculate the Sum06 index and for the April through October period for the W126 index for 1995 through 1999. It was not possible to identify the specific 3-month summation period for the Sum 06 index since the index was obtained by kriging. The summation period was estimated from the 3-month periods for Sum 06 indices calculated from monitored ozone data for sites within 50 km of the park. The Palmer Z index ranges from approximately +4.0 (extreme wetness) to –4.0 (extreme drought) with ±0.9 representing normal soil moisture.
Soil moisture status for the Sum06 index period.
| Palmer Z Index data for 3-month Sum06 period at CRLA | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| Month | 3.21 | -0.60 | 4.23 | 1.40 | -1.74 |
| Month 2 | -0.20 | 0.37 | -0.46 | -0.46 | -0.73 |
| Month 3 | -1.17 | -0.17 | -1.80 | -1.19 | -0.64 |
Soil moisture status for the April through October period for the W126 index.
| Palmer Z Index data for the 7-month W126 period at CRLA | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| April | 1.64 | 0.99 | -0.46 | -0.92 | -0.73 |
| May | -0.04 | 1.72 | -1.80 | 5.93 | -0.64 |
| June | 1.26 | -0.60 | 0.04 | 0.04 | -1.55 |
| July | 3.21 | 0.37 | 0.29 | 1.40 | -1.51 |
| August | -0.20 | -0.17 | -0.50 | -0.46 | 3.24 |
| September | -1.17 | -0.44 | 0.64 | -1.19 | -1.93 |
| October | -1.62 | -0.12 | 0.71 | -1.69 | -1.48 |
Risk Analysis
-
There are several ozone-sensitive species at the site, some of which are bioindicators for ozone.
-
The Sum06 index intermittently exceeds the threshold for injury. While the W126 accumulative value exceeded the threshold each year, the N100 count shows that the required number of hours was met in two of the years, although concentrations exceeded 100 ppb most years. The criteria for injury under the W126 exposure index are generally not satisfied.
-
The N-values for the site show concentrations frequently exceeded 60 ppb and occasionally exceeded 80 ppb. The concentration of ozone exceeded 100 ppb for a significant number of hours in two years, but there were three or fewer hours in the remaining years. The higher levels of exposure can injure vegetation.
-
There does not appear to be any association between either the 90-day Sum06 or the seasonal W126 index of ozone exposure and soil moisture status. Soil moisture levels during the Sum06 accumulation periods were generally normal and favored the uptake of ozone. There was one month of mild drought in each of four years, but there was no association with the level of ozone. Similarly, the seasonal W126 accumulative index and soil moisture conditions were not associated. In 1996 when the W126 ozone exposure was highest, soil moisture conditions were normal. The mid-level ozone years had two and four months of mild drought. The years with the two lowest exposures, 1995 and 1997, experienced two and one month of mild drought, respectively. Collectively, there is no relationship between the W126 index of exposure and soil moisture.
The risk of foliar ozone injury at Crater Lake National Park is moderate. The threshold level for injury is satisfied intermittently by the Sum06 index, and on occasion by the W126 index. The N-values indicate that exposures to concentrations of ozone greater than 100 ppb are highly variable, and in some years reach a significant number of hours. Since there is no association between the level of ozone and soil moisture, conditions favorable for the uptake of ozone occur at all levels of exposure. Annual variations in ozone exposure and soil moisture interact to create highly variable levels of risk among years. It is anticipated the risk of injury is greatest in years such as 1996 and 1998 when ambient levels of ozone are high, and soil moisture conditions favor uptake by plants.
A program to assess the incidence of foliar ozone injury on plants at the site could use one or more of the following bioindicator species: spreading dogbane, ponderosa pine, quaking aspen, Scouler’s willow, and common snowberry.
Klamath Network: Assessing The Risk of Foliar Injury From Ozone on Vegetation in Parks in the Klamath Network, October 2004
Lassen Volcanic National Park (LAVO)
Plant Species Sensitive to Ozone
| Latin Name | Common Name | Family |
| Apocynum androsaemifolium | Spreading dogbane | Apocynaceae |
| Artemisia douglasiana | Mugwort | Asteraceae |
| Pinus jeffreyi | Jeffrey pine | Pinaceae |
| Pinus ponderosa | Ponderosa pine | Pinaceae |
| Populus tremuloides | Quaking aspen | Salicaceae |
| Rhus trilobata | Skunkbush | Anacardiaceae |
| Salix scouleriana | Scouler’s willow | Saliaceae |
| Sambucus mexicana | Blue elderberry | Caprifoliaceae |
Representative Ozone Injury Thresholds
Sum06 — The running 90-day maximum sum of the 0800-2000 hourly ozone concentrations of ozone equal to or greater than 0.06 ppm. Index is in cumulative ppmhr.
| Natural Ecosystems | 8 – 12 ppm-hr | (foliar injury) |
| Tree Seedlings | 10 – 16 ppm-hr | (1-2% reduction in growth) |
| Crops | 15 – 20 ppm-hr | (10% reduction in 25-35% of crops) |
W126 — A cumulative index of exposure that uses a sigmoidal weighting function to give added significance to higher concentrations of ozone while retaining and giving less weight to mid and lower concentrations. The number of hours over 100 ppb (N100) is also considered in assessing the possible impact of the exposure. The W126 index is in cumulative ppm-hr.
| W126 | N100 | |
| Highly Sensitive Species | 5.9 ppm-hr | 6 |
| Moderately Sensitive Species | 23.8 ppm-hr | 51 |
| Low Sensitivity | 66.6 ppm-hr | 135 |
Ozone Exposure Data
Ambient concentrations of ozone monitored on-site were analyzed to generate annual exposure values. The exposure values include the Sum06 and W126 exposure indices in ppm-hr and the annual number of hours above 60, 80 and 100 ppb (N60, N80 and N100, respectively).
| Ozone air quality data for LAVO | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| Sum06 | 12 | 20 | 9 | 20 | 25 |
| W126 | 21.9 | 28.0 | 15.3 | 29.6 | 42.7 |
| N60 | 316 | 473 | 188 | 485 | 699 |
| N80 | 17 | 17 | 3 | 26 | 56 |
| N100 | 0 | 0 | 0 | 0 | 5 |
Soil Moisture Status
The uptake of ambient ozone by a plant is highly dependent upon the environmental conditions under which the exposure takes place, and the level of soil moisture is an important environmental variable controlling the process. Understanding the soil moisture status can provide insight to how effective an exposure may be in leading to foliar injury. The Palmer Z Index was selected to indicate soil moisture status since it represents the short-term departure of soil moisture from the average for each month for the site. The objectives of the assessment were to examine the relationship between high annual levels of ozone and soil moisture status, and to consider the impact reduced soil moisture status would have on the effectiveness of exposure.
The Palmer Z Index is calculated for up to 10 regions within a state and therefore is not a site-specific index. Without site-specific data, ozone/soil moisture relationships can only be estimated. Site-specific criteria such as aspect, elevation, and soil type can alter soil moisture conditions such that they depart from those determined for the region. However, in lieu of site-specific data, the Palmer Z Index is the best estimate of short-term soil moisture status and its change throughout the growing season.
Palmer Z data were compiled for the site for both the three months used to calculate the Sum06 index and for the April through October period for the W126 index for 1995 through 1999. The Palmer Z index ranges from approximately +4.0 (extreme wetness) to –4.0 (extreme drought) with ±0.9 representing normal soil moisture.
Soil moisture status for the Sum06 index period.
| Palmer Z Index data for 3-month Sum06 period at LAVO | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| Month 1 | 3.33 | 4.80 | -1.38 | 2.23 | -0.25 |
| Month 2 | 1.19 | 0.44 | 0.54 | 2.89 | 0.33 |
| Month 3 | -0.99 | 1.21 | -0.21 | 0.57 | -1.30 |
Soil moisture status for the April through October period for the W126 index.
| Palmer Z Index data for the 7-month W126 period at LAVO | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| April | 1.90 | 1.14 | -1.18 | 1.08 | -0.37 |
| May | 2.77 | 4.80 | -1.38 | 6.91 | -1.02 |
| June | 3.57 | 0.44 | 0.54 | 2.23 | -0.26 |
| July | 3.33 | 1.21 | -0.21 | 2.89 | -0.25 |
| August | 1.19 | -0.42 | 0.99 | 0.57 | 0.33 |
| September | -0.99 | -0.28 | 0.03 | 0.76 | -1.30 |
| October | -2.39 | -0.15 | 0.06 | -0.79 | -0.88 |
Risk Analysis
- There are several ozone-sensitive species at the site, some of which are bioindicators for ozone.
- The Sum06 index exceeds the threshold for injury to vegetation. While the W126 accumulative value exceeds the threshold, the N100 count shows that the onehour concentration of ozone reached 100 ppb in only one year with a count below the required number. Thus, the criteria for injury under the W126 exposure index are not satisfied.
- The N-values for the site show concentrations frequently exceeded 60 ppb and exceeded 80 ppb for a few hours each year. No year had more than five hours in which the concentration exceeded 100 ppb, and in most years that concentration was not reached. These levels of exposure are not likely to injure vegetation.
- Soil moisture conditions during the 90-day Sum06 accumulation period were generally favorable. Since only two months of mild drought occurred over the five-year assessment period, it is not possible to determine whether there is a relationship between the Sum06 ozone exposure and soil moisture. There appears to be no association between the seasonal W126 index of exposure and soil moisture conditions. There were two months of mild drought in both the highest and lowest ozone exposure years, 1999 and 1997 respectively, and only one month of moderate drought among the remaining three years. Overall, soil moisture levels were generally normal and favored the uptake of ozone.
The low levels of ozone exposure at Lassen Volcano National Park make the risk of foliar ozone injury to plants low. While the Sum06 indices exceed the threshold level for injury, the W126 do not since the N100 criterion is not satisfied. There are only a few hours with concentrations of ozone above 80 ppb, and exposures above 100 ppb are rare.
If the level of risk increases in the future, a program to assess the incidence of foliar ozone injury on plants at the site could use one or more of the following bioindicator species: spreading dogbane, mugwort, ponderosa pine, quaking aspen, skunkbush, Scouler’s willow, and blue elderberry.
Lava Beds National Monument (LABE)
Plant Species Sensitive to Ozone
| Latin Name | Common Name | Family |
| Pinus jeffreyi | Jeffrey pine | Pinaceae |
| Pinus ponderosa | Ponderosa pine | Pinaceae |
| Populus tremuloides | Quaking aspen | Salicaceae |
| Salix scouleriana | Scouler’s willow | Saliaceae |
Representative Ozone Injury Thresholds
Sum06 — The running 90-day maximum sum of the 0800-2000 hourly ozone concentrations of ozone equal to or greater than 0.06 ppm. Index is in cumulative ppmhr.
| Natural Ecosystems | 8 – 12 ppm-hr | (foliar injury) |
| Tree Seedlings | 10 – 16 ppm-hr | (1-2% reduction in growth) |
| Crops | 15 – 20 ppm-hr | (10% reduction in 25-35% of crops) |
W126 — A cumulative index of exposure that uses a sigmoidal weighting function to give added significance to higher concentrations of ozone while retaining and giving less weight to mid and lower concentrations. The number of hours over 100 ppb (N100) is also considered in assessing the possible impact of the exposure. The W126 index is in cumulative ppm-hr.
| W126 | N100 | |
| Highly Sensitive Species | 5.9 ppm-hr | 6 |
| Moderately Sensitive Species | 23.8 ppm-hr | 51 |
| Low Sensitivity | 66.6 ppm-hr | 135 |
Ozone Exposure Data
Ambient concentrations of ozone were not monitored on-site, but were estimated by kriging, a statistical interpolation process. The estimated hourly concentrations of ozone were then used to generate annual exposure values for the site. The exposure values include the Sum06 and W126 exposure indices in ppm-hr and the annual number of hours above 60, 80 and 100 ppb (N60, N80 and N100, respectively).
| Ozone air quality data for LABE | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| Sum06 | 11 | 15 | 11 | 22 | 20 |
| W126 | 15.1 | 31.5 | 16.5 | 28.5 | 34.3 |
| N60 | 251 | 603 | 286 | 498 | 638 |
| N80 | 33 | 99 | 27 | 123 | 94 |
| N100 | 2 | 11 | 1 | 23 | 8 |
Soil Moisture Status
The uptake of ambient ozone by a plant is highly dependent upon the environmental conditions under which the exposure takes place, and the level of soil moisture is an important environmental variable controlling the process. Understanding the soil moisture status can provide insight to how effective an exposure may be in leading to foliar injury. The Palmer Z Index was selected to indicate soil moisture status since it represents the short-term departure of soil moisture from the average for each month for the site. The objectives of the assessment were to examine the relationship between high annual levels of ozone and soil moisture status, and to consider the impact reduced soil moisture status would have on the effectiveness of exposure.
The Palmer Z Index is calculated for up to 10 regions within a state and therefore is not a site-specific index. Without site-specific data, ozone/soil moisture relationships can only be estimated. Site-specific criteria such as aspect, elevation, and soil type can alter soil moisture conditions such that they depart from those determined for the region. However, in lieu of site-specific data, the Palmer Z Index is the best estimate of short-term soil moisture status and its change throughout the growing season.
Palmer Z data were compiled for the site for both the three months used to calculate the Sum06 index and for the April through October period for the W126 index for 1995 through 1999. It was not possible to identify the specific 3-month summation period for the Sum 06 index since the index was obtained by kriging. The summation period was estimated from the 3-month periods for Sum 06 indices calculated from monitored ozone data for sites within 50 km of the park. The Palmer Z index ranges from approximately +4.0 (extreme wetness) to –4.0 (extreme drought) with ±0.9 representing normal soil moisture.
Soil moisture status for the Sum06 index period.
| Palmer Z Index data for 3-month Sum06 period at LABE | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| Month 1 | 1.18 | -0.57 | -0.04 | 0.75 | -0.57 |
| Month 2 | 2.33 | -0.13 | 1.36 | 1.36 | -0.11 |
| Month 3 | 2.35 | -0.28 | 0.74 | -0.28 | -1.35 |
Soil moisture status for the April through October period for the W126 index.
| Palmer Z Index data for the 7-month W126 period at LABE | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| April | 2.37 | 1.78 | -0.30 | 0.26 | -0.16 |
| May | 1.18 | 2.83 | -0.94 | 4.49 | -0.88 |
| June | 2.33 | 0.21 | 0.68 | 0.75 | -0.82 |
| July | 2.35 | 1.15 | -0.04 | 1.36 | -0.57 |
| August | 0.22 | -0.57 | 1.36 | -0.28 | -0.11 |
| September | -0.91 | -0.13 | 0.74 | -1.04 | -1.35 |
| October | -2.66 | -0.28 | 0.31 | -0.78 | -1.07 |
Risk Analysis
- There are a few ozone-sensitive species at the site, some of which are bioindicators for ozone.
- The Sum06 index exceeds the threshold for injury to vegetation. The W126 accumulative value exceeds the threshold each year and the N100 count generally meets the threshold requirement.
- The N-values for the site show concentrations of 80 and 100 ppb were highly variable. While one year had 23 hours over 100 ppb, another year had only one. The higher levels of exposure may injure vegetation.
- There does not appear to be any association between either the 90-day Sum06 or the seasonal W126 index of ozone exposure and soil moisture status. Soil moisture conditions were generally favorable. Over the five years, there was one month of mild drought during the Sum06 accumulation period, and four months of mild and moderate drought during the seasonal W126 period.
The risk of foliar ozone injury at Lava Beds National Monument is moderate. The threshold level for injury is consistently satisfied by the Sum06 index, and generally by the W126 index. The N-values indicate that exposure to concentrations of ozone greater than 100 ppb is highly variable. Since there is no association between the level of ozone and soil moisture, conditions favorable for the uptake of ozone occur at all levels of exposure. It is anticipated that the risk of injury is greatest in years such as 1996 and 1998 when ambient levels of ozone are high, and soil moisture conditions favor uptake by plants.
A program to assess the incidence of foliar ozone injury on plants at the site could use one or more of the following bioindicator species: Jeffrey pine, ponderosa pine, quaking aspen, and Scouler’s willow.
Oregon Caves National Monument (ORCA)
Plant Species Sensitive to Ozone
| Latin Name | Common Name | Family |
| Alnus rubra | Red alder | Betulaceae |
| Amelanchier alnifolia | Saskatoon serviceberry | Rosaceae |
| Apocynum androsaemifolium | Spreading dogbane | Apocynaceae |
| Artemisia douglasiana | Mugwort | Asteraceae |
| Pinus ponderosa | Ponderosa pine | Pinaceae |
| Salix scouleriana | Scouler’s willow | Saliaceae |
| Sambucus mexicana | Blue elderberry | Caprifoliaceae |
| Symphoricarpos albus | Common snowberry | Caprifoliaceae |
Representative Ozone Injury Thresholds
Sum06 — The running 90-day maximum sum of the 0800-2000 hourly ozone concentrations of ozone equal to or greater than 0.06 ppm. Index is in cumulative ppmhr.
| Natural Ecosystems | 8 – 12 ppm-hr | (foliar injury) |
| Tree Seedlings | 10 – 16 ppm-hr | (1-2% reduction in growth) |
| Crops | 15 – 20 ppm-hr | (10% reduction in 25-35% of crops) |
W126 — A cumulative index of exposure that uses a sigmoidal weighting function to give added significance to higher concentrations of ozone while retaining and giving less weight to mid and lower concentrations. The number of hours over 100 ppb (N100) is also considered in assessing the possible impact of the exposure. The W126 index is in cumulative ppm-hr.
| W126 | N100 | |
| Highly Sensitive Species | 5.9 ppm-hr | 6 |
| Moderately Sensitive Species | 23.8 ppm-hr | 51 |
| Low Sensitivity | 66.6 ppm-hr | 135 |
Ozone Exposure Data
Ambient concentrations of ozone were not monitored on-site, but were estimated by kriging, a statistical interpolation process. The estimated hourly concentrations of ozone were then used to generate annual exposure values for the site. The exposure values include the Sum06 and W126 exposure indices in ppm-hr and the annual number of hours above 60, 80 and 100 ppb (N60, N80 and N100, respectively).
| Ozone air quality data for ORCA | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| Sum06 | 4 | 8 | 5 | 9 | 8 |
| W126 | 6.5 | 23.5 | 11.0 | 19.8 | 22.3 |
| N60 | 92 | 443 | 187 | 319 | 430 |
| N80 | 11 | 93 | 11 | 80 | 59 |
| N100 | 1 | 13 | 1 | 15 | 5 |
Soil Moisture Status
The uptake of ambient ozone by a plant is highly dependent upon the environmental conditions under which the exposure takes place, and the level of soil moisture is an important environmental variable controlling the process. Understanding the soil moisture status can provide insight to how effective an exposure may be in leading to foliar injury. The Palmer Z Index was selected to indicate soil moisture status since it represents the short-term departure of soil moisture from the average for each month for the site. The objectives of the assessment were to examine the relationship between high annual levels of ozone and soil moisture status, and to consider the impact reduced soil moisture status would have on the effectiveness of exposure.
The Palmer Z Index is calculated for up to 10 regions within a state and therefore is not a site-specific index. Without site-specific data, ozone/soil moisture relationships can only be estimated. Site-specific criteria such as aspect, elevation, and soil type can alter soil moisture conditions such that they depart from those determined for the region. However, in lieu of site-specific data, the Palmer Z Index is the best estimate of short-term soil moisture status and its change throughout the growing season.
Palmer Z data were compiled for the site for both the three months used to calculate the Sum06 index and for the April through October period for the W126 index for 1995 through 1999. It was not possible to identify the specific 3-month summation period for the Sum 06 index since the index was obtained by kriging. The summation period was estimated from the 3-month periods for Sum 06 indices calculated from monitored ozone data for sites within 50 km of the park. The Palmer Z index ranges from approximately +4.0 (extreme wetness) to –4.0 (extreme drought) with ±0.9 representing normal soil moisture.
Soil moisture status for the Sum06 index period.
| Palmer Z Index data for 3-month Sum06 period at ORCA | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| Month 1 | 2.66 | -0.45 | -0.22 | 0.42 | 0.07 |
| Month 2 | 3.45 | 0.78 | 2.31 | -1.15 | -0.76 |
| Month 3 | 0.49 | -0.86 | -0.77 | -1.71 | 0.20 |
Soil moisture status for the April through October period for the W126 index.
Palmer Z Index data for the 7-month W126 period at ORCA
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| April | 4.01 | 3.39 | 2.31 | 0.56 | -0.76 |
| May | 0.06 | 3.89 | -0.77 | 5.06 | 0.20 |
| June | 2.66 | -0.45 | 1.10 | -0.04 | -1.11 |
| July | 3.45 | 0.78 | 0.50 | 0.42 | -0.31 |
| August | 0.49 | -0.86 | 1.76 | -1.15 | 2.48 |
| September | -0.26 | 0.78 | 1.69 | -1.71 | -1.94 |
| October | -1.34 | 2.27 | 2.11 | -0.46 | 0.32 |
Risk Analysis
- There are several ozone-sensitive species at the site, some of which are bioindicators for ozone.
- The Sum06 index intermittently exceeds the threshold for injury to vegetation, although the levels are marginal in value. While the W126 accumulative value exceeded the threshold each year, the N100 count shows that the required number of hours was met in two of the years, although concentrations exceeded 100 ppb every year. The criteria for injury under the W126 exposure index are generally not satisfied.
- In two years, the N-values for concentrations of 80 and 100 ppb are high and show there are a significant number of hours during which plants are exposed to potentially harmful levels of ozone. In the remaining years, the number of hours at these concentrations was significantly lower. The higher levels of exposure could injure vegetation.
- There does not appear to be any association between either the 90-day Sum06 or the seasonal W126 index of ozone exposure and soil moisture status. Soil moisture levels during the Sum06 accumulation periods were generally normal and favored the uptake of ozone. There were two months of mild drought in the year with the highest level of ozone, but no association with exposure can be assumed. Similarly, the seasonal W126 accumulative index and soil moisture conditions are not associated. In 1996 when ozone exposure was highest, soil moisture conditions were normal. The next two lower exposure years, 1999 and 1998, both had two months of mild drought. The second lowest exposure year had normal soil moisture, and the year with the lowest exposure, 1995, experienced one month of mild drought. Collectively, there is no relationship between the W126 index of exposure and soil moisture.
The risk of foliar ozone injury at Oregon Caves National Monument is moderate. The threshold level for injury is intermittently satisfied by the Sum06 index, and the criteria for the W126 index are satisfied in two years. The N-values indicate that annual exposures to concentrations of ozone greater than 100 ppb are variable. Since there is no association between the level of ozone and soil moisture, conditions favorable for the uptake of ozone occur at all levels of exposure. Annual variations in ozone exposure create highly variable levels of risk among years. It is anticipated that the risk of injury is greatest in years such as 1996 and 1998 when ambient levels of ozone are high, and soil moisture conditions generally favor uptake by plants.
A program to assess the incidence of foliar ozone injury on plants at the site could use one or more of the following bioindicator species: red alder, spreading dogbane, mugwort, ponderosa pine, Scouler’s willow, blue elderberry, and common snowberry.
Redwood National Park (REDW)
Plant Species Sensitive to Ozone
| Latin Name | Common Name | Family |
| Alnus rubra | Red alder | Betulaceae |
| Amelanchier alnifolia | Saskatoon serviceberry | Rosaceae |
| Apocynum androsaemifolium | Spreading dogbane | Apocynaceae |
| Artemisia douglasiana | Mugwort | Asteraceae |
| Liriodendron tulipifera | Yellow-poplar | Magnoliaceae |
| Oenothera elata | Evening primrose | Onagraceae |
| Physocarpus capitatus | Ninebark | Rosaceae |
| Pinus jeffreyi | Jeffrey pine | Pinaceae |
| Pinus radiata | Monterey pine | Pinaceae |
| Robinia pseudoacacia | Black locust | Fabaceae |
| Salix scouleriana | Scouler’s willow | Saliaceae |
| Sambucus mexicana | Blue elderberry | Caprifoliaceae |
Representative Ozone Injury Thresholds
Sum06 — The running 90-day maximum sum of the 0800-2000 hourly ozone
| Natural Ecosystems | 8 – 12 ppm-hr | (foliar injury) |
| Tree Seedlings | 10 – 16 ppm-hr | (1-2% reduction in growth) |
| Crops | 15 – 20 ppm-hr | (10% reduction in 25-35% of crops) |
concentrations of ozone equal to or greater than 0.06 ppm. Index is in cumulative ppmhr.
W126 — A cumulative index of exposure that uses a sigmoidal weighting function to give added significance to higher concentrations of ozone while retaining and giving less weight to mid and lower concentrations. The number of hours over 100 ppb (N100) is also considered in assessing the possible impact of the exposure. The W126 index is in cumulative ppm-hr.
| W126 | N100 | |
| Highly Sensitive Species | 5.9 ppm-hr | 6 |
| Moderately Sensitive Species | 23.8 ppm-hr | 51 |
| Low Sensitivity | 66.6 ppm-hr | 135 |
Ozone Exposure Data
Ambient concentrations of ozone were not monitored on-site, but were estimated by kriging, a statistical interpolation process. The estimated hourly concentrations of ozone were then used to generate annual exposure values for the site. The exposure values include the Sum06 and W126 exposure indices in ppm-hr and the annual number of hours above 60, 80 and 100 ppb (N60, N80 and N100, respectively).
Ozone air quality data for REDW
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| Sum06 | 4 | 18 | 13 | 26 | 22 |
| W126 | 7.8 | 26.6 | 14.7 | 27 | 32 |
| N60 | 121 | 522 | 259 | 481 | 601 |
| N80 | 18 | 99 | 27 | 134 | 97 |
| N100 | 1 | 12 | 1 | 26 | 8 |
Soil Moisture Status
The uptake of ambient ozone by a plant is highly dependent upon the environmental conditions under which the exposure takes place, and the level of soil moisture is an important environmental variable controlling the process. Understanding the soil moisture status can provide insight to how effective an exposure may be in leading to foliar injury. The Palmer Z Index was selected to indicate soil moisture status since it represents the short-term departure of soil moisture from the average for each month for the site. The objectives of the assessment were to examine the relationship between high annual levels of ozone and soil moisture status, and to consider the impact reduced soil moisture status would have on the effectiveness of exposure.
The Palmer Z Index is calculated for up to 10 regions within a state and therefore is not a site-specific index. Without site-specific data, ozone/soil moisture relationships can only be estimated. Site-specific criteria such as aspect, elevation, and soil type can alter soil moisture conditions such that they depart from those determined for the region. However, in lieu of site-specific data, the Palmer Z Index is the best estimate of short-term soil moisture status and its change throughout the growing season.
Palmer Z data were compiled for the site for both the three months used to calculate the Sum06 index and for the April through October period for the W126 index for 1995 through 1999. It was not possible to identify the specific 3-month summation period for the Sum 06 index since the index was obtained by kriging. The summation period was estimated from the 3-month periods for Sum 06 indices calculated from monitored ozone data for sites within 50 km of the park. The Palmer Z index ranges from approximately +4.0 (extreme wetness) to –4.0 (extreme drought) with ±0.9 representing normal soil moisture.
Soil moisture status for the Sum06 index period.
| Palmer Z Index data for 3-month Sum06 period at REDW | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| Month 1 | 1.18 | -0.57 | -0.04 | 0.75 | -0.57 |
| Month 2 | 2.33 | -0.13 | 1.36 | 1.36 | -0.11 |
| Month 3 | 2.35 | -0.28 | 0.74 | -0.28 | -1.35 |
Soil moisture status for the April through October period for the W126 index.
Palmer Z Index data for the 7-month W126 period at REDW
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| April | 2.37 | 1.78 | -0.30 | 0.26 | -0.16 |
| May | 1.18 | 2.83 | -0.94 | 4.49 | -0.88 |
| June | 2.33 | 0.21 | 0.68 | 0.75 | -0.82 |
| July | 2.35 | 1.15 | -0.04 | 1.36 | -0.57 |
| August | 0.22 | -0.57 | 1.36 | -0.28 | -0.11 |
| September | -0.91 | -0.13 | 0.74 | -1.04 | -1.35 |
| October | -2.66 | -0.28 | 0.31 | -0.78 | -1.07 |
Risk Analysis
- There are numerous ozone-sensitive species at the site, some of which are bioindicators for ozone.
- The Sum06 index exceeds the threshold for injury to vegetation. While the W126 accumulative value exceeded the threshold each year, the N100 count shows that the required number of hours was met in three of the years, although concentrations exceeded 100 ppb every year. The criteria for injury under the W126 exposure index are generally satisfied.
- In two years, the N-values for concentrations of 80 and 100 ppb are high and show there are a significant number of hours during which plants are exposed to potentially harmful levels of ozone. In the remaining years, the number of hours at these concentrations was significantly lower. The higher levels of exposure could injure vegetation.
- There does not appear to be any association between either the 90-day Sum06 or the seasonal W126 index of ozone exposure and soil moisture status. Soil moisture levels during the Sum06 accumulation periods were generally normal and favored the uptake of ozone; there was one month of mild drought in fiveyear period. Similarly, the seasonal W126 accumulative index and soil moisture conditions were not associated. In 1999 when ozone exposure was highest, there were two months of mild drought. There were only two additional months of drought in the remaining four years of the W126 assessments.
The risk of foliar ozone injury at Redwood National Park is moderate. The threshold level for injury is satisfied by the Sum06 index, and generally satisfied by the W126 index. The N-values indicate that annual exposures to concentrations of ozone greater than 100 ppb are variable. Since there is no association between the level of ozone and soil moisture, conditions favorable for the uptake of ozone occur at all levels of exposure. Annual variations in ozone exposure create highly variable levels of risk among years. It is anticipated that the risk of injury is greatest in years such as 1996 and 1998 when ambient levels of ozone are high, and soil moisture conditions favor uptake by plants.
A program to assess the incidence of foliar ozone injury on plants at the site could use one or more of the following bioindicator species: red alder, spreading dogbane, mugwort, yellow-poplar, evening primrose, ninebark, Jeffrey pine, Scouler’s willow, and blue elderberry.
Whiskeytown-Shasta-Trinity National Recreation Area (WHIS)
Plant Species Sensitive to Ozone
| Latin Name | Common Name | Family |
| Ailanthus altissima | Tree-of-heaven | Simaroubaceae |
| Apocynum androsaemifolium | Spreading dogbane | Apocynaceae |
| Artemisia douglasiana | Mugwort | Asteraceae |
| Liquidambar styraciflua | Sweetgum | Hamamelidaceae |
| Physocarpus capitatus | Ninebark | Rosaceae |
| Pinus jeffreyi | Jeffrey pine | Pinaceae |
| Pinus ponderosa | Ponderosa pine | Pinaceae |
| Rhus trilobata | Skunkbush | Anacardiaceae |
| Robinia pseudoacacia | Black locust | Fabaceae |
| Salix scouleriana | Scouler’s willow | Saliaceae |
| Sambucus mexicana | Blue elderberry | Caprifoliaceae |
| Symphoricarpos albus | Common snowberry | Caprifoliaceae |
Representative Ozone Injury Thresholds
Sum06 — The running 90-day maximum sum of the 0800-2000 hourly ozone
| Natural Ecosystems | 8 – 12 ppm-hr | (foliar injury) |
| Tree Seedlings | 10 – 16 ppm-hr | (1-2% reduction in growth) |
| Crops | 15 – 20 ppm-hr | (10% reduction in 25-35% of crops) |
concentrations of ozone equal to or greater than 0.06 ppm. Index is in cumulative ppmhr.
W126 — A cumulative index of exposure that uses a sigmoidal weighting function to give added significance to higher concentrations of ozone while retaining and giving less weight to mid and lower concentrations. The number of hours over 100 ppb (N100) is also considered in assessing the possible impact of the exposure. The W126 index is in cumulative ppm-hr.
| W126 | N100 | |
| Highly Sensitive Species | 5.9 ppm-hr | 6 |
| Moderately Sensitive Species | 23.8 ppm-hr | 51 |
| Low Sensitivity | 66.6 ppm-hr | 135 |
Ozone Exposure Data
Ambient concentrations of ozone were not monitored on-site, but were estimated by kriging, a statistical interpolation process. The estimated hourly concentrations of ozone were then used to generate annual exposure values for the site. The exposure values include the Sum06 and W126 exposure indices in ppm-hr and the annual number of hours above 60, 80 and 100 ppb (N60, N80 and N100, respectively).
Ozone air quality data for WHIS
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| Sum06 | 15 | 22 | 17 | 36 | 29 |
| W126 | 19.4 | 33.1 | 23.6 | 47.8 | 48.6 |
| N60 | 345 | 685 | 438 | 901 | 906 |
| N80 | 63 | 154 | 65 | 308 | 167 |
| N100 | 5 | 20 | 4 | 62 | 15 |
Soil Moisture Status
The uptake of ambient ozone by a plant is highly dependent upon the environmental conditions under which the exposure takes place, and the level of soil moisture is an important environmental variable controlling the process. Understanding the soil moisture status can provide insight to how effective an exposure may be in leading to foliar injury. The Palmer Z Index was selected to indicate soil moisture status since it represents the short-term departure of soil moisture from the average for each month for the site. The objectives of the assessment were to examine the relationship between high annual levels of ozone and soil moisture status, and to consider the impact reduced soil moisture status would have on the effectiveness of exposure.
The Palmer Z Index is calculated for up to 10 regions within a state and therefore is not a site-specific index. Without site-specific data, ozone/soil moisture relationships can only be estimated. Site-specific criteria such as aspect, elevation, and soil type can alter soil moisture conditions such that they depart from those determined for the region. However, in lieu of site-specific data, the Palmer Z Index is the best estimate of short-term soil moisture status and its change throughout the growing season.
Palmer Z data were compiled for the site for both the three months used to calculate the Sum06 index and for the April through October period for the W126 index for 1995 through 1999. It was not possible to identify the specific 3-month summation period for the Sum 06 index since the index was obtained by kriging. The summation period was estimated from the 3-month periods for Sum 06 indices calculated from monitored ozone data for sites within 50 km of the park. The Palmer Z index ranges from approximately +4.0 (extreme wetness) to –4.0 (extreme drought) with ±0.9 representing normal soil moisture.
Soil moisture status for the Sum06 index period.
| Palmer Z Index data for 3-month Sum06 period at WHIS | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| Month 1 | 3.33 | 1.21 | -0.21 | 2.89 | -0.25 |
| Month 2 | 1.19 | -0.42 | 0.99 | 0.57 | 0.33 |
| Month 3 | -0.99 | -0.28 | 0.03 | 0.76 | -1.30 |
Soil moisture status for the April through October period for the W126 index.
| Palmer Z Index data for the 7-month W126 period at WHIS | |||||
| 1995 | 1996 | 1997 | 1998 | 1999 | |
| April | 1.90 | 1.14 | -1.18 | 1.08 | -0.37 |
| May | 2.77 | 4.80 | -1.38 | 6.91 | -1.02 |
| June | 3.57 | 0.44 | 0.54 | 2.23 | -0.26 |
| July | 3.33 | 1.21 | -0.21 | 2.89 | -0.25 |
| August | 1.19 | -0.42 | 0.99 | 0.57 | 0.33 |
| September | -0.99 | -0.28 | 0.03 | 0.76 | -1.30 |
| October | -2.39 | -0.15 | 0.06 | -0.79 | -0.88 |
Risk Analysis
- There are numerous ozone-sensitive species at the site, some of which are bioindicators for ozone.
- The Sum06 index exceeds the threshold for injury to vegetation. While the W126 accumulative value exceeded the threshold each year, the N100 count shows that the required number of hours was met in three of the years, although concentrations exceeded 100 ppb every year. The criteria for injury under the W126 exposure index are generally satisfied.
- In three years, the N-values for concentrations of 80 and 100 ppb are high and show there are a significant number of hours during which plants are exposed to potentially harmful levels of ozone. In the remaining years, the number of hours at these concentrations was significantly lower. The higher levels of exposure could injure vegetation.
- There does not appear to be any association between either the 90-day Sum06 or the seasonal W126 index of ozone exposure and soil moisture status. Soil moisture levels during the Sum06 accumulation periods were generally normal and favored the uptake of ozone; there was one month of mild drought in five-year period. The seasonal W126 accumulative index and soil moisture conditions were also not associated. There were two months of mild drought in 1999 when ozone exposure was highest. Soil moisture was favorable in both the second highest year 1998 and the mid-level ozone year 1996. The second lowest exposure year had two months of mild drought and the lowest year, 1995, had one month of moderate drought.
The risk of foliar ozone injury at Whiskeytown-Shasta-Trinity National Recreation Area is high. The threshold level for injury is consistently satisfied by the Sum06 index, and intermittently by the W126 index. The N-values indicate that annual exposures to concentrations of ozone greater than 80 and 100 ppb are variable. Since there is no association between the level of ozone and soil moisture, conditions favorable for the uptake of ozone occur at all levels of exposure. Annual variations in ozone exposure create highly variable levels of risk among years. It is anticipated that the risk of injury is greatest in years such as 1996 and 1998 when ambient levels of ozone are high, and soil moisture conditions favor uptake by plants.
A program to assess the incidence of foliar ozone injury on plants at the site could use one or more of the following bioindicator species: tree-of-heaven, spreading dogbane, mugwort, ninebark, Jeffrey pine, ponderosa pine, skunkbush, Scouler’s willow, blue elderberry, and common snowberry.
Other pages in this section
*** previous title *** --- *** next title ***
