Project at a Glance

Title: Effects of ozone and sulfur dioxide mixtures on forest vegetation of the southern Sierra Nevada.

Principal Investigator / Author(s): Taylor, Clifton O.

Contractor: University of California, Riverside

Contract Number: A0-135-33

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Ecosystem Impacts, Impacts


In 1981 and 1982 a multidisciplinary study to assess the possible effects of ozone-sulfur dioxide mixtures on native vegetation was carried out within a 32-mile radius stretching from Oildale eastward to points in the Greenhorn, Breckenridge and Piute Mountain areas. The main objectives included: (1) continuous monitoring of ozone, sulfur dioxide and meteorological variables supplemented by a Huey sulfation plate network to detect sulfur dioxide at various elevations; (2) the measurement of sulfate content of surface soils and subsoils, and the sulfur content of pine needle and lichen tissue, including stable sulfur isotope ratios in tissues and soils along transects of increasing elevation; (3) determination of the stable sulfur isotope ratio of atmospheric sulfur in the source area and of soil and plant tissue sulfur in the receptor area; (4) fumigation of pine and giant sequoia seedlings with various mixtures of ozone and sulfur dioxide in outdoor open-top chambers and (5) a survey of native vegetation.

Comparison of hourly averages of ozone and sulfur dioxide for July through October 1982 showed that ozone at Oildale was slightly lower by 1-2 pphm than at Democrat Springs (2400 ft) and Shirley Meadow (6600 ft). Sulfur dioxide hourly averages at Democrat Springs and Shirley Meadow were approximately one-fifth and one-tenth (respectively) of those at Oildale. The sulfation rates indicated by Huey plates were of dubious value in remote areas where SO2 concentrations were less than ten ppb. It might be helpful to increase the exposure time from six weeks to four months.

The concentrations of extractable sulfate in soils, and sulfur in pine needles and lichens along transects extending east of Oildale tend to decrease (p < 0.01) with increasing elevation in the 0-5 cm layer on the Breckenridge Mountain transect and in pine needle tissue on both the Greenhorn Ridge and Breckenridge Mountain transects. Sulfur concentrations on pine needles and lichen thalli had not reached toxic levels.

The §42S trend in soils and plant tissue ran counter to the expected result because the isotopic composition is more similar to the source area at greater distances from the source where total sulfur content of surface and plant tissue is the lowest. The moderately negative soil §34S at lower elevations tends to dilute the input of sulfur with a positive §34S from the atmosphere. This method remains promising for detecting the source of sulfur pollution, but additional sampling of the atmosphere, soils and plant tissue is required in California.

Recently germinated seedlings of digger, ponderosa and jeffrey pines and giant sequoia exposed to pollutant mixtures showed reductions in root growth (p < 0.05) at 10 pphm SO2 and 20 pphm 03. The SO2*O3 interaction was not significant for top and root growth. Top growth reductions were significant less frequently at the above concentrations.

Mixed gas fumigations of older pine and giant sequoia seedlings identified the visible symptoms of single and mixed gas injury by ozone and sulfur dioxide on older foliage comparable to adult trees.

Surveys of forest vegetation in the Greenhorn District of the Sequoia National Forest showed increases of ozone damage to pines at selected sites between 1977 and 1981. Foliar symptoms indicated that sulfur dioxide was not acting jointly with ozone.

Addition of sulfur dioxide to the San Joaquin Valley air basin might accelerate forest deterioration if concentrations of both pollutants reach levels where joint action is possible.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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