Research Projects

Project at a Glance

Title: Assessment of acidic deposition and ozone effects on conifer forests in the San Bernardino Mountains. Final report. Standard operating procedure manual: Volumes 1 and 2

Principal Investigator / Author(s): Miller, Paul

Contractor: USDA Forest Service & Desert Research Institute

Contract Number: A032-180


Research Program Area: Atmospheric Processes, Ecosystem & Multimedia Effects

Topic Areas: Acid Deposition, Ecosystem Impacts


Abstract:

Evaluation of the possible long-term consequences of pollutant deposition to forest ecosystems requires an initial descriptive data base including as many attributes of the atmosphere, plants and soil as possible. This study addressed the need to evaluate the separate and combined effects of ozone and acidic deposition on the condition of pine and mixed conifer forests in the San Bernardino mountains of southern California. The hypothesis to be examined was whether ozone and acidic deposition have cumulative effects on a California mixed conifer forest ecosystem that together cause more perturbation to functional processes than either acting alone. The primary objectives of the project were to acquire a long-term data base of specified accuracy, precision and validity for atmospheric pollution concentration, local and stand meteorology, wet and dry deposition fluxes to forest canopies, and biological responses of forest vegetation and soils. Some of these data were used to parameterize and run simulations with the Big Leaf deposition model. Furthermore, to document the procedures used in the project, complete descriptions of measurement techniques, research protocols and quality assurance objectives for all aspects of the project were compiled in a companion document to the final report.

A forested area with moderate ozone damage in the vicinity of Barton Flats was selected for a study of the combined effects of ozone and acidic species on tree health and other ecosystem properties. Ozone damage to ponderosa (Pinus ponderosa ) and Jeffrey (P. jeffreyi) pines was reported here in the late 1960's and useful background information was available. A complete air quality and meteorological monitoring station was established near the Forest Service Visitor Information Center at Barton Flats on State Highway 38, at an elevation of 1982 m. Within 1.6 km from the monitoring station three forest vegetation monitoring plots were established (plot #1 at 1982 m, plot #2 at 2171 m and plot #3 at 2207 m elevation). At each plot the initial state of vegetation and soils was determined in the autumn of 1991 and spring of 1992. Also in the spring of 1992, precipitation and throughfall collectors and needle litter collectors were installed at all plots. At plot #2 a 29 m climbable scaffold was erected to allow measurements to be made above and below the top of the forest canopy with meteorology and air quality monitoring systems and container-grown trees. Most measurements in the plots were carried out in spring, summer and fall from 1992 to 1994.

The meteorology and air chemistry monitoring and analyses were carried out by the Energy and Environmental Engineering Center of the Desert Research Institute (Section 2). The meteorology in the study area was characterized by sea breeze and upslope / downslope flow patterns during summer which resulted in consistent diurnal patterns. In winter the synoptic scale weather system caused greater day-to-day variability. Ozone was the air pollutant most often present at phytotoxic concentrations. Hourly ozone concentrations exceeded the National Air Quality Standard of 120 ppb on over 20 percent of the sampling days. Peak ozone concentrations exceeding 200 ppb usually coincided with periods of high daily maximum temperatures. Particles emitted and formed in the Los Angeles Basin were transported to the Barton Flats station during spring, summer and early fall. Dry deposition samples for PM2.5 mass and ions (i.e., nitrate, sulfate, ammonium) were found above the lower quantifiable limits (LQLs) for more than 80 percent of the samples. Precursor gas (i.e., sulfur dioxide, nitrogen dioxide, nitric acid, ammonia) concentrations were above LQLs in over 70 percent of the samples. The sum of ionic species versus PM2.5 mass revealed that chloride, nitrate, sulfate and ammonium accounted for approximately 50 percent of PM2.5 mass. The relationship of daytime average concentrations for all the particulate species to the nighttime averages were similar during all seasons. Season-to-season variations were significant for PM2.5 mass, and ions, with the lowest values reported during winter and reaching maximum concentrations during summer.


 

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