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    Author(s): Andrzej Bytnerowicz; Mark Fenn; Edith B. Allen; Ricardo Cisneros
    Date: 2016
    Source: Ecosystems of California. Berkeley, CA: University of California Press: 107-128
    Publication Series: Book Chapter
    Station: Pacific Southwest Research Station
    PDF: Download Publication  (2.0 MB)


    At present, negative impacts of air pollution on California ecosystems are caused mainly by elevated levels of ozone and nitrogen deposition. Generally, ozone air pollution in California has been improving significantly since the 1970s; however, it still causes serious ecological and human health effects. The most serious ecological effects occur in mixed conifer forests of southern California and on the southwestern slopes of the Sierra Nevada. Ozone can be transported long distances, affecting remote areas. Nitrogen deposition to California ecosystems is dominated by dry deposition of ammonia and nitric acid vapor, which in complex terrain is much more spatially restricted than ozone distribution due to the high deposition velocity of these pollutants. Consequently, steep landscape gradients of nitrogen deposition occur in California mountain ranges, with the highest potential for negative effects near emission source areas while remote areas remain relatively unaffected. The most sensitive indicators of harmful nitrogen deposition effects on California ecosystems include shifts in epiphytic lichen communities and lichen-tissue nitrogen, and enhanced biomass of exotic grasses to levels capable of causing biodiversity changes and sustaining wildland fires. Increased nitrate concentration in streamwater and groundwater from montane catchments can also result from nitrogen deposition. Approximately 35% of California's land area exceeds critical loads of nitrogen deposition in seven major vegetation types. Particulate matter pollution is a serious health threat in California, especially in urban areas affected by emissions from mobile sources, but also the Central Valley which is affected by emissions from intensive agricultural activities, while vast arid areas suffer from suspended dust during high wind events. Potential exceedances of the national and California particulate matter air quality standards can hinder the use of prescribed fire as a management tool in forests. A critical research gap currently exists in the large-scale evaluation of California forest health in terms of the interactive effects of the changing levels of elevated ozone concentrations, nitrogen deposition, climate, insects, and diseases.

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    Bytnerowicz, Andrzej; Fenn, Mark; Allen, Edith B.; Cisneros, Ricardo. 2015. Atmospheric chemistry. In: Mooney, H; Zavaleta, E., eds. Ecosystems of California. Berkeley, CA: University of California Press: 107-128. Chapter 7.


    ozone, dry nitrogen deposition, air pollution, California, particulate matter, forest ecosystem damage, air quality

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