The Clean Air Act calls for the US Environmental Protection Agency (EPA) to issue and periodically review National Ambient Air Quality Standards (NAAQS) for “criteria” pollutants such as ozone. The secondary ozone NAAQS has been be set at a level to protect welfare (including effects on vegetation) from “known or anticipated” adverse effects of ozone exposure. The negative effects of ambient ozone pollution on terrestrial plants have been documented in the US for over six decades. Exposure to ozone pollution decreases photosynthesis and growth in plants and these effects can have consequences for ecosystems. However, much of the exposure-response research in the US has historically focused on trees and crops, and less attention has been paid to herbaceous species.
We combined recent EPA ozone monitoring data with published exposure-response relationships for 20 herbaceous plant species occurring in California. We used the USDA PLANTS database to identify county-level occurrence data of these plant species. California was selected as the study area because it has a wide range of ozone exposures and high plant biodiversity.
Results/Conclusions
We used kriging to generate an ozone exposure surface for 2016 from monitoring stations in California and surrounding states (Oregon, Nevada, and Arizona). The highest ozone exposures generally occurred downwind from urban areas and at high elevations. County-wide ozone exposure estimations were then combined with published exposure response-functions for focal plants, and maps were created to estimate ozone-induced growth losses in the counties where the plants occur.
The herbaceous plants had estimated annual growth losses from less than 1% to more than 20% based on exposure levels and sensitivity. We found that 17 of the 20 plant species had predicted biomass loss greater than 5% in at least one county, emphasizing the vulnerability of herbaceous species at current ozone concentrations. Butte, Nevada, Plumas, San Luis Obispo, and Shasta Counties had the highest number of plant species (6-7) with more than 10% estimated biomass loss. White clover was one of the most affected species with more than an estimated 15% annual estimated growth loss in several counties. Overall, these estimated growth losses show potential for shifts in plant communities and negative effects on ecosystems.
This abstract does not necessarily reflect the views or policies of the US EPA.