Abstract
Abstract Field surveys were conducted during 1998, 2000, 2003, and 2004 within the Mingo National Wildlife Refuge in southeastern Missouri to determine if ambient ground-level ozone was impacting ozone-sensitive refuge vegetation. Ozone-induced leaf symptoms (stipple) were observed within the refuge during each survey year. Percentage of bioindicator plants exhibiting stipple were wild grape (16.1%) > Common Milkweed (16.0%) > ash (7.5%) > Black Cherry (6.7%) > Flowering Dogwood (4.9%) > Sassafras (2.3%) > Sweetgum (1.2%). By year, the incidence of symptomatic plants were 1998 (22.8%) > 2003 (3.9%) > 2000 (3.4%) > 2004 (2.5%). Cumulative ambient ozone levels (SUM60, ppb.hrs) monitored at the closest EPA monitor (Bonne Terre, MO) at time of survey were 1998 (44,886) > 2000 (39,611) > 2003 (38,465) > 2004 (15,147). The cumulative SUM60 threshold value of ozone needed to cause foliar symptoms on ozone-sensitive plants within the refuge appears to be ca. 10,000 ppb.hrs. Ozone injury is likely to occur on ozon...
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