Lichen Recolonization in the Upper Ohio River Valley

Abstract

Improvement in the air quality of the upper Ohio River valley has led to lichen recolonization at previously depauperate sites. Between 1973 and 1989 the number of lichen species in the area almost doubled and the mean species per site increased from 0.8 to 3.5. An indicator species, Flavoparmelia caperata, was completely absent in 1973 but occurred at half of the study sites in 1989. While many papers have detailed the loss of lichens in poor air quality, only a few have reported the recovery of lichens in improving air quality. Sulfur dioxide air quality is now improving in most areas of the United States. One source (Placet & Streets 1987) estimates that total SO2 emissions in the United States decreased from 26.8 million metric tons in 1975 to 21.2 million metric tons in 1985. Ohio showed a similar decrease in SO2 emissions from 2.99 to 2.43 million metric tons during the same period. The upper Ohio River valley was once reputed to have the dirtiest air in the nation. This area was heavily industrialized with coal-burning power plants, steel mills, foundries, and coking ovens. However, the region was severely affected by the recession of the late 1970's and the concomitant decline of the U.S. steel industry. Old plants were closed and modernization and fuel switching at other facilities led to reduced SO2 emissions. This decrease in emission has had a dramatic effect on the ambient SO2 levels. Data from the North Ohio Valley Air Authority (Robert T. Carducci, pers. comm.) show that in 1975, Steubenville, Ohio had an annual average SO2 concentration of 118 ~g/m3. By 1985 this had almost halved to 60 jig/m3. East Liverpool, Ohio reported an annual average of 120 ig/m3 in 1975 and 44 ig/m3 in 1985. For comparison, the National ambient air quality standard is 80 Ug/m3. Data from several different monitoring sites in the area consistently show a sharp decline from high to much lower values about 1981. Lichen studies in the upper Ohio River valley were first conducted in 1973 around Cardinal Power Plant, located between Wheeling, West Virginia and Steubenville, Ohio. After the initial study, it was apparent that the regional SO2 background overwhelmed any contribution to ground-level SO2 by the power plant. Lichens were depauperate throughout the study area with no apparent differences between sites upwind and downwind from Cardinal Plant. Thus, studies were continued to monitor the impact of regional SO2 on lichens. Lichen resurveys were performed in 1983, 1988, and 1989.