THE INFLUENCE OF BEDROCK GEOLOGY ON THE ABILITY OF PENNSYLVANIA HEADWATER STREAMS TO RESIST ACIDIFICATION CAUSED BY ACID PRECIPITATION

The acidification of headwater streams due to acid rain is an ecological and economic problem. For multiple reasons, the ability to resist acidification is different for every stream. This primary objective of this project was to determine the effect of bedrock geology on the ability of a headwater stream to ameliorate influxes of acid rain. Eleven headwater streams in central Pennsylvania that originate in either the Tuscarora, Juniata, Bald Eagle (sandstones), or Reedsville (shale) formations were chosen for this study. The pH of these streams were measured and compared with each other to identify any trends in acidification associated with the geologic formations.

The North Branch of Buffalo Creek and Swift Run were chosen for a more focused study. The pH and other field parameters were monitored several times, water samples were analyzed for major and trace elements, and ecological health was estimated by examining macroinvertebrates and fish.

The headwater streams that originate in the Tuscarora formation are the most acidified (pH » 4.5). Due to acidification, these streams also have high aluminum concentrations and low aquatic diversity suggesting ecological degradation. Streams originating in the Juniata formation were the least acidified (pH » 6.2) suggesting they have the highest buffering capacity. Limestone gravel road runoff also apparently influenced the pH of some streams. Streams flowing parallel to limestone roads have a higher pH than expected. Bedrock geology and, in some locations, the presence of nearby limestone roads seem to govern the ability for a headwater stream to ameliorate acid precipitation.