Water Quality of Three Forest Streams in Pennsylvania Impacted by Acidic Atmospheric Deposition

Open Access
Reed, Brendan Christopher
Graduate Program:
Forest Resources
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 21, 2014
Committee Members:
  • Elizabeth Weeks Boyer, Thesis Advisor
  • acid deposition
  • water quality
  • forest stream
  • deposition
  • acid
  • clean air act
  • recovery
  • atmospheric deposition
Acidic atmospheric deposition has impacted forests and waterways of the northeastern United States. Acidic deposition is largely attributed to compounds emitted to the atmosphere from combustion of fossil fuels for power generation. Major impacts of acid deposition on forested watersheds are part of an acidification process. Declines in pH of soils can lead to leaching of base cations from soils that decrease the ability of a watershed to buffer itself from incoming acids. Declines in pH of streamwater are often accompanied by changes in stream base cation loads and increases in dissolved inorganic aluminum concentrations, which in turn negatively affect aquatic life. Due to the Clean Air Act Amendments of 1990 and other policies, rates of acidic atmospheric deposition have greatly decreased in the northeastern United States in recent decades. Questions remain, however, about whether acid-sensitive forested watersheds will be able to recover from decades of acid deposition, and the length of time that it will take for this recovery to occur. This project quantified improvement in water quality in forested Pennsylvania streams in response to decreases in acidic atmospheric deposition since the early 1990s. In addition to analyzing long-term records of a single sampling site on each stream, I conducted synoptic sampling of stream segments throughout three forested headwater watersheds under summer baseflow conditions in order to characterize how water quality in the main channels changed from headwaters to outlet. All three watersheds have been subject to heavy loadings of acid deposition in recent decades, two of the watersheds (Roberts Run and Stone Run) were poorly buffered and thus acid-sensitive, while one of the watersheds (Young Womans Creek) was well buffered and thus acid-tolerant. Results show that some chemical recovery (i.e., increased pH, decreased aluminum concentrations) has occurred in the acid-sensitive streams. However, the sensitive watersheds are still considered to be chronically acidified along much of their stream length in terms of water quality parameters. The measured acid neutralizing capacity has not shown significant increases over the period of record. The acid-sensitive streams are thus still at high risk of episodic acidification, and biological recovery has likely not yet fully occurred.