Great Smoky Mountains National Park Influence of Basin Characteristics on Acidification Response Continuous Water Quality Data

The park receives some of the highest rates of atmospheric acid deposition in the U.S. in the form of sulfates and NOX. Despite improvements in precipitation pH and sulfate concentrations over the past decade, there has been little recovery in stream water chemistry, in particular during storm flows where pH as been recorded to drop to as low as 4.0. Acids enter poorly buffered streams of the park through wet deposition, accumulated dry deposition washed from vegetation during rainfall, and transport originating from naturally occurring organic acids on the forest floor and soils. Additionally, Anakeesta pyritic geology has been identified as a natural source of acid in the GRSM. Although effects have not been observed directly, stream acidification is suspected to be the primary cause of native brook trout (Salvelinus fontinalis) extirpation in six headwater streams in the GRSM, including some streams that were populated as recently as 15 years ago. GRSM park-wide baseflow water quality monitoring began in 1993; currently, thirty-two stream sites are sampled bimonthly and an additional ten remote sites are sampled semiannually in the Hazel Creek watershed. Elevations above 3500 ft show low but stable pH ranging from 5.6 to 6.0. Elevations below 3500 ft show pH from 6.0 to 6.5, but show a long-term, slowly declining trend. In these lower elevation streams, the pH will be less than 6.0 within about 25 years if current trends continue. Results from this monitoring effort showed that all storms had significant ANC and pH depressions. Sulfate, nitrate, and organic acid concentrations increased during each episode. ANC contribution analysis indicated acid deposition was the primary cause of episodic acidification, but organic acids and cation dilution also contribute. In addition, large storms preceded by long, dry periods cause the largest pH depressions. Stream acidification may be driven by acid deposition, but additional inputs from varying vegetation and geology create unique and complex responses to observed stream acidification events. Although no mortality was observed, results from studies with trout in the field demonstrate that episodic stream acidification negatively affect native southern brook trout physiology in the park under actual field conditions whereby trout lose the ability to regulate critical blood ions. A new study design started in 2008, in which eight sub-watershed streams were selected to study how acid deposition impacts watersheds with different basin characteristics (i.e., elevation, basin area, and Anakeesta presence). The sites include: Road Prong, Newt Prong, Eagle Rocks Prong, Rock Creek, Lower Jake Creek, Beech Creek, Upper Palmer Creek, and Cosby Creek. The study is reported in Keil Neff's PhD dissertation from UTK.

Great Smoky Mountains National Park Influence of Basin Characteristics on Acidification Response Continuous Water Quality Data

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