Characterizing Episodic Stream Acidification Using a Concentration-Duration-Frequency Methodology in Watersheds of the Great Smoky Mountains National Park

Episodic stream acidification occurs as storm events temporarily reduce acid neutralizing capacity and pH. Stream acidification is suspected to have damaging effects on the health of aquatic ecosystems and biota and is dependent on various watershed characteristics such as drainage area, elevation, slope, and surficial geology. Here, a stochastic modeling approach is applied to continuous pH data for multiple stream monitoring sites within the Great Smoky Mountains National Park in order to characterize episodic acidification responses during stormflows for different streams. The approach summarizes voluminous pH data recorded by water quality sondes at 15-minute intervals into concentration-duration-frequency relationships. Unique to this study is the ability to characterize the episodic acidification response to watershed attributes without using baseflow or single-point stormflow measurements. A slope metric of mean pH event duration, a measure of episodic acidification response was determined to correlate with basin area and elevation. In contrast, baseflow studies have shown elevation to be the main driver of chronic acidification. It appears that during stormflows transport and flushing of stored anions and cations govern the response of streams included in this study.