EFFECTS OF ACID DEPOSITION ON CHEMISTRY AND BROOK TROUT POPULATIONS IN HEADWATER STREAMS ORIGINATING IN THE TUSCARORA FORMATION, VALLEY AND RIDGE PROVINCE, PA

Due to atmospheric acid deposition, a recent study showed that precipitation in Pennsylvania had a mean pH of 4.40 in 2003. Acidic precipitation adversely affects certain watersheds while other watersheds are protected from these low values by the underlying geology.

The Tuscarora and Shawangunk Formations are well sorted quartz arenites that form ridges and host small headwater streams in the Valley and Ridge Province of Pennsylvania. Among streams that originate in and flow through only the Tuscarora, mean pH was 5.4 ± 0.8 (all values 1 σ, n = 35). Shawangunk Formation streams sites had a mean pH of 6.0 ± 0.2 (n = 7). Stream sites in other adjacent sandstone and shale (non-Tuscarora) lithologies had a mean pH of 6.4 ± 0.2 (n = 21).

Mean alkalinity for non-Tuscarora streams was 2.4 ± 1.9 mg/L CaCO₃, while mean alkalinity for Tuscarora streams was 1.8 ± 6.3 mg/L CaCO₃. The lower pH and alkalinity values suggest that the buffering capability of the Tuscarora Formation is commonly inferior to that of the other sandstone formations. Dissolved aluminum concentrations for Tuscarora-originating streams (0.1 ± 0.2 mg/L) were commonly higher than 0.2 mg/L, the lethal limit for brook trout (Salvelinus fontinalis). Shawangunk and other non-Tuscarora streams had lower dissolved aluminum concentrations (0.02 ± 0.01 and 0.04 ± 0.07 mg/L, respectively).

Hook-and-line methods were used to determine the presence or absence of brook trout in 39 stream reaches that appeared to have suitable habitat. Trout Unlimited volunteers observed brook trout in 13 out of 14 non-Tuscarora streams and in all 7 Shawangunk streams. Contrastingly, brook trout were recorded at only 8 out of 18 Tuscarora streams. This study suggests that a carefully designed hook-and-line sampling can determine the presence or absence of brook trout and help confirm the biological impacts of acid deposition.

Our geographic information system analysis shows that approximately 15% of all stream lengths originating in and flowing through only the Tuscarora Formation are listed as “impaired” due to atmospheric deposition in the Pennsylvania Department of Environmental Protection 305(b) list (impaired waters). This study suggests that approximately 50% of Tuscarora streams are impaired due to atmospheric deposition.