Chemical Characteristics

Under baseflow conditions in undisturbed streams draining the crystalline Appalachians, concentrations of most cations (K⁺, Na⁺, Ca²⁺, Mg²⁺) and anions (Cl^-, SO4^2-) are usually low (<l mg/L) and concentrations of nutrients such as nitrate, ammonium, and phosphate may be very low (0.001-0.004 mg/L) (Swank and Douglass 1977, Silsbee and Larson 1982).  Bedrock geology, elevation, and disturbance history influence nutrient concentrations (Wallace and others 1992).

The pH, a measure of stream acidity or alkalinity, of most streams in the crystalline Appalachians is nearly neutral (about 7.0), and fewer than 3.2 percent of stream sites in the Blue Ridge had pH values below 6.4, indicating acid conditions (Messer and others 1986). However, in streams draining watersheds with Anakeesta formations, pH values may be considerably lower, around 5.2-5.5 (Silsbee and Larson 1982). Anakeesta groups contain pyrites and other sulfides that form dilute sulfuric acid solutions in water. As a result, pH and alkalinity are lower, and conductivity and magnesium concentrations are higher in the water. Similar pyritic rocks occur in several Appalachian locations (see Silsbee and Larson 1982) (Wallace and others 1992).

During episodic rainstorms or snow melt, pH can be depressed rapidly. In Raven Fork, North Carolina, pH occasionally decreased to below 5.0 during storms and, at the same time, total monomeric aluminum concentrations increased from <50 to >350 g/L (Jones and others 1983). Negative impacts of acidification on stream fishes and other organisms is largely due to the toxic effects of monomeric aluminum that is released from soils by acid rain (Rosseland and others 1992).  In some watersheds, the ability of soils and plants to assimilate nitrate from acid deposition can be exceeded and lead to nitrogen saturation and increased nitrate and acidification in streams draining the watershed.

Stream pH, alkalinity, Si, K, Na, and turbidity decrease with increasing elevation in the Great Smoky Mountain National Park, whereas nitrate concentrations increased with elevation (Silsbee and Larson 1982). In undisturbed streams in the Coweeta Basin of western North Carolina, highest values for nitrites and sulfates were also found at higher elevations (Swank and Douglass 1977).

An extensive chemical survey of streams draining various geological provinces in the eastern United States (Kaufmann and others 1988) showed that concentrations of many chemicals as well as acid-neutralizing capacity (ANC), conductivity, pH, and total base cations tend to increase downstream (Table: Chemical survey of streams).  Also, the southern Blue Ridge has lower ANC, calcium, conductivity, dissolved organic carbon, bicarbonate, nitrate, sulfate and total base cations than do the other southern Appalachian provinces.  Areas with slow weathering crystalline rock have streams with lower concentrations of dissolved substances. Alkalinity, pH, and concentrations of nutrients are usually higher in drainages with sedimentary rocks such as limestone (Wallace and others 1992).