Stream chemistry in the eastern United States: 2. Current sources of acidity in acidic and low acid‐neutralizing capacity streams

Abstract

We examined anion composition in National Stream Survey (NSS) data in order to evaluate the most probable sources of current acidity in acidic and low acid-neutralizing capacity (ANC) streams in the eastern United States. Acidic streams that had almost no organic influence (less than 10% of total anions) and sulfate and nitrate concentrations indicative of evaporative concentration of atmospheric deposition were classified as acidic due to acidic deposition. These acidic streams were located in small (<30 km 2) forested watersheds in the Mid-Atlantic Highlands (an estimated 1950 km of stream length) and in the Mid-Atlantic Coastal Plain (1250 km). Acidic streams affected primarily by acidic deposition but also influenced by naturally occurring organic anions accounted for another 1180 km of acidic stream length and were located in the New Jersey Pine Barrens, plateau tops in the Mid-Atlantic and Southeast Highlands, and the Florida Panhandle. The total length of streams acidic due to acid mine drainage in the NSS (4590 kin) was about the same as the total length of acidic streams likely affected by acidic deposition (4380 km). Acidic streams whose acid anon composition was dominated by organics were located in Florida and the Mid-Atlantic Coastal Plain. In Florida, most of the acidic streams were organic dominated, whereas about half of the streams in the Mid-Atlantic Coastal Plain were organic dominated. Organic-dominated acidic streams were not observed in the Mid-Atlantic and Southeast Highlands. was to determine the present chemical status of surface waters in regions of the United States containing the majority of streams and lakes considered to be at risk as a result of acidic deposition. The NSS was conducted in four Mid-Atlantic and five Southeast subregions of the United States (Figure i), identified on the basis of similar physiographic characteristics. The acid-base status and chemical characteristics of the NSS stream population have been presented in a companion paper [Kaufmann et al., this issue]. The fact that a stream is acidic, however, does not necessarily mean that it has been acidified by acidic deposition. There are other mechanisms by which streams can be acidified (e.g., naturally occurring organic acids or acid mine drainage). Thus, in this paper we have classified acidic and low ANC surface waters according to their probable source of acidity, based largely on anion composition, watershed characteristics, and expected concentrations assuming only deposition sources. During spring base flow of 1986, there was an estimated 1950 km of NSS streams most likely acidic due to acidic deposition in the Mid-Atlantic Highlands. Most of the acidic streams in Florida (462 km) were likely acidic due to organic acids. Acidic streams in the Mid-Atlantic Coastal Plain (2600 km) were affected by both organic acids and acidic deposition. NSS DESIGN AND METHODOLOGY

Characterizing Episodic Stream Acidity During Stormflows in the Great Smoky Mountains National Park

“…Sulfate and nitrate were found to be significant contributors to acidification across the MPLP sites, supporting the hypothesis that acid deposition is the dominant mechanism for stream acidification in these watersheds. Other regional studies 195 also identify that acidic deposition is a controlling acidification mechanism in low alkalinity waters of the Appalachian mountains (Herlihy et al 1991;Deviney et al 2006;Sullivan et al 2007). Site M3 was observed to have both the lowest measured baseflow and stormflow ANC, which is consistent with a prior regional study (Hyer et al 1995).…”

Dissolved Organic Matter in Freshwaters

“…Without any doubt, the greatest impetus since the early 1980s for the study of the acid-base properties of DOM was the large-scale research effort that was initiated in the 1980s to investigate the impact of acidic precipitation on terrestrial and aquatic ecosystems (e.g., Herlihy et al, 1991;Linthurst et al, 1986;Messer et al, 1986;Munson and Gherini, 1993). Longterm decreases in pH and alkalinity in many lakes and rivers were attributed to increased rates of input of natural and/or anthropogenic acids.…”

Long-Term Effects of Acidic Deposition on Water Quality in a High-Elevation Great Smoky Mountains National Park Watershed: Use of an Ion Input–Output Budget

“…It has been known for decades that atmospheric deposition of SO 4 2− and NO 3 − from coal-fired power plants, vehicles, and other sources can cause stream acidification in Appalachian regions with base-poor bedrock (Driscoll et al 1980;Herlihy et al 1991;Wigington et al 1996). Stream acidification in the GRSM was initially observed in the 1980s by Johnson and Lindberg (1992) and Cook et al (1994).…”