No abstract

To assess the regional acid-base status of streams in the mid-Atlantic and southeastern United States, spring base flow chemistry was surveyed in a probability sample of 500 stream reaches representing a population of 64,300 reaches (224,000 km). Approximately half of the streams had acid-neutralizing capacity (ANC) < 200 taeq L -1 . Acidic (ANC <-0) streams were located in the highlands of the Mid-Atlantic region (southern New York to southern Virginia, 2330 km), in coastal lowlands of the Mid-Atlantic (2600 km), and in Florida (462 kin). Acidic streams were rare (less than 1%) in the highlands of the Southeast. Inorganic monomeric aluminum (Alim) concentrations were highest in acidic streams of the Mid-Atlantic Highlands where over 70% of the acidic streams had Alim greater than !00 t•g L -1, a concentration above which deleterious biological effects have frequently been re13orted. Dissolved organic carbon concentrations were much higher in lowland coastal streams, compared with inland streams. Our data support a hypothesis that atmospheric sources and watershed retention control regional patterns in streamwater sulfate concentrations. Most stream watersheds retain the vast majority of the total nitrogen loading from wet deposition. The data suggest, however, that some deposition nitrogen may be reaching streams in the Northern Appalachians. These results show that acidic surface waters are found outside the glaciated northeastern portions of the United States and that watershed sulfate retention is not sufficient to prevent acidic conditions in some Mid-Atlantic Highlands streams. undertaken in the Northeast, Upper Midwest, Southeast [Linthurst et al., 1986], and mountainous areas of the West [Landers et al., 1987]. There remain, however, large areas in the Mid-Atlantic and Southeast where lakes are uncommon and where large numbers of streams with very low ANC are found. Despite the availability of a number of data sets collected at intensively studied stream research sites in the Mid-Atlantic and Southeast [Sharpe et al., 1984; Katz et al., 1985; Morgan and Good, 1988; Swank and Waide, 1988; Webb et al., 1989] and several stream surveys over small portions of these two regions [Silsbee and Larson, 1982; Lynch and Disc, 1985; Sharpe et al., 1987], no synoptic data sets existed prior to the recent National Stream Survey efforts from which a quantitative synoptic assessment could be made of the acid-base status of an explicitly defined population of streams in the Mid-Atlantic and Southeast. In the spring of 1986, the U.S. Environmental Protection Agency (EPA) conducted the National Stream Survey tNSS) on a probability sample of 446 streams in the mid-Atlantic and southeastern United States [Kaufmann et al., 1988; Sale et al., 1988]. This full-scale field effort was preceded a year earlier by a pilot survey of 54 streams in the Southern Blue Ridge. The pilot survey demonstrated the feasibility of the design, logistics, and analytical protocols used in the fullscale survey [Messer et al., 1986, 1988]. The objecti...

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

We characterized the major ion chemistry of over 800 lakes on the Kenai Peninsula, Alaska, from a probability sample of 59 lakes (August 1988). There were two groups: alkalinity < 300 μeq/L (78% of the lakes) and alkalinity > 700 μeq/L. Low-alkalinity lakes had significantly lower concentrations of base cations and silica and significantly higher average concentrations of dissolved organic carbon (DOC) than high-alkalinity lakes. Despite widespread acidic soils and bog vegetation, and resulting high DOC concentrations, none of the lakes sampled was acidic. Sulfate concentrations (~3 μeq/L) were similar in the two groups, as were Cl− concentrations, which decreased with distance from the coast. High-alkalinity lakes were similar chemically to rivers and shallow aquifers in the region, suggesting that the high alkalinity is a product of the major weathering reactions in this terrain; the substantially different ratios of base cations in the two groups also indicate quantitative and qualitative weathering differences. Low-alkalinity lakes were at higher elevations than high-alkalinity lakes, presumably in groundwater recharge zones. Consequently, the chemical differences between the two lake groups appeared to be controlled by relatively small differences in local hydrologic setting, and possibly by differences in mineralogy along the groundwater flowpaths.