Stream chemistry in the eastern United States: 1. Synoptic survey design, acid‐base status, and regional patterns

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 μeq 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 km). 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 100 μg L−l, a concentration above which deleterious biological effects have frequently been reported. 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.