Tracking the Effects of Acidic Deposition in Medium-Scale Forested Watersheds of the Eastern US

The US Geological Survey Hydrologic Benchmark Network (HBN) was established in the mid-1960's for continuously monitoring flow and seasonally monitoring water quality in medium-scale naturally-vegetated watersheds (100-500 km2) throughout the United States. Unlike small watershed research sites, the HBN sites are large enough to contain well-developed riparian zones, and as such are more representative of a natural reference landscape for assessing the relative effects of air pollution, development and agriculture on water quality in the US. During the past three years more frequent water quality monitoring (biweekly and during stormflows) has been established at 5 of these stations in the eastern United States. The stations are located in eastern Tennessee (Little River, 275 km2), western North Carolina (Cataloochee Creek, 127km2), north-central Pennsylvania (Young Woman's Creek, 120 km2), southeastern New York (Neversink River, 168 km2), and north- western Maine (Wild River, 180 km2), and thus lie along southeastern and northeastern gradients of decreasing sulfate deposition from west to east across the region. Concentrations of nitrate and sulfate in streamwater decrease in the Northeastern sites from the southwestern-most watershed to the northeastern-most watershed. Sulfate concentrations have decreased at the Little River, Neversink River and the Wild River during the period of record, but sulfate concentrations in Young Woman's Creek and Cataloochee Creek show no trend. No trend in sulfate concentrations is evident in any of the three Northeastern streams since 1995, when the last significant reduction in emissions was enacted. Sulfate concentrations in Little River have continued to fall since 1995. No trends are observed in ANC in any of the streams, but calcium concentrations in streamwater have decreased in Little River, Neversink River, and Wild River since the 60's. Calcium concentrations in streamwater decrease from a range of 80-120 umole per liter in Young Woman's Creek to 20-40 umole per liter in Wild River in the Northeastern streams. The stream chemistry patterns observed are similar to those in small research watersheds nested within several of the basins, and indicate that medium-scale forested watersheds are useful indicators of landscape response to changing emission standards.