Frank A. Deviney

Temporal patterns of nitrogen leakage from mid‐Appalachian forested watersheds: Role of insect defoliation

Fluxes of dissolved nitrogen (N) as nitrate from forested watersheds in the mid-Appalachian region have important water quality ramifications for small acid-sensitive streams and for downstream receiving waters such as the Chesapeake Bay. Previous studies of N leakage have suggested that annual dissolved N fluxes from small watersheds can vary by several orders of magnitude and may be increasing as second-growth forests gradually become N saturated from the accrual of atmospheric N loadings. In this study, we examined the temporal (intra-annual and interannual) variability in dissolved nitrate fluxes from five small (area < 15 km2) forested watersheds in the mid-Appalachian region from 1988 to 1995. At all sites, nitrate concentrations were observed to increase dramatically during storm flow events, with nitric acid contributing significantly to depressions in pH and acid-neutralizing capacity; annual nitrate fluxes were dominated by high-discharge periods. Interannually, the fluxes at each site varied by 1–2 orders of magnitude, but the patterns of N leakage displayed considerable synchrony with outbreaks of gypsy moth caterpillar defoliation that began in the late 1980s and early 1990s in this region. N leakage from forested watersheds apparently lagged the initial defoliation by several months to perhaps a year or more. Defoliation outbreaks by the gypsy moth caterpillar (or other herbivorous pests) thus provide an alternative explanation of N leakage from forest ecosystems. Poorly documented insect defoliations, rather than premature N saturation of intact forest ecosystems, need to be considered as a possible explanation of N leakage from forested watersheds in the mid-Appalachian region and elsewhere.

CHANGE IN THE ACID-BASE STATUS OF AN APPALACHIAN MOUNTAIN CATCHMENT FOLLOWING FOREST DEFOLIATION BY THE GYPSY MOTH

Infestation by the gypsy moth (Lymantria dispar) can alter biogeochemical conditions in affected catchments. Stream-water concentration data obtained over the period of 1980–1993 for White Oak Run, a stream in Shenandoah National Park, Va., indicate that change in catchment acid-base status is associated with forest defoliation by the moth larva. Stream-water concentration changes following defoliation included increasing concentrations of strong-acid anions, base-cations, and hydrogen ion, as well as decreasing concentrations of acid-neutralization capacity (ANC) and sulfate. The largest change was in the concentration of nitrate; annual discharge-weighted mean concentrations increased from predefoliation levels consistently less than 5 μeq L−1 to postdefoliation levels greater than 50 μeq L−1. An intensification of acidification was indicated by record-high hydrogen ion concentrations and record-low ANC concentrations. The long-term biogeochemical implications of the infestation are uncertain due to the nonlinearity of the observed responses and unknown patterns of recovery and recurrence.

Atmospheric Wet Deposition in Remote Regions: Benchmarks for Environmental Change

AbstractPrecipitation composition was characterized at 14 remote sites between 65°N and 51°S. Anthropogenic sources contributed to non-sea-salt (nss) SO42−, NO3−, and NH4+ in North Atlantic precipitation. Biogenic sources accounted for 0.4–3.3 μeq L−1 of volume-weighted-average (VWA) nss SO42− in marine precipitation. SO42− at the continental sites (2.9–7.7 μeq L−1) was generally higher. VWA NO3− (0.5–1.3 μeq L−1) and NH4+ (0.5–2.6 μeq L−1) at marine-influenced, Southern Hemispheric sites were generally less than those at continental sites (1.4–4.8 μeq L−1 and 2.3–4.2 μeq L−1, respectively). VWA pH ranged from 4.69 to 5.25. Excluding the North Atlantic, nss SO42−, NO3−, and NH4+ wet depositions were factors of 4–47, 5–61, and 3–39, respectively, less than those in the eastern United States during 2002–04. HCOOHt (HCOOHaq + HCOO−) and CH3COOHt (CH3COOHaq + CH3COO−) concentrations and depositions at marine sites overlapped, implying spatially similar source strengths from marine-derived precursors. Greater ...