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Input-output budgets for dissolved inorganic nitrogen (DIN) are summarized for 24 small watersheds at 15 locations in the northeastern United States. The study watersheds are completely forested, free of recent physical disturbances, and span a geographical region bounded by West Virginia on the south and west, and Maine on the north and east. Total N budgets are not presented; however, fluxes of inorganic N in precipitation and streamwater dominate inputs and outputs of N at these watersheds. The range in inputs of DIN in wet-only precipitation from nearby National Atmospheric Deposition Program (NADP) sites was 2.7 to 8.1 kg N ha-' yr-' (mean = 6.4 kg N ha-' yr-' ; median = 7.0 kg N ha-' yr-'). Outputs of DIN in streamwater ranged from 0.1 to 5.7 kg N ha-' yr-' (mean = 2.0 kg N ha-' yr-'; median = 1.7 kg N ha-' yr-'1. Precipitation inputs of DIN exceeded outputs in streamwater at all watersheds, with net retention of DIN ranging from 1.2 to 7.3 kg N ha-' yr-' (mean = 4.4 kg N ha-' yr-l; median = 4.6 kg N ha-l yr-'1. Outputs of DIN in streamwater were predominantly NO3-N (mean = 89%; median = 94%). Wet deposition of DIN was not significantly related to DIN outputs in streamwater for these watersheds. Watershed characteristics such as hydrology, vegetation type, and land-use history affect DIN losses and may mask any relationship between inputs and outputs. Consequently, these factors need to be included in the development of indices and simulation models for predicting 'nitrogen saturation' and other ecological processes.

Six rainfall events were intensively sampled below a mixed hardwood forest canopy in central Pennsylvania to determine sample size requirements for estimation of thronghfall volumes and ionic concentrations. Evaluation of the ionic parameters of thronghfall revealed that the concentrations of most major ions were nonnormally distributed. Differences in the distributions of concentrations were found to occur between ions as well as between storms. Significant departures from normality were mainly due to right‐skewness. Only H+ exhibited a left skewed sample distribution. None of the basic transformations were effective in normalizing all parameters. A high degree of spatial variability was observed for each of the chemical parameters. Nitrate and hydrogen ions (NO−3 and H+), were found to be the least variable, whereas vegetatively mobile ions such as K+ and Mg2+ exhibited the greatest variability. Because of high event‐to‐event variation in the distributions of ion concentrations, specific sample‐size requirements should be estimated for each ion through preliminary sampling of thronghfall precipitation from several storms.

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Concentrations of sulfate (SO4 2-) and free hydrogen ions (H+) in precipitation decreased from 10% to 25% over a large area of the Eastern United States from 1995 through 1997 as compared to the previous 12-year (1983−1994) reference period. These decreases were unprecedented in magnitude and spatial extent. In contrast, nitrate (NO3 -) concentrations generally did not change over this period. The largest decreases in both H+ and SO4 2- concentrations, which nearly mimicked one another, occurred in and downwind of the Ohio River Valley, the same area where Title IV of the 1990 Clean Air Act Amendments (CAAA) set limitations on sulfur dioxide (SO2) emissions from a large number of utility-owned coal-fired sources. Phase I of the CAAA required that these limitations be met by January 1, 1995. On the basis of our analysis of precipitation chemistry and emissions data, we conclude that significant declines in acid rain occurred in many parts of the Eastern United States from 1995 through 1997 because of large reductions in SO2 emissions in this region and a corresponding reduction in SO4 2- concentrations in precipitation.

A quantitative evaluation of stream temperature alterations due to a commercial forest harvesting practice and a research treatment is presented. Summer maximum stream temperatures averaged I C higher in the commercial clearcut and 9 °C higher in the clearcut-herbicided watershed than in the forested control. The largest average monthly temperature increase on the commercial clearcut (2.2 C) occurred during April; on the clearcut-herbicided basin it occurred during June (10.5 C). Significant changes in stream temperature were observed on both watersheds as early as February and as late as November.Changes in minimum stream temperatures are presented in detail along with the impact on diel temperature fluctuations. Changes in the stream temperature regimes of the clearcut watersheds from the headwaters to the mouth of the watersheds are also given. Potential impacts of the stream temperature alterations on aquatic ecosystems are summarized in relation to stress limits for brook trout and other organisms.

Fifteen years of streamflow and water quality data were evaluated to determine the effectiveness of Best Management Practices (BMP's) in controlling nonpoint source pollution from an 110. acre commercial clearcut located in the Ridge and Valley Province of central Pennsylvania. The analyses addressed both short‐ and long‐term changes in the physical and chemical properties and the hydro‐logic regime of the stream draining this 257‐acre watershed. Overall, the BMP's employed on this commercial clearcut were very effective in preventing serious deterioration of stream quality as a result of forest harvesting. Although statistically significant increases in nitrate and potassium concentrations and temperature and turbidity levels were measured the first two years following harvesting, the increases were relatively small and, with the exception of turbidity, within drinking water standards. Nevertheless, such increases may violate EPA's anti‐degradation policy. Nitrate and potassium concentrations and turbidity levels remained above pre‐harvesting levels for as long as nine years following harvesting. Clearcutting also significantly increased water yield, which in turn initially lowered the concentrations of most solutes because of dilution. Increased water yields returned to pro‐harvesting levels within four years as a result of rapid regrowth. The export of some ions increased; however, the increased export appeared to be insufficient to affect site fertility. Implementation of periodic post‐harvest inspections of harvested areas, increasing the width of the buffer zone, and utilizing buffer zones on all perennial and intermittent channels would reduce further impacts of silvi‐cultural activities on water quality.