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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