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.
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.
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