James A. Lynch

Long-term impacts of forest treatments on water yield: a summary for northeastern USA

Abstract Long-term changes in annual water yield are summarized and compared for 11 catchment studies in the northeastern USA. Substantial increases in water yield of up to 350 mm year−1 were obtained in the first year by clearing forest vegetation and controlling regrowth with herbicides. Commercial clearcutting with natural regrowth resulted in initial increases in water yield of 110–250 mm year−1. This range in response was due to differences in precipitation and configuration of cuttings. Unless regrowth was controlled with herbicides, yield increases declined quickly after cutting, seldom persisting for more than 10 years. However, yield increases were readily extended over 20 years or more with intermediate cuttings and/or repeated control of regrowth with herbicides. Nearly all increases in water yield occur during the growing season as augmentation of baseflow. Changes in species composition after forest cutting on several study catchments eventually resulted in decreased water yields compared with those from uncut, control catchments. Results are discussed in terms of implications for surface water supplies, global climate change, nutrient cycling, hydrological modeling, and long-term research.

Trends in precipitation chemistry in the United States: A national perspective, 1980–1992

Thirteen years (1980–1992) of precipitation chemistry data from 58 National Atmospheric Deposition Program/National Trends Network (NADP/NTN) sites are examined for trends using a general linear least squares model. SO42- concentrations are decreasing throughout the United States; significant (p < 0.05) trends are evident at 42 of the 58 sites included in this analysis and the average decrease is 12.026 μeq l−1. The largest concentration of sites with significant decreasing SO42− trends is located in the north central and western regions of the country. Eleven sites exhibit significant NO3− trends, nine of which are decreasing. Ca2+ and Mg2+ concentrations show the most widespread decline (44 and 52 sites, respectively) of all the major cations and anions in precipitation. Ca2+ concentrations have decreased 4.587 μeq l−1 since 1980; Mg2+ concentrations have decreased 2.034 μeq l−1. The most consistent and statistically most significant (p < 0.001) Ca2+ and Mg2+ trends occur in the northeast. Decreasing trends are also evident at 28 sites for Na+ and at 35 sites for K+. NH4+ concentrations exhibit very little change over this 13-year period. The widespread decline in base cations, particularly Ca2+ and Mg2+, appears to have offset the effects that decreasing SO42− concentrations should have on free acidity in precipitation. Only 17 sites exhibit both significant decreasing H+ and SO42− concentration trends, most of which are located in the north central portion of the United States. The average decrease in H+ at the 17 sites is 9.991 μeq l−1. Hawaii is the only site in the NADP/NTN network to exhibit a significant increasing H+ trend.

Statistical analysis of errors in estimating wet deposition using five surface estimation algorithms

Abstract Wet deposition measurements of H+, SO42− and NO3− from 29 monitoring sites located in (16) and around (13) Pennsylvania, U.S., were analyzed to quantify errors associated with extrapolating point estimates of deposition using five surface-fitting algorithms. The influence of site density on estimation errors associated with each surfacing algorithm was also investigated. The five surfacing differed little in their abilities to predict the concentration or deposition of individual ions found in precipitation in Pennsylvania. However, the size of estimation errors for all parameters, even those based on the densest network, were quite high relative to the variation observed among monitoring sites in Pennsylvania. All monitoring site observations were within 22.8, 17.6 and 23.1 per cent of the median concentration and 33.9, 35.3 and 36.7 per cent of the median deposition for H+, NO3− and SO42−, respectively. Maximum per cent errors indicate that estimation errors may severely obscure actual surface features in at least some portions of the estimated concentration and deposition grids in Pennsylvania. Deposition and concentration estimates based on higher density networks were generally more accurate; however, the improvements afforded by the additional sites were quite modest. Based on the magnitude of estimation errors, kriging produced the most accurate estimates, although no single algorithm consistently yielded the most accurate estimates for all parameters.

Long-term trends in NADP/NTN precipitation chemistry data: Results of different statistical analyses

This paper summarizes the results of four statistical approaches for the estimation of long-term trends (1983–92) in sulfate concentration data from 90 monitoring sites across the United States. Least squares regression models and nonparametric techniques were applied to these data. Sulfate concentrations were found to be generally decreasing on the order of 0–4% at most sites. There was general agreement that trends were significant in the Great Lakes, Pacific northwest, and southwest regions. Although strengths and weaknesses are described for each approach, all of these approaches are useful for long-term trend estimation. Visualization techniques are recommended for displaying trend patterns and associated levels of statistical significance.

Blizzard's effects on Appalachian stream chemistry assessed

From March 12–14, 1993, up to 1 m of snow fell on the northeast United States, with central Pennsylvania receiving some of the largest accumulations. The rain-on-snow events that followed provided a unique opportunity to monitor episodic acidification and fluctuations in dissolved aluminum concentrations during extreme flows in three forested Appalachian Plateau basins in north-central Pennsylvania. These events produced peak flows 2–5 times greater than previously monitored flows in the basins we studied, and in the Susquehanna River Basin, March discharge was the highest sustained flow on record. High flows during the event were accompanied by greater streamflow dilution by rain and meltwater and shifts to surface and near-surface hydrologic flow paths, which reduced contact of water with the soil matrix. In the three basins we monitored, these extreme flows caused little water quality degradation relative to earlier events of lesser magnitude. High flows resulted in stream acidification due to base cation dilution rather than increased acid anion concentrations as found in previously monitored events. Total dissolved aluminum concentrations peaked and then remained nearly constant as flow increased during the event; however, aluminum concentrations were elevated above levels toxic to native trout populations in these streams for an extended period of time.