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Schnitzer, M.; Khan, S. V. Humic Substances in the Environment; Marcel Dekker Inc.: New York, 1972. Bloy von Treslong, C. J.; Staverman,A. J. Recl. Trav. Chim.
Note No. 18, Civil Engineering Department, Massachusetts Institute of Technology, Cambridge, MA 1976.
Pays-Bas 1974, 93, 171.
Klotz, I. M.; Hunston, D. L. Biochemistry 1971,10, 3065. Westall, J. C.; Zachary, J. L.; Morel, F. M. M. Mineql, A Computer Program For The Calculation of Chemical Equilibrium Composition of Aqueous Systems. Technical
Received for review M a y 17, 1988. Accepted October 19, 1988. W e are grateful to the Swedish Nuclear Fuel and Waste Management Company for financial assistance and to Lisbeth Samuelsson for graphical assistance.
Acidification of Adirondack Lakes Clyde E. Asbury” Center for Energy and Environment Research, University of Puerto Rico, Rio Piedras, Puerto Rico 00936
Frank A. Vertucci Rocky Mountain Forest and Range Experiment Station, U.S.D.A. Forest Service, Ft. Collins, Colorado 80526
Mark D. Mattson Section of Ecology & Systematics, Corson Hall, Cornell University, Ithaca, New York 14853
Gene E. Likens Institute of Ecosystem Studies, The New York Botanical Garden, Millbrook, New York 12545
The acidification of lakes in the Adirondack Mountain region of New York was estimated directly by comparing data from historic (1929-1934) and modern (1975-1985) regional surveys of lake chemistry. We performed new analyses concerning the quality of the data, rejecting all historic pH data and many modern alkalinity values. When the historic data were corrected for a bias between titration procedures, we found a median loss of 50 pequiv/L alkalinity in 274 lakes with paired data. Eighty percent of the lakes showed a decline in alkalinity. The observed acidification was greatest in the lakes a t high elevation and was of the same magnitude as the current precipitation acidity in the region.
Introduction The lakes of the Adirondack Mountain region of New York State have been repeatedly cited as showing the effects of anthropogenic acidification (1-5). Much of the evidence for acidification is indirect, however: e.g., loss of sport fish populations (2, 3), changes in aquatic plant and invertebrate communities (6-8), changes in sediment metal concentrations (9),and results from empirical models of lake acidification (10). The Adirondacks is one of the few areas where historic data are available to measure directly the acidification of lakes through time. While previous researchers have examined smaller data sets from this region, they reached mixed conclusions regarding the changes in pH and alkalinity ( 2 - 4 , I I ) . In this paper we examine the chemical evidence from historic and modern lake surveys to determine if significant lake acidification has occurred in the Adirondack Mountain region. Methods The New York State Conservation Department surveyed hundreds of Adirondack lakes during the summers of 1929-1934. Included in the studies were measurements of alkalinity, pH, and C02 acidity (12). Extensive new data from the recent New York State Department of Environmental Conservation (DEC) survey (13) and the U.S. Environmental Protection Agency (EPA) survey (14) along 362 Environ. Sci. Technol., Vol. 23, No. 3, 1989
with existing DEC data (3, 15) were available to form a modern data set for the years 1975-1985. Historic and modern surface alkalinities for each lake were matched on the basis of a unique “pond number” system used by the surveys. In a few cases where pond numbers were not assigned, we used other information, including lake name and location to identify the lakes; all lakes identified ambiguously were removed from the data set. If redundant modern data were available, the most recent survey was used. Both the historic as well as the modern survey results were examined closely to detect any errors or inconsistencies in the data. Historic pH measurements are often unreliable because procedures used to measure pH employed various colorimetric indicator solutions that can alter the pH of the sample being measured (16),especially in the dilute waters of the Adirondacks. In addition, it is well-known that solution pH can vary due to COz exchange with the atmosphere (17). We examined these problems carefully and rejected the use of pH data in favor of a direct comparison of alkalinity values, which can be determined with great precision with procedures that are well documented, and alkalinity is conservative with respect to changes in C 0 2 (17). It has been reported (2,18) that the electrode used by the DEC in measuring both pH and alkalinity during the 1979 survey was malfunctioning. Examination of the laboratory notes kept by the DEC (19) confirmed that the Gran functions used to determine alkalinity were not linear, and the calculated values were biased low. We therefore eliminated 72 lakes from our data set that were included in the 1979 DEC survey. Moreover, 28 lakes that were known to have been treated with lime were not included in our analysis. Our final data set consisted of 274 lakes. In a pair-wise analysis of data such as these, it is important to remove any source of bias or systematic error between the historic and modern measurements. In this case, bias results from differences in the techniques used to measure alkalinities. The historic method employed titration to a fixed pH end point, determined by the
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A l k e l i n i t y Changes i n Adirondack Lakes (veq/l) Flgure 1. Frequency distribution of changes in alkalinity between the 1929-1934 Adirondack lake surveys and the 1975-1985 surveys for 269 lakes (5 lakes off scale are not shown). The data were corrected for the methyl orange overtitration described in text.
“faintest p i n k color of the methyl orange (MO) indicator dye, while modern surveys employed the Gran technique to determine the end point. Because the end point used in MO titrations is usually a t a lower pH than that determined by Gran titration, alkalinity measured by the MO technique generally overestimates Gran alkalinity (11,20). Therefore, it is necessary to estimate and correct for the bias between the two methods. We obtained an estimate of the pH end point of the MO alkalinity titration as it was performed in the 1929-1934 Adirondack lake survey. Twenty analysts were asked to perform independent titrations on triplicate samples of low-alkalinity (85 Fequiv/L) lake water, “until the faintest pink coloration appears: that is, until the color of the solution is no longer pure yellow”, following the instructions (21,22)cited by the historic survey. For each of the 60 samples, the end point pH was immediately measured with a standardized Radiometer pH meter. The “faintest pink” end point was expected to lie between the “orange” end point at ca. 4.6 and the “ p i n k end point at pH 4.0 (20, 23). The analysts titrated to a mean pH of 4.25 (SE = 0.05). This pH end point of 4.25 is in good agreement with the review by Kramer et al. (11) of the faintest pink end point. An exception is a reported faintest pink end point of 4.04 (24). Assuming a MO end point a t pH 4.25, the alkalinity correction for each lake can be determined from the alkalinity and C 0 2 acidity data as described by Kramer et al. (11). For our 274 lakes the average correction to historic alkalinity was a subtraction of 54.6 pequiv/L (SD = 1.1 pequiv/L). All other sources of error, including analytical error, seasonal variation, and spatial variation within each lake, are assumed to be random and will not introduce bias. It is assumed these types of errors will tend to average out when hundreds of lakes are sampled over a period of several years for each survey and will not invalidate the statistical results reported here.
Results and Discussion The historic data had a mean “uncorrected” alkalinity of 195.4 pequiv/L compared to the modern mean alkalinity of 99.8 pequiv/L. When these data are corrected for the MO overtitration bias, this results in a mean estimated acidification of -41 pequiv/L (SE = 6.8). The median
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A l k a l i n i t y Changes i n Adirondack Lakea [PQ/l) Figure 2. Frequency distribution of changes in alkalinity for lakes in the six major drainage regions in the Adirondack Mountains. Data as in Figure 1.
change in alkalinity for these 274 Adirondack lakes is -50 pequiv/L, with 80% of the lakes showing a loss of alkalinity (Figure 1). A Wilcoxon signed rank test indicates this loss of alkalinity is significant ( a < 0.01). The lakes show variation in the extent of acidification when the lakes are grouped by major drainage basin (Figure 2). These variations are negatively correlated ( r = -0.91) with the average elevation of the lakes within each major drainage basin. We conclude that lakes in the Adirondack Mountain region have been acidified significantly since the 1930s. Our best estimate of the median alkalinity change for the Adirondack lakes (-50 pequiv/L) may be an underestimate for the region, because the EPA surveys excluded lakes smaller than 4 ha, which may be more sensitive to acidification than larger lakes. Our results lie between those of Hendrey et al. (4),who reported a mean loss of 104.7 pequiv/L for 36 Adirondack lakes, and the results of Kramer e t al. ( I I ) , who reported that the median change in alkalinity was a gain of 1 pequiv/L when a pH end point of 4.04 was assumed. When Kramer et al. (11) assumed an alternate MO end point a t pH 4.19, their median loss of alkalinity, 44 pequiv/L, agrees closely with our results. The results of Hendrey et al. (4) are easily reconciled with our results, because the lakes examined by Hendrey et al. ( 4 ) are high-elevation lakes (all above 610 m) and most are located in the Mohawk-Hudson drainage basin where we found the largest losses of alkalinity (Figure 2). The results of Kramer et al. (11) deserve close examination since their data are largely a subset of ours. Kramer et Environ. Sci. Technol., Vol. 23, No. 3, 1989 363
al. (11) used the erroneous 1979 DEC data (discussed previously), which are included in the 1984 DEC report (15) as well as the 1980 DEC report (3),a fact presumably unknown to the authors. However, this error can not explain the discrepancy between our results, since the bias is in the wrong direction. Certainly, part of the discrepancy between our results and those of Kramer et al. (11)is due to the lower pH end points for the MO titration chosen by Kramer et al. (11). The lower end point of 4.04 lies outside the 95% confidence limits (4.15-4.35) of our study, and Kramer et al’s citation of Kolthoff and Stenger (25)to support this low end point is inconsistent since Kolthoff and Stenger (ref 25, p 53) give pH 4.4 as the beginning of the MO color transition range. Nevertheless, we find significant acidification of the lakes (a < 0.01) even if we apply the pH 4.04 correction of Kramer et al. (11) to our larger data set, indicating that our conclusions are not highly sensitive to the assumed pH end point for the MO titration. After careful evaluation, we believe that several assumptions in Kramer et al.’s (11)use of colorimetric pH data to both screen and adjust the alkalinities are in error. For example, Kramer et al. (11) attempted to correct historic colorimetric pH data by first assuming which of the several indicators was used in the analysis of each lake. This assumption is unreasonable since the procedure was not recorded and cannot be assumed as the pH ranges of the indicators overlap. Furthermore, Kramer e t al. (11) assumed the Hellige indicator solutions for measuring pH were in an alkaline, “neutral” (p 472) form, and were not adjusted to the appropriate pH range. This assumption is not supported by information from the Hellige Co. (26) and this results in data for adjusted pH to be biased low. As a consequence, 47.6% (pH 4.19 end point) to 60.9% (pH 4.04 end point) of the lakes in the historic data set were judged by Kramer et al. (11)to have inconsistencies between the adjusted pH data and the measured alkalinity and C 0 2 acidity. Kramer et al. (11)then removed these lakes with apparent inconsistencies from the original data set, resulting in a major truncation in the distributions [compare Kramer et al. ( I I ) , Figure 7.13a, with our Figure 11. The remaining data were further biased when Kramer et al. (11) averaged the measured historic alkalinity with an estimate based on the erroneously adjusted pH and C02 acidity. These biases, when combined with the previously discussed low MO end point at pH 4.04, are likely to have led to the nonsignificant results of their analysis. Thus, we believe our straightforward approach, which focuses on alkalinity rather than pH, gives a more robust and accurate estimate of acidification in the Adirondack Mountain region. The differences in acidification among lakes of the six major drainages (Figure 2) probably are due to a variety of factors, including regional differences in atmospheric deposition as well as differences between lakes themselves and differences in hydrologic, geologic, and edaphic conditions in the catchment areas. Modern precipitation acidity in the region is -63 pequiv/L with an increasing trend to the southwest (27). Precipitation and runoff also increase toward the southwest ( 3 ) ,and it is here, in the Mohawk-Hudson drainage region, where we found the greatest acidification (Figure 2). The magnitude of acidification in any given lake may be even greater than that suggested by the precipitation acidity if dry deposition contributes additional acidity and the resultant solution is further concentrated by evapotranspiration (28). In calcareous regions changes in lake alkalinity may be minor or possibly could increase if biologically generated alka364
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linity were sufficiently large (29). Such processes would be more likely to occur in the eastern Adirondacks, where the soils contain about twice the calcium content as soils in the western Adirondacks (30). Sensitivity of lakes to acidification has been related to crystalline bedrock and thin acid soils (4,31),which are generally associated with high-elevation lakes. Our data show a direct relationship between the mean lake elevation and the mean acidification for lakes in each of the major drainages. Recent reports suggest that dry periods may increase lake alkalinity (12,32, 33). This factor may account for some of the variability between drainage regions, since they were sampled in different years in the early survey. For example, the two drainage regions that show the greatest acidification, the Raquette and the Mohawk-Hudson, were sampled during two of the driest summers (1933,1934) on record for Lowville, NY (34). After careful evaluation of the relationship of recent lake alkalinity to precipitation in the Adirondack region (35),and a comparison of both historic and modern precipitation records (34),we do not believe that variations in precipitation alone can explain the acidification of lakes over the 50-year period. The lakes sampled during the dry summers of 1933 and 1934 are offset by lakes sampled during wet summers earlier in the survey (1929-1932), and the modern surveys included both wet and dry summers.
Conclusions Because atmospheric deposition, hydrology, and edaphic conditions are interrelated, we cannot gauge their relative effects from this analysis. However, the general pattern and magnitude of acidification in the Adirondack Mountain region during this 50-year period is consistent with anthropogenic inputs of acids from atmospheric deposition, and these results support the earlier studies (2, 3, 6-8) showing the consequent changes in the natural biota of these lakes that have been attributed to anthropogenic acidification. Acknowledgments We thank, L. 0. Hedin, C. T. Driscoll, and two anonymous reviewers for their comments on the manuscript.
Literature Cited Schofield, C. L.; Driscoll, C. T. Biogeochemistry 1987, 3, 67. Schofield,C. L. In Acid RainlFisheries; Johnson, R., Ed.; American Fisheries Society: Bethesda, MD, 1982; p 57. Pfeiffer, M. H.; Festa, P. J. Acidity Status of Lakes in the Adirondack Region of New York in Relationship to Fish Resources; New York State Department of Environmental Conservation, Albany, NY, 1980. Hendrey, G. R.; Galloway, J. N.; Norton, S. A,; Schofield, C. L.; Shaffer, P. W.; Burns, D. A. Geological and Hydrochemical Sensitivity of the Eastern United States to Acid Precipitation; U.S. Environmental Protection Agency. U.S. Government Printing Office: Washington, DC, 1980; EPA-60013-80-024. Kretser, W. A.; Colquhoun, J. R.; Pfeiffer, M. H. T h e Conservationist 1983, 37(5), 22. Hendrey, G. R.; Vertucci, F. A. In Proceedings of a n International Conference on the Ecological Impact of Acid Precipitation, Drablos, D.; Tollan, A,, Eds.; SNSF Project, P.O. Box 61, 1432 As-NLH; Norway, 1980; p 314. Charles, D. F. Verh. Int. Ver. Theor. Angew. Limnol. 1984, 22, 559. Confer, J. L.; Kaaret, T.; Likens, G. E. Can. J.Fish. Aquat. Sei. 1983, 40, 36. Galloway, J. N.; Likens, G. E. Limnol. Oceanogr. 1979,24, 427.
Henriksen, A. Nature 1979, 278, 542.
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Kramer, J. R.; Andren, A. W.; Smith, R. A.; Johnson, A. H.; Alexander, R. B.; Oehlert, G. In Acid Deposition: Long Term Trends; National Research Council; National Academy Press: Washington, DC, 1986; p 231. Biological Survey of the Champlain Watershed, 1929; St. Lawrence Watershed, 1930; Oswegatchie and Black River Systems, 1931; Upper Hudson Watershed, 1932; Raquette Watershed, 1933; Mohawk-Hudson Watershed, 1934; New York State Conservation Department: Albany, NY, 1929-1934. Lake Survey; Adirondack Lake Survey Corp., New York State Department of Environmental Conservation: Albany, NY, 1984-1985; Vol. 1-10. Characteristics of Lakes in the Eastern United States; U.S. Environmental Protection Agency. US.Government Printing Office: Washington, DC, 1986, EPA/600/4-86/007; Vol. 1-3. Colquhoun, J. R.; Kretser, W. A.; Pfeiffer, M. H. Acidity Status of Lakes and Streams in New York State; New York State Department of Environmental Conservation: Albany, NY, 1984. Haines, T. A,; Akielaszek, J. J.; Norton, S. A.; Davis, R. B. Hydrobiologia 1983, 107, 57. Stumm, W.; Morgan, J. J. Aquatic Chemistry, 2nd ed.; Wiley: New York, 1981; pp 184-188. Baker, J.; Harvey, T. Critique of Acid Lakes and Fish Population Status in the Adirondack Region of New York State; draft final report, NAPAP Project E3-25, U S . Environmental Protection Agency. U.S.Government Printing Office: Washington, DC, 1985. Pfeiffer, M. H. Department of Environmental Conservation, Raybrook, NY, personal communication, 1986. Standard Methods, 13th ed.; American Public Health Association: New York, 1971. Standard Methods, 4th ed.; American Public Health Association: New York. 1926.
Standard Methods, 6th ed.; American Public Health Association: New York, 1930. Wetzel, R. G.; Likens, G. E. Limnological Analyses; Saunders: Philadelphia, PA, 1979. Kramer, J. R.; Tessier, A. Environ. Sci. Technol. 1982,16, 606A. Kolthoff, I. M.; Stenger, V. A. Volumetric Analysis; Wiley: New York, 1947; Vol. 11. Esposito, J., Chemist, Hellige Co., New York, personal communication, 1985. Stensland, G. J.; Whelpdale, D. M.; Oehlert, G. In Acid Deposition: Long Term Trends; National Research Council; National Academy Press: Washington, DC, 1986; p 128. Reuss, J. 0.;Johnson, D. W. J. Enuiron. Qual. 1985,140) 26. Kilham, P. Limnol. Oceanogr. 1982,27(5)856. Heimberger, C. C. Forest-Type Studies in the Adirondack Region; Memoir 165; New York State Agricultural Experiment Station, Cornel1 University: Ithaca, NY, 1934. Acid Deposition: Processes of Lake Acidification; National Research Council, National Academy Press: Washington, DC, 1984. Rapp, G., Jr.; Allert, J. D.; Liukkonen, B. W.; Ilse, J. A.; Loucks, 0. L.; Glass, G. E. Environ. Int. 1985, 11, 425. Peters, N. E.; Driscoll, C. T. Biogeochemistry 1987,3, 163. North East Climate Data Center, Cornell University, Ithaca, NY. Unpublished data. Mattson, M. D.; Driscoll, C. T. In preparation. Received for review June 9, 1988. Accepted October 24, 1988. We gratefully acknowledge the financial support of the Mary Flagler Cary Charitable Trust and the Andrew W. Mellon Foundation. A Contribution to the program of the Institute of Ecosystem Studies, The New York Botanical Garden.
Uptake of Airborne Tetrachloroethene by Spruce Needles Hartmut Frank" and Wllfrled Frank Institut fur Toxikologie, Wilhelmstrasse 56, D-7400 Tubingen, Federal Republic of Germany
Tetrachloroethene in spruce needles is quantitatively determined by extraction with hexane, separation by capillary gas chromatography, and detection by chemicalionization mass spectrometry, monitoring the negatively charged chlorine ions. Needle samples from spruces growing in forests and in a city in Southwest Germany and from spruces in exposure chambers have been analyzed; concurrently, the respective air levels have been determined. The concentrations in the needles are correlated to atmospheric levels; below an air concentration of 5 pg/m3, the partition ratio is 520, above it is 50. Introduction
C1 and C2 halocarbons are widely used as solvents in textile and metal industries. During application they escape into the atmosphere, the extent of which is estimated to be -70%. Due to their relatively long atmospheric lifetimes (1) they are transported into rural areas, considered as "clean-air regions" in respect to the air pollutants NO, and SOz. The atmospheric levels of halocarbons in rural areas are 3-5 times lower than over urban centers (2),but sometimes relatively high values may occur in rural air (3). It has been suggested that reactive intermediates of halocarbons generated by photochemical processes may be involved in the phytotoxicological phenomena of forest decline ( 4 ) ,which is most serious in remote areas. 0013-936X/89/0923-0365$01.50/0
An important feature of the less volatile halocarbons is their great lipophilicity (5);as shown in model experiments, they may be enriched in lipids and waxes of cuticles and cellular membranes (6) due to their large partition ratios (Ostwald solubility coefficients), e.g. 2000 (22 "C) for tetrachloroethene. Lipids represent -5% of the weight of a 1-year-old needle, so relative to needle weight partition ratios of 100 are to be expected. The goal of the present study is to ascertain whether this is also true for needles of trees exposed to tetrachloroethene at concentrations in their natural environment, or at levels as they are used in exposure chamber experiments. Tetrachloroethene concentrations have been determined in spruce needles (Picea Abies excelsa) from trees in the Black Forest, from trees growing in the city of Tubingen, and from 8-year-old spruces exposed in chambers to controlled air concentrations of tetrachloroethene. Air samples a t all three locations were taken a t the same time and analyzed for halocarbons. Atmospheric concentrations were determined as described previously (7); for determination of tetrachloroethene in needles, the more selective detection by negative-ion chemical-ionization mass spectrometry was employed.
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Experimental Section Sample Preparation. Culture tubes (8.5 X 100 mm) equipped with screw caps lined with Teflon-laminated rubber seals and disks of polished aluminum foil, thickness
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