Acid Deposition Long-Term Trends (1986) / Chapter Skim
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9. Paleolimnological Evidence of Trends in Atmospheric Deposition of Acids and Metals
9. Paleolimnological Evidence of Trends in Atmospheric Deposition of Acids and Metals
Pages 335-434
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From page 335... ...
S Norton prepared the sections on chemical stratigraphy of lake sediments and peat bogs.
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sediment to more than 20 years for lakes with slow sedimentation rates. Several components of sediments provide information on factors related to lake acidification.
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. Stratigraphic analysis of fossil diatom assemblages can be used to investigate changes in lakes resulting, for example, from shifts in climate, development of watershed soils and vegetation, local human disturbance of watersheds, and acid deposition (e.g., Battarbee 1979, 1984, Pennington 1981, Fritz and Carlson 1982, Brugam 1983, 1984, Del Prete 1972)
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, (4) calibration data sets (the current relationship between water chemistry and surface sediment diatom assemblages)
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He recognized the strong relationship between diatom distributions and lake-water pH and defined the following pH occurrence categories: Acidobiontic -- optimum distribution at pH below 5.5 Acidophilic -- widest distribution at pH less than 7 Circumneutral/indifferent -- distributed equally above and below pH 7 Alkaliphilic -- widest distribution at pH greater than 7 Alkalibiontic -- occurs only at pH greater than 7 Assignments of diatom taxa to these categories can be based on literature references and on the distribution of taxa within waters of particular geographic regions. Changes in the percentages of diatom valves in each pH category in a sediment core can be used to estimate trends in lake-water pH.
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Predictive equations can also be developed from multiple linear-regression analysis of measured lakewater pH with the percentages of diatoms in each pH category (e.g., Davis and Anderson 1984, Charles 1985a, Figure 9.2)
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. 8 -amp ~ ^1: 1 ~ -4 -3 -2 -1 0 1 2 3 L°G1 0 0t 4 oo FIGURE 9.1 Logarithm of Nygaard's alpha index for surface sediment diatom assemblages versus lake surface water pH (Norton et al.
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versus measured surface pH for 37 Adirondack lakes. The dashed lines represent the 95 percent confidence intervals for an individual prediction of pH from diatom data (Charles 1985a)
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Evaluation of Lake Acidification Causes Diatom and chrysophyte data can be used not only to infer the past pH trend of a lake but in many cases to suggest the causes of the changes. There are three major potential causes of acidification of relatively undisturbed, acid-sensitive lakes in eastern North America: (1)
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; Berry Pond, Massachusetts (Rochester 1978) ; Heart Lake, Upper Wallface Pond, and Lake Arnold in the Adirondack Mountains, New York (Reed 1982; Whitehead et al.
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-' I~,~ _7~'mp . 1 4.5 5.5 6.5 7.5 AVERAGE INFERRED pH FIGURE 9.3 Weighted average diatom-inferred pHs for Heart Lake, Upper Wallface Pond, and Lake Arnold, Adirondack Mountains High Peaks Region.
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Watershed Disturbance Logging, fire, blowdown, and similar disturbances can potentially change lake pH and alkalinity, although there is evidence that these changes are often relatively minor and short lived (Rosenqvist 1978, Gorham et al. 1979, Wright 1981, Nilsson et al.
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From page 347... ...
This could occur if the appropriate sediment interval representing the disturbance time were not analyzed or if altered diatom and chrysophyte assemblage composition were not discernible because of sediment mixing or some other factor. Atmospheric Deposition of Strong Acids Precipitation containing excess strong acids is falling on large areas of eastern North America (Chapter 5)
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This effect, in and of itself, can cause changes in the composition of diatom assemblages. Atmospheric Deposition of Strong Acids Lake acidification can be attributed to acid deposition if (1)
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Fourth, assessments of regional acidification trends should be based on studies of several lakes within a region. ASSESSMENT OF RECENT LAKE ACIDIFICATION TRENDS IN EASTERN NORTH AMERICA To evaluate recent acidification trends in eastern North America, 27 diatom data sets meeting minimum criteria were assembled and reviewed.
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2. Minimal or, if not minimal, well-known watershed disturbance or influence from local emission sources, industrial effluents, or other factors.
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5. Quality of sediment dating and the availability of data for other sediment characteristics related to acid deposition and lake acidification.
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The surface sediment diatom flora suggest more acidic conditions than do the pre-1800 flora. Changes in sediment diatom assemblage composition in New England lakes indicate recent acidification (Norton
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~ ~ · ~ ~ 6.0 6.5 ~ 5 -10 -15 _20 -30 -35 INDEX + SD - MR 0.28 B 033 ....... ct 0.33 ~ 95% Cl 0.40 FIGURE 9.5 Profiles of inferred pH from Big Moose Lake (core 2)
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bracYsira, and diatom 3, Cyclotella stelligera, represent the dominant taxa in the core and occurred in subsets of 38 study lakes with mean pH values of 4.8, 5.9, and 6.8, respectively (Charles 1984)
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. data are useful and are included here because they provide further evidence that sediment diatom assemblages can indicate changes caused by increased deposition of strong acids.
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The differences in diatom assemblages are generally
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. Recent studies of surface sediment diatom assemblages of lakes in the Killarney region of Ontario show that euplank sonic Cyclotella species are common in lakes with a pH less than 5.5.
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, clearwater lakes with pH less than 5.5 are rare. However, in these regions and in regions now receiving excess acid deposition there are lakes that have pH less than 5.5 and are moderately to highly colored (platinum-cobalt units > 25)
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. The increase in percentages of diatom taxa such as Stauroneis gracillima and Fragilaria acidobiontica toward the top of some Adirondack lake sediment cores suggests that recent increases in aluminum concentration may have occurred.
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In reality, patterns of pa decrease probably represent a continuum, but the above cases are likely typical of most responses. Evaluation of Trends in Acid Deposition Trends in diatom-inferred pH can be used to evaluate hypotheses concerning trends in acid deposition for eastern North America.
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Big Moose Lake represents the best case of an acidified lake in which increased acid deposition is the only reasonable cause to which recent acidification can be attributed. Diatom related changes in other lakes, such as Upper Wallface Pond and Deep Lake, are greater than would generally be expected from natural variation and are also probably due primarily to increased acid deposition, although watershed disturbance may play a minor role.
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From page 362... ...
. Ronald Davis and Dennis Anderson of the University of Maine and other investigators are completing analysis of diatom assemblages from sediment cores of three Adirondack lakes (Panther, Sagamore, and Woods)
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. Chrysophyte assemblages in surface sediments of many lakes in eastern Canada are being studied also (J.
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Diatom and Chrysophyte Ecology Interpretation of diatom data is limited by a lack of complete knowledge of diatom autecology, including information on habitats, seasonality, and relationships to water chemistry characteristics. More information on how diatoms and chrysophytes interact among themselves and with other organisms would help to explain seasonal and long-term successional patterns.
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Recommendations: 1. Perform more field work to determine how diatoms and chrysophytes are transported to lake sediments and which taxa or types of diatoms tend to be overestimated or underestimated within the sediments.
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They do not account for characteristics of assemblages in sediment cores being analyzed. Error
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the study lakes are well buffered and have changed little in alkalinity or diatom composition even though atmospheric loading of acids may have increased substantially; (2) there was a major watershed disturbance, such as fire, logging, and cultural development, that obscures the relationship between acid deposition and the watershed changes as causes of acidification; and (3)
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Interpretations of diatom and chrysophyte data with respect to changes in acid deposition (or other factors influencing lake-water acidity) should account for limnological processes (e.g., sediment buffering, sulfate reduction in the hypolimnion and sediments, and change in organic acids)
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Physical, biological, and chemical processes in the lake sequester a fraction of the flux of these pollutants in lake sediments. In the absence of long-term, regional studies of atmospheric fluxes and deposition of pollutants the chemistry of lake sediments may serve as one of the few surrogate indicators of atmospheric pollution.
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. Also, lakes with greatly increased deposition rates caused by accelerated erosion and deposition with no accompanying
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1981) and may have high sedimentation rates but low deposition rates.
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) , subsampling of the sediment, dating of the sediment, chemical analysis of the sediment, and drainage-basin and lakebasin processing of atmospheric pollutants make it difficult to reconstruct precisely historic atmospheric deposition rates from net deposition rates.
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deposition rates, trends in deposition in sediments may be observed. The types of data gathered for sediment chemistry are variable but include the following: 1.
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This can be done only for chemically immobile elements, such as lead, and in sedimentary environments with little mixing. Secondary effects of acid deposition may affect the sedimentary record.
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(1982) found that in dated cores from lakes proximal to the smelter the variations in concentrations (and also deposition rates)
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Researchers study this type of lake assuming that changes in sediment chemistry could be assigned unambiguously to changes in atmospheric chemistry. One of the earliest studies of heavy metals in sediment cores from remote lakes was made by Iskandar and Keeney (1974)
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(1978) , using sediment chemistry of pollendated cores from New England lakes ranging from culturally eutrophic to pristine and oligotrophic, suggested that the ubiquitous rise in the concentration of zinc in lake sediments in the 1800s could best be explained as having been caused by atmospheric deposition.
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This was the first serious attempt at evaluating atmospheric deposition rates of trace metals from analysis of lake sediments. At about the same time, in Quebec, Ouellet and Jones (1983)
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1.60 _ a' 1.20 _ ~ 0.80 _ 0.40 _ 0.00 G E E E Q Q CD a, I {:L CL a LO 1O DATE DEPTH (cm) FIGURE 9.11 Sediment chemistry from lakes Tantare and Laflamme, Quebec, Canada (from Ouellet and Jones 1983)
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CONCENTRATION VS. YEAR FIGURE 9.12 Sediment chemistry from Jerseyfield Lake, Adirondack Mountains, New York.
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. over a range of about 100 percent, suggesting significant atmospheric input and retention of the atmospherically derived metals.
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17.5m 1 1 1 1 1.0 1.5 2.0 2.5 CDMA (g/cm2) FIGURE 9.14 Zinc concentrations versus CDMA (cumulative dry mass (of sediment)
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This selection of representative data from the remote lakes of eastern North America demonstrates the influence of an improving analytical technology on the evolution in our understanding of the record of changing atmospheric deposition of heavy metals as revealed in lake sediments. Neither the concentration nor the deposition rates of the heavy metals can be directly related to the acidity of precipitation, however.
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385 50 >lo, By Cal 'Ct o C)
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These studies are also not yet sufficiently developed to be useful in studying trends in deposition. A number of solid products are formed and injected into the atmosphere as a result of the combustion of fossil fuels.
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Renberg and Wik (1984) have found similar trends and used their results to develop a chronology, using soot particles, in varved lake sediments in Sweden.
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and Tan and Heit (1981) reported biogenic and anthropogenic PAHs in sediment cores from two relatively pristine lakes in the Adirondack Mountains of New York.
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390 7 6 5 4 N 3 2 o 1800 1 820 1840 1860 1880 1900 1 920 1940 1960 1 982 210Pb DATE Pb I_/ _ — 1 1 1 1 1 300 200 1 Cat 100 PAH TV in/ \_\ OL I ~ I I I I I I 1 800 1820 1840 1860 1880 1 900 1 920 1 940 1 960 1 982 210Pb DATE FIGURE 9 .17 PAH and lead deposition rates for a core from Big Moose Lake, New York (lead data from Norton, unpublished; PAH data, courtesy of R Hites, Indiana University, Bloomington, unpublished)
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If the loss of metal is predepositional and not caused by post-depositional diagenesis of sediment, trends in zinc, calcium, and manganese sediment deposition rates, if they are independent, may be useful in tracking the process of lake acidification. Peaks in concentration and apparent deposition rates of zinc below the surface sediment in acidic lakes may be related partially to sulfate reduction in the sediment and precipitation of zinc sulfide below the sediment/ water interface, i.e., in older sediment.
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Evidence for the actual acidity of precipitation cannot be inferred from the chemistry of sediments but decreases in the pH of aquatic systems are suggested by recent declines (relative to immobile elements) in the deposition rates of elements mobilized by increasing lake-water acidity.
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Analysis of data in the literature for Scandinavia (Pakarinen 1981a) suggests that over the decades of the 1960s and 1970s, metal concentrations increased in mosses/lichens, implying that atmospheric deposition rates increased, too.
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1 .... ~ ..,, 1 0 2000 PPM DRY FIGURE 9.18 Chemistry of a hollow peat core from Big Heath, Mount Desert Island, Maine.
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40 50- . ~ ' 0 100 PPM DRY 0 2000 PPM DRY FIGURE 9.19 Chemistry of a hummock peat core from Big Heath, Mount Desert Island, Maine.
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activity in a hummock peat profile, Bull Hummock, in Bull Pasture Plain, New Brunswick (August 29, 1981) (from Olson 1983)
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Dating methods include pollen stratigraphy; chronostratigraphic markers, such as charcoal, cesium-137, and lead-210; increment dating; and magnetic stratigraphy. Pollen stratigraphy and the use of charcoal are typically imprecise for dating purposes because atmospheric particulate material can penetrate through the living surface into older peat.
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Consequently, the chronology of trends in peat chemistry, and thus inferred changes in atmospheric deposition of metals as well as net deposition rates, are imprecise. Madsen (1981)
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has dated, by lead-210, and chemically analyzed 10 pairs of cores from adjacent hummock-hollow associations from ombrotrophic bogs in Maine. Only cores from hollows have heavy-metal stratigraphy and deposition rates, especially for lead and zinc, that resemble those of lake sediments in the eastern United States (Figure 9.22)
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The metals lead and zinc r however, are known to be transported in large proportions for hundreds to a few thousands of kilometers. Thus, cores may give information about both short- and long-range transport of atmospheric pollutants.
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- -. 0 10 20 30 40 50 60 70 80 Depth, cm FIGURE 9.23 Magnetic and chemical stratigraphy from a hummock peat core (1982)
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Big Moose Lake Deep Lake Panther Lake Sagamore Lake Woods Lake Branch Pond, Vt.
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IGN 50 CONCENTRATION VERSUS DEPTH (cm) FIGURE 9.24 Sediment chemistry of Lake Husted, Rocky Mountain National park.
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For Big Moose Lake, analyses of data on diatoms, chrysophytes, and sediment chemistry all indicate recent acidification (Appendix Table E.5; Figures 9.5 to 9.7, and 9.25)
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. Unpublished data from S
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The diatom-inferred pa also suggests that pH had been declining slowly since at least the early 1800s, possibly resulting from long-term gradual acidification from natural processes. Sediment chemistry data (Figures 9.25 and 9.26)
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This untested model would explain the observations of relatively invariant diatom-based pH with a concurrent decline of sediment deposition rates for calcium, manganese, and zinc (relative to TiO2 and A12O3) caused by leaching of particulates on the land before deposition; increased water clarity; and hydrogen-, calcium-, aluminum-, and sulfate-rich waters.
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From page 408... ...
Deposition rates (not shown) of of the diatom assemblages at the top of the Panther Lake core, in light of recent taxonomic revisions, indicates a significant percent of the Melosirae should be reclassified as indifferent rather than acidophilic, and the diatom-inferred pH decrease may not be as great as first determined (D.
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From page 409... ...
Diatom and chrysophyte data for 31 lakes were evaluated to assess regional trends in lake acidification. The lakes in each region (Adirondack Mountains, eleven; New England, ten; eastern Canada, six; and the Rocky Mountains, four)
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6. Analysis of the three lakes in the Adirondacks (Big Moose Lake, Deep Lake, and Upper Wallface Pond)
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Interpretations of lake acidity and atmospheric deposition changes based on stratigraphic analysis of both diatom assemblages and sediment chemistry are generally consistent. REFERENCES Alhonen, P
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1983. Comparative water chemistry of four lakes in Rocky Mountain National Park.
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1983. The relationship between fossil diatom assemblages and limnological conditions.
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1985a. Relationships between surface sediment diatom assemblages and lakewater characteristics in Adirondack lakes.
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1980. Atmospheric deposition in Norway during the last 300 years as recorded in SNSF lake sediments II.
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1981. The utility of diatom analysis of lake sediments for evaluating acid precipitation effects on dilute lakes.
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Pp. 55-75 of Geological Aspects of Acid Deposition, O
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From page 418... ...
1979. Atmospheric enhancement of metal deposition in Adirondack Lake sediments: Limnol.
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1983. Diatom assemblages in East Africa: classification, distribution and ecology.
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From page 420... ...
1974. Concentration of heavy metals in sediment cores from selected Wisconsin lakes.
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1980. A comparison of dating methods in laminated lake sediments in Maine.
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Pp. 23-35 of Geologic Aspects of Acid Deposition, O
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1983. Sediment chemistry of four lakes in Rocky Mountain National Park, Colorado.
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1981. Responses of northern New England lakes to atmospheric inputs of acids and heavy metals.
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1981. History of particulate atmospheric pollution from magnetic measurements in dated Finnish peat profiles.
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1983. Paleolimnological evidence for the long-range atmospheric transport of acidic pollutants and heavy metals into the Province of Quebec, eastern Canada.
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1981. Distribution and chemical forms of heavy metals in sediment cores from two Norwegian lakes affected by acid deposition.
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1976. Post-pleistocene diatom assemblages in New England lake sediments.
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1984. Alteration of fish communities in lakes stressed by acid deposition and heavy metals near Wawa, Ontario.
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1980. Polycyclic aromatic hydrocarbons in recent lake sediments.
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1982. Diatom assemblages in lacustrine sediments of Lake Shibu-ike, L
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