Acid Deposition Long-Term Trends (1986) / Chapter Skim
Currently Skimming:
1. Summary and Synthesis
1. Summary and Synthesis
Pages 1-47
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 1... ...
A wide variety of effects have been attributed to acid deposition, its gaseous precursors, and certain products of their chemical reactions including ozone. Possible environmental consequences include adverse effects on human health, acidification of surface waters with subsequent decreases in fish populations, the acidification of soils, reduced forest productivity, erosion and corrosion of engineering materials, degradation of cultural resources, and impaired visibility over much of the United States and Canada.
|
From page 2... ...
Some of the questions asked about the spatial relations of acid deposition and related phenomena were the following: Is the deposition of acidic sulfates and nitrates highest in areas where densities of emissions of sulfur and nitrogen oxides are highest? Are patterns of ecosystem changes attributed to acid deposition also .
|
From page 3... ...
In some cases however, longer and more extensive records do exist for systems thought to be affected by acid deposition or its airborne precursors. These records include long-term data on visibility, chemical composition of waters in lakes and streams, chemical and biological composition of lake sediments, fish populations, Growth patterns in trees as evidenced in ring widths, distributions of lichens, erosion of tombstones, and chemical composition of glacial ice cores, groundwater, and soils.
|
From page 4... ...
These data permit spatial analyses of the chemistry of wet deposition in the region, but the time period of this record is not sufficiently long to establish statistically significant temporal trends. Time series of longer duration, dating from the early to the middle 1960s, are available at a few sites, however, and we have performed trend analyses on some of these data.
|
From page 5... ...
Some tree ring data are available for red spruce populations in the higher elevation forests of the northern Appalachian Mountains. It became apparent during the evaluation processes that we would not be able to rely exclusively on the published literature if we were to meet our goal of examining spatial patterns or temporal trends of multiple phenomena.
|
From page 6... ...
From this result and because of the existence of plausible mechanisms linking the phenomena, we conclude that in eastern North America a causal relationship exists between anthropogenic sources of emissions of SO2 and the presence of sulfate aerosol, reduced visibility, and wet deposition of sulfate. Our analysis also indicates that for Bench-Mark streams in watersheds showing no evidence of dominating internal sources of sulfate there is a cause-and-effect relationship between SO2 emissions and stream sulfate fluxes.
|
From page 7... ...
Changes in sulfate observed in Bench-Mark streams are consistent with changes in SO2 emissions on a regional basis. Analysis of a sulfur mass balance for 626 lakes in the northeastern United States and southeastern Canada demonstrates that the sulfate output from lakes in general is proportional to sulfate inputs in wet deposition.
|
From page 8... ...
Sulfate concentrations in wet-only deposition in the region of the Adirondack Mountains and sulfate concentrations in Adirondack lakes are relatively high in comparison with those in other areas in the northeastern United States and southeastern Canada. We have demonstrated that increasing sulfate in surface waters is associated with decreasing alkalinity in low-alkalinity surface waters.
|
From page 9... ...
10. Geographically widespread reductions in tree ring width and increased mortality of red spruce in highelevation forests of the eastern United States began in the early 1960s and have continued to the present.
|
From page 10... ...
Continuing the earlier example, sulfate and nitrate in wet deposition have a clear, consistent relationship, but neither experiment nor mechanism implicates changes in one as causing changes in the other. In fact, we know that they both arise from a common source, the high-temperature combustion of fossil fuels (National Research Council 1983)
|
From page 11... ...
The figure does not depict all the possible environmental interactions of sulfur and nitrogen oxides or the many possibilities for their ultimate fates. It does, however, indicate relationships among the phenomena examined in this report: emissions, visibility, chemistry of precipitation, chemistry of lake and stream waters, fish populations, forests, and chemical and biological stratigraphy of lake sediments.
|
From page 12... ...
While other types of airborne particles including moisture, carbonaceous particles, and road dust cause visibility reductions, sulfate aerosol is believed to account for a large fraction of the observed effect in the eastern United States, and in some areas visibility reduction may be the most directly observable effect resulting from emissions of sulfur dioxide. (See Chapter 4.)
|
From page 13... ...
in wet and dry deposition are related to sulfur and nitrogen oxide emissions, while the "acidity" of wet deposition is the result of concentrations of both acidic compounds (i.e., strong acids (nitric and sulfuric acids) as well as weak organic acids)
|
From page 14... ...
In general, lakes and streams in watersheds having hydrologic flow paths through highly acidic soils are expected to match an increase in sulfate concentration with a higher proportion of acid cations (H+ and A1+3) , thereby reducing surface water alkalinity.
|
From page 15... ...
Changes in atmospheric chemical inputs to soils can modify leaching rates of certain chemical species from the terrestrial environment that serve as inputs to surface waters. ~ Additionally, many constituents deposited from the atmosphere, both solids and liquids, may be incorporated directly into accumulating sediment.
|
From page 16... ...
. Concentrations of these metals typically are low in lake sediments in unpolluted regions and increase in more densely populated regions.
|
From page 17... ...
and components of fly ash. Although these trace substances are not so direct a measure of acid deposition as are the measurement of sulfur and nitrogen oxides, their presence in elevated concentrations in lake sediments is indicative of emissions from the same sources.
|
From page 18... ...
can reach toxic concentrations in sufficiently acidified surface waters. Factors unrelated to acidity such as chances in stocking policy, beaver activity, or intensified sport fishing may affect fish populations.
|
From page 19... ...
Thus, for example, a sustained increase in SO2 and Ned emissions on a wide geographic basis may result in a number of responses, including reduced visibility, increased concentrations of sulfate and nitrate in precipitation and surface waters, and increased deposition in lake sediments of other pollutants associated with these same emissions sources. A premise of this study is that simultaneous examination of trends and spatial patterns in all the relevant phenomena may help to establish further evidence of linkages despite the complicating factors that may frustrate interpretation of data about a single phenomenon.
|
From page 20... ...
Measurements have shown that dry deposition is an important fraction of total deposition in areas close to point sources. It is suspected that in some ecosystems, particularly in forested areas where the forest canopy may serve as an efficient collector of dry sulfate, net dry sulfate deposition may be equal to or greater than wet-deposited
|
From page 21... ...
Such disparity may cause confusion in interpreting historical trends. SPATIAL PATTERNS AND TEMPORAL TRENDS Regions It was helpful in our analyses to define six specific geographical regions in eastern North America (Figure 1.2)
|
From page 22... ...
Eastern Ontario, New Brunswick, FIGURE 1.2 Designated regions for analysis of temporal trends and regional patterns.
|
From page 23... ...
To test for possible spatial associations, we first compared the magnitudes of various parameters on a regional scale. For example, Figure 1.3 shows that the areas of highest SO2 emission density are, in general, areas where the concentrations of sulfate and hydrogen ions in wet deposition are highest.
|
From page 24... ...
in wet deposition; (d) concentration of sulfate aerosol (pg/m3)
|
From page 26... ...
. In a different type of analysis, we examined the spatial association between sulfate in wet precipitation and sulfate in 626 lakes in the northeastern United States and southeastern Canada (Chapter 7)
|
From page 27... ...
Regions where lakes demonstrate the greatest excess of sulfate output (mi > 1) , suggesting that wet deposition accounts for only part of the sulfate input, are those nearest to large emission sources (CT-MA-RI, NY, ME-NH-VT)
|
From page 28... ...
log x axis 0.5 1.0 1.5 ·.~ . \ a-' m j = -0.004 NF loo x axis 1 1 1 0.0 0.5 1.0 1.5 LOG SULFATE INPUT (9 m~2 yr~1 ~ FIGURE 1.4 Regional relationships between the log of sulfate flux into lakes from wet deposition and the log of sulfate flux out of lakes from outflow.
|
From page 29... ...
Surface waters in these areas tend to have low alkalinity and receive relatively high inputs of atmospheric deposition of sulfate and nitrate. Although data are sparse, well-documented fish declines have occurred in a few locations in lakes of the Adirondack Mountains and in rivers of Nova Scotia, waters that have experienced increases in acidity thought to be caused by acid deposition.
|
From page 30... ...
However, they demonstrate strong regional association in spatial patterns among density of SO2 emissions, atmospheric concentrations of sulfate, range of visibility, concentration of sulfate in wet precipitation, and fluxes of sulfate in Bench-Mark streams. Temporal Trends The Record Since Industrialization (about 1880)
|
From page 31... ...
Coal Consumption Regions (B.
|
From page 32... ...
YEAR Big Moose Lake Sediment Conc.
|
From page 33... ...
5.0 4.5 1 .4 X UJ Z 1.2 A CC ink' 1.0 0.8 0.6 (9) 29 27 25 23 F 21 19 17 15 13 Big Moose Lake Adirondacks 6.0 ~ Reconstructed pH / smallmouth bass lost lake whitefish lost —longnose sucker lost ~ lake trout lost 1 1 1 1 1 1 1 780 V 1 880 1 900 1 920 6.0 1 1 1 1 1 4.5 1 940 1 960 1 980 YEAR Red Spruce at Lake Arnold Ad irondacks telex.
|
From page 34... ...
demonstrates that the most rapid rate of increase in coal consumption in the eastern United States (Regions B through E) and the northeastern United States (Region B)
|
From page 35... ...
Ring width in red spruce is affected by winter temperatures, and the onset of the decline at Lake Arnold and elsewhere coincided with the occurrence of cold winters in the northeastern United States, as demonstrated in the temperature record in New England in Figure 1.5(g)
|
From page 36... ...
Any interpretation of changes in alkalinity and pH in New York lakes based only on water chemistry data is somewhat equivocal because the calculations are sensitive to the value assumed for the pH of the endpoint of the methyl orange (MO) indicator, a standard chemical used in the determination of historical lake alkalinities.
|
From page 37... ...
Relationship of Trends in Diatom-Inferred pH and Fish Populations Analysis of diatoms in sediments of selected lakes offers another indication of long-term acidification. Unlike the lake surveys in Wisconsin, New York, and New Hampshire, the lakes from which diatom data were obtained were selected on the basis of acid sensitivity (i.e., alkalinity less than 200 peq/L)
|
From page 38... ...
The lakes with current values of pH of about 5.2 or less have become more acidic in recent times and have lost fish populations, whereas lakes with higher current values of
|
From page 39... ...
For 9 of the lakes, concurrent data exist on measured pH, sediment chemistry, and fish populations. The data are generally consistent and support the findings based on diatom analysis.
|
From page 41... ...
41 'e ~ t D O ~ ace c,, .0 ~ ,~ ° fi ~ D O <~ O ~ ~ ~ ~ ~ ~ ~ ~ ~ O ~ ~ O ° '4~ =. ° Ce ~ ~ ~ ells in= ~ == == ~ ~ 0 <~> e A 3 .
|
From page 42... ...
Total coal consumption in the eastern United States is currently comparable to consumption during the peak years of the early 1940s, owing to increased consumption after the decline in the 1950s. However, there has been a considerable shift in the regional patterns of consumption over the past two decades; some areas currently consume far greater amounts of coal than they did in the early 1940s and some areas consume far less.
|
From page 43... ...
However, if acid deposition is a cause, it may be difficult to determine whether the effect is a consequence of relatively recent changes in fuel use or consumption since 1945, or whether it is a result of cumulative exposure to acid deposition over many decades. Regional Trends Estimates of SO2 emissions in eastern North America suggest that the decade of the 1950s was a period of constant or declining emissions in all of the designated Regions A through E
|
From page 44... ...
The mechanisms outlined earlier suggest that SO2 emissions, atmospheric sulfate, light extinction, and stream sulfate are related and may exhibit similar temporal trends. We examined this suggestion on a regional basis by testing for associations among the regional trends of these variables by using Friedman's test.
|
From page 45... ...
In summary, based on statistical tests of regional temporal trends, a strong association exists between SC2 emissions and light extinction (30-year records, 1950 to 1980)
|
From page 46... ...
1981. The utility of diatom analysis of lake sediments for evaluating precipitation effects on dilute lakes.
|
From page 47... ...
1983. Seasonal acid precipitation and emission trends in the northeastern United States.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.