ES&T
FEATURE Red herrings in acid rain research Common misconceptions regarding the effects of acid deposition on aquatic ecosystems
Magda Havas Thomas C. Hutchinson Institute for Environmental Studies University of Toronto Toronto, Ontario M5S I A4, Canada Gene E. Likens Institute of Ecosystem Studies New York Botanical Garden Cary Arboretum Millbrook.N.Y. 12545
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A "red herring," according to Funk and Wagnalls' Standard College Dictionary, is "a diverting of attention from the main subject by introducing some irrelevant topic." Of the thousands of articles concerned with the phenomenon of acid rain, several, which include promin e n t red h e r r i n g s (for e x a m p l e Poundstone 1980, Frantisak 1980, Hamilton 1981), are commonly re-
ferred to in the popular literature. Articles that make bold statements contrary to the published literature, or those that cast doubt on well-established ideas by purporting to report the "facts," are bound to attract attention. Science thrives on the testing of hypotheses. However, if untested hypotheses receive wide publicity and are compatible with the political climate, they will unduly influence both
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scientific r e s e a r c h and political thought. By such repetition they often become accepted truths without having been tested. We have selected five common misconceptions, red herrings, regarding the effects of acid deposition on aquatic ecosystems in an attempt to clarify some of the confusion they have created. These misconceptions are the following: • Bog lakes have been acidic for thousands of years; thus the acidification of lakes is not a recent phenomenon. • The early methods for measuring pH are in error; therefore, no statements can be made regarding historical trends. • A c i d i f i c a t i o n of l a k e s a n d streams results from changed land use practices (forestry, agriculture, animal husbandry) and not acid deposition. • The decrease in fish populations is caused by overfishing, disease, and water pollution—not acidification. • Because lakes that receive identical rainfall can have considerably different pHs, regional lake acidification cannot be due to acid precipitation. Red herring number one Bog lakes have been acidic for thousands of years; thus the acidification is not a recent phenomenon. Claims that naturally acidic lakes have existed for hundreds or thousands of years and are able to support a diverse flora and fauna have diverted attention from the central issue by confusing naturally acidic lakes with those that have been acidified by airborne pollutants within the past few decades. The erroneous conclusion that follows is that all acidification is natural and therefore not of recent anthropogenic origin. There are considerable differences between naturally acidic, brown-water lakes, which are also known as dystrophic lakes, and anthropogenically acidified clear-water lakes. In some cases, these differences are quite visible to the observer without sophisticated sampling equipment and detailed chemical analyses. Naturally acidic bog lakes usually have brown to yellow water. This color is caused by the presence of humic substances— that is, peat-derived fulvic and humic acids and tannins, which are the primary organic acids contributing to the low pH. Dissolved organic carbon concentrations are high while transparency is low in these waters. In contrast, lakes that have been
FIGURE 1
Concentration of total aluminum and pH in Swedish lakes during summer and autumn 1976a
a
The two "outliers'* are very humic waters Source: Dickson 1980.
acidified by acid deposition generally have clear water, with greater transparency at lower pHs (Kwiatkowski and Roff 1976, Schindler 1980, Yan 1983). This increased clarity in anthropogenically acidified lakes has been attributed to reduced phytoplankton biomass (Kwiatkowski and Roff 1976), to precipitation of organic matter by aluminum (Aimer 1978), and to dissolution of iron and manganese colloids (Kramer 1978). Inorganic acids, particularly sulfuric and nitric acids, predominate in these lakes. Dissolved organic carbon concentrations are low, seldom exceeding a few milligrams per liter. The type of acidity (inorganic vs. organic) has profound effects both on lake water c h e m i s t r y (Stevenson 1976, Benes et al. 1976) and on the biota inhabiting these waters (Forman 1979). For example, lake water pH is strongly correlated with trace metal concentrations. As the pH decreases, the concentrations of several potentially toxic metals, such as aluminum, iron, manganese, copper, nickel, zinc, lead, cadmium, and mercury, increase (Dickson 1980, Norton
et al. 1981, Tomlinson et al. 1980, Schofield 1982, Havas and Hutchinson 1983). Data for aluminum concentrations over a broad range of pHs indicate a well-defined curve (Figure 1). Notably, the two points that fail to fit the curve are from brown-water lakes, again demonstrating the differences between these two environments. Most important, the organic acids in brown-water lakes reduce metal toxicity. Aluminum, which has been identified as one of the most important metals affecting the survival and reproduction offish in acidified lakes (Schofield and Trojnar 1980), is less toxic to fishes when o r g a n i c a l l y bound (aluminum citrate) than it is in its free form (Al"+), or when it is inorganically bound (A1F„) (Baker and Schofield 1980). As a consequence, some fish species can survive in brown-water lakes at metal concentrations (organically bound) that would otherwise be toxic. Protozoans, rotifers, some crustaceans, and many algal species thrive in such waters. Brown-water lakes and clear-water lakes with pHs between 6 and 7 have Environ. Sci. Technol., Vol. 18, No. 6, 1984
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similar acid-neutralizing capacities. However, if these two lake types have pHs below 5, the brown-water lakes generally have a greater acid neutralizing capacity. This suggests that brown-water lakes should be less sensitive to the acidifying effects of precipitation than clear-water lakes. In addition to the organic acids, the high concentrations of total dissolved solids and high level of biological activity also contribute to the acid-neutralizing capacity of these waters (Dickson 1980, Johannessen 1980). Brown-water lakes and streams have distinctive flora and fauna that differ considerably from those of recently acidified clear-water lakes (Forman 1979). Fish, such as the sphagnum sunfish {Enneacanthus obesus), the blue-spotted sunfish (E. gloriosus), the yellow bullhead (fctalurus natalis), the pirate perch (Aphredoderus sayanus), and the swamp darter {Etheostoma fusiforme) mentioned by Patrick et al. (1981) can survive in these organically rich environments. These species have had a long time to adapt to these waters. In poorly buffered clear-water lakes, however, once the bicarbonate alkalinity is exhausted, the pH decreases rapidly, giving little time for the species to adapt. Some of the more sensitive taxa, such as blue-green algae, some bacteria, snails, mussels, crustaceans, mayflies, and fish are either significantly reduced or completely eliminated in these recently acidified waters (Brock 1973, Leivestad et al. 1976, Okland and Okland 1980, Seva l d r u d e t a l . 1980). The disappearance of biota from lakes and streams is one of the major concerns of scientists studying the effects of acid rain. The major issue is not whether brown-water lakes have existed for hundreds of years, nor whether these lakes are becoming more acidic, but rather how poorly buffered o l i g o t r o p h i c lakes a n d streams, located in geologically sensitive areas, are responding to acid deposition. Failure to differentiate between natural brown-water lakes and recently acidified clear-water lakes diverts attention from the main issue of acid deposition. Red herring number two The early methods for measuring pH are in error; therefore, no statement can be made regarding historical trends. The glass electrode p H meter, which is now the most commonly used method for measuring pH, was not in general use for field surveys prior to the 1950s. Many of 178A
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FIGURE 2
Comparison of colorimetric and electrometric pH values for Adirondack lake water"
Meter measurements were performed by the New York State Department of Environmental Conservation (DEC) and Cornell University Source: Schofield 1982.
the early studies relied on colorimetric comparators for measuring pH. The colorimetric method has been criticized recently for having a positive bias; that is, it gives pH values higher than they actually are (Pfeiffer and Festa 1980). Because both methods are now available, some of the bias in the early analyses can be determined and the appropriate corrections made. In fact, these two techniques have been compared. Aimer et al. (1974), Davis et al. (1978), and Norton et al. (1981) all reported a good correlation between the methods with a difference between new colorimetric and electrometric determinations of 0.1-0.2 pH units. However, the report that monotonously receives the most attention by groups wishing to downplay the effects of acid deposition is the one by Pfeiffer and Festa (1980), which claims as much as a 1.0 p H unit difference between these two techniques, with the glass electrode pH meter giving the lower reading. The report by Pfeiffer and Festa
(1980) has been criticized recently by Schofield (1982) who pointed out an error in their pH measurements. The p H s determined electrometrically were, in fact, too low to account for the measured conductivity values. A comparison of electrometric pH values on a new set of water samples from these Adirondack lakes with the original colorimetric values indicates a closer agreement between the two methods (Figure 2). The procedure of aerating one set of samples (electrometric) but not the other (colorimetric) is another potential source of error in the report by Pfeiffer and Festa. Best et al. (in prep.) analyzed samples from 46 Adirondack lakes using the same Hellige colorimeter used by Pfeiffer and Festa (1980) together with a Fisher Acumet pH meter. They found that while there was some positive bias with the Hellige colorimeter, it was not as great as that reported by Pfeiffer and Festa. Three color reagents (Bromcresol Green-D, Chlorphenol R e d - D , and B r o m t h y m o l Blue-D), which cover the pH range
from 4.0 to 7.6, were used. Maximum deviation between the two methods (0.7 pH units) was observed with Chlorphenol Red. Mean deviations for Bromcresol Green and Bromthymol Blue were 0.3 and 0.2 pH units, respectively—that is, still high but significantly lower than the values reported by Pfeiffer and Festa. At least part of the deviation between the two methods results from the acidity-alkalinity of the color reagent, which can alter the pH of the original sample and give a false reading. Great care must be taken to use exact volumes of the color reagent and sample water, especially if the water is poorly buffered. This and several other potential sources of error are discussed by Kramer and Tessier (1982), Haines et al. (in press), and Best et al. (in prep.). Likewise, Sverdrup and Bjerle (unpublished manuscript) examined several data sets where Colorimetric and potentiometric measurements have been compared. They found that the older colorimetric measurements of pH were as reliable as more recent measurements done by other methods. Despite the problems mentioned above, both methods will give reliable results if used properly (Haines et al., in press). To determine whether historical acidification has occurred, Pfeiffer and Festa compared the old with the
new Hellige colorimetric pHs. This comparison, they reasoned, should reduce much of the bias introduced by different methods. Their results indicate that lake acidification has occurred in the Adirondack Mountains. There are fewer lakes with pHs above 7.0 and more lakes with pHs below 6.0 in their recent (1979) survey compared with the historic (1930-1934) survey. Most of the acidification occurred in lakes that originally had pH values above 6.5 (Figure 3). Norton et al. (1981) reported similar results for northern New England lakes. Interestingly, articles in which the work of Pfeiffer and Festa is quoted in relation to colorimetric bias seldom present the "unbiased" results and conclusions regarding trends in historic acidification of lakes in the Adirondack Mountains. In their enthusiasm to use Pfeiffer and Festa, it may be that many of the "quoters" have not read this paper in its entirety. Data from a variety of sources strongly suggest that poorly buffered lakes on hard granitic bedrock that have been exposed to acid deposition have become more acidic. An excellent review of historical trends in lake and, to a lesser degree, in stream acidification is provided by Haines (1981), and consequently will not be presented here. Data are available for Sweden (Oden and Ahl 1970, Aimer etal. 1974, Dickson 1975, Wright and
Gjessing 1976); Norway (Gjessing et al. 1976, Seip and Tollan 1978, Wrightand Henriksen 1978); Jutland (Rebsdorf 1980); Scotland (Wright and Henriksen 1980); Canada (Ontario—Beamish and Harvey 1972, Dillon et al. 1978, Scheider et al. 1979; Quebec—Jones et al. 1980; N o v a S c o t i a — W a t t et al. 1979, Thompson et al. 1980; also see Harvey et al. 1981); and for the U.S. (New York—Schofield 1976; New Jersey—Johnson 1979; Maine—Davis et al. 1978; northern New England states—Norton et al. 1981 ; Florida— Crisman et al. 1980; North Carolina—Hendrey et al. 1980). Additional information from analysis of sediment profiles, not presented by Haines (1981), corroborates historical acidification. The pH profileof sediments from Lake Horsikan, Sweden, shows a progressive decrease from pH 6 below a depth of 8 cm, to pH 4.5 at the surface, with a concomitant decrease of calcium (Dickson 1980, see Figure 4). The sharp increase in the concentrations of lead, zinc, and cadmium during the same period could well result from atmospheric deposition. Another method for determining historical changes in pH is to analyze shifts in diatom composition in sediment cores. Some species of diatoms occur predominantly below pH 5.5 and are referred to as acidiobiontic.
FIGURE 3
Comparison of historic and recent pH values (colorimetric) for a set of 138 Adirondack lakes
S o u r c e : Pfeiffer and Festa 1980.
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FIGURE 4
Metals and pH in the sediment of Lake Horsikan, Swedish west coast 1977-79 Sediment depth
pH
(cm)
4.5 5.0 5.5 6.0
L
Ca g/kg 1 2 I I
3 I
4 j_L
Na g/kg 0.25 0.50
Pb mg/kg 100 200
Zn mg/kg 100 200 300
0-2 2-4
-
4-6
-
6-8 8-10
10-12 12-14 14-16 16-18 18-20
Source: Dickson 1980.
Other species have optimum growth below pH 7 (acidophilous), at pH 7 (circumneutral), or above pH 7 (alkaliphilous) (see Van Dam et al. 1980). Because diatom frustules are relatively resistant to decay and because characteristics of these frustules can be used to identify different species, the species composition in undisturbed sediment cores can provide a historical record of lake water chemistry. In a number of lakes that are now acidic, there has been a shift from circumneutral or alkaliphilous diatoms in the deeper sediments to acidophilous or acidiobiontic species in surface sediments. Based on these types of data, pHs were calculated for Lake Gardsjon in Sweden (Renberg and Hedberg 1982). The results show a significant decrease in pH starting in the late 1950s (pH 6) and continuing until 1979 (pH 4.5). The explanation provided in this study is that surface sediments have acidified as a result of contact with overlying acidic water. It is no longer reasonable to simply dismiss historical trends as being due to potential bias in the early colorimetric measurements. The reported changes in pH frequently exceed the colorimetric bias. This evidence, combined with changes in sediment and water chemistry and with shifts from acid-sensitive to acid-tolerant diatoms in sediment profiles, clearly indicates that many poorly buffered lakes in regions receiving acid precipi180A
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tation are more acidic now than they were a few decades ago. Red herring number three Acidification of lakes and streams results from changed land use practices (forestry, agriculture, animal husbandry) and not acid deposition. While it is true that disturbances within the drainage basin of lakes and streams can have a profound effect on water quality (e.g., Likens et al. 1970), it is misleading to suggest that the regional acidification observed in S c a n d i n a v i a and e a s t e r n N o r t h America is due predominantly to changes in land use practices and not to atmospheric pollutants. First, many of the lakes that have acidified during the past few decades are located in relatively remote regions where land use practices have not changed significantly. Many of these lakes are pristine, high-elevation lakes that are accessible only on foot (Norton et al. 1981). The most sensitive lakes—that is, those that have a low acid-neutralizing capacity ( A N C ) — a r e frequently found at high altitudes. Some of these are above the treeline and have become acidic (e.g., New England, Scotland, Norway, and Sweden). Many of the Ontario lakes studied by Dillon et al. (1978) are also in unlogged basins. This eliminates changes in forestry practices as a possible cause of acidification. Second, sensitive lakes predomi-
nate in regions underlaid by hard granitic bedrock. Outcroppings are common, and where soils do exist they a r e often s h a l l o w a n d i n f e r t i l e (Kwiatkowski and Roff 1976, Pfeiffer and Festa 1980). Such areas do not lend themselves readily to agriculture. Also, there is no evidence that extensive grazing has occurred in eit h e r the A d i r o n d a c k M o u n t a i n s , N.Y., or in the La Cloche region of Ontario, where lake acidification is well documented (Beamish and Harvey 1972,Schofield 1976). Therefore, for a large number of acidified lakes at least, land use practices have not changed and therefore cannot be responsible for the observed acidification. Third, in regions where land use practices have changed, there is no clear relationship with lake acidification. Even though Krug and Frink (1983) dismiss the work of Drablos and Sevaldrud (1980), this latter study is one of the few studies that specifically address the hypothesis that changes in land use are responsible for lake water acidity. Drablos and Sevaldrud examined poorly buffered lakes in southern Norway for which there are good historical data on fish and land use. They found that since 1965 the pH decreased from 5.5 to 5.0, and that within the last decade, severe damage to fish populations was reported in many mountain lakes. They eliminated changes in forestry and drainage as
area is not exposed to acid rain. Dur ing the five-year period, pH increased in many of the lakes that had some disturbances within their drainage basins (i.e., a major windstorm, fire, or clear-cut logging), but remained constant in "undisturbed" lakes. In the White Mountains of New Hampshire, forest clearing resulted in a temporary increase in stream water acidity that lasted for two years. The drainage water then became less acidic than it was prior to the defores tation (Likens, in press). Similarly, Johnson ( 1979) reported that burning had no long-term effect on the pH of streams in the New Jersey Pine Bar rens. These studies show that while there is an immediate and often dra matic effect following such distur bances, this effect is short-lived. Although changes in land use can not be eliminated entirely as a mecha nism for surface water acidification, they cannot explain convincingly the widespread regional acidification of lakes and streams in parts of Scandi navia and eastern North America ex posed to acid deposition. On a region-
possible sources of this increased acidity in four of the five areas stud ied, because most of the affected lakes are above the treeline. They found that neither dairy farming nor sheep grazing correlated with loss of fish populations (Figure 5). Moreover, acidified lakes and damage to fish populations were found in a r e a s where reindeer pasturing has in creased, where it has remained stable, and where it has not occurred at all. Watt et al. (1979) resampled 21 lakes in Nova Scotia that had been s t u d i e d p r e v i o u s l y by G o r h a m (1957). In both of these studies, glass electrodes were used for measuring pH. Sixteen of the lakes, which had had no disturbances within their wa tersheds, were more acidic in 1977 than in 1955. Of the five watersheds with disturbances, four showed an in crease in pH during the same 22-year period. Such disturbances tend to fa vor an upward shift in pH. Schindler and Ruszczynski (1983) found similar results for lakes in the Experimental Lakes Area in western Ontario between 1973 and 1978. This
FIGURE 5
Fish status development in catchments with and without abandoned dairy pasturing farms and small holdings3 Lakes with fish
(%) All catchments (n = 57)
100 A
Catchments with mountain dairy farms (n = 19)
•
Catchments without mountain dairy farms (n - 38)
80
60
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20
1940
1950
1960
1970 1975 Year
a
These catchments are in the Nissedal 0sthei region of Norway
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Source: Drablos et al. (1980), based on work by I. H. Sevaldrud.
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al scale, the correlation between areas receiving acid rain and those with acid lakes is so strong that land use does not seem to matter. Red herring number four The decrease in fish populations is caused by overfishing, disease, and water pollution—not acidification. One of the major concerns regarding acidification of aquatic ecosystems relates to its adverse effects on biota—particularly on fish. Commercial fishing and recreational fishing have been seriously affected by acid deposition. Liming programs and fish stocking programs have been tried in Scandinavia and North America in an attempt to reverse the rapidly declining trends and to help maintain healthy populations (Scheider et al. 1975, Bengtsson et al. 1980, Gunn and Keller 1980). In some cases, the waters are so acidic that even these
programs fail. It has been suggested that the decline of fish populations in acid or acidifying lakes and rivers over much of eastern North America and Scandinavia is caused by overfishing, disease, or water pollution and not by acidification. While this is true in some cases, such as Lake Erie and the Hudson River, in the majority of cases studied, little scientific evidence supports this point of view. Most of the available evidence strongly suggests that acidification is the major factor responsible for the declining fish populations. Abundant data show a significant correlation between increasing acidity and decreasing fish populations, or the absence of fish, below pH 5.5 in poorly buffered oligotrophic waters receiving acid deposition (Harvey 1975, Leivestad et al. 1976, Schofield 1976, Wright and Snekvik 1978). The
FIGURE 6
Age-class composition of white sucker (Catostomus in Lumsden Lake, Ontario Number of fish
120 —
100
Age in years Source: Beamish 1970. cited in Harvey et al. 1981.
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commersoni)
loss of fish populations can be quite dramatic, as observed in southern Norway (Leivestad et al. 1976). The sharp drop in the yield of Atlantic salmon (Salmo salar) between 1910 and 1917 cannot be attributed to an increase in exploitation since the number of bag-nets used during that period decreased 30%. Fish kills were observed during spring snowmelt or after heavy autumn rains, which we now know can be extremely acidic. Mass mortality of adult fish was first observed in 1911 and has continued to the present. During one episode at the end of March 1975, thousands of dead brown trout were found along a 30km section of the Tovdal River. Veterinary tests failed to find signs of known fish diseases. Based on laboratory experiments, the levels of hydrogen ions (pH 5.0) in the river were shown to be high enough to kill adult fish in a matter of days. Acidity, however, has several subtle and characteristic effects on fish in addition to the gross consequences reflected by changes in fish populations. Thus, it is possible to differentiate between the effects of acidification and those characteristic of overfishing, disease, and other types of water pollution. Morphological deformities, spawning failure, characteristic changes in age-class distribution, and changes in blood chemistry have all been linked to acidification both in field observations and in laboratory experiments (Beamish and Harvey 1972, Mount 1973, Leivestad and Muniz 1976, Harvey 1975). Mount (1973) examined the chronic effect of low pH on the fathead minnow (Pimephales promelas) during a 13-month experiment. He reported that at pH 6.6, except for a reduction in the number of eggs produced, the fish appeared to be normal compared with the control (pH 7.5). At pH 5.9, mild deformities were observed, the number of eggs produced per female was low, and all eggs were abnormal (that is, fragile and soft). At pH 5.2 the adults were hyperactive. Males had a hunch-backed appearance with smaller than normal heads. Females produced many eggs although they did not spawn. At pH 4.5, which was the lowest pH tested, the fish were deformed and had smaller heads. No spawning occurred. Similar observations have been reported for fish in acidic lakes. Beamish and Harvey (1972) found that some white suckers {Catostomus commersoni) in Lumsden Lake, Ontario, had curved spines, similar to those reported by Mount (1973) for
fathead minnows. It was later determined that this curvature resulted from decalcification of the spinal column, which occurs in acidic waters (Fraser et al. 1982). For fish living in acidic waters, an imbalance in calcium regulation also may cause reproductive problems. Female white suckers with abnormally low calcium concentrations in serum failed to spawn in Lumsden Lake. This resulted in missing age classes in the population and a shift to older and larger individuals (Figure 6). Overfishing, in contrast, would tend to remove the more desirable larger fish. Fish populations in Lumsden Lake have decreased steadily during the past 20 years. The age-class distribution in Lumsden Lake has also been found in fish living in other acidified waters (Harvey 1975, Harvey et al. 1981) and is considered to be a typical response by fish to acidification. Reduced reproductive success, combined with natural mortality, eventually results in a significant decrease in population size, which is now obvious in many acidified waters. Liming experiments have been conducted in an attempt to improve reproductive success. Field experiments have demonstrated that spawning success can be improved by neutralizing water acidity. One of the earliest accounts was by Sunde ( 1926, cited in Leivestad et al. 1976), the inspector for freshwater fisheries in Norway. He wrote: " T h e salmon hatcheries in the southern counties had had great difficulties particularly with mortality among egg and newly hatched fry. Professor Dahl has suggested that water acidity could be the reason for the mortality. To test this, I neutralized the water by filtering through lime. The result has been most favourable, and at the same time the suspicion has been verified. Water with a natural acidity of pH 5.4 is critical for roe and yolk sac fry and the mortality increases as the water acidity increases. . . . The only hatchery that has been run with no accident is at Tovdal River. The river here has been found to be naturally neutral. This river has not had the great reduction in salmon fisheries that is found in most rivers in the southern counties. . . ." More recently, Gunn and Keller (1980) examined the effect of limestone on rainbow trout (Salmo gairdneri) in George Lake, Ontario (pH 5.3). Their results showed that the addition of limestone raised the water pH and significantly improved hatching success as well as survival of sac
Mirror Lake in New Hampshire fry and emerging alevins. While it is not possible to conclude from these experiments that acidity was the only cause of the poor reproduction, it is possible to conclude that reproduction can be improved by neutralizing the acidity. Problems with calcium regulation that can affect reproduction and cause morphological deformities also appear to affect otoliths, the auditory appendages in fish. As a fish grows, the otoliths produce annual rings similar to those produced by trees. Under normal conditions calcium is deposited and appears as a white band. During acidic episodes, no calcium is deposited, and a dark band can be seen (Hultberg 1977). Although it is not yet known what effect this has on fish, the occurrence of these dark bands may be used to record acidic episodes in remote lakes that still support fish. A change in blood chemistry is another sign that fish are acid-stressed. Leivestad and Muniz (1976) found that sodium and chloride concentrations in the blood of brown trout {Salmo trutta), in acidic tributaries of the Tovdal River, were lower in dead and dying fish than in healthy individuals. They could experimentally induce chloride loss by exposing fish to acidified water (pH 4.0). The rate of chloride loss was strongly correlated with the rate of mortality in
these e x p e r i m e n t s . These results could be induced either by lowering the pH or by adding aluminum to the water (Muniz and Leivestad 1980). Aluminum, which is mobilized from soils and sediments by H + ions, tends to accumulate in acidic lakes and has recently been identified as an important factor affecting the survival of fish (Schofield and Trojnar 1980). A more detailed review of the physiological response of fish to acidity is provided by Fromm (1980). All of the data point in the same direction. Changes in fish populations appear to be caused primarily by surface water acidification, as a result of atmospheric pollutants, and not by overfishing or fish diseases. These conclusions are based on a considerable body of information that includes failure of restocking programs, episodic fish kills, correlations between fish populations and pH, characteristic age-class distributions, and distinctive physiological blood parameters. Toxicity data both from field and laboratory studies provide ample evidence that the acidity and the levels of aluminum found in many acidified lakes are severe enough to limit the distribution of fish. Red herring number five Because lakes that receive identical rainfall can have considerably different pHs, regional lake acidifiEnviron. Sci. Technol., Vol. 18, No. 6, 1984
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TABLE 1
Morphometric and limnological characteristics of Woods, Sagamore, and Panther lakes Characteristic pH Elevation (m) Watershed area (km 2 ) Lake surface area (km 2 ) Volume ( 1 0 6 m 3 ) Mean depth (m) Outflow ( 1 0 6 m 3 / y ) Flushing time (d) Maximum depth (m) Till depth (m) Till permeability Buffering capacity Percent cover (open/deciduous/ coniferous)
Woods 4.7-5.1 615 2.07 0.23 0.813 4.22 1.59 180 13 2.2
Sagamore 5.0-6.4 586 49.65 0.72 7.54 11.6 42.0 65 21
— —
Panther 5.3-7.8 562 1.24 0.18 0.709 3.51 1.19 230 6 17
less permeable acidified
poorly buffered
highly permeable well buffered
3/90/7
2/82/16
9/63/28
Source: Integrated Lake-Watershed Acidification Study, 1983
cation cannot be due to acid precipitation. The hydrology and chemistry of lakes and streams arc highly individualistic. For some lakes, direct atmospheric input may predominate; for others, surface or subsurface runoff from a drainage basin may provide the major source of water, hydrogen ion, and other chemicals. The type and condition of vegetation cover, the type and depth of soil, and the bedrock characteristics can all affect the chemistry of drainage waters. Thus it is not at all unexpected that lakes, even those adjacent to one another, may differ appreciably in their responses to acid deposition. Base-rich glacial till, local exposures of marl, limestone, and carbonate-rich soils, all can confer local immunity on a lake or a stream, while its neighbors, lacking this additional buffering, succumb to acidification. The lake's size and depth, and the area of the drainage basin, as well as the residence time of water in the lake also arc individual features that may alter the rate of acid input. Red herring number five arose largely as a result of the Integrated Lake-Watershed Acidification Study ( I L W A S ) in the Adirondack Mountains, N.Y. The purpose of this study was to investigate how lakes become acidic. Three Adirondack lakes (Woods, Panther, and Sagamore) and their watersheds were studied extensively by a team of scientists for four years, starting in the fall of 1977. These lakes were chosen because, al184A
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though they receive the same precipitation, they have significantly different pHs. Some basic limnological parameters for these three lakes are provided in Table l. Because Sagamore is so different from either Woods or Panther, it will not be considered here. Both Woods and Panther are quite similar with respect to morphometric parameters although they differ considerably with respect to p H . Woods is an acid lake with pH ranging from 4.7 to 5.1. Panther is a circumncutral lake with pH fluctuating between 5.3 and 7.8. Another significant difference between these two lakes is related to till characteristics. The till around Woods Lake is thinner (2.2 m vs. 1 7 m), less permeable, and more acidic than the till around Panther Lake. A larger fraction of the water that enters Panther Lake percolates through a large volume of till where neutralization occurs (Newton 1983). Chemical analyses of soil horizons indicate an increase in pH from the surface organic layer (pH 2.6-3.5), through the leached layer (pH 3.54.0), to the lower inorganic layer (above pH 5.5) (Clen et al. 1983). Results from shallow and deep lysimeters tend to support the hypothesis that runoff is neutralized and therefore less acidic in deeper soils than in shallow surface soils (Cronan 1983). The conclusion arrived at by the I L W A S scientists is that the difference in till depth, permeability, and
buffering capacity can account for much of the pH difference between Woods and Panther lakes. Other differences (that is, percent coniferous vs. deciduous cover) that would tend to favor the more rapid acidification of Panther Lake (Vasudevan and Clesceri 1983), appear to be less important. Differences in the pHs of lakes quite close to each other spatially have been reported from the Killarney District of Ontario, from Norway, and from Sweden. Such differences, in almost all cases, can be ascribed to watershed characteristics as described above. It is important to recognize that lakes vary in their susceptibility to acidification. Biogeochemical parameters, surface topography, lake depth, volume, and flushing time can all influence the sensitivity of lakes to acidification. Therefore, it would be unrealistic to expect all lakes receiving identical rainfall to have identical pHs. However, despite the many differences between lakes and their drainage basins, regions where lakes are particularly vulnerable to acidification have been identified. Common characteristics include hard granitic or m e t a m o r p h i c bedrock, thin or poorly developed soil, and relatively high levels of precipitation. If that precipitation is also acidic, the acidity will eventually be reflected in surface water chemistry. Conclusion
It is easy to suggest a whole series of alternative, and often unlikely, explanations of the causes and consequences of acid deposition. These keep scientists busy for years assembling and examining data only to conclude that the explanation is not valid. These tactics are a waste of time and money. Why are polluting industries not treated like the pharmaceutical industry that has to prove the safety of products released into the environment? Why is it up to the private sector, government, and the academic community—in the face of fierce opposition—to prove beyond all reasonable doubt that these emissions are harmful and have already damaged the environment? Why must we tolerate decades of emissions, damage to the environment and often to human health before abatement measures are even considered? These tactics cause, and perhaps are designed to cause, continuous delay in remedial action. They fail to take into account the large body of i n f o r m a t i o n t h a t deals with t h e sources of the acid deposition and the
seriousness of its effects. But should we really be surprised that those in dustries that are so good at produc ing smoke are also expert at produc ing smoke screens'? The time is long overdue for cooperation between in dustry, government, and universi ties—as has happened with other matters of national importance—to solve the problem of acid rain and not simply to debate whether or not it exists. Acknowledgment Wc wish to acknowledge the original suggestion by Tom Butler to write this article. We also would like to thank the three reviewers, W. Dickson of The Na tional Swedish Environment Protection Board; E. Gorham of the Department of Ecology and Behavioral Biology, Univer sity of Minnesota; and D. W. Schindler of the Department of Fisheries and Oceans, Freshwater Institute, in Winnipeg, Mani toba, for their comments. Financial sup port was provided in the form of a Nation al Science and Engineering Research Council of Canada Postdoctoral Fellow ship to Magda Havas. The research for this article was com pleted while all three authors were at Cor nell University, Ithaca, N.Y., either in the Ecosystem Research Center or in the Sec tion of Ecology & Systematics.
Magda Havas is α university research fel low and assistant professor at the Univer sity of Toronto. Her research interests include acid rain effects on aquatic eco systems, metal toxicity to aquatic inver tebrates, and general adaptation by plants and animals to stress. She received her PhD in 1980 from the Department of Botany, University of Toronto.
Thomas C. Hutchinson (I.) is α professor of botany and forestry at the University of Toronto. His research interests include heavy metal toxicity, acid precipitation effects and effects of hydrocarbons on ecosystems. His studies also include re sponses of phytoplankton and higher
plants to stress. He received his PhD Sheffield University. U.K.. in 1966.
from
Gene E. Likens {r. ) currently is director of the Institute of Ecosystem Studies and vice-president of The New York Botani cal Garden. He received his PhD in 1962 from the University of Wisconsin, Madi son. His major research interests are in biogeochemistry. analysis of ecosystems, limnology, chemistry of precipitation, and management of landscapes.
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