After the Clean Air Act was passed in 1970, utilities often sought to meet its standards by building very tall stacks. The EPA calculates that there are now 180 stacks more than 500 feet tall as compared to only two in 1969. Tall stacks can relieve local air pollution, but they increase acid precipitation in downwind areas. In 1974, American Electric Power ran ads boasting that it was the "pioneer" of tall stacks. The ads proclaimed that the tall stacks dispersed "gaseous emissions widely in the atmosphere so that ground-level concentrations would not be harmful to human health or property." These emissions, American Electric Power said, are "dissipated high in the atmosphere, dispersed over a wide area, and come down finally in harmless traces." The ads derided "irresponsible environmentalists" who wanted strict controls over the emissions and accused them of "taking food from the mouths of the people to give [themselves] a better view of the mountain." Except for one thing: It's clear now that those "harmless traces" are not harmless.
The effect of acid precipitation on a body of water depends on the nature of the rock and soils in the watershed. A watershed containing readily available calcium and magnesium or carbonates weathered from limestone can buffer acid in much the way an Alka-Seltzer or a Rolaids tablet will neutralize an upset stomach. Some parts of North America, such as the Middle West with its more alkaline soils, have great buffering capacities, but there are other areas that have hard rock and/or infertile sandy soil, and these have minimal buffering capacity (see map on page 78). Geologic outcroppings and anomalies can make for vast differences within an area. How much acid precipitation it takes to acidify a specific body of water depends on that body's acid-neutralizing capacity, chemically measured as its total alkalinity. A lake with, say, 10 parts per million total alkalinity is low on alkalines, and in time acid can destroy it. Knowledge of the total alkalinity of a body of water and whether that alkalinity is decreasing is essential because pH can be a deceptive figure, dropping sharply only as buffering capacity is finally destroyed.
Snowfall can play a key role in acidification. Dr. Ernest W. Marshall, a geologist specializing in snow and ice, believes he can track different storms through the Adirondacks weeks after they have occurred by digging into the snowpack and examining individual storm layers. To Marshall, it's no coincidence that the Adirondack lakes that suffer most each spring lie on the range's western slope and receive the greatest snowfall. "The snow and ice store acids for three to four months," Marshall says, "and then when the spring melt comes, lakes and streams get one hell of a slug of acids. It's as though a pack-a-day smoker gave up cigarettes for four months and then tried to make up for what he had missed by smoking dozens of packs in just 10 days." High acid episodes during snowmelt are not unusual in lakes and streams that otherwise seem normal. In Norway, these episodes have been linked with large fish kills.
At 6.5 pH level, brook, brown, and rainbow trout experience significant reductions in egg hatchability and growth. At 5.5, largemouth and smallmouth bass, walleyes and rainbow trout are eliminated and declines in other trout and salmon populations can be expected. Below 5, most fish are unable to survive.
A low pH can cause female fish to retain their eggs, but even if the eggs are laid, mortality can be high in acidified waters because fish are ultra-sensitive in the egg, larval and fry stages. Ironically, as new year-classes of fish fail to develop, the older fish become bigger because of reduced competition for the food, and anglers will often report sensational catches.
Why do the fish die? Low pH by itself interferes with the salt balance freshwater species need to maintain in their body tissues and blood plasma. But apart from that, there's another factor at work: aluminum. Acid precipitation "mobilizes" (puts into circulation) aluminum, one of the most abundant metals in the crust of the earth, and as Dr. Carl Schofield, a Cornell University aquatic scientist, discovered, aluminum can be lethal to fish and other organisms at pH levels that are normally considered safe for the host fish themselves. Acidification also mobilizes mercury and cadmium, and fish that don't die may become poisonous to predators who eat them—including the human kind—because of the accumulation of such heavy metals in the fish's tissues.
Besides losing its fish life, it appears an acidified body of water also loses hundreds of other organisms, including insects, mollusks and certain types of algae. However, a few species can actually thrive. The water in an acidified lake is often a crystalline blue, but the bottom is sometimes carpeted with fibrous mats of algae, thick enough to be picked up and shaken like a rug. Bacteria that can thrive without oxygen live beneath such mats, where they decompose plant matter and produce gases that bubble to the surface in the summer months. "I suspect that this is the cause of the garbage-dump-like odor that wafts over the surface of some acidified Adirondack lakes during the warmest part of the year," says Brookhaven's Hendrey.
There's another bizarre touch: Tree leaves that fall into streams, lakes and ponds become pickled and simply stay there. The bacteria and fungi that would normally begin to break down the leaves are inhibited, and the same holds for stoneflies and other aquatic insects that eat leaf detritus. Given this, leaves can build up in a body of water, and as Hendrey says, "Acidification is accelerating the rate of the filling-in of ponds. The accumulation of material is abnormal, and it's increasing so rapidly that soon it may have negative effects for human beings."
Scientists at the Freshwater Institute in Winnipeg, Canada are attempting to document the most minute changes that occur in acidified lakes. In 1969, the Canadian government established the Experimental Lakes Area southeast of Kenora, Ontario by setting aside 46 lakes for scientific investigation of pollutants. Like thousands of other lakes in eastern Canada, ELA lakes are situated on the granitic Canadian geologic shield, and because they are remote from sources of pollution, they are basically undisturbed. Inasmuch as the hydrological, meteorological, chemical, biological and physical characteristics of all 46 lakes have been measured, any one of them can serve as an experimental laboratory, with others acting as controls. Early research in the ELA centered on the effects of phosphate detergents, which led to their reduced use in Canada, and in 1976 the emphasis shifted to the effects of acid precipitation. The scientists took one lake—it has no name, just the designation Lake 223—and over the course of the next four years added three metric tons of sulfuric acid to it. Dramatic changes have already occurred. The pH of 223 has dropped from 6.5 to 5.6; aluminum, zinc and other toxic metals have been mobilized and are present in increasing concentrations; a small mysid shrimp, an important food for lake trout, has disappeared, as has the fathead minnow; the population of slimy sculpins has dropped sharply; and there is a greater incidence of deformed lake-trout embryos.
Although the phenomenon of acid precipitation has been recognized only in recent years, it probably began about a century ago. Dr. Stephen A. Norton and his colleagues at the University of Maine have found buildups of lead and zinc far greater than the natural background levels in sediment cores extracted from the depths of New England and Scandinavian lakes. The cores show that the initial buildups began 100 years ago and then increased startlingly in the 1940s. In approximately 100 years lead has increased as much as 300% over the background level and zinc as much as 700%. Moreover, additional studies of the sedimentary remains of diatoms, microscopic one-celled algae, and of cladocerans, microscopic Crustacea, indicate "biological changes related to acidification of some of the lakes."