Is Acid Rain still a problem? Yes it is. Lakes and ponds in the Adirondacks are not recovering. Scientists predict that the modest gains to date in reducing acid deposition will not prevent more lakes from dying. By 2040, according to an EPA report, 43% of the 2,800 lakes and ponds in the Adirondacks are likely to have a pH under 5.0, the critical threshold for most fish and many other species. That is an increase of 27% now. How can the damage here continue to worsen despite the gains made in controlling acid deposition? There are several reasons. First, acid deposition is still far above pre-industrial levels, especially in the Adirondacks. Although SO2 emissions have decreased, further decreases are necessary, and decreases in NOx emissions per source have been offset by increases in the number of electric plants, the number of cars, and decreasing fuel efficiency. Second, the resiliency of the natural systems, their "buffering capacity," has been damaged. Deep soils derived from limestone, like those in the Midwestern U.S., have naturally good buffering capacity. Shallow soils derived from granite, like those in the Northeast, especially at high elevations, have very little natural buffering capacity. Calcium, one of the chemicals that buffer soils, is also a nutrient for trees and plants, as well as for humans. Where calcium exists in the soil, it also helps to buffer the soil. Acid deposition can leach the calcium from shallow soils faster than it can be replenished. Entire stands of trees appear to have ceased growing in some parts of the Northeast. Because tree growth is a complex phenomenon that involves many factors, it is difficult to say with certainty that acid deposition has slowed forest growth, but the scientific evidence is worrisome. The different parts of the ecosystem are tightly linked. Scientists are discovering that acid deposition worsens other environmental problems. Acid precipitation leaches mercury, a potent neural toxin, into water where it gets into the food chain. Mercury levels are high enough in some Adirondack lakes that people are warned to limit their consumption of the fish caught there. Natural systems also have a limit to how much nitrogen they can contain, beyond which they become nitrogen saturated. There is evidence that the nitrogen oxides in acid precipitation are causing nitrogen saturation in some parts of the Northeast. The excess nitrogen then flows directly into rivers and is discharged into marine ecosystems where it causes a great deal of harm by upsetting nutrient balances. Each of these effects is bad by itself. Applied in combination to ecosystems that will be increasingly stressed by climate change, there is every likelihood that they will produce substantial, long-continuing, and unpredictable change. |
