It used to be said that rain provided the most pure form of water available outside of the laboratory. Now we know better. At least in the Northeast and, to a lesser degree, as far south as the Carolinas, the rain is so acid you could almost pickle beets in it.
I'm told it is great for shampooing particularly greasy hair -- provided you don't do it too often. For the rest it's not so good. It erodes statues and monuments in city parks and the marble and granite facing on public buildings. Worse still, it is denuding some of the higher elevations of trees. And while it produces some of the most sparkling streams and lakes you might ever wish to see, it is poisoning the fish that live in those crystal-clear waters.
On the home front acid rain can affect the productivity of the garden. Fortunately, however, there are some effective steps we can take to buffer our soils against the onslaught. Lime, wood ashes, compost, leaves, and old newspapers are some of the available tools.
On a recent visit to the Waltham Experiment Station near here, I learned that the rain in the area last year was consistently as low as 4, and often lower, on the pH scale. That put it almost on a par with vinegar in terms of its acidity.
Under such circumstances it could be expected that my garden soil would be pretty acid, too. In fact, a recent test showed it to be almost neutral and it was assumed that I had limed heavily to balance the soil. I had done no such thing, at least not in the past five years. But I have consistently mulched the soil with leaves, composted heavily; applied wood ashes, and substituted newspaper mulch when the preferred leaves ran out.
Perhaps it is best to understand what is causing us to be doused with dilute sulfuric and nitric acids every time it rains.
In the first place, this is not a natural phenomenon. The wastes that billow out of factory smokestacks every day combine in the atmosphere to form acidic materials that are dissolved in water and fall to earth each time it rains. The reason the Eastern half of the country is plagued by the problem while the Western half gets off largely scot-free is that the prevailing winds are from west to east. Ironically, the acid rain that damages Eastern soils would be welcome in many areas in the West, where it would help neutralize the naturally alkaline soils.
These acidic rains became a problem in the last decade because of an attempt to clean up the air around heavily industrialized regions. Remember when factories were ordered to build much higher stacks so the pollutants could be easily scattered to the four winds rather than trouble neighboring residents?
Well, in effect what those polluted areas have said to others hundreds, and even thousands, of miles farther east is: "Here, we don't want this problem; you have it!" In fact, they gave them a much worse problem. Locally and at low levels the pollutants are not acidic. It is the action of the sun and moisture vapor at higher altitudes over several days that produces the chemical changes, resulting in acid compounds that dissolve in the rain water.
These acids, falling from the sky, damage the soil life in the top few inches of soil and rapidly leach out the calcium, magnesium, and potassium. On the other hand, acidic soils bind up the nitrogen and phosphorus, two other important nutrients. In other words, they waste one set of nutrients while locking up another set in the safe, so to speak, starving the plants in the process.
The rains also dissolve heavy metals, such as lead and aluminum, which normally remain stable in the soil. Once dissolved, they can be taken up by plants and ingested by fish and other aquatic life forms. It is not so much the acid water, but the heavy-metal poisons in the water, that account for the declining fish population.
Fortunately, the soil, which is rich in decaying vegatable matter, is an effective buffer against acid rain. So, our gardens can be protected much more easily than the forest lands, particularly the higher elevations where the topsoil is thin.
Despite the acid rain, my topsoil is loaded with earthworms and consequently is rich in the invisible life forms, too. A mulch of shredded leaves provides the first line of defense. Calcium within the mulch begins the neutralizing, but it is the compost and the other largely decayed organic materials within the soil itself that provide the all-important buffering action, allowing the soil to become neither too acid nor too alkaline.
A dressing of lime also helps neutralize the acid. So do wood ashes. In addition, the wood ashes are a source of potash, an important mineral which acidic rains leach out of unbuffered soils. The ash contains some calcium, too.
Having ascertained that newspaper ink contains no lead or other harmful additives (the suggestion that PCB is an ingredient is totally false, according to the National Association of Printing Ink Manufacturers), I periodically mulch the soil with shredded newspaper when my supply of shredded leaves runs low.
Newspaper breaks down slowly but steadily in the soil, providing some enduring beneficial effects which are similar to decomposed sawdust. But unlike sawdust, which can be slightly acidic during the breakdown, newsprint -- which is treated with lye during the manufacturing process -- has no such drawback.