In order to truly understand acid rain and it’s eventual effect on earthworms, it would be best to look at the causes of acid rain. How and why does altered acidity in precipitation have a devastating effect? Acid rain is characterized as “Precipitation that has a pH lower than about 5.0” (Allaby, Michael (1994) Ecology, Oxford Press,). Acid rain is created by many things, of which pollution from cars contributes the most. Ever since the Industrial revolution, the acidity of rain has been haywire. Sulfur and nitrogen are found widely throughout the world in the air, “even in unindustrialized tropics” The Changing Atmosphere, Scientific American). The way in which acid rain is created from here is that About 70 percent of acid rain comes from sulphur dioxide (SO2), which dissolves into the water to form sulphuric acid. The rest comes from various oxides of nitrogen (mainly NO2 and NO3, collectively called NOx). These gases are produced almost entirely from burning fossil fuels, mainly in power satations and road transport.
Tremendous quantities of this nitric acid and sulfuric acid mix are reflected in the lowering of the acidity of rain. Earthworms (Annelids) are a species of worm which are many segmented. They live in damp soil, usually forming intricate tunnels beneath the surface. Their bodies are lond and cylindrical, and have “bluntly tapered ends and are somewhat depressed posteriorly.” As earthworms burrow, thew swallow large quantities of earth that often contain large amounts of vegetable remains, often depositing, or casting, their very nutritive remains to the soil, which adds to it’s enrichment.
The first person to truly recognize the importance of earthworms was Gilbert White, when he wrote in his book, The Natural History of Selbourne (1788) that “soil was loosened, aerated, and made more fertile by earthworms.” The Natural History of Selbourne) Earthworms are typically very sensitive to low pH levels. Therefore, it isn’t surprising that “pH of soil is sometimes a factor that limits distribution, numbers, and species of earthworms.” There have been many experiments done on this, which indicate that earthworms prefer soils with a pH of about 7.0. Some improtant workers include Arrhenius in 1921, Moore in 1922, Phillips in 1923, and Petrov in 1946. All these studies concluded the above stated fact, that worms prefer 7.0 However, in Denmark, Bornebusch found “Dendrobaena octaedra, which is an acid-tolerant species” Studies have also been conducted in Egypt, where it was found by El-Duweini and Ghabbour that soil can also be “too alkaline to favour earthworms”.
In a study done by Satchell in 1955, in which earthworms were placed in plots of soil with pH values ranging from 4-7, the worms in soils with the higher acidities were “jerking and convulsing…..after 1 to 2 hours became motionless and flaccid. After 24 hours, fifty-eight out of sixty worms exposed to pH below 4.4 were dead.” (Edwards and Lofty, (1977) Biology of Earthworms, Chapman and Hall) Earthworms are easily used for experimentation by researchers because they are “widely distributed, familiar organisms, which are readily and cheaply available in large numbers.” In soils of pH less than 5, earthworms are usually scarce, and soil breakdown is usually slow, making a “deep layer of slowly decomposing plant remains.” This is a very obvious sign of wether or not earthworms are present, and more often than not, the pH range can be determined on sight. If you look through soil and see plant material broken down and mixed through the soil, you know that earthworms are there and are playing a major role in soil breakdown and nutrition.
