To What Extent Does Acid Precipitation Affect Annelids? Essay, Research Paper

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 charecterized 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” (Graedel, Thomas, et. al, (1989, V261 n3 p.

58-68 Sep. 1989) 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. (Kucera, (1973) The Challenge of Ecology, The Mosby

Company.)

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.” (Storer, et. al, (1972) General Zoology

5th ed., McGraw Hill Books.) 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.” (Gilber White (1788) 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.” (Edwards and Lofty

(1977), Biology of Earthworms, Chapman and Hall)

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” (Bornebusch, 1930) 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” (El-Duweini and Ghabbour, 1956).

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.” (Pierce, et. al, (Sep, 1988 Volume 70) Science Notes, School

Science Review.)

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.” (Pierce, et. al, (Sep, 1988 Volume 70) Science Notes, School

Science Review.) 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.