To What Extent Does Acid Precipitation Affect Annelids?


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.