To What Extent Does Acid Precipitation Affect Annelids?
In order to truly understand acid rain and it's eventual effect onearthworms, it would be best to look at the causes of acid rain. How andwhy does altered acidity in precipitation have a devastating effect? Acid rain is charecterized as "Precipitation that has a pH lower than about5.0" (Allaby, Michael (1994) Ecology, Oxford Press,). Acid rain is createdby many things, of which pollution from cars contributes the most. Eversince the Industrial revolution, the acidity of rain has been haywire.Sulfur and nitrogen are found widely throughout the world in the air, "evenin 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 percentof acid rain comes from sulphur dioxide (SO2), which dissolves into thewater to form sulphuric acid. The rest comes from various oxides of nitrogen(mainly NO2 and NO3, collectively called NOx). These gases are producedalmost entirely from burning fossil fuels, mainly in power satations androad transport. (Kucera, (1973) The Challenge of Ecology, The MosbyCompany.) Tremendous quantities of this nitric acid and sulfuric acid mix arereflected in the lowering of the acidity of rain. Earthworms (Annelids) are a species of worm which are many segmented. Theylive in damp soil, usually forming intricate tunnels beneath the surface.Their bodies are lond and cylindrical, and have "bluntly tapered ends andare somewhat depressed posteriorly." (Storer, et. al, (1972) General Zoology5th ed., McGraw Hill Books.) As earthworms burrow, thew swallow largequantities 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 theimportance of earthworms was Gilbert White, when he wrote in his book, TheNatural History of Selbourne (1788) that "soil was loosened, aerated, andmade more fertile by earthworms." (Gilber White (1788) The Natural Historyof Selbourne) Earthworms are typically very sensitive to low pH levels. Therefore, itisn't surprising that "pH of soil is sometimes a factor that limitsdistribution, 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 thatearthworms prefer soils with a pH of about 7.0. Some improtant workersinclude Arrhenius in 1921, Moore in 1922, Phillips in 1923, and Petrov in1946. All these studies concluded the above stated fact, that worms prefer7.0 However, in Denmark, Bornebusch found "Dendrobaena octaedra, which isan acid-tolerant species" (Bornebusch, 1930) Studies have also beenconducted in Egypt, where it was found by El-Duweini and Ghabbour that soilcan 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 inplots of soil with pH values ranging from 4-7, the worms in soils with thehigher acidities were "jerking and convulsing........after 1 to 2 hoursbecame motionless and flaccid. After 24 hours, fifty-eight out of sixtyworms exposed to pH below 4.4 were dead." (Edwards and Lofty, (1977) Biologyof Earthworms, Chapman and Hall) Earthworms are easily used forexperimentation by researchers because they are "widely distributed,familiar organisms, which are readily and cheaply available in largenumbers." (Pierce, et. al, (Sep, 1988 Volume 70) Science Notes, SchoolScience Review.) In soils of pH less than 5, earthworms are usually scarce, and soilbreakdown is usually slow, making a "deep layer of slowly decomposing plantremains." (Pierce, et. al, (Sep, 1988 Volume 70) Science Notes, SchoolScience Review.) This is a very obvious sign of wether or not earthwormsare present, and more often than not, the pH range can be determined onsight. If you look through soil and see plant material broken down andmixed through the soil, you know that earthworms are there and are playing amajor role in soil breakdown and nutrition.