Environmental Science: The Effects of Acid Rain on the Shells of Birds.
(Process skills used in this experiment were: observation and prediction.)
August 9th: Today, after brainstorming different environmental concerns of our planet, our class began an experiment to demonstrate the effects of acid rain on the eggs of birds. We placed a raw chicken egg in a jar of vinegar (4% acetic acid). Each student wrote a prediction on what they thought would happen to the shell of the egg. The first observation that students made was that the jar was filled with bubbles. These appeared to be on the egg shell. 24-hours later, we observed the egg again. Many students who had predicted that they would see pieces of shell floating on top were surprised when the only thing they saw was a white frothy scum floating on top of the vinegar. The egg sat in the vinegar over the weekend. What students observed when they came in on Monday was that the shell was completely dissolved by the vinegar and that the egg was enlarged.
Reaction:
The acetic acid in the vinegar reacts with the calcium carbonate (CaCO3) in the egg shell and releases carbon dioxide (CO2) that can be seen as bubbles on the shell. The egg insides remain intact and are held together by two fragile membranes just inside the shell.
The egg is bigger than when it was first put into the vinegar because the vinegar and some of the water has moved through the membranes to the inside of the egg. These membranes are semi-permeable and allow water to move through them. This process is called osmosis.
We will follow up this experiment by placing the already enlarged egg into a jar of plain water. Since the inside of the egg is already around 90% water, we will demonstrate that, by placing it into a container of 100% water, the water should start to move through the membrane to equalize the amount of water both inside and outside the membrane. Students will add food coloring to help them see this process of osmosis more clearly.
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Resources:
Sources of Acid Rain
- Acid rain has increased since the dawn of the Industrial Revolution.
Humans generally produce acid rain through emissions from factories that release combinations of sulfur, nitrogen and carbon into the air and mix with naturally occurring water molecules. Volcanic eruptions also cause acid rain to form.
Food Chain
- Declines in snail populations herald drops in nesting success for some bird species.
Acid rain depletes calcium in soil. Snails that typically feed on that calcium as they excrete their shells die off in areas of acidic soils. Birds that rely on the snails as food can survive by eating other prey, but are unable to produce sturdy eggs.
Read more: (Acid Rain & Bird Eggs | eHow.com
Effects of Acidity on Plants and Animals
As a first example of the effects of acid rain, we can examine a case which is not obvious - effects on non-aquatic, tree nesting birds. This study was carried out in the Netherlands. It was observed that the proportion of birds laying defective eggs rose from roughly 10% in 1983-84 to 40% by 1987-88. The defective eggs had thin and highly porous egg shells, which resulted in eggs failing to hatch because of shell breakage and desiccation. As a result, there was also a high proportion of empty nests and clutch desertion. It was also observed that these effects were limited to areas of acid rain.
Since the birds did not appear to be directly affected by the acidity, the food chain was examined (these birds are positioned at the upper part of the local food chain). The difference between areas of normal soil pH (buffered by high calcium content due to limestone and marble outcrops and bedrock) and those with acidic soil appeared to be the presence of snails. The snails depend on the soil as their calcium source as they secrete their shells. With much of the CaCO3 leached out of the soil by the acid precipitation, the snails could not survive in the area. The birds did not, at first, appear to be affected, because they continued to eat spiders and insects which, while supplying a sufficiently nutritious diet for the birds, where a poor source of calcium.
To test the hypothesis that the lack of calcium was the cause of the bird's laying defective eggs, ecologists "salted" the area with chicken egg shell fragments. The birds began to eat the chicken egg shells, and those that did laid normal eggs.
In this case, acid precipitation had effects that passed on up the food chain.
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