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Testing Water Quality
To obtain the average pH of the water in which I found my specimens, I tested two samples collected from the Jubilee Road outlet on a sunny day and two samples collected on a rainy day, in order to find the average pH in the Jubilee area. I determined the pH using a very precise pool-testing kit for commercial pools. The pH was determined to be 8.7. To compare this with my control, I tested two water samples collected from the Graves Island site on a sunny day and two samples collected on a rainy day. After analysis, I found the Graves Island water to have a pH of 8.0. I also measured the chlorine levels found in the polluted water, as this substance is extremely toxic to aquatic life. Utilizing two water samples collected at low tide on a sunny day and two samples collected on a rainy day, I used the same commercial pool-testing kit to determine the amount of free active chlorine. I used a series of three reagents and compared my results against a chart measuring chlorine levels from 0.05 to 1.0 mg/L. The average result determined for the North West Arm water was 0.4 mg/L. Interestingly, this is higher than the level (0.37 mg/L) the U.S. Environmental Protection Agency deems possible for the survival of fish. I compared this with results from the Graves Island control site and found that the amount of chlorine in this area was less than 0.05mg/L. According to the "Pollution Control" part of the Halifax Harbor Report, "high concentrations of nutrients have led to decreased oxygen levels." This supports a hypothesis I formed after reading that dumped sewage contributes high concentrations of nitrates and phosphates to an area. These nutrients may initially stimulate the growth of aquatic plants, but the excessive amounts in 12 million liters of sewage a day promote the uncontrolled growth of algae and waterweeds, which block the waterway and expend large amounts of oxygen. This in turn creates a high level of carbon dioxide in the water. The low level of oxygen and the high level of carbon dioxide kill aquatic life. Using a filter apparatus, white filters, and a standard color chart to measure turbidity, I found the turbidity of North West Arm water to be 52 NTUs. This compares to the Graves Island control site, which had a water turbidity of 10 NTUs.
Comparing Periwinkles The diameter of the shells collected from the Arm ranged from 10 to 35 millimeters, while the specimens collected from Graves Island were consistently larger in diameter, ranging from 26 to 50 millimeters. The thickness of the North West Arm shells was thinner than those collected from Graves Island. The thickness of shells from the North West Arm site ranged from 1 to 2 millimeters, while the shells collected from the control site were between 1.5 and 3 millimeters.  This drawing shows the common periwinkle, Littorina littorea, anatomy. The shells of specimens collected at the North West Arm site displayed less variation in color and were thinner than those collected at the control site.  The sole of the foot acts as a suction and allows the periwinkle to hold on to rocks and other materials. The shells I examined displayed whorls that increased in diameter along a center point, referred to as the columella. The whorls become increasingly smaller in diameter as they reach the summit of the spire. The largest whorl contains an oval opening that houses the foot and the head of the periwinkle. The operculum is a piece of tough skin that acts to close off the aperture when the foot and head are inside the shell. The foot is located in the ventral region and is used to attach to surfaces for locomotion. The head is located at the anterior end. The head is composed of two tentacles, with one eye next to each tentacle, and a snout that houses a mouth at the end. The only difference in morphology that I could determine between my periwinkles was that, in general, the features of the specimens taken from Graves Island were larger in size, though they generally looked the same as the North West Arm specimens. |
When a specimen in the tank died, I took the opportunity to perform a dissection on it. I removed the shell using nutcrackers. I found that behind the head on the dorsal side is a depression known as the mantle cavity; this is where the gills are located. In healthy specimens, the gill structure has a faint white pigmentation. However, in the specimen I examined, the pigmentation of the gills was light brown. Within the mantle cavity is the kidney, which is described as pinkish-brown. During my dissection, I discovered the kidney to be gray. I was able to locate the stomach among the intestines, but I found it difficult to follow the path of the intestine to the rectum. I also closely examined the heart, which appeared to be a healthy brown color. I also located the ventricle and the atrium. I was able to determine the atrium from the ventricle because the aorta exits from the ventricle. After thoroughly examining the specimens I had collected, I devised a series of experiments to test the similarities and differences between gastropods from an environment polluted with fecal wastes, metals, petroleum, and a host of other chemicals, and those collected from a relatively pristine environment. The first experiment I conducted tested the strength of the shell, or how much force the shell could endure without becoming permanently disfigured (i.e. cracked). I deemed a strong shell to be integral to the survival of a periwinkle, as it is their main defense against predators. To test this, I used a ruler, five Newton scales, four periwinkle shells from the control site, and four periwinkle shells from the North West Arm site. I attached each periwinkle shell to a hook at the end of a single spring scale. If the periwinkle did not demonstrate cracking after I exerted the scale's maximum force of 30 Newtons (N), I attached a second spring scale and continued to pull until the shell cracked or that scale also reached its maximum force. The results were as follows: Comparison of Shell Strength
The results of this experiment indicate that the shells of Littorina littorea inhabiting the North West Arm are weaker than those in the healthier Graves Island environment. This feature compromises the ability of the animal to confront attackers and survive. I was also interested to see if pollutants in an environment affect a periwinkle's sensitivity to light. I reasoned that pollutants may slow an organism's response to various stimuli, such as light and touch. To test light sensitivity, I used a variety of lamps, each with a different bulb wattage; a petri dish; four periwinkles from the North West Arm; and four periwinkles from the Graves Island control site. The experiment was conducted in a darkened room while the specimen had its head and foot exposed. Comparison of Periwinkles' Sensitivity to Light
Although I had hypothesized that pollutants would slow an organism's response to light, the results of this experiment indicated otherwise. The experiment showed that periwinkles exposed to fecal bacteria and high levels of metals, petroleum, and phosphates, may have an increased sensitivity to light. I reasoned that perhaps the stimulus of mild light has a greater effect on an animal that lives in a dark environment as a result of high water turbidity. I also wanted to find a way to test the concentration of heavy metals not only in the water of the North West Arm, but also in the specimens themselves. To test for heavy metals, I recalled a flame color experiment that indicated the presence of various metal ions by the color of a burning alcohol flame. To carry out this experiment, I used 15 milliliters of rubbing alcohol, a 50-milliliter ceramic bowl, hydrochloric acid, matches, and nichrome wire. To determine if the heavy metals already documented to be in the North West Arm were also present in the body of a periwinkle from that area, I used the liquids I extracted during my dissection. I accumulated about one milliliter of fluid. I then mixed this with one milliliter of hydrochloric acid. I dipped the nichrome wire in the mixture, held the wire over the alcohol flame, and examined the color. The flame was not significantly affected in color by the presence of the mixture. This indicates there were not sufficient amounts of metal present to be detected through this method. Through experimentation, I found that at least two milliliters of a particular metal had to be present to produce a conclusive effect on the flame. Examining this species has given me insight into the ability of creatures to adapt to even the most hostile of environments. In an environment where many creatures can no longer survive, the common periwinkle has demonstrated that chemical changes alone in its environment will not eradicate it, as the species will find ways to adapt. |
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