Investigating the Effects of Water Pollution on Daphnia magna
Part of the Young Naturalist Awards Curriculum Collection.
It all began in the summer before seventh grade. I have always loved nature and knew that the environment was quickly being polluted by many point and non-point sources. I began researching many types of pollution and soon found that water pollution was the one that I could most relate to. I began looking further, and I spoke with my mentor, Ernest Schiller, the high school biology teacher. He answered many of my questions about biology. Before I knew it, I was ordering my new best friends, Daphnia magna. Daphnia magna are small invertebrate crustaceans, the size of the tip of a needle. They are a key source of food for many fish. I chose Daphnia magna for my tests because they are easy to see with a microscope and they are often used in toxicity tests
While waiting for the Daphnia magna to arrive, I searched the countryside for ponds to use. I wanted one with pollution and one without. I ended up picking one with crops surrounding it and one that was in a person‘s yard. The pond surrounded by crops I assumed was polluted since the farmer used fertilizers on all of the crops (Figure 1). The other pond was in a person‘s yard, which was not fertilized or treated with any chemicals. I assumed this pond was not polluted (Figure 2). I had a harder time traveling to the crop-surrounded pond since it was three-quarters of a mile away from the road. If I was lucky I could use a farm truck, but if I couldn't then I had to tread through chest-high weeds (Figure 3). There was more. If the farmer had cattle in the pasture, then I had to unlock and lock the gate every time I entered or left. It was a long walk but it was worth it.
I started research in my seventh-grade year on how different fertilizers would affect the Daphnia magna and how different pond waters affect them. Treading out to two ponds every three months became my new ritual. On my first visit, I didn't realize how much mud could be found surrounding a pond. Therefore, when I stepped in, mud oozed up above my feet and I couldn‘t move. I remember my grandmother laughing at how naive I was.
I found that collecting water in sanitized milk jugs was the hardest part of my research. During the duration of my research, I was trying all sorts of "inventions" to make collection time quicker and easier. That year I never really found a great way to collect water, but most of the time I used a milk jug attached to a pole with duct tape (Figure 4). At the pond sites, I tested the water temperature and the pH level. When I got the samples home, I tested the water for phosphate and nitrate using a water test kit (Figure 5). I have to say, that was an experience. I had to sit and stir all of these different concoctions. Then after that I had to compare colors. I didn't like doing the tests this way because the results weren't exact.
The Daphnia arrived soon after I collected the water. When they did, I began the first experiment. I set up three two-gallon aquariums: one tank with control water (aged tap water), one with the polluted pond water, and one with the non-polluted pond water. In each tank I put six Daphnia. I checked their population daily, and their heart rate and, later, reflexes, every other day. I repeated this procedure every time I collected water. This was to see how the two different pond waters affected the Daphnia. I found through this study that the Daphnia population increased more in the control and non-polluted pond water than in the polluted pond water (Figure 6) .
One of my favorite things about conducting research projects is that you get to meet different people. During the first months of research, I made a visit to the campus of Iowa State University and met Dr. Charles Drewes. He has been my mentor for two years now. There I learned about Daphnia‘s eye movement, which I compared to a reflex. I used the reflex as a measurement to show whether the brain was being damaged due to the pond water or fertilizers.
After the trip to Iowa State University I began my second experiment to complete my research for the year. This was to determine which fertilizers would hurt the Daphnia the most. I used three fertilizers (Dap, urea, and potash) and a combination of the three. I used these fertilizers because the farmer of the crops around my first pond used them. I also used three different measurements of the solutions (0.1 ml, 0.2 ml, and 0.3 ml) to see how different concentrations would affect the Daphnia (Figure 7). I found that fertilizers did affect the Daphnia‘s population growth and heart rate (Figures 8–9). When beginning this project I did not know that it would bring me all that it has. I will always remember the day that I found my shocking results (Figure 5) .
I was taking the heart rate of all of the Daphnia. I had just put one urea-exposed Daphnia on a slide. I slipped it under the microscope. I had the microscope on the lowest magnification so that I could see all of the Daphnia. As I began to examine it, I noticed a small, round, ball-like object. I zoomed in to notice that whatever this was, it was firmly fixed to the side of the mid-gut, or feeding tube, of the Daphnia. I quickly called my grandparents in to verify that I wasn‘t just imagining this. They agreed that I was seeing something that had grown in the Daphnia. I quickly began more tests to determine if this was just a fluke, or whether it had occurred with all of the urea-exposed Daphnia. Well, as fate would have it, the growth did come back every time I repeated the experiment. I contacted people who were experienced with Daphnia and told them of this occurrence. None of them knew what this could be.
As I entered the eighth grade and began the next year of research, I made many changes. The first was that I received a grant that would allow me to send my water to the University of Iowa Hygienic Lab to be tested. During the process to get the grant, I got to meet John Miller, a limnologist at the Des Moines facility. I was very pleased to meet him, and there I came up with my second change. The second change was that I would be putting an age control on my Daphnia in order to ensure that they would not die immediately due to old age. I also was going to test my water year-round so that I could see if there were any seasonal changes. The first year I had repeated my tests only one time. This year I would repeat them every three months, four times in the year. I also added measurements of turbidity and Atrazine to the list of phosphate, nitrate, and pH.
I began my pond visits in December. Lucky me, I had to chop ice on the pond in order even to get to the water (Figure 10). There were six to seven inches of ice on each pond. Unlike my first visit to the pond, I didn't have to worry about getting stuck in mud. This time I had to learn how to stand up and walk on ice without falling. I sent my water samples to the lab, and within three weeks I had my results. This became another one of my rituals. I also tried finding additional people that might know something about the growth forming on my Daphnia magna.
I contacted many people, including Dieter Ebert in Switzerland, who studies parasites of the Daphnia, and Kirsten Christoffersen in Copenhagen, who studies Daphnia. I sent them pictures of this growth, and they both replied that neither of them had ever seen anything of this kind in a Daphnia. I kept contacting people, and it seemed that no one had ever seen anything like this. This aroused my curiosity to try and find out more about this growth. I continued to work on my pond tests while investigating this growth. Wanting to get a better look at this growth, I contacted Thomas Moninger at the Central Microscopy Lab on the campus of the University of Iowa. That brings me to the present day.
After sending in tests four times now, I am seeing a pattern. Both Atrazine levels and turbidity were greater in the spring for both ponds. The non-polluted pond‘s Daphnia population was close to the control‘s population, which was the highest. Their heart rates remained lower in the pond waters and in the fertilizer tests than in the control water. Finally, the reflex was only altered in the urea-exposed Daphnia after the growth had formed. This could mean that the brain effects and the growth are directly related.
I haven‘t found what this growth is. That‘s what I am currently working on, along with some additional studies. I have visited the Microscopy Lab a few times and have found many incredible things. It shocks me to think that I have worked on this project for two years. The time has gone by so quickly. I never thought that I would be talking to people from Copenhagen, Switzerland, and many other places. I have learned so much not only about Daphnia, but also about chemistry, research, and science in general. I never could have dreamed that my research would turn out this way, and to think this is only the beginning...
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