An Analysis of Water Quality on the Severn River over Two Years
Part of the Young Naturalist Awards Curriculum Collection.
On the surface, a little rain may seem like a harmless thing. Where I live, on a tributary of the Chesapeake Bay, rain can cause erosion. This issue presents a major problem to the bay's health.
The bay has been around for eons, so why is erosion dangerous to the bay's health now? The answer: us. Humans, by developing new ways of living, are threatening the bay. Impervious surfaces such as driveways prevent liquids from being absorbed into the ground and generate stronger water flow during rain or similar events. This increased water volume may pick up harmful debris (such as pesticides) and carry it into the bay, where it can be harmful or deadly to species of marine life.
How much does rain affect the bay? Would rain result in more erosion and therefore impact the turbidity of the water? These questions caught my interest and spurred my investigation. I was also curious about this topic because the bay closely affects my life, and I have often wondered how clean the water actually is. The next step was to research my topic. The facts I learned helped me focus my investigation and increased my interest in water quality. I set out to discover if there was a direct connection between rainfall and the amount of sediment in the Severn River, a tributary of the Chesapeake Bay.
I began collecting water samples in the fall of 2005 from two sites: a secluded lagoon on the west side of my neighborhood, and a community beach on the south side. My motivation for choosing different sites was that I wanted to see if the area around each location and amount of water flow would affect my data. The beach has open, sometimes swift-running water; the lagoon's water flows in and out via a narrow channel and is fairly calm. At the beach, I used a small ladder off the pier to access the water since I did not want the wave action in the shallow water to impact the data. At the lagoon, I stood on a sand shelf near the channel and reached into the water.
I continued collecting one sample per site from October 16 to November 9. I aimed to collect water every three days, although this was not always possible. My collection containers were bottles, jars, and other vessels. After each collection, I labeled each sample with the collection date and site, along with any interesting observations that might have affected the data. Some things I noted were extreme high and low tides and unusual amounts of seaweed. After I had collected water for almost a month, I analyzed the amount of sediment in the water.
My method for determining the amount of particles in my samples was fairly straightforward. I laid out graph paper (16 squares per square inch) on a counter and covered this with plastic tubs, labeled by site and date. I shook my samples to evenly distribute the sediment and poured 500 ml of water into the corresponding tub. For the samples I had collected with more than 500 ml in the container, I swirled each sample after I removed the top to prevent the sediment from settling. This ensured all the tubs had the same ratio of sediment to water that they had in their initial container. I let my samples settle for an hour before I analyzed them.Once my samples were laid out, I counted the sediment according to a sizing method I created. I divided the particles into three sizes: large, medium, and fine. Large particles were larger than 1 mm long. These were very easy to see and noticeably larger than the other sediment. Particles 1 mm long I recorded as "medium." These were roughly the size of a grain of pepper, large enough to be seen but not as big as the large particles. The fine particles were smaller than 1 mm long and considerably harder to see. Since most samples had a large amount of fine sediment, I counted the number of fine particles per 1/16 sq. in., using the graph paper to assist me. For large and medium particles, I recorded the amount in the total container. I also went online to find the dates during my collection that it had rained. At the conclusion of this process, I had data that I could work with to develop a conclusion.
My need for more data led me to collect water again in the spring of 2006. I also wanted to see if seasonal changes would impact the turbidity of the water. Although I began to sample in the winter, I was only able to collect on January 22. I began collecting again on March 19 and continued until April 8. I used the same methods for sampling and analyzing as before. During the late winter of 2006 the lagoon was dredged, and as a result the sand shelf I collected from was occasionally underwater. My January collection occurred in the middle of this construction, and I noted that there was a "film" on the water. I anticipated that this construction would impact my data, and I was eager to see if this was the case.
After analyzing my samples, I took a break from collecting until the spring of 2007. I collected water six times, from January 7 to March 3. This time I tried to collect using the same type of container, a bottle with a capacity of exactly 500 ml. I also tried to be diligent about rinsing the containers thoroughly before use. I hoped these changes would control my data more, although I was not always able to carry out both of these measures.
During this collection phase, the beach was renovated. Sand was gradually moving from the beach out into the water and was getting pulled away from under the cabana. Since this posed a potential risk to the cabana, I guessed this was the reason for the change. When I collected water on February 4, around the time I noticed the construction, the water had a foul smell and sand had been pushed up against the cabana. There was large construction equipment, and the water was murky and dark. I wanted to see if I could find any patterns in my data relating to the state of the beach before and after the construction.
In order to analyze my data, I made graphs and averaged the numbers in order to see patterns better. When I used the data concerning fine particles, I used the number for 1/16 sq. in. instead of multiplying to see how many were in the whole container. If I had used the total number, my graphs would have had fine particle numbers in the thousands, and large and medium particle numbers in the tens and ones, which would have been difficult to work with.
When I looked at my data to determine if there was any relationship between rainfall and sediment, I was surprised. My hypothesis was that the amount of sediment would increase after rain, but there were few consistent trends. Sometimes the amount of sediment decreased, and sometimes it increased or stayed the same. There were a few occurrences where the sediment seemed to drop after a rain, then steadily rise until the next rainfall. I am unsure why rain would reduce the amount of sediment, since it is logical that rain would wash loose debris into the water. There are several variables that might affect the sediment during a rain: how the water was acting during the rainfall, the amount of wind, the tides, etc. These factors might have caused the sediment to increase or decrease on a given day. Another confusing find was that the amount of medium sediment often did the opposite from the large and fine particles. Between the October 19 and October 25 collections, the number of medium particles rose at the lagoon, while the number of large and fine dropped. On these same dates at the beach, the amount of medium particles decreased, but the amount of fine particles increased, and large particles remained the same. Even though there appeared to be some trends, my data often appeared to contradict itself, so I would have to say the data is inconclusive.
When I looked at the different seasonal averages, I discovered a distinct connection between the season and the amount of sediment in the sample. Both sites showed practically half the amounts of sediment in spring 2006 that they contained in fall 2005. This might have been caused by leaf matter in the water. The January 22, 2006, sample from the lagoon showed an increased number of particles compared to the other samples, indicating that the dredging increased the amount of sediment in the water. In spring 2007, the average amount of sediment in the lagoon was less than half as much as during spring 2006. This might have been a result of the dredging, and perhaps the 2007 data was a more accurate representation of the sediment in the water. At the beach, there was more sediment in spring of 2007 than during the spring of 2006. I am fairly sure this was a result of the construction, since outliers during the renovation affected the averages.
The lagoon consistently had more particles than the beach, except for the spring of 2007. I am very certain this was from the construction at the beach. I originally assumed the calmer water in the lagoon would contain fewer particles because the water has the opportunity to settle, and that the wave action at the beach would stir up sediment. There are more trees around the lagoon, which might have added particles into the water. Also, some sides of the lagoon are open soil with little vegetation, which probably increased the amount of erosion. The beach does not have as much open soil as the lagoon, which might explain why the lagoon has more sediment. This was an interesting find for me.
At the conclusion of my project, I was satisfied with my results. Conducting this investigation over three seasons helped me to gather sufficient data and gave me the chance to study seasonal change. It also gave me time to perfect my methods and reflect on my progress after each data collection. I was also glad I used two different sites, because this added an interesting dimension to the project and provided me with an unexpected discovery. The construction at both sites also provided me with a strong conclusion. If I were to continue this investigation, in addition to testing the conclusions I reached here, I would add the variables of rainfall and sediment. I might improve my methods by setting up my own rain gauges instead of relying on the Internet, and I could collect samples on a more regular basis. This might provide me with a more accurate picture of trends in the data. I could also test my samples for certain chemicals and study pH and dissolved oxygen levels. Even though there are certain things I would change, I'm pleased with my findings.
At the end of this investigation, I have learned about the Chesapeake Bay and the factors that affect it. I am more aware of problems facing the bay and will use this knowledge to reduce my impact on the bay. I have also learned that predictions are not always right. However, my data revealed clear trends and patterns that appear to be very conclusive. I have also learned how to analyze data, keep on a schedule, and creative ways to carry out an investigation. Whether or not I continue this exploration, I am very pleased with the opportunities it has provided me and with the conclusions I have reached.
Bibliography
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