An Oyster Growers Dilemma
Research Question: Where along the Thames River is water color and clarity best for oyster growing? Make sure you consider how conditions will change seasonally.
Part A: Background
Water Clarity and Color
Water clarity is a measure of how clear or cloudy the water is. This is important because the water clarity will determine how much light is able to penetrate into the water. Sunlight is essential for photosynthesising marine plants and phytoplankton. It also allows animals that depend on their eyesight to find food or to avoid predators. The more transparent (clear) the water is, the deeper the light will reach.
The secchi disk is a tool used to measure the clarity or turbidity of the water. The black and white disk is weighted to help it sink. It is lowered into the water until the black and white pattern on the disk is no longer visible. This depth, known as the ‘secchi depth’, is then recorded to the nearest quarter of a meter.
Water color is an indication of what is suspended in the water - this can include phytoplankton, suspended sediment, dissolved organic material and even pollution. Water color is measured using an international scale known as the Forel Ule scale. Visit this website to see the Forel Ule scale and learn more about water color.
Water color and water clarity are related. Typically open ocean waters are an indigo blue color because the water is clearer - sediment that washes down rivers mostly settles out before the water reaches the open ocean, and open ocean water has less nutrients and therefore less phytoplankton than coastal waters. In an estuary like Long Island Sound, brownish-green colors are common because these waters are nutrient-rich, abounding in phytoplankton, and may also contain sediments from rivers. Water color in coastal areas like Long Island Sound is highly influenced by weather, because storms can dramatically increase the amount of sediment travelling down rivers. Water clarity and color can also vary seasonally - for example, sediment levels in the water are typically higher during seasons with high rainfall, or during seasons that are stormy.
Oysters and water color/clarity
Because oysters are filter feeders, they improve water clarity by removing phytoplankton and sediment from the water. However, too much suspended sediment in the water is bad for oysters for several reasons. First, small oysters can be completely smothered by sediment that settles out of the water onto them. Second, sedimentation can slow the growth rates of larger oysters. Finally, too much sediment can cause the adult oysters to have a ‘muddy’ taste that may not be appealing to consumers.
Part B: Prediction and Reasoning
If you haven’t already, take the Google Earth tour and think about how the Thames River might vary from its headwaters (where it starts, in Norwich) to its mouth.
Write the answers to the following questions on your sheet of paper.
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Make a prediction. Where along the Thames River do you expect the water clarity to be the highest in the summer? Specify a sampling location (labelled A-F on the map).
2. At the location you chose above, what season of the year do you expect the water clarity to be the highest?
3. Explain your reasoning. WHY do you think the water clarity will be highest at that location/season?
Part C: Analyze the Data
Click this link to open a spreadsheet of water clarity data, then click "file" and "download" to download this spreadsheet to Microsoft Excel. Alternatively, save this spreadsheet to your Google Sheets by clicking "file" and "make a copy".
Use the dataset to make a graph. The type of graph is up to you - decide what would work best to show the result. Your graph should have clear labels on both the x-axis and the y-axis. Hint: You will likely need to process the data (for example, by calculating some averages) before you are able to make your graph. If you have not done this type of data processing before, view this tutorial to learn how.
Part D: Interpret the Results and Make Arguments from Evidence
Write answers to the following prompts on your sheet of paper.
1. Make a claim that answers the research question at the top of this section (one sentence).
2. What evidence was used to write your claim? Reference specific parts of your graph.
3. Explain your reasoning. Make sure to connect your answer to what you have learned about oyster biology, water clarity, and seasonality.
4. Was your prediction supported by the results? Use evidence to explain why or why not.
5. Are these readings within the normal range for this area? Standard Ranges for Water Chemistry
6. Revisit the prediction you made at the very beginning, about where might be the best place for an oyster farm. Has your choice of location changed based on what you have learned about oysters, water clarity, and seasonality? Explain why or why not.
7. How does water clarity change with seasons in the Thames River, and how would you expect these seasonal changes to affect oysters?
8. How would you follow up to learn more about the potential impacts of water clarity and color on your oyster farm? Describe a new question that should be investigated to build on these results, and what future data should be collected to answer your question.
Congratulations! Your final analysis should include the following components:
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Your initial prediction and reasoning about the best location for an oyster farm.
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A statement of the research question that you chose/were assigned
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Your prediction and your reasoning about the research question
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Your labeled graph
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Your answers to the results questions
Share your results with your teacher!