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Introduction to Oceanography: Abiotic
Sunlight
Research Question: How and why does the percentage of light penetration change from surface to bottom?
Part A: Background Information
Sunlight is the main source of energy for the entire estuary food web. Primary producers at the surface always get adequate sunlight for photosynthesis, which produces glucose that is usable by all other parts of the food web. Plants below the surface get variable amounts of light depending on the clarity or turbidity of the water. Many particles can cloud the water: sediment like sand or silt, organic matter from dead organisms, even plankton and algae. With more dissolved or suspended in the water, less light can penetrate to depth.
Part B: Sampling Method
Source: Project Oceanology
The light meter is an instrument used to measure the amount of light reaching different depths in the water. There is a sensor on the top of the roof of the Enviro-Lab that detects the amount of ambient light, or how much light is above the water. The sensor at the end of the probe measures light below the water, and is deployed to the surface and then each meter of depth until reaching the bottom. By comparing the “Deck Sensor” reading with the “Underwater Sensor” reading, we can calculate the percentage of the light penetrating to each depth. This percentage gives scientists an idea of how much light is available to organisms at different depths.
Part C: Prediction and Reasoning
Study the background information provided on sunlight penetration (above) and look at the field notes (below). Write answers to the following prompts on your sheet of paper.
Sample Location: Mouth of the Thames River estuary. (View map here)
Time of Year: Early May
Field Notes
Weather Conditions: Day time air temperatures are about 61 Fahrenheit and evening air temperatures
are about 48 Fahrenheit.
Sample Depth: Temperature samples were collected at the surface (0 meters) and recorded every meter
until reaching the bottom at 9 meters. This is called a depth profile.
Write answers to the following prompts on your sheet of paper.
1. Make a prediction: How will the amount of available light change from the surface to the bottom? If you are predicting that the amount of light will change, do you think the change will be gradual or drastic?
2. Explain your reasoning. WHY do you think the light levels will or will not be different?
Part D: Analyze the Data
Look at the dataset below. On your piece of paper, illustrate the data by making a special graph called a depth profile. The axes look a little different than you might be used to; simply plot column 1 numbers on the vertical axis and column 2 on the horizontal. The origin is still (0,0). Connect your points with a curved line.
This table shows the read-outs on the light meter. You’ll need to calculate the percent of the light for each depth using the formula below:
(Underwater Sensor ÷ Deck Sensor) × 100= % Surface Light
Part E: 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 (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 factors that impact light penetration.
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. Extension: Organisms within an estuary can be significantly affected by changes to light penetration through the water. Check out this website for information about seagrass beds, and this one about the animals who live there. Write a paragraph that (1) identifies at least one factor that would cause the light levels that penetrate to the bottom of the estuary to change, (2) explains how changes in light levels would affect sea grasses, and (3) explains how this affects (or is affected by) people.
Congratulations! Your final analysis should include the following components:
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A statement of the research question that you chose/were assigned
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Your prediction and your reasoning
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Your labeled graph
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Your answers to the results questions
Share your results with your teacher!
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**Educators and/or homeschool parents: educator guides are available for all research projects.
Email mjacobs@oceanology.org to request an educator guide**
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