Introduction to Oceanography: Abiotic
Salinity
Research Question: How and why does the salinity change from surface to bottom of Long Island Sound?
Part A: Background Information
Salinity is the measurement of salt concentration in water. Salinity is usually measured in parts per thousand (ppt). Oceans are consistently salty with the average salinity of about 35 ppt while freshwater environments like lakes and ponds have little to no salt (0 ppt). Estuaries are environments where ocean water and river water meet and mix. This makes the salinity variable. The salinity is higher at the mouth of the river because it’s closer to the salt water source and becomes less salty as you move towards the head of the river or farther away from the salt water.
The salinity in estuaries like Long Island Sound changes constantly over the course of a day. It is influenced by how much salt water is flowing in from the Atlantic Ocean tides and how much freshwater is flowing down the Thames River (and the other major rivers in Connecticut).
Saltwater and freshwater have different densities. Dense salt water will sink below less dense fresh water. Therefore, the estuary is often composed of layers of water of different densities and salinities.
Part B: Sampling Method
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Source: Project Oceanology
The YSI Meter is a very important tool that can measure water temperature, salinity and dissolved oxygen all at the same time. The photo above (left) shows the sensor portion of the YSI meter that is deployed into the water (the weight attached helps the sensor to sink down straight). The photo above (right) shows the handheld computer portion of the YSI meter. Each number on the screen represents the temperature, salinity or dissolved oxygen reading in real time. This sensor is deployed just under the surface of the water for the first reading and then it’s lowered every meter after that until it reaches the bottom of the sample location.
To learn more about the YSI meter watch this brief video:
Part C: Prediction and Reasoning
Study the background information provided on Salinity (above) and look at the field notes (below).
reaching the bottom at 9 meters. This is called a depth profile.
Sample Location: Mouth of the Thames River estuary. (View map here)
Time of Year: Early May
Weather Conditions: Day time air temperatures are about 61 Fahrenheit & evening air temperatures are
Field Notes
Sample Depth: Salinity samples were collected at the surface (0 meters) and recorded every meter until
about 48 Fahrenheit.
Write answers to the following prompts on your sheet of paper.
1. Make a prediction: Will the salinity be the same at the surface and the bottom?
2. Explain your reasoning. WHY do you think the salinity will or will not be different?
Part D: Analyze the Data
Look at the data table 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 (y) and column 2 on the horizontal (x). The origin is still (0,0). Connect your points to form a line. Remember good graphs have a title, a labeled x-axis (including units), a labeled y-axis (including units) and an appropriate scale.
This table shows the salinity measured at each depth from surface to bottom in May.
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 the density of salt and fresh water in the estuary.
4. Was your prediction supported by the results? Use evidence to explain why or why not.
5. What do these numbers mean for the health of Long Island Sound? Are these readings within the normal range for this area? Standard Ranges for Water Chemistry
6. How would you follow up? Describe a new question that should be investigated to build on these results, and what future data should be collected to answer your question.
7. Extension: Organisms within an estuary can be significantly affected by the salinity of their environment. Check out this website and this infographic for information about Eastern Oysters. Write a paragraph that (1) identifies at least one factor that might cause salinity in an estuary to change, (2) explains how salinity affects oysters, 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!