Introduction to Oceanography: Abiotic
Sediment Type
Research Question: How does the sediment type vary between locations in the estuary?
Part A: Read the Background Information
In an estuary, the sediment type on the bottom depends on how fast the water is moving. Areas with fast-moving water and/or big waves are sandy or gravelly, while areas with slow-moving water and smaller waves are muddier. Another important factor that affects bottom type is the location in or near the river. Rivers carry sediment from land areas down to Long Island Sound, and that sediment settles out of the water in and near the mouth. The diagram below shows an example river with different types of sediment labelled, although it’s important to keep in mind that every river mouth is different. In this example, the muddiest areas are on the edges or slow-moving parts of the river, and areas of high flow or waves in the middle of the river and outside the mouth are sandier.
Animals and bottom type
Sediment type can affect the organisms that can live in the sediment. Very few animals live in coarse sand, because it shifts around so much. Silt and fine sand are better habitats for burrowing animals such as clams and worms, both because they can more easily burrow in it, and because so much food (in the form of organic debris) settles out of the water in these quieter areas. Extremely muddy areas often have a sulfur smell - this is because bacteria eating the organic matter consume all the oxygen, leaving the sediment below the surface fit only for anoxic bacteria (which stink like rotten eggs). Some animals do still live in this type of sediment too - they just have to have special adaptations to get enough oxygen! For example, lugworms have special gills and blood cells that allow them to extract even very low levels of oxygen from the water that moves through their burrows.
Lugworm showing gills (the red feathery things). Photo credit: Encyclopedia of Life
Part B: Sampling Method
Source: Project Oceanology
The gravity core sampler is a heavy weight with a pvc pipe attached to it. It is lowered over the side of the boat with a winch until it reaches the water line and then free falls to the bottom. As the name implies the weight of the sampler drives the pvc pipe into the sediment to collect a core sample. The crank on the winch is turned to bring the gravity core sampler back on deck and the pvc pipe is removed and the core sample is pushed out using a long wooden pole.
Source: Project Oceanology
Example of a sediment sediment sample captured with the gravity core.
The core sample can be sliced open from end to end. Particle size, color and other characteristics such as odor can be recorded about each layer. From this information you should be able to learn a lot about the environment of the study area. To learn more about the gravity core watch this brief video
Part C: Prediction and Reasoning
Study the background information provided on the Gravity Core Sampling method and the types of sediment typically found in river mouths (above). Write answers to the following prompts on your sheet of paper.
1. The map below has three locations: Mitchell Beach, Black Ledge, and Seaflower Reef. Which location do you think will be the muddiest, and which will be the sandiest?
2. Explain your reasoning. WHY will the sediment be muddier or sandier at the locations you chose?
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Part D: Analyze the Data
Project Oceanology scientists collected core samples at the three locations on the map. Look at the core samples diagrams below for samples 1, 2, and 3, and read the field notes for each core. Which core do you think came from which location on the map? Make sure you have written down your prediction before you move on to Part E
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This copy of the Project O sand card is provided to help you understand the sediment types on the sediment core diagrams.
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 at the top of this page (one sentence).
2. What evidence was used to write your claim?
3. Explain your reasoning. Make sure to connect your answer to what you have learned about the sediment in Long Island Sound.
4. Core 1 was collected at Black Ledge, Core 2 was collected at Seaflower Reef, and Core 3 was collected at Mitchell Beach. Was your prediction supported by the results? Use evidence to explain why or why not.
5. Extension: Organisms within an estuary can be significantly affected by the bottom substrate type in their environment. Check out this website for information about the benthic community in the Chesapeake Bay estuary, and also review the background information above. Write a paragraph that (1) predicts at least one animal we might find living in or on the bottom at Mitchell Beach, Black Ledge, and Seaflower Reef, (2) explains why benthic animals are important to food webs, and (3) explains how human activity might affect benthic animals.
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 of which location should be sandiest and which location should be muddiest, and your reasoning
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Your prediction of which core you think came from which location.
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Your answers to the results questions
Share your results with your teacher!