Students will explore the effects of an increase in nitrogen and phosphorus in aquatic ecosystems. They will collect data from an algae growth investigation and complete a reading about human-produced nutrient inputs. Using these sources of evidence, students will develop a causal explanation of the relationship between human activity, nutrient cycles, and changes to organisms' population sizes during eutrophication of aquatic ecosystems. Throughout the lesson they will create and revise a Claim-Evidence-Reasoning statement that explains the phenomenon of algae blooms.
How do disruptions to a physical component of an ecosystem lead to shifts in all its populations? Specifically, how do increases in nutrient levels change aquatic ecosystems?
Students complete an I Notice, I Wonder activity and write an initial Claim-Evidence-Reasoning (CER) explanation for the algal bloom phenomenon they observe.
Students conduct an algae growth investigation.
Students identify the steps that occur during the process of eutrophication, learn about nutrient cycles, and identify where in nutrient cycles humans add excess nutrients to systems. They also revise their CER.
Students read an article about specific kinds of human nutrient inputs and create Cognitive Comics illustrating how excess nutrients cause changes in population sizes during an algal bloom.
Students synthesize the data they collected and scientific concepts to make a final revision to the CER that explains the phenomenon they observed in the Engage section.
CER Scaffolds (attached; optional; one per student)
CER Rubric (attached; for instructors' use)
Eutrophication Reading (attached; one per student)
Eutrophication Reading Short Version (attached; optional; one per student)
What's Blooming Data Sheet handout (attached; one per student)
What's Blooming? Investigation handout (attached; one per student)
What's Blooming? Investigation Teacher Guide (attached; for instructor's use)
Lab investigation material (see What's Blooming Lab - Teacher Guide for more details):
Cheesecloth or coffee filters
Pond/lake water (or commercial algae culture)
Bottled spring water
Nutrient kits (from aquarium shop or pet store)
Fertilizer (powdered or granulated)
Powder detergent containing phosphates
Nitrile or latex gloves
Digital scale or balance
Begin the lesson by projecting the image of a fish in a eutrophied pond on slide 5. Use the I Notice, I Wonder strategy to have students make observations and ask questions about the picture they see. Take a few minutes for students to share with the class what they noticed and wondered about the picture and record their responses where everyone can see.
Go to slide 6 and ask students to make a claim about what caused the phenomenon they observe in the picture. Students should try to explain the cause of the phenomenon they see (as best as they can at this point in the lesson) using the CER strategy. They can use their observations of the picture as evidence to support their claims of what they think happened.
Go to slide 7. Put students into lab groups (2-4 students) as you see fit and provide each student with a copy of the What's Blooming? Investigation handout and What's Blooming? Data Sheet handout.
Give students instructions to obtain materials for the investigation (listed for teachers on What's Blooming? Investigation - Teacher Guide and for students on their What's Blooming? Investigation - handout). On day 1, be sure to give students specific guidance for how to complete the nutrient measurements since the procedures will vary depending on your testing kits.
At the end of the 14-day investigation, have each lab group analyze their data. Show slide 8 of the lesson slides. Ask students to describe what happened to the jars based on their visual observations and how the nutrient levels changed over time. Based on their analysis, students should draw a conclusion about the relationship between nutrients and the water conditions. The last page of the Data Sheet includes space for students to record their ideas in a way that will support their ongoing CER revisions.
Pair up students from different lab groups so that they can discuss their findings. Go to slide 9. In these pairs, students should explain to each other, one at a time, their group's conclusions for the What's Blooming? Investigation. They will determine if there were any differences between their conclusions, why their conclusions are different, and which conclusions are supported by their data. They should record any new conclusions they agree upon on their What's Blooming? Data Sheets.
Ask students to return to their original lab groups and pick a speaker. Have each group speaker share their conclusions with the class. Next, move to slide 10 and formally introduce the terms eutrophication and algal bloom to describe the phenomenon they investigated. Help students explain what happens in the aquatic ecosystem when an algal bloom occurs. Asking students to walk through what occurs in a sequential order will help them develop an understanding of the impacts of eutrophication for themselves. Move to slide 11 after students have attempted to explain it themselves.
Go to slide 12 and ask the students if they have enough information to explain how the nutrients contributed to the algal bloom. (They don't yet!)
Introduce students to the nitrogen and phosphorus cycles using slides 13 and 14. Move to slide 15 and students to draw one model that illustrates how both phosphorous and nitrogen enter aquatic ecosystems.These cycles usually produce normal amounts of nutrients, but severe algal blooms come from excess nutrient input. Ask students the questions listed on slide 15:
Where in the cycles are extra nutrients most likely to enter the aquatic ecosystem?
Why are these parts of the cycle more likely to produce extra nutrients?
Go to slide 16. At the end of notetaking and discussion, each student should revise their initial CER to reflect the data they collected in the investigation. Using new vocabulary they learned, they should include details about the nutrient cycles.
Next, students will read about two of the major human inputs of excess nutrients specific to algal blooms. Go to slide 17 and give students a copy of the Eutrophication Reading (or the shorter Eutrophication Reading Short Version). Using the reading, as well as the resources and notes they have gathered so far, ask students to create a Cognitive Comic that describes how nutrient inputs change population sizes of organisms during an algal bloom. These can be done individually, in pairs, or in their previous lab groups, at your discretion.
Have students present their comics to the class. At the end, highlight the steps of the process and give students time to make notes about anything they missed in their drawings.
To wrap up the lesson, review the phenomenon discussed during the Engage section by moving to slide 18. Have students create a final CER that explains what caused the phenomenon. Students should address both the green color of the water and the dead fish as part of their CER.
The CER Rubric attachment is a generic rubric for instructors' use that you can modify to include the specifics of this lesson. Students' claims should reference increased nutrient input and evidence should come from their investigation data. Encourage them to reference their notes, the reading, and class discussions when explaining their reasoning.
Gioffre, D. (n.d.). Eutrophication Reading. Hillsborough; Hillsborough Middle School. Funded by the National Science Foundation, Biocomplexity in the Environment Program, Award #0120453.
Graham, J.L. (2018). Cyanobacterial accumulation at Binder Lake, Iowa [Photograph]. US Geological Survey. https://toxics.usgs.gov/photo_gallery/photos/emer_cont/cyanobac/dead_fish_binder_lake_iowa_7_l.jpg
K20. (n.d.). Claim, Evidence, Reasoning (CER). Strategies. https://learn.k20center.ou.edu/strategy/156
K20. (n.d.). Cognitive Comics. Strategies. https://learn.k20center.ou.edu/strategy/198
K20. (n.d.). I Notice, I Wonder. Strategies. https://learn.k20center.ou.edu/strategy/180
ModelTeaching. (2019, January 29). Claim-Evidence-Reasoning (CER). https://www.modelteaching.com/education-articles/writing-instruction/claim-evidence-reasoning-cer
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Eutrophication comic (slide 17)