Pond Mystery Worksheet Ecologist's Field Report
Case File: Blueberry Pond Ecosystem
Status Under Investigation
CODE: 05-LS2-MA
Lead Scientist
Observation Date
The Background
Massachusetts ecologists are studying Blueberry Pond . In a healthy pond, energy and matter flow through a food web. Algae (producers) are eaten by insects and small fish. Bullfrogs eat the insects. Then, herons eat the frogs.
Recently, fertilizer runoff from nearby farms entered the pond. Fertilizer has nutrients like nitrogen that help plants grow. In the pond, this caused an algae bloom —a thick layer of green slime on the surface. This layer blocks sunlight from reaching plants underwater. When those plants die, bacteria (decomposers) break them down and use up all the oxygen in the water.
Population Count
Year Bullfrog Count 2021 145 2022 138 2023* 92 2024 41 2025 12
*Year algae bloom began.
Observation Notes
2021 (Baseline)
"Water is clear. Many insects buzzing. Bullfrogs heard croaking loudly."
2023 (Change)
"Water has a green tint. Thick slime appearing. Fewer frogs heard."
2025 (Critical)
"Water is dark green and smells. Very quiet; no frogs seen or heard."
Ecosystem Living and non-living things working together.
Runoff Rain washing chemicals into a body of water.
Decomposers Organisms like bacteria that eat dead matter.
CER Investigation Analysis
Investigation Question
How did the fertilizer runoff affect the bullfrog population in Blueberry Pond?
Claim Answer the question in one complete sentence.
Evidence Use numbers and observations from the report.
Quantitative Evidence (Numbers)
Qualitative Evidence (Observations)
Reasoning Explain why this happened. Connect the science.
Review Your Work:
Used data Used science words Full sentences
Pond Mystery Answer Key Answer Key & Teacher Guide
Pond Mystery CER Investigation
Standard
MA 5.LS2-1
Instructional Scaffolds (WIDA 4)
Visual Analysis
Have students use a highlighter to connect the year "2023" to the phrase "Thick slime" in the notes. This visual connection is crucial for scientific evidence.
Sentence Frames
Provide: "Based on the table, the population ________." and "This change happened because ________." to reduce cognitive load while writing.
Misconception Management
Fertilizer = Growth?
Students often think fertilizer is always "good" for plants. Remind them that in an ecosystem, an overgrowth of one species (algae) can kill others by blocking light and oxygen.
Water Oxygen
Many 5th graders don't realize animals breathe oxygen dissolved in water. Clarify that while frogs can breathe air, the loss of a healthy water environment affects their whole life cycle (eggs/tadpoles).
Timeline Connection
Watch for students who ignore the dates. Ensure they link the arrival of algae (2023) directly to the population crash that followed.
Full Exemplar Student Response
Claim
The fertilizer runoff caused the bullfrog population in Blueberry Pond to decrease significantly.
Evidence
Quantitative: According to the report table, the bullfrog population dropped from 145 frogs in 2021 down to only 12 frogs by 2025.
Qualitative: The field notes state that the water quality changed from "clear" in 2021 to "dark green" and smelled like "rotten eggs" by 2025.
Reasoning
The fertilizer runoff provided extra nutrients that caused an algae bloom. This layer of algae blocked sunlight, which killed the plants at the bottom of the pond.
Bacteria (decomposers) broke down the dead plants and used up most of the dissolved oxygen in the water. Because frogs and other aquatic animals need oxygen to survive, many died or left the pond.
This explains why the population count dropped so quickly from 92 to 12 after the algae bloom began in 2023.
Pond Mystery CER • Teacher Reference • Page 2 of 2
Pond Mystery Slides Case File #402
The Pond Mystery
Investigating Changes in a Massachusetts Ecosystem
Evidence
Reasoning
The Setting
Blueberry Pond is a local ecosystem in Massachusetts.
Healthy Food Web:
Algae (Producers)
Insects
Bullfrogs
Herons (Apex Predator)
Think: How does matter flow through this pond?
Our Research Question
How did the fertilizer runoff affect the bullfrog population?
C
Claim
E
Evidence
R
Reasoning
Numbers (Quantitative)
Evidence #1
Year Population 2021 145 2023* 92 2025 12
*Algae bloom starts appearing.
Analyze the Data:
"In 2021, there were _____ frogs. By 2025, the number dropped to _____."
Significant Decrease detected.
Observations (Qualitative)
Evidence #2
2021
"Water is clear. Many insects. Frogs heard loudly."
2023
"Water has a green tint. Thick slime appearing on edges."
2025
"Dark green water. Smells like rotten eggs. Very quiet."
The Science Reasoning
1. Fertilizer
Runoff enters the pond with nutrients.
2. Algae Bloom
Thick algae blocks sunlight. Plants die.
3. No Oxygen
Decomposers use up all the oxygen.
4. Population Drop
Frogs cannot survive without oxygen.
Connect your Evidence to the Science using words like therefore, because, and consequently.