Debate kit Grade 6 Science
Closing Caldmere Reservoir's Ramps to Slow the Mussels
A grade 6 science debate on whether a fictional town should close its boat ramps to keep zebra mussels out, with two-sided evidence on spread, food webs, and cost.
Objectives
- Students will argue from monitoring data about how a new species would change a reservoir food web.
- Students will explain why clearer water is not always evidence of a healthier lake.
- Students will rebut an opposing claim by naming the record that weakens it.
Vocabulary
Key words: zebra mussel, larva, plankton, water clarity, food web, intake screen
Teacher overview
This debate runs as a town council hearing across two class periods. Two teams of five argue over whether a fictional town should close its boat ramps to trailered boats to keep zebra mussels out of its drinking water reservoir, a moderator keeps time, and the rest of the class serves as the council and votes. The question is genuinely open, because the same closure that lowers the chance of a permanent invasion also shuts down the lake for the people who use it, and other doors into the lake would stay open. A common misconception worth naming before students read the evidence is that clear water is proof of clean, healthy water. Zebra mussels filter plankton out of a lake and make it look noticeably clearer, yet plankton is the food base that young fish depend on, so the clearer lake can hold fewer fish. Students who equate clarity with health will read the strongest piece of evidence backward.
Resolution & Background
Resolution: "The town of Camberton should close the Caldmere Reservoir boat ramps to trailered boats."
Camberton is a fictional town, and Caldmere Reservoir is its fictional water supply. The reservoir sits behind Caldmere Dam. Everything here about Camberton and Caldmere is fictional and was written for this debate.
A zebra mussel is a small striped shellfish about the size of a fingernail. It came to North America from Europe. Adults glue themselves to hard surfaces such as rocks, pipes, and boat hulls. Their young, called larvae, are too small to see and drift in the water. Larvae ride from lake to lake in bilge water, live wells, and bait buckets, and adults ride on hulls and trailers.
Zebra mussels are filter feeders. Each one pulls in water and strains out the tiny floating plants and animals called plankton. A dense bed of mussels can strain a large volume of water every day.
Caldmere Reservoir supplies drinking water to Camberton and also feeds a small power plant at the dam. Mussels stick to intake screens and inside pipes, which is why the utility has a stake in the vote.
Roles. Five students argue for closing the ramps. Five argue against. One student moderates and keeps time. Everyone else serves as the town council, writes questions on index cards, and votes.
Format. Each team gives a four-minute opening. Teams take six minutes to prepare. Each team gives a three-minute rebuttal and a two-minute closing. The council asks four questions from the cards, then votes. Each team turns in its written opening and its rebuttal notes.
Evidence File
Every record below is a fictional record written for this debate, except where an outside source is named.
Case for closing the ramps
- Mussel larvae are too small to see, so a boat can carry them without anyone knowing. A trailer pulled from an infested lake in the morning can launch here the same afternoon. (Source: a fictional county boating study.)
- Mussels turned up in Mirefield Lake, about 40 miles away, two summers ago. A fictional ramp survey found that roughly one boat in five launching at Caldmere had been at Mirefield within the past month. (Source: a fictional ramp survey.)
- There is no known way to clear an established mussel bed out of a whole lake. Once they take hold, a town manages them rather than removes them. (Source: a fictional state biologist's memo.)
- A lake north of here has had mussels for six years. Its clarity rose from about 4 feet to about 11 feet, its plankton counts fell by more than half, and its young walleye counts fell in the same years. Clearer water in that lake came with less food for young fish. (Source: a fictional state lake monitoring record.)
- At that same lake, the utility now cleans its intake screens every three weeks instead of twice a year, and crews scrape mussels off the dam's cooling lines each fall. (Source: a fictional utility maintenance log.)
Case against closing the ramps
- Boats are not the only door. A fictional inspection log at Caldmere recorded plant fragments stuck to kayak trailers and to waders, and waterfowl move between lakes on their own. A closure aimed at trailered boats leaves those paths open. (Source: a fictional inspection log.)
- A closure costs the town. A fictional chamber of commerce estimate puts the loss at $260,000 a year across the marina, the campground, and the spring fishing tournament, along with three jobs. (Source: a fictional chamber of commerce estimate.)
- Inspection is a cheaper tool that keeps the lake open. A fictional pilot at a nearby lake inspected about 900 boats in one season, found mussels or standing bilge water on six of them, and stopped all six at the ramp. (Source: a fictional inspection pilot report.)
- Mussels need calcium in the water to build their shells. The fictional district biologist reports that Caldmere runs near 9 mg/L of calcium, which she calls low compared with the lakes where these mussels have taken hold. A lake that is a poor fit may not need the strongest rule. (Source: a fictional district biologist's memo.)
- Enforcement is not free either. A fictional sheriff's estimate says shoreline patrols would take one deputy shift a week, and boats turned away at the ramp may launch from unwatched banks where no one checks them at all. (Source: a fictional sheriff's estimate.)
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Rubric
| Criterion | Emerging | Developing | Proficient | Advanced |
|---|---|---|---|---|
| Use of evidence | States a position with no evidence from the file | Names one record but does not say what it shows | Names at least two records and explains what each shows about the reservoir | Names several records, explains each, and says which one carries the most weight and why |
| Reasoning about the food web | Treats the mussels only as something that clogs pipes | Mentions filtering without connecting it to other living things | Connects mussel filtering to lower plankton and then to young fish | Traces the chain from filtering through plankton to fish, uses the clarity record correctly, and notes what the data cannot settle |
| Rebuttal | Does not respond to the other team | Responds in general terms without naming a record | Answers a specific opposing point using a named measurement or record | Answers more than one opposing point and explains why the team's own evidence is stronger |
| Delivery and organization | Hard to follow; no clear order | Has an order, but transitions are unclear | Follows a clear claim, evidence, and conclusion structure within the time limit | Clear, well paced, and responsive to council questions as well as to the opening arguments |
Differentiation
Support
Give these students a card holding only the two strongest points for their side, printed in larger type with the measurement circled. Provide a simple food web drawing of the fictional reservoir with plankton, young fish, and mussels, and have them draw the arrows before they speak. Offer rebuttal frames such as "The other team said ___, but the monitoring record shows ___." Allow a written opening to be read aloud.
Extension
Ask a pair to serve as the council's science advisers rather than debaters. They answer questions about what the fictional monitoring records can and cannot show, and they flag any claim that runs past the record. A second option is to write the council's decision with one condition attached, such as an inspection schedule, and to justify the condition with named evidence.
ELL supports
Pre-teach "mussel," "larva," "plankton," "clarity," and "intake screen" with labeled pictures and a short demonstration: stir flour into a jar of water, then pour it through a coffee filter so students can see filtering remove what was floating. Provide a bilingual glossary card. Allow students to speak from a written script and give extra preparation time before the rebuttal round.
Extensions
Have students find out whether their own state runs boat inspection stations, and report what an inspector checks and what a boater is asked to do before launching. A second option is to design a one-page card for boat owners at the fictional Caldmere ramp that explains, in five steps, how to clean, drain, and dry a boat, and to explain which step targets the larvae rather than the adults.