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Debate kit Grade 7 Science

Should Caldon County Require Buffer Strips Along Yarnell Creek?

A two-session grade 7 science debate on a proposed rule requiring planted stream buffers on farms, with two-sided evidence on nutrients, fish, land cost, and fairness.

Objectives

  1. Students will construct an argument about a proposed farm rule using named water quality evidence.
  2. Students will rebut an opposing team's strongest point with evidence rather than opinion.
  3. Students will explain how nutrients entering a creek can lower the oxygen fish need.

Vocabulary

Dissolved oxygen
Dissolved oxygen is the oxygen gas mixed into water that fish and other underwater animals breathe. Cold, moving water holds more oxygen than warm, still water.

Also: buffer strip, nutrient, runoff, algae bloom, cost-share

Teacher overview

This kit runs as a two-team structured debate across two class sessions, with preparation in the first session and four timed rounds in the second. Teams argue for or against a county rule that would require every farm along a creek to keep a planted strip between its fields and the water. Buffer rules of this kind exist in some places and are voluntary in others, and the disagreement is real: the science on nutrients and oxygen is settled, while the questions of who pays, how wide a strip has to be, and whether a rule or a payment program works better are genuinely open.

Should Caldon County Require Buffer Strips Along Yarnell Creek? — Grade 7 Science
Name: ____________________________ Date: ______________

Resolution & Background

Resolution: Caldon County should require every farm along Yarnell Creek to keep a 35-foot strip of planted, unplowed land between its fields and the water.

Background: Caldon County and Yarnell Creek are fictional places written for this debate. Farms in the county grow corn and hay. Farmers add fertilizer to help those crops grow. Fertilizer holds nitrogen and phosphorus, which plants need. Rain washes some of that fertilizer off the fields. The runoff carries it into ditches and then into the creek.

In the creek, those same nutrients feed algae. The algae grow fast and form thick mats. When the algae die, bacteria break them down. Those bacteria use up oxygen in the water. Most fish need dissolved oxygen above 5 mg/L to stay healthy, so a big drop in oxygen can push fish out of a stretch of stream or kill them outright.

A buffer strip is a band of grass, shrubs, or trees left between a field and the water. Runoff slows down when it hits the thick plant cover. Some of it soaks into the ground instead of reaching the creek. Roots take up part of the nitrogen. Soil particles drop out before they reach the water. Buffers do not stop every nutrient, and how well they work depends on the slope, the soil, and how wide they are.

Farming is also the largest single user of fresh water. Agriculture accounts for roughly 70 percent of global freshwater withdrawals, so what happens on farmland matters to water quality and supply in many places. (Source: FAO and UN Water.)

Roles: Each team of four fills these roles. The opening speaker states the claim and two reasons. The evidence lead presents three pieces of evidence from the file. The rebuttal speaker answers the other team's strongest point. The closing speaker explains why the team's evidence outweighs the other side's. One student acts as moderator and keeps time. Students not on a team serve as judges and score with the rubric.

Evidence File

Case for requiring buffer strips

  1. Monitoring created for this debate shows the difference. Crews sampled Yarnell Creek at two sites for one summer. Below fields with no buffer, nitrate averaged 6.1 mg/L. Below fields with a wide planted buffer, nitrate averaged 2.4 mg/L. Both sites had the same soil and slope. (Illustrative data written for this debate, not a documented study.)
  2. Fish need oxygen, and nutrients take it away. Most fish need dissolved oxygen above 5 mg/L. Nutrients feed algae, and the bacteria that break down dead algae pull oxygen out of the water. Cutting nutrients at the edge of the field protects the oxygen fish depend on. (Source: standard water quality benchmark, EPA and USGS.)
  3. A rule applies to everyone at once. A fictional Caldon County extension agent notes that under the current voluntary program, a farm that installs a buffer gives up cropland while the farm next door gives up nothing. A county-wide rule removes that penalty for acting. (Illustrative testimony written for this debate.)
  4. Buffers hold the bank in place. Roots grip the soil during high water, so less streambank washes away. That means less mud in the creek, and mud carries phosphorus with it.

Case against requiring buffer strips

  1. The land cost is real and uneven. A 35-foot strip along 2 miles of creek bank covers about 8.5 acres. On a small farm, that is a large share of the tillable ground, while a large farm gives up a smaller share of its total. (Calculation written for this debate using its own stated numbers.)
  2. A flat rule ignores where the problem is. A field on a steep slope sends far more runoff to the creek than a flat field with a cover crop. A fictional county soil scientist argues that spending the same money on the steepest fields would cut more nutrients than requiring the same strip everywhere. (Illustrative testimony written for this debate.)
  3. Buffers need ongoing care after planting. A fictional Caldon County farmer testifies that buffers must be mowed, replanted after floods, and kept free of invasive weeds. Without cost-share payments, that work competes with other farm expenses. (Illustrative testimony written for this debate.)
  4. A mandate can slow progress. The county's voluntary cost-share program has already enrolled part of the watershed. A fictional county board member warns that a rule could bring legal challenges and stall improvements that are happening now. (Illustrative testimony written for this debate.)

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
Evidence use States a position with no evidence from the file Names one piece of evidence but does not connect it to the claim Names at least two pieces of evidence and explains how each supports the claim Uses several pieces of evidence, explains each, and shows why they outweigh the other side's
Scientific reasoning Does not mention nutrients, algae, or oxygen Mentions the nutrient pathway but skips steps Traces the pathway from fertilizer to runoff to algae to oxygen loss Traces the pathway and notes what conditions would change how much the buffer helps
Rebuttal quality Does not respond to the opposing team Restates the team's own claim instead of answering Answers a specific opposing point using evidence from the file Answers more than one opposing point and identifies the weakest assumption behind them
Organization and delivery Hard to follow, with no clear order Has an order but transitions are unclear Follows a clear claim, evidence, and conclusion structure Clear, well-paced, and directly responsive to the resolution throughout

Differentiation

Support

Give students an evidence card for their side listing only the two strongest points, each rewritten in one sentence. Provide rebuttal sentence starters: "The other team said ___, but the monitoring in our file shows ___." Allow the rebuttal speaker to read from prepared notes.

Extension

Ask students to design a compromise the county board could adopt, such as a narrower required strip paired with payments for wider buffers on the steepest fields, and to defend that compromise against both original positions in a written closing statement.

ELL supports

Pre-teach "buffer," "runoff," "nutrient," and "bloom" with a labeled cross-section drawing showing a field, a grass strip, and a creek. Provide a two-column note sheet with the headings "Our evidence" and "Their evidence" so students can track the debate visually while it runs.

Extensions

Have students locate a stream on a county or city map, mark where fields, lawns, or parking lots reach the bank without a planted strip, and write a one-page letter to a local board proposing which stretch should be buffered first and why.