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Difficulty: MediumStrengthening Arguments

To reduce agricultural nitrate pollution in local river systems, a regional water district plans to install floating artificial wetlands across its primary collection reservoirs. Critics argue that because the wetland plants enter dormancy during the winter—the season when agricultural runoff peaks—the system will fail to reduce nitrate levels when treatment is most needed. Nevertheless, environmental engineers maintain that installing these floating wetlands will substantially reduce the total annual amount of nitrates reaching the rivers. Which of the following, if true, provides the strongest support for the environmental engineers' prediction?

  1. A
    Broadleaf cattails planted on floating wetlands absorb nitrates at a faster rate during peak summer growth than any other aquatic plant species native to the region.
  2. B
    During winter dormancy, decaying plant foliage from the floating wetlands releases trapped nitrogen compounds back into the reservoir water.
  3. Even when the plants are dormant, dense root matrices beneath the floating mats host cold-tolerant bacterial colonies that decompose nitrates throughout the winter.Answer
  4. D
    The initial cost of installing floating artificial wetlands is significantly lower than the cost of constructing conventional chemical water treatment facilities.
  5. E
    Floating artificial wetlands provide valuable shelter and nesting habitats for migratory waterfowl populations during spring and autumn months.

Answer

Even when the plants are dormant, dense root matrices beneath the floating mats host cold-tolerant bacterial colonies that decompose nitrates throughout the winter.
The engineers predict a net annual reduction in nitrate runoff despite critics' objection that plants go dormant in winter during peak runoff. The option stating that cold-tolerant bacterial colonies within root matrices decompose nitrates through the winter directly resolves this concern. By providing a continuous mechanism for nitrate removal when plant uptake is dormant, this choice strongly reinforces the engineers' prediction.

Step-by-Step Solution

1
Identify the argument's structure and core conflict.
Premise: Critics point out that wetland plants are dormant in winter when agricultural runoff peaks. Conclusion: Engineers predict that floating wetlands will still significantly lower annual nitrate runoff to rivers.
Strengthening requires finding evidence that fills the logical gap or addresses the vulnerability raised by critics.
2
Determine the necessary strengthening mechanism.
The argument needs evidence showing that nitrate levels will still be reduced in winter despite plant dormancy, or that winter plant dormancy does not impede overall annual removal.
Overcoming the objection about winter inefficiency directly supports the engineers' annual reduction claim.
3
Evaluate the answer choices against the required mechanism.
The fact that cold-tolerant bacteria in the root matrix break down nitrates continuously during winter supplies a missing mechanism that explains how the system works despite plant dormancy.
Supplying an active process for nitrate breakdown during plant dormancy resolves the main vulnerability in the engineers' prediction.

Key Concept

Strengthening Arguments by Supplying a Missing Mechanism or Countering an Objection
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Strengthening Arguments

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