B. Life Systems · Interactions in the Environment

Reducing Harm, Increasing Good: How Well Do Our Solutions Work?

B1.2 A1.1 A1.3 A1.4 A1.5 A3.2About 60 minutes

Learning goals

I can describe ways to reduce the negative impacts and increase the positive impacts of human activities on the environment.
I can assess how effective a solution is, using criteria and evidence.
I can use the engineering design process to build and test a model that reduces an environmental impact.
I can plan a realistic action and explain how I would measure whether it worked.

Words to know

mitigate
To make a harmful effect less serious.

effectiveness
How well something does what it is supposed to do, shown by evidence.

criteria
The standards you use to judge or compare things (for example: cost, how well it works, side effects).

restoration
Helping a damaged ecosystem return to a healthier state.

protected area
Land or water set aside to protect nature, such as a provincial park, national park or Indigenous Protected and Conserved Area.

unintended consequence
A result of an action that was not planned or expected.

engineering design process
A cycle engineers use to solve problems: define the problem, brainstorm, plan, build a prototype, test, improve and share.

Does it actually work?

A school puts one big sticker of a hawk shape on a large window, hoping it will stop birds from flying into the glass. Does it work? Many people would guess yes. But studies of bird collisions have found that one or two stickers do not help much: birds simply try to fly around the sticker, through the open-looking glass beside it.

Wanting to help the environment is a great start. But to really help, we need to ask: Does this solution work? How do we know? Is there a better one? That is what this lesson is about.

A large window with a grid of small white dots on the glass, reflecting trees and sky. — Tests show that closely spaced dots like these help birds see the glass. Measuring whether a solution works is how we judge it. AI-generated image

Two goals: reduce harm and increase good

Mitigating negative impacts means making harmful effects smaller. Enhancing positive impacts means doing things that actively help ecosystems.

Here are some kinds of approaches, with examples:

Laws and rules: Canada's Species at Risk Act and Ontario's species-at-risk law (the Species Conservation Act, 2025, which replaced the Endangered Species Act in 2026) protect species at risk and their habitats. Fishing and hunting rules set limits and seasons.
Protected areas: parks and Indigenous Protected and Conserved Areas protect habitats from development. Canada has set a goal of protecting 30% of its land and fresh water and 30% of its oceans by 2030.
Better design: wildlife crossings (bridges and tunnels for animals) with fencing along highways; bird-friendly glass; buffer strips on farms.
Restoration: replanting forests, restoring wetlands, bringing back native species.
Changing habits: reducing, reusing and recycling; walking, cycling or taking transit; turning off lights at night during bird migration; using less road salt.
Enhancing nature: pollinator gardens with native plants, green roofs, rain gardens, planting trees in cities, and citizen science that helps researchers track species.

How to assess effectiveness

Use criteria to judge a solution. Common criteria:

Evidence it works: Has it been tested or measured? What changed?
Size of the effect: Does it make a big difference or a small one?
Cost and effort: Is it affordable and practical?
How long it lasts: One-time fix or long-term?
Side effects: Could it cause unintended consequences?
Fairness and participation: Who is affected? Were the people who live there, including First Nations, Métis and Inuit communities, involved? Will people actually use it?

Two real examples with good evidence:

Wildlife crossings in Banff National Park, Alberta: dozens of overpasses and underpasses, combined with fences along the Trans-Canada Highway, have greatly reduced collisions between vehicles and large animals such as elk, deer and bears. Cameras have recorded animals using the crossings many thousands of times. In Ontario, ecopassages under some highways, such as Highway 69 near Georgian Bay, help turtles, snakes and other animals cross safely.
Sudbury, Ontario: after decades of mining and smelting pollution left hills bare and acidic, the community spread crushed limestone and planted millions of trees, starting in the late 1970s. Pollution controls at the smelters also cut emissions. Forests are growing back, though recovery is still going on.

A wildlife crossing seen from above. Fences along the highway guide animals toward the overpass, so they cross above the traffic instead of on the road.

Worked example

Let's compare solutions using criteria

Birds keep hitting the large windows of a school library. Three solutions are suggested: (A) stick one hawk-shaped decal on each window; (B) cover the outside of the glass with a film of small dots spaced about 5 cm apart or closer; (C) close the blinds and turn off the library lights at night. Assess each one.

Evidence: research on bird collisions shows that a few decals far apart do not work well: birds fly through the gaps. Patterns of markings spaced about 5 cm apart or less, on the outside of the glass, greatly reduce collisions. Turning lights off at night helps birds that migrate at night, which are attracted to lit buildings.
(A) Hawk decals: cheap and easy, but low effectiveness. Score: low.
(B) Dot film: costs more, but high effectiveness day and night, and lasts for years. Score: high.
(C) Lights off: free and saves electricity, helps at night, but does not stop daytime collisions from reflections. Score: medium.
Side effects: dot film slightly changes the view; lights-off needs people to remember (a timer helps).

The best plan combines (B) and (C): dot film for daytime and lights off at night. Solution (A) feels helpful but has little evidence of working. Choosing solutions by evidence and criteria is how you assess effectiveness.

Criterion	A: hawk decal	B: dot film	C: lights off
Evidence it works	Weak	Strong	Strong for night migrants
Size of effect	Small	Large	Medium
Cost	Low	Higher	Free (saves money)
How long it lasts	Years	Years	Every night, needs habit or timer
Side effects	Few	Slightly changes the view	Few

A criteria table makes comparing solutions clearer.

Why the evidence favours dot film. Birds treat the glass beside a single decal as open sky. Markings close together on the outside of the glass look like a barrier, so birds turn away.

Watch for unintended consequences

Some solutions cause new problems:

Biofuels made from crops can reduce fossil fuel use, but growing more crops may mean clearing more land.
Paper bags instead of plastic bags avoid plastic litter, but making paper bags uses a lot of water and energy. Reusing any bag many times is better than using a new bag each time.
Planting trees is great, but planting only one species, or planting trees on a natural prairie, can harm biodiversity.

That is why scientists monitor a solution after it starts and adjust it if needed.

Cross-subject connection

Assessing solutions uses math (measuring, graphing before-and-after data, comparing costs), language (writing a persuasive proposal to your principal or council) and social studies (how governments make laws and how communities make decisions). Real environmental problems are solved by combining subjects.

Just for fun

The lonely hawk sticker tried its best. Sadly, the birds just read it as a sign saying "Please fly around me," and went straight for the glass next to it. That's why scientists test solutions!

Hands-on activity

Engineering challenge: build a runoff filter

Problem: rain washes soil from farms, lawns and construction sites into streams. Buffer strips and rain gardens slow and filter this runoff. Design a model filter that makes muddy water as clear as possible.

You need: a clear plastic 2-litre bottle, scissors (a grown-up cuts), a cup of garden soil, water, a large clear jar, and filter materials to choose from: gravel or small pebbles, sand, cotton balls, a coffee filter, a clean cloth, dried grass or leaves.

Make "runoff": mix 2 big spoonfuls of soil into 500 mL of water in the jar. Stir. Save a small cup of it to compare.
Prototype: a grown-up cuts the bottle in half. Turn the top half upside down (like a funnel) into the bottom half. Plug the neck lightly with a cotton ball. Add layers of materials in the order you think is best.
Test: pour 250 mL of runoff through your filter. Time how long it takes.
Measure clarity: hold the filtered water in a clear cup in front of printed text. Rate it 1 (can't see the text at all) to 5 (reads like clear water). Compare it with the unfiltered sample.
Improve: change one thing (order, thickness, a new material) and test again with fresh runoff. Record both results in a table.
Share: draw your best design, label the layers, and explain how it is like a buffer strip or wetland.

Safety: a grown-up does all cutting. Do not drink the filtered water: it is clearer, but it is not clean or safe to drink. Wash your hands after handling soil. Pour used water onto the garden, not down the sink (soil can block drains).

What to look for: a labelled design, a fair comparison (only one change between tests), results recorded with clarity ratings and times, and a clear link to real solutions. Usually, layers from coarse to fine (gravel, then sand, then cotton or filter) work well, but slower filters often give clearer water: a real trade-off.

Plan your own action

Choose a local problem you care about (litter in a park, birds hitting windows, salt in a stream, a lack of pollinator plants). Then:

Research the problem and possible solutions, with reliable sources.
Compare at least two solutions using criteria.
Choose one and plan it: who, what, when, materials, cost.
Measure: decide what you will count or observe before and after (bags of litter collected, birds found under windows, number of pollinator visits in 10 minutes).
Share your results and what you would change next time.

Your turn

What does mitigate mean?

Give one way to reduce a negative impact and one way to enhance a positive impact.

Name four criteria for assessing a solution.

Why does one hawk decal on a big window not work well?

What evidence shows that wildlife crossings in Banff work?

What is an unintended consequence? Give an example.

In the runoff filter challenge, why should you change only one thing between tests?

More practice: warm-up

What is a protected area?

What Canadian law protects species at risk across Canada?

Name one Ontario city that restored land damaged by mining pollution.

What percent of its land has Canada set a goal to protect by 2030?

Is filtered runoff from your model safe to drink?

More practice: on your own

A town plans to cut road salt use by 30%. Name two criteria you would use to judge whether the plan is effective, and what you would measure.

Why should people who live in an area, including First Nations, Métis and Inuit communities, be involved in choosing solutions?

Explain why the best plan for the library windows combined two solutions.

Explain how a buffer strip of plants along a stream is like your runoff filter.

A group plants 500 trees in a park but doesn't water them, and half die. What does this show about assessing effectiveness?

Challenge

Your class wants to help pollinators. Option A: hand out 100 packets of mixed wildflower seeds (some species not native). Option B: plant one 10 m² garden of native Ontario plants with the school, and record pollinator visits each month. Assess both with at least three criteria and recommend one.

Explain why monitoring after a solution starts is important. Use one example of an unintended consequence.

In your runoff filter, the clearest water came from the thickest sand layer, but it took 12 minutes to drain. In a real rainstorm, why might that be a problem, and how could engineers balance the trade-off?

Check your understanding

Quiz

To mitigate a negative impact means to...

Which is the best evidence that a solution is effective?

Based on research, which works best to stop birds hitting a large window in the daytime?

Wildlife crossings with fences along highways mainly help by...

Which is an example of enhancing a positive impact?

Why do engineers test a design, change one thing, and test again?

Planting a single tree species over a large area could cause which unintended consequence?

For parents and teachers

Big idea: good intentions are not enough. To protect ecosystems we must assess solutions with criteria and evidence, watch for unintended consequences, and monitor results over time. Solutions can reduce harm (mitigate) or actively help (enhance).

How to help at home:

Do the runoff filter challenge together; a grown-up does the cutting. Encourage improving the design and recording results.
Pick a small family action (a native plant pot for pollinators, bird-friendly window markings, a litter clean-up) and measure before and after.
When you hear about an environmental solution in the news, ask together: How do they know it works?

Safety: grown-ups handle scissors or knives. Filtered water is not safe to drink. Wash hands after soil.

Common difficulties:

Choosing solutions because they feel helpful, without evidence.
Measuring effort (trees planted) instead of results (trees surviving).
Changing several things at once in the engineering test.