B. Biology: Sustainable Ecosystems and Climate Change · Sustainable Ecosystems and Climate Change

Air Quality, Water Quality and Soil Health

B2.4 B2.5 A1.2 A1.5About 75 minutes

Learning goals

I can describe key indicators of air quality, water quality and soil health.
I can explain how each one supports or limits ecosystem sustainability.
I can explain acid deposition and how Sudbury's landscape recovered.
I can test soil texture and water infiltration and interpret my results.

Words to know

air pollutant
A substance in the air at levels that can harm living things, such as fine particles, ground-level ozone, sulfur dioxide or nitrogen oxides.

acid deposition
Acids (mostly from sulfur dioxide and nitrogen oxides) that fall to Earth in rain, snow or dry particles; often called acid rain.

buffering capacity
The ability of soil or water to resist changes in pH, often because it contains limestone (calcium carbonate).

dissolved oxygen (DO)
Oxygen gas dissolved in water, measured in mg/L; fish and aquatic insects need it.

turbidity
How cloudy water is because of suspended particles.

humus
Dark, decomposed organic matter in soil that holds water and nutrients.

soil horizon
A layer in the soil with its own colour and makeup (O, A, B, C).

infiltration
Water soaking into the soil instead of running off the surface.

Remember from Grade 8

In Grade 8 Water Systems you measured water quality with physical, chemical and biological indicators (temperature, turbidity, pH, dissolved oxygen, nutrients and benthic invertebrates). This lesson connects water quality with air quality and soil health, three of the factors your Grade 9 curriculum lists, and explains how each one keeps ecosystems sustainable.

Let's start in Sudbury

For most of the 1900s, smelters near Sudbury released huge amounts of sulfur dioxide while processing nickel and copper ore. Trees died, soil washed away, and the hills turned bare and black. Nearby lakes became so acidic that fish disappeared.

Then things changed. Smelters cut their emissions sharply, and the 1972 Superstack spread the remaining gases higher. Starting in 1978, the community spread crushed limestone on the acidic soil and planted millions of trees. Today many hills are green, and fish have returned to many lakes. Sudbury's story shows how air, water and soil are linked, and how ecosystems can recover when people act.

Air quality

Key air pollutants and their effects on ecosystems:

Fine particulate matter (PM2.5): tiny particles from vehicle exhaust, industry and wildfire smoke. They harm lungs (people and animals) and can settle on snow and ice, darkening them.
Ground-level ozone (O₃): forms when nitrogen oxides and other pollutants react in sunlight (smog). It damages leaves and lowers crop yields.
Sulfur dioxide (SO₂) and nitrogen oxides (NOₓ): from burning coal, oil and gas, and from smelting. They form acid deposition.

Canada reports air quality with the Air Quality Health Index.

The Air Quality Health Index (AQHI) scale used across Canada. Wildfire smoke can push it into the high or very high range, even far from the fire.

Acid deposition

SO₂ and NOₓ react with water in clouds to form sulfuric and nitric acid. Normal rain is already slightly acidic (pH about 5.6) because CO₂ dissolves in it; acid rain has a lower pH.

Lakes and soils on limestone are well buffered: the limestone neutralizes acid.
Lakes on the granite of the Canadian Shield have little buffering, so their pH drops. Below about pH 5, many fish, snails, clams and amphibians cannot reproduce.
Acid soil releases aluminum that harms roots, and washes away nutrients such as calcium.

Canada and the United States signed agreements to cut SO₂ emissions (including the 1991 Canada–U.S. Air Quality Agreement), and many lakes are slowly recovering.

How acid deposition forms. Sulfur dioxide and nitrogen oxides react in clouds to form acids that fall far downwind. Lakes on the granite of the Canadian Shield have little natural buffering, so many became acidic.

Water quality

You studied water quality indicators in Grade 8. Here is why they matter for sustainability:

Dissolved oxygen (DO): fish and aquatic insects need it. Cold water holds more oxygen than warm water, so warming water (from climate change or removing shade trees along streams) lowers DO.
Temperature: cold-water species such as brook trout need cool, well-oxygenated streams.
Nutrients (N and P): small amounts are needed; too much causes algae blooms (Lesson 9).
pH: most aquatic life does best between about pH 6.5 and 8.5.
Chloride (from road salt) and turbidity (from erosion) stress aquatic life.
Benthic macroinvertebrates: mayfly, stonefly and caddisfly larvae are pollution-sensitive; finding many of them means good water quality.

Water temperature (°C)	Maximum dissolved oxygen (mg/L, fresh water at sea level)
0	about 14.6
10	about 11.3
20	about 9.1
25	about 8.3

Warmer water holds less oxygen. Many fish become stressed when DO falls below about 5 mg/L.

Soil health

Healthy soil is a living ecosystem. A good garden loam is roughly 45% minerals, 25% water, 25% air and 5% organic matter, by volume. Signs of healthy soil:

Organic matter (humus): dark colour, holds water like a sponge, stores nutrients and carbon.
Good structure: crumbly clumps with spaces for air, water and roots, so rain infiltrates instead of running off.
Lots of life: bacteria, fungi (including mycorrhizal fungi that partner with roots and help them absorb water and phosphorus), earthworms, insects and mites. They decompose matter and cycle nutrients.
Suitable pH and nutrients for the plants growing there.

Soil health declines with erosion (bare soil washed or blown away), compaction (heavy machines or foot traffic squeeze out air spaces), loss of organic matter, salt buildup, acid deposition and contamination.

A soil profile (not to scale). Healthy topsoil (A horizon) is rich in organic matter and full of roots and living things. It can take hundreds of years to form just a few centimetres of topsoil.

Air, water and soil are connected

Pollutants rarely stay in one sphere. Sulfur dioxide from a smokestack (air) becomes acid rain that lowers the pH of soil and lakes (water). Eroded soil makes water turbid and adds phosphorus. Healthy soil and plants, in turn, filter water and store carbon. When you assess an ecosystem, check all three.

Worked example

Let's use dissolved oxygen data

A brook trout stream in southern Ontario is shaded by trees and stays at about 12 °C in summer. A developer removes the trees, and the summer water temperature rises to 22 °C. Use the table to explain the likely effect on brook trout.

Look up DO at 10 °C (about 11.3 mg/L) and 20 °C (about 9.1 mg/L). At 12 °C the maximum is a bit below 11.3 mg/L; at 22 °C it is a bit below 9.1 mg/L.
So the maximum oxygen the water can hold drops by more than 2 mg/L.
Real streams are often below the maximum, especially where decomposing matter uses up oxygen, so DO could approach stressful levels.
Brook trout need cold, well-oxygenated water; 22 °C is already stressful for them even before oxygen falls.

Removing the shade warms the water, lowers the oxygen it can hold, and stresses or eliminates brook trout. Planting trees along stream banks protects water quality.

Worked example

Let's compare infiltration rates

A student pushes an open-ended can into the ground in three places, pours in 500 mL of water and times how long it takes to soak in: garden bed 45 s, lawn 3 min 20 s, hard-packed path 14 min. Rank soil health for water infiltration and explain.

Convert to seconds: garden 45 s; lawn 3 × 60 + 20 = 200 s; path 14 × 60 = 840 s.
Fastest infiltration: garden bed (loose soil, organic matter, root and worm channels).
Slowest: path: foot traffic has compacted the soil and closed its air spaces.
On compacted soil, rain runs off instead of soaking in, carrying soil and pollutants into streams.

Garden (45 s) > lawn (200 s) > path (840 s). The path's soil is compacted and in the poorest health for infiltration.

Hands-on activity

Soil health check (A1.2, A1.5)

You need: a clear jar with a lid, a trowel, water, a ruler, an empty metal can with both ends removed (a grown-up should remove the ends and check for sharp edges), a measuring cup, a timer.

Part 1: Soil texture jar

Fill the jar one-third with soil from a garden (remove rocks and roots). Fill almost to the top with water, close tightly and shake hard for 2 minutes.
Set it down. After 1 minute, mark the top of the layer on the bottom (sand). After 2 hours, mark the next layer (silt). After 24 hours, mark the top layer of settled material (clay). Organic bits may float.
Measure each layer and calculate its percentage of the total settled soil.

Part 2: Infiltration test

Push the can about 3 cm into the ground in two or three places (for example, a garden, a lawn, and beside a path).
Pour 500 mL of water into the can and time how long until it has soaked in.
Record and compare. Also count earthworms in a 20 cm × 20 cm square dug 15 cm deep in each spot, if allowed.

Conclusion: which spot has the healthiest soil? Use texture, infiltration and earthworm evidence.

What to look for: sandy soils drain fast but hold few nutrients; clay holds water but drains slowly; loam (a mix) with organic matter is best for most plants. Compacted soil drains slowly.

Safety (A1.5): a grown-up removes can ends and checks edges; wear gloves; wash hands after handling soil; get permission before digging and fill holes back in.

Just for fun

A single teaspoon of healthy soil can hold more living microorganisms than there are people on Earth. Your garden is basically a crowded megacity with no traffic lights.

Your turn

Name two air pollutants and one effect of each on ecosystems.

Why were lakes near Sudbury and elsewhere on the Canadian Shield especially hurt by acid rain?

Why does warm water usually have less dissolved oxygen?

List four signs of healthy soil.

What does the AQHI measure, and what do readings of 2 and 8 mean?

How did people help Sudbury's land recover?

What do mycorrhizal fungi do?

More practice: warm-up

What is the pH of normal, unpolluted rain (about)?

Which soil horizon is topsoil?

What is humus?

Name a pollution-sensitive aquatic insect larva.

What does compaction do to soil?

More practice: on your own

In the soil jar test, the layers measured 3.0 cm sand, 1.5 cm silt and 0.5 cm clay. Find each percentage.

Why does a lake on limestone recover from acid rain faster than a lake on granite?

Explain how soil erosion can lower water quality in a nearby river.

Wildfire smoke drifts over Toronto and the AQHI reads 9. Who should limit outdoor activity, and why?

Why is organic matter in soil important for climate as well as plants?

Challenge

Explain how one smelter's emissions could affect air, water and soil, and the food web of a lake 100 km away.

A farm field has dropped from 4% to 2% organic matter over 30 years. Predict three effects on the field, and suggest one way to rebuild organic matter.

Design a fair test to find out whether leaf mulch helps a garden soil hold water. Include the variable you change, what you measure, and two controls.

Check your understanding

Quiz

Which pollutants cause most acid deposition?

Water at 20 °C can hold about how much dissolved oxygen compared with water at 10 °C?

Which soil would allow rain to infiltrate fastest?

An AQHI value of 5 means...

Why can lakes on limestone resist acid rain?

Which of these is a sign of poor water quality?

For parents and teachers

Big idea (B2.4 air and water quality and soil health, links to B2.5): clean air, clean water and healthy soil are linked, and each supports ecosystem sustainability. Acid deposition shows how a pollutant moves from air to water and soil; Sudbury shows that recovery is possible. The soil tests are investigations with safety practices (A1.2, A1.5).

How to help: Help with the can (remove both ends and tape or file any sharp edges). Check the AQHI with your teen on a weather app or the Government of Canada website, especially on smoky days.

Common difficulties:

Thinking all rain is neutral (pH 7). Normal rain is about 5.6.
Forgetting that soil is alive. Most soil functions depend on organisms.
Percent calculations from the jar test. Divide each layer by the total settled height.

Sources: AQHI categories (Government of Canada); Sudbury regreening history (City of Greater Sudbury and Vale/Laurentian University publications: liming and tree planting from 1978); dissolved oxygen solubility values are standard tables.