A. Global Settlement: Patterns and Sustainability · Global Settlement: Patterns and Sustainability

How Human Settlement Affects the Environment

A3.5About 50 minutes

Learning goals

I can describe ways human settlement affects water, air, soil, land and wildlife.
I can explain how paved surfaces change what happens to rainwater.
I can trace a chain of effects from one settlement decision.
I can give Canadian and world examples of settlement affecting the environment.

Words to know

pollution
Harmful substances or energy (such as noise or light) added to the environment.

impermeable surface
A hard surface that water cannot soak through, such as pavement, concrete or a roof.

runoff
Rain or melted snow that flows over the land into streams, rivers and lakes instead of soaking into the ground.

algal bloom
A rapid growth of algae in water, often caused by too many nutrients from fertilizer or sewage. Some blooms are toxic.

brownfield
Land that was used by industry or a business, such as an old factory or gas station, and may have contaminated soil.

habitat
The natural home of a plant or animal, where it finds food, water and shelter.

urban heat island
A city area that is warmer than the countryside around it because pavement and buildings absorb and give off heat.

light pollution
Too much artificial light at night, which brightens the sky and affects people, birds and other animals.

Let's start with a question

On a clear night far from any town, you can see thousands of stars and the Milky Way. In a big city, you might see only a few dozen stars. Why? The city's lights brighten the whole sky. That is one way settlements change the environment, and there are many more.

In Grade 7 you studied how extracting and using natural resources affects the environment. Now the focus is on the effects of the settlements themselves: our homes, roads, cities and farms.

The Milky Way in a starry night sky over dark forest, with an orange glow of city lights on the horizon. — Far from town, thousands of stars are visible. The orange glow on the horizon is light pollution from a settlement, one way cities change the environment. AI-generated image

Water

Sewage. In older parts of many Canadian cities, rainwater and sewage flow through the same pipes. During heavy rain the pipes can overflow, sending a mix of stormwater and sewage into rivers and lakes. Cities are building large tunnels and tanks to store this water until it can be treated.
Farm runoff. Fertilizer and manure washed off fields add nutrients to lakes and can cause algal blooms. In August 2014, a toxic algal bloom in Lake Erie forced the city of Toledo, Ohio, to tell hundreds of thousands of people not to drink their tap water for several days.
Industry can release chemicals into water.
Road salt. In winter, salt keeps roads safe but washes into streams, where too much salt harms fish and other living things.

Runoff and flooding

Roofs, roads and parking lots are impermeable surfaces. Rain can't soak in, so it runs off quickly into storm drains and streams, carrying oil, salt and litter. Streams rise faster and higher, which can cause flooding, and less water soaks in to refill the groundwater.

Left: in a forest, rain soaks into the soil. Right: in a built-up area, rain hits pavement and roofs and runs off quickly into the river. Schematic, not to scale.

Air, soil and land

Air pollution. Vehicles, factories, power plants and wood burning release pollutants that can form smog and harm people's lungs and hearts.
Soil contamination. Old factories, gas stations and dumps can leave harmful chemicals in the ground. These sites are called brownfields, and they must be cleaned up before new homes or parks are built on them. Pesticides can also build up in soil.
Loss of farmland. As cities sprawl, good farmland is covered with buildings and roads.
Waste. Settlements make a lot of garbage, which needs landfills that take up land and must be managed so they don't pollute water.
Desertification. At the dry edges of deserts, such as the Sahel south of the Sahara, too much grazing, cutting trees for fuel and unsustainable farming, combined with drought, can turn dry land into desert-like land.

Wildlife and habitat

Deforestation and habitat loss. Forests, meadows and wetlands are cleared for homes, roads and farms. Animals and plants lose the places they need to live.
Disrupted migration routes. Roads, fences and buildings cut across the paths animals use. In Banff National Park, wildlife overpasses and underpasses help animals cross the Trans-Canada Highway safely. Many birds also die by flying into glass windows, especially in cities along their migration routes.
Light pollution confuses birds that migrate at night and many insects, and hides the stars. Some places in Canada are protected as dark-sky preserves to keep the night sky dark.

Heat

Cities are often warmer than the countryside around them. Dark pavement and buildings soak up the sun's heat and give it off at night. This urban heat island makes heat waves more dangerous.

Settlement activity	Effect on the environment	Example
Paving roads and parking lots	More runoff and flooding; less groundwater	Streams that flood quickly after storms in built-up areas
Sewage and stormwater systems	Overflows of sewage into lakes and rivers	Combined sewer overflows in older city areas
Farming to feed cities	Nutrient runoff and algal blooms	Lake Erie algal blooms
Driving and industry	Air pollution and smog	Smog warnings on hot summer days
Clearing land for suburbs	Habitat loss; loss of farmland	Sprawl at the edges of growing cities
Night lighting	Light pollution	Birds disoriented during migration

Some ways settlement affects the environment.

Worked example

Example: Let's trace a chain of effects

Pretend scenario: A forest and wetland at the edge of a town are cleared and paved for a large shopping centre and parking lot. Trace the chain of effects on the environment.

First effect: trees and wetland plants are removed, so animals lose habitat.
Next: the land is now impermeable (asphalt and roofs), so rain runs off instead of soaking in.
Then: runoff carries oil, road salt and litter into the nearby creek, and the creek floods more quickly after storms.
Then: less water soaks into the ground, so groundwater is not refilled as much, and the creek may run low in dry weather.
Also: the dark parking lot creates heat in summer, and bright lights at night add light pollution.

One decision causes a chain of effects: habitat loss → more runoff → pollution and flooding in the creek → less groundwater, plus heat and light pollution.

The chain from the example as a flow chart: one decision at the top leads to several connected effects below it.

Think in chains

Environmental effects are usually connected. When you describe an effect, ask "and then what happens?" two or three times. This is the interrelationships way of thinking that geographers use.

Hands-on activity

Sponge versus plate: a runoff experiment

You need: a kitchen sponge, a dinner plate, a measuring cup, a baking pan or tray, and water. Do this in a sink or outside to avoid spills.

Put the dry sponge on the tray, tilted a little. Slowly pour 250 mL of water over it. Squeeze out and measure any water that ran off onto the tray (not what stayed in the sponge).
Now put the plate on the tray, tilted the same way. Slowly pour another 250 mL over it. Measure the water that ran off.
Compare: Which surface sent more water running off? Which acts like soil and plants, and which acts like pavement?
Write two sentences about what would happen to a creek if a forest (sponge) were replaced with a parking lot (plate).

What to look for: the plate sends almost all of the water running off; the sponge holds much of it. Paving land increases runoff, so creeks rise faster and floods are more likely.

Just for fun

Why does rain like forests better than parking lots?

Because in a forest, things finally sink in.

Your turn

Give three ways settlements can pollute water.

What is an impermeable surface? Give two examples.

Why do paved areas flood more easily?

What caused the 2014 drinking-water problem in Toledo, Ohio?

What is a brownfield?

Name two ways settlements affect wildlife.

What is an urban heat island?

More practice: warm-up

What is runoff?

What is light pollution?

Name one source of air pollution in cities.

What do wildlife overpasses in Banff National Park help animals do?

What is a habitat?

More practice: on your own

Explain how road salt can harm the environment, and why towns still use it.

Explain why a brownfield must be cleaned up before homes are built on it.

How does feeding a growing city affect the environment?

What is desertification, and how can settlement contribute to it?

Why can light pollution be harmful to birds?

Challenge

Trace a chain of at least three connected effects starting with: "A city grows by building new suburbs on farmland."

Some effects of settlement are local (in one place) and some are global. Classify these and explain: light pollution over a town; carbon dioxide from cars; a contaminated brownfield.

A town must choose between draining a wetland for houses or building the same number of homes as apartments on an old parking lot. Using environmental effects, which choice is better and why?

Check your understanding

Quiz

What happens to rain that falls on a parking lot?

Which is a cause of algal blooms in lakes?

What is a brownfield?

Which is an example of light pollution?

Why are cities often warmer than the countryside?

How do wildlife crossings in Banff National Park help?

For parents and teachers

Big idea: A3.5 asks students to describe various ways in which human settlement has affected the environment. The curriculum's examples include water, air and soil pollution, deforestation and habitat loss, loss of farmland to sprawl, light pollution, disrupted migration routes and desertification. All are in this lesson.

Common difficulties:

Listing effects without explaining them. Ask, "How does that happen?"
Single effects only. Encourage "and then..." chains (interrelationships).
Feeling hopeless. Reassure your child that the next lessons are about solutions: what people and communities do to make settlements more sustainable.

How to help: Do the sponge-and-plate experiment together, then look at a storm drain on your street (many say "Drains to river" or have a fish symbol) and talk about where that water goes.