Science High School Reviewer | Grade 4 Science | Life Science | Exploring Ecosystems | Lesson 12: Humans Change the Environment

Human activities change environments. When
ecosystems change, some organisms die or leave the area.
Other organisms adapt to the changes and survive.

Like all organisms, humans interact with their
environment. We get our food, shelter, and water
from the land and organisms that surround us.
Unlike other organisms, we can change large parts
of the environment to meet our needs. We cut down
trees to provide us with lumber and land for houses.
We clear prairies to plant crops or build roads. When
we change the environment, however, we sometimes
upset the balance of ecosystems.
We also affect ecosystems with wastes from the
products we make and use. These waste products can
pollute the air we breathe and the water we drink.
Many of the things we do release dust, dirt, and
harmful gases into the air. Automobiles and factories
can release harmful chemicals into the air. These
chemicals can harm plants. Animals that depend on
these plants may lose their source of food or shelter.

Polluted Water
Water becomes polluted when wastes and chemicals
get into rivers, lakes, and oceans. Some of these
substances enter the water through sewer systems. Other
chemicals are used on land to help plants grow or to kill
insects. Rain washes these chemicals off the land and
into the water. Some of these chemicals can harm or kill
fish and other plants and animals that live in or near
the water.
Some of the pollutants in rivers and streams may
end up in Earth’s oceans. Oil is a pollutant that can
harm the ocean’s plants and animals. Sometimes, spills
and leaks occur during the drilling and shipping of oil.
Algae, plants, mollusks, and fish become coated with oil
and die. Birds that are coated with oil often drown.

Land Pollution
Garbage, litter, and other substances can pollute the land.
Humans produce huge amounts of garbage. Every day, each
person throws away about 2 kilograms of garbage. Most of this
trash is dumped into landfills and then covered with soil.
Disposing of hazardous wastes can cause another kind
of land pollution. Hazardous wastes are substances that
are very harmful to humans and other organisms. These
substances may be poisonous, cause disease, start fires, or
react dangerously with other substances. Until recently, most
hazardous wastes were put into containers and buried in the
ground. Some of these containers leaked. The hazardous wastes
seeped into the ground or water and damaged nearby habitats.

Stripping Away the Land
Many valuable substances lie under
Earth’s surface. One of these substances
is coal. Strip mining has been one way
to get coal from the Earth. At one time,
huge machines dug up and cleared away
the top layers of soil. Large holes were left
behind. The land surrounding the holes
began to erode. Piles of soil and rock were
washed into ponds and rivers. The nearby
ecosystems were greatly affected.
Restoring the land is important for the environment. Habitats
are restored and animals can return to the area. If this is not
possible, crops are planted so that the land is useful.

Land Reclamation
Federal law requires that land disturbed by mining must be
reclaimed. Reclaiming means that mining companies must
replace rock and soil that were removed. They must replant the
area with crops or native trees and grasses. Mining companies
must submit a plan to reclaim the land they use before the first
shovel ever touches the ground.
Coal mining in some states began in the 1840s. For more
than 100 years, no repairs were made to lands that had been
strip-mined. Then, beginning in the 1970s, laws were passed to
regulate strip-mining. For example, the Surface Mining Control
and Reclamation Act law requires that coal companies study
the ecosystems before any digging begins. The companies then
must plan how to restore the land after they finish mining.
California is one state that has reclaimed some mining areas.
An area in Sacramento County where gravel was dug has now
been restored to its natural water habitat. Other areas grow
alfalfa, corn, and other crops. A field of strawberries now covers
one mining area.

Preserving the Environment
Our nation has many natural treasures.
You can watch millions of gallons of water
cascade over Niagara Falls or look out
over the breath-taking Grand Canyon.
The United States has established the
National Parks system to preserve
nature’s beauty, historic sights,
and the habitats of many plants
and animals.