Impact on Water Chapter Notes | Science for Grade 5 PDF Download

Introduction

Water is very important for all living things on Earth, including humans, animals, and plants. This chapter, "Impact on Water," explains how human activities affect Earth's water resources, like rivers, lakes, and oceans. It also discusses how we can use technology, like satellites, to monitor water quality and how we can reduce harm to water systems. You will learn about water usage, pollution, and ways to protect this precious resource for all life on Earth.

How Do Humans Use Water?

• Water covers most of Earth's surface and is a key part of all living things, from whales to tiny algae.
• Humans need water to live, but we often use more than necessary.
• Humans use water for daily activities like washing cars, doing laundry, and farming.
• Most water in the United States is used by power plants to make electricity and cool machines.
• Household water use, like showering or cooking, is only a small part of total water use.
• Using water affects the environment in many ways, like changing ecosystems or reducing water availability.

What impacts do humans have on water distribution and availability?

• Humans mostly use freshwater, which is only 3% of all water on Earth.
• Freshwater comes from groundwater, lakes, rivers, and other surface water sources.
• As the human population grows, we use more water, which can stress natural water systems.

Case Study: The Aral Sea

• The Aral Sea in Central Asia was once the fourth largest lake in the world.
• It got freshwater from two rivers, the Amu Darya and Syr Darya, and lost water only through evaporation.
• In the 1960s, the Soviet government took water from these rivers to grow crops like cotton.
• This caused the Aral Sea to shrink because more water evaporated than flowed in.
• The shrinking sea made it harder for fishermen to reach the water, and the water became very salty.
• High salinity destroyed the fishing industry by 1980.
• Fertilizers from farms mixed with salt left behind, creating harmful dust that lowered crop growth and caused health problems.
• The loss of the Aral Sea changed the local climate and caused economic and health issues.

Changing the Flow of Surface Water

• People depend on freshwater sources like rivers and lakes for water supply.
• Dams are built to store water in reservoirs, like the Hoover Dam on the Colorado River.
• The Hoover Dam creates Lake Mead, used for drinking, irrigation, recreation, and hydroelectric power.
• Dams control water flow and prevent flooding but have negative effects.
• Dams increase erosion along riverbanks and block migratory fish like salmon.
• Some rivers, like the Colorado River, dry up before reaching the ocean because of dams.

Environmental Issues Associated with Dams

• Dams provide steady electricity without harmful gases or pollutants.
• They can quickly adjust how much electricity they produce, saving energy.
• Building dams can destroy farmland, homes, or cities when reservoirs flood the land.
• Flooding from reservoirs destroys plants and animal habitats.
• Dams change how rivers flow, making water flow more steady but trapping sediment.
• Trapped sediment fills up reservoirs and reduces nutrients downstream, causing erosion and habitat changes.
• Dams release cold, clear water from deep in reservoirs, changing the natural warm, muddy river water.
• Dams block adult migratory fish from swimming upstream and can kill young fish in turbines.

Impacts on Groundwater

• Groundwater is water under the Earth's surface and is more plentiful than freshwater in lakes and rivers.
• It supports streams, lakes, wetlands, and plants with deep roots.
• About 20% of the water used daily in the United States comes from groundwater.
• People get groundwater by drilling wells into aquifers, which are underground areas of rock or sediment that hold water.
• Groundwater flows into wells from aquifers and is pumped to the surface.

Groundwater

• Precipitation refills groundwater, but during droughts, less water is replaced.
• If water is pumped out faster than it is replaced, wells can dry up.
• Removing too much groundwater creates empty spaces underground.
• These empty spaces cannot support the ground above, causing sinkholes where the ground collapses.

A Closer Look: San Joaquin Valley

• The San Joaquin Valley in California is a major farming area with high water demand.
• Farmers have been taking groundwater since the 1920s, causing the land to sink up to 8.5 meters (28 feet) by the 1970s.
• Removing water leaves empty spaces in the soil, causing it to compact, like a dry sponge shrinking.
• Sinking land, called subsidence, damages water supplies, bridges, roads, wells, and groundwater storage.
• California has spent about $100 million on repairs due to subsidence since the 1960s.
• The valley continues to sink, especially during droughts, at about 30 cm per year.

How do humans pollute earth's water?

• Groundwater pollution is a growing problem as the human population increases.
• Pollutants enter groundwater when water seeps into the ground.
• Human activities cause water pollution, leading to issues like dead zones and unsafe drinking water.

Water Pollution

• Agricultural runoff carries fertilizers, upsetting nutrient balance in lakes and oceans.
• Industrial waste from factories pollutes water with harmful chemicals.
• Oil spills from ships or offshore drilling harm marine life and ecosystems.
• Sewage from homes and cities pollutes water with waste and chemicals.
• Litter, like plastic bags and bottles, pollutes water and harms wildlife.

Flushing Chemicals into Fish Habitats

• Wastewater from toilets and faucets can carry chemicals like estrogen into lakes and rivers.
• Estrogen is a chemical that affects reproduction in animals and is found in some medicines.
• Estrogen in water harms fish by disrupting their ability to reproduce.
• Most fish develop as male or female based on environmental factors like temperature or food.
• Estrogen in water can cause male fish to produce fewer sperm or even eggs, and females to stop producing eggs.
• In a lake experiment in Ontario, Canada, adding estrogen caused fathead minnows to nearly disappear after three years.
• Stopping the estrogen allowed the fish population to recover.

Ocean Pollution

• Ocean pollution harms the physical, chemical, and biological health of ocean ecosystems.
• Some pollution comes from natural sources like volcanic eruptions.
• Most ocean pollution is caused by human activities.
• Only 13% of ocean pollution comes from shipping or offshore mining.
• 87% comes from land-based sources like garbage, hazardous waste, and fertilizers.
• Airborne pollution from power plants and cars also affects oceans.
• Trash, like plastic, dumped into oceans harms animals like turtles that get tangled or eat it.

Solid Waste

• Trash like plastic bottles, bags, and foam containers harms marine animals.
• Animals get tangled in plastic or mistake it for food, which can kill them.
• Plastic breaks into small pieces but does not degrade easily.
• The Great Pacific Garbage Patch, in the North Pacific Gyre, is a large area of collected debris.
• It is about twice the size of Texas, with 80% of debris from land-based activities in North America and Asia.

Excess Sediments

• Land-based sediments wash into oceans, some from natural erosion.
• Human activities, like cutting trees near rivers, increase sediment erosion.
• Without tree roots, sediments erode easily into water.
• Excess sediments clog filtering structures of marine animals like clams and sponges.
• Sediments block sunlight, harming organisms that need light for photosynthesis.

Excess Nutrients

• Algae need nutrients like nitrogen and phosphorus to grow.
• Too many nutrients cause algal blooms, where algae grow rapidly.
• Algal blooms can make water appear red, green, brown, or glow at night.
• Fertilizers from agriculture and coastal upwelling add excess nitrates and phosphates.
• These nutrients come mostly from land-based fertilizers washing into oceans.

Did You Know?

Ocean pollution has both short-term and long-term impacts on marine life. “Marine” refers to anything related to the oceans. Chemical waste can be especially dangerous, as it poisons marine organisms, which then pass the toxins up the food chain. Large oil spills, along with solid waste like garbage, extra sediments, and excess nutrients, also harm marine ecosystems. Even everyday trash can have serious effects on ocean health.

Dead Zones

• Dead zones are areas in the ocean with no life because of human activities on land.
• In the Gulf of Mexico, a dead zone forms every year from runoff carrying nitrogen and phosphorus from fertilizers, animal waste, and sewage.
• This runoff comes from the Midwest, flows into the Mississippi River, and reaches the Gulf.
• Nutrients cause algae to grow a lot, creating algal blooms.
• When algae die, they sink and use up oxygen as they decompose, killing other sea life.
• Simple changes, like using less fertilizer or containing animal waste, can help stop dead zones.
• Better septic and sewage systems can also help keep nutrients out of the water.

How can we monitor and minimize human impact on water?

• All life needs water, but humans often use and pollute it unnecessarily.
• Human impacts on water affect all living things on Earth.

Management Solutions

• Laws like the U.S. Clean Water Act help reduce water pollution.
• The Clean Water Act sets rules for controlling wastewater and pollution.
• The Safe Drinking Water Act protects drinking water supplies.
• These laws help ensure clean water for all living things.
• In 1969, the Cuyahoga River caught fire due to pollution, leading to the Clean Water Act.

What You Can Do

• Conserve water by taking shorter showers or turning off the tap while brushing teeth.
• Encourage others to save water to make a bigger impact.
• Recycle plastic bottles to prevent them from ending up in oceans.
• Reduce plastic use to create less waste.
• Dispose of harmful chemicals properly to prevent water pollution.
• Volunteer to clean up litter from local streams.
• Conserve water to ensure enough is available for all living things.