Grade 8 - Fresh and Salt Water Systems
Section 1: A World of Water
Living things need water to survive. Ecosystems also depend on it. The land is shaped by it. The climate and weather are influenced by it. About 74% of the Earth's surface is covered by water. However, 97% of this water is saltwater.
Water makes up a large component of living things with about 65% in humans, 84% in apples and 98% in water melons.
Agricultural practices such as irrigation use up about 70% of water. About 22% of water is used in various industrial applications and only 5% is used for domestic uses including drinking. Of course humans and other animals also obtain water through the food/feed they consume.
The Water Cycle
The water cycle is made up of three manin processes.
- Evaporation
- Condensation
- Precipitation
Evaporation
When water heats up, some of it changes into a gas called water vapor. This process is called evaporation.
Water evaporates from lakes, oceans, rivers, ponds and other water bodies.
Water can also evaporate from the surface of leaves in a process called transpiration.
Condensation
The water vapor travels in the air. As it rises into the air, it cools down and turns back into a liquid. The change from gas to liquid is called Condensation.. If many water droplets in the sky come together they form clouds. A cloud is a group of water droplets in the atmosphere.
Precipitation
The water in the clouds and the water vapor in the air will then fall down to the ground as rain or other kids of precipitation.
Precipitation refers to any liquid or frozen water that forms in the atmosphere and falls back to the earth. It comes in many forms, like rain, sleet, and snow.
If its too cold, the water droplets in clouds will freeze into ice. Freezing refers to the change from liquid to solid.
Some of the water that falls as precipitation collects on land and flows downhill. A watershed is an area from which water is drained. Precipitation that flows across the land’s surface and is not absorbed will flow into rivers, lakes, and streams as runoff. Most of the water will flow from rivers to the ocean. Some of the water will settle underground and become groundwater.
Plants and animals also play a role in the water cycle. Plants absorb water from the ground through their roots. Excess water in the plant is lost through transpiration. Animals drink water and then release the excess as waste and sweat.
Four countries (Brazil 18%, Canada 9%, China 9%, and United States 8%) hold nearly half of the Earth’s renewable supply of freshwater.
Section 2: Earth’s Frozen Water
Ice Ages
The Earth has had 7 major Ice Ages over the last several million years. During this time glaciers covered approx. 28% of the Earth’s surface. In the last Ice Age, Canada was completely covered by a continental glacier.
A small change in the average temperature is enough to start a chain of events that can produce an Ice Age. For example, reduced thermal energy from the Sun, increased volcanic activity (adding clouds of ash into the atmosphere, thus reducing how much thermal energy from the Sun reaching Earth), Mountain building (more snow to accumulate and reflect sunlight resulting in reduced temperature, movement of Earth’s tectonic plates alters the shape of the oceans and affects ocean currents, causing less mixing of hot and cold water. a change in the tilt of the Earth’s axis may also alter the temperature etc.
Glaciers: A glacier is a thich sheet of ice that creeps over land. Glaciers form where snow collects quickly and melts slowly. Year after year, the snow builds higher. The weight on top of the mound puts pressure on the snow below. The bottom of the glacier slowly turns to ice. Melting makes the bottom of the glacier slippery. It begins to flow downhill. The bottom and sides freeze onto rocks. As the glacier continues to move, it tears rocks from the ground. It scratches, flattens, breaks, or carries away the things in its path. A glacier can make a valley wider and steeper. Glacial debris can be made of large boulders or small rocks. They can have bits of gravel, sand, soil, and clay. The glacier drops most of this debris at its downhill end, or terminus. Materials that a glacier picks up or pushes can forms mounds. These mounds are called moraines. Today, you can find glacial till and moraines across Canada and northern parts of the United States.
The Importance of Glaciers:
Icefields, glaciers, and snow – high up in the mountains – act as natural reservoirs, collecting snow in the cold months and releasing it as meltwater as it warms up. This meltwater helps run hydroelectric plants, irrigate crops, water cattle and supply drinking water. Glaciers slow the water cycle and provide important clues to understand historical climate patterns.
All glaciers begin as snowflakes. These snowflakes accumulate, becoming grains, ice crystals and the weight of the snow creates pressure that gradually changes the ice crystals into glacial ice.
Valley Glaciers
Glaciers form high in the mountains and move through valleys between mountain peaks. These are called valley glaciers.
Continental Glaciers
Those covering large areas of land are called continental glaciers or icecaps. Continental glaciers cover Antarctica and Greenland.
Glacial Features
The shapes that develop in flowing ice are unique. Where a glacier flows over a steep cliff and breaks up, an icefall results. A crevasse is a fissure, or crack, in the ice.
Pack ice is a sheet of ice that is rarely more than 5 meters thick that breaks easily. This usually happens in freezing sea water when large pieces break off as they move into warmer water.
Icebergs are large chunks of ice that break loose, or calve, from continental glaciers as the glaciers flow into the ocean. These chunks are visible as they move through the ocean, melting faster below the surface than above.
The collection of rocks, boulders, sand, clay and silt that is left behind as a glacier slows down and melts, is called till.
Long Term Temperature Changes
The greenhouse effect and global warming are two unrelated events that affect the average temperature on the Earth.
The greenhouse effect is the natural warming of the Earth caused by gases in the Earth’s atmosphere trapping heat.
Global warming is the increase of these greenhouse gases, which causes more heat to be trapped and the temperature around the world increases – causing ice caps to melt producing widespread flooding.
Section 3: Fresh Water Systems
Water exists in all three forms on the Earth: solid, liquid and gas. It is found underground, on the surface and in the air.
A lake and a pond are holes in the ground filled with water. A lake is deeper than a pond and sunlight does not reach the bottom, whereas in a pond sunlight will penetrate right through to the bottom, depending on the clarity of the water. The clarity is determined by the amount of suspended solids in the water. In lowland areas, wetlands exist. They are saturated with water most of the time. Wetlands provide habitat for a vast diversity of living organisms.
An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms-aquatic life-that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems
The organisms in water ecosystems are divided into three main categories. Plankton are creatures that drift freely in the water. They are not able to swim. Some plankton, such as diatoms, are producers, and others are consumers, such as some animal larvae.
The second group includes the larger, active swimmers in a body of water called nekton. Fish, turtles, and whales are all nekton. The third group, organisms that live on the bottom of a body of water, are called benthos. Many benthos are scavengers or decomposers because they feed on material that floats down from shallower water.
Unlike land ecosystems, water is never a limiting factor. However, the amount of light, dissolved salt, and dissolved oxygen are important. They can all affect the types of organisms that can live in bodies of water.
Running-Water Ecosystems: Faster-moving bodies of water tend to have more oxygen, because air mixes in as the water flows. Other nutrients are washed into the water from the land. Organisms that live in fast-moving streams or rivers have adaptations to prevent them from being swept away. Slower-moving waters have less oxygen and are less dependent on the land for nutrients. More producers, such as algae, are able to survive in slow-moving water.
Standing-Water Ecosystems: The typical freshwater lake or pond is divided into three zones. The shallow-water zone along the shore is where most of the organisms live. Cattails, sedges, arrowgrass, and other rooted plants grow here. The open-water zone includes the water away from the shore. This zone may be too deep for rooted plants to survive. Algae and plankton float near the surface. Nekton, such as trout, whitefish, and pike are found here. The third zone is below the openwater zone and includes the bottom. Very little light reaches the bottom, so producers cannot grow here. Benthos, including worms and mollusks, are found in this zone.
Freshwater Wetlands: Wetlands, such as marshes, swamps, and bogs, are regions that are wet for most of the year. Grasslike plants, moss, and some shrubs are found in wetlands. Beavers, muskrats, otters, birds, and fish live in wetlands.
A groundwater system is similar to a river system. Connecting pores in rocks and soil enable the water to seep through – making it permeable. This is called an aquifer. When the water reaches the bedrock, which is impermeable. The layer of porous rock, in which the connecting pores are full of water, forms the water table.
Wells and Springs: Wells are dug to reach the aquifer, below the water table. If too many wells are dug too close to each other, they may deplete the aquifer and the wells will dry up. If the water in an aquifer flows naturally to the surface, it is called a spring. Hot springs occur when this water is heated by rocks that come into contact with molten material below the Earth’s surface.
Watersheds and Land Use
Storm drains in a city act as a watershed to remove water from the streets after a heavy rainfall. The paved roadways change the run-off patterns in a city, because the water would normally seep into the ground. Logging can also affect watersheds. GIS (Geographic Information Systems) are used to store data and generate maps showing a river’s watershed, allowing them to predict what would happen if runoff patterns changed. The amount of water discharged by a watershed is influenced by soil conditions, vegetation, and human activity.
Aquifer Depletion: Underground aquifers supply water to many cities, farming communities and industries. If too much is used, the aquifer can become depleted, drying up creeks, springs and wells for many kilometres. Responsible use of water is essential in order to sustain this natural resource.
Contaminants in groundwater can spread the effects of dumps and spills far beyond the point source. Non-point sources are those where a pollutant comes from a wide area (run-off from agricultural land is an example). Hydro-geologists are scientists who study groundwater by drilling test wells to determine groundwater availability, movement, quantity and quality.
Section 4: The Oceans
Features on the Ocean Floor
There are several landforms at the bottom of the ocean, some that look like mountains and others look like valleys. An ocean basin is a large underwtaer area between continents. Along the coast of a continent, the ocean floor is called the continental shelf. At this point, the water is shallow but as you go further from the coast, the slope gets sharp. This is called Continental slope.
A submarine canyon is a steep sided valley in a continental slope. These are frequently associated with the mouth of a large river. At the end of a continental slope is another downward slope called a continental rise. Over 40% of the ocean floor is flat. These flat areas are called Abyssal plains. Trenches are the deepest parts of the ocean floor. They are usually long and narrow. A seamount is an underwater mountain that rises from the ocean floor but stops before it reaches the surface of the ocean. Mid-ocean ridges are underwater mountain ranges. An indentation called a rift valley occurs along the top of these mountains.
Ocean Waves
Waves are surface movements 'a disturbance, or variation transferring energy progressively from point to point in a medium' occurring whenever a force comes in contact with water.
Causes of Water Waves
Most waves are caused by the wind (a force). Stronger forces cause larger waves. As ocean waves move closer to the shore their bottoms drag on the ocean floor and their tops rise and break onto the shore (causing damage by their force). Waves begin on the open sea. The smooth waves near the shore are caused by winds and storms far out at sea and are called swells.
Tsunamis
A tsunami (Japanese for harbor wave) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions. In the open ocean, tsunamis move at speeds of 500 to 1,000 kilometers per hour. However, a tsunami slows down as it approaches a shore. The length of each wave decreases, but the height increases. The water piles up, and it is often pulled away from the coastline as the tsunami approaches land. Finally, the tsunami crashes onto the shore as a giant wall of water.
Tides
The water level along the coast of continents changes constantly. This water level is called a tide. High tide is the highest level the water will reach on shore, while low tide is the lowest level it will reach onshore. Usually there are two high tides and two low tides each day. The largest tidal movements are spring tides, whereas the smallest tidal movements are called neap tides. The difference in level between high tides and low tides is called tidal range. What Causes Tides? The gravitational force of the moon and the rotation of the Earth on its axis cause tides.
Surface Currents
Currents of water are driven by winds. There are three factors that influence the direction of winds and surface currents:
1. Uneven heating of the atmosphere (convection)
2. Rotation of the Earth (bending)
3. The continents (deflecting)
Almost all of the heat in the ocean comes from the Sun. Temperature varies throughout the ocean, getting much colder as you go deeper. The temperature of the ocean current not only affects the air temperature, but they also affect the amount of precipitation that an area receives.
Water has a very high heat capacity – meaning it takes a long time to heat up and a long time to loss heat. Large bodies of water act as heat reservoirs in the winter, remaining relative warmer than the nearby land. This difference in temperature can affect the convection currents producing breezes that can alter the processes of evaporation and condensation near the shoreline. A cold current can do the opposite.
Section 5: Living In Water
Large bodies of water like oceans and lakes have layers or zones. Some organisms live in only one or two zones, while other organisms can live in all three.
Lakes and Ponds
Diversity refers to the variety of different kinds of organism species (both plant and animal) living in a particular ecosystem or environment
Lake Diversity:
| Lake Zone | Zone description | Species that might inhabit this zone |
|---|---|---|
| Upper Zone | The zone of a lake from the shore to where the aquatic plants stop growing | Plants: Bulrushes, water lilies Animals: Small fish, clams, insects, snails, worms, leeches, and frogs |
| Middle Zone | The open water zone that still has light penetration | Phytoplankton are food for fish that live here. Some of the fish that live in this zone also travel to the deeper zones |
| Lowest/Deep Zone | Zone where no light penetrates, so no plants grow there. Food for organisms living in this zone comes from the zones above, in the form of waste. | Deep water fish (large size species) |
Rivers and Streams
Streams and rivers usually alternate between areas where water is calm (pools) and areas where water is moving quickly (riffles). Because of the constantly moving environment, organisms often attach themselves to rocks as their habitat.
Ocean Diversity
Oceans have similarities to lakes in terms of zones, but with greater differences in water motion, salinity and depth, diversity is much greater in the oceans. In summary, the shallow part of the ocean ecosystem is called the intertidal zone. Every day, the pull of the Moon’s gravity causes ocean tides to rise and fall over the intertidal zone. Beyond the intertidal zone is the neritic zone. The key resource in this zone is sunlight. Algae, kelp, and other producers grow in huge numbers near the surface water where sunlight can penetrate. The third zone of the ocean is the oceanic zone. It is divided into the bathyal zone and the abyssal zone. The bathyal zone is home to many large consumers, such as sharks, but few producers. Further down is the abyssal zone, where it gets darker and colder because the sunlight is completely blocked. Organisms in this zone tend to be scavengers or decomposers. They live on nutrients that float down from other zones.
| Ocean Zones | Zone description | Species that might inhabit this zone |
|---|---|---|
| Estuary | One of the most diverse and richest ecosystems. This is where freshwater and saltwater mix to form brackish water | Marshes grow here providing a habitat for many different kinds of plants, insects and other animals that can tolerate the brackish water. These ecosystems are also rich in bird life, because of the abundance of food and shelter available |
| Intertidal Zone | The shoreline of an ocean | Plants and animals living in this zone must be able to withstand the pounding of the waves and the rise and fall of tides. Animals with special adaptations live in this zone. |
| Continental Shelf | Warmer water than out in the deep ocean and this area has full light penetration.. | Many varieties of plants and animals live in this zone because of the rich nutrients available. Phytoplankton are food for fish that live here. Some of the fish that live in this zone also travel to the deeper zone. |
| Oceanic Zone | The zone where very little light penetrates, so no plants grow there. | Food for organisms living in this zone comes from the zones above, usually in the form of waste. Deep water fish (large size species). |
Adaptations for an Aquatic Life
An adaptation is a physical characteristic or behaviour of a species that increases that species' chances of survival in a particular environment.
There are five factors that have led to the development of adaptations by aquatic species.
Temperature: Fish that live in extremely cold water (Arctic) have a natural anitfreeze that keeps their blood and tissues from freezing. Other organisms that live in the very deep parts of the ocean near volcanic vents, organisms can actually survive in extremely hot water.
Light: Plants need light for photosynthesis. In the deepest parts of the ocean some organisms have adapted to the absence of light by producing their own light from spots on their bodies called photophores.
Pressure: As you travel deeper in the ocean, the pressure increases. Those animals that have adapted to different regions of the ocean would be unable to survive in other regions because of the pressure difference.
Salinity: Ocean water has very high salinity levels. Organisms that live in this ecosystem cannot survive in freshwater. Freshwater organisms cannot live in saltwater (think osmosis). Some organisms, can survive in both ecosystems. Salmon can survive in freshwater (where they are born) and saltwater (where they live most of their lives).
Water Movement: Some organisms are able to live in fast moving water. Other organisms are adapted to dig themselves into the sand for protection. Many aquatic animals use the buoyancy of the water to help them move and their streamlined shape in the water reduces drag.
Aquatic Plants
There are two types of aquatic plants: those attached to the bottom and those that float freely in the water (called phytoplankton). Aquatic plants need sunlight and therefore can only survive in water where sunlight can penetrate. Seaweeds are marine plants, that do not have roots, flowers or leaves. They do photosynthesize and use the energy of the sun to create food. Phytoplankton are tiny plants that live on the surface of lakes and oceans and produce oxygen. Their tiny irregular shape, and long spines are adaptations that help them stay in the zone of water where light can penetrate. Diatoms are one example of this type of aquatic plant.
Nutrients in Water
Nutrients are not always abundant in aquatic ecosystems throughout the year. The growth cycle of aquatic plants depends on the availability of sunlight and nutrients (which can be moved by currents, wind, and wave action).
Aquatic Food Chains and Populations
A population is a group of organisms of the same species that live in a particular area.
There are three types of population changes: seasonal, short-term and long-term.
Seasonal Changes - There are dramatic changes in populations of freshwater organisms between the seasons such as changes observed in northern regions (Canada) because of extreme temperature changes. Populations swell in the summer and disappear in the winter. During the winter, surviving individuals may be dormant, or hibernating. Breeding cycles can also cause seasonal changes in populations.
Short-Term Changes - Short-term changes take place over a relatively short period of time and don't last very long. They happen irregularly and may be part of a natural event, or caused by human activities. El NiÑo is a natural event that might adversely affect fish populations.
Long-Term Changes - Long-term changes in populations also result from natural events or human activities. These changes can cause ripple effects because of the interactions that occur within every ecosystem.
Toxins In Aquatic Habitats
Residues from pesticides, fertilizers and industrial chemicals can find their way into the water system. When this happens, the concentrations of these toxins can be magnified as they move up the food pyramid. This is called biomagnification. Animals that have a large amount of fatty tissues are highly susceptible to the toxins effects. This is because the toxins are stored in the fatty tissues.
Fishing
Fishing can affect the balance of fish populations. Over-fishing, specialized fishing, introduction of new species and pollution can all affect the fish populations. When the population of specific species of fish are modified by any of the reasons above, the populations of other species will also be affected within the same ecosystem.
Section 6: Water Quality and Management
Water contains dissolved solids (salts such as sodium, calcium and magnesium). If it contains a lot of calcium and magnesium it is called hard water, whereas soft water contains less. Hard water can cause scaly deposits in pipes, fixtures and appliances
Throughout the world, water is recycled through the water cycle but this doesn't mean that every area in the world will have the same amount of water. No one area can expect the same amount of water year after year. People are also part of the water cycle.
There are direct (domestic or personal use) and indirect (industrial and agricultural) ways that humans use water. Many of these indirect uses can have negative effects on Earth's water supply.
Runoff from farmland may contain fertilizers, manure or compost that can cause excessive plant growth. It may also contain toxic chemicals (pesticides and herbicides) that can kill living organisms.
Some industries can discharge warm water into lakes or rivers causing thermal pollution, which can kill organisms that cannot tolerate the increased temperature. Industrial discharge can also contain toxic chemicals with unpredictable effects such as tumors, birth defects, sterility and even death or organisms.
Sewage contains large amounts of nitrogen, which causes micro-organism populations to increase, using up most of the oxygen and creating zones of low oxygen which affects other organisms causing death.
Oil Spills can cause harm to plants and animals in, on or near the water.
Measuring Water Quality
Below are several factors that can be measured to assess water quality:
- General properties: Such as temperature, rate of flow, color, odor, oxygen levels etc.
- Solids: sediments, turbidity
- Acidity: pH
- Nutrients: Phosphorus, Nitrogen etc.
- Toxic substances: Heavy metals, other chemicals
- Organims: Bacteria, plants and other organisms.
The diversity of aquatic organisms in a water system helps to indicate the quality of the water. The level of dissolved oxygen will determine which species will be able to survive and, which ones will perish. High levels of dissolved oxygen would likely see a vast diversity of aquatic organisms. However, not all of these species are positive indicators, because some micro-organisms can cause disease and death.
Monitoring Water Quality: Water systems everywhere need to be monitored and cleaned up if they are causing a problem. One way to help guard against problems with water quality is to monitor the water supply. To monitor means to observe, check, or keep track of something for a specific purpose. Town and city water supplies have to be monitored on a regular basis to ensure that the quality of the water remains high.
Water Management: Maintaining a reliable and safe water supply is called water management. To make water safe to drink, or potable, for humans it has to be treated. The treatment of water involves screening, mixing, sedimentation, filtering, and adding chemicals. After water has been used by humans, the solid and liquid waste (sewage), has to be treated again before it goes back into the water system as effluent. In rural areas an underground treatment system for this sewage involves using a septic tank. Three additional processes are used to increase the potable water supplies in different parts of the world. Desalination (removing salt from water) Distillation and Reverse Osmosis.