>About this Guide
>Table of Contents
1. What you can do
5. Environmental Issues
6. Keystone species
7. Get Wet!-
Field Study Ideas
8. The Zoo Experience
9. Frogs & Friends
10. Case Studies
Wetland Curriculum Resource
Unit 2. Water - Background for Educators
Water covers the earth in oceans, lakes, rivers, and streams. Of the earth's total water resources, estimated at 1360 cubic kilometres, 97.1% is saltwater and only 2.8% freshwater. Amazingly, as the table below shows, most freshwater is tied up as ice in glaciers or as ground water. Only a tiny fraction of the world's water is found in lakes or rivers.
All living organisms depend on water. This dependence on water is well illustrated by amphibians; frogs, toads, newts and salamanders. Amphibians do not drink water, but absorb all the moisture that they need through their skin. Most adult amphibians breathe air like you and I, but their moist skin also allows oxygen to diffuse through their skin, entering the blood stream directly. The sensitive skin of amphibians makes them extremely dependent on clean water for survival. Many amphibians lay eggs, have an aquatic larval stage, or hibernate in water. Amphibians can be included as a measure of the health of wetlands and wetland biodiversity.
Northern Ontario receives an annual rainfall of 71 centimetres, while southern Ontario's annual rainfall is 84 centimetres. Approximately 680,000 billion litres of rain falls on the total area of Ontario each year. But where does it all go?
IDEA! Have students calculate how many bathtubs full of water equal 680,000 billion litres (an average bathtub holds 150 litres of water)
The amount of water that exists on the earth today has changed little since the earth was created 4.5 billion years ago. Water is continually recycled through nature. The water cycle is powered by the sun. Energy from the sun causes the water to enter the atmosphere as vapour. This process occurs in two ways. It enters through transpiration from vegetation (the loss of water through the pores in the leaves of plants) and by evaporation (from bodies of water).
Once in the atmosphere, the water vapour rises and cools. When the vapour rises beyond the temperature level at which condensation occurs, it forms clouds. Eventually, enough moisture collects in the clouds to form precipitation. Depending on the temperature, the water falls back to the earth as rain or snow. Once the water reaches the earth, it can return to a body of water directly as surface run-off, or percolate into the ground to gradually return to a body of water, or be absorbed by the roots of plants. Regardless of the route it takes, water is either stored in underground aquifers or it returns to the atmosphere and repeats the cycle.
A watershed is the entire land area that is drained by a river or stream, and their tributaries, usually flowing into a larger body of water (i.e. ocean or lake). They are usually outlined on a map by drawing a line around the region drained by the particular river and its tributaries. Most drainage patterns resemble branches of a tree or veins in a leaf. A watershed may also be referred to as the drainage basin for a specific water body, for example, the "Ottawa River drainage basin".
Lakes and rivers make up 17% (177,389 square kilometres) of Ontario's total land area of 1,068,582 square kilometres. The largest drainage system in southern Ontario is the Ottawa River, which drains an area of about 49,900 square kilometres. The Trent system is second with a drainage area of approximately 12,220 square miles, and the Grand River is the third largest with a drainage area of 6,800 square kilometres.
Even the schoolyard has the potential to show a water drainage system. Studying where and why ponds and puddles form is important for understanding water drainage and watershed processes.
Studying the characteristics of ponds and puddles is also necessary to understand what makes a good pond for amphibian populations. Students can observe where puddles form on or near school property. If possible, visit an area before and after a rainstorm. If your study cannot wait until a rainstorm, use a hose or bucket to create a puddle. Water does not accumulate everywhere, but flows to low spots and remains there until it soaks into the ground or evaporates.
If your schoolyard has a sloping or hilly area, try to explain the path the water will take by demonstrating with several tennis balls. Place them on different spots on different sides of the hill to adequately demonstrate the path that running water will take. Where the tennis balls accumulate, will likely represent an area where puddles may form after a rainstorm.
It is surprising how much water actually falls to earth as rain. Storm water run-off can be sudden when precipitation lands on an impervious parking lot (water is unable to infiltrate and will run off suddenly). However, unlike pavement, soil, puddles, and wetlands can retain water and release it slowly. Storm water retention keeps water in watersheds where it can be utilized by species dependant on water, and prevents the sudden rush of water into storm sewers and out into lakes and rivers. Water quality is actually improved when run-off filters through the soil and wetlands.
As water recycles itself through nature, the supply would seem inexhaustible but, water pollution reduces the amount of life-supporting, quality water that is available for wild life and for human use. The following are the common pollutants and their effects:
The health of an ecosystem can be identified by the presence (or absence) of certain plants or animals that are known as indicator species. Generally, organisms can tolerate limited amounts of a contaminant. Any levels beyond that limit cause severe stress and possible death. Indicator species are sensitive to environmental stresses at their lowest, commonly referred to as threshold, levels. Amphibians are considered to be good indicator species. They are sensitive to environmental stresses, and as a result, often disappear from unreliable water sources or unhealthy ecosystems. The amphibian tadpole eats aquatic plants, and the terrestrial adult eats invertebrates. With a two-stage life cycle, amphibians may be exposed to contaminants in the air, water, plants or invertebrates. Thus, changes in amphibian populations may be an indicator of environmental change. The permeable skin of amphibians is particularly sensitive to shifts in pH, which often affects the distribution of many species. Although most species avoid acidic conditions, some species, such as the Wood Frog (Rana sylvatica) exhibit a higher tolerance and can be found in more acidic environments.
Wetlands are vulnerable to pollution when there is a low turnover of fresh water. The lack of moving water in a wetland reduces the amount of dissolved oxygen found in the water and increases the likelihood of contaminants accumulating in bottom sediments.
An important part of any aquatic study is monitoring and interpreting water quality. You can evaluate the health of an ecosystem by measuring parameters, such as pH and dissolved oxygen, which determine water quality. You can do this on either a short-term comparative basis between sites, or over a long-term at a single site.
Each aquatic species has specific requirements and tolerance levels for water quality, and their distribution and abundance is related to changes in environmental conditions. You can use the presence or absence of indicator species to verify the results of your water testing. For example, frogs are highly sensitive to acidity. The burning of fossil fuels causes acid deposition. Acid deposition causes the pH levels in many aquatic ecosystems to drop, resulting in a rapid decrease in the habitat that can sustain a diversity of wild life.
Several relationships exist between tests for the various chemical parameters (i.e., oxygen and carbon dioxide, carbon dioxide and pH, carbon dioxide and alkalinity.) By understanding these relationships, values can be more easily interpreted. A discussion of these relationships and of water quality testing techniques appears in "Unit 7: Get Wet! -Pointers for Field Studies."
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