Ecology: The Water Cycle

The Water (Hydrologic) Cycle:

From the beginning of time when water first appeared, it has been constant in quantity and continuously in motion. Little has been added or lost over the years. The same water molecules have been transferred time and time again from the oceans and the land surface into the atmosphere by evaporation, dropped on the land as precipitation, and transferred back to the sea by rivers and groundwater. This endless circulation is known as the "hydrologic cycle". Water is the the only natural substance which exists at the surface of the earth in three states:  solid (ice), liquid (water), and gas (water vapor).  In order to change the state of water from one form to another, heat is needed. In the natural environment, this heat energy comes from the sun.

Oceans represent 97.24 percent of all the Earth's water.  All of the water in lakes and rivers will eventually end up in an ocean, and it is the oceans of the world which undoubtedly contribute most of the water vapor in the atmosphere.  As a result of the oceans' impact on the water cycle, it is no wonder why oceans influence weather and climatic condition of the globes.

Water source	Water volume, in cubic miles	Percent of total water
Oceans	317,000,000	97.24%
Icecaps, Glaciers	7,000,000	2.14%
Ground water	2,000,000	0.61%
Fresh-water lakes	30,000	0.009%
Inland seas	25,000	0.008%
Soil moisture	16,000	0.005%
Atmosphere	3,100	0.001%
Rivers	300	0.0001%
Total water volume	326,000,000	100%

Table 1: Global water distribution

Source: Nace, U.S. Geological Survey, 1967 and

The Hydrologic Cycle (Pamphlet), U.S. Geological Survey, 1984

The biggest determinant in water quality is what water runs over ex.: unpolluted soil, porous rocks, or concrete. Let's look at the three most common environments we live in...

The Rural Water Cycle includes fields, woodlands, and streams. Because of this, as long as humans don't pollute these areas, the water is cleaner than water coming off road ways. Their are other concerns for water in these areas though, like bacteria, animal pollutants, and stagnant water. Humans must never drink from a water source they are unsure of as bacteria in the water can make us sick.

The Suburban Water Cycle includes small neighborhoods where houses using wells and city water add possible contaminants like pesticides, heavy metals, paints, oils, and gas. Some neighborhoods use septic systems where contaminated water from toilets and sinks is pumped into an underground storage tank and slowly allowed to peculate to the surface.

Urban Environments need to use man-made waste treatment plants to clean the water of garbage, chemicals, and other dangerous materials before sending it back into the natural environment. Storm drains carry water from roads to Water Treatment plants while pipes from your bathroom carry dirty water to sewage plants where the water is cleaned and chemically sterilized before being sent by more pipes into streams or rivers.

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Watch the Introduction to the Water Cycle on the BBC website.

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Students will review the What is an Aquifer? site to learn about ground water.

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Vocabulary:

Condensation 

Water vapour is also emitted from plant leaves by a process called transpiration. Every day an actively growing plant transpires 5 to 10 times as much water as it can hold at once.

Sublimation

The changing of water from a solid to a gas.

Surface runoff

Excessive rain or snowmelt can produce overland flow to creeks and ditches. Runoff is visible flow of water in rivers, creeks and lakes as the water stored in the basin drains out.

Precipitation

Precipitation is made up of any type of water that falls to the earth like snow, hail, mist, or rain. Most of it (80 percent) evaporates or transpires through plants and never reaches lakes, streams, or ground water. The rest, about 6-10 inches of precipitation, runs off the land into lakes, streams, wetlands or rivers (also called "surface water"), or, it soaks right into the ground.

Percolation

Some of the precipitation and snow melt moves downwards, percolates or infiltrates through cracks, joints and pores in soil and rocks until it reaches the water table where it becomes groundwater.

Infiltration

Infiltration happens when water soaks into the soil from the ground level. It moves underground and moves between the soil and rocks. Some of the water will be soaked up by roots to help plants grow. The plant's leaves eventually release the water into the air through the plant's pores.

Some of the water keeps moving down into the soil to a level that is filled with water, called ground water. The very top of this layer filled with ground water is called the water table.

Ground Water

Ground water is simply water under the ground where the soil is completely filled or saturated with water. This water is also called an "aquifer." Ground water moves underground from areas where the elevation is high, like a hilltop, to places that are lowland areas. Water movement is slow and might move anywhere from less than a millimeter up to a mile in a day.

Where the water table meets the land surface, a spring might bubble up or seep from the ground and flow into a lake, stream woodland, or the ocean. Ground water that meets the land surface also helps keep rivers, streams, lakes and wetlands filled with water.

The Water Table

The Water Table is found underground where the rock and soil begin to be filled or "saturated" with water. It also marks the very top of the ground water layer.

Where the water table meets the land surface, a spring might bubble up or seep from the ground and flow into a lake, stream woodland, or the ocean. When ground water meets the land surface, it flows out and helps keep rivers, streams, lakes and wetlands filled with water.

Evaporation

Warmth from the sun causes water from lakes, streams, ice, and soils to turn into water vapor in the air. Almost all of the precipitated water (80 percent) goes right back into the air because of evaporation. The rest runs off the land or soaks into the ground to become ground water.

Water Vapor

Water vapor is water in a gas form that is held in the air until it changes back to water. You know, sometimes it #s sticky outside in the summer - that #s just water held in the air. The water can change into fine droplets by "condensing" in the air, and we get clouds. When the droplets get big enough, they are pulled to the earth by gravity as precipitation, better known as rain, sleet, snow, hail, dew, or frost.

Transpiration (evaporation of water from plants):

Plants give off water from their surfaces in a process called transpiration. This water leaves through stomata, which are tiny openings on the surface of a plant and are especially abundant on the undersides of leaves. Stomata open and close to let gases in and out. Water vapor is one of the released gases. Some leaves have more than a million stomata. In forests, trees need a large amount of water because about 98 percent of the water they take in is lost through the stomata. The leaves of tropical and temperate plants have stomata that are open longer periods of time and have larger openings than those of desert plants. In the desert, plants can survive with less water because the stomata of the plants do not open as wide and remain closed most of the time. The time stomata remain open as well as the size of their openings are largely controlled by the availability of water and of sunlight.

As the water evaporates from leaves during transpiration, more water is pulled into the plant at the roots. The water moves from the roots to the leaves through tubelike structures called xylem tubes. The water carries nutrients through plants.

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The Water-Climate Relationship

Water plays a basic role in the climate system through the hydrologic cycle, but water is intimately related to climate in other ways as well. It is obvious, from a water resource perspective, how the climate of a region to a large extent determines the water supply in that region based on the precipitation available and on the evaporation loss. Perhaps less obvious is the role of water in climate. Large water bodies, such as the oceans and the Great Lakes, have a moderating effect on the local climate because they act as a large source and sink for heat. Regions near these water bodies generally have milder winters and cooler summers than would be the case if the nearby water body did not exist.

The evaporation of water into the atmosphere requires an enormous amount of energy, which ultimately comes from the sun. The sun's heat is trapped in the earth's atmosphere by greenhouse gases, the most plentiful of which by far is water vapour. When water vapour in the atmosphere condenses to precipitation, this energy is released into the atmosphere. Fresh water can mediate climate change to some degree because it is stored on the landscape as lakes, snow covers, glaciers, wetlands and rivers, and is a store of latent energy. Thus water acts as an energy transfer and storage medium for the climate system.

The water cycle is also a key process upon which other cycles operate. For example one needs to properly understand the water cycle in order to address many of the chemical cycles in the atmosphere.

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Assessment Projects:

#1: Transpiration Activity:

Purpose
To determine how the number of stoma affects water loss.

Materials
4-by-8-inch (10-by-20-cm) piece of poster board
two 10-ounce (25-cm-diameter) plastic cups
pencil
scissors
paper hole punch
tap water
black marking pen
transparent tape

Procedure

• Fold the poster board piece in half by placing the short sides together.
• Stand one of the plastic cups upside down on the poster board.
• Use the pencil to trace around the mouth of the cup on the poster board.
• Cut out the circle tracing, cutting through both layers of the poster board.
• Use the paper hole punch to cut 2 holes in one of the paper circles, one hole across from the other.
• Randomly cut 20 holes in the other paper circle.
• Fill the cups with an equal amount of water so that they are about three-fourths full with water.
• Use the pen to mark a line on each cup that is even with the surface of the water.
• Use the tape to secure the edges of one paper circle over the opening of each cup. You want the holes in the circle to be the only openings.
• Set the cups near a window that gets direct sunlight.
• After 3 or more days, compare the level of the water in each cup to the black water mark on each cup.

Results
There is less water in the cup with many holes in its cover than in the cup with only two holes in its cover.

Why?
The fact that the water level goes down shows that water has left the cups. Water in the cups evaporates, forming water vapor, which escapes through the holes in the covering. The amount of vapor escaping increases with the number of holes in the covering. The holes represent stomata in the leaves of plants. The more stomata in the leaves, the greater the amount of water lost by transpiration. Desert plants have fewer stomata, which are closed most of the time, as well as stomata with small openings, so they lose a smaller amount of water than do other plants, which have leaves containing many large stomata that are open most of the time.

#2: Students will create a Mini Water Cycle Terrarium.

#3: Students will create a Water Cycle Disk.

#4: Students will create a bulletin board showing the different aspects of the Water Cycle:

Water Cycle 2 by misskprimary

Ecology: Working from the ground up.

Ecology is the scientific analysis and study of interactions among organisms and their environment, such as the interactions organisms have with each other and with their abiotic environment. 

For this post, we will be looking at the health of our local soil and water supply.

There are three soil components – Clay, Sand and Silt

Clay is the smallest mineral component. These tiny flat particles fit closely together to have the greatest surface area of all soil types. Clay soil contains needed nutrients and also stores water well. So well in fact, that drainage is slow in clay soil. It is the slowest to warm in the spring.

Sand makes up the largest particles in soil. They are rounded, rather than flat. This allows for larger space between the particles and water drains quickly.  Because of this, the nutrients drain faster than clay soil and your plants will need more water and fertilizing.

Silt represents the middle size pieces. It is made up of rock and mineral particles that are larger than clay but smaller than sand. Individual silt particles are so small that they are difficult to see. To be classified as silt, a particle must be less than .005 centimeters (.002 inches) across.

The Mason Jar Soil Test

Use a clear, clean, empty jar with a tight lid. A pint or quart Mason jar works fabulously.

Fill the jar about half full of garden soil. You can use soil from different areas of the garden to get an overall view, or make a test for each garden bed.

Fill the jar nearly to the top with water. Leave room for shaking.

Tighten the lid and shake the jar for several minutes so that all the particles are in suspension.

Set your mason jar soil test aside for several hours, so the particles have a chance to settle. They will separate into clay, silt, and sand layers.

Read the Results of your Mason Jar Soil Test

• The bottom layer will be the heavier particles, sand and rocks
• The next layer will be the silt particles
• Above that are the clay particles
• Organic matter may be floating on the surface of the water

The color of the soil gives a clue to its character – light colors usually have less organic content than dark soils and dark soil warms faster in the spring.

• If your jar test is 20% clay, 40% Silt, 40% sand = Loam, you have the perfect combination
• 30% clay, 60% silt, 10% sand = Silty Clay Loam
• 15% clay, 20% silt, 65% sand = Sandy Loam
• 15% clay, 65% silt, 20% sand = Silty Loam

#1 – You can test your soil pH with vinegar and baking soda

Collect 1 cup of soil from different parts of your garden and put 2 spoonfuls into separate containers. Add 1/2 cup of vinegar to the soil. If it fizzes, you have alkaline soil, with a pH between 7 and 8.

If it doesn’t fizz after doing the vinegar test, then add distilled water to the other container until 2 teaspoons of soil is muddy. Add 1/2 cup baking soda. If it fizzes you have acidic soil, most likely with a pH between 5 and 6.

If  your soil doesn’t react at all it is neutral with a pH of 7 and you are very lucky!

#2 – You can make a cabbage water pH test

Measure 2 cups of distilled water into a sauce pan. Cut up and add 1 cup of red cabbage. Simmer for 5 minutes. Remove from heat and allow it to sit for up to 30 minutes.

Strain off the liquid – which will be purple/blue. This will have a neutral pH of 7.

To test: add 2 teaspoons of soil to a jar and a few inches of cabbage water. Stir and wait for 30 minutes. Check the color. If it turns up pink, your soil is acidic.  If it is blue/green, your soil is alkaline.

Thank you Preparednessmama for posting these!

Soil and Water Test Kits:

For those wanting a more in-depth evaluation of your soil there are two options I'd like to recommend:

#1: Ferry-Morse Soil Test Kit

This is a good kit for small plots of land like school gardens. It's also a good kit if you are trying to show a small group of students results without spending too much.

#2: County Extension Service Kit

We use the University of Florida's Extension Service to test our ground water and soil composition each season. They don't cost very much and you get a detailed report back in a few weeks.