And with water we have made all living things. The Koran, SURA XXI (AL ANBIYA):30 He sendeth the springs into the valleys, which run among the hills. They give drink to every beast of the field; the wild asses quench their thirst. PSALM 104:10, 11
HAD THE EARLIEST explorers of our solar system been transgalactic adventurers from another part of the universe, their first sight of this planet might have led them to name it Water. From space, you can see that ours is not the green planet but the blue planet, with its great oceans and its gossamer veil of clouds.
An astounding 70.8 per cent of Earth’s surface is ocean; with an average depth of 3.73 kilometres, the oceans contain a total of 1.37 billion cubic kilometres of water. When inland seas, lakes, glaciers and polar icecaps are included, a total of 379.3 million square kilometres—74.35 per cent of the planet’s surface—is covered by water. The landmasses above the surface are just bumps. If the solid part of Earth were to be smoothed and levelled, a single ocean would wrap the entire globe to a depth of 2.7 kilometres.
Human beings are landlubbers on this watery planet, island people marooned on dry land, surrounded by and dependent on an alien element, an old home we left long ages ago and yet carry still within us. Water is the raw material of creation, the source of life. When the waters break, the child is born from them, just as the gods of old parted the dark, primeval ocean and fashioned the Earth, just as the first land creatures struggled up out of the tide.
Perhaps that is why water is at the heart of human ritual. Baptism, for example, often welcomes the child into the human family, washing away the past, marking a new start. The powerful symbolism of water—as transformation, purification, sharing—permeates our lives. Water flows through our memories: that sunlit swim in a creek, that wish made as a coin falls into a fountain, that first sigh of pleasure when tired feet are slipped into a cold mountain stream. Our literature is saturated with our uncertain relationship with this crucial substance—the water we come from, the water we cannot do without, the water that may drown us or flood away our world.
Full fathom five thy father lies;
Of his bones are coral made:
Those are pearls that were his eyes:
Nothing of him that doth fade,
But doth suffer a sea-change
Into something rich and strange.
WILLIAM SHAKESPEARE, The Tempest
The ocean—shifting, changeable, mysterious—has a powerful influence on human life and grips the human imagination. Rising and falling around Earth’s shores, it moves to more than terrestrial rhythms. Pulled three ways, by Earth, the moon and the sun, the tides wax and wane day by day, month by month, season by season, dancing to the rhythmic gyrations of planet, satellite and star. Somehow we have always known this and listened for un-Earthly messages in the motions of the sea. The ancient Greeks called the messenger Proteus the old man of the sea, herdsman of the ocean’s seals. He saw the future and would tell you the truth about it—if you could catch him. Metamorphosis was his escape; changing his shape from lion to dragon to a stream of water, becoming a flame, a tree, he slipped through your fingers in a dizzying series of transformations. In the same way, the waters he represented are eternal shape-shifters, continually transforming themselves and the rest of the planet. They bring us a strange and ancient truth that is hard for us to grasp: a vision of the sources of life and its endless metamorphoses.
Life may have evolved in the ocean—where it stayed for about 3.5 billion years—but in comparison, life’s success on land has been spectacular and swift. Once plants started to colonize Earth’s terrestrial margins, about 475 million years ago, the diversity of life expanded quickly. Today, it is estimated that there are two species on land for every one in the ocean. And all of this life is crammed into a space a fraction of the ocean’s depth and breadth. What is it that caused this spectacular explosion of life?
We know that terrestrial organisms carry the ocean within them—in fluid-filled cells, for instance. This is how organisms were able to exploit the land, but Dianna and Mark McMenamin took the idea further. They suggest there is another “ocean” that flows through life on land. Whereas marine organisms are passively and individually bathed in fluid, terrestrial organisms are connected physically with other organisms, creating complex networks through which fluids can move. For example, parasites may travel through the blood of an animal, tree roots intertwine with the tiny threads, or hyphae, of a fungus that weave through the soil, and aphids drink the sap of a plant. The crux of the McMenamins’ idea is that organisms on land became increasingly successful, pressured largely by the influence of fungi and parasites, and were able to diverge and colonize new habitats as they learned to exploit fluids. But they weren’t using just the obvious fluids, such as surface water, but also the internal seas flowing in blood, sap and cellular fluid. These fluid connections resulted in another aquatic habitat on land, an internal sea flowing between living things.
If air is the fuel, the spirit that animates all living things, water gives them body and substance. Water was absolutely necessary for life as we know it to have evolved. Life originated in the oceans, and the salty taste of our blood reminds us of our marine evolutionary birth. But we, like many other animals and plants, cannot live on salt water. Our lives are made possible by the hydrologic cycle, the miraculous process whereby salty water is transformed into fresh water by evaporation and is redistributed around the planet. Energy from the sun causes water to evaporate from the ocean as water vapour, which rises into the atmosphere and then falls back onto the land as precipitation. Water reaching Earth’s surface as rain seeps into the ground or runs into rivers and lakes and eventually returns to the oceans (Figure 3.1).
The hydrologic cycle is crucial to all life, though sometimes we may wish it were not. “It’s raining again!” is a common complaint in Seattle and Vancouver. “It poured for five days,” a disappointed tourist grumbles in the Choco rain forest in Colombia, forgetting that the lush splendour he has come so far to experience was created and maintained by the rain he deplores. Rains bring life. Those working close to the land know this. Coastal fishers hold a collective breath if warm, dry weather lingers late into the fall. They anxiously watch as salmon, ripening with eggs and milt, mill in the estuaries waiting for the rains to come and the rivers to fill. Prairie farmers gazing gloomily upwards into a cloudless sky understand the hydrologic cycle better than most. So do aboriginal people, whose rain dances beg the clouds to cry, and cultures in other parts of the world, whose elaborate festivals entreat the gods to send the life-giving monsoons.
Living organisms are active participants in the hydrologic cycle, absorbing and filtering water and breathing it back into the atmosphere. Plants play a particularly important role through transpiration, or the loss of water through their leaves.
FIGURE 3.1: The hydrologic cycle.
Adapted from Charles C. Plummer and David McGeary, Physical Geology, 5th ed.
(W.M.C. Publishers, 1991), p. 234.
A forest is an intricate device for catching, holding, using, and recycling water. You might liken it to a large sponge, except that it is far more complex. That tangle of tree roots snaking across the forest floor absorbs water while holding the soil so effectively that creeks don’t flood and the water flowing in them is clean and clear after many days of rain. Millions of tonnes of water in rain forests are lifted from the soil and thrust back into the sky by transpiration. In essence, forests rain upwards, into the heavens.
Forests also harvest moisture from the sky. Particularly in coastal areas, where there is a high incidence of fog and mist, trees comb the air. Water droplets condense on needles and leaves and fall to the forest floor, drip by precious drip contributing to the forest’s stores of water. And trees’ capacity to gather water can be significant. Studies in Australia showed that “cloud forests” can capture 10 to 25 per cent more water from atmospheric vapour than falls as rain. Imagine what would happen if these trees, with their towering canopies stretching towards the heavens, were gone.
Within and without, forests help regulate climate and the hydrologic cycle. Forests hold water in the soil, in roots, trunks and branches. The water is slowly meted out over days and weeks, and any excess is returned to the air.
Large areas of forest create their own local weather, raining on themselves and remaining moist during dry spells. At the same time, they modify the climate of the entire region and beyond. When large tracts of forest are removed, the barren soil hardens, causing rain to evaporate or run off rapidly.
This cycle between air, water and forest is most striking in the tropical rain forest of the Amazon Basin. This largest tract of tropical forest on Earth is an important heat engine, cycling massive amounts of water each day through the forest as trees and other plants absorb water and then breathe it out. Every year, a single large tree can move 700 tonnes of water out of the soil, plumbed through its trunk into the forest canopy and, ultimately, the atmosphere. There is so much moisture locked in the Amazon’s forests that it acts like a green ocean, seeding the clouds sailing above it with moisture, just as clouds form above the seas. The Amazon forest’s influence is far-reaching, fuelling major atmospheric and oceanic currents, which in turn drive world climate and weather patterns.
Suppose we were to follow a single molecule of water vented from an active volcano on a Hawaiian island. We’ll call this molecule Aqua. Liberated with a mix of other gases from deep within the planet, Aqua is blown skyward, buffeted by convection forces and atmospheric winds that are constantly blowing across the planet. Eventually, Aqua finds itself streaming east from the islands, 10 kilometres above the ocean, moving along a ribbon of moisture that is like a great atmospheric river.
Reaching the coast of North America, Aqua moves inland until it encounters the upthrust of the Rocky Mountains. The cloud Aqua is in begins to cool, condense and finally liquefy, and the water molecule falls towards the land as part of a drop of rain. On striking Earth, Aqua slithers into the soil, pulled by the forces of gravity, moving erratically around grains of sand that loom like miniature planets.
As Aqua sinks into the soil, it encounters a slender rootlet of a tree, which slurps Aqua up into its xylem tissue, drawing the molecule by capillary action up through the trunk into the branches. Eventually Aqua ends up in one of the seeds in a pinecone. A bird pecks at the cone, dislodging and swallowing the seed containing Aqua. As the bird flies south on its annual migration, it absorbs Aqua into its bloodstream.
Resting in a tropical rain forest in Central America, the bird is preyed upon by a mosquito. Aqua is sucked into the mosquito’s gut, and as the blood-laden insect drops close to a creek, it is snapped up by a sharp-eyed fish, which incorporates Aqua into its muscle tissue. An aboriginal fisher spears the fish and triumphantly carries it, and Aqua, home for a meal. And so it goes, the endless, eventful peregrination of every molecule of water.
Across continents, the network of waterways resembles the circulatory system of a body. And in fact, that is the role that lake and river systems perform. Water that runs off after rain or from melting snow or from plant roots accumulates in ditches and creeks, which carry it to the rivers draining into lakes or the oceans, where it evaporates back into the atmosphere. Patterns of rootlets, roots and branches; rivulets, creeks and rivers; veins and capillaries in living tissue—they all reflect the same physical realities and bind us all together in the Earth’s vital processes. In the words of aquatic ecologist Jack Vallentyne:
If water is the blood of Mother Earth and soil the placenta, river courses are veins, oceans are compartments of the heart and the atmosphere is a giant aorta. Comparing Earth beats to human heart beats, the life expectancies of rivers would range from millions to billions depending on whether Earth beats were measured in days or years.
Water sits still as well as flowing—wrapping a film around minute particles of soil, pooling in the interstices of rocks and gathering to a greatness in deep underground aquifers, which have existed since the dinosaurs roamed the land. This “fossil” water may move a few metres every thousand years; the water in the aquifer below the city of London is deemed to be twenty thousand years old. Water isn’t constantly generated de novo; what is here on Earth has always been here. But the transformational process by which it maintains life, cartwheeling around the planet, moving from cloud to rain to ground and back again in the hydrologic cycle, has not always existed. It is the product of a multitude of factors—temperature, chemistry, soil and life itself.
In the early life of Earth, the atmosphere was too hot for water to exist in liquid form. Water vented from volcanoes was vaporized, and only after tens of millions of years, when the atmosphere had cooled enough, was water able to condense into clouds. Eventually, those clouds were able to release their contents by raining onto the rock that formed the surface of the planet.
Imagine the dry, lifeless rockscape that was then Earth: immense mountains pierce the sky; deep trenches scar the surface. As the rain falls relentlessly, water accumulates in every depression, filling each one and flowing down towards the next containment. Pulled by gravity, water overflows the depressions, becoming creeks and rivers, dragging rocks along, scouring out channels, always running down towards lower places.
After millions of years, fresh water covered most of the Earth. The relentless flow of water dissolved compounds out of rock and wore away minute quantities of elements, washing them away to the largest bodies of water. The salty seas were formed by this imperceptible accretion, an enormous change achieved by infinitesimal alterations over immense periods of time.
Life began in the Archean period, 3.8 to 2.5 billion years ago, and even in these early days life seems to have played a part in maintaining Earth’s supply of water. During that period oxides in basalt rock continually reacted with carbon dioxide and water, producing various carbonates (compounds of oxygen and carbon) of sodium, potassium, calcium, magnesium and iron and releasing hydrogen into the atmosphere. Since hydrogen is extremely light and cannot be held by the gravitational pull of the planet, it was lost into space. Had this reaction continued for a billion years or more, all of the planet’s water might have been lost, and Earth’s atmosphere would be like that of Mars. Instead, cyanobacteria (and later, algae and plants) capitalized on the abundant resources available to them—water, sunlight and carbon dioxide—to fuel a chemical reaction that would change their world. Photosynthesis produced oxygen as a by-product, but it also held some of the hydrogen from water in the carbon ring of glucose, thus clutching hydrogen to the planet. In addition, the free hydrogen produced by the oxidation of iron in rock was exploited by bacteria as a source of energy. Oxygen, hydrogen and sulfur react chemically to produce water and hydrogen sulfide, which has recoverable energy within its structure. Thus, the forces of life may very well have prevented the desiccation of the planet by capturing the hydrogen that is necessary for water and thereby preventing it from drifting into space.
Life is animated water.
VLADIMIR VERNADSKY, in M.I. Budyko, S.F. Lemeshko
and V.G. Yanuta, The Evolution of the Biosphere
Like air, water is essential to our survival. But whereas the lack of air will kill us within minutes, water takes longer to make its necessity known to us. Deprived of water for a few hours, especially after exercise or on a hot day, we notice our throats becoming parched; our bodies are urging us to take a drink. If no water is available, we might survive for as long as ten days, depending on the ambient temperature, our degree of activity and the clothes we are wearing. But in the end we would die a terrible death. Water is the elixir of life; without it, this planet would have remained barren.
Living beings need this elixir because they are made of it. Protoplasm, the living matter of all plant and animal cells, is mostly water. The average human being is roughly 60 per cent water by weight, nearly 40 litres of it carried in trillions of cells. Three fifths of the water in our bodies is inside cells and is called intracellular fluid, and two fifths is outside cells, in blood plasma, cerebral spinal fluid, the intestinal tract and so on. The proportion of water by weight varies with age and gender as shown in Table 3.1.
The reason for the difference lies in the proportion of fluid that is inside and outside of cells and the proportion of body fat, for fat cells contain less water than other cells.
Though we appear to be solid, we are in fact, liquid bodies, similar in a way to gelatin, which also seems to be solid but is in fact largely water, “gelled” by the presence of an organic material.
DANIEL HILLEL, Out of the Earth
TABLE 3.1: Proportion of Weight in Water for Humans Grouped by Age and Gender
Basically, each of us is a blob of water with enough macromolecular thickening to give us some solidity and to keep us from dribbling away. Every day, about 3 per cent of the water in our bodies is replenished with new molecules. The water molecules that perfuse every part of our bodies have come from all the oceans of the world, evaporated from prairie grasslands and the canopies of all the world’s great rain forests. Like air, water physically links us to Earth and to all other forms of life.
Although we live on land, we are creatures of water, and, as such, we have our own hydrologic cycle. We lose moisture with every breath, in each bead of sweat, in every tear we shed, every time we urinate and defecate. We can replenish some of this water ourselves through metabolic processes such as the breaking down of carbohydrates and fats, which produces carbon dioxide, water and energy. But metabolic production of water only accounts for 11.5 per cent of the normal requirement of 2.5 litres a day. The rest usually comes from the fluids we drink (52.2 per cent of our daily needs) and from solid food (36.3 per cent). This intake is balanced with our daily losses—about 1.5 litres in urine, 0.9 litre in expired air and sweat, and 0.1 litre in feces.
Our bodies are perpetually on water alert, because our daily intake must be exquisitely matched to our daily output. When you start to become dehydrated, the concentration of salts in your body fluids begins to rise. A small change is enough to induce the posterior lobe of the pituitary gland to release the hormone adiuretin (ADH, or vasopressin). ADH acts directly on the kidney, inducing it to decrease the excretion of water.
Other biological alarms are set off when dehydration reduces the volume of the blood. Stretch receptors monitor blood volume inside the heart and send signals to the “thirst centre” of the hypothalamus in the brain to inhibit the production of saliva. Dryness in the mouth registers in our consciousness as “thirst,” stimulating us to drink. The cottony mouth sensation is one of the early signs of dehydration, which commonly results after extensive bleeding, burns or diarrhea, along with profuse sweating.
If you drink too much water, these alarm systems work in reverse. When the concentration of salts in your body fluids becomes diluted, the production of ADH is inhibited, stimulating the kidneys to excrete more water. A more dilute concentration of urine is sent to the bladder, and usually the excess is eliminated within an hour.
As well as maintaining the water balance in the body, the kidney plays a major housekeeping role in purifying the crucial fluids in blood. It removes dissolved metabolic wastes, such as ammonia from the breakdown of amino acids, urea produced in the liver from degraded protein products, uric acid from nucleic acid, and phosphoric and sulfuric acids from protein by-products. These toxic compounds are filtered out of the blood and flushed away. About 1.2 litres of blood passes through the kidneys every minute for a total of almost 2000 litres per day. The nephrons and their network of minute filtration structures filter 180 litres of blood each day.
As you will see in chapter 5, on energy, one property of water, its high absorption of heat to change from a liquid to a gaseous state, plays a critical role in regulating body temperature. Water within the body reaches the surface of the skin by diffusion (perspiratio insensibilis) or via sweat glands that are activated by the autonomic nervous system, which functions without our awareness. After it reaches the surfaces of the skin as sweat, the water evaporates. Evaporation requires energy, so drying sweat takes heat from the body as energy, thereby cooling the skin. Evaporation of a litre of fluid requires 2428 kilojoules of heat.
There is a remarkable equilibrium between your body and its surroundings. The inside and the outside of your body combine to manage the ebb and flow of water within and around you. Ambient humidity and air temperature, together with your level of physical activity, determine how much water moves through your skin into the surrounding air. In the same way, external and internal conditions regulate the water you imbibe and the water you eliminate. The same is true of all other creatures; this lifelong balancing act is part of a global circus, a performance stagemanaged by the planet and its inhabitants together.
Water enters our bodies, circulates through it to the rhythm of the heart, ceaselessly carrying food, fuel, and cellular and molecular detritus to and from various organs of the body. Water seeps through our skin, escapes from our lungs as vapour and exits every opening in the body. It then reenters the hydrologic cycle, trickling into the soil, entering plants, evaporating into the atmosphere, entering bodies of water. In this way, water circulates endlessly from the heavens to the oceans and land, held briefly within all living things before continuing the cycle. You might see the whole enterprise of life as just a vehicle for the transformation of water. If a hen is the egg’s way of being born, then human beings are the way water molecules get to talk to one another.
Water is so fundamental to life that the search for extraterrestrial life is essentially a search for water. Guided by the mantra “follow the water,” researchers are on the lookout for water throughout our solar system. Thus far, the leading candidate is Mars, with its polar ice caps and evidence of the largest-known flood in the solar system. Three and a half billion years ago, Mars was awash, but where did the water of this ancient flood go? In 2002, the Mars Odyssey may have found the answer when it discovered enough icestudded soil to fill Lake Michigan twice over just below the planet’s surface. Tantalizing new images from Mars rovers and spacecraft suggest that there may also be underground reserves of water that break through the planet’s surface as springs.
Mars is 700 billion billion tons of iron and rock, wrapped in an unfamiliar landscape of canyons, craters and calderas. Nonetheless, the most compelling thing we could find on this enormous, orange orb would be a microgram of wet chemistry able to reproduce, move, grow, and evolve.—SETH SHOSTAK, astronomer, SETI Institute
Although Mars is the front-runner as a potential home of extraterrestrial life, other planets and satellites are in the race, too. Europa, one of Jupiter’s moons, is not only ice-covered but also thought to have an ocean about ten miles below its surface. If, as is surmised, volcanic vents below this sea are spewing hot, nutrient-rich water into its abyss, the recipe for life (water, plus an energy source and nutrients) might just exist. The Jovian moons Ganymede and Callisto may also house great oceans under their icy crusts, but recently all eyes have turned to Enceladus, one of Saturn’s moons. Images captured by the spacecraft Cassini show tantalizing images of spouting geysers, making Enceladus the first world other than Earth with the most convincing evidence of liquid water.
Looked at closely, water molecules turn out to be very strange things. Water is so familiar that most of us accept its behaviour as normal. But to a physicist water is an anomaly. For example, water is liquid at room temperatures. That is quite odd; a compound such as hydrogen sulfide, which has a low molecular weight similar to that of water, becomes a gas at –60.7°C. Whereas most substances contract when they solidify, water expands. This means water is less dense as a solid than as a liquid. Water has other unusual properties, such as high melting, boiling and vaporization points.
Life depends in toto on water’s constancy. The ability of water to absorb large amounts of energy buffers photosynthesis in cytoplasm and the transfer of oxygen in animal blood from chaotic flux; moderates the Earth’s climate by using oceans and lakes for heat storage; eases seasonal change and our bodies’ adaptation to it by slowing, without shocks, the change of weather; and protects plants like cacti from boiling under desert skies. Most of all, water’s specific heat, heat of vaporization and heat of fusion give life its ability to maintain in hard times. Without these molecular traits, climatic extremes would turn living creatures over to their Maker at unprecedented rates.
PETER WARSHALL, “The Morality of Molecular Water”
Water has one property that is particularly striking: the amount of heat required to raise the temperature of a unit of water by 1°C is ten times higher than for iron, thirty times higher than for mercury and five times higher than for soil. This property makes water an effective “sink” for heat; it absorbs large quantities of heat and then radiates it out. Because of this property, large bodies of water, such as lakes and oceans, absorb a great deal of heat in summer, release it in winter and thus modulate surface temperatures. Ocean currents absorb large amounts of heat in the tropics and transport it to temperate regions, where it warms the surrounding air. When the water reaches the polar areas, it is cooled and then moves back towards the equator, where it will lower air temperatures as it absorbs more heat. The planet’s water supplies have other effects on climate as well: the whiteness of snow and clouds reflects sunlight away from the Earth, whereas water vapour behaves as a greenhouse gas and reflects heat back onto the surface.
FIGURE 3.2: The atomic structure of a water molecule.
Water’s special qualities are the result of the strong attraction between molecules of water, giving it a high internal cohesion. At the molecular level, water is a deceptively simple substance. Made up of two atoms of hydrogen combined with a single atom of oxygen, the hydrogen atoms do not line up with the oxygen atom in a linear array as H-O-H. Instead, the hydrogen atoms form a 105-degree angle to each other (Figure 3.2). They are on one side of the molecule and have a positive charge, while the large oxygen atom bulges out at the other end and has a negative charge. Thus, the molecule is said to be dipolar, like a tiny magnet. This dipolar arrangement gives the hydrogen atoms an attraction for an oxygen nucleus on another water molecule, a kind of chemical affinity that is called hydrogen bonding (Figure 3.3). The extraordinary ramifications of the dipolarity of water can be seen in the formation of crystals or snowflakes. There are so many possible ways this simple molecule can combine that the shapes of snowflakes appear to be infinite. It took a curious, self-educated young farmer to show us this was so. In 1885, Wilson “Snowflake” Bentley became the first to photograph a single snow crystal. He went on to photograph over five thousand snowflakes and, indeed, never found two alike. His images are still among the best ever taken of water in its crystalline state.
FIGURE 3.3:
The formation of hydrogen bonds between water molecules.
Figures 3.2 and 3.3 adapted from Cecie Starr and Ralph Taggart, Biology: The Unity and Diversity of Life, 6th ed. (Belmont, CA: Wadsworth, 1992), p. 27.
Water molecules cling to each other, but unlike actual chemical bonds, the hydrogen bonds change constantly. A molecule may change hydrogen-bonded partners 10 billion to 100 billion times a second, thus linking adjacent molecules in a fleeting embrace. These rapid-fire interactions are like a frenetic dance of water molecules. Chemist Richard Saykally describes the dance in this way:
… it’s like water has two hands and two feet. The hands of water are the hydrogens that are more or less positively charged, and the feet are the electron pairs that are the negative part associated with oxygen. And these two hands want to grab the feet of two other water molecules, and the two feet want to interact with the hands of two other water molecules. So in each water molecule, hydrogen bonds to four others, making very extensive networks in the liquid.
This constant shifting makes liquid water so stable that it requires a great deal of heat energy to enable molecules to break free as a gas.
In ice, each molecule of water grabs the “hands” and “feet” of its four nearest neighbours. This forms a tetrahedron, a pyramid with four triangular faces. What happens to this shape when the ice melts? According to Richard Saykally and other chemists, liquid water looks surprisingly similar to ice. The only difference is that about 10 per cent of the hydrogen bonds are broken. The molecules with broken bonds continue to reform, break and move around. The ability of water to retain most of the hydrogen bonds may be the secret to explaining why water, liquid water in particular, has so many unusual properties. When water freezes, the crystal it forms has more space between molecules than does the liquid phase. Thus, ice expands and therefore floats rather than sinking, as most freezing liquids do. That’s why instead of forming along the bottom of lakes and rivers, ice rises to the top. More important, the ice that forms insulates the rest of the body of water and keeps it in liquid form, enabling aquatic life to survive the winter.
Water is a universal solvent, dissolving many minerals and organic compounds. It does so because the dipolarity of water molecules enables them to surround atoms or molecules at sites of electric charge (Figure 3.4). Because it is a universal solvent, water is an effective agent in weathering and decomposing rocks. As it percolates through the soil, it dissolves nutrients and materials and carries them with it. It also makes cellular molecules soluble and thereby transports materials within living organisms. But water is more than a solvent; it also enters into metabolic reactions to become part of breakdown products or is released as a byproduct when large molecules such as fats are broken down.
FIGURE 3.4: The basis for water’s ability to dissolve salt.
Adapted from Cecie Starr and Ralph Taggart, Biology: The Unity and Diversity of Life, 6th ed. (Belmont, CA: Wadsworth, 1992), p. 29.
Many of the systems for quantifying and measuring the physical world use water as their reference point, acknowledgement of its unique place on this planet and in our lives. The metric system of weights and measures defines 1 gram as the weight of 1 millilitre of water. The centigrade scale sets 0°C as the freezing point of water and 100°C as its boiling point. Units of energy are measured in calories, defined as the amount of energy needed to raise the temperature of 1 cubic centimetre of water by 1°C; in food, 1000 calories or 1 kilocalorie is 1 Calorie.
Water, water, everywhere,
Nor any drop to drink.
SAMUEL TAYLOR COLERIDGE, The Rime of the Ancient Mariner
Human beings, like most other terrestrial animals and plants, have an absolute need for fresh water—and that is the rarest form of water on Earth. More than 97 per cent of the planet’s water is salty, toxic for terrestrial organisms, which require sweet water to sustain life. Of the water that is sufficiently free of salt to drink, more than 90 per cent is locked away in glaciers and ice sheets or is deep underground. Only about 0.0001 per cent of fresh water is readily accessible.
Human beings lived along waterways that they used for food and travel long before there was a history. We can infer this fact from prehistoric middens and sites of habitation. And it was on the great floodplains that humans first established permanent settlements, exploiting for agricultural use the regular floods that fertilized the deltas. At the junction of the Tigris and Euphrates Rivers in Mesopotamia the first civilizations arose, followed by settlements along the Nile River. Other great rivers of Earth, such as the Amazon, Mississippi and Ganges, have provided a living to indigenous people for millennia. The origins of villages and towns are tightly linked to the presence of water; even today most major cities are next to oceans, lakes or rivers. Elsewhere people have had to learn how to find water, digging wells, catching and storing rainwater, even trapping mists and clouds so that they can grow crops in arid regions.
A river rose in Eden to water the garden.
GENESIS 2:10
TABLE 3.2: Distribution of Water on Earth
It is the hydrologic cycle that allows the unpotable water of the oceans to rise into the skies as sweet water and sustain life on the land. Even though a minute quantity of potable water is readily accessible to land organisms, the hydrologic system draws fresh water from the oceans and land and returns it as rain and snow. Each year, over 113,000 billion cubic metres of water fall to Earth, enough to cover all the continents to a depth of 80 centimetres. Two thirds of this amount evaporates back into the atmosphere, while surface and subsurface waters are replenished by the rest. That water is not evenly distributed, of course; some regions get a great deal of water and others do not get much at all.
The amount of water determines the nature and abundance of vegetation in each region. The vast continent of Australia, for example, is often referred to as “underpopulated”; in fact, it is too poor in water in relation to its land base to support a larger human population. In contrast to the great river systems meandering through North America—the Mississippi, the Columbia, the Mackenzie—an enormous desert occupies the centre of Australia.
Very great rivers flow underground.
LEONARDO DA VINCI
Canada is one of the “have” nations of the world, with more than half of the planet’s fresh water by area and 15 to 20 per cent by volume. It may be hard to believe, but this country was blessed by the last ice age, more than eight thousand to ten thousand years ago, when glaciers gouged out the land to create depressions into which water settled. The Great Lakes alone, which Canada shares with the United States, contain nearly 5 per cent of all the fresh water on Earth and serve the needs of some 40 million people living around them. Canadians have a volume of 130,000 cubic metres of flowing river water a year per person, compared with 90 cubic metres a year per person in Egypt. The average American uses 2300 cubic metres annually; Canadians are the second most prolific users at 1500 cubic metres.
Where Alph, the sacred river, ran
Through caverns measureless to man
Down to a sunless sea.
SAMUEL TAYLOR COLERIDGE, Kubla Khan
Water defies human boundaries and human ownership. Sweeping invisibly through the air as vapour, flowing across the surface of the planet, percolating through soil, seeping into underground caverns and channels, it moves in its own mysterious ways. The mobility of water complicates human affairs at many levels. Neighbours tapping into the same aquifer for well water must share a source that has little or no relationship to their property lines. Factory waste entering a stream or draining into the soil at a specific point has ramifications for plants, animals and human beings over a large, often unpredictable area. One of the greatest bodies of fresh water in the world, the Great Lakes, along with their rivers, are administered by two federal governments and two provincial and four state jurisdictions, while dozens of cities and towns have a vital stake in the water. The Nile River in Africa flows through seven countries, each of which draws on it for irrigation and drinking water while flushing sewage and effluent into it. Egypt, the last nation downstream, inherits the collective consequences. Not surprisingly, water, not oil, is the real flashpoint issue over which wars will be fought in the Middle East and elsewhere.
All the rivers run into the sea, yet the sea is not full.
ECCLESIASTES 1:7
Together with the sun, the oceans drive the planet’s climate. Whereas the temperature of the air changes rapidly, the oceans absorb massive amounts of energy and release it slowly. Thus, the oceans stabilize the temperature of Earth. In the mid-latitudes, huge wind-driven gyres (circular systems of currents) transport heat polewards from near the equator, ameliorating terrestrial temperatures and weather. The warm Kuroshio Current flowing from the western Pacific Ocean south of Japan across to North America affects weather as far inland as the Midwest and from California to Alaska. Its counterpart in the Atlantic, the Gulf Stream, meanders north from the Gulf of Mexico, bringing the gift of warmth north to Canada’s east coast. South of Newfoundland the Gulf Stream meets the cold Arctic waters of the Labrador Current; the meeting of warm and cold currents creates the famous fogs of this region. Moving across the North Atlantic, the Gulf Stream divides; the northern branch wraps the British Isles, bringing palm trees to sheltered spots in northwest Scotland and a milder climate to the whole country than that latitude would otherwise enjoy. The southern arm curves south past Portugal to join the Northern Equatorial Current (Figure 3.5).
FIGURE 3.5: Ocean currents of the mid-latitudes.
There are deep-water currents as well—great aquatic conveyor belts moving waters of differing temperatures and salinities. In winter in Antarctica for example, as seawater freezes into ice, salt is concentrated and so water becomes supercooled and superdense, sinks to the bottom and flows in immense, slow-moving “rivers” carrying ice-cold water around the Indian Ocean, past the tip of Africa northward deep in the Pacific trench.
Sweeping over great distances, the currents carry eggs and larvae of animals that have evolved to ride with the movement of the ocean. The currents waft carcasses of plants and animals, as well as minerals and elements and soil, towards the ocean floor. Humans have long taken advantage of the ocean currents: accepting gifts delivered to our coastal doorsteps, fishing in the nutrient-rich zones where warm and cold currents meet, and using these currents as moving highways, routes to profitable trade. But they are far more than that; when we use the currents, we are in touch with the great forces of the planet—its rotation in space, the prevailing winds, the slow, curling drift of ocean water transporting heat, maintaining the planet’s atmospheric equilibrium. Connecting continent to continent, pole to pole, the currents are like a living web, moving and winding and mixing, wrapping itself perpetually around the whole world.
When we look at the wonderful array of plants and animals on Earth, the overwhelming lesson is that life is opportunistic, taking advantage of niches through mutation and new combinations of genes. Plants and animals have evolved to exploit both marine and freshwater environments. The oceans are filled with plants—immense kelp forests and massive blooms of phytoplankton that are the base of the marine food chain. The abundance of forms that cooperate to make the coral reef community, the forests of mangroves lining the ocean beaches, the gatherings of creatures in estuaries—all attest to the power of evolution to hone organisms for diverse habitats. On land, plants and animals alike have found strategies to flourish where water is abundant and where it is rare. Species are found in the ice of polar sheets, on arid mountaintops and in the dry heart of the desert. Anadromous fishes such as eels and salmon have evolved life cycles that exploit both marine and freshwater environments, and numerous species inhabit both water and air or water and land at different stages of their life cycles. Many species have adaptations to help them retain each precious molecule of water. Instead of broad leaves, cacti have needles with a small surface area and a tough outer coating to minimize water loss; the extremely hairy nostrils of camels trap and condense moisture as it is breathed out. The microscopic tardigrade, or water bear, can live for decades, possibly even centuries, in an inactive, desiccated state. Within hours of receiving the gift of even a single drop of water, the tardigrade revives and resumes its normal state. The eggs of brine shrimp, Artemia, can be dried and still remain viable for years. When introduced to water, the eggs hatch and thrive. (Thus the secret of how colonies of “sea monkeys” could be shipped to eager comic book readers via the mail.) Many organisms can cope with a scarcity of water, but no species has evolved to do without it, and no species has been as imaginative and as demanding in its use of water as human beings.
Every day each of us requires a certain amount of water to compensate for what is lost and to maintain a constant internal balance, but that amount is a small fraction of the water that we use for other reasons or that is used on our behalf. Much more water is used in rich countries than in poor countries, however; a person in an industrialized country uses between 350 and 1000 litres of water daily, whereas a person living in rural Kenya, for example, may use 2 to 5 litres of water a day. To further the inequity, much of the water in developing countries is of poor quality. Today, 1.1 billion people live without clean drinking water, and 3900 children die every day from water-borne diseases. That’s about one classroom of children every fifteen minutes.
Many water-rich countries, such as Canada, use water as if it were limitless. We often meet our food, energy and material needs through the copious use of water, whether we know it or not. On any North American dinner table irrigation may have produced the vegetables, hydroelectric power may have cooked them, and the dish they’re served in may have taken litres of water to manufacture. And the amounts of water used for agriculture and manufacturing can be staggering. For example, it takes about 20,000 litres of water to produce one kilogram of coffee, 11,000 litres for a quarter-pounder hamburger, between 2000 and 5000 litres for a kilogram of rice, and 2000 to 4000 litres for one litre of milk. We grow twice as much food today as we did a generation ago, but we use three times as much water to grow it. To quench the thirst of these crops, many are highly irrigated, and much of the water is being pumped from underground reserves, which take eons to replenish. Industry uses water on our behalf in a multitude of ways—as part of the reaction mix where chemicals are used or as a medium for carrying material such as wood fibres in pulp or for washing away excess material.
The fate of the Great Lakes illustrates the dilemma we face. For the aboriginal people who lived on the shores of the Great Lakes, the waters were sacred, an endless source of food and water and a great waterway to other parts of the continent. The arrival of Europeans began a different relationship with the lakes. As forests surrounding the lakes were cleared, watersheds were altered and the quality of the water was diminished. Onceabundant native fish were reduced by overfishing, and new kinds of fish were introduced to replace them. When the Welland Canal was built to enable boats to bypass Niagara Falls, parasitic lamprey were able to hitch a ride into the upper lakes, where they devastated fish populations. More recently, exotic zebra mussels have grown with explosive force since being introduced from water ballasts taken on by ships in other parts of the world. As a result, the Great Lakes are now in a period of massive upheaval as alien species alter the ecological makeup of the lakes. The waters have been commandeered for agricultural irrigation, for industry and for drinking water; at the same time they have become a repository for sewage and effluent from surrounding urban populations. Shorelines have been altered by urban development, exposing them to rapid erosion, while the lakeside marshes that once filtered out organic matter and fed native wildlife have been filled in, paved over or polluted. The relentless increase in population has added an intolerable burden to the lakes’ ability to support healthy life-forms.
The sale of bottled water has soared in recent years—in 2002, Americans spent a staggering $7.7 billion for bottled water, which costs on average a thousand times more than tap water. Savvy marketing has positioned brands of water as safer, healthier or trendier. In reality, bottled water is a marketing phenomenon and an environmental disaster. Despite the promise of a healthier alternative, there is no guarantee that bottled water is safer than tap water. Regulation of the industry is uneven, and tests have found bottled water with coliform bacteria, arsenic and synthetic chemicals. Testing for tap water is much more rigorous than it is for bottled water.
The source of water is also a problem. About one quarter of bottled waters are simply bottled tap water, while other “manufacturers” pump their water from springs and aquifers, critical reserves of water for our planet.
And then there are the plastic bottles. Each of those bottles takes energy and resources to manufacture, transport and recycle or dispose of. In the United States alone, it takes 1.5 million barrels of oil for a year’s supply of bottles, and nine out of ten of these bottles end up as garbage or litter. The plastic may also contaminate the water it is meant to hold. A study by Consumer Reports showed that eight of the ten plastic water jugs tested leached the endocrine disrupter bisphenol a into the water.
When so many of the world’s people lack the basic human right of safe drinking water, it seems misguided to direct so much money and so many resources into designer bottled water. Surely it would be better to direct this energy into advocating for tap water that is safe, accessible and affordable to all.
Lake Erie, around which about 11.6 million people live, has been the focus of scrutiny and scientific study for decades. Erie has the greatest stress of all of the Great Lakes, with seventeen large cities on its shore and an enormous impact from urbanization, industry and agriculture. It reached perhaps its lowest point in June 1969 when the Cuyahoga River, which flows into the lake, caught fire. The media declared the lake dead, and political pronouncements to clean up Erie and other Great Lakes followed. And there have been improvements over the years, with stricter regulations on effluents, better sewage control and treatment, reduction of phosphates in detergents, and the banning of pesticides such as DDT. Still, serious problems persist.
Of great concern are the “hand-me-down” chemicals such as PCBS or PBDES (found in flame retardants) that are extremely stable and are passed on through food chains. For years, biologists still could not determine why they were finding so many organisms with unusual deformities, reduced size, reproductive failure or aberrant parental behaviours, such as birds being inattentive to their eggs or chicks. Studies now show that many of the persistent chemicals in the Great Lake food chains affect the endocrine system, which regulates hormones in glands related to metabolism and reproduction. This disruption interferes with the sexual development of wildlife. For instance, salmon in the Great Lakes have greatly enlarged thyroid glands, which result from inadequate levels of thyroid hormones. This deficiency, in turn, disrupts reproduction and the normal development of eggs and offspring. Evidence points strongly towards persistent chemicals in the food chain that block proper functioning of thyroid hormones.
Humans, of course, are not immune from these persistent toxins. Studies of women living near Lake Michigan showed that the higher a mother’s consumption of Lake Michigan fish, the lower her baby’s birth weight.
In Toronto, which depends for its drinking water on Lake Ontario, the last in the chain of five lakes, many Torontonians now pay for bottled water rather than drink water from their taps. The aquatic ecologist Jack Vallentyne made an extremely conservative estimate of the number of persistent toxic chemicals contained in a glass of water from Lake Ontario. Assuming that the concentrations of industrial chemicals are reduced to one millionth of those currently reported in the Niagara River and Lake Ontario, he calculated that a cupful of Toronto tapwater from Lake Ontario contains:
• 10,000,000,000,000,000,000 chloride ions from a Paleozoic sea, about half from salt spread on roads during winter
• 30,000,000,000,000 molecules of water from human urine upstream
• 100,000,000 molecules of bromodichloromethane from the chlorination of sewage
• 10,000,000 molecules of industrial solvents such as carbon tetrachloride, toluene and zylene
• 4,000,000 molecules of freons (chlorofluorocarbons) from refrigerator coolants and spray can propellants
• 1,000,000 molecules of pentachlorophenol, a wood preservative
• 500,000 molecules of PCBS from discarded capacitors and generators
• 10,000 molecules of p, p’-DDT, p, p’-DDD, p, p’-DDE, endosulfan, lindane and other insecticides and insecticide decomposition products
If we lack the knowledge to keep water pure, then it makes sense to control those factors that we know cause problems with water and to protect nature, which has provided clean water since the beginning of time. Water is integral to supporting and maintaining life on this planet as it moderates the climate, creates growth and shapes the living substance of all of Earth’s creatures. It is the tide of life itself, the sacred source.
We are water—the oceans flow through our veins, and our cells are inflated by water, our metabolic reactions mediated in aqueous solution. Like amphibians and reptiles, we mammals have moved from continuous immersion in water but cannot avoid the need for water in reproduction. In the most intimate of human acts, spermatozoa are set free in seminal fluid to swim towards their target, the fertilized egg embeds itself in the rich, blood-lined walls of the uterus, and the growing embryo floats in a primeval sea of amniotic fluid, sprouting gills in a recapitulation of our aquatic origins. Water is created in the metabolism of life; we absorb it from solid food and from any liquid we imbibe. As air is a sacred gas, so is water a sacred liquid that links us to all the oceans of the world and ties us back in time to the very birthplace of all life.
Of all our natural resources, water has become the most precious… In an age when man has forgotten his origins and is blind even to his most essential needs for survival, water along with other resources has become the victim of his indifference.
RACHEL CARSON, Silent Spring
Within our lifetimes, the lakes have changed with dramatic speed. In the late 1940s, I lived in the centre of Canada on the shores of Lake Erie in Leamington, a town near Point Pelee, the southernmost part of the country. Each spring, an immense hatch of mayflies emerged from the lake, filling the air with the throb of their wing beats and engulfing homes and roads. Their carcasses piled up on the shores to a depth of a metre and more. Fish in the lake went into a frenzy of feeding, while birds, small mammals, and other insects feasted on this annual banquet. In a decade, this enormous biomass that gave tangible evidence of the water’s productiveness was gone and the lake was declared “dead.” Eutrophication—excess algal growth stimulated by phosphates—had choked off oxygen from other aquatic organisms, while DDT from farm runoff polished off invertebrates.
In the late 1950s, while crossing the Niagara River on a train, I glanced down into the gorge to see fishers pulling fish from the water as fast as they could cast a hook. They were intercepting the annual spawning run of silver bass, a wondrous sight of water jammed with the flashing bodies. Again, by the 1960s, the bass were gone, casualties of overfishing and pollution. Today the Great Lakes are reeling under the impact of introduced fish and plant species, agricultural and industrial effluents, and development of the watersheds that recharge them.
