Freshwater

Environmental Issues, Global Perspectives

James Fargo Balliett

• Verlag: Routledge
• Jahr: 2014
• ISBN:
  9781317470144
• Auflage: 1
• Thema: Biowissenschaften
• Thema: Ökosysteme & Lebensräume

Freshwater is our planet's most precious resource, and also the least conserved. Freshwater makes up only 3 percent of the total water on the planet, and yet the majority (1.9 percent) is held in a frozen state in glaciers, icebergs, and polar ice fields. This leaves approximately one-half of 1 percent of the total volume of water on the planet as freshwater available in liquid form.

This book traces the complex history of the steady growth of humankind's water consumption, which today reaches some 9.7 quadrillion gallons per year. Along with a larger population has come the need for more drinking water, larger farms requiring extensive irrigation, and more freshwater to support business and industry. At the same time, such developments have led to increased water pollution. Three detailed case studies are included. The first looks at massive water systems in locations such as New York City and the efforts required to protect and transport such resources. The second shows how growth has affected freshwater quality in the ecologically unique and geographically isolated Lake Baikal region of eastern Russia. The third examines the success story of the privatized freshwater system in Chile and consider how that country's water sources are threatened by climate change.

INTRODUCTION TO FRESHWATER

1	The Wonders of Freshwater

Water is a paramount resource on planet Earth. Four billion years ago, it played a central role in the creation and evolution of living creatures, which continue to rely on it as a vital, life-sustaining resource. Although the planet was named nearly 1,000 years ago after the Anglo-Saxon word erda, meaning “soil,” a more apt name might have been oceanus, meaning “ocean,” due to the abundance of water.

Of the world’s 328 million cubic miles (1,367 million cubic kilometers) of water, salt water from the oceans makes up 96.5 percent of the total. The remaining 3.5 percent consists of freshwater, the majority of which (1.74 percent of all water) is frozen in the polar ice caps and glaciers; 1.7 percent, a fraction of the worldwide water total, is available to humankind on or below the surface in freshwater liquid form such as ponds, lakes, streams, rivers, wetlands, and underground aquifers.

Of the 1.75 million species that have been identified worldwide living in both terrestrial and marine environments, some 80 percent rely on freshwater to survive, as their bodies cannot process salt water. In fact, ingestion of salt water by humans can be deadly. Human kidneys, similar to the organs of other living creatures, can only remove a certain amount of salt (sodium chloride) from water before they begin to draw freshwater from other cellular tissue to compensate. If too much salt water is consumed, a chain reaction results in kidney failure, as well as the loss of nerve and muscle functions, eventually causing death by heart failure or seizure. The fact that so much life on the planet relies on freshwater, a resource that makes up such a small percentage of the total, is an incredible scenario.

ASSESSMENT OF GLOBAL WATER SOURCES
Location (Type)	Amount of Time Held	Percentage of Worldwide Total
Oceans/Seas (salt water)	Thousands of years	97.4
Polar ice caps/ice floes, glaciers (freshwater)	Thousands of years	1.9
Groundwater (freshwater in bedrock)	Days to thousands of years	0.6
Soils and permafrost (freshwater)	Days to weeks	0.0809
Lakes (freshwater)	Days to years	0.008
Atmosphere (freshwater)	Days to weeks	0.001
Rivers (freshwater)	Days to weeks	0.0001

Source: United Nations Educational, Scientific, and Cultural Organization. U.N. World Water Development Report: Water in a Changing World. London, United Kingdom, 2009.

Freshwater Defined

Water is a dynamic substance. It is a chemical compound made from three atoms: two hydrogen and one oxygen. Under a microscope, the molecules look somewhat like a mouse’s head, with two smaller hydrogen atoms attached on opposite sides (105-degree angles) to the larger oxygen atom. The two hydrogen atoms arc positively charged, while the oxygen atom is negatively charged, and this draws the two elements together.

Water on Earth has several universal properties. It is the only known substance that can exist in three states of matter simultaneously—that is, in a liquid, solid (frozen), or gaseous state. A critical medium for dissolved chemicals, it is able to hold more than seventy elements at the same time.

In order for water to be classified as freshwater, it must contain less than .05 percent of dissolved salts. Ocean salt water typically has between 3.1 and 3.8 percent salinity.

Each molecule of water has two hydrogen nuclei, and these are held to a central oxygen molecule with two charged electrons. This very durable molecular structure, also called a covalent chemical bond, can absorb large amounts of energy with little change in temperature because of the way the hydrogen bonds are connected to the oxygen molecules. This structure also means that it is easy to adhere other chemicals to water; thus, water often is referred to as a “universal solvent.”

Although scientists once thought that water was an individual element, it is, in fact, a compound substance, and water molecules readily change their structure as the temperature changes:

• When water turns into a gas (when heated to 212 degrees Fahrenheit, or 100 degrees Celsius), the vapor molecules are far apart from each other. In this phase, the molecules do not bond easily, because they are moving too quickly.

• When water becomes a liquid (between 211 degrees Fahrenheit, or 99 degrees Celsius, and 33 degrees Fahrenheit, or 1 degree Celsius), the individual molecules bond to each other but do not hold on tightly. The connections between droplets constantly change in form and size. As the temperature decreases, they grow tighter in formation.

• When water transforms into ice (when cooled below 32 degrees Fahrenheit/0 degrees Celsius), the bonds are altered to lock into a tight formation held together by hydrogen bonds. The solid connections give ice hardness and durability.

The History of Freshwater

Five billion years ago, the solar system was still developing. The sun was in the process of forming, and a massive amount of solid and gaseous material began to swirl around it in a cloud of debris. The considerable gravitational pull of the sun eventually pressed dust, rocks, and gases into clusters. These masses, also called proto-planetary discs, eventually took the shape of eight planets, five dwarf planets, dozens of smaller moons, and thousands of meteors and asteroids.

Over millions of years, these balls of matter took shape and established orbits a certain distance from a new sun. Earth eventually positioned itself roughly 93 million miles (150 million kilometers) from this sun. Approximately 4.5 billion years ago, the molten Earth began the slow process of cooling. Dense materials, such as nickel, flowed toward the center of the planet, and lighter materials, such as basalt, gravitated toward the outside.

Trapped deep inside the Earth’s bedrock under intense pressure was a large amount of water. It slowly emerged on the surface as a liquid and gas through wide cracks or fissures in the surface of the bedrock or was released by the eruption of volcanoes. Over time, the lower-lying basins and valleys collected this water.

By 500 million years ago, a single, large body of water had formed. The estimated volume of this water was 343 sextillion (which is a number followed by 21 zeroes) gallons (1.3 sextillion liters), which is close to the volume of today’s oceans combined. However, 96.5 percent of the planet-wide water eventually contained dissolved sodium, chlorine, magnesium, and calcium, turning it into a salty brew that was distinctly different from freshwater. The amount that did not contain these elements (a little more than 3.4 percent) could be found in three main places: in the atmosphere, such as in clouds and storms; underground, held in place by rocks; and at the surface, in rivers, streams, and polar ice.

The presence of so much water, both saline and fresh, also played a central role in the formation of the Earth’s atmosphere and the evolution of land and water species. When the planet first formed, Earth’s air was full of helium and sulfur, but eventually nitrogen and oxygen were the majority components of the air, similar to what is breathed in today. The chemical transformation of the atmosphere was primarily due to the presence, over millions of years, of oxygen-producing aquatic plants called algae.

The Hydrologic Cycle

Although today’s oceans cover 71 percent of the planet, the distribution and volume of freshwater varies from place to place, depending on weather patterns. In addition, all unfrozen water is in constant motion. Moving from one area of the planet to another, water repeatedly circulates through a series of states commonly known as the hydrologic cycle.

Sometimes the pattern of water movement is predictable, but it also may be random. For example, rain falls on the Earth’s surface, and this precipitation trickles above and below land to arrive in rivers. Once there, the water is transported to the oceans. Along the way, some water evaporates back into the atmosphere.

COMPARISON OF FRESHWATER AND SALT WATER CHEMICAL CONTENTS
Element	Freshwater (Rainwater, ppm*)	Salt Water (Typical, ppm)
Calcium	0.2	412
Chloride	0.2	19,500
Magnesium	0.05	1,290
Potassium	0.1	380
Silicate	0	7
Sodium	0.2	10,770

*ppm=parts per million

Source: Trevor Day. Lakes and Rivers. New York: Chelsea House, 2006.

As water moves, air pressure and temperature variations cause its molecules to shrink, expand, accelerate, or slow down. Five main processes are included in the hydrologic cycle: 1) evaporation; 2) condensation; 3) transpiration; 4) percolation; and 5) precipitation.

Evaporation

Evaporation occurs when water in an ocean, lake, pond, puddle, or other body changes from a liquid to a gas after being heated by the sun or another energy source, such as underground magma. As water turns to a gas, the molecules speed up their molecular movement, eventually breaking apart from one another. The vapor that forms often is carried away to another location by thermal currents or wind.

Evaporation rates are controlled by a number of factors, including the type of water (fresh or salt), the surface area of the water, the movement of air over the water, the temperatures of the air and water, and the intensity of hea...