A Natural History of Water in America

copyright Jessica Snyder Sachs, as first appeared in National Wildlife

FOR TENS OF MILLIONS of years, a corps of natural hydrologists ensured the continuous cleansing of our continent's water supplies. In woodlands across North America, some 200 million beavers slowed rivers and streams to a silt-dropping crawl with their semiporous dams. Moreover their relentless logging created an elaborate network of wetland meadows that absorbed and cleansed surface runoff.

Beyond the forests, tens of millions of bison and elk worked in tandem with wildfires to sustain the short-grass and tallgrass prairies that soaked up the torrential downpours of seasonal thunderstorms. Beneath these same grasslands, hundreds of thousands of prairie dogs dug vast networks of tunnels that channeled groundwater deeper, to feed and refresh underground rivers that, in turn, continually recharged the continent's lakes and above-ground streams.

In these ways, a network of keystone species helped maintain a clean supply of the continent's most vital, life-sustaining substance. For while many forms of life can survive without oxygen, none can do so without water. Indeed, 60 to 80 percent of every living cell consists of water, and all vital biological processes begin or end with this simple molecule.

So far as science can discern, life on this planet began in a watery cradle. And when astronomers scan other planets for the potential to support life, they look first for signs of the molecule H20.

As seen from space, the sparkling blue ball that is Earth reveals itself to be a paradise of wetness. Above the oceans and lakes that cover more than 70 percent of the planet's surface drifts an ever-shifting lace of water-vapor clouds. Water pours from our skies, courses down our mountains and flows across every continent, back to the seas where the warming sun sends it skyward again. In this manner, our planet continually recycles an estimated 370 quintillion gallons (18 zeros), most of it older than the oldest fossils.

As life in North America and elsewhere evolved around water's unique properties, elaborate ecosystems developed to ensure continual recycling and purification. In Water: A Natural History, environmental engineer Alice Outwater describes the consequences of disrupting these ecosystems, particularly the large-scale decimation of North America's pre-Columbian populations of beaver, bison, elk and prairie dogs. "By tampering with and in some cases eliminating the ecological niches where water cleans itself," she says, "we have simplified the pathways that water takes through the American landscape, and we have ended up with dirty water."

Without wetlands and prairie grasslands to absorb rainfall, water slaloms across the landscape, picking up and dumping sediment into streams and lakes. Without beaver dams to brake their flow, streams frequently deepen into brown-water gulleys, continually eating away at their own banks. In an even more dramatic manner, development that clears natural vegetation speeds sediment-laden runoff during rainstorms, while adding a potentially toxic load of pesticides and other chemicals. The U.S. Geological Survey's recently completed ten-year assessment of the nation's water resources found multiple pesticides and unnaturally elevated levels of phosphorus and nitrogen in virtually all streams and groundwater sampled outside undeveloped wilderness. The majority of these streams contained pesticides at levels that exceeded--and often far exceeded--federal guidelines for the protection of aquatic life. These same chemicals can likewise endanger humans if they enter the drinking water supply.

"Scientific studies have repeatedly shown that our ability to protect our water sources from pollutants--and there are many of them--relates closely to our ability to safeguard our own health, especially that of our children, with their growing bodies," observes Monty Fischer, National Wildlife Federation policy director of water resources. "As conservationists, we're also keenly aware of the crucial role an untainted and abundant water supply plays in sustaining wildlife."

Certainly, Fischer points out, part of the solution is increased water efficiency--from turning off the faucet when we brush our teeth to making sure that our municipalities repair leaky water mains and otherwise invest in efficient water-delivery systems. But more important, he says, "is a public understanding of the linkage between the water flowing out of your tap and the wild places where it comes from, both in terms of the quantity and quality of that water, and the commitment it takes to protect those water sources."

Outwater agrees, adding: "An undeniable symbiosis exists between our country's water, the land from which it springs and the life that the two support together. Safeguarding that symbiosis is a responsibility all of us must share."

New Jersey journalist Jessica Snyder Sachs wrote about the effects of pesticides on endangered species in the December/January issue.

SIDEBAR:

H₂O: The Incredible Molecule

What is it that makes H₂O the liquid of life itself?

In chemical structure, the water molecule could hardly be simpler: two hydrogen atoms stuck like Mickey Mouse ears onto a single atom of oxygen. But in that simplicity can be found water's unique properties.

In essence, every water molecule is a tiny magnet, and its strong polar nature gives it the ability to dissolve an unparalleled range of substances, including a wide range of salts. In addition to the familiar sodium-chloride molecule we know as table salt, these include scores of biologically important substances such as potassium chloride, magnesium chloride and calcium sulfate. Indeed, all living beings--from plants to humans--depend on water to release the life-sustaining minerals contained in these salts.

Water's remarkable solvent powers provide the perfect medium for virtually every biological reaction that occurs inside a living cell--from energy-storing photosynthesis to energy-consuming respiration. And water has the remarkable ability to dissolve gases--most importantly, oxygen and carbon dioxide. It is water's oxygen-carrying capacity that sustains aquatic animal life.

A water molecule's mini-magnet configuration generates a host of other queer qualities, as well. Given its simple structure and small size, it should fly apart into gaseous form at extremely low temperatures. But water molecules cluster into tight groups, with each molecule's negatively charged oxygen atom lining up with the positively charged hydrogen on its neighbors. The considerable amount of energy needed to break these "hydrogen bonds" gives water the unusually high boiling point of 212 degrees F (100 degrees C). As a result, the planet's surface water never completely evaporates under the beating sun. Instead, oceans and lakes act as impressive energy sinks for storing and slowly releasing solar energy to temper seasons, and smooth out temperature differences between day and night.

As temperatures drop toward freezing, the hydrogen bonds between water molecules perform another impressive trick. They preassemble into the open-lattice structure that gives snowflakes their beautiful patterns and makes ice lighter than water. This bizarre quality of water being lighter as a solid than as a liquid has a huge consequence: It is the reason that lakes and oceans don't freeze from the bottom up, solidifying into a global ice block that even the hottest summer would never melt.--Jessica Snyder Sachs