Freshwater: Earth's Life Force

From Discovery Channel

Imagine an entire planet where the universe's finest liqueur is boiled out of fermenting seas by a brilliant yellow star, distilled in the skies and rained back down on the land, forming lakes and rivers of the inebriating brew. The planet, of course, is Earth, and the liqueur is freshwater.

Without freshwater Earth's land masses would be barren, the continents might be in different locations, mountains would be far taller, and life virtually impossible. Earth's very character and appearance are the result of the planet being fairly drunk on this precious grog.

Liquid Destroyer

Luckily for us land animals, Earth can't help but make freshwater. It happens when the sun heats and evaporates water from the oceans. The salts and other minerals are left behind, creating pure water vapor in the air. As it is carried higher to cooler air, it condenses and makes clouds, which can produce rain or snow when forced higher over land.

That's the water cycle, of course. It's something taught to every schoolchild — for good reason. Not only does the water cycle give us the water we drink and use to grow food, it is also the carver of coastlines, sculptor of mountains and the burier of seas. It might even play a critical role in plate tectonics, the process that keeps creating and destroying crustal plates that make up the surface of the planet.

One of the more dramatic examples of what a few gazillon raindrops and snowflakes of freshwater can do over time is the Grand Canyon. Over the past 5 million years, the Colorado River has just as steadily cut its way through the constantly bulging Colorado Plateau, making the mile-deep, 18-mile-wide, 200-mile-long Grand Canyon along the way.

By moving such gigantic masses of rock from one place to another, freshwater also removes weight from the Earth's crust in one place and weighs down others. By wearing away rocks of the Himalaya, for instance, rain and snow make the mountains lighter and actually speed up the rate at which the range buoys upward on the more plastic layer below the crust — the zone called the mantle.

In turn, by affecting the pressure in the mantle, it's thought by some geophysicists that currents can be generated in the mantle that influence how, when and where tectonic plates move. This top-down theory to what drives plate tectonics makes freshwater a central player in the making of every inch of Earth's surface today.

Watery Creator

But freshwater does far more than move rocks around. Some of Earth's most unusual and beautiful living landscapes are created and kept thriving by freshwater. The verdant and little explored Tepuis of Venezuela, for instance, are islands in the sky, loaded with species found nowhere else. These plateaus and mountains are perpetually bathed in freshwater. In this unique ecoregion, it's virtually always raining or socked in by thick, moisture-laden clouds.


Life in such torrentially wet places evolves to take quick advantage of their decaying neighbors. Wait too long, for instance, and the next downpour will wash away what nutrients there are. In such a place, mold, fungus and large trees with broad, shallow roots form the basis of the food chain.

Downstream from these water-rich places, forests and other highland rivers fill broad basins with forest waste and worn rock, piling up tens of thousands of feet of mud and silt for millions of years. The Mississippi River sediments deposited along the Gulf Coast are now so heavy that they are squeezing Earth's mantle. The sedimentation is believed to be one of the reasons New Orleans and other parts of Louisiana are subsiding and becoming more vulnerable to hurricanes and sea level rise.

Grace of Water

Despite its great influence, all the freshwater that makes up the lakes, rivers, streams, creeks, marshes, potholes, bogs, fens, mires, swamps, ponds, billabongs, lagoons, mud holes and groundwater of Earth has only recently been accounted for. Monitoring where water goes is a big job and can only really be done affordably for the entire planet from space.

NASA's Gravity Recovery and Climate Experiment (GRACE) satellites do this task by measuring local changes in gravity over time. All matter — including water — has mass and gravity. So when there's less water in a particular area, its gravity is slightly less. More water — whether in lakes, streams or underground — means the gravity is greater. GRACE has now managed to watch as the continents swell and shrink with water on a seasonal basis — showing Earth's water cycle actually at work on a global scale.

Bad & Good News

Freshwater, however, is in trouble. Human activities have polluted and depleted freshwater in many parts of the world. Wetlands have been drained to build and farm on. Nutrient levels in many rivers and streams are so high from sewage, agricultural and industrial runoff, air pollution, and erosion that they are choked and starved of oxygen — bad news for fish and invertebrates that make for healthy streams and lakes.

The good news is that conservationists have succeeded in protecting more than 800 of the world's most vital wetlands all over the globe. It's even profitable. A 1991 study by the International Institute for Environment and Development found that a wetland in the arid north of Nigeria provided 30 times more profit from fish, firewood, cattle grazing and natural crops than if the water had been diverted to a large agricultural project. That's freshwater for you — it's heady stuff.

http://dsc.discovery.com/convergence/planet-earth/guide/fresh-water.html