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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.
