2 November 2000

Water, water everywhere!

Every school child draws the water cycle: water evaporating from the sea, then blown inland, forming clouds that rain down to journey back to the sea.

This is no small issue. Planet-wide, something on the order of 10 million billion gallons of water are transported through the water cycle each year. (That's a one with 16 zeros behind.)

But there's more to that simplistic view we remember from childhood. The water cycle involves the soil, plants, and animals–including us. This life-giving circle is better viewed as a complex three-dimensional circuit with nearly infinite branches and off-shoots that involves most of the atmosphere and the upper levels of earth's crust.

Probably the most complex section of the water cycle is what happens when the rain (or snow, or hail, or sleet) reaches the ground. Certainly, much of it runs off our trees and roofs and down our hills and sidewalks. But quite a bit of it–usually most of it–soaks into the ground.

Under the surface, the water binds itself to the soil particles until the soil is saturated. Or until a plant takes it up. The water picked up by plant roots is either chemically converted into more plant or is passed through the leaves back into the air.

Water is pulled deeper underground until it meets a barrier. The water collects above of the barrier; the "water table" is the top of that layer of water.

Rivers, streams, and lakes are not just "where the water collects on the land," they're usually more accurately described as "where the water table breaks through the surface."

Wetlands occur where the water table is at or near the surface. Long thought to be "wastelands," we now know wetlands perform many vital functions. The life and chemistry of wetland soils clean impurities out of the water. Wetland soils–and the wetland's position in the cycle–collect and hold floodwaters, then slowly disperses them. Wetlands along the edges of open waters buffer the shoreline from erosion. Wetlands produce and recycle huge amounts of plant and animal life, much of which is passed on to adjacent land and water habitats. Further, rich wetland ecosystems are critical permanent or nursery habitat for myriad species of plants and animals.

And while we may envision a water cycle that takes in whole continents at a regular pace, that's not always the case. The cloud/ground/cloud loop can be quite short. For example, ground or pavement moistened by evening fog may readily evaporate in the next morning's sun, the water producing frail wisps as it dissipates back to the air. Conversely, some water may be locked up in places of the water cycle for millions of years; in ice or deep underground.

So here we are, an intimate part of the water cycle, as we step over puddles of surface water, eat plants that grew on soil water, drink water stored in lakes or deep below the surface, and enjoy wildlife nurtured in wetlands.

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Related articles on this site include salmon, wetland functions, and ponds and lakes.