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  GOES 8 weather satellite image of the earthWater      

The spectacular vista of a glistening deep blue earth set against a backdrop of black - perhaps it is little wonder that we have nicknamed our home, the "Blue Planet." Covering about two-thirds of the globe, water is the very lifeblood of the earth. It is the one natural resource upon which all life forms depend. Without water, life has to struggle, and in some cases, may cease to exist altogether. Throughout history, man has used his ingenuity to find creative ways to intercept and divert the natural pathways of water for a variety of needs. We have built reservoirs to supply drinking water for the masses. We have expanded agricultural production by irrigating crops. We have generated electricity for millions by harnessing the power of water, and we have expanded economic markets by using waterways to transport goods.

Iceberg     Girl drinking water
  Tom Bevil Lock and Dam, Alabama  

Water, however, is also a resource that we have long taken for granted - we have viewed water as free, like the air we breathe. But as our demand for water grows, our attitudes are beginning to change. In many regions of the world, this odorless, colorless, tasteless fluid is now viewed as a valuable commodity - a commodity that is not only to be protected, but also to be bartered.

While man's attempts to tame and use water have benefited the quality of our lives beyond basic survival, these actions may have come at a high price to the natural environment and its ecosystems. Climatic changes, contamination, habitat destruction, and depleted supplies are but a few of the issues we are now facing.

Fish Hatchery   Ball Mountain Lake, Vermont  
  Grand Bay National Estuarine Research Reserve   Ice on berries

What is hydrology?
Water pollutionHydrology is the study of water. The science of hydrology encompasses the properties, occurrence, distribution, and movement of water in the atmosphere, on the earth's surface, and in soil and rocks. Hydrologists are those scientists and engineers who study the quantity, quality and availability of water. Hydrologists apply scientific knowledge and use mathematical principles to describe and understand hydrologic processes and water-related problems within our environment. Scientists and engineers alike spend time collecting and analyzing a variety of physical, chemical, and biological data in order to understand and assess the processes controlling the hydrologic environment. Examples of some basic field activities that hydrologists may conduct include measuring stream flow; collecting samples of water, sediment, or aquatic organisms from streams; measuring ground-water levels in wells; or drilling cores to collect soil and rock samples.

What is the hydrologic cycle?
Simply put, the hydrologic cycle is a continuous process where by water circulates from the land surface and the oceans to the atmosphere and back again. In this continuous cycle of movement, water travels along various pathways in the atmosphere, over and beneath the land surface, and through plants. In the end, however, water falling as rain or snow, eventually returns to the atmosphere by evaporation.

The Hydrologic Cycle

Water falling onto the soil may evaporate quickly back into the atmosphere as the soil dries, or it may be taken up by plants and then transpired back into the atmosphere. Water falling on the land surface may drain to rivers or streams where it becomes surface water, which eventually flows back to the oceans. Some water falling onto the land surface may percolate down through the soil profile to become ground water.

Depending on the pathway traveled, the length of time that it takes for water to circulate through the hydrologic cycle varies. Natural storage times and transport through the hydrologic cycle are interrupted wherever man diverts water for human activities. Although water that is temporarily diverted from the hydrologic cycle is eventually returned back to the cycle, the quality of that "used" water usually is changed.

Center-pivot irrigation field    
    Grand Bay National Estuarine Research Reserve, Mississippi

As we face record consumption, uncertain supplies, and growing demands for protection against flooding and contamination, continued study and thoughtful management of this critical resource is essential for maintaining the welfare of our "Blue Planet".


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