The Liquid of Life
(NOTE: The following is excerpted from Urban Watersheds: Geology, Contamination, and Sustainable Development by Kaufman, M.M., Rogers, D.T. and Murray, K.S. | ©2011 Boca Raton, CRC Press)
The importance of water on Earth cannot be overstated. Water, along with energy and organic molecules were the prerequisites for the origin of life here billions of years ago. Today, water plays a central role in maintaining our survival as a species, preservation of the natural environment, and therefore achieving a sustainable planet (United Nations 2003). Yet, there are immense challenges facing humans with respect to securing water for their basic needs and long-term quality of life. Although almost three-fourths of Earth’s surface is covered by water, most of this water is not potable, and a high percentage of the fresh stuff is either frozen, underground, or in a gaseous phase.
Wait—there are other complications. Because of the spherical nature of the Earth, the arrangement of land and water, and differences in surface elevation it is not possible to achieve a uniform distribution of the incoming solar energy we receive. Surpluses and deficits of energy arise at different locations and create uneven atmospheric pressures and densities. In a thermodynamic system these inequalities try to even themselves out, so fluids move in a quest to achieve overall energy equilibrium. Air (via wind) transports part of the solar energy it has absorbed and moves it from zones of higher pressure to zones of lower pressure. Water moves the excess energy it has absorbed from the equatorial region in a general poleward direction via ocean currents. All of this movement results in Earth’s topside having a peculiar and unpredictable precipitation pattern: some areas receive precipitation almost daily; others may not get any for years; and many places lie between these extremes.
Precipitation from the atmosphere recharges the underground water reservoirs, and plays a central role in shaping the geology of urban areas through weathering, sediment transport and deposition, chemical precipitation and dissolution, and erosion. Given the haphazard nature of precipitation, it is a good thing nature is so organized. Surface flows of water are controlled hierarchically by a system of topographically-bounded spatial units called watersheds, which are really just water collection bowls. Small watersheds consisting of small streams feed larger watersheds with larger streams; for example the Scioto River watershed in Ohio delivers its flows into the Ohio River, which then flows into the larger Mississippi River. Some of the precipitation is intercepted by vegetation, some pools on the surface, and a good part of it moves downward through the soil where it recharges the groundwater reservoir.
Water is unique because it is the only substance on Earth found in all three states (liquid, solid, and gas) within our planet’s temperature ranges. Liquid water is essential to life, as it comprises approximately 60% of the human body by weight and 70% of the human brain. Some organisms are 90% liquid water by weight.
Without water, humans simply would not exist. The ability of water to dissolve so many different substances allows cells to use the nutrients, minerals, and chemicals in biological processes. In natural systems, wherever water goes—the air, the ground, streams and lakes, biota, or through our bodies—it takes valuable chemicals, minerals, and nutrients picked up along the way. This transport ability also means water can carry substances harmful to humans and the environment. If these contaminants are present at a sufficient concentration and the exposure is long enough, potentially harmful effects can occur. The damage can be immediate and obvious, as when oil is washed up on a beach and kills waterfowl—or slow developing and silent—a scenario represented all too often by the benzene that originated from a leaking gasoline tank and carried by groundwater into a drinking water well.
This is why we spend so much time and effort studying water.
Water is constantly on the move through the four spheres of the geosphere—the atmosphere, biosphere, hydrosphere, and lithosphere. This movement of water is cyclical and is called the hydrologic cycle or water cycle. In this cycle, water changes phase many times and exists as a liquid (surface waters and groundwater), solid (snow and ice), or gas (water vapor). The global movement of water is initiated by solar energy, which evaporates surface water into the atmosphere. Much of this water vapor condenses and falls as some form of precipitation on a distant land surface where it either: evaporates; flows back into the oceans through rivers and streams; is taken up by vegetation and slowly released into the atmosphere as evapotranspiration; or infiltrates into the ground. Groundwater also migrates back to the oceans (Jones 1997; Alley et al. 1999). Figure 3.5 depicts the water cycle on Earth.
About the Authors of Urban Watersheds: Geology, Contamination, and Sustainable Development
Martin M. Kaufman is a professor of earth science at the University of Michigan-Flint. He has over 25 years of experience in geographic information systems, hydrologic investigations, and watershed management.
Daniel T. Rogers is currently the director of environmental affairs at Amsted Industries Incorporated. Throughout his career, Rogers has managed and conducted hundreds of geologic and hydrogeologic investigations and remediated and successfully closed industrial sites in the United States and internationally.
Kent S. Murray is a professor of geology at the University of Michigan-Dearborn. He has over 35 years experience in environmental geology, groundwater hydrology, and low-temperature geochemistry.
As part of the 2012 UM-Flint Critical Issues Forum, internationally renown water activist and expert, Maude Barlow, will discuss the issues citizenries around the world must face regarding our most vital natural resource.
The documentary Democracy à la Maude chronicles many of Barlow’s efforts to bring about environmental and social justice.