Chapter nine

Title Page Photo “ Water is the one substance from which the earth can conceal nothing; it sucks out its innermost secrets and brings them to our very lips. ”—Jean Giraudoux (U.S.G.S. Water Quotes, http://ct.water.usgs.gov/EDUCATION/morewater.htm)

Vocabulary thermohaline circulation (p. 269) tidal bore (p. 268) tidal range (p. 267) tides (p. 267) waterless zone (p. 283) water table (p. 281) zone of aeration (p. 281) zone of confined water (p. 282) zone of saturation (p. 281) lake (p. 273) marsh (p. 278) permafrost (p. 273) permeability (p. 280) porosity (p. 280) runoff (p. 263) salinity (p. 266) subartesian (well) (p. 283) swamp (p. 278) aquifers (p. 281) artesian well (p. 283) global conveyer-belt circulation (p. 269) groundwater (p. 281) hydrologic cycle (p. 261) iceberg (p. 271) ice floe (p. 271) ice pack (p. 271) ice shelf (p. 271)

The Hydrologic Cycle Water is distributed very unevenly around Earth. Less than 1% of Earth’s total moisture is involved in the hydrologic cycle.

The Hydrologic Cycle A series of storage areas interconnected by various transfer processes, in which there is a ceaseless interchange of moisture in terms of its geographical location and its physical state.

The Hydrologic Cycle Surface-to-Air Water Movement Air-to-Surface Water Movement Movement on and Beneath Earth’s Surface Residence Times

Surface-to-Air Water Movement Evaporation is responsible for most of the moisture that enters the atmosphere from Earth’s surface. Of the moisture evaporated, more than 84% comes from ocean surfaces. The water evaporated becomes water vapor, and though it stays in atmosphere only briefly (hours to days), it can travel a considerable distance, either vertically or horizontally.

Air-to-Surface Water Movement Water vapor will either condense to liquid water or sublimate to ice to form cloud particles. Clouds drop precipitation (rain, snow, sleet, hail). Precipitation and evaporation/transpiration balance in time. They do not balance in place. Evaporation exceeds precipitation over oceans. Precipitation exceeds evaporation over lands.

Movement on and Beneath Earth’s Surface Runoff—flow of water from land to oceans by overland flow, streamflow, and groundwater flow. Runoff is why the oceans do not dry up and continents become flooded despite the imbalance of evaporation and precipitation through space (oceans and continents). Runoff water amounts to 8% of all moisture circulating in global hydrologic cycle.

Residence Times At any given movement, the atmosphere contains only a few days’ potential precipitation. Residence time of a molecule of water can be hundreds of thousands of years to only a few minutes.

The Oceans Knowledge of seas has been very limited until very recently. Only in about last four decades have we developed technology that allows us to catalog and measure details of ocean environment. The “world ocean” has a surface area of 360 million square kilometers and contains 1.32 billion cubic kilometers of salt water.

The Oceans Just one ocean, which is divided into four principal parts: Pacific Atlantic Indian Arctic Most smaller bodies of water are considered portions of ocean. A few are so narrowly connected that they warrant separate consideration. Examples are the Black Sea, Mediterranean Sea, and Hudson Bay.

Characteristics of Ocean Waters Significant difference from place to place. Almost all known minerals found to some extent in seawater, but sodium and chloride most important. Salinity —a measure of the concentration of dissolved salts.

Characteristics of Ocean Waters Geographic distribution of surface salinity varies because of Varying evaporation rates Varying fresh water discharge rates.

Characteristics of Ocean Waters Temperatures decrease with increasing latitude. Western sides of oceans nearly always warmer than eastern margins (movement of major ocean currents). Density varies with temperature, degree of salinity, and depth.

Movement of Ocean Waters Most motion occurs in waves, currents, and tides. Affects surface more than deeper water. Disturbances in Earth’s crust under ocean can trigger motion.

Tides Tides cause the greatest vertical movements of ocean waters; can also cause horizontal movement. Rhythmic oscillations about every 6 hours, from gravitational attraction of nearby heavenly bodies.

Causes of Tides Although both the Sun and Moon have an influence on the Earth’s tides, because of its considerably greater distance, the Sun produces a smaller percentage of Earth’s tides than does the Moon. As Earth rotates tidal progression appears to move westward. There are two tidal cycles a day. Two high tides and two low tides every 25 hours.

Causes of Tides Tidal magnitude varies greatly in time and place. Water flows toward the coast in a period of 6 hours and 13 minutes in what is known as a flood tide. After reaching high tide, the water then begins to recede over a period of 6 hours and 13 minutes in what is known as an ebb tide. Once the water has reached its lowest level, the cycle begins again.

Tidal range Refers to the vertical distance in elevation between the high and low tide. Changes in the positions of Earth, Sun, and Moon have influences on periodic variations in tidal ranges. When all are aligned, the Earth experiences spring tides. When out of alignment, the Earth experiences neap tides.

Tidal range Tidal range also affected by distance of Earth to Moon. During the Moon’s perigee (its closest distance to the Earth), tidal ranges are greater than when it is at its apogee (its farthest distance from the Earth).

Global Variations in Tidal Range Coastline configuration and shape also have an influence on tidal ranges. Greatest tidal range found in Bay of Fundy in eastern Canada. A tidal bore (a wall of sea water) several centimeters to more than a meter high rushes up the Petitcodiac River in New Brunswick. Inland bodies of water experience the smallest tidal ranges.

Currents Currents shift water both horizontally and vertically. Primarily caused by wind flow, but also by contrasts in temperature and salinity. Influenced by size and shape of particular ocean, configuration and depth of sea bottom, and Coriolis effect.

Deep Ocean Circulation Deep ocean circulation occurs because of differences in water density that arises from differences in salinity and temperature. This circulation is also known as the thermohaline circulation. Sinking happens predominantly at higher latitudes because more fresh water is locked up in glacial ice, which causes ocean water to be more saline and denser in these regions.

Global Conveyor-belt Circulation Circulation pattern formed from deep ocean water movement through thermohaline circulation combined with surface currents (Figure 9-10).

Waves Waves tend to be just shapes, with very little forward progress.

Permanent Ice/The Cryosphere Second largest storage reservoir for moisture (still minuscule in comparison to ocean). Land portion of ice is larger than oceanic ice.

Permanent Ice/The Cryosphere Ocean ice has several names Ice pack—an extensive and cohesive mass of floating ice. Ice shelf—a massive portion of a continental ice sheet that projects out over sea. Ice floe—a large, flattish mass of ice that breaks off from larger ice bodies and floats independently. Iceberg—a chunk of floating ice that breaks off from an ice shelf or glacier.

Permanent Ice/The Cryosphere Oceanic ice is made up of fresh water because the ice crystals do not take in the minerals of seawater. Recently, several large, once-stable ice shelves have broken off of Antarctica.

Permafrost Permanent ground ice of permanently frozen subsoil; makes up most of ice beneath land surface.

Surface Waters Make up only 0.25% of world’s total moisture supply. Lakes Swamps and Marshes Rivers and Streams

Lakes A body of water surrounded by land. Lakes make up more than 90% of surface water of the continents. More than 40% of lake water is salt water. Lakes distributed unevenly through world. Most common where glaciers had been.

Lakes Lake genesis and continued existence occurs through two conditions: Some sort of natural basin having a restricted outlet: Sufficient inflow of water to keep the basin at least partly filled.

Human Alteration of Natural Lakes Diversion of streams by humans has had a large influence on reducing the volume of some lakes. Mono Lake, CA, has been reduced by 50% of its previous volume. The destiny of most lakes is to disappear.

Reservoirs Creation of artificial lakes has had immense ecological and economic consequences, not always beneficial.

Swamps and Marshes Swamp—water body with water-tolerant plants, predominantly trees. Marsh—water body with water-tolerant plants, primarily grasses and sedges. Both are flattish surface areas that are submerged in water at least part of the time but shallow enough to permit growth of water-tolerant plants.

Rivers and Streams Physical geographers call any flowing water a stream, no matter size. Drainage basin is all the land area drained by a river and its tributaries.

Underground Water The total amount of water underground is more than 2.5 times that in lakes and streams. Underground water more widely distributed than surface water. Quantity sometimes limited; Quality sometimes poor; Sometimes at great depth.

Underground Water All underground water originally comes from above. Two factors affect underground water flow: Porosity—a measure of the capacity of rock or soil to hold water and air; the percentage of total volume of a material that consists of voids. Permeability—capacity of soil or rock to transmit water; determined by the size of pores and by the degree of interconnectedness. Interstices—the pore spaces; a labyrinth of interconnecting passageways among the soil particles that makes up nearly half the volume of an average soil.

Underground Water Aquifer—where underground water is stored; a permeable subsurface rock layer that can store, transmit, and supply water. Aquiclude—an impermeable rock layer that hinders or prevents water movements. Excludes water because of high density, or as in case of clay, because interstices are many but too small to transmit water.

Hydrologic Zones Underground layers involved in general distribution of underground water: Zone of aeration Zone of saturation Zone of confined water Waterless zone

Hydrologic Zones Zone of aeration—the topmost hydrologic zone within the ground, which contains a fluctuating amount of moisture (soil water) in the pore spaces of the soil (or soil and rock). A mixture of solids, water, and air; of variable depth.

Hydrologic Zones Zone of saturation—the second hydrologic zone below the surface of the ground, whose uppermost boundary is the water table. The pore spaces and cracks in the bedrock and the regolith of this zone are fully saturated . Groundwater—water found in the zone of saturation. Water table—the top of the zone of saturation within the ground. Where water table intersects Earth’s surface, water flows out. A lake, swamp , marsh, or permanent stream is almost always an indication that the water table reaches the surface there.

Hydrologic Zones Perched water table—occurs when a localized zone of saturation develops above an aquiclude. Cone of depression—occurs when water is removed from well faster than underground water can replace it; this lowers the water table, which becomes the approximate shape of an inverted cone in the immediate vicinity of well. Zone of confined water—the third hydrologic zone below the surface of the ground, separated from zone of saturation by impermeable rock. Occurs in many, but not most parts of world. It contains one or more permeable rock layers (aquifers) into which water can infiltrate. If drilled into, confining pressure will force water to rise in the well.

Hydrologic Zones Piezometric surface—the elevation to which water will rise under natural confining pressure in a well. Artesian well —the free flow that results when a well is drilled from the surface down into a zone of confined water and the confining pressure is sufficient to force the water to the surface without artificial pumping. Subartesian well —the free flow that results when a well is drilled from the surface down into a confined aquifer but which requires artificial pumping to raise the water to the surface because the confining pressure forces the water only part way up the well shaft.

Hydrologic Zones Waterless zone —the lowermost hydrologic zone that generally begins several kilometers or miles beneath the land surface and is characterized by the lack of water in pore spaces due to the great pressure and density of the rock.

Groundwater Mining Accumulation of groundwater is tediously slow, but humans can use it up rapidly. High rates of groundwater use can be likened to mining because a finite resource is being removed with no hope of replenishment.

Groundwater Mining Largest U.S. aquifer—Ogallala, underlies 585,000 square km (225,000 square mi) of eight states. Water accumulated here for some 30,000 years. Farmers began to tap into it in early 1930s. Water table is sinking. Used to take 50-foot wells, now some 150 to 250 feet (45 to 75 meters) to access water. Less careful neighbors can harm those farmers who are trying to be very conservative in their water use.

Groundwater Mining Regional variations in saturated thickness. Nebraska Sandhills are in the best shape with great thickness, small usage, and a rapid recharge rate. The 13 counties of southwestern Kansas have withdrawal rates that far exceed the recharge rate.

People and the Environment: Oceans Becoming More Acidic The oceans take in carbon dioxide and form carbonic acid. As a result of increased carbon emissions from industrialization, the oceans are estimated to be more acidic than they were during the pre-industrial era. It is estimated that the pH of the oceans could drop to 7.7 by the end of the century. The possible consequences of a slightly more acidic ocean are as follows: The limiting of the growth of organisms such as coral polyps and foraminifera. Creatures such as these will have a difficult time building their shells because there are fewer calcium ions in acidic seawater. This could lead to the decline of coral reefs that provide habitats for many organisms. Foraminifera are at the bottom of the food web so their decline could possibly affect other organisms higher up the food web.

People and the Environment: Thawing Permafrost in Alaska Permafrost, permanently frozen soil, is abundant in Alaska. Active layer—the upper 30 to 100 centimeters of the soil that thaws during the summer. Beneath the active layer, the soil is frozen to a depth of approximately 50 meters. Higher average temperatures have led to ground temperatures high enough to melt the permafrost. Problems associated with melting of permafrost: Wet thermokarst conditions—where the ground surface subsides and it becomes saturated with water. This in turn leads to the subsidence of structures such as roads and pipelines. This also makes many roads impassible. May also lead to an increase in the activity of microorganisms in the soil, which in turn will decompose organic material. This will then release carbon dioxide that will contribute to further warming.

Focus: The Aral Sea and Lake Chad Within the last half century, two of the largest lakes in the world (Aral Sea, Uzbekistan/Kazakhstan and Lake Chad, Central Africa) have been diminished to a fraction of their former sizes. Aral Sea 1960s Soviet irrigation projects diverted vast quantities of water from the two rivers that flow into the Aral Sea. Today the Aral Sea is 25% of its former size. This destroyed the fishing industry and has generated choking wind-blown dust and salt from the dry lake bottom. Recent reengineering of the Syr Darya River will allow the northern remnant of the Aral Sea to remain near its current size. The southern portion of the sea will most likely disappear within a couple of decades. Lake Chad Ongoing drought has reduced the lake to about 10% of its former size. Some water diversion projects have contributed to the problem, but the greatest cause is climate change in the region.

Human Alteration of Natural Lakes Fig. 9-C. Aral Sea is shrinking due to dam construction and diversion of water for irrigation of agricultural land.

People and the Environment: Subsidence From Groundwater Extraction Continued extraction of groundwater can lead to the compaction of aquifer sediments. Especially a problem if the rate of groundwater extraction exceeds the rate of recharge. Several U.S. regions have been affected by this. In Las Vegas, NV, the land has subsided as much as 2 meters since the 1950s. Fissures have developed on the surface, and well casings have been damaged. Satellite Interferometric Synthetic Aperture Radar (InSAR) allows for the monitoring of ground subsidence. Bounced radar signals measure the distance, and the change in distance through time, from the satellite and ground surface. This technology also allows scientists to detect and monitor new faults.

The hydrosphere encompasses all moisture in, on, and above Earth. The hydrological cycle is the ceaseless interchange of moisture between water storage areas on Earth. Earth’s water storage areas include the oceans, glaciers, lakes, marshes and swamps, rivers and streams, and underground aquifers. Summary

More than 97 percent of all moisture is contained in the world ocean, which generally is subdivided into four major parts —Pacific, Atlantic, Indian, and Arctic. About 2 percent of the world’s moisture is locked up in ice. Most of this in in land ice (glaciers) and a small part is in floating sea ice. Surface waters contain only a tiny fraction of the world’s water supply.

Underground water is more widely distributed than surface water, but its availability and quality vary considerably from place to place.

Chapter nine

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Chapter nine

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