chapter 7.1 water: a vital resource water covers 325 cubic miles of earth (71% of the surface) about...

Chapter 7.1Water: A Vital Resource

water covers 325 cubic miles of Earth (71% of the surface) about 97.5% of this volume is salt water remaining portion is freshwater, but 2/3 of this

is frozen in polar ice caps and glaciers thus, only 0.77% of the world’s water is

available for human use the water cycle recharges this small

fraction thanks to evaporation from oceans and precipitation

water in the developing world

1.5 billion people in the developing world still lack access to safe drinking water

2.6 billion do not have access to adequate sanitation

more than 1.7 million deaths each year stem from waterborne diseases (mostly in children under 5)

in addition, because of the infrastructure used to control water, seas are being lost and rivers are running dry

Chapter 7.2Hydrologic Cycle: Natural Cycle, Human Impacts

hydrologic cycle (commonly called the water cycle) consists of water rising to the atmosphere through evaporation and transpiration, then returning to the surface through condensation and precipitation

weak attraction from hydrogen bonds has major impact on behavior of water

water is a powerful greenhouse gas, providing about 2/3 of the total warming from all GHGs

purification

processes of evaporation and condensation purify water naturally when water in an ocean or lake evaporates, only the

water molecules leave the surface; dissolved salts and other solids are left behind

when water condenses again, it is purified (except for pollutants or other aerosols it make pick up in the air)

water in the atmosphere turns over every 10 days, so water is constantly being purified

precipitation

warm air rises from the Earth’s surface because it is less dense than the cooler air above

with lower atmospheric pressure at upper altitudes, the warm air gradually cools as it expands

when relative humidity reaches 100% and cooling continues, condensation occurs and clouds form

as condensation intensifies, water droplets become large enough to fall as precipitation

arrival of a cold front is almost always a rain-causing event

rain shadow

Chapter 7.2 (cont.)Groundwater

as precipitation hits the ground, it may either (a) soak into the ground (infiltration) or

this water has two alternatives: may be held in soil as capillary water

returns to atmosphere by evaporating from soil or by transpiration from plants

water may percolate through the soil, eventually accumulating as groundwater (upper surface of groundwater is known as water table)

(b) run off the surface runoff flows over the surface of the ground into streams and

rivers, which make their way to the ocean or inland seas all the land area that contributes water to a particular stream

or river is referred to as the watershed

recharge

aquifer: layers of porous material through which groundwater moves often difficult to detect location of aquifer groundwater in aquifers may be found at

various depths between layers of impervious rock

recharge area: area where water enters an aquifer

hold 99% of all liquid freshwater

purification

as water percolates through the soil, debris and bacteria from the surface are generally filtered out however, water may dissolve and leach out certain

minerals in most cases, the minerals that leach are harmless—

like calcium from limestone groundwater may reach the surface via seeps

(water flowing out over a relatively wide area) or springs (water exits the ground from a small opening)

human impacts on the hydrologic cycle

many of environmental problems stem from direct or indirect impacts on the water cycle:

(1) changes to the surface of the Earth as forests are cleared or land is overgrazed, the pathway of

the water cycle is shifted from infiltration and groundwater recharge to runoff

water runs into streams or rivers sudden influx of water may cause floods and bring increased

sediments and pollutants due to surface erosion floods have increased in many parts of the world due to

deforestation and overgrazing increased runoff means less infiltration and therefore less

evapotranspiration and groundwater runoff

human impacts on the hydrologic cycle

(2) climate change clear evidence that Earth’s climate is warming because of the

rise in greenhouse gases warmer climate means more evaporation wetter means more precipitation and flooding

(3) atmospheric pollution aerosol particles form nuclei for condensation more particles lead to formation of more clouds increase in particles from burning coal (sulfates), burning wood

(carbon), and dust particle sizes suppress rainfall

(4) withdrawing water supplies

Chapter 7.3Water: A Resource to Manage, a Threat to Control

uses Americans use less water now than in 1975 most of the water used in homes and industries is for

washing and flushing away unwanted materials known as nonconsumptive uses (after treatment, water is

again available for human use) irrigation is a consumptive use because the water

does not return to its original source (can only percolate into the ground and return via evapotranspiration)

70% of world’s water is used for irrigation; 20% for industry; 10% for direct human use

groundwater remediation

used when dumps, leaking storage tanks, or spills of toxic materials have contaminated groundwater to the point of threatening drinking water

techniques involve drilling wells, pumping out the contaminated groundwater, purifying it, and reinjecting the purified water back into the ground or discharging it into surface water

dam impacts

large dams have an enormous social impact, leading to the displacement of people and the drowning of ecosystems valuable freshwater habitats are lost implications often extend beyond river

wetlands that are filled by occasional floods no longer receive water, leading to loss of habitat for waterfowl

fish attempting to swim upriver to spawn often have problems with fish ladders

Chapter 7.4Water Stewardship: Public Policy Changes

hydrologic cycle provides enough freshwater to meet all human needs however, water is not distributed evenly results in persistent scarcity in many parts of

the world expanding populations create an ever-

increasing demand for additional water for irrigation, industry, and municipal use

3. desalting seawater

with increasing water demands, there is a new emphasis on desalination

two technologies are used: microfiltration (reverse osmosis)

forces seawater through a fine membrane filter that removes salt distillation

often use waste heat to evaporate water, then recondense the purified water vapor

costs of building and maintaining plants (even when using waste heat) are considerable in best case, desalinized water costs $2 per 1000 gallons (2-

4x what most in the U.S. pay)

Chapter 17.1Water Pollution

according to EPA, pollution is “the presence of a substance in the environment that, because of its chemical composition or quantity, prevents the functioning of natural processes and produces undesirable environmental and health effects.”

pollutant: any material that causes pollution

sources

water pollution is usually described as having a point source or a nonpoint source point sources

relatively easy to identify involve discharge from factories, sewage systems, power plants,

underground coal mines, oil wells nonpoint sources

poorly defined and scattered over broad areas examples include agricultural runoff and storm-water drainage

two basic strategies are used in attempting to bring water pollution under control: (1) reduce or remove the sources (best for nonpoint) (2) treat the water before it is released to remove pollutants or convert

them to harmless forms (best for point)

(a) pathogens

most serious water pollutants are infectious agents that cause sickness and death animal excrement often contains pathogens

(disease-causing bacteria, viruses, and other parasitic organisms)

diseases are easily spread from one individual to another when sanitation is poor

(b) organic wastes

along with pathogens, animal wastes also contain organic matter that create problems in water if it enters untreated

other kinds of organic matter (leaves, grass clippings, etc.) can enter due to runoff, and may lead to excessive aquatic plant growth when bacteria and detritus-feeders decompose

organic matter in water, the consume oxygen dissolved in the water

organic wastes— dissolved oxygen

the amount of oxygen that water can hold in solution is very limited in cold water, dissolved oxygen (DO) can

read concentrations of up to 10 parts per million

even less can be held in warm water bacteria keep water depleted in DO as long

as there is dead organic matter to support their growth

organic wastes—biological oxygen demand (BOD)

biological oxygen demand (BOD): measure of the amount of organic material in water, in terms of how much oxygen will be required to break it down biologically, chemically, or both

higher BOD greater chance of decreased DO decreased animal life (fish and shellfish die at DO levels

of 2-3 ppm) if the system becomes anaerobic (no oxygen),

only bacteria can survive

(c) chemical pollutants because water is an excellent solvent, it is able to hold many

chemical substances in solution that have undesirable effects water-soluble inorganic chemicals constitute an important class

of pollutants that include heavy metals (lead, mercury, arsenic), acids from mine drainage (sulfuric acid) and precipitation (sulfuric and nitric acids), and road salts used to melt snow (sodium and calcium chlorides)

organic chemicals are another potential source of water pollution petroleum products may enter large bodies of water due to oil spills or

small streams as a result of runoff from parking lots pesticides and industrial chemicals (i.e. PCBs) may also pollute

waterways many of these pollutants are toxic even at low concentrations and can

concentrate as they move up the food chain

(d) sediments as natural land forms weather, a certain amount of sediment enters streams

and rivers load of sediment can be greatly increased by erosion from farming,

overgrazing, mining, and other activities large amounts of sediment changes the water quality and the habitat, along

with killing animals by clogging their gills and smothering eggs and organisms along the bottom

water-soluble inorganic chemicals classified as nutrients because they are essential to plants two most important nutrients are phosphorus and nitrogen more nutrients means more plant growth, which may stimulate undesirable

plant growth in the water sewage outfalls are most likely point source agricultural runoff (animal waste, fertilizer) is most likely nonpoint source

(e) nutrients