chapter 7.1 water: a vital resource water covers 325 cubic miles of earth (71% of the surface) about...
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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
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
Chapter 17.3Eutrophication
“trophic” refers to feeding “eutrophic” means “well nourished” eutrophication can occur naturally, but the
addition of pollutants to bodies of water has greatly increased the scope and speed of the process
aquatic plants benthic plants
aquatic plants that grow attached to, or are rooted in, the bottom of the water
submerged aquatic vegetation (SAV) grows totally underwater
requires water that is clear enough to allow sufficient light to penetrate to allow photosynthesis
as water becomes more turbid, light is diminished (increasing turbidity decreases the depth at which SAV can
survive) absorb required nutrients from the bottom sediments through
roots emergent vegetation grows with lower parts in the
water and upper parts emerging from the water
aquatic plants phytoplankton
consists of numerous species of photosynthetic algae, protists, and chlorophyll-containing bacteria (known as cyanobacteria)
grows in groups or “threads” of cells live suspended in the water and are found wherever
light and nutrients are available in extremes, may completely cover surface of water
and absorb all sunlight this density is only approached in nutrient-rich water
because they must absorb nutrients from the water
impacts of nutrient enrichment
oligotrophic—body of water in which light penetrates deeply (bottom is visible from the immediate shoreline) lake is fed by watershed that holds its nutrients well low nutrient levels limit growth of phytoplankton, allowing
enough light to penetrate to support the growth of SAV benthic plants support diverse aquatic ecosystem by
providing food, habitats, and dissolved oxygen
eutrophication
as the water of an oligotrophic body of water becomes enriched with nutrients, many changes are set in motion: enrichment allows the rapid growth and multiplication of
phytoplankton, increasing the turbidity of the water increasing turbidity shades SAV, causing many of them to
die-off with die-off of SAV, there is a loss of food, habitats, and
dissolved oxygen from their photosynthesis
Chapter 17.4Public Policy
Clean Water Act (1972) gave EPA jurisdiction over, and for the first
time required permits for, all point-source discharges of pollutants
set strong water quality standards encourages uses of best achievable pollution
control technology
Safe Drinking Water Act (1974) gave EPA authority to regulate quality and
safety of public drinking water supplies, maintain standards for numerous contaminants, and set requirements for chemical and physical treatment of drinking water