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Unit 6- Water: Global Resources and Pollution
Transcript of Unit 6- Water: Global Resources and Pollution
Ch 13, 20
Ch 13- Water Resources
Sources of Freshwater:
Surface Water and Groundwater Depletion
We generally view water as a cheap, abundant resource, however we have seen that water shortages are occurring.
How to Protect Groundwater Resources
-shape the earth's surface
-dilute and remove pollutants
-purify or disperse heavy concentrations of contaminants
This is an issue due to our growing human population and increasing input of toxins generated by
agricultural, industrial, and residential
The WHO estimates that
1.6 million people die
each year from preventable diseases contracted from
contaminated drinking water
So why can't we all just drink
Less than 1%
of all the Earth's water supply is readily available as freshwater.
When it rains, some water percolates downward through the soil, gravel or porous rock until it reaches a layer that is not permeable.
Typically, the first few layers below the surface trap air rather than water =
ZONE OF AERATION
The deeper subsurface layers that fill all available porous space with water =
ZONE OF SATURATION
The upper limit of the zone of saturation =
The height of the water table fluctuates in response to dry/wet seasons or over-withdrawal by humans.
are deep underground layers of porous rock material, gravel, sand, silt, or clay where
Aquifers can be recharged by:
- through percolation of precipitation
- through the movement of water from rivers and streams
Exists as rivers, lakes, wetlands, estuaries, and the ocean
Recharge to these waters is in the form of
from precipitation and snowmelt that doesn't infiltrate the soil layers
watershed (drainage basin)
is the land that surrounds surface water and contributes to surface runoff.
Surface water can also be
from groundwater sources.
Therefore if groundwater is withdrawn faster than it is replenished this can reduce the volume of surface water in rivers, lakes, and stream.
Main uses of groundwater and surface water:
1. Irrigation (70%)
2. Industrial Processes (20%)
3. Human Consumption (10%)
most water goes to thermoelectric power plants as a coolant
large amounts are also used to produce consumer goods
residential uses- #1 use in the home is flushing toilets!
many live without electricity or running water
most freshwater is used for crop production
Just like we saw with food, there is a huge
disparity in the distribution
has 20% of Earth's freshwater, but only 0.5% of the population.
has 30% of Earth's freshwater, but 60% of the population.
uses majority of water for irrigation (arid land), but receive less precipitation than the eastern US.
Some regions experience
- long periods of time where regions receive 30% or less of their average annual rainfall.
With increasing population, comes increased demand for food, electricity, consumer goods, etc.
This will continue to intensify water shortages and current and future heated battles over water rights.
Populations rely heavily on aquifer resources to provide irrigation and drinking water .
Sustainability of that groundwater depends on the
rate of recharge vs. the rate of withdrawal.
Overdraft occurs when water is withdrawn faster than it can be recharged.
= a sinkhole occurs when the top of the underground cavern collapses
If this happens in a coastal area then
occur which causes the aquifer to become unusable.
1. subsidize water conservation strategies
2. implement water conservation practices in residential homes
3. increase the price of water to discourage waste
4. reduce the number of water-intensive crops being grown in arid regions
Using Surface Water Resources
-surface water is easily accessible and
therefore have been used in a variety of ways
- fast flowing rivers are dammed to create freshwater reservoirs to provide hydroelectric power.
*Once a river is dammed, the terrestrial area
behind the dam will flood.
-no CO2 emissions
-provides irrigation and drinking water
-recreation in reservoir
-displaces people living behind dam
-decreases nutrient rich silt downstream
-fish harvest below dam decreases
-disrupts migration of some fish
Water Transfer Projects
since water isn't distributed evenly, many countries and states have created water transfer projects to provide resources to areas with limited supply
*Many of these projects have resulted in devastating loss of water in ecosystems
EX: Aral Sea, California Water Transfer Project, China Water Transfer Project
The cheapest and fastest way to improve water conservation is to
reduce the loss of irrigation water by evaporation
and to fix residential and industrial
Improving Irrigation Practices
is used in some parts of the
US and often in developing countries.
large amounts of water are pumped directly onto agricultural land and allowed to flow by gravity into ditches in the soil for crops to absorb.
Almost half of this water never reaches the crops since it is lost as evaporation and surface runoff.
- delivers small amounts of water more directly to the roots of crops
-series of pipes run along crop rows
-reduces evaporation and improves efficiency by 95%
- numerous metal frames on wheels that extends large water pipes over crops by using low pressure sprinklers
-reduces evaporation and improves
efficiency by 80%
1. Irrigate with treated urban wastewater
2. Irrigate at night to reduce evaporation
3. Use soil moisture monitors to water only
4. Use rainwater barrels
Improving Residential and Industrial Water Conservation
1. Fix leaks in pipes
2. Require the use of water meters
3. Use low flow shower heads and low volume toilets
4. Recycle water-
GREY WATER SYSTEMS ----> collect water from showers, bathtubs, and dishwashers and then reuse this to water lawns, wash cars, or flush toilets
Increasing Freshwater Supply
Can we just use saltwater and turn it into freshwater!?
- process that removes salts from ocean water
- aka microfiltration, uses external pressure to
push salty water through membranes that separate
from the solvent (water)
- heats water until evaporation begins, the steam is
collected and condenses as freshwater. The salts are left behind in
WATER POLLUTION SOURCES AND TYPES
Point Source Pollution
Single source pollution discharges from a specific location like drain pipes, ditches, or sewers that flow directly into a body of water
Developing countries still have a hard time controlling this, but most developed countries have laws protecting against this.
Nonpoint Source Pollution:
Dispersed source pollution are scattered and diffused release of pollutants that cannot be traced to any single site of discharge
The majority of surface water problems comes from nonpoint source pollution. This type is much harder to control and regulate.
Leading Sources of Water Pollution:
Agriculture- leading cause of water pollution!
-surface water runoff carries eroding soil sediments, excess fertilizers, and pesticides into waterways
-animal waste from feedlots also make their way into water
Industrial- industrial processes create large amounts of inorganic and
- acids, heavy metals, fertilizers
- pesticides, gasoline, motor oil, food processing waste, PCBs, VOCs
Mining- exposes large areas of the earth to erosive forces like wind and rain
Creates runoff of precipitation and sediments that carry with it harmful chemicals such as sulfuric acid, arsenic, and cyanide used to extract gold
Erosion can also release heavy metals from the rock layers, like Mercury
Most developed countries have enacted water quality laws that monitor nonpoint sources, regulate point source, and increase the number of wastewater treatment plants.
Developing countries do not have the same laws...
More than half of China has no form of sewage treatment and over 300 million people live without access to clean drinking water.
The Ganges River in India is heavily polluted with sewage. Religious beliefs dictate that bodies be burned in wood fires, then thrown in the Ganges River.
oxygen demanding wastes and increases pathogenic bacteria
India's government started building sewage treatment plants along the Ganges and is encouraging cremation of bodies that are put into crematoriums.
Lakes are more vulnerable to contamination because the stratification of the lake layers and very little water flow, which would dilute pollutants.
(for the millionth time!)
1. Excess nutrients (like nitrates and phosphates) lead to algal blooms
2. As plant and algae die off, decomposers must work overtime to break down the dead material.
3. Aerobic Decomposers use up the
4. Oxygen levels deplete
Remediation/Prevention of Cultural Eutrophication
1. Mecahnical removal of excess plant growth
2. Pumping oxygen into the water to prevent depletion
3. Use of herbicides and algaecides
4. Increase buffer riparian zones
5. Removal of nitrates and phosphates from wastewater
Great Lakes Water Pollution:
experiences cultural eutrophication problems
-sewage and runoff of fertilizers, phosphate
detergents, industrial pollutants
-heavy removal of riparian zones
Lake Washington Water Pollution:
located near popular urban area of Seattle
-increased amounts of treated wastewater are put back into Lake Washington (but still contains nitrates and phosphates)
-cultural eutrophication increased sharply and fish began to die
-government decided to divert wastewater treatment to Puget Sound and water clarity in the lake improved drastically
Another big way to reduce water pollution is by improving Wastewater Treatment
Primary Treatment- physical process that uses screens and a grit tank to remove large floating debris and allows solids to settle out as sludge
Seconary Treatment- biological process that uses aerobic bacteria to remove oxygen demanding waste, more sludge is removed, water is bleached usually with chlorine.
-Chlorine though has been linked to
endocrine and nerve damage so UV light and
ozone are used intead
Tertiary Treatment- physical or chemical process to remove specific pollutants.
hypoxia vs. anoxic
Organic Solvents, pesticides, fertilizers, gasoline, and oil that are either poured directly onto the ground or leak from buried storage containers and seep into lower layers
So, if groundwater is moving, why can't it recover from pollutants like rivers do?
1. Slow flow rate (1 ft/day)
2. Cold Temperatures
3. Low populations of decomposing bacteria
4. Lower concentration of DO
5. Nondegradable waste like arsenic and
lead remain in water permentantly
6. DDT is very persistent and degrades slowly
Since removal of pollutants from groundwater is very difficult, preventing groundwater contamination in the first place is the best solution.
1. Hazardous waste disposal in landfills and injection wells should be banned.
2. Very toxic chemicals should be stored above ground with leak detection
Oceans typically dilute, disperse, and degrade large quantities of degradable contaminants.
Remember, over half of the world lives within 50 miles of coastal areas so mangroves, estuaries, and coral reefs are seeing great human impact.
Developing countries often use the ocean as a dumping site for sewage and industrial waste.
Other sources of ocean pollution include a high number of viruses, plastic floats, trash from storm drains...
Major Ocean Oil Spills
EXXON VALDEZ (1989) GULF OIL SPILL (2010)