Chapter 15: Freshwater Resources
Natural System,
Human Impact and
Conservation
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A: Freshwater Systems
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glaciers
icecaps
underground aquifers
rivers & lakes
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Wetlands
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diverse ecological systems
slow runoff
reduce flooding
recharge aquifers
filter pollutants
combinations of freshwater and dry land
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marshes: plants are allowed to grow above water level
swamps: same as marshes but present in forest areas
bogs: ponds roughly covered by vegetation
Lakes and Ponds
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open standing water
ecosystems vary according to depth
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littoral zone~ shores
benthic zone~ bottom of lake
limnetic zone~ away from shores, top of lake
profundal zone~ similar to benthic, no sunlight
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Diversity of Ecosystems in Lakes and Ponds
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Groundwater
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precipitation that percolates through the soil
20% of Earth's freshwater
unequal distribution
climate change causing water shortage
Aquifers
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porous spongelike formation of rock, sand
and gravel formed by
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zone of aeration: not completely saturated
zone of saturation: saturated with water
water table: limit between zones of aeriation
and saturation
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confined aquifer: rain cannot get to it by filtration
unconfined aquifer: no upper layer that confines it
Average Water Usage
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world wide→ 170,616 gal/yr/person
U.S.A.→ 509,000 gal/yr/person
poor countries→ 16,425 gal/yr/person
source: U.N. Environmental Program 2002
Water Usage
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altering environmental systems
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consumptive use~ water is consumed
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dams
canals
diversions
irrigation
nonconsumptive use~ water is returned to the
system after use
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hydroelectric
Dam's Drawbacks
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risk of failure
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www.northlasvegaschamber.com
blocks flow of water
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Three Gorges dam cracks and sedimenting
fisheries fail (salmon in Columbia river)
sedimentation (Answar dam in Egypt)
population displacement (Three Gorges dam)
affects ecosystems
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Hoover dam was recently opened to restore the ecosystem
Dam's Benefits
~prevents floods
~provide drinking water
~facilitate irrigation
~generates electricity
~emissions drop
~shipping
geochange.er.usgs.gov/.../natural/codrought/
Dikes and Levees
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flood prevention
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along banks of rivers
can fail
flooding is a natural process
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heavy rain
snow melt
spreads nutrient-rich sediments
Today's Problems Caused by Overuse
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major rivers' deltas are dry
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causes tidal erosion
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Rio Grande, Colorado, Yangze between others
Yangze delta is eroding due to tides
affecting industry and population
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Aral sea shrinking and salinating
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fishing industry
agricultural industry
Ground Water Depletion
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we are overusing it
160 km³ = 100 cubic miles of water used
that is not replaced by rain
water table is dropping
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causing salt intrusion at deltas
salt water can get to aquifers making water
undrinkable
drop of water table causes sinkholes
Solutions to Water Depletion
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reducing demand
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conservation
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xeriscaping
water lawn at night
efficiency
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showers
washing machine
dishwasher
low-flow faucets
toilets
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Solutions
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desalination plants
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freshwater from sea water
expensive
requires energy
creates large amounts of salty waste
Solutions
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reduce agricultural demand
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choose crops that match the land and climate
improve efficiency of irrigation systems
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drip irrigation
low pressure spray
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target individual plants
genetic modification
Economic Approaches for Water
Conservation
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end subsidies to inefficient practices
let water become a commodity
privatization of water supplies
decentralization of control over water
education
B: Water Pollution
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nutrient pollution: eutrophication
oligotrophic
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eutrophic
Pollution
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pathogens and waterborne diseases:
contamination by human or animal waste
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cholera
diphtheria
Escherichia coli
salmonella
Pollution
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toxic chemicals: synthetic chemicals
toxic metals
pesticides
petroleum based products
acids from mining drainage
acid rain
Pollution
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sediment
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mining
clear-cutting
careless cultivation
thermal pollution
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too warm can cause oxygen depletion
too cold can cause invasive species to thrive
Sources of Water Pollution
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point sources
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oil spills
industrial waste
sewage plants
non-point sources
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animal feedlots
fertilizers from farms, homes and clubs
pesticides from farms, homes and clubs
herbicides from farms, homes and clubs
salt and sand on winter roads
chemicals from urban runoffs
Water Quality Indicators
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biological
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presence of fecal coliform bacteria
disease causing pathogens
physical
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turbidity→ presence of sediments
color→ indicates presence of certain chemicals
temperature→ can affect biological processes
Groundwater Pollution
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extremely difficult to monitor
non-point sources
retains contaminants until they decompose
decomposition can take decades
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less O2
less microbes
less organic matter
Sources of Groundwater Pollution
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natural
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occur naturally in the environment
can cause toxicity in water
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arsenic in Bangladesh water wells
Sources of Groundwater Pollution
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human activity
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pathogens and pollutants
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underground liquid hazardous waste
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septic tanks
tanks of industrial chemicals
oil/gas tanks
nitrates from agriculture fertilizers
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cancer
– miscarriages
– blue-baby syndrome
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industrial and military waste
http://oceanservice.noaa.gov/education/kits/pollution/media/supp_pol02d.html
Legislation
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Federal Water Pollution Control Act (1972)
later Clean Water Act (1977)
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illegal to discharge pollution from a point source
unless permit was given
standards for wastewater
standards for contaminant levels
funds for sewage treatment plants
Prevention vs. Mitigation
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prevention is cheaper
consumer choice
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phosphorus-free detergents
environmentally friendly products
local groups of volunteers collect pollutant data
state and federal regulation
Wastewater
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water that has been used
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sewage
showers
washing machines
dishwashers
manufactures
businesses cleaning processes
storm water runoff
Treatments
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Municipal wastewater
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septic systems in rural areas
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underground
microbes break organic matter
needs to be taken to landfill periodically
emits gases
lawcoswm.org/septictank.htm
bcn.boulder.co.us
Treatments
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sewer systems in populated areas
primary treatment
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physical removal of up to 60% suspended solids
secondary treatment
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water is aerated to promote bacteria activity
90% of solids are removed
chlorine and UV rays applied to kill all bacteria
water is piped back to rivers/lakes/ocean
reclaimed water used as "grey water"
leftover sludge is disposed, incinerated or used as fertilizer
Treatments
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artificial wetlands
primary treatment is done in a conventional
manner
microbes, aquatic plants, fishes, algae
filter and clean the water
biosolids used for energy
problems may happen
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prairie dogs
The End
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