22. Eutrophication

Report
Syllabus statements: 5.4.15.4.3
Chapter
Video
Labs:
EUTROPHICATION
SYLLABUS STATEMENTS
5.4.1: Outline the process of eutrophication
 5.4.2: Evaluate the main impacts of
eutrophication
 5.4.3: describe and evaluate pollution
management strategies with respect to
eutrophication

VOCABULARY
Biological oxygen demand
 Eutrophication
 Positive feedback

EUTROPHICATION IS
The natural or artificial enhancement of a body
of water, particularly with respect to nitrates
and phosphates, that results in depletion of the
oxygen content of the water
 It is accelerated by human activities that add
detergents, sewage or agricultural fertilizers to
bodies of water


Satellite imagery of
the Caspian Sea
showing increased
turbidity
(cloudiness) in the
north and east 
eutrophication
PROCESS OVERVIEW
1.
2.
3.
4.
5.
Increase in nitrates and phosphates
Rapid growth of algae
Accumulation of dead organic material
High rate of decomposition
Decrease in oxygen
ENHANCING NATURAL EFFECT
In natural conditions  plant communities
uptake nutrients and clays in soils trap them
 Human alterations remove this storage and
increase inputs as well
 Sewage effluent – nutrients from waste plus
detergents (phosphates)
 Agriculture – animal waste & inorganic fertilizer
runoff

FEEDBACK MECHANISM
Positive feedback involved
 More nutrients mean more plants
 More dead plants means more organics means
more nutrients
 More plants…


Until death and decomposition outweighs
everything else…
EUTROPHICATION IMPACTS
Death of Aerobic organisms
 Increased turbidity
 Loss of macrophytes
 Reduction in the length of food chains
 Loss of biodiversity

DEAD ZONE FORMATION
Worldwide problem in coastal waters (146
areas)
 In Gulf of Mexico – mouth of Mississippi – area
the size of Massachusetts gets so O depleted
(hypoxic) that every aerobic organism that can’t
flee dies
 Varies in size but growing
 Nearshore waters are important fisheries (Gulf
one is 18% of US catch) and nursery grounds
 They are in jeopardy

RECALL POLLUTION MANAGEMENT
Human pollutants produce long term and far
reaching effects
 Strategies for reducing impacts can be directed
at three different levels in the process

1.
2.
3.
Altering the human activity
Reducing the quantity of pollutant released at the
point of emission
Cleaning up the pollutant and restoring the
ecosystem after pollution occurs
ALTERING THE ACTIVITY THAT POLLUTES
Phosphate free
detergents in the home
 Reduced residential
use of lawn fertilizers
 Move agriculture away
from inorganic broad
scale fertilizers to
specifically applied
organic fertilizers and
manures
 Soil conservation

REGULATING AND REDUCING EMISSIONS

Sewage treatment modifications
 Traditionally
remove solids and purify but leave
nutrients in effluent
 Advanced (more $$$) but removes nutrients for
agricultural application

Treatment marshes on farms
 Use
natural wetland capabilities for farm waste
treatment
Secondary
Primary
Bar screen
Grit
chamber
Settling tank
Aeration tank
Settling tank
Chlorine
disinfection tank
To river, lake,
or ocean
Raw sewage
from sewers
Sludge
(kills bacteria)
Activated sludge
Air pump
Sludge digester
Sludge drying bed
Disposed of in landfill or
ocean or applied to cropland,
pasture, or rangeland
Effluent from
secondary
treatment
Alum
flocculation
plus sediments
Activated
carbon
Desalination
(electrodialysis
or reverse osmosis)
98% of
suspended solids
90% of
phosphates
Nitrate
removal
Specialized
compound
removal
(DDT, etc.)
To rivers, lakes,
streams, oceans,
reservoirs, or industries
98% of
dissolved
organics
Recycled to land
for irrigation
and fertilization
Most of
dissolved salts
CLEAN UP AND RESTORATION
Mud can be pumped out of eutrophic lakes
 Plants can be reintroduced to restart natural
nutrient cycling
 Once that takes hold reintroduce fish

REMEMBER THERE ARE MANY FACTORS TO STOP
Discharge of untreated
municipal sewage
(nitrates and phosphates)
Nitrogen compounds
produced by cars
and factories
Natural runoff
(nitrates and
phosphates
Inorganic fertilizer runoff
(nitrates and phosphates)
Discharge of
detergents
( phosphates)
Discharge of treated
municipal sewage
(primary and secondary
treatment:
nitrates and phosphates)
Lake ecosystem
nutrient overload
and breakdown of
chemical cycling
Dissolving of
nitrogen oxides
(from internal combustion
engines and furnaces)
Manure runoff
from feedlots
(nitrates,
phosphates,
ammonia)
Runoff from streets,
lawns, and construction
lots (nitrates and
phosphates)
Runoff and erosion
(from cultivation,
mining, construction,
and poor land use)

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