Transcript EUTROPHICATION

EUTROPHICATION, etc.
READINGS:
FREEMAN, 2005
Chapter 54
Pages 1261-1262
EUTROPHICATION
• Eutrophication is the accumulation of
nutrients in aquatic ecosystems.
• It alters the dynamics of a number of plant,
animal and bacterial populations; thus,
bringing about changes in community
structure.
• It is a form of water pollution and like all other
forms of pollution is the result of human
activities influencing ecological cycles.
POLLUTION
• Pollution is the contamination of the
environment by humans adding any
substance or energy.
• Heavy metals, gases, oil, sewage, noise,
heat, radiation and pesticides are common
pollutants that can affect the environment
adversely.
• A pollutant is any matter or energy introduced
by human activities that produces harmful
effects on resident populations thus altering
community structure.
Pollutants, Population Dynamics and
Community Structure
Pollutants may be toxic (effect survival and/or
reproduction of individuals) thus directly affect
population dynamics.
1. Radioactive Atoms (Radioisotopes)
….. I131, St90, etc.
2. Heavy Metals
….. Cu, Hg, Pb, etc.
3. Man-made Organic Molecules
….. DDT, PCB’s, Dioxin, 2-4-5 T, etc.
Pollutants, Population Dynamics and
Community Structure
Pollutants may alter the abiotic environment
thus indirectly affect population dynamics
1. Increases in Atmospheric Gases
…ozone (smog, uv radiation)
…sulfur dioxide (acid rain)
…CO2 (greenhouse effect)
…ammonia/nitrates (nitrogen deposition)
2. Waste Heat (thermal pollution)
3. Nutrient Enrichment (eutrophication)
Trophic Transfer, Biological Magnification
and Toxic Substances I
• The movement on compounds
(molecules) through trophic levels is
called trophic transfer.
• Toxic substances, like nutrients, can be
transferred through trophic levels.
• Substances that can not be metabolized
are particularly suitable for trophic
transfer, as are radioactive atoms.
Trophic Transfer, Biological Magnification
and Toxic Substances II
• Biological magnification is the increase
in concentration of a substance in
successive members of a food chain.
• Toxic substances may accumulate in
members of higher trophic levels as a
result of biomagnification.
• Two classic examples of substance that
are biomagnified are 1) Strontium90 and
2) DDT.
Trophic Transfer and Biological
Magnification of Strontium90 I
• St90 is a radioactive material with a 1/2 life of
28.1 years.
• Half life is a measure of how long it will take
for the mass of the substance to decrease
over time. For example, a kilogram of a
radioactive compound with a 1/2 life of 10
years will weigh one half of a kilogram is left
to sit from 1996 to 2006. By 2016, it will weigh
one quarter of a kilogram.
Trophic Transfer and Biological
Magnification of Strontium90 I
• St90 is a radioactive
material with a 1/2
life of 28.1 years.
• Half life is a
measure of how
long it will take for
the mass of the
substance to
decrease by half.
Trophic Transfer of Strontium90 in a
Canadian Lake II
The concentration of St90 tends to increase at successive
trophic levels.
The lake was thousands of miles from the South Pacific
location of the nuclear test. The radioactive materials had
been carried by atmospheric circulation.
Trophic Transfer and Biological
Magnification of Strontium90 III
• The Canadian lake example shows how a
radioactive material is concentrated as it
enters a food web. This is known as
biomagnification.
• Biomagnification of St90 is due to:
1) physiological similarity with calcium; a mineral
nutrient retained by plants and animals;
2) biomass transfer through food chains.
Trophic Transfer and Biological
Magnification of DDT (I)
• DDT is one of a class
of compounds known
as chlorinated
hydrocarbons.
• Widely used to kill
mosquitoes after
WWII.
• Widespread use
banned in US in 1972.
Trophic Transfer and Biological
Magnification of DDT (II)
• DDT, like radioactive
elements, once released
into the environment may
enter meteorological and
ecological cycles that
distribute it and
concentrate it to
dangerous levels.
• Studies show that it can
persist in the environment
for 15 to 25 years.
Trophic Transfer and Biological
Magnification of DDT (III)
• The concentration of DDT tends to increase
in food chain from one trophic level to the
next.
• Those at the top of the food chain receive the
largest doses.
• Biomagnification of DDT is due to:
1) high solubility in tissue fats; low in water;
2) very low rate of metabolism; low loss from body;
3) biomass transfer from one trophic level to next.
Trophic Transfer, Biological Magnification
and Toxic Substances
• Pesticides, PCB’s,
dioxins, radioisotopes,
heavy metals and
similar substances are
biomagnified.
• As a rule of thumb, their
concentration increases
10 fold as biomass is
transferred from one
trophic level to the next.
• See illustration.
Pollutants that Act Through the Abiotic
Environment
• There are groups of pollutants that are not directly
toxic as they are emitted into the abiotic environment
but accumulate to such an extent that they effect
community structure.
• Examples are:
1. Increases in Atmospheric Gases
…nitrogen oxides (smog, uv radiation)
…sulfur dioxide (acid rain)
…CO2 (greenhouse effect)
…ammonia/nitrates (nitrogen deposition)
2. Waste Heat (thermal pollution)
3. Nutrient Enrichment (eutrophication)
Nitrogen Oxides and Ozone (I)
• Nitrogen oxides (N2O,
NO and NO2) form a
major component of
photochemical smog.
• When they combine
with hydrocarbons in
the presence of
sunlight, the result is
ozone (O3), the major
component of smog.
Pollution Sources of Nitrogen Oxides
• Photochemical smog in
urban areas is common
due to the fact that
vehicles emit both
nitrogen oxides and
hydrocarbons.
• It is responsible for
respiratory problems.
• It is also known to result
in damage to crops.
Global Effects of Nitrous Oxide (N2O)
• The concentration of nitrous oxide has been
increasing in the atmosphere for the last 3040 years at a rate of 0.2-0.3% per year.
• It absorbs infrared radiation (heat); thus,
contributes to global warming.
• In the stratosphere, it reacts with ozone in the
stratosphere and thus contributes to ozone
depletion. Thus, allowing increased ultraviolet
radiation to reach the earth.
Sulfur Dioxide and Acid Rain
• Sulfur dioxide (SO2) is a
colorless gas produced
by combustion of fossil
fuels at power plants
and certain industrial
sources.
• It along with nitrogen
oxides results in acid
rain.
• The impact of acid rain
in Europe has been
sever and is most
noticed in forests of the
northeastern US.
Other Pollutants that Act Through the
Atmosphere
• The increased use of fossil
fuels has resulted in an
increase in CO2, a
greenhouse gas. Its effects
will be discussed in the
lecture on climate change.
• Increases in atmospheric
ammonia and nitrate find
their way into the rain that
hits the earth. The potential
effects of nitrogen deposition
on natural ecosystems will
be discussed in lecture in
two weeks.
Acid Rain
• Sulfuric and nitric acids
formed in cloud droplets
can give extremely low
pH.
• Water collected at the
base of clouds in
eastern US have been
as low as 2.6
• In L.A, values as low as
2 have been recordedthe acidity of lemon
juice.
Thermal Pollution
• Many industries take
water from a lake,
stream or inlet and use
it to cool equipment or
products.
• Often this increases the
temperature of the
water so that it kills fish
or stimulates algal
growth. The result is
eutrophication.
• Sometimes this
increase in productivity
is beneficial.
EUTROPHICATION
• The nutrient enrichment of an aquatic
ecosystem.
• Natural Eutrophication -- a process that
occurs as a lake or river ages over a period of
hundreds or thousands of years.
• Cultural Eutrophication -- a process that
occurs when humans release excessive
amounts of nutrients; it shortens the rate of
aging to decades.
Natural Eutrophication
Lake classification based on
nutrient content and production
of organic matter. Oligo- nutrient
poor; meso- middle nutrient;
eu- nutrient rich.
Cultural Eutrophication
• The addition of excess
nutrients from a variety
of sources results in the
rapid aging of aquatic
ecosystems.
• During this process the
species composition of
the aquatic community
changes.
Water Chemistry and
Eutrophication (I)
• Eutrophication brings
about changes in water
chemistry.
• These include:
pH
Dissolved O2
CO2
Ammonia
Nitrates/Nitrites
Phosphates
Water Chemistry and
Eutrophication (II)
• pH -- The pH of water reflects the CO2 contents as
well as the presence of organic and inorganic
acids. Values below 5 and above 9 are definitely
harmful to fish and limit growth of algal and
invertebrate populations.
• Dissolved O2 -- The amount of dissolved oxygen in
water varies with temperature and pressure; high
temperature or pressure, low oxygen. Most
invertebrates die if oxygen levels fall below 4-5
mg/l for extended periods of time. Game fish
(bass, perch, trout, etc) require oxygen to be in the
range of 8-15 mg/l.
Water Chemistry and
Eutrophication (III)
• CO2 -- Carbon dioxide is largely a product of
aerobic and anaerobic decomposition of
organic matter. It reacts with water to form
carbonic acid. Normal concentrations are
usually less than 1 mg/l. Fish are affected at
higher levels and continued exposure to
10mg/l or more is fatal to many species.
• Phosphates -- Present in low quantities in
natural waters; less than 0.01 mg/l. Released
during decomposition. High levels stimulate
algal blooms.
Water Chemistry and
Eutrophication (IV)
• Ammonia (NH3 or NH4+) -- Ammonia is a product
of decomposition of animal and plant protein. It is
an important plant nutrient. Natural bodies of
water contain > 1 mg/l. Levels higher than this
stimulate algal growth and are toxic to fish.
• Nitrates/Nitrites -- These N containing
compounds are formed during decomposition and
are inter-converted by certain species of bacteria.
Natural concentrations rarely exceed 10 mg/l and
are often > 1mg/l.
Major Sources of Excess
Nutrients
• Major sources of
excess nutrients are
agricultural fertilizers,
domestic sewage and
livestock wastes.
• Agricultural fertilizers
provide inorganic
nutrients.
• Sewage and wastes
provide both inorganic
and organic nutrients.
Overview of Cultural
Eutrophication
• Start with clear water stream or blue
water lake.
• Introduction of organic and/or inorganic
nutrients.
• The pathways of these two nutrient
sources differ.
• Follow organic pathway first; inorganic
nutrient pathway second.
Oligotrophic Aquatic
Ecosystems
• A clear water stream or deep
blue lake contains enough
bacteria to decompose
organic material from
organisms that die.
• Water is neither acidic or
basic.
• Inorganic nutrients are
present in low concentrations.
• Ammonia produced by
animals and bacteria is taken
up and used for plant growth.
Excess Organic Matter
• Untreated sewage, manure,
paper pulp, packing plant
wastes are sources of
excess organic matter added
to aquatic ecosystems.
• Results in exponential
growth of bacterial
populations.
• Bacteria deplete dissolved
oxygen in the water.
Low Oxygen Levels Cause
Die-off
• Rapidly growing
bacterial populations
need exponentially
increasing amounts of
oxygen.
• Once dissolved oxygen
levels become too low,
fish and many
freshwater invertebrates
die, thus adding more
organic matter.
Oxygen Depleted Waters
• As oxygen disappears,
anaerobic bacteria produce
methane, hydrogen sulfide and
ammonia.
• Bacterial respiration increases
carbonic acid.
• In all but the most oxygen
depleted waters, tubificid
worms, midge larvae and
mosquito larvae replace
oxygen-loving invertebrates.
Oxygen Replenishment
• If organic material is not
continually added or the
water moves downstream,
bacteria eventually use up
their food and populations
decline.
• The concentration of
dissolved oxygen increases,
either through atmospheric
replenishment or increased
photosynthesis.
Recovering Aquatic
Ecosystem
• If stocks are available
then fish can recolonize
and the stream or lake
will recover.
• Carp, which tolerate low
oxygen levels, do well.
• Oxygen-loving species
such as trout, bass and
other game fish may
return.
Recovering Aquatic
Ecosystem
• If available freshwater
invertebrates recolonize,
then the stream or lake
can recover.
• Oxygen-loving species
such dragonfly, mayfly,
caddis fly, stone fly
larvae may return.
Oligotrophic Aquatic
Ecosystems
• A clear water stream or deep
blue lake contains enough
bacteria to decompose
organic material from
organisms that die.
• Water is neither acidic or
basic.
• Inorganic nutrients are
present in low concentrations.
• Ammonia produced by
animals and bacteria is taken
up and used for plant growth.
Excess Inorganic Nutrients
• Agricultural runoff from
fertilizers and effluent
from secondary sewage
treatment plants are the
primary sources of
inorganic nutrient addition
to aquatic ecosystems.
• These sources are rich in
nitrogen and phosphorus.
Nutrients Stimulate Algal
Blooms
• Nitrogen and
phosphorus from
runoff and effluents
or decay of organic
matter stimulates
aquatic plant
growth.
• In particular, algal
“blooms” give the
water a green or
blue-green color.
Plants Die, Bacteria Grow,
Deplete Oxygen, Fish Die
1. Plants exhaust
nutrients and die.
2. Bacteria thrive on
organic decay of plants
and lower dissolved
oxygen.
3. Fish and invertebrates
die when oxygen gets
too low.
Oxygen Replenishment and
Ecosystem Recovery
• In temperature regions, the growing season
ends.
• Bacteria eventually use up their food and
populations decline.
• The concentration of dissolved oxygen
increases, either primarily through
atmospheric replenishment.
• If stocks are available then fish and
invertebrates can recolonize and the stream
or lake will recover.
The Good News
• Since the 1970’s, many of the worst
conditions that lead to air and water pollution
have been abated.
• The last above ground nuclear tests occurred
in China.
• The catalytic converters lowered hydrocarbon
emissions, but increased nitrogen oxide
emissions; thus requiring new technology.
• Some of the worst cases of water pollution
have been addresses and in some cases
reversed.
EUTROPHICATION, etc.
READINGS:
FREEMAN, 2005
Chapter 54
Pages 1261-1262