EUTROPHICATION, etc.

1
EUTROPHICATION, etc.

• READINGS FREEMAN,
  2005
• Chapter 54 Pages
  1261-1262

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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.

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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.

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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, PCBs, Dioxin, 2-4-5 T, etc.
  

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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)

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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.

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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.

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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.

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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.

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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.
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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.
  

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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.

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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.

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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.

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Trophic Transfer, Biological Magnification and
Toxic Substances

• Pesticides, PCBs, 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.

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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)

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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.

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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.

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Global Effects of Nitrous Oxide (N2O)

• The concentration of nitrous oxide has been
  increasing in the atmosphere for the last 30-40
  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.

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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.

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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.

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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 recorded-the
  acidity of lemon juice.

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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.

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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.

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Natural Eutrophication

• Lake classification based on
• nutrient content and production
• of organic matter. Oligo- nutrient
• poor meso- middle nutrient
• eu- nutrient rich.

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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.

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Water Chemistry and Eutrophication (I)

• Eutrophication brings about changes in water
  chemistry.
• These include
• pH
• Dissolved O2
• CO2
• Ammonia
• Nitrates/Nitrites
• Phosphates

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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.

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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.

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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 gt 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 gt 1mg/l.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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The Good News

• Since the 1970s, 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.

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EUTROPHICATION, etc.

• READINGS FREEMAN,
  2005
• Chapter 54 Pages
  1261-1262