EUTROPHICATION

• Eutrophication is the accumulation of nutrients in aquatic ecosystems.

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Eutrophication

• It alters the dynamics of a number of plant, animal and bacterial populations; thus, bringing about changes in community structure.

Eutrophication - 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 harm our environment.
• A pollutant is any matter or energy introduced by human activities that produces harmful effects on resident populations thus altering community structure.

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.

Steps to Eutrophication

1. Untreated sewage, fertilizers, manure, of other sources of excess organic matter are added to aquatic ecosystems.

2. Algal Blooms: Excess limiting nutrients results in exponential growth of algae.

Toxic Algal Blooms

Blue-green algae (Cyanobacteria) replaces green algae

Blue-green algae

Green algae

lake erie HAB

3. Algae die and are decomposed by bacteria in the ecosystem. Bacteria grow exponentially.

4. Hypoxia: Bacteria deplete dissolved oxygen in the water.

Low Oxygen Levels Cause Die-off

• Rapidly growing bacterial populations need exponentially increasing amounts of oxygen.

5. Once dissolved oxygen levels become too low, fish and many freshwater invertebrates die, thus adding more organic matter.

6. Dead Zone - the ecosystem collapses as most life disappears as oxygen is used by decomposing bacteria,

Oxygen Depleted Waters

• As oxygen disappears, anaerobic bacteria produce methane, hydrogen sulfide and ammonia.
• Bacterial respiration increases carbonic acid.
• 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.

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READINGS:� FREEMAN, 2005

Chapter 54� Pages 1261-1262

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