Nutrient Pollution and Eutrophication

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Nutrient Pollution and Eutrophication
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Eutrophication

• Lecture Question
• What is eutrophication?

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Eutrophication
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Cultural Eutrophication

• Lecture Question
• What causes cultural eutrophication?

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Limiting Nutrients
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Cultural Eutrophication

• Lecture Question
• So whats wrong with increased productivity?

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Coastal HAB Events in the US
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HAB Effects on Humans

• Amnesia Shellfish Poisoning
• Toxin domoic acid (can be fatal)
• GI and neurological disorders
• Symptoms nausea, vomiting, abdominal cramps,
  diarrhea
• Severe cases include neurological symptoms
  headache, dizziness, seizures, disorientation,
  memory loss, respiratory difficulty, coma
• Ciguatera Fish Poisoning
• Toxins ciguatoxin/maitotoxin (usually not fatal)
• GI, neurological and CV symptoms
• Diarrhetic Shellfish Poisoning
• Toxin okadaic acid (not fatal)
• GI symptoms
• Neurotoxic Shellfish Poisoning
• Toxins brevetoxins (not fatal)
• Syndrome almost identical to ciguatera poisoning
  but slightly less severe
• Paralytic Shellfish Poisoning
• Toxins saxitoxins (can be fatal)
• Rapid neurological symptoms
• Tingling, numbness, burning, drowsiness, etc
• Respiratory arrest can occur within 24 hours

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Dead Zones

• Questions
• What are dead zones? What are some famous dead
  zones?

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Global Location of Dead Zones
Source NASA http//daac.gsfc.nasa.gov/oceancolor/
scifocus/oceanColor/dead_zones.shtml
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Nutrient Pollution from the Mississippi
Satellite picture shows the effect of nutrient
discharge on algae levels (the green color
reflects chlorophyll-a concentration)
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Formation of Gulf Dead Zone

• Gulf of Mexico Dead Zone forms every summer
• When the algae die they settle to the bottom and
  begin degrading (and consuming oxygen)
• Oxygen is depleted (mostly below the pycnocline)
  creating the dead zone
• The dead zone has grown in size from 3200 mi2
  (1985-1991) to 6200 mi2 (1993-2001)
• Currently about 7900 mi2 (approx size of New
  Jersey)

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Hypoxia in Lakes

• Question
• How exactly does hypoxia (low oxygen conditions)
  develop in the bottoms of lakes in response to
  eutrophication?

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Lake Stratification (Usually in Summer)

• Inflection point in the thermal profile is called
  the thermocline.
• Mixing across the thermocline is very slow.

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Ocean Thermal Profile

• 3 main temperature zones
• surface ocean warm, 100-200 m
• thermocline down to 1 km
• deep ocean cold, extends to floor

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Lake Stratification

• Question
• How does lake stratification occur in the summer?

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Development of Summer Stratification
Lake Ontario in 1965
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Development of Summer Stratification
Lake Ontario in 1965
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Ideal Development of Stratification in a Dimictic
Lake
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Observed Seasonal Stratification in a Lake
Measurements from Lake Lawrence (MI)
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Seasonal Stratification in Lakes

• Question
• Do all lakes mix completely twice a year?

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Types of Holomictic Lakes
mixed types (mainly varients of warm monomictic)
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Oxygen Depletion in Eutrophic Lakes

• Questions
• Soabout oxygen depletion in eutrophic lakes? And
  whats the purpose of the aerators in Westhampton
  Lake?

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Idealized Seasonal Oxygen Depletion in Dimictic
Lakes
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Oxygen Depletion in Lake Michigan
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Oxygen Depletion in Eutrophic Lakes

• Question
• Is the hypolimnion the only part of a stratified
  lake that ever becomes hypoxic?

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Idealized Diurnal Effects (Stream, Lake
Epilimnion)
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Effects of Oxygen Depletion on Chemical
Composition?

• Low DO favors reduced species
• Release of chemicals from sediment in reduced
  form
• Reduced form of many chemicals are more mobile
  than their oxidized form
• Release of gases methane (CH4), hydrogen sulfide
  (H2S), ammonia (NH3)
• smelly!
• Release of some toxic metals
• Release of nutrients from sediment
• Increases effectiveness of nutrient recycling
• Feedback loop leading to further algae blooms,
  eutrophication

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Effect of Productivity on Composition Nitrogen
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Effect of Productivity on Composition Phosphorus
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Sediment Release The Oxidized Microzone

• How/why does the sediment release chemicals into
  the water under reducing (low DO) conditions?

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Release of Phosphorus from the Sediment

• Phosphate doesnt have a reduced form under
  natural conditions. So why is it released from
  the sediment under reducing (low DO) conditions?