nutrient pollution and eutrophication. eutrophication lecture question –what is eutrophication?
TRANSCRIPT
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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 what’s 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
• HAB events seems to be rising (may reflect better detection)
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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 StratificationLake Ontario in 1965
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Development of Summer StratificationLake 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
– So…about oxygen depletion in eutrophic lakes? And what’s 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
Common Chemical Species in Lakes
Oxidized Forms Reduced Forms
CO2, H2CO3, HCO3-, CO3
2- CH4(g)
SO42-, HSO4
- H2S(g), HS-, S2-
NO3-, NO2
-, HNO2 N2(g), NH3(g), NH4+
MnO2(s), etc Mn2+(aq)
FeOOH(s), etc Fe2+ (aq)
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Effect of Productivity on Composition: Nitrogen
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Effect of Productivity on Composition: Phosphorus
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•How/why does the sediment release chemicals into the water under reducing (low DO) conditions?
Sediment Release: The Oxidized Microzone
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Release of Phosphorus from the Sediment• Phosphate doesn’t have a reduced form under natural conditions. So why is it released from the sediment under reducing (low DO) conditions?