1. Nutrient Pollution and Eutrophication

2. Eutrophication
Lecture Question
What is eutrophication?

3. Eutrophication
define the terms productivity and the trophic levels given above

4. Cultural Eutrophication
Lecture Question
What causes cultural eutrophication?

5. Limiting Nutrients

6. Cultural Eutrophication
Lecture Question
So what’s wrong with increased productivity?

7. Coastal HAB Events in the US

8. 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)

9. Dead Zones
Questions
What are dead zones? What are some famous dead zones?

10. Global Location of Dead Zones
Source: NASA

11. Nutrient Pollution from the Mississippi
Satellite picture shows the effect of nutrient discharge on algae levels (the green color reflects chlorophyll-a concentration)

12. 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 ( ) to 6200 mi2 ( )
Currently about 7900 mi2 (approx size of New Jersey)
Gulf of Mexico dead zone: record is 8006 sq mi (about the size of Massachusetts) in Forms in the summer. Size fluctuates depending on nutrient load and weather. Has grown from 3200 sq mi ( ) to 6200 sq mi ( ) – about doubling in area
Chesapeake has a problem with with hypoxia due to nutrients. An important input is atmospheric deposition
the entire Black Sea is completely anoxic below the pycnocline
generally: coastal areas have a real problem with nutrient pollution

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

14. Lake Stratification (Usually in Summer)
Inflection point in the thermal profile is called the thermocline.
Mixing across the thermocline is very slow.

15. Ocean Thermal Profile 3 main temperature zones:
surface ocean: warm, m
thermocline: down to ~1 km
deep ocean: cold, extends to floor

16. Lake Stratification Question
How does lake stratification occur in the summer?

17. Development of Summer Stratification
Lake Ontario in 1965
this is Lake Ontario in 1965

18. Development of Summer Stratification
Lake Ontario in 1965
full stratification develops

19. Ideal Development of Stratification in a Dimictic Lake

20. Observed Seasonal Stratification in a Lake
Measurements from Lake Lawrence (MI)

21. Seasonal Stratification in Lakes
Question
Do all lakes mix completely twice a year?

22. Types of Holomictic Lakes
holomictic lakes are lakes in which the epilimnion and hypolimnion undergo some type of mixing (ie, overturns)
meromictic lakes are permanently stratified. Often these lakes are fed by underground saline springs; the deepest water is too salty & cold (dense) to ever mix. The upper layer can undergo stratification “within” itself.
above figure shows geographic tendencies of the lake types. Many exceptions exist.
amictic lakes are perennially ice-covered
monomictic lakes undergo thermal stratification once a year. Warm monomictics undergo thermal stratification and mix freely in fall, winter and spring; cold monomictics circulate only in the summer (water temps never exceed 4 C)
polymictic lakes are characterized by frequent or continuous periods of mixing throughout the year. Further subdivided into cold and warm polymictics
oligomictic lakes are usually stratified but undergo rare irregular mixing under cooler conditions
some lakes are too shallow throughout for stratification to ever occur; they are continuously mixed.
very deep lakes are “mostly permanently” stratified, but mixing can occur every few years
mixed types (mainly varients of warm monomictic)

23. Oxygen Depletion in Eutrophic Lakes
Questions
So…about oxygen depletion in eutrophic lakes? And what’s the purpose of the aerators in Westhampton Lake?

24. Idealized Seasonal Oxygen Depletion in Dimictic Lakes

25. Oxygen Depletion in Lake Michigan
mention the aerators in Westhampton Lake. Two functions: oxygenation and circulation (ie stirring)

26. Oxygen Depletion in Eutrophic Lakes
Question
Is the hypolimnion the only part of a stratified lake that ever becomes hypoxic?

27. Idealized Diurnal Effects (Stream, Lake Epilimnion)
sudden overnight oxygen depletion can result in fishkills

28. 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

29. Effect of Productivity on Composition: Nitrogen
nitrate reduction (part of N-cycle, remember – catalyzed by microorganisms, eg in denitrification) occurs in hypolimnion
again, very idealized. In reality, nitrate levels in the epilimnion of stratified eutrophic lakes may fall to low values due to assimilation

30. Effect of Productivity on Composition: Phosphorus
release of phosphate from sediments is very significant – it constitutes an internal supply of nutrients. Basically, past nutrient (P) pollution comes back to haunt you
such internal P sources becomes more prevalent as productivity increases (positive feedback)
how does it happen? The P doesn’t change oxidation state; something else must be at work here

31. Sediment Release: The Oxidized Microzone
How/why does the sediment release chemicals into the water under reducing (low DO) conditions?

32. 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?
phosphate binds to the surface of hydrous iron (III) oxides, shown as Fe(OH)3.PO4 in the figure
basically, reductive dissolution of Fe(III) is followed by release of phosphorus. Reduction can occur due to iron-reducing bacteria or due to reaction with sulfide produced by sulfate-reducing bacteria
one way to immobilize P in lake sediment: treatment with Ca or Al, both of which bind phosphate and neither of which are reduced at typical pE values. Note, however, that both metals are mobilized by acidic conditions, so this only works well in a lake with decent alkalinity (definitely don’t want to add Al to an acidic lake – toxic!)