Nutrient Pollution and Eutrophication

Eutrophication• Lecture Question

– What is eutrophication?

Eutrophication

Cultural Eutrophication• Lecture Question

– What causes cultural eutrophication?

Limiting Nutrients

Cultural Eutrophication• Lecture Question

– So what’s wrong with increased productivity?

Coastal HAB Events in the US

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)

Dead Zones• Questions

– What are dead zones? What are some famous dead zones?

Global Location of Dead Zones

Source: NASA http://daac.gsfc.nasa.gov/oceancolor/scifocus/oceanColor/dead_zones.shtml

Nutrient Pollution from the Mississippi

Satellite picture shows the effect of nutrient discharge on algae levels (the green color reflects chlorophyll-a concentration)

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)

Hypoxia in Lakes• Question

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

Lake Stratification (Usually in Summer)

• Inflection point in the thermal profile is called the thermocline.

• Mixing across the thermocline is very slow.

Ocean Thermal Profile

3 main temperature zones:

•surface ocean: warm, 100-200 m

•thermocline: down to ~1 km

•deep ocean: cold, extends to floor

Lake Stratification• Question

– How does lake stratification occur in the summer?

Development of Summer StratificationLake Ontario in 1965

Development of Summer StratificationLake Ontario in 1965

Ideal Development of Stratification in a Dimictic Lake

Observed Seasonal Stratification in a Lake

Measurements from Lake Lawrence (MI)

Seasonal Stratification in Lakes

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

Types of Holomictic Lakes

mixed types (mainly varients of warm monomictic)

Oxygen Depletion in Eutrophic Lakes• Questions

– So…about oxygen depletion in eutrophic lakes? And what’s the purpose of the aerators in Westhampton Lake?

Idealized Seasonal Oxygen Depletion in Dimictic Lakes

Oxygen Depletion in Lake Michigan

Oxygen Depletion in Eutrophic Lakes• Question

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

Idealized Diurnal Effects (Stream, Lake Epilimnion)

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)

Effect of Productivity on Composition: Nitrogen

Effect of Productivity on Composition: Phosphorus

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

Sediment Release: The Oxidized Microzone

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?