Nutrient Pollution and Eutrophication

Eutrophication Lecture Question What is eutrophication?

Eutrophication define the terms productivity and the trophic levels given above

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) Gulf of Mexico dead zone: record is 8006 sq mi (about the size of Massachusetts) in 2001. Forms in the summer. Size fluctuates depending on nutrient load and weather. Has grown from 3200 sq mi (1985-1992) to 6200 sq mi (1993-2001) – 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

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 Stratification Lake Ontario in 1965 this is Lake Ontario in 1965

Development of Summer Stratification Lake Ontario in 1965 full stratification develops

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 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)

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

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) sudden overnight oxygen depletion can result in fishkills

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

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

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

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

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!)