Phosphorus

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Phosphorus

• What are main forms of P in lakes and
• sediments?
• How are P and N cycles different?
• What is the iron curtain?
• How do Fe, Mn, and S cycles interact to
• control P?
• What are advantages and drawbacks to
• various P mitigation strategies?

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Nutrient Concentrations in Global Aquatic Biota
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P and Eutrophication

• Empirical relationship between P in water and
  trophic state

4
Little P loss
Big P loss
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P Cycling in Lakes
Natural Source Rock Weathering
Very Rapid Biological Cycling
Sink PIP and POP in sediments
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Seasonal P Concentrations in Epilmnion
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Forms of P in Seds

• CaCO3-bound P, authigenic P
• P bound to Fe, Mn, Oxide P
• Organic P
• Detrital P (non-reactive mineral P)
• Clay-sorbed P

8
P Release Anoxia?
Mortimer, 1941, Lake Windermere

• Lower Eh, P release
• High internal loading in anoxic lakes
• - Runaway eutrophication
• - Tropical endless summer

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The Iron Curtain
Driven by effects of Eh on metal solubility (Fe)
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Bacterial Cycles of Fe and Mn
Oxic Respiration

• Reduction (heterotrophic)

CH2O 2MnO2 4H lt--gt CO2 2Mn2 3H2O CH2O
4FeO(OH) 8H lt--gt CO2 4 Fe2 7 H2O
Denitrifying bacteria
Mn reducing bacteria
Insoluble particles Soluble
More Reducing, lower Eh
Fe reducing bacteria
Sulfate reducers
Methanogens
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Seasonal Dynamics

• Low Fe, Mn in epilimnion
• Buildup in anoxic hypolimnion first of Mn, then
  Fe
• Oxidation during overturn

Mn
Fe
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Sulfur

• Essential nutrient amino acids, enzymes
• Sources Rock weathering, aerosols, rainfall,
  delivered to lakes as SO42-
• Oxidation states -2 --gt 6

Sulfate reduction/sulfide oxidation 2CH2O SO42-
? 2HCO3- H2S
Sulfurized Organic Matter
Reoxidation H2S O2 ? SO42- 2H
FeS, FeS2
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Caraco, 1993
FeO(OH)-PO4 Fe3(PO4)2
FeS

• Microbial SO42- reduction to S2-, reacts with
  reduced Fe2 to FeS
• Decrease FeP ratio, low rates of P binding

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High O2
No O2
P
P
SO4 rich SO4 poor
Suplee and Cotner, In press
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Whole-lake P Dynamics
P
Anoxic
P sink
Oxidized Fe P sink
P source
Sediments
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P and Lake Management
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N, P, and Lake Management

• Increasing P causes shifts to N-fixing
  cyanobacterial
• P much easier to manipulate than N, focus of
  control of eutrophication
• Control strategies?

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P Remediation
Lake Washington P abatement
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Conclusions

• Phosphorus is often limiting nutrient in lakes,
  controls lake productivity and algal species
  abundances
• P is delivered by rock weathering and is lost via
  precipitation of Fe, Ca, Al, OM sedimentation
• P cycling in water column is extremely rapid,
  involves exchanges between DOP, algae, zoops, and
  bacteria
• Internal P loading is controlled largely by Redox
  interactions, particularly Fe and S, and
  secondarily by benthic biota
• Anthropogenic PO4 addition has severely affected
  many lakes oxygenation, alum treatment, and
  point-source mitigation have all been used to
  treat P