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Phosphorus

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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Phosphorus

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  1. 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?

  2. Nutrient Concentrations in Global Aquatic Biota

  3. P and Eutrophication • Empirical relationship between [P] in water and trophic state

  4. Little P loss Big P loss

  5. P Cycling in Lakes Natural Source: Rock Weathering Very Rapid Biological Cycling Sink: PIP and POP in sediments

  6. Seasonal P Concentrations in Epilmnion

  7. 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”

  9. The Iron Curtain Driven by effects of Eh on metal solubility (Fe)

  10. Bacterial Cycles of Fe and Mn Oxic Respiration Reduction (heterotrophic) Denitrifying bacteria CH2O + 2MnO2 + 4H+ <--> CO2 + 2Mn2+ + 3H2O CH2O + 4FeO(OH) + 8H+ <--> CO2 + 4 Fe2+ + 7 H2O Mn reducing bacteria Insoluble particles Soluble More Reducing, lower Eh Fe reducing bacteria Sulfate reducers Methanogens

  11. PO4 Seasonal Dynamics Mn • Low Fe, Mn in epilimnion • Buildup in anoxic hypolimnion first of Mn, then Fe • Oxidation during overturn Fe

  12. Sulfur • Essential nutrient: amino acids, enzymes • Sources: Rock weathering, aerosols, rainfall, delivered to lakes as SO42- • Oxidation states: -2 --> +6 Sulfate reduction/sulfide oxidation 2CH2O + SO42-  2HCO3- +H2S Sulfurized Organic Matter Reoxidation H2S + O2  SO42- +2H+ FeS, FeS2

  13. Caraco, 1993 • Microbial SO42- reduction to S2-, reacts with reduced Fe2+ to FeS • Decrease Fe:P ratio, low rates of P binding FeO(OH)-PO4 Fe3(PO4)2 FeS

  14. High O2 No O2 High O2 No O2 P P SO4 rich SO4 poor Suplee and Cotner, In press

  15. Whole-lake P Dynamics P Anoxic P sink Oxidized Fe P sink P source Sediments

  16. P and Lake Management

  17. 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?

  18. P Remediation Lake Washington P abatement

  19. 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

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