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Photolysis of DOM from Marine Cyanobacteria in the Gulf of Mexico

This project investigates the photolytic transformation of dissolved organic matter (DOM) produced by Trichodesmium, a marine cyanobacteria, in the Gulf of Mexico. The research aims to quantify the rates of NH4+, NO2-, DPA, and PO43- photoproduction from filtered seawater with Trichodesmium DOM compared to controls. Experiments included various incubation conditions, chemical analyses, and examination of nutrient dynamics. Results suggest variable trends in nutrient photoproduction, highlighting the role of DOM in influencing nutrient availability for phytoplankton within the marine biogeochemical cycle.

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Photolysis of DOM from Marine Cyanobacteria in the Gulf of Mexico

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  1. An REU Experience and Research Project: Photolysis of DOM Produced by a Marine Cyanobacteria in the Gulf of Mexico by Michael D’Amico

  2. ? ? Karenia Brevis HAB’s Trichodesmium

  3. Photoproduction of Labile Substrates from Dissolved Organic Matter Produced by Trichodesmium Michael D’Amico Mentored by Dr. Deborah Bronk & Marta Sanderson

  4. DOM Phytoplankton Trichodesmium Bloom NH4+ NO2- DPA PO43- Processes of photochemical transformation of DOM play an important part in the global marine biogeochemical cycle.

  5. Goal: • To quantify rates of DOM photoproduction of NH4+, NO2-, DPA, and PO43- in filtered sea water and water containing DOM produced by Trichodesmium. • Hypothesis: • Water withTrichodesmium DOM will have higher rates of photoproduction than those without.

  6. 0.2µm filtered seawater from chlorophyll max Sea Water + Trichodesmium DOM Sea Water Quartz Dark Quartz Dark Incubated in flow through seawater tub At 3 hrs. and dusk (~12 hrs.) samples from each bottle were collected This was done for two experiments in the Gulf of Mexico

  7. Trichodesmium DOM 2 days prior to each experiment, • Plankton tows using a 64μm mesh net at 10m for 10 minutes collected Trichodesmium. • Approx. 1000 colonies of Trichodesmium were incubated in 0.2μm Supor filtered seawater for 24 hours. • At 24 hours, the water containing Trichodesmium was filtered through a 0.2μm Supor filter, and refrigerated overnight

  8. Chemical Analyses • NH4+ concentrations and PO43-concentrations: • spectrophotometer • Grasshoff et al. (1983) colorimetric. • NO2- concentrations: • Alpkem Flow Solution IV nutrient autoanalyzer • Parsons et al. (1984) • DPA concentrations: • Spectrofluorophotometer • Parsons et al. (1984)

  9. Photoproduction and consumption occur NH4+ Photoproduction/balance between consumption occurs PO43- photoproduction occurs NO2- is consumed DPA concentrations showed no trends

  10. NH4+ concentrations Ambient Dark Quartz Ambient w/DOM Dark w/DOM Quartz w/DOM • P1 Seawater*: • Consumption in dark • Minor consumption in quartz • P1 DOM water*: • Photoproduction @3h • And @12h • P2 Seawater*: • Consumption in dark • Minor Consumption in quartz • P2 DOM water*: • Consumption in dark • Minor consumption in quartz

  11. NO2- concentrations Ambient Dark Quartz Ambient w/DOM Dark w/DOM Quartz w/DOM • P1 Seawater*: • Photoproduction @3h? Not @12h • Quartz Consumption • P1 DOM water*: • No Photoproduction • Quartz Consumption • P2 Seawater: • No Photoproduction • Quartz Consumption • P2 DOM water: • No Photoproduction • Quartz Consumption

  12. PO43-concentrations Ambient Dark Quartz Ambient w/DOM Dark w/DOM Quartz w/DOM • P1 Seawater: • Photoproduction @3h • And @12h • P1 DOM water*: • Photoproduction @3h • And @12h • P2 Seawater: • No Photoproduction • P2 DOM water: • Photoproduction @3h • And @12h

  13. DPA concentrations Ambient Dark Quartz Ambient w/DOM Dark w/DOM Quartz w/DOM • DPA: No consistent • trends observed

  14. Evidence for Photoproduction

  15. Evidence for Consumption Inconsistent Trends

  16. Conclusions • NH4+: • increasing concentrations in quartz tubes • decreasing concentrations in dark tubes • Quartz: NH4+ photoproduction • Or • Balance between consumption and production • Dark: NH4+ consumption • Humics absorb NH4+

  17. Conclusions • NO2-: • decreasing concentrations in quartz tubes • Quartz: NO2- consumption • Photolysis of NO2- in sea water: • NO2- + hv→ NO + O-

  18. Conclusions • PO43-: • increasing concentrations in quartz tubes • Quartz: PO43- photoproduction DPA ???????

  19. Phytoplankton Trichodesmium Bloom NH4+ NO2- DPA PO43- • Hypothesis: The treatments that added water with Trichodesmium DOM will have higher rates of photoproduction than those without. • General Trends show yes in some cases • Not true in all cases Importance: Photoproduction of labile substrates from DOM influences the availability of nutrients to phytoplankton DOM

  20. Mahalo!

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