An REU Experience and Research Project:

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

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

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

12. 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.

13. 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

14. 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

15. 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)

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

17. 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

18. 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

19. 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

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

21. Evidence for Photoproduction

22. Evidence for Consumption Inconsistent Trends

23. 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+

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

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

26. 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

27. Mahalo!