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

Karenia Brevis HAB’s Trichodesmium ? ?

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

Processes of photochemical transformation of DOM play an important part in the global marine biogeochemical cycle. DOM Phytoplankton NH 4 + NO 2 - DPA PO 4 3- Trichodesmium Bloom

Hypothesis:Hypothesis: Water withTrichodesmium DOM will have higher rates of photoproduction than those without. Goal:Goal: To quantify rates of DOM photoproduction of NH 4 +, NO 2 -, DPA, and PO 4 3- in filtered sea water and water containing DOM produced by Trichodesmium.

0.2µm filtered seawater from chlorophyll max 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 Sea Water Sea Water + Trichodesmium DOM Quartz Dark

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

Chemical Analyses NH 4 + concentrations and PO 4 3- concentrations: spectrophotometerspectrophotometer Grasshoff et al. (1983) colorimetric.Grasshoff et al. (1983) colorimetric. NO 2 - concentrations: Alpkem Flow Solution IV nutrient autoanalyzerAlpkem Flow Solution IV nutrient autoanalyzer Parsons et al. (1984)Parsons et al. (1984) DPA concentrations: SpectrofluorophotometerSpectrofluorophotometer Parsons et al. (1984)Parsons et al. (1984)

Photoproduction and consumption occur NH 4 + Photoproduction/balance between consumption occurs PO 4 3- photoproduction occurs NO 2 - is consumed DPA concentrations showed no trends

P1 Seawater*:P1 Seawater*: Consumption in dark Minor consumption in quartz P1 DOM water*:P1 DOM water*: P2 Seawater*:P2 Seawater*: Consumption in dark Minor Consumption in quartz P2 DOM water*:P2 DOM water*: Consumption in dark Minor consumption in quartz NH 4 + concentrations Ambient Dark Quartz Ambient w/DOM Dark w/DOM Quartz w/DOM

P1 Seawater*:P1 Seawater*: Quartz Consumption P1 DOM water*:P1 DOM water*: No Photoproduction Quartz Consumption P2 Seawater:P2 Seawater: No Photoproduction Quartz Consumption P2 DOM water:P2 DOM water: No Photoproduction Quartz Consumption NO 2 - concentrations Ambient Dark Quartz Ambient w/DOM Dark w/DOM Quartz w/DOM

P1 Seawater:P1 Seawater: P1 DOM water*:P1 DOM water*: P2 Seawater:P2 Seawater: No Photoproduction P2 DOM water:P2 DOM water: Ambient Dark Quartz Ambient w/DOM Dark w/DOM Quartz w/DOM PO 4 3- concentrations

DPA: No consistentDPA: No consistent trends observed trends observed Ambient Dark Quartz Ambient w/DOM Dark w/DOM Quartz w/DOM DPA concentrations

Evidence for Photoproduction Estuary NH 4 +, DPA Bushaw-Newton and Moran (1999) Estuary NH 4 + Bushaw et al. (1996) Groundwater, Estuaries NH 4 + Koopmans and Bronk (2002) Coastal Waters NO 2 - Kieber et al. (1999) Lake Water PO 4 3- Francko and Heath (1982) Lake Water PO 4 3- Vähätalo and Salonen (1996)

Evidence for Consumption Inconsistent Trends Estuary NH 4 + Bushaw-Newton and Moran (1999) Estuary NH 4 + Bushaw et al. (1996) Groundwater, Estuaries NH 4 + Koopmans and Bronk (2002) Natural Waters NO 2 - Jankowski et al. (1999) Natural Waters NO 2 - Jorgensen et al. (1998, 1999) Lake Water NO 2 - Vähätalo and Salonen (1996) Groundwater, Estuaries NO 2 -, DPA Koopmans and Bronk (2002) Diatom Culture PO 4 3- Gobler et al. (1997) Fresh Water Lake PO 4 3- Jorgensen et al. (1998)

Conclusions NH 4 + : increasing concentrations in quartz tubesincreasing concentrations in quartz tubes decreasing concentrations in dark tubesdecreasing concentrations in dark tubes Quartz: NH 4 + photoproductionQuartz: NH 4 + photoproduction Or Or Balance between consumption and production Balance between consumption and production Dark: NH 4 + consumptionDark: NH 4 + consumption Humics absorb NH 4 +

Conclusions NO 2 - : decreasing concentrations in quartz tubesdecreasing concentrations in quartz tubes Quartz: NO 2 - consumptionQuartz: NO 2 - consumption Photolysis of NO 2 - in sea water: NO h v → NO + O - NO h v → NO + O -

Conclusions PO 4 3- : increasing concentrations in quartz tubesincreasing concentrations in quartz tubes Quartz: PO 4 3- photoproductionQuartz: PO 4 3- photoproduction DPA ???????

Trichodesmium Bloom Phytoplankton NH 4 + NO 2 - DPA PO 4 3- Importance: Photoproduction of labile substrates from DOM influences the availability of nutrients to phytoplankton DOM Hypothesis: The treatments that added water with Trichodesmium DOM will have higher rates of photoproduction than those without.Hypothesis: The treatments that added water with Trichodesmium DOM will have higher rates of photoproduction than those without. General Trends show yes in some casesGeneral Trends show yes in some cases Not true in all casesNot true in all cases

Mahalo!