HR: 0800h
AN: OS11B-0502    [Abstracts]
TI: Organic nutrient enrichment in the oligotrophic ocean: Impacts on remineralization, carbon sequestration, and community structure
AU: * Mackey, K R
EM: kmackey@stanford.edu
AF: Department of Civil and Environmental Engineering, Stanford University, Terman Engineering Bldg, Stanford, CA 94305, United States
AU: Paytan, A
EM: apaytan@ucsc.edu
AF: Institute of Marine Science, University of California Santa Cruz, UCSC, Santa Cruz, CA 95064, United States
AU: Post, A F
EM: apost@mbl.edu
AF: H. Steinitz Marine Biology Laboratory, The Interuniversity Institute of Marine Sciences POB 469, Eilat, 88103, Israel
AB: In oligotrophic seas where inorganic nitrogen (N) and phosphorus (P) are below the limits of detection, organic forms of these nutrients may constitute greater than 90% of the total N and P in the euphotic zone. The combined enzymatic activity of phytoplankton and heterotrophic bacteria determines the rate of nutrient remineralization, thereby influencing phytoplankton growth rates and carbon sequestration in these regions. In this study we investigated the effects of fertilization with ammonium (NH₄), nitrate (NO₃), nitrite (NO₂), and phosphate (PO₄) as well as various forms of organic N (urea, glycine) and P (deoxyribonucleic acid, 2- aminoethyl phosphonic acid, phytic acid) on the growth and taxonomic composition of the phytoplankton community in the Gulf of Aqaba, Red Sea. The impacts of these changes on nutrient cycling and biological assimilation were also assessed. Organic N additions led to phytoplankton growth when given together with PO₄, yielding 2-3 fold increases in chlorophyll a (Chl a) and cell density relative to initial levels. Moreover, our results show that addition of NH₄ or NO₃ led to accumulation of extra-cellular NO₂, suggesting that incomplete assimilatory reduction of NO₃ by phytoplankton as well as chemoautotrophic oxidation of NH₄ by ammonium oxidizing microbes contributed to NO₂ formation. These findings conflict with earlier studies in the Gulf that attributed NO₂ formation solely to the phytoplankton community. Organic P additions also led to 2-3 fold increases in Chl a and cell density relative to initial levels when given together with NH₄ and NO₃. Compared to other P additions, DNA led to the rapid accumulation of extra-cellular PO₄, indicating substantial nucleotidase activity in excess of the amount needed to meet phytoplankton growth requirements. These results show the importance and interconnectivity of phytoplankton and heterotrophic bacteria communities in contributing to nutrient cycling and carbon sequestration in oligotrophic marine regions.
DE: 0419 Biomineralization
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4806 Carbon cycling (0428)
DE: 4815 Ecosystems, structure, dynamics, and modeling (0439)
DE: 4845 Nutrients and nutrient cycling (0470, 1050)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting