Production and Partitioning of Organic Matter during Simulated Phytoplankton Blooms

• Published in: Limnology and oceanography 2003-09, Vol.48 (5), p.1808-1817
• Main Authors: Wetz, Michael S., Wheeler, Patricia A.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Carbon; Chaetoceros; Diatoms; Fundamental and applied biological sciences. Psychology; Leptocylindrus minimus; Marine; Nitrates; Nitrogen; Oceans; Particulate matter; Phytoplankton; Sea water; Sea water ecosystems; Standard deviation; Synecology; Upwelling water
• ISSN: 0024-3590; 1939-5590
• DOI: 10.4319/lo.2003.48.5.1808

Few studies have examined the partitioning of organic matter in upwelling systems, despite the fact that these systems play a key role in carbon and nitrogen budgets in the ocean. We examined the production and partitioning of phytoplankton-derived organic matter in deck incubations off Oregon during the upwelling season. During exponential growth of the phytoplankton, ≥78% of total accumulated organic matter was in particulate (POM) form. This suggests that dissolved organic matter (DOM) is a small fraction of primary production during the exponential growth of coastal phytoplankton blooms. After nitrate depletion, carbon-rich (C: N ≥ 16) DOM accumulated in incubations dominated by the diatom Chaetoceros sp., accounting for 38% (±8.5%) of accumulated total organic carbon (TOC) and 24% (±8%) of accumulated total organic nitrogen (TON). However, in a bloom dominated by the diatom Leptocylindrus minimus, a relatively smaller amount of DOM accumulated, accounting for only 15% of accumulated TOC and 7% of accumulated TON. On the basis of measured concentrations of nitrate and accumulated TOC, ∼70%-157% more carbon was fixed than would be predicted by Redfield stoichiometry (referred to as "excess carbon fixation"), with 20%-69% of the excess carbon fixation occurring after nitrate depletion. The accumulation of carbon-rich DOM and excess carbon fixation suggests that nitrate assimilation (i.e., new production) might not equate to net production of POM in coastal upwelling systems.