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During a 3-yr study in the Gulf of Mexico, we measured dinitrogen (N 2) fixation and nitrogen (N) release by Trichodesmium and compared these rates with water column N demand and the estimated N necessary to support blooms of Karenia brevis, a toxic dinoflagellate that severely affects the West Florida shelf. Net and gross N 2 fixation rates were compared(More)
In oceanic, coastal, and estuarine environments, an average of 25 to 41 percent of the dissolved inorganic nitrogen (NH(4) (+) and NO(3) (-)) taken up by phytoplankton is released as dissolved organic nitrogen (DON). Release rates for DON in oceanic systems range from 4 to 26 nanogram-atoms of nitrogen per liter per hour. Failure to account for the(More)
Ž. Ž. Ž. We compared the persulfate PO , ultraviolet UV , and high temperature oxidation HTO methods used to analyze total Ž. dissolved nitrogen TDN concentrations in aquatic samples to determine whether the three methods differed in terms of Ž. standard parameters blanks, limits of detection and linearity, and precision or in oxidation efficiency of(More)
Humic substances are a collection of colored organic acids characterized by high molecular weight and low nitrogen (N) content that are thought to be biologically recalcitrant. We examined a suite of nonaxenic estuarine phytoplankton isolates to determine their ability to take up 15 N-labeled humic substances formed in the laboratory and supplied as the(More)
This research addresses the hypothesis that environmental conditions affect temporal connectivity between daily transcription of ribulose-1,5 bisphosphate carboxylase/oxygenase (Rubisco) genes and photosynthetic capacity among phytoplankton. From surface samples collected in the Mississippi River plume (MRP) and Orinoco River plume (ORP), we made(More)
Seasonal and interannual variation of the stable carbon (C) and nitrogen (N) isotope composition of suspended particulate organic matter (POM) was measured in the brackish and tidal freshwater regions of the Mattaponi River, a tributary of the York River, Virginia, and a pristine end member on a continuum of anthropogenic modification within Chesapeake Bay.(More)
The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively(More)