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Nitrogen uptake and phytoplankton growth in coastal upwelling regions

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  • Uptake of nitrogenous nutrients by microplankton off the Washington and Oregon coasts was measured during the 1985 upwelling period. Nitrogen uptake rates in low-NO3- waters (<5 μM) were 0.020–0.258 μmol N liter-1 h-1 and were primarily supported by regenerated nitrogen (71% of total uptake). Nitrogen uptake rates in high-NO3- waters (≥20 μM) were 0.281–1.480 μmol N liter-1 h-1 and new (NO3-) nitrogen supported 83% of total uptake. Phytoplankton N was estimated by assuming a constant Chl a : PN for phytoplankton and was used to calculate phytoplanktonspecific uptake rates. Despite differences in nutrient concentrations, PN and Chl a at three upwelling sites (Oregon, Benguela, and Peru), NO3- uptake normalized to Chl a, and estimates of NO-3-supported phytoplankton growth rates are remarkably similar. Nitrate uptake supports growth rates on the order of 1–2 d-1. Estimates of phytoplankton growth from rates of NH4+ + NO3- uptake range from 1.36 to 4.79 d-1 and are negatively correlated with concentrations of NO3- and phytoplankton N. The apparent increase in phytoplankton growth rates for waters with lower nitrogen availability may result from heterotrophic bacterial utilization of NH4+ nitrogen.
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  • Kokkinakis, Steven A., Wheeler, Patricia A., ( 1987), Nitrogen uptake and phytoplankton growth in coastal upwelling regions, Limnology and Oceanography, 32, doi: 10.4319/lo.1987.32.5.1112.
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  • 32
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  • 5
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  • 0024-3590
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