Microbial ammonium cycling in the Mississippi River plume during the drought spring of 2000
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چکیده
Microbial potential uptake and regeneration rates of ammonium (NH4 ) were studied along a salinity gradient (salinities 0.2–34.4) in the Mississippi River plume during an extreme drought in spring 2000. Chlorophyll concentrations up to 30 g L 1 were highest in the lowand mid-salinity regions (salinities 8.5–28.2) and comparable to records of other years but extended over smaller areas than during periods of normal river flow. Bacterial biomass (5.1–28.3 g C L ) was at the low end of the range observed in normal flow years, decreased with distance from the river mouth and did not peak with chlorophyll. Heterotrophic nanoflagellate abundance (1.4–4.0 g C L ) did not reflect phytoplankton and bacterial spatial distribution but peaked at 9.2 g C L 1 at salinity 8.5. Microbial NH4 +
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