Factors Determining the Location of the Chlorophyll Maximum and the Fate of Algal Production within the Tidal Freshwater James River |
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| Authors: | Paul A Bukaveckas Laura E Barry Matthew J Beckwith Valerie David Brent Lederer |
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| Institution: | 1.Department of Biology and Center for Environmental Studies,Virginia Commonwealth University,Richmond,USA;2.Université La Rochelle,La Rochelle,France |
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| Abstract: | Longitudinal variation in factors affecting phytoplankton production were analyzed to better understand the mechanisms that
cause the formation of a chlorophyll maximum within the tidal freshwater James River. Phytoplankton production was two- to
threefold higher in the region where persistent elevated chlorophyll concentrations occurred. Near this site, the morphology
of the James transitions from a narrow, deep channel to a broad expanse with shallow areas adjoining the main channel. Shallower
depths resulted in greater average irradiance within the water column and suggest that release from light limitation was the
principal factor accounting for the location of the chlorophyll maximum. Grazing rates were low indicating that little of
the algal production was directly consumed by zooplankton. Low exploitation by zooplankton was attributed to poor food quality
due to high concentrations of non-algal particulate matter and potential presence of cyanobacteria. Metabolism data suggest
that two thirds of net primary production was respired in the vicinity of the chlorophyll maximum and one third was exported
via fluvial and tidal advection. Comparison of water column and ecosystem metabolism indicates that the bulk of respiration
occurred within the sediments and that sedimentation was the dominant loss process for phytoplankton. |
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