Intra-annual variability of water quality and phytoplankton in the North Fork of the St. Lucie River Estuary, Florida (USA): A quantitative assessment

D. F. Millie, H. J. Carrick, P. H. Doering, K. A. Steidinger

Research output: Contribution to journalArticlepeer-review

28 Scopus citations

Abstract

Water quality and phytoplankton were examined within the North Fork of the St. Lucie River Estuary, Florida (USA) from March 2000 to March 2001. Alterations in water-quality parameters and phytoplankton assemblages mirrored salinity regimes resulting from the 'wet'/'dry' seasonality of south Florida. Salinity was greatest during the 'dry', winter months whereas water temperature and nitrogen and phosphorus concentrations were greatest during the 'wet', summer months. A seasonal dissimilarity in phytoplankton occurred; cell abundance of cyanobacterial picoplankton (Synechocystis sp., Synechococcus sp.) and a diatom (Skeletonema costatum (Greville) Cleve) and cell carbon of a dinoflagellate (Gyrodinium sp.) and S. costatum were greatest during summer whereas abundance of chrysophytes (Chrysochromulina parva Lackey, Chromulina sp.) and carbon of dinoflagellates (Gymnodinium spp., Heterocapsa rotundata (Lohmann) Hansen) and a diatom (Cyclotella sp.) were greatest during winter. Water-column chlorophyll a concentrations reached up to 29μgL-1 and were negatively associated with salinity. Diatom chlorophyll comprised the majority and at times, greater than 90% of the total chlorophyll a. Picoplanktonic cyanobacteria comprised up to 5% and 1.4% of total phytoplankton carbon and chlorophyll a, respectively throughout the estuary; as such, its impact on overall assemblage rate processes and system-level function appeared minimal. Sediment and whole-water incubations confirmed the presence of heterotrophic dinoflagellates within the estuary. Dissolved oxygen concentrations did not correspond with total chlorophyll a concentrations and salinity, indicating that hypoxia within bottom waters during summer was not solely attributable to phytoplankton biomass or water-column stratification but likely, a result of multiple, interacting physical/chemical and biological factors.

Original languageEnglish
Pages (from-to)137-149
Number of pages13
JournalEstuarine, Coastal and Shelf Science
Volume61
Issue number1
DOIs
StatePublished - Sep 2004

Keywords

  • estuaries
  • hypoxia
  • microalgae
  • nutrients
  • picoplankton
  • seasonal
  • south Florida

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