Phytoplankton reference communities for Chesapeake Bay and its tidal tributaries |
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Authors: | Claire Buchanan Richard V Lacouture Harold G Marshall Marcia Olson Jacqueline M Johnson |
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Institution: | 1. Interstate Commission on the Potomac River Basin, 51 Monroe Street, PE-08, 20850, Rockville, Maryland 2. Estuarine Research Center, Morgan State University, 10545 Mackall Road, 20685, St. Leonards, Maryland 3. Department of Biological Sciences, Old Dominion University, 23529-0266, Norfolk, Virginia 4. Chesapeake Bay Office, National Oceanographic and Atmospheric Administration, 410 Severn Avenue, Suite 107A, 21403, Annapolis, Maryland 5. Interstate Commission on the Potomac River Basin, Environmental Protection Agency, Chesapeake Bay Program, 410 Severn Avenue, Suite 109, 21403, Annapolis, Maryland
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Abstract: | Phytoplankton reference communities for Chesapeake Bay were quantified from least-impaired water quality conditions using
commonly measured parameters and indicators derived from measured parameters. A binning approach was developed to classify
water quality. Least-impaired conditions had relatively high water column transparency and low concentrations of dissolved
inorganic nitrogen and orthophosphate. Reference communities in all seasons and salinity zones are characterized by consistently
low values of chlorophylla and pheophytin coupled with relative stable proportions of the phytoplankton taxonomic groups and low biomasses of key bloom-forming
species. Chlorophyll cell content was lower and less variable and average cell size and seasonal picophytoplankton biomass
tended to be greater in the mesohaline and polyhaline reference communities as compared to the impaired communities. Biomass
concentrations of the nano-micro phytoplankton size fractions (2–200 μm) in 12 of the 16 season-specific and salinity-specific
reference communities were the same or higher than those in impaired habitat conditions, suggesting that nutrient reductions
will not decrease the quantity of edible phytoplankton food available to large consumers. High (bloom) and low (bust) biomass
events within the impaired phytoplankton communities showed strikingly different chlorophyll cell content and turnover rates.
Freshwater flow had little effect on phytoplankton responses to water quality condition in most of the estuary. Improved water
column transparency, or clarity, through the reduction of suspended sediments will be particularly important in attaining
the reference communities. Significant nitrogen load reductions are also required. |
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