Variable climatic conditions dominate recent phytoplankton dynamics in Chesapeake Bay

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  • Harding, Lawrence W.
    • Other Affiliation: Department of Atmospheric and Oceanic Sciences; University of California; Los Angeles
  • Mallonee, Michael E.
    • Other Affiliation: Interstate Commission on the Potomac River Basin; United States Environmental Protection Agency Chesapeake Bay Program Office
  • Perry, Elgin S.
    • Other Affiliation: Statistics Consultant
  • Miller, W. David
    • Other Affiliation: US Naval Research Laboratory
  • Adolf, Jason E.
    • Other Affiliation: Marine Science Program; University of Hawaii at Hilo
  • Gallegos, Charles L.
    • Other Affiliation: Smithsonian Environmental Research Center
  • Paerl, Hans W.
    • Affiliation: University of North Carolina at Chapel Hill
Abstract
  • Variable climatic conditions strongly influence phytoplankton dynamics in estuaries globally. Our study area is Chesapeake Bay, a highly productive ecosystem providing natural resources, transportation, and recreation for nearly 16 million people inhabiting a 165,000-km2 watershed. Since World War II, nutrient over-enrichment has led to multiple ecosystem impairments caused by increased phytoplankton biomass as chlorophyll-a (chl-a). Doubled nitrogen (N) loadings from 1945–1980 led to increased chl-a, reduced water clarity, and low dissolved oxygen (DO), while decreased N loadings from 1981–2012 suggest modest improvement. The recent 30+ years are characterized by high inter-annual variability of chl-a, coinciding with irregular dry and wet periods, complicating the detection of long-term trends. Here, we synthesize time-series data for historical and recent N loadings (TN, NO2 + NO3), chl-a, floral composition, and net primary productivity (NPP) to distinguish secular changes caused by nutrient over-enrichment from spatio-temporal variability imposed by climatic conditions. Wet years showed higher chl-a, higher diatom abundance, and increased NPP, while dry years showed lower chl-a, lower diatom abundance, and decreased NPP. Our findings support a conceptual model wherein variable climatic conditions dominate recent phytoplankton dynamics against a backdrop of nutrient over-enrichment, emphasizing the need to separate these effects to gauge progress toward improving water quality in estuaries.
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  • Article
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  • In Copyright
Journal title
  • Scientific Reports
Journal volume
  • 6
Journal issue
  • 1
Language
  • English
ISSN
  • 2045-2322

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