Vertical stratification of phytoplankton biomass in a deep estuary site: implications for satellite-based net primary productivity

The accuracy of satellite estimates for water column net primary productivity (NPP) are contingent upon the reliability of surface phytoplankton biomass, specifically chlorophyll a (Chl. a ) and carbon (C phyt ), as indicators of euphotic biomass and photosynthetic rate. We assessed patterns in wate...

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Bibliographic Details
Published in:	Frontiers in Marine Science 2024-01, Vol.10
Main Authors:	Gall, Mark, Zeldis, John, Safi, Karl, Wood, Simon, Pinkerton, Matthew
Format:	Article
Language:	eng
Subjects:	Accuracy Algorithms Biomass Chemical stratification Chlorophyll Chlorophyll a Coastal zone Coasts Continental shelves Estuaries Estuarine dynamics Euphotic zone Instrumentation interannual variability Light MODIS-aqua New Zealand Nutrient deficiencies Nutrient deficiency Nutrient enrichment Nutrients Optical properties phenology Photosynthesis Physiology Phytoplankton Plankton Primary production Productivity Rivers Satellites seasonal patterns Seasonal variations Stratification Summer Surface water Vertical distribution VGPM Water column
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Summary:	The accuracy of satellite estimates for water column net primary productivity (NPP) are contingent upon the reliability of surface phytoplankton biomass, specifically chlorophyll a (Chl. a ) and carbon (C phyt ), as indicators of euphotic biomass and photosynthetic rate. We assessed patterns in water column biomass at a deep estuary site (~40 m) in the Firth of Thames, Hauraki Gulf, New Zealand, using ten years (2005-2015) of in situ sampling (40 seasonal voyages and moored instrumentation). Seasonal biomass stratification coincided with physical and chemical stratification and exhibited a reasonable predictability based on surface Chl. a measures from mooring timeseries. High Chl. a (but not C phyt ) accumulated from late-spring (Nov.) in the lower portion of the water column, under nutrient deficient, clear surface water with deep euphotic zone conditions, peaking in mid-summer (Jan.) and ending by early autumn (Mar.). Satellite (MODIS-Aqua) NPP (2002-2018), was estimated with and without correction for deep biomass in two vertically generalized production models (Chl. a -VGPM and C phyt -CbPM). Mean annual NPP (220-161 g C m -2 y -1 , VGPM and CbPM respectively) increased 5-18% after accounting for euphotic zone deep biomass with a mid-summer maxim (Jan.: 30-33%). Interannual anomalies in biomass and NPP (about -10% to 10%) were an order of magnitude greater than small decreasing trends (
ISSN:	2296-7745 2296-7745