Relative effects of physical and biological processes on nutrient and phytoplankton dynamics in a shallow estuary after a storm event |
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Authors: | Stephanie K Moore Mark E Baird Iain M Suthers |
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Institution: | 1. Fisheries and Marine Environmental Research Laboratory, School of Biological, Earth and Environmental Sciences, University of New South Wales, 2052, Sydney, New South Wales, Australia 3. Centre for Environmental Modelling and Prediction, School of Mathematics, University of New South Wales, 2052, Sydney, New South Wales, Australia
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Abstract: | The effects of advection, dispersion, and biological processes on nitrogen and phytoplankton dynamics after a storm event
in December 2002 are investigated in an estuary located on the northern New South Wales coast, Australia. Salinity observations
for 16 d after the storm are used to estimate hydrodynamic transports for a one-dimensional box model. A biological model
with nitrogen limited phytoplankton growth, mussel grazing, and a phytoplankton mortality term is forced by the calculated
transports. The model captured important aspects of the temporal and spatial dynamics of the bloom. A quantitative analysis
of hydrodynamic and biological processes shows that increased phytoplankton biomass due to elevated nitrogen loads after the
storm was not primarily regulated by advection or dispersion in spite of an increase in river flow from <1 to 928×103 m3 d−1. Of the dissolved nitrogen that entered the surface layer of the estuary in the 16 d following the storm event, the model
estimated that 28% was lost through exchange with the ocean or bottom layers, while 15% was removed by the grazing of just
one mussel species,Xenostrobus securis, on phytoplankton, and 50% was lost through other biological phytoplankton loss processes.X. securis grazing remained an important loss process even when the estimated biological parameters in the model were varied by factors
of ± 2. The intertidal mangrove pneumatophore habitat ofX. securis allows filtering of the upper water column from the lateral boundaries when the water column is vertically stratified, exerting
top-down control on phytoplankton biomass. |
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