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Title

Simulation of annual biogeochemical cycles of nutrient balance, phytoplankton bloom(s), and DO in Puget Sound using an unstructured grid model. Article in Ocean Dynamics (2012) 62:1353–1379.

 
Publication number Date Published
12-03-055November 2012
VIEW NOW Simulation of annual biogeochemical cycles of nutrient balance, phytoplankton bloom(s), and DO in Puget Sound using an unstructured grid model. Article in Ocean Dynamics (2012) 62:1353–1379. (Number of pages: 27) (Publication Size: 4064KB)
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Author(s) T. Khangaonkar and W. Long (Pacific NW National Laboratory) and B. Sackmann, T. Mohamedali, and M. Roberts (Department of Ecology)
Description Nutrient pollution from rivers, nonpoint source runoff, and nearly 100 wastewater discharges is a potential threat to the ecological health of Puget Sound with evidence of hypoxia in some basins. However, the relative contributions of loads entering Puget Sound from natural and anthropogenic sources, and the effects of exchange flow from the Pacific Ocean are not well understood. Development of a quantitative model of Puget Sound, is thus presented to help improve our understanding of the annual biogeochemical cycles in this system using the unstructured grid Finite-Volume Coastal Ocean Model framework and the Integrated Compartment Model (CE-QUAL-ICM) water quality kinetics.

Results based on 2006 data show that phytoplankton growth and die-off, succession between two species of algae, nutrient dynamics, and dissolved oxygen (DO) in Puget Sound are strongly tied to seasonal variation of temperature, solar radiation, and the annual exchange and flushing induced by upwelled Pacific Ocean waters. Concentrations in the mixed outflow surface layer occupying approximately 5–20 m of the upper water column show strong effects of eutrophication from natural and anthropogenic sources, and spring and summer algae blooms, accompanied by depleted nutrients but high DO levels. The bottom layer reflects DO and nutrient concentrations of upwelled Pacific Ocean water modulated by mixing with biologically active surface outflow in the Strait of Juan de Fuca prior to entering Puget Sound over the Admiralty Inlet.

The effect of reflux mixing at the Admiralty Inlet sill, resulting in lower nutrient and higher DO levels in bottom waters of Puget Sound than the incoming upwelled Pacific Ocean water, is reproduced. By late winter, with the reduction in algal activity, water column constituents of interest were renewed, and the system appeared to reset with cooler temperature, higher nutrient, and higher DO waters from the Pacific Ocean.
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Contact Brandon Sackmann at 360-407-6684 or bsac461@ecy.wa.gov
Keywords biogeochemical model, Puget Sound, plankton, dissolved oxygen, algae
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