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Abstract Estuaries in the northern California current system (NCCS) experience seasonally reversing wind stress, which is expected to impact the origin and properties of inflowing ocean water. Wind stress has been shown to affect the source of estuarine inflow by driving alongshelf currents. However, the effects of vertical transport by wind‐driven Ekman dynamics and other shelf and slope currents on inflow are yet to be explored. Variations in inflow to two NCCS estuarine systems, the Salish Sea and the Columbia River estuary, were studied using particle tracking in a hydrodynamic model. Particles were released in a grid extending two degrees of latitude north and south of each estuary every two weeks of 2017 and tracked for sixty days. Inflow was identified as particles that crossed the estuary mouths. Wind stress was compared with initial horizontal and vertical positions and physical properties of shelf inflow particles. Inflow to the Salish Sea came from Vancouver Island and Washington slope water upwelled through canyons during upwelling‐favorable wind stress, and from Washington slope water or Columbia River plume water during downwelling‐favorable wind stress. Inflow to the Columbia River estuary came from Washington shelf bottom water during upwelling‐favorable wind stress and Oregon shelf surface water during downwelling‐favorable wind stress. For both estuaries, upwelling‐favorable wind stress direction was significantly correlated with a denser and deeper shelf inflow source north of the estuary mouth. These results may help predict the source and properties of inflow to estuaries in other regions with known wind or shelf current patterns.
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Satellite observations estimating the effects of river discharge and wind-driven upwelling on phytoplankton dynamics in the Chesapeake Bay
Abstract Phytoplankton growth in estuaries is regulated by a complex combination of physical factors with freshwater discharge usually playing a dominating role controlling nutrient and light availability. The role of other factors, including upwelling-generating winds, is still unclear because most estuaries are too small for upwelling to emerge. In this study, we used remotely sensed proxies of phytoplankton biomass and concentration of suspended mineral particles to compare the effect of river discharge with the effect of upwelling events associated with persistent along-channel southerly winds in the Chesapeake Bay, a large estuary where upwelling and its effects on biogeochemical dynamics have been previously reported. The surface chlorophyll-a concentrations (Chl-a) were estimated from Visible Infrared Imaging Radiometer Suite (VIIRS) satellite data using the Generalized Stacked-Constraints Model (GSCM) corrected for seasonal effects by comparing remotely sensed and field-measured data. Light limitation of phytoplankton growth was assessed from the concentration of suspended mineral particles estimated from the remotely sensed backscattering at blue (443 nm) wavelength bbp(443). The nine-year time series (2012–2020) of Chl-a and bbp(443) confirmed that a primary factor regulating phytoplankton growth in this nearshore eutrophic area is discharge from the Susquehanna River, and presumably the nutrients it delivers, with a time lag up to four months. Persistent southerly wind events (2–3 days with wind speed >4 m/s) affected the water column stratification in the central part of the bay but did not result in significant increases in remotely sensed Chl-a. Analysis of model simulations of selected upwelling-favorable wind events revealed that strong southerly winds resulted in well-defined lateral (East–West) responses but were insufficient to deliver high-nutrient water to the surface layer to support phytoplankton bloom. We conclude that, in the Chesapeake Bay, which is a large, eutrophic estuary, wind-driven upwelling of deep water plays a limited role in driving phytoplankton growth under most conditions compared with river discharge. Integr Environ Assess Manag 2022;18:921–938. © 2022 SETAC KEY POINTS River discharge is a primary factor regulating phytoplankton growth in the Chesapeake Bay. Upwelling-generating wind events were insufficient to support phytoplankton blooms. Generalized Stacked-Constraints Model (GSCM) is a useful method for processing ocean color satellite imagery in the nearshore areas.
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- Award ID(s):
- 2048902
- PAR ID:
- 10565328
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Integrated Environmental Assessment and Management
- Volume:
- 18
- Issue:
- 4
- ISSN:
- 1551-3777
- Format(s):
- Medium: X Size: p. 921-938
- Size(s):
- p. 921-938
- Sponsoring Org:
- National Science Foundation
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