CSU Campus or Other Affiliation

California State University Bakersfield

Faculty Mentor

Eric Riggs


This research examines factors that control pH in Humboldt Bay – a shallow, tidally-driven estuary in northern California (USA) that supports shellfisheries which are economically important to the state. Time-series data from hydrographic sensors at two Central and Northern California Ocean Observing System (CenCOOS) stations, as well as multiple 2021 undergraduate cruises, were used to understand the role of tides, biological productivity and carbonate dissolution in controlling pH on various timescales. Differences in pH, dissolved oxygen, chlorophyll, and temperature between an in-bay sensor and a coastal sensor indicate that the tidal flux exerts a long term, seasonal control on pH, but biological productivity substantially modifies carbon and oxygen thereby controlling pH on daily and weekly timescales. Sediment samples were also collected from the bay in 2021 to study carbonate dissolution. Sediments were incubated for three days in both stirred and unstirred conditions (to mimic tidal mixing and no tidal mixing respectively) and DO, pH and alkalinity were monitored. For all stirred incubations, large increases in pH and alkalinity suggested considerable carbonate sediment dissolution. When scaled to the bay’s in-situ suspended sediment concentrations, carbonate dissolution may exert a supplementary control on pH at similar time scales as biological productivity, but the magnitude of its effect is less.

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig1.jpg (2309 kB)
Figure1.jpg Humboldt Bay

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig2.jpg (1440 kB)
Figure2.jpg CenCOOS Stations

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig3.jpg (1581 kB)
Figure3.jpg Sediment Sampling Locations

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig4.jpg (1484 kB)
Figure4.jpg Eelgrass and Oyster locations in HB

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig5.jpg (647 kB)
Figure5.jpg pH v. temperature

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig6.jpg (470 kB)
Figure6.jpg Yearly pH HB v, Trinidad

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig7.jpg (916 kB)
Figure7.jpg pH v. depth HB & Trinidad

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig8.jpg (776 kB)
Figure8.jpg pH v. depth July 2018 HB

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig9.jpg (590 kB)
Figure9.jpg pH v. ODO HB & Trinidad

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig10.jpg (668 kB)
Figure10.jpg pH v. Chlorophyll HB & Trinidad

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig11.jpg (491 kB)
Figure11.jpg Incubation DO evolution

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig12.jpg (436 kB)
Figure12.jpg Incubation pH evolution

Tidal_Geological_and_Biological_Impacts_to_HumboldtBays_pH_Fig13.jpg (415 kB)
Figure13.jpg Incubation Alkalinity evolution



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