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.
Barriquand T., Abell J., Boulanger H., Bernbeck K., Gaul L., Mattos J., Macknight A., Pacheco V., Chowdhury I. & Barandas S., 2023. Tidal, geological, and biological impacts to Humboldt Bay’s pH. CSU Journal of Sustainability and Climate Change 3(1). doi: 10.55671/2771-5582.1018. Article.
