Benthic processes in South San Francisco Bay: The role of organic inputs and bioturbation

Measurements of benthic processes over the last 13 years in South San Francisco Bay have spanned a range of hydrologic and water quality conditions. However, benthic fluxes of O₂, NH₄⁺ and NO₃⁻ have shown little variation. NH₄ and NO₃⁻ flux during this period were relatively constant in magnitude and direction. Sediment O₂ consumption was lower in the early 1980s than in the early 1990s. The reason for this difference is unclear, but may be a result of methodology or a lower density of the tube dwelling Asychis elongata. Although dissolved inorganic phosphate fluxes generally have been close to zero, in fall, there is a net flux into the sediments. Dissolved Si fluxes were consistently out of the sediments, while dissolved organic carbon fluxes were large and exhibited shifts in direction. Compared with other estuarine and coastal systems, temperature was not a major control on benthic fluxes because of the small annual temperature range. Irrigation by macrofauna enhances O₂ consumption and may control NH₄⁺ fluxes in the shoals, where NH₄⁺ flux was correlated with the biomass of mollusks. Porewater profiles of NH₄⁺, TCO₂ and radon suggest that irrigation is important in controlling dissolved constituent concentrations. Organic inputs such as deposition of phytoplankton may also affect benthic fluxes. In the channel, NH₄⁺ flux was positively correlated to phaeopigment concentrations in sediments. Ratios of sediment O₂ consumption to DIN (NH₄⁺ + NO₃⁻ ) or DIP flux were very different than ratios of remineralization of organic matter with a Redfield ratio, and suggest that both denitrification and phosphorus burial were occurring at both locations.Conference PaperPublishedAt head of title: Seventy-fifth Annual Meeting of the Pacific Division/American Association for the Advancement of Science held at San Francisco State University, San Francisco, California, June 19-24, 1994