The central California coast between San Francisco Bay (SFB) and Monterey Bay (MB) is an upwelling-dominated marine ecosystem with a coastal population of 8.5 million. Anthropogenically enhanced terrestrial nutrients enter the ocean via three primary pathways: (1) SFB exchanges across the Golden Gate Strait, (2) coastal rivers, and (3) municipal wastewater discharged to ocean outfalls. The consequences of these inputs on primary production, acidification and hypoxia remain poorly understood. Here, we investigate these effects with a submesoscale-resolving ocean biogeochemical model. Simulations show that while terrestrial nutrient inputs collectively affect a broad region, the stronger impacts are found in nearshore waters, increasing dissolved inorganic nitrogen by 11.4%, primary production by 6.5%, and chlorophyll concentration by 4.5% along a 15-km coastal band. While exchanges from the SFB dominate these effects, all sources, including coastal rivers and ocean outfalls, produce distinct, localized footprints. Subsurface oxygen and pH decline due to terrestrial nutrient loading, but vigorous upwelling and circulation limit the intensity of these changes. Enhanced nutrient inputs are predicted to promote conditions favorable for diatom growth, potentially including Pseudo-nitzschia spp., creating an environment more conducive to domoic acid (DA) production. Model results show that chlorophyll concentrations exceed the threshold associated with elevated DA risk on 10-45% more days under nutrient-enriched conditions, compared to a scenario without terrestrial inputs. These findings highlight the need for expanded observational and modeling efforts to better understand the ecological consequences of anthropogenic nutrient inputs along the central California coast.
Sandoval-Belmar M. S., Damien P., Sutula M. A., Kessouri F., McWilliams J. C., Ho M., Moscoso J. E., Edwards C. A., Izett J. G., Molemaker J. & Bianchi D., 2025. Biogeochemical effects of Golden Gate Strait exchange and other land-base inputs to the San Francisco and Monterey Bay coasts. ESS Open Archive. Article.
