Investigating the summer 2022 harmful algal bloom in San Francisco Bay: impacts and contributing factors

Harmful algal blooms (HABs) pose growing threats worldwide to biological resources, human health, and regional economies, and over the last decade HABs have emerged as a high priority water quality management issue in San Francisco Bay (SFB). Despite SFB being highly-enriched in nitrogen and phosphorus, monitoring over several decades indicated the system was relatively resistant to the severe water quality impacts that commonly afflict other nutrient-enriched estuaries (e.g. low dissolved oxygen, HABs). However, there has been growing evidence in recent years suggesting that SFB’s resistance to nutrient impacts is weakening, including increases in phytoplankton production and biomass and frequent detections of multiple HAB-taxa and phycotoxins. In August 2022, SFB experienced its first severe HAB event, with excessive growth of the dinoflagellate Heterosigma akashiwo leading to widespread oxygen-depletion and fish kills. After early reports in late-July of discolored water in channels around Alameda, the bloom’s spread to South Bay was initially detected by remote-sensed imagery in early August, and was thereafter intensively monitored by regional scientists over the subsequent month through field surveys, water quality moorings, and remote sensing. This seminar will describe the HAB event’s progression and biogeochemical/water-quality impacts, and the application of observational data and numerical models to explore potential factors that contributed to the bloom’s initiation, spread, and eventual termination.

Speaker: David Senn, San Francisco Estuary Institute