Do light, nutrient, and salinity interactions drive the "bad Suisun" phenomenon? A physiological assessment of biological hotspots in the San Francisco Bay-Delta

Start/End: February, 2018 to January, 2020

The San Francisco Bay-Delta ecosystem has experienced a dramatic decline in pelagic fish since 2001, particularly in Suisun Bay. Research suggests that this decline is caused by reduced phytoplankton biomass. High ammonia concentrations in wastewater effluent have been implicated as part of the issue but less understood are the interactions with light, temperature, salinity, and flushing rates on phytoplankton growth. As work is underway to reduce wastewater nitrogen pollution, understanding the mechanism underlying the “bad Suisun” is important to restoring the health of the ecosystem.

This project will assess the physiological basis for reduced phytoplankton growth in Suisun, prior to the major upgrade at the Sacramento Regional Wastewater Treatment Plant that is responsible for 90% of the nitrogen released into the Bay.

Through field mapping, physiological measurements will be coupled with observations of the ambient light field to examine if light limitation has an interactive effect with nutrient physiology. These relationships will then be examined at a finer scale in the laboratory via culturing experiments.

By illuminating the interacting effects of bottom-up drivers such as light, nutrients, and salinity on phytoplankton, this research aims to provide a fundamental understanding of this complex ecosystem.

Results of the project will guide expectations and management actions related to nutrient reduction and yield new tools and approaches for monitoring ecological health in the San Francisco Bay-Delta.

Research Mentor: Raphael Kudela, University of California Santa Cruz
Community Mentors: James Cloern, U.S. Geological Survey and David Senn, San Francisco Estuary Institute