In the 1970s and 1980s, phytoplankton production in much of San Francisco Bay was limited not by nutrient levels but by the reduced availability of light for photosynthesis. The murky conditions were caused by suspended sediment. Beginning in about 1993, however, water clarity began to improve as several watershed projects were implemented that were designed to decrease the loading of sediments and other pollutants. In addition, loads of toxic contaminants that also might have been inhibiting phytoplankton production were reduced. As a result, phytoplankton biomass increased by more than 5 percent a year from 1993 to 2004. San Francisco Bay switched from a light-limited system to a nutrient-limited system (Bricker et al. 2007).
Cloern et al. (2006) developed a conceptual model, listing eight possible mechanisms that affect phytoplankton biomass in San Francisco Bay either positively or negatively: introduced invertebrate herbivores, upwelling or relaxation, nutrients, toxicity, water transparency, nodal cycle, deposition, and stratification. The authors eliminated nutrients and stratification as causes, leaving six mechanisms deemed influential in determining phytoplankton biomass.
Reference:
Bricker, S., B. Longstaff, W. Dennison, A. Jones, K. Boicourt, C. Wicks, and J. Woerner. 2007. Effects of Nutrient Enrichment In the Nation’s Estuaries: A Decade of Change. NOAA Coastal Ocean Program Decision Analysis Series No. 26. National Oceanic and Atmospheric Administration, National Centers for Coastal Ocean Science, Silver Spring, MD. Accessed October 2016. https://yosemite.epa.gov/oa/EAB_Web_Docket.nsf/(Filings)/3BE82A42C7ED8C3585257B120059CB8A/$File/Opposition%20to%20Petition%20for%20Review%20–%20Ex.%2010%20Part1…23.53.pdf.
Cloern, J.E., A.D. Jassby, T.S. Schraga, and K.L. Dallas. 2006. What is causing the phytoplankton increase in San Francisco Bay? in The Pulse of the Estuary: Monitoring and Managing Water Quality in the San Francisco Estuary. SFEI Contribution 517. San Francisco Estuary Institute, Oakland, CA. Accessed October 2016. http://www.sfei.org/sites/default/files/biblio_files/ThePulse2006_LowRes-Screen.pdf Exit