The nutrient ammonia in the Sacramento River is derived from multiple sources, including effluent from the SRWTP. Ammonia may be used by phytoplankton for growth, but some studies have suggested that excessive concentrations of it may inhibit phytoplankton growth.
We supported a field and laboratory study by UC Santa Cruz on the health and productivity of phytoplankton, the base of the Delta food web, related to environmental factors in the Sacramento River and Delta. The project is named the “Bad Suisun” study because previous field observations determined that there is reduced phytoplankton growth in Suisun Bay.
Results of the field study indicate that phytoplankton are commonly stressed in Suisun Bay and occasionally stressed in other regions of the watershed, but this stress is largely related to factors other than ammonia. The laboratory results suggest that different phytoplankton species responded differently to the various treatments of nutrients and light levels. However, at ammonia concentrations present in the environment, the growth rate of phytoplankton would not be inhibited. Furthermore, while typical ammonia concentrations in Suisun Bay did not inhibit growth of two diatom phytoplankton species isolated from the Bay, their growth responded positively to increased light levels in the range likely to be present in the environment.
The laboratory research is now published in the scientific journals Journal of Phycology and Aquatic Biology and is available “open source”:
Variation in growth rate, carbon assimilation, and photosynthetic efficiency in response to nitrogen source and concentration in phytoplankton isolated from upper San Francisco Bay. 2017. Gry Mine Berg, Sara Driscoll, Kendra Hayashi, Melissa Ross, Raphael Kudela. Journal of Phycology. Volume 53, Issue 3, Pages 664–679.
Effects of nitrogen source, concentration, and irradiance on growth rates of two diatoms endemic to northern San Francisco Bay. 2019. Gry Mine Berg, Sara Driscoll, Kendra Hayashi, Raphael Kudela. Aquatic Biology. Volume 28, Pages 33-43.