Causes and Relevance of Phytoplankton Blooms in the Northern Sacramento-San Joaquin Delta

Science Center Objects

Phytoplankton are an important part of aquatic food webs and ecosystems. These single-celled plants grow faster in the stronger light of spring or summer, resulting in population explosions called phytoplankton blooms. These blooms in turn feed zooplankton (free-floating aquatic microorganisms), providing food for many aquatic species, including fish, shrimp, crabs, and other invertebrates.

Microscopic view of a phytoplankton cell collected in San Francisco Bay

Microscopic view of a phytoplankton cell collected in San Francisco Bay

Phytoplankton blooms occur in most aquatic systems. One such system is California’s Sacramento-San Joaquin Delta. In recent years, the size and frequency of phytoplankton blooms have become inconsistent, creating a concern for the region’s food web. These fluctuations may be tied to many conditions, including changes in suspended sediment levels, water clarity, and the increased presence of nutrients and other contaminants.

In 2016 there were a rare series of large phytoplankton blooms that formed in the northern part of the delta. This offered scientists the opportunity to examine phytoplankton population increase and the benefits blooms provide to the lower food web. However , a lack of funds cut short the research needed for the publication of a conclusive report.


Scientists will examine data on recent phytoplankton blooms to better understand their formation. Using data from 2016, scientists will study the causes for that year’s upsurge. Scientists will research how increased levels of sediment, certain nutrients, and other contaminants, might inhibit such growth. Having more complete data on this topic will provide guidance on the release of such elements, and on the flow of sediment, into the delta. This information will assist in habitat conservation measures and research related to the restoration of the delta ecosystem.

Science Plan

Scientists will analyze data from samples of phytoplankton blooms from the 2016 study for water quality, nutrients, sediment, temperature, pH, and other relevant environmental factors. They will also use this data to support an inventory of nutrient mapping across delta. Data taken from other sources, such as monitoring stations, will also be examined and included. The goal of this research is to understand the relationship between phytoplankton growth and nutrient concentrations, temperature, light, time, water conditions, and other factors.