When Do Good Algae Go Bad? Flow and Nutrient Thresholds for Harmful Algal Blooms Down a River Network

EPA Grant Number: F13E30980
Title: When Do Good Algae Go Bad? Flow and Nutrient Thresholds for Harmful Algal Blooms Down a River Network
Investigators: Bouma-Gregson, Keith
Institution: University of California - Berkeley
EPA Project Officer: Lee, Sonja
Project Period: August 21, 2014 through August 21, 2016
Project Amount: $84,000
RFA: STAR Graduate Fellowships (2013) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Aquatic Ecology


Harmful algal blooms are often associated with lakes, estuaries, or the coastal ocean. However, toxic cyanobacteria have been detected in California rivers and implicated in dog deaths in Northern California. These toxic algae grow on rocks in the riverbed, posing a public health threat and degrading aquatic ecosystem health. This research will investigate the environmental conditions causing harmful algal blooms in California rivers. What are the environmental thresholds that cause harmful algal blooms? How resilient to shifting into a toxic state are nontoxic algal assemblages in rivers? Do invertebrate grazers inhibit or promote the growth and spread of toxic cyanobacteria?


The research will be based on experimental field manipulations and surveys of flow, nutrients and macroinvertebrates in the Eel River in Northern California. Mini-flumes will be deployed in the river to increase or decrease the flow conditions over an algal assemblage. Algal biomass, toxin concentrations and species abundance data will be collected to document how algal assemblages respond to flow alterations. In addition, fine-scale flow measurements will be made with an acoustic Doppler velocimeter to study how hydraulic bed shear stress affects cyanobacterial accrual on the riverbed. Nutrient diffusing substrates also will be deployed to measure how nutrient concentrations affect colonization rates and growth of toxic cyanobacteria. Finally, the density of invertebrate grazers will be manipulated to determine if invertebrate grazing facilitates or inhibits toxic algal growth.

Expected Results:

Low river flows are expected to increase the growth rates of toxic cyanobacteria. It is expected that cyanobacteria will not be able to accrue biomass in high-energy water because the force of the water will scour the fragile filaments off the riverbed. The effect of nutrients on toxic algae is expected to be species specific, because some toxic cyanobacteria can fix atmospheric nitrogen but others cannot. Invertebrate grazers often avoid cyanobacteria, consuming diatoms instead. If grazers are consuming other algal taxa, this could release toxic cyanobacteria from competition and increase cyanobacterial growth rates.

Potential to Further Environmental/Human Health Protection

This research will identify conditions and processes that affect the growth of toxic cyanobacteria in rivers. River managers can use this information to maintain environmental conditions that prevent the occurrence of toxic algae thereby protecting public health and maintaining productive aquatic ecosystems.

Supplemental Keywords:

cyanobacteria, harmful algal blooms, toxins

Progress and Final Reports:

  • 2015
  • Final