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Project: Nutrient Dynamics and Macroalgal Blooms: A Comparison of Five Southern California Estuaries

Background and Objective

Though macroalgae are natural components of estuarine systems, large macroalgal blooms can reduce the habitat quality of estuaries. They may deplete the water column and sediments of oxygen, leading to changes in species composition and shifts in community structure. While the relationships between algae and nutrient levels have been well-studied in laboratory settings, less information exists that characterizes these relationships in the environment where one or more complicating factors may be present (e.g., sediment processes, resource competition, changes in flow). In addition, Pacific coast estuaries have not been studied as often as the Atlantic and Gulf coast systems.

The objective of this research was to investigate the relationships among water and sediment nutrient concentrations and macroalgal biomass for five southern California estuaries. The estuaries studied varied in area, watershed size, dominant surrounding land use, freshwater influence and tidal flushing.


This project was conducted from 2001 to 2003.


Three sampling sites were utilized in each of five estuaries: Carpinteria Salt Marsh Reserve, Mugu Lagoon (West), Mugu Lagoon/Calleguas Creek, Upper Newport Bay, Los Penasquitos Lagoon, and Tijuana River Estuary. Monitoring for a variety of water quality parameters was done quarterly over 15 months. These included water column salinity, temperature, dissolved oxygen, nitrate, ammonia, total Kjeldahl nitrogen, soluble reactive phosphorus, and total phosphorus. Other measurements included percent cover and biomass of macroalgal species, algal tissue N and P concentration, redox potential, organic content, nutrient concentration, and grain size. Data were examined for relationships among parameters, then entered into a database to be used by USEPA Region IX in developing regulatory numeric targets for nutrient concentrations.

Location of five estuaries in southern California sampled for this project.


Significant findings were:

• Spatial and temporal patterns in water column nutrients, salinity and sediment characteristics suggested that the watershed of each estuary was an important source of nutrients. Additionally, the proximity of certain land use practices (e.g., agriculture, urban areas) to the estuary sometimes showed significant impacts on estuarine water quality. Nutrient contribution from the watersheds varied seasonally, with higher nitrate inputs during the winter wet season.

• Patterns of macroalgal abundance were largely determined by a combination of nutrient availability and the physical characteristics of each estuary. Macroalgae proliferated in areas with suitable habitat, such as broad mudflats and high light availability.

• The timing of macroalgal blooms varied across systems, and relationships between nutrient availability and macroalgal abundance were inconsistent, indicating that blooms could not be predicted by water column nutrient concentrations alone. Additional study is needed to observe the relationships between annual nutrient loading and macroalgal response, and to look at mitigating factors (which might vary among estuaries) to control the biological response to nutrient loads.


This project was conducted in collaboration with University of California, Los Angeles.

For more information on Nutrient Dynamics and Macroalgal Blooms: A Comparison of Five Southern California Estuaries, contact Martha Sutula at (714) 755-3222.
This page was last updated on: 6/30/2014