Research Areas > Nutrients > Dissolved Oxygen Concentration as a Potential Indicator of Water Quality in Newport Bay

Project: Dissolved Oxygen Concentration as a Potential Indicator of Water Quality in Newport Bay

Background and Objective

As coastal populations have grown and the land developed, the frequency of macroalgal blooms has increased in many estuaries worldwide, including Newport Bay in southern California. Macroalgae can reduce the habitat quality of estuaries in several ways, such as depletion of dissolved oxygen (DO) in the water column. This depletion may lead to decreased ecosystem productivity through several mechanisms. The relationship between macroalgal blooms and DO led the Santa Ana Regional Water Quality Control Board (SARWQCB) to investigate the utility of DO as an indicator for nutrient impairment.

The objective of this project was to provide technical support to the SARWQCB by summarizing the existing known causes and effects of low DO in estuarine and coastal marine systems, as well as analyzing historical DO concentrations in Newport Bay.  SCCWRP scientists then reviewed methodologies that have been used in other systems for development of DO criteria, and provided further recommendations for additional technical analyses.

Status

This project was completed in 2003.

Methods

SCCWRP researchers performed a comprehensive literature review and data search to: 1) Determine the effects of hypoxia on aquatic organisms and physical components of estuarine systems, 2) Obtain historical DO concentrations in Newport Bay and other regional estuaries, 3) Summarize the USEPA’s approach to DO criteria development for the east coast of the US and the Chesapeake Bay, 4) Provide findings in the context of using DO criteria as a water quality management tool, and 5) Highlight the remaining information gaps that must be addressed before implementing DO criteria in Newport Bay.

Findings

Significant findings were:

• Hypoxia had a range of effects on estuarine ecosystems, including: fish and invertebrate mortality, changes in organism behavior, sub-lethal effects like reduced growth or reproduction, release of toxic compounds with the flux of sediment nutrients into the water column, reduction in species diversity and abundance.

•  Historical data indicated that hypoxia may have become a problem in Newport Bay during the 1970s. Its occurrence was more common at night, during the summer, and in poorly flushed areas.

•  Compared to other systems for which DO criteria have already been developed, Newport Bay's physical dynamics and predominance of macroalgae differed significantly.

•  Because DO criteria for Newport Bay must address the link between DO and other cause and effect variables, future investigations into the relationship between DO and other variables (such as nutrient loading, macroalgal abundance, and life history needs of aquatic species) would be valuable.

Partners

This project was conducted in collaboration with the Santa Ana Regional Water Quality Control Board.