Factors controlling variability in nearshore fecal pollution: the effects of mortality

Area of Science:

• Environmental microbiology
• Coastal oceanography
• Water quality modeling

Background:

• Fecal indicator bacteria (FIB) are crucial for assessing coastal water quality and public health risks.
• Understanding factors controlling FIB concentrations, such as fluid dynamics and mortality, is essential for effective management.

Purpose of the Study:

• To investigate the impact of mortality and fluid dynamics on fecal indicator bacteria (FIB) concentrations at Huntington Beach.
• To evaluate the performance of various mortality models compared to a baseline advection-diffusion model.

Main Methods:

• Employed a suite of physical-biological models, including an advection-diffusion model.
• Incorporated six different forms of mortality into the models to simulate FIB decay.
• Assessed model skill improvement based on the inclusion and type of mortality parameters.

Main Results:

• All mortality models significantly outperformed the baseline advection-diffusion model, particularly at offshore stations.
• Model skill for Escherichia coli and Enterococcus improved substantially with the addition of mortality terms.
• Models with cross-shore variable mortality rates demonstrated superior accuracy in reproducing FIB decay, especially when accounting for solar dose response.

Conclusions:

• Mortality, particularly when spatially variable, is a critical factor in accurately modeling FIB concentrations in coastal waters.
• The best model for Escherichia coli incorporated both solar-dependent and cross-shore variable mortality.
• Further research may be needed to identify a single best model for Enterococcus due to similar performance across variable mortality models.