Date of Award

7-2018

Access Restriction

Thesis

Degree Name

Master of Science

Department

Environmental Science & Civil Engineering

School or College

Seaver College of Science and Engineering

First Advisor

John Dorsey, Ph.D.

Second Advisor

Jeremy Pal, Ph.D.

Abstract

Santa Monica Bay and its vast beaches are important Los Angeles icons, while also providing significant ecosystem services to over millions of recreational visitors annually. Contaminated runoff from numerous watersheds surrounding the Bay, especially the 87% urbanized Ballona Creek Watershed, have historically resulted in poor water quality along areas of the Bay shoreline. Decades of monitoring for fecal indicator bacteria (FIB) along the Bay’s shoreline has been associated with NPDES wastewater discharge and stormwater programs. Many projects have been implemented throughout the watersheds (e.g. sewer improvements, biofiltration systems, low-flow diversions (LFDs)) to lessen flows of runoff from contaminating surf zone recreational waters. Despite decades of monitoring, there has been no long-term assessment of trends in shoreline FIB, especially in response to implementation of projects to improve water quality. The goal of this study was to assemble 30 years of monitoring data (1988-2017) for E. coli and enterococci to assess trends along the entire shoreline of Santa Monica Bay. Data were analyzed by calculating rolling 30-day geometric means, and comparing means by geographic subdivision, between wet and dry weather, and over time. Resulting trends for both E. coli and enterococci were: 1) concentrations peaked around 2005 when many stations shifted to sampling points where runoff mixed directly with surf zone water; 2) after 2005, concentrations fell to present levels, especially at beaches where LFDs were implemented; 3) concentrations were extremely variable during the 2016-17 wet season; 4) the north and central areas of the Bay, impacted by runoff from the Ballona Creek and Malibu Creek Watersheds, had greater concentrations relative to the south area; and 5) dry weather concentrations were steadily low, whereas wet weather displayed a higher degree of variability and may present a more significant challenge to meet water quality standards going forward. Implementation of LFDs and other best management practices to restrict polluted runoff from flowing into the surf zones of the Bay’s beaches most likely improved water quality throughout the Bay.

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