Practicum Project | 2011

Effect of Urban Runoff on Water Quality Indicators in Ballona Creek, CA

Students: Uma Bhandaram, Andrew Guerra, Brooke Robertson, Heather Slattery, Kailey Tran

Client: Heal The Bay

Advisor: Dr. Rebecca Shipe

Final Report

Urban runoff has the potential to dramatically affect water quality in high-density coastal urban regions. In this study, we define water quality as a function of trash, fecal indicator bacteria (FIB), and harmful algal bloom (HAB) concentrations. Thus far, no studies have investigated the effects of runoff on all three of these water quality indicators. This study fills that gap by comparing water quality in dry and wet weather at the mouth of Ballona Creek in Marina Del Rey, California. Additionally, we examine the mechanism through which urban runoff affects water quality by measurements of total suspended solids (TSS), nitrate concentrations, salinity, and temperature. All samples and measurements were gathered at three sites at the creek-ocean interface twice weekly from February to April 2011. We observed a significant correlation between FIB and wet weather (r = 0.88), HAB and wet weather (r = 0.89) but not between trash and precipitation. TSS, salinity, and nitrate concentrations were related to abundances of FIB and HAB; nitrate from runoff or upwelling seem to support HAB whereas TSS and FIB likely enter coastal waters in runoff. Our study shows that rainfall has a negative effect on the health of Ballona Creek waters, where FIB will accumulate and persist within the creek for days after a rain event. There is not a consistent spatial pattern in all variables amongst the three sites; the furthest upstream site was more influenced by runoff whereas the further downstream sites were influenced by upwelled waters. Understanding the factors that affect coastal water quality are crucial as this has economic, ecological, and health implications for other similar geographic areas.