Date of Completion
5-16-2025
Degree Type
Honors Thesis - Campus Access
Discipline
Biology (BIOL)
First Advisor
Sarah Joy Bittick, Ph.D
Abstract
Salinas de San Pedro is a restored salt marsh in Cabrillo Beach Coastal Park in San Pedro, CA, where Zostera marina seagrass grows. Given its urban location, the area is influenced by two storm drain outlets, one within the marsh and one outside, raising concerns about microplastic contamination from urban runoff. This study investigated microplastic contamination in surface sediment and examined how microplastic density relates to both storm drain proximity and seagrass presence. Four sites were surveyed, two inside and two outside the marsh, with one site adjacent to a storm drain and one farther away in each area. At each site, seagrass percent cover and shoot density were measured, and sediment cores were collected for microplastic analysis. Microplastics were found in all 60 samples, totaling 1,133 microplastic particles identified. While linear regression showed no significant relationship between microplastic density and distance from storm drains (R² = 0.0057, p = 0.566), Site 1, nearest to the storm drain outside the marsh, had significantly higher microplastic levels than all other sites (p = 0.00013), suggesting localized input. Seagrass presence was a stronger predictor of microplastic levels. Microplastic density was positively correlated with seagrass cover (R² = 0.1732, p = 0.000944) and shoot density (R² = 0.2381, p = 0.000077), supporting the idea that seagrass may enhance microplastic retention. However, the co-occurrence of high seagrass density and stormwater input at the most contaminated site complicates interpretation and suggests interaction between multiple factors. This study underscores the widespread presence of microplastics even in restored, ecologically valuable habitats and highlights the need for improved plastic pollution mitigation and urban runoff management to protect vulnerable coastal ecosystems.
Recommended Citation
Devine, Tessa E. and Bittick, Sarah J., "Influence of Storm Drain Proximity and Zostera marina Seagrass Presence on Microplastic Levels in Sediment of a Restored Salt Marsh Habitat" (2025). Honors Thesis. 594.
https://digitalcommons.lmu.edu/honors-thesis/594
