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Student study finds plastics dominate litter trapped at bridge piers and debris dams on Bakersfield’s Lower Kern River
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Summary
A student study of litter at four bridges on the Lower Kern River found plastics are the dominant material trapped in debris dams and bridge piers; mean litter mass and material composition varied by site and habitat.
Dana Garcia (CSU Bakersfield graduate student) presented preliminary summer 2025 findings from a study of anthropogenic litter in the Lower Kern River downstream of Bakersfield.
Methods: The study established transects upstream and downstream of four road bridges. Under bridge piers the team identified paired debris dams and non‑debris locations and sampled deposits, drying, categorizing and measuring items by material (plastic, paper/cardboard, metal, wood, etc.) and rigidity (flexible vs rigid).
Findings: Plastics were the most abundant material across sites and habitat types; paper and cardboard were the second most common in aggregate. Relative material composition varied by site (for example, one site had a local spike in bistiroform items). Contrary to some prior studies that found more flexible items, this dataset showed more rigid items overall, though rigidity differences were not statistically significant. Mean litter mass varied by site and by habitat (upstream vs downstream), with some large bridges showing greater downstream mass accumulation in summer low flows.
The presenter noted that fieldwork took place while the riverbed was predominantly dry and that sampling will continue during flowing conditions to observe transport processes. Dana suggested follow‑up analyses linking litter types to nearby land uses and informal sheltering or dumping locations, and recommended booms or targeted monitoring in channels to identify dominant upstream sources.
“If you see wrappers or cups, it often points to nearby convenience stores or recreation nodes,” an audience member said; the presenter agreed that future source attribution work would be useful for targeted interventions.
The presenter described plastics and styrofoam as particularly harmful due to breakdown into microplastics and potential ingestion by wildlife; she noted the public‑health and ecosystem implications of debris transport downstream and into coastal environments.
The study is ongoing and planned to expand sampling under flow conditions to capture transport dynamics and temporal patterns.
