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SDSU researchers show fluorescence sensors and radar detect sewage proxies in Tijuana River and coastal plumes
Summary
San Diego State University demonstrated fluorescence-based in situ sensors and remote sensing methods that correlate with E. coli and can map transboundary plumes; sensors require turbidity correction and frequent maintenance, and remote-sensing plumes require boat/shore validation.
Trent Biggs, professor of geography at San Diego State University and director of related monitoring projects, presented results from fluorescence sensors (tryptophan-like fluorescence and CDOM) and remote-sensing instruments deployed to map sediment and sewage contamination in the Tijuana River, estuary and nearshore plumes.
Biggs described two sensor workflows: lab bench measurements with an AquaLog that produced a strong linear correlation between tryptophan signal and wastewater percentage in controlled mixtures, and in situ Manta3 sensors that provided real-time telemetry but showed saturation and event-specific variation above about 40 percent wastewater. He noted turbidity can strongly interfere with tryptophan signals and that an event-by-event turbidity correction improved agreement with E. coli lab results.
"Fluorescence based measurements provide useful proxies of bacteria," Biggs said, adding that bench-top results were more consistent than in-situ sensors, which require calibration and maintenance. He described persistent operational challenges — sensor fouling by sand and organisms, calibration-standards needs and staffing to maintain deployments — and cautioned that sensors currently perform best for relatively high contamination and are not yet reliable for routine decisions around a numeric threshold such as 110 MPN per 100 mL.
On remote sensing, Biggs described shore‑mounted hyperspectral cameras and satellite imagery (Planet, Sentinel) and showed radar-detected plumes where the largest frequent plume signature appeared to come from a Punta Bandera treatment plant outlet, not the Tijuana River mouth. He said satellite SAR can see through clouds but requires validation with boat and shore sampling and integration with hydrodynamic models.
Biggs said the team will continue deploying sensors at Hollister and the estuary, expand shore and boat validation campaigns for radar plumes, intercalibrate labs across the border, and link remote sensing with modeling to produce forecasting products for regional water-quality monitoring.
