In a collaboration with the Biggs Lab, we are evaluating a real-time water quality platform to serve as an early warning of contamination for Imperial Beach and other coastal communities.

- View this Fox5 Newscast and this CBS8 report on research to track cross-border pollution in the Tijuana River.

Loadings of fecal indicator bacteria (FIB), nutrients, and carbon discharged to the ocean from the Tijuana River Estuary during continuous cross-border flow (post 2023) exceeded intermittent flow loadings (occurring pre-2022) by an order of magnitude for chemical constituents and 7 orders of magnitude for FIB.
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SARS-CoV-2 in the Tijuana River. Covid concentrations in river water were found to predict reported covid cases in Tijuana.

Tijuana River pollution can be solved! The solution is in finding value for wastewater.

Reuse of wastewater holds a lot of promise for landscape and agricultural irrigation in Tijuana and surrounding areas. Tijuana's Ecoparque (operated by Colef) is a model for decentralized wastewater reuse, with water used for urban greening and slope stabilization. Treating and reusing wastewater at a local scale can reduce pollution, stem soil erosion, protect unstable slopes, and keep sediment out of the Tijuana River.

Large, centralized treatment systems also have a role.  Mladenov's ENVE 445 Water and Wastewater Treatment student teams designed a Tijuana River Water Reuse Facility and found that 20 MGD of treated wastewater provides enough clean water to irrigate all of Tijuana's public roadway landscapes. Recharge of Tijuana River's treated wastewater into the aquifer in the US, pumped using groundwater wells in Tijuana, is a solution to water scarcity. Currently, treated wastewater is a lost resource, discharged to the Pacific Ocean via an ocean outfall. ENVE 647 student teams designed Tijuana River treatment systems for landscape, agricultural, and industrial water reuse in the region.

Tryptophan (TRP)-like and humic (CDOM) fluorescence have been verified as surrogates of untreated wastewater in the Tijuana River Estuary.

Wastewater addition experiments reveal that inner filter effects quench the fluorescence of organic compounds in wastewater and limit the ability of fluorescence-based sensors to track more concentrated wastewater inputs (>25% of wastewater). 

Photolysis rates were determined for 100% and 20% untreated wastewater mixed with clean river water. Humic fluorescence is more susceptible to sunlight; TRP-like fluorescence is more photo-resistant but is reduced by microbial activity under the Tijuana River's plug flow reactor conditions. Greater contributions of wastewater also shade chemicals and microbes from photolysis and reduce in-stream degradation processes.

Current work is exploring the vertical distribution of pollutants in the Tijuana River Estuary during spring tides and neap tides. Early results show high concentrations of fecal indicator at the surface and at depth during spring tides. During neap tides, greater stratification may keep pollutants concentrated in the near-surface zone where polluted fresh water is positioned atop cleaner, denser, saline, ocean water.