Book Description

Although the Tijuana River Estuary (TRE) remains the largest, most-intact coastal wetland in Southern California, it has a history of major changes, much of this related to its location immediately north of the US / Mexico Border. One of the primary challenges is cross-border flows from the rapidly growing city of Tijuana, Baja California, Mexico, and the delivery of wastewater, debris, and sediment to sensitive coastal wetland ecosystems. There is a need to more fully investigate these environmental changes to assess the ecosystem health of the Tijuana River Estuary over time, especially related to pollution impacts. This can inform an understanding of changes in both species and stressors, and can also help assess the effectiveness of past management strategies. Since 1986, the NOAA Mussel Watch and California Surface Water Ambient Monitoring Programs have periodically collected data on chemical contaminants and biological indicators of water quality in the TRE. This project builds on these past monitoring efforts and established methodologies to assess status and trends of contaminants in sediment and organisms. This work was accomplished by conducting a thorough review of available datasets and literature to document past changes in the estuary and refine sampling approaches. Sampling was conducted at three locations in the Tijuana River Estuary to assess spatial variability. Compared to national thresholds, most contaminant concentrations were at relatively low levels in 2021, with some having decreased from previously higher levels in the 90s. When comparing species groups, fishes had the highest organic concentrations, indicating the ongoing processes of bioaccumulation and biomagnification. Levels of some organics in fish, such as total DDT and PBDEs, remain at levels which could be of some concern for sensitive piscivorous birds. Also, the highest concentrations were near a local urban outfall point rather than from the Tijuana River itself. Overall, this information improves our ability to document and interpret long-term trajectories of contaminant change in the ambient environment and key taxa. This project's results include communication and management tools depicting the estuary's ecosystem health over time.