International Debris

Cross-border challenges and protection for the Tijuana River National Estuarine Research Reserve (TRNERR)

After storm events, the Tijuana River, which flows along the US-Mexico border, carries trash downstream, depositing it along the river bed as the river dries. Although several collection basins at the bottom of the Tijuana River catch most debris and sediment, containing it from flowing into the Estuary and the ocean, the basins must be cleared periodically by TRNERR, which creates an enormous cost burden.

After storm events, the Tijuana River, which flows along the US-Mexico border, carries trash downstream. Some trash is deposited along the river bed as the river dries (above). The rest flows into several collection basins at the bottom of the Tijuana River. Although the basins catch most debris and excess sediment, containing it from entering the Reserve and the ocean, the basins must be periodically cleared, and the waste trucked off-site, which creates an enormous cost burden for TRNERR. And not all trash gets stopped.

The Tijuana River Valley, winding along the US-Mexico border south of San Diego, California, is a verdant plain scattered with fluffy swaths of willows and sprawling ranches. Past the edges of development, the plain opens onto a wide marsh – the Tijuana River National Estuarine Research Reserve (TRNERR), an unexpected spot of calm tucked amid the chaos of development and civilization encroaching from all sides. But despite the urban growth sprawling south from San Diego, and north to the border fence from Tijuana, TRNERR enjoys a protection status that keeps it open and undeveloped, as one of the last remaining intact estuarine systems in California.

The collection basins at the bottom of the Tijuana River are currently mostly clear of debris, but after major storm events they fill up with trash and sediment washing down from upstream urban areas, and must be cleared periodically by TRNERR.

The collection basins at the bottom of the Tijuana River are currently clear of debris, but after major storm events they fill with trash and sediment from upstream urban areas, and must be cleared by TRNERR.

TRNERR was founded in 1981 as part of the National Estuarine Research Reserve System (NERRS). This country-wide system of 28 coastal and Great Lakes estuarine reserves is a federal-state partnership, in which the National Oceanic and Atmospheric Administration (NOAA) collaborates with state agencies to manage each reserve. TRNERR is jointly operated by the California State Department of Parks and Recreation and the U.S. Fish and Wildlife Service, with the cities of San Diego and Imperial Beach, San Diego County and the U.S. Navy providing additional resources and protection. The site was also designated a “Wetland of International Importance” by the International Ramsar Convention of 2005, bringing it global recognition as a vital natural ecosystem.

The US-Mexico border zone provides a buffer to help shield the TRNERR from urban expansion on all sides, but the effects of booming development still make their way into the Reserve, in the form of increased debris, sediment and pollution run-off. Above, the border fence curves along the mesas, with Tijuana visible in the background.

The US-Mexico border zone provides a buffer to help shield TRNERR from urban expansion on all sides, but the effects of booming development still make their way into the Reserve, in the form of increased debris, sediment and pollution run-off. Above, the border fence curves along the mesas, with Tijuana visible in the background.

TRNERR’s unique position along an international border presents it with challenges beyond its own ecology and surroundings. Booming urban development in and around Tijuana has driven increasing levels of sediment and trash run-off into the Tijuana River. One of the main problems is the amount of sediment and loose debris that washes down the Tijuana River after large rain events. Although two large catchment basins near the bottom of the river capture most of this excess sediment and debris, preventing it from flooding the reserve and clogging natural habitats, TRNERR must invest in costly removal and transport measures to keep the basins from overflowing. Dr. Jeff Crooks, the TRNERR manager, notes that because most of the Tijuana River watershed is in Mexico, where skyrocketing development and paving frees sediment and increases surface run-off, the Reserve must work across borders and socio-economic barriers to deal with sewage problems and high levels of debris flowing down the river and into the estuary.

Map of San Diego, CA (upper left) and Tijuana, Mexico (lower right), with the Tijuana River National Estuarine Research Reserve outlined in red (center). The inset map shows the region's location in California.

Map of San Diego, CA (upper left) and Tijuana, Mexico (lower right), with the Tijuana River National Estuarine Research Reserve outlined in red (center). The inset map shows the region’s location in California.

TRNERR also conducts in-depth monitoring, in order to track the system’s health and study its functionality. The Reserve’s diverse habitats and long history of protection make it an important source of long-term information on marshland ecology, as well as a reference site for other local estuarine restoration projects.

And although TRNERR is the largest intact estuarine-marsh system remaining in Southern California, and enjoys coveted protection status, it still faces threats from sea level rise and climate change. Additional effects of climate change could soon make themselves felt in estuaries around the U.S., although researchers aren’t yet certain how these systems will respond to ocean-related climate effects (the South Slough Estuarine Reserve in Oregon, a NERRS sister to TRNERR, has observed increasing pH levels from 2002-2010, and no strong correlations between estuarine pH and nearshore ocean pH trends, although its estuarine-scale processes still aren’t clearly understood). Regardless, coastal and estuarine ecosystems will likely feel the effects of multiple stressors in coming years, so understanding current baseline levels and fluxes can cue us into these changes. A little extra breathing room from long-term national protection doesn’t hurt, either

Although surrounded on all sides by urban development, TRNERR still provides much open space for walking, bird-watching and research. The Reserve is a combination of mudflats, shoregrass and high marsh transition zones.

Although surrounded by urban development, TRNERR still provides much open space for walking, bird-watching and research. The Reserve is a combination of mudflats, shoregrass and high marsh transition zones.

In addition to its status as a valuable estuarine system, TRNERR is also a beautiful recreation area open to the public, and includes Border Field State Park. Although vehicle access roads can be closed after heavy rains, there are ample trails for hiking, bird-watching (we spotted a roadrunner and red-tailed hawks on our visit there!) and horseback riding, as well as access to California’s beautiful southernmost beach.

 ***

Thank you very much to Jeff Crooks, manager of the Tijuana River National Estuarine Research Reserve, for an insightful, information-packed and unique tour of TRNERR! 

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