August 2013, Vol. 25, No.8

Extra

Natural solution for cleaner California waters

Phil Cruver

For many coastal waterbodies, excess nutrients cause an increase in algae and phytoplankton that blocks sunlight to the lower depths. The decrease in sunlight eventually kills bottom-dwelling plant life, leading to lower dissolved-oxygen concentrations in the water and decimating prosperous habitats for other species. 

Traditional methods to reduce nutrients include upgrading water resource recovery facilities (WRRFs) and reducing stormwater runoff, which carries fertilizer and wastes from the land into estuaries and coastal waters. 

But bivalve shellfish also offer the ability to filter the water column and remove nitrogen. Incredibly, a single adult oyster can filter up to 190 L/d (50 gal/d). The clearer water allows sunlight to penetrate so that foundations of the food chain can thrive; once water clarity increases, bottom vegetations, such as eelgrass, flourish. 

In Southern California, native Olympia oysters were once ecologically and economically dominant along the coast. These bivalve shellfish were ecosystem engineers for the bays and estuaries, as well as enablers of prosperous habitats for other species. They also were considered commercially important as a delectable food source until a combination of overharvesting, dredging, pollution, and wetlands destruction in the 1930s depleted natural populations. 

Now, KZO Education (Long Beach, Calif.), a research and education nonprofit organization, is collaborating with scientists from the University of Southern California (Los Angeles) Wrigley Institute for Environmental Studies (Catalina Island, Calif.) and the U.S. National Oceanic and Atmospheric Administration’s Milford (Conn.) Laboratory to quantify and document the environmental effects of farming oysters and mussels offshore in California as part of its Offshore Mariculture Monitoring Program. This team of scientists also might explore the potential of bivalve shellfish for the bioextraction of nutrients from Long Beach Harbor. 

  

Nutrient pollution in San Pedro Bay  

The combined Los Angeles and Long Beach harbors consist of about 730 ha (1800 ac) of water in the inner navigation channels and 2430 ha (6000 ac) of water in sheltered anchorages and navigation channels. As with many coastal waters, these harbors have been degraded by nutrient pollution, and the Los Angeles River is a major culprit. The river runs 82 km (51 mi) from the Santa Monica Mountains across 18 municipalities that are home to 1 million residences before dumping 5180 m3/s (183,000 ft3/s) of nutrient-loaded water into San Pedro Bay. 

According to a study conducted in 2000 by the City of Los Angeles, the Los Angeles Regional Water Quality Control Board, and the Southern California Coastal Water Research Project, the Los Angeles River contains three primary sources of pollution: discharge from three WRRFs, outflow from river tributaries into the river, and storm-drain outfalls. 

According to the report Characterization of Water Quality in the Los Angeles River, the study was conducted in what would be considered a fairly dry month and showed that, “[t]he three water reclamation plants discharged the majority (72%) of the volume flowing in the Los Angeles River during this study.” This discharge was found to contain “the highest concentrations and greatest mass emissions of nutrients including nitrate, nitrite, ammonia, and total phosphate,” the report says. 

The Los Angeles River Estuary connects the Los Angeles River to San Pedro Bay. It has 4.2 km (2.6 mi) of soft bottom, with an average width of 122 m (400 ft). The estuary is about 1.8 m (6 ft) deep, depending on the season and tidal influences, and produces about 302,800 m3/d (80 mgd) during drier months. Point and nonpoint source urban runoff and the three WRRFs provide year-round river flow. 

  

Bivalve shellfish bioextraction services 

Employing a 6-m × 7.6-m (20-ft × 25-ft) mussel raft in New York City’s Bronx River as their field location, researchers from the U.S. National Oceanic and Atmospheric Administration’s Northeast Fisheries Science Center’s Milford Laboratory completed a 2-year pilot study to test how effectively ribbed mussels can remove nitrogen and other excess nutrients from water. Scientists monitored the condition of the mussels, which were grown on lines hanging below the raft, as well as local water quality, to understand how each responded. They also monitored mussel-feeding activities within a filtration apparatus. Local water was pumped directly across each mussel before exiting the chamber. 

The mussel-raft study was part of longer-term efforts to improve water quality in Long Island Sound. The pilot project evaluated the potential for shellfish aquaculture to increase biological filtration activity in an urban environment. Results from the pilot study also contributed to a system-scale evaluation of bioextraction for all of Long Island Sound and helped characterize the ecosystem services that would be provided by this approach, such as improvements in water quality, removal of bacteria, and assimilation of nutrients. Nearly $1.5 million in research and development funds have been expended to document that the bivalves on the raft filtered more than 18,925 m3/d (5 mgd). 

The Milford Laboratory researchers are planning to transfer and apply lessons learned, as well as their technologies and methodologies, to Long Beach this summer to quantify bivalve bioextraction potential at the first offshore shellfish farm in U.S. federal waters about 16 km (10 mi) from the outflow of the Los Angeles River. 

The Los Angeles River Estuary would be an ideal location for restoring native Olympia oyster beds, which are typically found in the subtidal zone and are bordered by mud flats at high elevations and by eelgrass at low elevations. Olympia oysters are found at depths of zero to 61 m (zero to 200 ft) and attach to rocks and gravel. They survive in a broad range of habitats but are most abundant in estuaries and small rivers. While tolerating brief exposure to low salinities, they thrive at salinities greater than 25 ppm. 

Hard-bottom or substrate habitats are ecologically important, as they provide food, shelter, and spawning and nursery areas to various fish, shellfish, and other organisms. Hard-substrate habitats in San Pedro Bay include the breakwaters and jetties within the harbor complex, as well as pilings that support wharves and piers, and along the shoreline of the basins and channels. 

 

Restoring native Olympia oysters is a promising proposition for the Long Beach Harbor ecosystem, resulting in cleaner water for San Pedro Bay. The City of Long Beach is presented with a timely opportunity for demonstrating and validating the efficacy of innovative bivalve bioextraction technologies for coastal California. 

Phil Cruver is president of KZO Education (Long Beach, Calif.), a 501(c)(3) education and research organization.