Benthic - Soft Bottom



	SOFT BOTTOM HABITAT, comprised of unconsolidated, soft sediment (sand, silt, and clay), makes up most of the Bay's seafloor. This habitat supports a large number of organisms, including more than 100 species of demersal or bottom-dwelling fish, like White croaker, Queenfish, Surfperch, California halibut, and Barred sandbass. The soft bottom habitat has been one of the most highly impacted in the Bay, primarily due to discharges from the Bay's two largest sewage treatment plants. Through the 1970s, benthic habitats were severely degraded in the areas surrounding treatment plant outfalls. Tumors, fin erosion and other problems were once common sights on demersal fish. Today, thanks to improved wastewater treatment technologies, the affected areas around outfalls have become significantly smaller, although the effects of wastewater on nearby fish and invertebrate communities are still noticeable. Because much of the invertebrate community resides in soft bottom sediments that may be impacted by storm water runoff and wastewater discharges, the benthic community serves as a valuable indicator of environmental stress in the Bay. One technique used to assess impacts to the benthic community, called the Benthic Response Index (BRI), measures changes to the abundance and diversity of benthic species and compares those changes to conditions at reference areas (locations within the Southern California Bight far from human activity). Scientists using the BRI on wastewater treatment plant discharge monitoring data from the 1970s and '80s found that many of the Bay's benthic communities were severely degraded near wastewater outfalls. By 1994, most of the data indicated only marginal deviations from reference conditions near treatment plant outfalls. Again, these changes were due to significant improvements in wastewater treatment at the Joint Water Pollution Control Plant (JWPCP) and the Hyperion Treatment Plant. The planned upgrade of the JWPCP to full secondary treatment in late 2002 and the already completed full secondary upgrade to Hyperion should result in even more improvements to the Bay's soft bottom habitat. Yet, sediment contamination, which resulted from the historical discharge of toxic chemicals, continues to impact to some fish species and poses a threat to the health of humans that consume them. From 1947 to the early 1970s, the Montrose Chemical Corporation, at its former plant near Torrance, discharged wastewater containing DDT into sewers leading to the Joint Water Pollution Control Plant (JWPCP). That plant then discharged treated wastewater into the Pacific Ocean off the Palos Verdes Peninsula. Several other industries discharged PCBs, a group of toxic chemicals, into the same sewer system. Much of the DDT and PCBs settled on the ocean floor, creating a 17-square-mile contaminated sediment deposit. Although disposal of these chemicals ceased in the early 1970s, they persist in the seafloor sediments. To date, concentrations of these chemicals in the muscle tissue of bottom-feeding fish, especially White croaker, remain high, although concentrations become lower at sampling sites further away from the Shelf. While concentrations of DDT and PCBs in species such as Kelp bass have declined significantly over the last 25 years, others such as California scorpionfish, California corbina, and Queenfish may also be contaminated with DDT and PCBs in some locations near the Palos Verdes Shelf. As a result, fish consumption advisories and health warnings have been posted in southern California since 1985. For more information, visit our Public Health page. After years of litigation by federal and state governments against the Montrose Corporation and other companies, a settlement was reached in October of 2000. More than $70 million will be paid by the Montrose Corporation and others to clean up contaminated areas and restore impacted habitats and species. In August of 2000, the EPA began a pilot "in situ capping" project on a small area of the Palos Verdes Shelf. Clean sediment was deposited over a small portion of the contaminated ocean floor. It is hoped that this cap will prove effective in isolating the contaminants and reducing the amount of DDT and PCBs transferred to the water and marine life. The EPA will use the data from this project, along with other relevant information, to decide whether to propose full-scale capping as a cleanup action for the Palos Verdes Shelf site. Storm water and dry-weather urban runoff are the most significant uncontrolled sources of pollution to the Bay's benthic habitats. Pollutants found in storm water and dry-weather runoff, including pathogens, toxic metals, nutrients, and trash, cause impairments to benthic communities and toxicity in sediments. A 1994 survey during the Southern California Bight Pilot Project found that one-quarter of the Bay's bottom area contained man-made materials including glass bottles, cans, plastic, fishing gear and metal debris. In an effort to control storm water and urban runoff pollution in the Bay, the Los Angeles Regional Water Quality Control Board (RWQCB) issued the Los Angeles County Municipal Storm Water NPDES Permit in 1996 (reissued in 2001). The goal of the permit is to reduce discharged pollutants to the maximum extent possible in order to attain water quality objectives. Additionally, the SMBRP has funded numerous storm water and treatment projects throughout the watershed. If you would like to learn more about the soft bottom habitat in the Bay, visit our Habitats and Species page.