|Santa Monica Bay is a major recreational and commercial resource for the Greater Los Angeles region. Industrialization and the dramatic increase of population in the region over the past 100 years have strained the bays resources and polluted its sediments. To help evaluate any possible hazards posed by contamination, scientists from the U.S. Geological Survey (USGS) and local cooperating organizations are studying the processes that modify, transport, and redeposit sediments within Santa Monica Bay.|
Santa Monica Bay, offshore of Greater Los Angeles, provides crucial habitat for a rich web of marine life and supports important commercial and recreational fisheries. The bay and its beaches attract residents and visitors alike. More than 45 million people visit the bays beaches each year, helping to support a regional tourism industry of $10 billion annually.
In the late 1980s, several sewage spills entered Santa Monica Bay, forcing
popular beaches to be closed. These closures, along with concern over water
quality, kept people away from beaches, even during unseasonably hot weather,
resulting in serious economic losses for beach-front businesses. Much has since
been done by the city of Los Angeles to reduce spills and improve overall sewage
treatment, but water quality in the bay is still a concern.
More than 10 million people now live in the Greater Los Angeles metropolitan
area, a dramatic increase from 100,000 in 1900. Rapid population growth, industrialization,
and their consequences, especially the increased need for waste disposal, have
strained the resources of Santa Monica Bay. As the region grew, industrial,
agricultural, and household contaminants increasingly flowed or were washed
into the bay. Many of these pollutants are known to pose health hazards for
people and for fish and other wildlife. Some of the contaminants of greatest
concern are DDT (dichlorodiphenyltrichloroethane, a pesticide banned in the
United States in 1972 because of its high toxicity to fish and reproductive
hazard to birds), PCBs (polychlorinated biphenyls, toxic compounds widely
used as insulation in electrical transformers until the 1970s), toxic
metals (such as lead from industrial applications, fuel combustion, and tire
and brake wear), and PAHs (polycyclic aromatic hydrocarbons, chemicals
resulting from fuel combustion, oil spills, or natural oil seeps).
Much work has been done in Santa Monica Bay to monitor and determine the present
distribution of contaminants. However, in order to effectively manage the bay
in the future, it is important to also understand historical sources and sites
of contamination and the processes that modify and redistribute contaminated
sediments within the bay. To achieve this goal, the U.S. Geological Survey (USGS),
in cooperation with the Southern California Coastal Water Research Project (SCCWRP)
and the City of Los Angeles Bureau of Sanitation, is conducting a detailed study
in Santa Monica Bay.
Part of this study has shown that discharge from creeks
draining highly developed areas of Greater Los Angeles, such as Ballona
Creek, is affecting water quality in Santa Monica Bay. Pesticides, fertilizers,
oil and gas residue from automobiles, litter, and pet waste are washed off by
rainwater, untreated, into storm drains and creeks that flow into the bay. Although
the city of Los Angeles is increasingly diverting storm-water discharge to the
regions Hyperion Treatment Plant, much untreated wastewater from storm
drains still reaches the bay.
Because contaminants bind with sediment, historical
contamination in Santa Monica Bay can be studied by taking cores of the upper
few feet of sea-bottom sediment. Research cruises in 1997, 1998, and 1999 collected
sediment cores in the bay. Samples from the cores were dated using the radioactive
isotope lead-210 (210Pb), which is a naturally occurring product of the decay
of radon gas and has a short half-life of 22 years. These dates were used to
identify five key timelines within the cores:
1900Before most development began in the Los Angeles region.
1945When development was increasing in the region.
1970When pollution of the bay is thought to have been severe.
1985When sewage treatment was being improved following implementation
of the Clean Water Act.
1997When cores began to be collected.
Using this time framework, it was possible to analyze cores for historical
changes in manmade contamination sources and types. This was done by examining:
ContaminantsMeasurements were made of DDT, PCBs, toxic metals,
PAHs, and other contaminants. Total organic carbon was measured as an
indicator of sewage discharge.
Toxicity of samplesThe toxicity of contaminants in samples of bottom
sediment was estimated in the laboratory using sea-urchin fertilization tests
and survival tests on amphipods (small crustaceans).
ForaminiferaThe abundance and distribution of foraminifers (microscopic
single-celled animals) in the cores were examined to provide information about
the environment in which they lived. Changes or deformities in their tests (shells)
were also noted as indicators of contamination.
Infaunal distributionsThe distribution patterns of burrowing (infaunal)
marine animals in the cores were examined to determine their relations to sediment
toxicity results and the physical and chemical characteristics of the sediment.
To help determine the sources of contaminants found in the cores, as well as
the processes that modify, transport, and redeposit sediments within Santa Monica
Bay, scientists conducted additional studies that included:
MineralogyThe mineral composition of samples from the cores was studied
to provide information on the sources and transport pathways of sediments. This
analysis was also important because some minerals, particularly the clay mineral
smectite, adsorb contaminants.
SedimentologySediment texture and grain size in the cores were examined
to help determine the likely distributions of contaminants, as well as identify
various habitats of bottom-dwelling marine organisms. Grain-size information
also provided critical baseline data for developing sediment transport models.
Additional studies were done to help reveal how sediment has accumulated and
been deposited in Santa Monica Bay during the past 10,000 years.
OceanographyMoorings placed in various locations in Santa Monica Bay
in both El Niño and non-El Niño years collected information about
temperature, salinity, and current conditions in the water column and near the
sea floor, key parameters that influence sediment transport.
The ongoing efforts of the USGS and its cooperators in studying pollution in
Santa Monica Bay show that contamination and sediment toxicity in the bay are
being reduced by improvements in sewage treatment, especially the ending in
1987 of sewage sludge discharge from the Hyperion Sewage Treatment Plant. These
studies also reveal that some chemicals, such as DDT, occur at depths associated
with dates prior to their manufacture. Most likely, geologic events and storms,
or more commonly, burrowing marine animals, have reworked the sediment to bury
the contaminants deeper, which makes the contaminants less likely to enter the
marine food chain. Sediment transport models are being developed from the new
data provided by analysis of cores taken from the bay. Understanding the transport
of sediment will be a critical tool for future management of Santa Monica Bay
and its watershed.
By Homa J. Lee, Megan McQuarrie, and Lori Hibbeler
Edited by Peter H. Stauffer and James W. Hendley II
Graphics by Sara Boore, and Susan Mayfield; Web layout by Carolyn Donlin
City of Los Angeles Bureau of Sanitation
Santa Monica Bay Restoration Project
Southern California Coastal Water Research Project
For more information contact:
U.S. Geological Survey
345 Middlefield Road, MS-999
Menlo Park, CA 94025
PDF version of this fact sheet (1.1
See also Probing the Los Angeles BasinInsights into Ground-Water Resources and Earthquake Hazards (USGS Fact Sheet 086-02)
For questions about the content of this report, contact Homa Lee
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URL of this page: https://pubs.usgs.gov/fs/2003/fs155-02/
Maintained by: Michael Diggles
Created: May 12, 2003
Last modified: May 17, 2005 (mfd)