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    The Bay Institute Ecological Scorecard San Francisco Bay Water Quality Index

    October 17, 2003 Page 1

    Suisun

    BaySan Pablo

    Bay

    CentralBay

    South

    Bay

    Figure 1. San Francisco Bay consists of four inter-

    connected embayments. For indicator analysis,

    each embayment was considered as a subregion of

    the Bay.

    San Francisco BayWater Quality Index

    INDICATOR ANALYSIS AND EVALUATION

    A. Background

    San Francisco Bay is a large

    dynamic estuary, connected to largerivers and small ephemeral streams,

    urban and agricultural watersheds,

    and the Pacific Ocean. The Bay is

    also an unusual "inland" estuary,consisting of four interconnected

    embayments or subregions, each of

    which differs with respect to theamounts and sources of freshwater

    inflow, and the levels of

    urbanization along its shores (Figure1). Water quality in the Bay, and its

    effects on the animals and plants

    that live in the estuary and peoplewho enjoy those resources, is

    strongly influenced by inputs from

    each of these connections.

    Assessing and monitoring water

    quality in such a large and complex

    ecosystem is challenging. Transportof many contaminants into the Bay

    coincides with periods of high

    freshwater inflow, episodic andoften short-duration events in

    California's Mediterranean climate (see Freshwater Infow Index). Dispersal of

    contaminants within the Bay is driven by multiple freshwater inflows, strong tidal

    influences, and the complicated topography of the Bay. The list of contaminants detectedin Bay waters continues to grow: new chemicals replace those found to be too harmful to

    use while older chemicals, discharged into the Bay or its tributaries years ago, still seepinto Bay waters. Water quality standards, identifying contaminant concentrations that areharmful to aquatic life or human health, have been established for a number of

    contaminants found in the Bay but, for many chemicals, no guidelines exist.

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    B. Indicators

    The Water Quality Index measures the levels of contamination of San Francisco Bay

    waters for several classes of toxic compounds and other adverse water quality conditions

    that are harmful to aquatic life and impair ecosystem function. The Index has five

    indicators, each based on a class of contaminants or water quality conditions:

    1. Trace elements Trace elements include elements, such as arsenic, and metals,including mercury and copper. Typically these contaminants enter Bay waters during

    high flow events or are re-suspended from Bay sediments. For many aquatic organisms,

    exposure to high levels of dissolved metals or other trace elements can be lethal oradversely affect reproduction or early development. Toxicity of a number of these

    contaminants is dependent on other water quality characteristics, primarily hardness

    (concentration of calcium carbonate, CaCo3, mg/L); for example, toxic effects of some

    dissolved metals are reduced in hard water compared to soft water. In addition, for theprotection of aquatic life, different water quality standards may apply for fresh and salt

    waters. A number of trace elements, principally mercury and selenium, bioaccumulate inaquatic organisms in the Bay's food web.

    2. Pesticides Pesticides, herbicides and fungicides used throughout the San Francisco

    Bay Area and its upstream watersheds enter Bay waters as runoff and their concentrationsin Bay waters often peak following rainfall events. These compounds, which are

    intended to control terrestrial pests, can be equally harmful or lethal to aquatic organisms.

    3. PCBs Polychlorinated biphenyls (PCBs) are a class of man-made chemicalsdeveloped in the 1920s and used extensively in a variety of industrial applications. By

    the 1970s, the health risks associated with PCBs were identified and publicized and,

    following direction by the U.S. Congress in 1976, the US EPA banned the manufactureof these compounds in 1978. PCBs are resistant to degradation and persist for many

    years in the environment. In addition, PCBs bioaccumulate in the food web and are

    stored in the body fat of animals and humans.

    4. PAHs Polycyclic aromatic hydrocarbons (PAHs) are a group of chemicals that occurnaturally in coal, crude oil, and gasoline. Most PAHs enter the environment fromincomplete burning of oil, wood, garbage or coal, where they can persist for months of

    years. Identified health effects of PAH exposure include cancer and adverse reproductive

    and developmental effects. Present water quality standards for PAHs are for theprotection of human health based on consumption of exposed aquatic organisms.

    5. Dissolved oxygen Low dissolved oxygen concentrations can kill fish andinvertebrates and exclude many aquatic animals from large areas of habitat. Oxygen

    depletion usually results from high rates of microbial and/or algal respiration that exceed

    the capacity of the water body to replenish oxygen through phytoplankton photosynthesis

    and diffusion from the air. Excessive inputs of organic material and nutrients, for

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    Figure 2. Regional Monitoring Program water samplingstation in San Francisco Bay.

    example from poorly treated sewage discharges or surface runoff, can accelerate

    respiration rates and trigger localized and regional oxygen depletion.

    Individual contaminants in each of the indicators are shown in Table 1.

    Sediment Contamination Pollutants are not only present in the Bay's open waters butare also found in the sediments on the Bay's bottom, particularly near the mouths of

    tributary streams. Contaminant-laden sediments are reintroduced to the Bay's open

    waters when shipping channels or other areas are dredged; as a result of tidal action;and/or during peak rainfall events. Thus, sediments can be a source of continued

    contamination to Bay waters as well being directly toxic to benthic (bottom-dwelling)

    organisms. Sublethal contamination of benthic organisms is also an important pathwayfor bioaccumulation and biomagnification of contaminants in the food web. Future

    versions of the San Francisco Bay Water Quality Index will include an indicator for

    sediment quality to assess the condition of Bay sediments and changes in contaminationlevels through time.

    C. Methods and Calculations

    1. Data sources

    The Indicators were calculated for

    each year using data from the San

    Francisco Estuary Regional

    Monitoring Program for TraceSubstances (RMP)

    1, which has

    conducted two or three surveys per

    year since 1993, sampling 26stations distributed throughout Bay

    (Figure 2). Half of the stations are

    located in areas of the Bay that arepredominantly salt water and half in

    more estuarine areas with lower and

    more variable salinities. Additionaldata for dissolved oxygen

    concentrations and for general

    evaluation of long-term trends in

    Bay water quality were obtained

    from the U. S. Geological SurveyEcology and Contaminants Project.2

    1More information on the RMP can be obtained at www.sfei.organd at www.sfei.org/rmp/index/html.RMP water quality data can be downloaded at www.sfei.org/rmp/data/rmpwater.htm.2More information on the USGS Ecology and Contaminants Project can be obtained at

    http://wwwrcamnl.wr.usgs.gov/tracel/. Water quality data from this program are available for download at

    http://sfbay.wr.usgs.gov/access/wqdata.

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    2. Water Quality Standards

    The concentrations of dissolved oxygen or contaminants assessed by each indicator were

    evaluated in relation to water quality standards established for the protection of aquatic

    life and human health by the U.S. Environmental Protection Agency (USEPA), California

    Toxics Rule (CTR), California Regional Water Quality Control Board (RWRCB), SanFrancisco Bay Region), and the California Department of Fish and Game (CDFG) (Table

    1).3 Water quality standards for the protection of aquatic life identify levels of

    contaminants that can be directly harmful to exposed plants and animals. Standards forthe protection of human health are intended to prevent unacceptable accumulation of

    contaminants in aquatic organisms such that consumption of the organisms by human

    would be safe. Although the RMP monitors more than 120 contaminants, water qualitystandards have been established for only 41 chemicals and for dissolved oxygen. For a

    number of contaminants, concentrations deemed safe for the protection of aquatic life or

    human health differ between fresh water (defined as having salinity5 ppt more than 75% of the time). For samples

    collected from the intermediate and variable salinity estuarine waters of the Bay, the mostprotective of the salt and fresh water standards was applied. For several dissolved metals

    with toxicities dependent on water hardness (concentration of calcium carbonate, CaCo3,in mg/L), the applicable standard was calculated based on hardness of the measured water

    sample.

    3. Calculations

    Each indicator was calculated using methods developed by the British Columbia Ministryof the Environment, Lands and Parks (Zandbergen and Hall, 1998)

    4and adopted by the

    Canadian Council of Ministers of the Environment (CCME, 2001). Using this method,calculation of each indicator incorporated three different measurements:

    Scope(how many?) - the number of contaminants that exceeded water qualitystandards

    Frequency(how often?) - the proportion of samples for each contaminant that

    exceeded water quality standards

    Amplitude(how much?) - the amount by which the samples exceeded water quality

    standards

    3For more information on water quality standards used for the Water Quality Index see

    www.epa.gov/ost/standards/wqslibrary/ca/131.38.pdf, www.swrcb.ca.gov/%7erwqcb2basinplan.htm, and

    www.sfei.org/rmp/index/html.4Zandbergen and Hall (1998) is available at http://www.cciw.ca/33-4/33-4-519.htm.

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    Scopewas calculated as:

    Scope = [(number of failed variables/total number of variables)]*100where "failed variables" are the contaminants considered in the indicator that

    exceeded the standard.

    Frequencywas calculated as:Frequency = [(number of failed tests)/(total number of tests)]*100

    where "failed tests" are the samples tested for each contaminant considered in the

    indicator that exceeded the standard.

    Amplitudewas calculated in three steps as:

    a) Excursioni= [(failed test valuei)/(objectivei)]-1

    where "i" is each sample test.

    n

    b) NSE = [excursioni)/(number of tests)]i=1where NSE is the normalized sum of the excursions.

    c) Amplitude = {NSE/[(0.01(NSE) + 0.01]}where amplitude scales the NSE to a 100-point scale.

    Each of these three measurements yielded results in a 100-point scale, with high values

    indicating greater contamination than low values.

    The indicator5was calculated from the Scope, Frequency and Amplitude results as:

    Indicator = 100 {[sqrt(scope2+ frequency

    2+ amplitude

    2)]/1.732}

    where "sqrt" is the square root.

    This final calculation also yielded results in a 100-point scale but, in contrast to its

    component metrics, high Indicator values corresponded to low levels of contamination(i.e., good water quality) and low values indicated high levels of contamination (i.e., poor

    water quality).

    Calculations were conducted using a Microsoft Excelmacro, CCME Water QualityIndex 1.0, available on request from the Canadian Council of Ministers of the

    Environment.

    6

    For the PCBs and Dissolved oxygen indicators, data from stations in eachof the Bay's four embayments, or subregions (i.e., South, Central, San Pablo, and Suisun

    5Although we use the result of this calculation as the "indicator", this value is referred to as the "CCMEWater Quality Index" by the Canadian Council of Ministers of the Environment (CCME, 2001).6For further scientific information contact on the CCME Water Quality Index, see http://www..ec.gc.caor

    contact Environmental Canada, Guidelines and Standards Division, 351 St. Joseph Blvd., Hull, QC K1A

    0h3, email: [email protected].

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    Bays), were partitioned and contaminants in each region were treated individually.

    Therefore, for these indicators, the "Scope" calculation yielded information on thenumber of subregions in the Bay in which the water quality standard was exceeded. For

    reference and validation of the collective Indicator results, expressed as the Water

    Quality Index, an additional calculation using the CCME Water Quality Index 1.0 Excel

    calculator was made using the data from all contaminant categories and all subregions(see F. Alternative Calculation of the Water Quality Index).

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    Table 1. Water quality standards for the protection and aquatic life and/or human healthused for calculation of Water Quality Indicators. RWRCB=Regional Water ResourcesControl Board, San Francisco Basin Plan; USEPA=U.S. Environmental ProtectionAgency; CTR=California Toxics Rule; CDFG=California Department of Fish and Game.

    Contaminant Standard Source Comments

    Dissolved oxygen(mg/L) >5.0 mg/L RWRCBTrace elements*Ag (silver)**As (arsenic)Cd (cadmium)**Cr VI (chromium VI)Cu (copper)**Hg (mercury)Ni (nickel)**Pb (lead)**Se (selenium)Zn (zinc)**

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    D. Evaluating Results and Grading

    For each indicator, the grading scale followed the "ranking" scale recommended by the

    CCME (2001). That scale also used five categories or levels that corresponded to

    specific levels of water quality impairment (Table 2). The Water Quality Index was

    calculated as the "grade point average" of the component indicators, and was reported asa Grade(i.e., A-F) and a Score(i.e., the grade point average is expanded to a 100 point

    scale using a multiplication factor of 25).

    Table 2. Grading scale and rationale used for the all Water Quality Indicators.

    Indicator

    (100-point scale) Ecological conditionGradepoint Grade

    95-100Excellent:water quality is protected with virtual

    absence of threat or impairment; conditionsvery close to natural or pristine levels

    4 A

    80-94 Good:water quality is protected with only minordegree of threat or impairment; conditionsrarely depart from natural or desirable levels

    3 B

    65-79

    Fair:water quality is usually protected butoccasionally threatened or impaired;conditions sometimes depart from natural ordesirable levels

    2 C

    45-64Poor (marginal*):water quality is frequently

    threatened or impaired; conditions oftendepart from natural or desirable levels

    1 D

    0-44Very poor (poor*):water quality is almost always

    threatened or impaired; conditions usuallydepart from natural or desirable levels

    0 F

    * The CCME identifies the two lower levels with the terms "marginal" (for a grade of D) and "poor" (for agrade of F), rather than "poor" and "very poor" as is used for indicators in other Scorecard Indexes.

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    Figure 3. The Trace Elements Indicator measures the concentration of dissolved trace

    elements in Bay waters in relation to the water quality standards for the protection of

    aquatic life. The Indicator is calculated from three metrics. Scope measures the number of

    contaminants and regions of the Bay in which concentrations were were above the

    standards. Frequency measures the proportion of water samples in which standards were

    not met. Amplitude measures the magnitude of each exceedence, the amount by which the

    measured concentration for a contaminant exceeded the standard.

    0

    25

    50

    75

    100

    0

    25

    50

    75

    100

    1993 1995 1997 1999 2001

    0

    25

    50

    75

    100

    1993 1995 1997 1999 2001

    0

    20

    40

    60

    80

    100

    Scopehow many?

    Frequencyhow often?

    Amplitude

    how much?

    A

    B

    C

    D

    F

    Grade

    Trace Elements

    E. Results

    Indicator 1. Trace elements

    The RMP monitors 14 trace elements in the Bay. These contaminants occur in Bay

    waters in both particulate and dissolved forms, but water quality standards apply only todissolved trace elements and have been established for only ten of the monitored

    elements. Toxicity of the several of the dissolved metals depends on other water qualityconditions, principally hardness and salinity. Figure 3 shows the results of the Trace

    elements indicator calculations.

    Water quality standards for most toxic trace elements found in the Bay were met in

    most water samples collected at most stations in the Bay.From 1993-2001, an average of 10% (range: 2-18%) of all water samples exceeded the

    standard for one or more trace elements. In 2001, 10% of samples failed for at least onecontaminant.

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    Figure 4. Concentrations of mercury, Selenium, and

    copper in the four subregions of the San Francisco Bayfrom 1993-2001. Each point is the contaminant

    concentration measured at a single station during a

    survey. Each line is the linear regression of the

    contaminant concentrations over time from a subregion.

    Note that mercury and selenium graphs use a log scaleon the Y axis.

    1994 1996 1998 2000 2002

    Copper(ug/L)

    0

    1

    2

    3

    4

    5

    6

    South Bay Central Bay San Pablo Bay Suisun Bay

    fresh and salt water: 3.1 ug/L

    Selenium(ug/L)

    0.01

    0.1

    1

    10

    Mercury(ug/L)

    0.0001

    0.001

    0.01fresh water: 0.012 ug/L

    salt water: 0.025 ug/L

    no data 2000-2001

    fresh water: 5 ug/L

    Copper, mercury, selenium, and

    nickel concentrations exceeded

    water quality standards in some

    years (Figure 4).

    Water quality standards for copper

    were exceeded in all years.Mercury concentrations (measured

    for only 1993-1999) exceeded

    standards in 1994, 1997 and 1998.Selenium concentration standards

    were exceeded in each of the last

    five years of the survey. Nickelstandards were exceeded at least

    once in most years.

    Trace element contamination

    was most severe in South andSan Pablo Bays.

    Water quality exceedences for thefour problem trace elements

    occurred exclusively in South and

    San Pablo Bays (Figure 4). Noexceedences were measured in

    either Central or Suisun Bays.

    Concentrations of most of the

    problem trace element

    contaminants are declining

    (Figure 4).

    Mercury concentrations in South and San Pablo Bays declined significantly from 1993 to1999 (regression, p

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    Figure 5. The Pesticides Indicator measures the concentrations of pesticides in Bay

    waters in relation to the water quality standards for the protection of aquatic life. The

    Indicator is calculated from three metrics. Scope measures the number of contaminants

    and regions of the Bay in which concentrations were were above the standards.

    Frequency measures the proportion of water samples in which standards were not met.

    Amplitude measures the magnitude of each exceedence, the amount by which the

    measured concentration for a contaminant exceeded the standard.

    0

    25

    50

    75

    100

    0

    25

    50

    75

    100

    1993 1995 1997 1999 2001

    0

    25

    50

    75

    100

    1993 1995 1997 1999 2001

    0

    20

    40

    60

    80

    100

    Scopehow many?

    Frequencyhow often?

    Amplitude

    how much?

    A

    B

    C

    D

    F

    Grade

    Pesticides

    Indicator 2. Pesticides

    The RMP monitors 29 pesticides or pesticide breakdown products in the Bay but water

    quality standards have been established for only 17 of these contaminants. Figure 5

    shows the results of the Pesticides indicator calculations.

    Water quality standards for most pesticides found in the Bay were met in most

    water samples collected at most stations in the Bay.From 1993-2001, an average of 31% of all water samples exceeded the standard for one

    or more pesticides. In 2001, only 17% of samples had pesticide concentrations greaterthan the water quality standard. The percentage of water samples containing pesticide

    concentrations in excess of water quality standards was substantially lower in 2000 and

    2001 (mean: 14%), the last two years for which data were available, than in any yearbetween 1993 and 1999 (mean: 36%). However, fewer water samples were collected in

    2000 and 2001 (18 samples/year compared to an average of 45 samples/year).

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    10

    100

    1000

    10000

    1

    10

    100

    1000

    Concentration(pg/L)

    1

    10

    100

    1000

    1994 1996 1998 2000 2002

    100

    1000

    10000

    100000

    p,p -DDE

    Heptachlor epoxide

    Dieldrin

    Diazinon

    South Bay Central Bay San Pablo Bay Suisun Bay

    Figure 6. Concentrations of mercury, Selenium, and

    copper in the four subregions of the San Francisco Bay

    from 1993-2001. Each point is the contaminant

    concentration measured at a single station during asurvey. Each line is the linear regression of the

    contaminant concentrations over time from a subregion.

    Note that mercury and selenium graphs use a log scale

    on the Y axis.

    Concentrations of diazinon,

    dieldrin, heptachlor epoxide, or

    DDT compounds exceeded water

    quality standards in all years

    (Figure 6).

    Dieldrin and DDE (a compoundrelated to DDT) exceeded water

    quality standards in all years.

    Standards for Diazinon andHeptachlor epoxide were exceeded

    in most years.

    Pesticide contamination was most

    severe in South, San Pablo Bays,

    and Suisun Bay.

    Most pesticide exceedences

    occurred in South and San PabloBays (Figure 6). For most of the

    problem pesticides, the highestcontaminant concentrations

    occurred in South and Suisun Bays.

    Concentrations of heptachlorepoxide were significantly higher in

    Suisun Bay than all other subregions

    while Diazinon concentrations werehighest in South Bay. (Kruskal-

    Wallis, p

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    Figure 7. The PCB Indicator measures the concentration of PCBs in Bay waters in

    relation to water quality standard for the chemical. The Indicator is calculated from three

    metrics. Scope measures in how many regions of the Bay PCB levels exceeded the

    standard. Frequency measures the proportion of water samples in which the standard

    was exceeded. Amplitude measures the magnitude of each exceedence, the amount by

    which the measured PCB concentration exceeded the standard.

    0

    25

    50

    75

    100

    0

    25

    50

    75

    100

    1993 1995 1997 1999 2001

    0

    25

    50

    75

    100

    1993 1995 1997 1999 2001

    0

    20

    40

    60

    80

    100Scope

    how many?

    Frequencyhow often?

    Amplitude

    how much?

    A

    B

    C

    D

    F

    Grade

    PCBs

    Indicator 3. PCBs

    The RMP has identified 56 different polychlorinated biphenyls in San Francisco Bay

    waters. However, water quality standards for protection of aquatic life and human health

    (based on consumption of aquatic organisms exposed to PCB in fresh and salt water) for

    these chemicals apply to the summed concentration of all isomers and congenercompounds (U.S. EPA and CTR). Figure 7 shows the results of the PCBs indicator

    calculations.

    PCB concentrations in San Francisco Bay exceeded water quality standards in every

    year, in every subregion of the Bay, and at nearly every sampling station.

    From 1993-2001, most water samples exceeded the standard by more than three-fold,with a median PCB concentration of 471 ng/L (compared to the standard of 170 ng/L).

    In South Bay, all but one water sample collected over the nine-year period exceeded the

    standard, while in Suisun Bay nearly 35% of all samples were in compliance with thePCB standard. In 2001, PCB concentrations in San Francisco Bay exceeded water

    quality standards for the protection of human health by nearly three-fold.

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    1994 1996 1998 2000 2002

    PCBs(ng/L)

    100

    1000

    10000

    South Bay Central Bay San Pablo Bay Suisun Bay

    water quality

    standard

    (31 ng/L)

    Figure 8. PCB concentrations in the four subregions ofthe San Francisco Bay from 1993-2001. Each point is

    the PCB concentration measured at a single stationduring a survey. Each line is the linear regression of

    the contaminant concentrations over time from a

    subregion. Note that the Y axis uses a log scale.

    PCBs concentrations were highest in South Bay, intermediate in San Pablo Bay, and

    lowest in Central and Suisun Bays.

    From 1993-2001, median PCB concentrations in South Bay, 1172 ng/L, were

    significantly higher than those measured in all other areas of the Bay (Kruskal-Wallis

    ANOVA, p

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    Figure 9. The PAHs Indicator measures the concentration of polycyclic aromatic

    hydrocarbons in Bay waters in relation to the water quality standards for the

    protection of aquatic life and human health. The Indicator is calculated from threemetrics. Scope measures the number of contaminants and regions of the Bay in

    which concentrations were were above the standards. Frequency measures the

    proportion of water samples in which standards were not met. Amplitude measures

    the magnitude of each exceedence, the amount by which the measured concentration

    for a contaminant exceeded the standard.

    0

    25

    50

    75

    100

    0

    25

    50

    75

    100

    1993 1995 1997 1999 2001

    0

    25

    50

    75

    100

    1993 1995 1997 1999 2001

    0

    20

    40

    60

    80

    100

    Scopehow many?

    Frequencyhow often?

    Amplitude

    how much?

    A

    B

    C

    D

    F

    Grade

    PAHs

    Indicator 4. PAHs

    The RMP has identified 25 different polycyclic aromatic hydrocarbons in San Francisco

    Bay waters. However, water quality standards have been established for only 12 of these

    individual PAH compounds. Figure 9 shows the results of the PAHs indicator

    calculations.

    Concentrations of PAHs in Bay waters exceeded water quality standards in four of

    nine years.

    Water quality standards for at least one of the 12 PAH compounds for which standards

    have been established were exceeded in 1995, 1996, 1997 and 2001. In 2001, one water

    sample from the South Bay had concentrations of two PAH compounds,benzo(b)fluoranthene and benz(a)anthracene, that exceeded standards for those

    chemicals.

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    Figure 10. Total PAH concentrations in four subregions of

    San Francisco Bay from 1993-2001. Each point is the

    total PCB concentration measured at a single station

    during a survey. Each line is the linear regression of the

    contaminant concentrations over time from a subregion.

    Note that the Y axis uses a log scale.

    1994 1996 1998 2000 2002

    Total

    PAHs(ng/L)

    1

    10

    100

    1000

    South Bay Central Bay San Pablo Bay Suisun Bay

    South and San Pablo Bays had

    the highest levels of PAH

    pollution (Figure 10).

    Total PAH concentrations were

    highest in South Bay, intermediate

    in San Pablo Bay lowest in Centraland Suisun Bays (Kruskal-Wallis,

    p0.1, all tests)

    (Figure 10).

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    Figure 11. The Dissolved Oxygen Indicator measures the concentration of dissolved

    oxygen in Bay waters in relation to the water quality standard for the protection of aquatic

    life. The Indicator is calculated from three metrics. Scope measures the number of

    regions of the Bay in which dissolved oxygen levels fell below the standard. Frequency

    measures the proportion of water samples in which the standard was not met. Amplitude

    measures the magnitude of each exceedence, the amount by which the measured

    dissolved oxygen concentration was below the standard.

    0

    25

    50

    75

    100

    0

    25

    50

    75

    100

    1993 1995 1997 1999 2001

    0

    25

    50

    75

    100

    1993 1995 1997 1999 2001

    0

    20

    40

    60

    80

    100

    Scopehow many?

    Frequencyhow often?

    Amplitude

    how much?

    A

    BC

    D

    F

    Grade

    Dissolved Oxygen

    5. Dissolved oxygen

    Current water quality standards for dissolved oxygen in Bay waters require a minimum of

    5 mg/L of dissolved oxygen. However, availability of oxygen for aquatic animals is

    more closely related to the % saturation of oxygen in the water, which is a function of

    water temperature and salinity as well as dissolved oxygen concentration. Oxygensaturation levels below 60-80% can be harmful to many aquatic animals and, in cooler

    and fresher Bay waters, oxygen concentrations above the minimum standard of 5 mg/L

    may be still be inadequate for the protection of aquatic life. Figure 11 shows the resultsof the Dissolved oxygen indicator calculations.

    Dissolved oxygen concentrations were above the minimum standard in all areas of

    the Bay except the South Bay.In several years from 1993 and 2001, dissolved oxygen concentrations fell below the

    standard at the San Jose, Sunnyvale and Coyote Creek stations near the southern end of

    South Bay. In 2001, one water sample, collected at San Jose, failed to meet the minimumstandard for dissolved oxygen.

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    Figure 13. Dissolved oxygen concentration measured at

    South Bay sampling stations by the RMP and the USGSEcology and Contaminants Program.

    2

    4

    6

    8

    10

    12

    14

    1972 1976 1980 1995 2000

    Dissolvedoxygen

    (mg/L)

    2

    4

    6

    8

    10

    12

    14

    Regional Monitoring Program

    (South Bay, 1993-2001)

    USGS Ecology and Contaminants Project(South Bay, 1971-1978, 1993-2001)

    water quality standard(5 mg/L)

    1994 1996 1998 2000 2002

    Dissolved

    oxygen(mg/L)

    2

    4

    6

    8

    10

    12

    14

    South Bay Central Bay San Pablo Bay Suisun Bay

    water qualitystandard(31 ng/L)

    Figure 12. Dissolved oxygen concentration measured in

    the in four subregions of San Francisco Bay from 1993-

    2001. Each point is the dissolved oxygen concentration

    measured at a single station during a survey.

    Dissolved oxygen concentrations

    in South Bay were lower than

    levels measured in other

    subregions of the Bay.

    South Bay oxygen concentrations

    were consistently and significantlylower than those measured in all

    other regions of the Bay (Kruskal-

    Wallis, p

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    1993 1995 1997 1999 2001

    0

    25

    50

    75

    100

    GradeScore

    A

    B

    C

    D

    F

    Figure 14. The Water Quality Index aggregates theresults of the Trace elements, Pesticides, PCBs, PAHs,

    and Dissolved oxygen indicators.

    Figure 15. Comparison of San Francisco Bay Water

    Quality Index calculated using the CCME Water Quality

    Index and all Bay contaminants (upper panel) and the

    Index calculated as the grade point average of the five

    Indictors (lower panel).

    1994 1996 1998 2000 2002

    Wa

    terQualityIndex

    (valueca

    lculatedfromthreemetrics)

    40

    60

    80

    100

    1994 1996 1998 2000 2002WaterQualityIndexScore

    (expandedgradepointaverage)

    0

    20

    40

    60

    80

    100

    CCME Rank

    Grade

    Excellent

    Good

    Fair

    Marginal

    Poor

    (excellent)

    (good)

    (fair)

    (very poor)

    (very poor)

    A

    B

    C

    D

    F

    6. Water Quality Index

    The San Francisco Bay Water

    Quality Index aggregates the

    results of the Trace elements,

    Pesticides, PCBs, PAHs, andDissolved oxygen indicators

    (Figure 14).

    Between 1993 and 2001, water

    quality in the open waters of the

    Bay was fair (Grade = C) to good(Grade = B). Although the Water

    Quality Index has fluctuated

    slightly from year to year, it hasnot significantly increased or decreased during the nine-year period for which indicator

    data were available (regression, p>0.05).

    F. Alternative Calculation of the Water Quality Index

    In the above analysis, the WaterQuality Index was calculated from

    separate analyses of several classes

    of contaminants, each class equally

    weighted despite different numbersof constituent contaminants. An

    alternative approach to calculate

    the Index uses the CCME WaterQuality Index calculator for all of

    the contaminants monitored in the

    Bay, a method that weights eachindividual contaminant equally.

    Figure 15 shows the Water Quality

    Index calculated using thisalternative method and compares it

    with the Water Quality Index

    calculated as the grade point

    average of the five Indicators.

    Both approaches yielded similarresults: San Francisco Bay water

    quality from 1993-2001 wasgenerally fair to good and the small

    year-to-year variations in pollutionlevels were consistent between the

    two calculation methods.

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    Figure 16. Ammonia nitrogen and copper concentrations

    in wastewater effluent discharged into South Bay.

    Redrawn from U. S. Geological Survey, San FranciscoBay Program: Lessons learned for managing coastal

    water resources, http://water.usgs/wid/html/sfb/html.

    Ammonianitrogen(mg/L)

    0

    5

    10

    15

    20

    25

    30

    1970 1975 1980 1985 1990 1995

    Copper(ug/L)

    0

    30

    60

    90

    120

    150

    Ammonia nitrogen

    Copper

    Concentration

    G. Long-term Trends in Bay Water Quality

    Although the earliest data from the San Francisco Estuary Regional Monitoring Program

    for Trace Substances (RMP) are from 1993, the U. S. Geological Survey has been

    conducting both monitoring and focused special studies on Bay water quality since the

    1970s. Because the USGS monitoring studies are less comprehensive than the RMP withrespect to the diversity of contaminants, the Water Quality Index indicators were

    calculated using only the RMP data. However, the USGS results were used to evaluatelong-term trends in Bay water quality for selected contaminants.

    Concentrations of ammonia

    nitrogen and copper declined

    substantially during the late

    1970s and early 1980s (Figure

    16).

    Following implementation of

    advanced wastewater treatment,concentrations of ammonianitrogen and copper in effluents

    discharged into South Bay declined

    substantially. Excessive nitrogeninputs can promote bacterial and

    algal blooms that can result in

    periodic and localized dissolved

    oxygen depletion. Since the 1970s,incidences of low dissolved

    oxygen in the South Bay have also

    been reduced (see Dissolvedoxygen indicator and Fig. 13).

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    H. References

    CCME (2001) Canadian water quality guidelines for the protection of aquatic life.

    CCME Water Quality Index 1.0 User's Manual. In: Canadian environmental quality

    guidelines, 1999, Canadian Council of Ministers for the Environment, Winnipeg.

    Cloern, J. E., S. N. Luoma, and F. H. Nichols (1995) San Francisco Bay Program: lessons

    learned for managing coastal water resources. U.S. Department of Interior, U. S.Geological Survey, Fact Sheet FS-053-95.

    This article is available at http://water.usgs.gov/wid/html/sfb.html.

    Menconi, M. and C. Cox (1994) Hazard assessment of the insecticide diazinon to aquatic

    organisms in the Sacramento-San Joaquin river system. Administrative Report 94-2.

    California Department of Fish and Game. Rancho Cordova, CA.

    San Francisco Estuary Institute (SFEI) (2003) The Pulse of the Estuary: Monitoring and

    Managing Contaminants in the San Francisco Estuary. SFEI Contribution 74. SanFrancisco Estuary Institute, Oakland, CA.

    Zandbergen, P. A. and K. J. Hall (1998) Analysis of the British Columbia Water Quality

    Index for watershed managers: a case study of two small watersheds. Water Qual. Res. J.Canada 33: 519-549.

    This article is available at http://www.cciw.ca/33-4/33-4-519.htm.