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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.