Background
Monitoring
of ambient water toxicity in San Francisco Bay has been an integral
component of the RMP since its inception. This monitoring includes
collection of ambient waters from throughout the Bay system, exposing
test organisms to these waters using a standardized test protocol
(as per EPA guidelines, these ambient waters, along with the control
water, are adjusted to uniform salinities via addition of artificial
sea salts prior to use in testing), and observation of the response
of these organisms to these waters. Tests and test species used
in this monitoring have included algal growth tests with the diatom
Thallassiosira pseudonana, bivalve embryo development tests with
mussels (Mytilus sp.) and oysters (Crassostrea gigas),
and crustacean survival and growth tests with Mysidopsis bahia.
RMP ambient water toxicity testing is currently limited to testing
with Mysidopsis bahia.
During
the routine baseline monitoring cruise in the winter of 19951996,
significant ambient water toxicity was observed throughout the northern
San Francisco Bay system (Figure 3.43),
with virtually complete mortality of Mysidopsis bahia taking place
in waters at several of the RMP sampling sites. This was the first
observation of significant ambient water toxicity since the inception
of the RMP, indicating that, for the most part, the ambient waters
in San Francisco Bay are relatively free of toxicity. However, the
fact that these toxic water samples were collected immediately following
a major rainstorm event suggested that ambient water toxicity was
occurring on small time scales, probably the result of stormwater
runoff.
Year
One: The Pilot Study
Based
upon these observations and hypotheses, a Pilot Study was initiated
the following winter to investigate episodic toxicity following
rainstorm events. During this initial winter of 19961997,
samples were collected at the mouths of Guadalupe and Alviso sloughs
(Guadalupe River) in the South Bay, and in the Napa River and at
Mallard Island in the North Bay. In addition, the baseline cruise
sampling and testing in January again occurred on the heels of a
major rainstorm event. The goal for the South Bay and Napa River
sites was to sample stormwater runoff as it began to mix with estuarine
water (as evidenced by elevated salinity). Mallard Island, located
at the head of the Estuary near Chipps Island, is an ideal sampling
site as it represents the influence of upstream waters (from the
Sacramento and San Joaquin watersheds) that flow into the northern
Bay system.
The
results of the toxicity tests are summarized in Table
3.1.
The
rainfall pattern in 19961997 was quite unusual, and this influenced
the progress of the project. In South Bay samples, toxicity was
observed during three storm events. This toxicity is apparently
associated with elevated concentrations of the organophosphate pesticide
chlorpyrifos.
Heavy
rains early in the winter and major flooding on the Sacramento and
San Joaquin rivers disrupted the planned sampling and testing at
Mallard Island such that there was little opportunity to collect
water samples that might be impacted by the upstream activities
that take place during a normal water year. None of the few samples
collected were toxic. However, the baseline cruise sampling, which
occurred after a rainstorm event, revealed significant toxicity
at northern Bay sites (Figure 3.44),
suggesting that stormwater runoff was resulting in widespread ambient
toxicity over a small time scale.
Changes
in the Ambient Water Toxicity Monitoring Strategy
Considering
the unusually heavy rains and flooding, the results of the Pilot
Study were considered interesting enough to initiate a re-evaluation
of the overall RMP strategy for monitoring ambient water toxicity.
Exemplifying the "adaptive management" approach of the
RMP, participants decided to modify the ambient water toxicity testing
program. Sampling during the bi-annual baseline cruise was scaled
back from thirteen stations to five to six stations in the South
Bay and North Bay. The testing itself was reduced from two species
to one species (Mysidopsis), from testing a partial dilution
series to testing at the 100% ambient water concentration only,
and from monitoring of survival and growth as test endpoints to
monitoring of survival only. The resulting savings in resources
was re-allocated to increase the level of episodic monitoring during
the winter of 19971998 with the following objectives:
- Document
the frequency and duration of toxic episodes in the North Bay.
- Expand
the spatial extent of urban stormwater runoff monitoring in the
Bay system.
In
order to address the first objective, water sampling at Mallard
Island was modified and increased to collection of three samples
per week for a continuous four-month period covering winter and
spring (February through May), with each sample being tested for
toxicity on an individual basis. Using this approach, the frequency
of short-term toxic events could be determined; equally as important,
the observation of toxicity in consecutive samples could be used
to infer that the ambient waters in the North Bay were continuously
toxic over this same time period. Prior to this continuous sampling,
Mallard Island water samples were collected only following storm
events in October though December, followed by biweekly sampling
in January.
In
order to address the second objective, urban creek stormwater runoff
sampling and testing was expanded to include the mouth of Pacheco
Slough which drains the Concord-Pleasant Hill-Walnut Creek area.
Unlike other major urban creek drainages (e.g., Alameda Creek, Guadalupe
Slough, etc.), the Pacheco Slough drainage has not yet been subjected
to stormwater runoff toxicity characterization, particularly downstream
in the mixing zone with Bay water. Water samples were collected
here, as well as in Guadalupe Slough, immediately following storm
events.
Episodic
Toxicity During the Winter-Spring of 1997-1998
The
results of the toxicity testing performed during the winter and
spring of 19971998 are summarized in Table
3.2.
A total
of fourteen storm events were sampled at Guadalupe Slough, two of
which resulted in significant mysid mortality (50% or greater).
Of the fourteen water samples collected, eight had elevated concentrations
of diazinon and/or chlorpyrifos (as measured by ELISA analysis).
In one of the toxic Guadalupe Slough water samples, the measured
chlorpyrifos concentration exceeded the reported acute LC50
for Mysidopsis bahia. However, in the other toxic sample,
the measured concentrations of diazinon and chlorpyrifos were below
toxic levels, suggesting that other contaminants were responsible
for the observed toxicity.
Pacheco
Slough
A total
of thirteen storm events were sampled at Pacheco Slough, five of
which resulted in statistically significant mortality, although
only one toxic sample exhibited greater than 50% mortality. Of the
thirteen water samples collected, ten had measurable concentrations
of diazinon and/or chlorpyrifos. In one of the toxic Pacheco Slough
water samples, the measured chlorpyrifos concentration exceeded
the reported acute LC50 for Mysidopsis bahia.
However, in the other four toxic samples, the measured concentrations
of diazinon and chlorpyrifos were below toxic levels, again suggesting
that other contaminants were responsible for some of the observed
toxicity.
Mallard
Island
Ambient
water samples were collected at Mallard Island and tested from October
9, 1997 through May 30, 1998 (the results of these tests are summarized
in Figure 3.45). Of the seventy
water samples collected, ten resulted in significant mysid mortality
(eight of which exhibited > 50% mortality). More importantly,
there were two time periods, February 1217 and May 59,
during which three consecutive water samples were toxic, suggesting
that the ambient waters in North Bay were similarly toxic for at
least two extended time periods during this monitoring effort.
In
order to save costs, ELISA analysis was not performed routinely
on the water samples collected from Mallard Island. We believe that
the greatest likelihood of elevated pesticide concentrations in
these ambient waters will be during stormwater runoff events; therefore,
diazinon and chlorpyrifos were measured in the Mallard Island water
samples only following significant rainstorms and at the same time
that Guadalupe and Pacheco Slough water samples were being analyzed.
Only two of the toxic water samples from Mallard Island had diazinon
or chlorpyrifos concentrations that exceeded the reported LC50.
In six of the toxic water samples, including two of the three consecutively
toxic samples in February, both diazinon and chlorpyrifos were below
the ELISA detection limit (well below the LC50s), indicating
that other contaminants were responsible for the observed toxicity.
Summary
and Conclusions
The
Regional Monitoring Program has been assessing aquatic toxicity
of ambient waters in the San Francisco Bay system two or three times
annually since 1993. It is now known that variations in contaminant
concentrations occur on smaller time scales due to events, such
as urban runoff following rainstorms or from similar surface runoff
following application of pesticides in agricultural areas, and our
monitoring has revealed significant toxicity coincident to such
events. Moreover, this year's monitoring has indicated that the
North Bay waters may be toxic for extended periods of time, perhaps
as long as a week, following such events. This observation is even
more problematic given that at least one important resident invertebrate,
the crustacean Palaemon macrodactylus, is reported to be
even more sensitive to these pesticides than Mysidopsis. While there
is a growing body of information (including these RMP studies) that
suggest that pesticides in surface water runoff may cause toxicity
to invertebrates in waters within the Sacramento-San Joaquin River
basins and the San Francisco Estuary, no link has yet been conclusively
established. Long-term studies of zooplankton distribution and abundance
in the Sacramento-San Joaquin Delta have reported significant declines
in zooplankton, with recent zooplankton densities being one to two
orders of magnitude lower than in the early 1970s. Use of pesticides
such as diazinon and chlorpyrifos has increased substantially since
their introduction in the 1950s and 1960s, suggesting a possible
link between pesticide toxicity and zooplankton declines.
Maintaining
healthy, viable invertebrate communities in the San Francisco Estuary
is and should be an objective in and of itself. However, it can
be argued that an even more important role for these invertebrate
resources is as food for key fish populations. Numerous studies
have documented that virtually all of the important fish populations
in the San Francisco Estuary rely upon these invertebrates, particularly
during their vulnerable early life stages. If pulses of toxicity
through this ecosystem diminish the available invertebrate resources
at critical periods, such as when larval fish are using the invertebrates
for food, then adverse effects on fish populations can be expected.
This potential problem is of paramount importance as the period
of high pesticide concentrations in these waters (JanuaryJune)
coincides with the presence of early life stages of most of the
fish populations currently in decline.
While
pesticides, particularly diazinon and chlorpyrifos, are most commonly
linked with ambient water toxicity in the Estuary, it must be pointed
out that several of the water samples which were toxic in our study
had diazinon and chlorpyrifos concentrations well below levels reported
to be toxic. This indicates that other contaminants are also contributing
to the observed toxicity problems. A future objective of studies
investigating the ambient water toxicity in this Estuary should
be the characterization and identification of these other toxicants
using the toxicity identification and evaluation (TIE) process.
Finally,
while many of the urban creek watersheds have been studied, and
while our own monitoring is beginning to provide a clearer picture
of ambient water toxicity apparently resulting from Sacramento-San
Joaquin River (and possible 'within Delta' sources) surface water
runoff into northern San Francisco Bay, other significant inputs
into the Bay, such as the Napa River or Petaluma River, have yet
to be as well studied. Therefore, an additional objective of future
studies should be the characterization of possible ambient water
toxicity resulting from contaminant input from these other watersheds
that include both urban and agricultural land uses.
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