Water Monitoring Discussion The Big Storm The Effect of the Big Storm on Contaminant Concentrations Comparison to Water Quality Guidelines Effects of Water Contamination References

The Big Storm

In the 1996 Annual Report, the water monitoring discussion focused on seasonal and spatial patterns that emerged over the first four years of the RMP. While these general patterns largely persisted in 1997, the extremely unusual hydrology of early 1997 did have a conspicuous impact on the concentrations of some contaminants. As described by Cloern et al. (see Water-Quality Variability in San Francisco Bay: General Patterns of Change During 1997, this Chapter), 1997 was the year of the Big Storm, with record-setting precipitation in the watershed in December and January (Hunrichs et al., 1998). Heavy rainfall and record streamflow in January was then followed by unusually dry weather in February and March and low freshwater inflow for the rest of the year. This discussion will focus on ways in which the 1997 results were unusual in comparison to the persistent general patterns observed in RMP water monitoring from 1993 to 1996.

The extreme hydrological variation in early 1997 created a sharp contrast in conventional water quality parameters between the first two sampling cruises of the year. During the January sampling, the surface waters of the Bay were approximately 90% freshwater, with low salinity waters pushing well into Central Bay. By the April cruise the surface waters of the Bay were down to about 50% freshwater. The January sampling therefore characterized a very different water mass than the April sampling, with the January sampling overwhelmingly influenced by the high flows from the Sacramento and San Joaquin rivers and the April sampling more equally influenced by the Rivers and saline waters within the Bay. The January flows also carried a relatively large load of suspended solids, producing the highest baywide mean concentration of total suspended solids (TSS) observed in the five years of the RMP. The mean TSS in April was less than half of the January mean.

The Effect of the Big Storm on Contaminant Concentrations

Dissolved concentrations of several trace elements, including chromium, lead, mercury, nickel, and zinc, were relatively high in January. Dissolved concentrations of chromium, mercury, and lead were especially high, leading to the highest baywide average concentrations (including all stations shown in figures 3.4­3.23) of these elements for any cruise since the beginning of the RMP.

The average concentration of dissolved mercury in January (0.0045 µg/L) was four times higher than the average concentrations in April and August (0.0011 and 0.0010 µg/L, respectively). The January average was heavily influenced by an extremely high value (the second highest observed in the RMP) at the Petaluma River (BD15). Dissolved mercury was also elevated in January at the other Northern Estuary and Rivers stations. The average concentration of dissolved chromium in January (1.86 µg/L) was even more sharply elevated over the April average (0.24µg/L), an eight fold difference. Concentrations were uniformly elevated at the Northern Estuary and Rivers stations. Ten of the eleven highest chromium concentrations recorded in the RMP were measured in the northern reach. The highest chromium concentration (8.79 µg/L) was measured at the Petaluma River station (BD15). The average dissolved lead concentration in January (0.17µg/L) was three times higher than the April average (0.05 µg/L). In the South Bay, concentrations of dissolved mercury, chromium, and lead were not strongly affected by the Big Storm. The high dissolved concentrations observed during high flow conditions in the watershed suggest mobilization and transport of large masses of more bioavailable forms of these elements during this period.

Total (dissolved + particulate) concentrations of some trace elements that are transported primarily in the particulate phase were also sharply elevated in January. The highest baywide average total concentrations of chromium, copper, mercury, nickel, lead, and zinc since the beginning of the RMP were measured in January. Baywide average TSS concentrations fell from 91 mg/L in January to 38 mg/L in April, and baywide average concentrations of these elements showed similar declines, generally dropping to about 50% of the January concentrations. Total mercury, for example, fell from a baywide average of 0.036 µg/L in January to 0.014 µg/L in April. The largest drop was observed for chromium, from 17.7 µg/L in January to 5.3 µg/L in April, a 3.3-fold difference. As for the dissolved concentrations, the high baywide averages in January were principally due to high concentrations in the northern reach, and the South Bay was relatively unaffected by the Big Storm. The dissolved and particulate forms of trace elements mobilized during the Big Storm were likely derived from both natural and anthropogenic sources.

High concentrations of some organics were also observed in January. Dissolved chlordanes and DDTs were highest in January at all Northern Estuary stations, although the magnitude of this seasonal difference was not as great as for dissolved mercury, chromium, and lead. The Petaluma River (BD15) and Napa River (BD50) stations in January had the highest concentrations of dissolved DDTs and chlordanes observed in the northern reach. Dissolved chlordanes and DDTs did not exhibit clear seasonal variation in the southern reach.

Diazinon is found almost entirely in the dissolved phase in RMP samples. Unlike chlordanes and DDTs, diazinon concentrations showed seasonal variability in both the northern and southern portions of the Bay. The highest concentrations for the year were observed at the Northern Estuary and Rivers stations in January, ranging between approximately 10 and 40 ng/L. These concentrations were high relative to RMP data from other years, but not the highest.

Total (dissolved + particulate) chlordanes and DDTs were also elevated in the January sampling. Total DDT concentrations at the Rivers were the highest yet observed for these stations in the RMP. Total DDT concentrations were also elevated in January at the Northern Estuary stations. Total concentrations of dieldrin and chlordanes at the Northern Estuary stations were the highest yet observed for these stations in the RMP. The high dissolved + particulate concentrations of DDTs, chlordanes, and dieldrin in the Northern Estuary suggest transport of contaminated sediment particles from the Central Valley during the high flows in January.

In contrast to the organochlorine pesticides, dissolved + particulate PCB concentrations at the Rivers and Northern Estuary stations were not elevated during the Big Storm. This suggests that the sediment particles washing into the Estuary from the Central Valley were relatively uncontaminated with respect to PCBs. This observation is consistent with previous observations of relatively low TSS-normalized concentrations of PCBs at the Northern Estuary and Rivers stations (Jarman and Davis in the 1995 Annual Report).

Overall, due to a combination of high flows and elevated concentrations, the mass loading of many contaminants to the Bay was greatly increased during the Big Storm of 1997.

Comparison to Water Quality Guidelines

This section provides a brief overview of how 1997 data compare to relevant water quality guidelines (Table 3.7). Of the ten trace elements measured, concentrations of chromium, copper, mercury, nickel, and zinc were higher than guidelines on one or more occasions (Table 3.8). Nickel, mercury, and chromium concentrations were most frequently above guidelines. Several trace organics also had concentrations above guidelines, including PCBs, DDTs, chlordanes, dieldrin, and PAHs (Table 3.9). Congener-based ÂPCBs were well above the congener-based 170 pg/L guideline in most of the samples.

Effects of Water Contamination

Clear statistically and biologically significant toxicity was observed in the Mysidopsis test in January 1997 at Sacramento River (BG20) and San Joaquin River (BG30). Statistically significant toxicity with higher percent survival was also observed at Grizzly Bay (BF20) and Napa River (BD50). In August 1997 clear toxicity was also observed in the Mysidopsis test at four South Bay stations: Redwood Creek (BA40), Coyote Creek (BA10), Sunnyvale (C-1-3), and San Jose (C-3-0). Percent survival was 33% at Redwood Creek (BA40), and 0% at the other three stations.

Toxicity tests using Mytilus larvae indicated statistically significant toxicity in January at Grizzly Bay (BF20), Pinole Point (BD30), Redwood Creek (BA40), and Sunnyvale (C-1-3), but percent normal development in these samples was relatively high. The statistical significance of these results is due to the low variability in the control treatments and does not indicate toxicity in the samples.

In 1996 a special study was initiated to investigate episodic toxicity following storm events, as described in detail in Ogle and Gunther (this Chapter). In the winter of 1996­1997, ambient toxicity monitoring was conducted at the mouths of Guadalupe Slough and Alviso Slough in the South Bay and in Napa River and at Mallard Island in the North Bay. In the winter of 1997­1998, more temporally-intensive sampling was performed at Mallard Island, sampling continued at Guadalupe Slough, and sampling at Pacheco Slough was added. Toxicity has been detected consistently in this special study. In some instances, ELISA analysis of diazinon and chlorpyrifos in the samples has yielded results consistent with these organophosphates being the possible cause of toxicity. In most samples, however, diazinon and chlorpyrifos concentrations were below toxic levels, suggesting that other contaminants were responsible for the observed toxicity.

References

Hunrichs, R.A., D.A. Pratt, and R.W. Meyer. 1998. Magnitude and frequency of the flood of January 1997 in northern and central Californiapreliminary determinations. U.S. Geological Survey Open File Report 98-628. Sacramento, CA.

SFBRWQCB. 1995. 1995 Basin Plan. San Francisco Bay Regional Water Quality Control Board, Oakland, CA.

U.S. EPA. 1997. Water Quality Standards; Establishment of Numeric Criteria for Priority Toxic Pollutants for the State of California; Proposed Rule. Federal Register Vol. 62, No. 150, August 5, 1997.