A record of estuarine water contamination from the Cd content of foraminiferal tests in San Francisco Bay, California

Abstract

A five-year dissolved Cd time series from San Francisco Bay and adjacent coastal water shows that the composition of surface water towards the mouth of the estuary is determined largely by the effect of coastal upwelling. Cd concentrations Ž . inside and outside the estuary 0.2-1.0 nmolrkg increase as Cd-rich deep water is advected to the surface near the coast Ž . during spring and summer. On average, the mean Cd concentrations inside San Francisco Bay 0.54 nmolrkg during Ž . 1991-1995 was significantly higher than outside 0.35 nmolrkg , however. Surface samples collected throughout San Francisco Bay confirm an internal Cd source unrelated to river discharge. The Cd content of the test of a benthic foraminifer Ž . Elphidiella hannai in a dated sediment core from San Francisco Bay was measured to determine if the water column Cd enrichments in San Francisco Bay could be related to the rapid development of the watershed. The method is based on the observation that the CdrCa ratio of carefully cleaned tests of foraminifera is determined by the dissolved Cd content of overlying water at the time of test formation. Pre-industrial foraminiferal CdrCa ratios in the sediment core average Ž . Ž . 274 " 15 nmolrmol n s 19 nmolrmol. Foraminiferal CdrCa ratios increased to 386 " 33 nmolrmol n s 19 over the past several decades indicating a 40% increase in the mean Cd content of surface water in Central San Francisco Bay. We suggest that, in addition to Cd discharges into the estuary, indirect consequences of agricultural development in the Central Valley of California could have contributed to this increase. This new method to reconstruct estuarine contamination is not affected by some of the processes that complicate the interpretation of changes in bulk sediment metal concentrations. q

Open Water Processes of the San Francisco Estuary: From Physical Forcing to Biological Responses

“…Relatively little work has been done on the biogeochemical transformations in the sediments of the San Francisco Estuary of substances other than contaminants (e.g., van Geen and Luoma 1999). General patterns of sediment chemistry are a well-established function of oxidation-reduction potential (Heip et al 1995).…”

Groundwater seepage into northern San Francisco Bay: Implications for dissolved metals budgets

“…The flow of groundwater into estuaries, lakes, and coastal zones can transport nutrients and contaminants from aquifers or from benthic sediments to surface waters [ Church , 1996]. Groundwater seepage could influence water quality in San Francisco Bay because there are high levels of contaminants, including metals, in its benthic sediments [ Luoma and Phillips , 1988; Rivera‐Duarte and Flegal , 1997a, 1997b; van Geen and Luoma , 1999]. Therefore we determined groundwater seepage rates and bioirrigation rates in northern San Francisco Bay, and estimated the importance of benthic seepage on the transport of dissolved metals to its surface waters.…”

“…Nonconservative excesses [ Officer , 1979] of nutrients and dissolved metals in northern San Francisco Bay surface waters [ Flegal et al , 1991; Smith and Flegal , 1993; van Geen and Luoma , 1999] indicate that there are sources of dissolved metals within the bay, between the Sacramento/San Joaquin Rivers and the Pacific Ocean. Preliminary mass balance calculations indicate that these internal sources are larger than known inputs to the bay [ Rivera‐Duarte and Flegal , 1997a, 1997b].…”

“…After accounting for estimated industrial and municipal inputs, and biological scavenging, the amount of dissolved cadmium added to northern San Francisco Bay by unknown sources is estimated to be 103 mol/d. Because particles transported into San Francisco Bay by rivers are a relatively small source of cadmium to the surface water, dissolved cadmium sources are located within San Francisco Bay [ van Geen and Luoma , 1999]. In northern San Francisco Bay, the largest dissolved cadmium enrichments are near the Carquinez Strait (Figure 1) [ van Geen and Luoma , 1999].…”

Sedimentary Processes of the Qingdao Nearshore Traced Using a Multi-radionuclide Approach

“…Santschi et al (2001) studied the accumulation rate of organic carbon, bioturbation, and the source and lateral transport of sediments on the Palos Verdes Shelf based on the profiles of 137 Cs, 239,240 Pu,210 Pb,234 Th, 238 U and 14 C in sediment cores. Fuller et al (1999) used 210 Pb, 234 Th, 137 Cs, 226 Ra and 239,240 Pu as tracers to investigate the sediment chronology of San Francisco Bay, California, and evaluated the historic changes in metal, polycyclic aromatic hydrocarbons, chlorinated hydrocarbon pesticides, and polychlorinated biphenyls (Hornberger et al 1999;Hostettler et al 1999;Pereira et al 1999;Ritson et al 1999;van Geen and Luoma 1999;Venkatesan et al 1999). Liu et al (2001) measured various radionuclides in sediment cores collected from the Pearl River Estuary and, with the chronologies of 210 Pb and 137 Cs, compared the profiles of 228 Th, 228 Ra and 238 U to confirm that the sources of sediment have changed sharply since ∼ 1970.…”