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Geology topics

Research about San Francisco Bay

Source-linked reports with geographic coverage including San Francisco Bay.

At least 199 records · Page 11Linked to original sources
USGS2003

Movement of spilled oil as predicted by estuarine nontidal drift

Information on water movement obtained from bimonthly releases of surface and seabed drifters in the San Francisco Bay and adjacent Pacific Ocean is used to understand major processes controlling dispersal of oil after a spill of 3,200 m3 of Bunker C in the bay in January 1971. River-induced nontidal estuarine circulation was the dominant factor controlling net movement of the oil spilled at the entrance of the bay system, reinforcing ebbing tidal currents and causing the seaward movement of floating oil, which followed paths taken by surface drifters released 3 weeks before the spill. In contrast, some oil formed globules which sank to the near-bottom waters, had the same relative buoyancy as seabed drifters, and moved similarly, beaching in eastern San Pablo Bay after being transported landward in the near-bottom waters. No oil or surface drifters floated into the south bay because surface waters were drifting seaward, away from the south bay. Notable seasonally modulated phenomena which must be considered in predicting surface and near-bottom oil drifts of future spills include a summer (low-river discharge period) diminution of the estuarine circulation mechanism in the north and central bayadjacent ocean region and a seasonal reversal in two-layer drift in the south bay.

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USGS2003

Molecular and isotopic tracers used to examine sources of organic matter and its incorporation into the food webs of San Francisco Bay

Multiple indicators (Chl a , C : N ratios, [ δ 13 C]POC, and two classes of lipid biomarker compounds- sterols and phospholipid ester-linked fatty acids) were used to evaluate spatial and temporal variations in the origin of particulate organic matter (POM) in the San Francisco Bay (SFB) estuary. Comparisons were made between the northern and southern subestuaries of SFB, as well as along the salinity gradient of northern SFB. Two sample types were collected-seston, which was used to characterize the bulk POM, and tissues of the suspension-feeding bivalve Potamocorbula amurensis -in order to evaluate the assimilable portion of the POM. Samples were collected around biological and physical events (phytoplankton blooms and freshwater inflow) thought to be the primary mechanisms controlling temporal variability in organic matter sources. Seston samples indicate that phytoplankton sources of POM are important throughout the entire SFB system, with additional inputs of organic matter from bacterial and terrestrial vascular plant sources delivered to the northern region. Analysis of biomarker compounds in P. amurensis tissues indicates that phytoplankton supply a large fraction of the assimilable carbon to clams throughout SFB, although isotopic analysis of clam tissues suggests that the origin of this reactive carbon varies spatially and that freshwater algae are an important source of reactive organic matter to clams living in northern SFB.

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USGS2003

Diagnostic modeling of trace metal partitioning in south San Francisco Bay

The two-dimensional numerical model ELAmet was used to investigate the effect of adsorption kinetics on the apparent distribution coefficients of Cu, Cd, and Zn in south San Francisco Bay, California. The numerical experiments were designed to determine whether adsorption kinetics can control the basin-scale variability of the observed partitioning and to define the conditions under which adsorption kinetics could account for strong interannual variability in partitioning. The numerical results indicate that aqueous speciation will control basin-scale spatial variations in the apparent distribution coefficient, K d a , if the system is close to equilibrium. However, basin-scale spatial variations in K d a are determined by the location of the sources of metal and the suspended solids concentration of the receiving water if the system is far from equilibrium. The overall spatial variability in K d a also increases as the system moves away from equilibrium.

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USGS2003

Assessing toxicant effects in a complex estuary--A case study of effects of silver on reproduction in the bivalve, Potamocurbula amurensis, in San Francisco Bay

Contaminant exposures in natural systems can be highly variable. This variability is superimposed upon cyclic variability in biological processes. Together, these factors can confound determination of contaminant effects. Long term, multidisciplined studies with high frequency sampling can be effective in overcoming such obstacles. While studying trace metal contamination in the tissues of the clam, Potamocorbula amurensis , in the northern reach of San Francisco Bay, an episode of high Ag concentrations was identified (maximum of 5.5 µg g −1 ) at two mid-estuary sites. High concentrations were not seen in clams up-estuary (maximum of 1.92 µg g −1 ) from these sites and were reduced down-estuary (maximum of 2.67 µg g −1 ). Silver is not common naturally in the environment, so its elevated presence is usually indicative of anthropogenic influences such as municipal and industrial discharge. Monthly sampling of reproductive status of clams characterized the reproductive cycle and differences in the patterns of reproductive activity that corresponded to changes in Ag tissue concentrations. The proportion of reproductive clams was less than 60% during periods when tissue concentrations were high (generally >2 µg g −1 ). When tissue concentrations of Ag decreased (≤1 µg g −1 ), the proportion of reproductive clams was 80 to 100%. A comparison between the annual proportion of reproductive clams and annual Ag tissue concentrations showed a significant negative correlation. No other measured environmental variables were correlated with reproductive impairment. The weight-of-evidence approach strongly supports a cause and effect relationship between Ag contamination and reduced reproductive activity in P. amurensis .

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USGS2003

Structure and mechanics of the Hayward-Rodgers Creek Fault step-over, San Francisco Bay, California

A dilatational step - over between the right-lateral Hayward and Rodgers Creek faults lies beneath San Pablo Bay in the San Francisco Bay area. A key seismic hazard issue is whether an earthquake on one of the faults could rupture through the step - over , enhancing its maximum possible magnitude. If ruptures are terminated at the step - over , then another important issue is how strain transfers through the step . We developed a combined seismic reflection and refraction cross section across south San Pablo Bay and found that the Hayward and Rodgers Creek faults converge to within 4 km of one another near the surface, about 2 km closer than previously thought. Interpretation of potential field data from San Pablo Bay indicated a low likelihood of strike-slip transfer faults connecting the Hayward and Rodgers Creek faults. Numerical simulations suggest that it is possible for a rupture to jump across a 4-km fault gap, although special stressing conditions are probably required (e.g., Harris and Day, 1993, 1999). Slip on the Hayward and Rodgers Creek faults is building an extensional pull-apart basin that could contain hazardous normal faults. We investigated strain in the pull-apart using a finite-element model and calculated a ∼0.02-MPa/yr differential stressing rate in the step - over on a least-principal-stress orientation nearly parallel to the strike-slip faults where they overlap. A 1- to 10-MPa stress-drop extensional earthquake is expected on normal faults oriented perpendicular to the strike-slip faults every 50-500 years. The last such earthquake might have been the 1898 M 6.0-6.5 shock in San Pablo Bay that apparently produced a small tsunami. Historical hydrographic surveys gathered before and after 1898 indicate abnormal subsidence of the bay floor within the step - over , possibly related to the earthquake. We used a hydrodynamic model to show that a dip-slip mechanism in north San Pablo Bay is the most likely 1898 rupture scenario to have caused the tsunami. While we find no strike-slip transfer fault between the Hayward and Rodgers Creek faults, a normal- fault link could enable through-going segmented rupture of both strike-slip faults and may pose an independent hazard of M ∼6 earthquakes like the 1898 event.

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USGS2003

Preliminary analysis of cores from north San Francisco Bay, California

During the mid-to late-1800's, large quantities of tailings from hydraulic gold mining in the Sierra Nevada were deposited in San Francisco Bay (Gilbert, 1917; Jaffe et al., 1998; Capiella et al., 1999). This rapid deposition also choked river systems and deposited mercury-contaminated sediments in the rivers and Bay. Hydraulic mining was stopped in 1884 by a California Supreme Court decision. Deposition in the Bay slowed in the late 1800's and early 1900's as a result of this decrease in sediment supply (Jaffe et al., 1998; Capiella et al., 1999). During the mid-1900's, sediment supply was further reduced by water works projects (dams, diversions, etc.), creating an erosional system in the study area by the late 1900's. The re-working of these sediments poses environmental and biological concerns regarding mercury in the bay. The location of these deposits is important for understanding the health of the bay waters. In March 2000, the U.S. Geological Survey collected sediment cores in the study area to determine the location of mercury-contaminated hydraulic mining debris. The study area (Figure 1) comprises 400 km2 and consists of San Pablo Bay and Suisun Bay, both of which are part of the San Francisco Bay estuary. Grizzly Bay, a subembayment of Suisun Bay, is also part of the study area. For the purpose of this report the term Suisun Bay will be used collectively for both areas. The present channel system in Suisun Bay is composed of three channels that flow through the bay. The primary channel runs in the southern section of Suisun Bay. A smaller channel flows between Roe Island and Ryer Island. The deepest channel flows through Suisun Cutoff, north of Ryer Island, and past Grizzly Bay. All three channels join at Carquinez Strait where they continue through the southern section of San Pablo Bay, and into San Francisco Bay. The average depths in San Pablo and Suisun Bays at mean sea level are 3.7 m and 5.8 m, respectively (Smith et al., 2002).

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USGS2003

Preliminary location and age database for invertebrate fossils collected in the San Francisco Bay region, California

Most geologic maps published for central California in the past century have been made without the benefit of microfossils. The age of Cretaceous and Tertiary rocks in the structurally complex sedimentary formations of the Coast Ranges is critical in determining stratigraphic succession and in determining whether the juxtapositon of similar appearing formations means that a fault is present. Since the 1930’s, at least, oil company geologists have used microfossils to assist them in geologic mapping and in determining the environments of deposition of sedimentary rocks. This information has been confidential, but in the past 20 years the attitude of petroleum companies about this information has changed, and much material is now available. We report here on approximately 4,700 samples, largely foraminifers, from surface localities in the San Francisco Bay region of California. The information contained here can be used to update geologic maps, to analyze the depth and temperature of ocean water covering parts of California during the Mesozoic and Cenozoic eras, and for solving other geologic problems.

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USGS2003

Salinity and temperature in South San Francisco Bay, California, at Dumbarton Bridge: Results from the 1999-2002 water years and an overview of previous data

Salinity and temperature were measured in near-surface waters at Dumbarton Bridge in South San Francisco Bay during the 1999–2002 water years (1999WY–2002WY). The complete data set from this site, which included 1990WY–1993WY and 1995WY–1998WY, provided a time–series of observations covering a wide range of hydrologic conditions. These conditions included critically dry years and years with above-normal and near–record precipitation and discharges from the major rivers and local streams. Data collection at 15–minute intervals allowed resolution of variability associated with daily tides and other short-term phenomena. Both local stream discharges to South San Francisco Bay and Sacramento–San Joaquin River discharges to North San Francisco Bay affected salinity at Dumbarton Bridge. Salinity at Dumbarton Bridge varied with the daily tides, and the lowest salinity values (annual) coincided with precipitation and freshwater inflows usually in winter. Short–term and seasonal variations in temperature at Dumbarton Bridge typically followed changes in air temperature and solar irradiance.

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USGS2003

Comparison of salinity and temperature at continuous monitoring stations and nearby monthly measurement sites in San Francisco Bay

Salinity and temperature are crucial state variables affecting estuarine habitat an d, thus, are measured by various San Francisco Estuary programs. This article presents a comparison of salinity and temperature data collected at seven continuo us monitoring stations throughout San Francisco Bay (Figure 1) with data collected monthly by the US Geological Survey (USGS) research vessel ( RV ) Polaris . The data comparison was done to determine if the continuous monitoring stations, which mostly are located near shore and always on structures in the water, are representative of water conditions in the main channel of the estuary where the RV Polaris collects measurements.

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USGS2003

Specific-conductance, water-temperature, and water-level data, San Francisco Bay, California, for water years 2001-2002

This article presents time-series plots of specific-conductance, water-temperature, and water-level data collected in San Francisco Bay during water years 2001 and 2002 (October 1, 2000, through September 30, 2002). Specific-conductance and water-temperature data were recorded at 15-minute intervals at the following US Geological Survey (USGS) locations (Figure 1): • Suisun Bay at Benicia Bridge, near Benicia, California (BEN) (site # 11455780) • Carquinez Strait at Carquinez Bridge, near Crockett, California (CARQ) (site # 11455820) • Napa River at Mare Island Causeway, near Vallejo, California (NAP) (site # 11458370) • San Pablo Strait at Point San Pablo, California (PSP) (site # 11181360) • San Pablo Bay at Petaluma River Channel Marker 9, California (SPB) (site # 380519122262901) • San Francisco Bay at Presidio Military Reservation, California (PRES) (site # 11162690) • San Francisco Bay at Pier 24, at San Francisco, California (P24) (site # 11162700) • San Francisco Bay at San Mateo Bridge, near Foster City, California (SMB) (site # 11162765). Water-level data were recorded only at PSP through January 1, 2001. Suspended-sediment concentration data also were collected at most of these sites and were published by Buchanan and Ganju (2003). The data from PSP, PRES, P24, and SMB were recorded by the California Department of Water Resources (DWR) before 1988, by the USGS National Research Program from 1988 to 1989, and by the USGSDWR cooperative program since 1990. BEN, CARQ, NAP, and SPB were established in 1998 by the USGS.

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USGS2003

Sediment dynamics drive contaminant dynamics

Many contaminants of greatest concern in San Francisco Bay, including mercury and PCBs, are primarily associated with sediment particles rather than dissolved in water. Therefore, the movement and fate of sediment determines the movement and fate of many contaminants in the Bay. Because of this close association, the RMP monitors and seeks to understand the quantity and movement of sediment suspended in the water. Through study of suspended sediment dynamics, the RMP is developing a better understanding of trends and patterns of contaminants and how the Bay will respond to management actions during the next several decades. Recent RMP efforts to develop predictive models of contaminant fate in the Bay have highlighted the fundamental importance of understanding sediment dynamics. Sediment movement in the Bay is determined by tides, wind, and freshwater inflow. Tides flood and ebb twice a day, wind typically is strongest in the afternoon, and freshwater inflow is greatest during the winter rainy season (see sidebar on next page). To characterize these fluctuations, the U.S. Geological Survey (USGS) began continuous monitoring of suspended sediment concentration in 1991. Continuous suspended sediment concentration monitoring stations were established in each major region of San Francisco Bay (Figure 1), establishing a continuous monitoring network. The sensors at each station measure the amount of material in the water every 15 minutes. Results are available on the internet at . In addition to the network, sensors have been deployed at as many as 14 additional sites in the Bay for periods of several months as part of focused studies of sediment transport in Bay locales of special interest.

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USGS2003

Cross-channel variability in benthic habitat

Benthic invertebrates play an important role in estuarine food webs and biogeochemical cycling of carbon, nutrients, and contaminants. The generally sedentary benthic invertebrates continuously integrate local water, sediment, and food conditions. This makes them good indicators of the type and quality of aquatic habitat at the location where they are found. The Interagency Ecological Program’s Environmental Monitoring Program (EMP) has monitored benthic invertebrates since the mid-1970s. A recent review of the EMP found that the spatial study design of the benthos monitoring element was in need of a thorough reexamination through intense special studies and extensive historic data analyses. This article reports the results of preliminary analyses of historical EMP data focusing on cross-channel variability. Specific questions are: (1) do benthic habitats and community assemblages vary between positions across a river channel? (2) Are benthic samples taken at a single channel position sufficiently representative of benthos assemblages across the channel to characterize long term changes in the benthos community of a particular section of a river?

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USGS2002

Stable carbon and nitrogen isotope composition of aquatic and terrestrial plants of the San Francisco Bay estuarine system

We report measurements of seasonal variability in the C‐N stable isotope ratios of plants collected across the habitat mosaic of San Francisco Bay, its marshes, and its tributary river system. Analyses of 868 plant samples were binned into 10 groups (e.g., terrestrial riparian, freshwater phytoplankton, salt marsh) to determine whether C‐N isotopes can be used as biomarkers for tracing the origins of organic matter in this river‐marsh‐estuary complex. Variability of δ 13 C and δ 15 N was high (~5–10‰) within each plant group, and we identified three modes of variability: (1) between species and their microhabitats, (2) over annual cycles of plant growth and senescence, and (3) between living and decomposing biomass. These modes of within‐group variability obscure any source specific isotopic signatures, confounding the application of C‐N isotopes for identifying the origins of organic matter. A second confounding factor was large dissimilarity between the δ 13 C‐δ 15 N of primary producers and the organic matter pools in the seston and sediments. Both confounding factors impede the application of C‐N isotopes to reveal the food supply to primary consumers in ecosystems supporting diverse autotrophs and where the isotopic composition of organic matter has been transformed and become distinct from that of its parent plant sources. Our results support the advice of others: variability of C‐N stable isotopes within all organic‐matter pools is high and must be considered in applications of these isotopes to trace trophic linkages from primary producers to primary consumers. Isotope‐based approaches are perhaps most powerful when used to complement other tools, such as molecular biomarkers, bioassays, direct measures of production, and compilations of organic‐matter budgets.

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USGS2002

Microphytobenthos potential productivity estimated in three tidal embayments of the San Francisco Bay system

In this paper we describe a three-step procedure to infer the spatial heterogeneity in microphytobenthos primary productivity at the scale of tidal estuaries and embayments. The first step involves local measurement of the carbon assimilation rate of benthic microalgae to determine the parameters of the photosynthesis-irradiance (P-E) curves (using non-linear optimization methods). In the next step, a resampling technique is used to rebuild pseudo-sampling distributions of the local productivity estimates; these provide error estimates for determining the significance level of differences between sites. The third step combines the previous results with deterministic models of tidal elevation and solar irradiance to compute mean and variance of the daily areal primary productivity over an entire intertidal mudflat area within each embayment. This scheme was applied on three different intertidal mudflat regions of the San Francisco Bay estuary during autumn 1998. Microphytobenthos productivity exhibits strong (ca. 3-fold) significant differences among the major sub-basins of San Francisco Bay. This spatial heterogeneity is attributed to two main causes: significant differences in the photosynthetic competence (P-E parameters) of the microphytobenthos in the different sub-basins, and spatial differences in the phase shifts between the tidal and solar cycles controlling the exposure of intertidal areas to sunlight. The procedure is general and can be used in other estuaries to assess the magnitude and patterns of spatial variability of microphytobenthos productivity at the level of the ecosystems.

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USGS2002

Effects of tidal current phase at the junction of two straits

Estuaries typically have a monotonic increase in salinity from freshwater at the head of the estuary to ocean water at the mouth, creating a consistent direction for the longitudinal baroclinic pressure gradient. However, Mare Island Strait in San Francisco Bay has a local salinity minimum created by the phasing of the currents at the junction of Mare Island and Carquinez Straits. The salinity minimum creates converging baroclinic pressure gradients in Mare Island Strait. Equipment was deployed at four stations in the straits for 6 months from September 1997 to March 1998 to measure tidal variability of velocity, conductivity, temperature, depth, and suspended sediment concentration. Analysis of the measured time series shows that on a tidal time scale in Mare Island Strait, the landward and seaward baroclinic pressure gradients in the local salinity minimum interact with the barotropic gradient, creating regions of enhanced shear in the water column during the flood and reduced shear during the ebb. On a tidally averaged time scale, baroclinic pressure gradients converge on the tidally averaged salinity minimum and drive a converging near-bed and diverging surface current circulation pattern, forming a "baroclinic convergence zone" in Mare Island Strait. Historically large sedimentation rates in this area are attributed to the convergence zone.

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USGS2002

Tidal asymmetry and variability of bed shear stress and sediment bed flux at a site in San Francisco Bay, USA

The relationship between sediment bed flux and bed shear stress during a pair of field experiments in a partially stratified estuary is examined in this paper. Time series of flow velocity, vertical density profiles, and suspended sediment concentration were measured continuously throughout the water column and intensely within 1 meter of the bed. These time series were analyzed to determine bed shear stress, vertical turbulent sediment flux, and mass of sediment suspended in the water column. Resuspension, as inferred from near-bed measurements of vertical turbulent sediment flux, was flood dominant, in accordance with the flood-dominant bed shear stress. Bathymetry-induced residual flow, gravitational circulation, and ebb tide salinity stratification contributed to the flood dominance. In addition to this flow-induced asymmetry, the erodibility of the sediment appears to increase during the first 2 hours of flood tide. Tidal asymmetry in bed shear stress and erodibility help explain an estuarine turbidity maximum that is present during flood tide but absent during ebb tide. Because horizontal advection was insignificant during most of the observation periods, the change in bed mass can be estimated from changes in the total suspended sediment mass. The square wave shape of the bed mass time series indicates that suspended sediment rapidly deposited in an unconsolidated or concentrated benthic suspension layer at slack tides and instantly resuspended when the shear stress became sufficiently large during a subsequent tide. The variability of bed mass associated with the spring/neap cycle (about 60 mg/cm2) is similar to that associated with the semidiurnal tidal cycle.

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USGS2002

Rocks and geology in the San Francisco Bay region

The landscape of the San Francisco Bay region is host to a greater variety of rocks than most other regions in the United States. This introductory guide provides illustrated descriptions of 46 common and important varieties of igneous, sedimentary, and metamorphic rock found in the region. Rock types are described in context of their identification qualities, how they form, and where they occur in the region. The guide also provides discussion about of regional geology, plate tectonics, the rock cycle, the significance of the selected rock types in relation to both earth history and the impact of mineral resources on the development in the region. Maps and text also provide information where rocks, fossils, and geologic features can be visited on public lands or in association with public displays in regional museums, park visitor centers, and other public facilities.

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