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Research about San Francisco Bay

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

At least 181 records · Page 10Linked to original sources
USGS2005

Climate anomalies generate an exceptional dinoflagellate bloom in San Francisco Bay

We describe a large dinoflagellate bloom, unprecedented in nearly three decades of observation, that developed in San Francisco Bay (SFB) during September 2004. SFB is highly enriched in nutrients but has low summer‐autumn algal biomass because wind stress and tidally induced bottom stress produce a well mixed and light‐limited pelagic habitat. The bloom coincided with calm winds and record high air temperatures that stratified the water column and suppressed mixing long enough for motile dinoflagellates to grow and accumulate in surface waters. This event‐scale climate pattern, produced by an upper‐atmosphere high‐pressure anomaly off the U.S. west coast, followed a summer of weak coastal upwelling and high dinoflagellate biomass in coastal waters that apparently seeded the SFB bloom. This event suggests that some red tides are responses to changes in local physical dynamics that are driven by large‐scale atmospheric processes and operate over both the event scale of biomass growth and the antecedent seasonal scale that shapes the bloom community.

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USGS2005

Highly magnetic Upper Miocene sandstones of the San Francisco Bay area, California

[1] A high-resolution aeromagnetic survey of the San Francisco Bay area shows prominent positive anomalies over distinctive blue sandstones of Late Miocene age. The total-field survey was measured at a nominal height of 300 m above the land surface along flight lines spaced 0.5 km apart. Anomalies with amplitudes up to 200 nT correlate with sandstones of the San Pablo Group, and these anomalies are similar in strength to the magnetic signatures of serpentinites and basalts in the surveyed region. Andesitic sandstone of the Neroly Formation, the upper part of the San Pablo Group, has high magnetic susceptibility (0.013 SI units, volume) and relatively strong natural remanent magnetization (0.29 A/m). Total magnetization of the sandstone is two thirds induced and one third remanent magnetization. The presence of coarse-grained magnetite detritus, low coercivity of remanence, low thermal stability of remanence, and multidomain properties is consistent with the NRM being a viscous remanent magnetization that grew during the Brunhes normal-polarity chron. The strong magnetic signature of the Upper Miocene sandstones allows their delineation over distances as great as 100 km, through areas where they are concealed by landslides and younger deposits. The sandstones are important structural markers for understanding the complex folding and faulting associated with active fault systems in the San Francisco Bay area.

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USGS2005

Predator removal and nesting waterbird success at San Francisco Bay, California

The efficacy of long-term predator removal in urbanized areas is poorly understood. The impact of predation on ground-nesting waterbirds, as well as predator abundance and composition in predator removal versus non-removal or reference sites were examined at South San Francisco Bay. The success of natural nests and predator activity was monitored using track plates, trip cameras, wire haircatchers and simulated nests. Removal sites had higher nest densities, but lower hatching success than reference sites. Predator composition and abundance were not different at the removal and reference sites for any predator other than feral Cat ( Felis domesticus ). Striped Skunk ( Mephitis mephitis ) comprised the majority (84%) of predators removed, yet remained the most abundant predators in removal and reference sites. Urban environments provide supplemental food that may influence skunks and other nest predators to immigrate into vacancies created by predator removal. Based on the findings from this study, predator removal should be applied intensively over a larger geographic area in order to be a viable management strategy for some mammalian species in urbanized areas.

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USGS2005

Putting down roots in earthquake country: Your handbook for the San Francisco Bay region

This handbook provides information about the threat posed by earthquakes in the San Francisco Bay region and explains how you can prepare for, survive, and recover from these inevitable events. If you live or work in the region, you need to know why you should be concerned with earthquakes, what you can expect during and after a quake, and what you need to do beforehand to be safe and reduce damage.

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USGS2005

South San Francisco Bay 2004 topographic lidar survey: Data overview and preliminary quality assessment

Tidal wetlands in South San Francisco Bay (South Bay) have decreased by over 80% in the past 150 years. The California Coastal Conservancy, in conjunction with other state and federal agencies, is collaboratively managing an effort to restore approximately 61 km 2 (15,100 acres) of commercial salt evaporation ponds in South Bay to mixed intertidal habitat. In order to best develop restoration strategies, as well as to track morphologic change throughout the restoration process, a topographic lidar survey was conducted in May of 2004. The survey collected more than 250 million elevation points in a 334 km 2 area extending from just south of the San Francisco and Oakland airports to the Alviso salt ponds. This report details the collection of lidar in South Bay, the ground-truthing efforts, preliminary accuracy assessments, and known limitations of the data set. We describe the data generated from the survey and how to obtain it. In addition, we present maps and sample imagery that provides a revealing look into the intricate topographic features of South Bay.

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USGS2005

Locations and descriptions of gravity, box, and push cores collected in San Francisco Bay between January and February, 1990 and 1991

A project to study San Francisco Bay sediments collected over 300 sediment gravity cores; six push cores, and three box cores in San Francisco Bay during the years 1990-91. The purpose of the sampling effort is to establish a database on the Holocene sediment history of the bay. The samples described and mapped are the first effort to catalog and present the data collected. Thus far the cores have been utilized in various cooperative studies with state colleges and universities, and other USGS divisions. These cores serve as a base for ongoing multidisciplinary studies. The sediment studies project has initiated subsequent coring efforts within the bay using refined coring techniques to attain deeper cores.

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USGS2005

Phytoplankton community ecology: Principles applied in San Francisco Bay

In his seminal 1961 paper 'The paradox of the plankton' Am Nat 95:137-147, G. E. Hutchinson asked why many species of phytoplankton can coexist while competing for a small number of limiting resources in an unstructured habitat. Hutchinson anticipated the resolution of his paradox, recognizing that communities are organized by processes beyond resource competition including species interactions, habitat variability and dispersal. Since 1961 we have made fundamental discoveries that have revolutionized our conceptual understanding of pelagic ecology, including (1) habitat heterogeneity at all scales relevant to plankton population dynamics, (2) community shifts in response to global climate cycles, (3) fast and selective predation as a powerful top-down force to shape phytoplankton communities, (4) turbulent mixing as a physical process that selects species on the basis of their size and form, (5) mixotrophy that allows some algal species to tap organic nutrient pools and function at multiple trophic levels, (6) taxon-specific life cycles including alternating vegetative and resting stages, and (7) the pelagic as an open system where communities are continually reshaped by species immigration. Here we synthesize these discoveries to show how they validate and amplify Hutchinson's hypothesis that phytoplankton communities are assembled by many processes. Our synthesis is built around observations of phytoplankton species composition from a decade of study in San Francisco Bay, used as a case study to illustrate the contemporary principles of phytoplankton community ecology. We apply these principles to address 2 central questions: (1) What processes assemble phytoplankton communities? (2) How does phytoplankton community composition influence ecosystem functions such as production in pelagic and benthic food webs?

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USGS2005

Specific conductance and water temperature data for San Francisco Bay, California, for Water Year 2004

This article presents time-series graphs of specificconductance and water-temperature data collected in San Francisco Bay during water year 2004 (October 1, 2003, through September 30, 2004). Specific-conductance and water-temperature data were recorded at 15-minute intervals at seven U.S. Geological Survey (USGS) locations (Figure 1, Table 1). Specific-conductance and water-temperature data from Point San Pablo (PSP) and San Mateo Bridge (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. Benicia Bridge (BEN), Carquinez Bridge (CARQ), and Napa River (NAP) were established in 1998 by the USGS. San Pablo Bay (SPB) was initially established in 1998 at Channel Marker 9 but was moved to Channel Marker 1 in 2003. The monitoring station at Alcatraz (ALC) was established in 2003 by the USGS to replace the discontinued monitoring station San Francisco Bay at Presidio Military Reservation.

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USGS2005

Bay sediment budget: Sediment accounting 101

Comparison of a budget developed for 1955-1990 with a budget developed for 1995- 2002 showed decreasing sediment inflow and increased amounts leaving the Bay to upland disposal and sand mining, resulting in an increased rate of erosion of sediment from the Bay floor Finding a way to shift disposal from the Ocean back to the Bay could provide sediment for restoration projects and decrease dredging costs Increased erosion of the Bay is mobilizing legacy contaminants from the sediment bed Restoration projects could increase erosion and mobilization of legacy contaminants Sand mining, ignored in previous budgets, removes almost twice as much sediment from the Bay as dredging

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USGS2004

Modeling selenium bioaccumulation through arthropod food webs in San Francisco Bay, California, USA

Trophic transfer is the main process by which upper trophic level wildlife are exposed to selenium. Transfers through lower levels of a predator's food web thus can be instrumental in determining the threat of selenium in an ecosystem. Little is known about Se transfer through pelagic, zooplankton‐based food webs in San Francisco Bay ([SFB], CA, USA), which serve as an energy source for important predators such as striped bass. A dynamic multipathway bioaccumulation model was used to model Se transfer from phytoplankton to pelagic copepods to carnivorous mysids ( Neomysis mercedis ). Uptake rates of dissolved Se, depuration rates, and assimilation efficiencies (AE) for the model were determined for copepods and mysids in the laboratory. Small (73‐250 μm) and large (250‐500 μm) herbivorous zooplankton collected from SFB ( Oithona/Limnoithona and Acartia sp.) assimilated Se with similar efficiencies (41‐52%) from phytoplankton. Mysids assimilated 73% of Se from small herbivorous zooplankton; Se AE was significantly lower (61%) than larger herbivorous zooplankton. Selenium depuration rates were high for both zooplankton and mysids (12‐25% d −1 ), especially compared to bivalves (2‐3% d −1 ). The model predicted steady state Se concentrations in mysids similar to those observed in the field. The predicted concentration range (1.5‐5.4 μg g −1 ) was lower than concentrations of 4.5 to 24 μg g −1 observed in bivalves from the bay. Differences in efflux between mysids and bivalves were the best explanation for the differences in uptake. The results suggest that the risk of selenium toxicity to predators feeding on N. mercedis would be less than the risk to predators feeding on bivalves. Management of selenium contamination should include food webs analyses to focus on the most important exposure pathways identified for a given watershed.

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USGS2004

Food web pathway determines how selenium affects aquatic ecosystems: A San francisco Bay case study

Chemical contaminants disrupt ecosystems, but specific effects may be under-appreciated when poorly known processes such as uptake mechanisms, uptake via diet, food preferences, and food web dynamics are influential. Here we show that a combination of food web structure and the physiology of trace element accumulation explain why some species in San Francisco Bay are threatened by a relatively low level of selenium contamination and some are not. Bivalves and crustacean zooplankton form the base of two dominant food webs in estuaries. The dominant bivalve Potamocorbula amurensis has a 10-fold slower rate constant of loss for selenium than do common crustaceans such as copepods and the mysid Neomysis mercedis (rate constant of loss, k e = 0.025, 0.155, and 0.25 d -1 , respectively). The result is much higher selenium concentrations in the bivalve than in the crustaceans. Stable isotope analyses show that this difference is propagated up the respective food webs in San Francisco Bay. Several predators of bivalves have tissue concentrations of selenium that exceed thresholds thought to be associated with teratogenesis or reproductive failure (liver Se >15 μg g - 1 dry weight). Deformities typical of selenium-induced teratogenesis were observed in one of these species. Concentrations of selenium in tissues of predators of zooplankton are less than the thresholds. Basic physiological and ecological processes can drive wide differences in exposure and effects among species, but such processes are rarely considered in traditional evaluations of contaminant impacts.

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USGS2004

Spatial and temporal variability of suspended-sediment concentrations in a shallow estuarine environment

Shallow subembayments respond differently than deep channels to physical forces acting in estuaries. The U.S. Geological Survey measured suspended-sediment concentrations at five locations in Honker Bay, a shallow subembayment of San Francisco Bay, and the adjacent channel to investigate the spatial and temporal differences between deep and shallow estuarine environments. During the first freshwater pulse of the wet season, the channel tended to transport suspended sediments through the system, whereas the shallow area acted as off-channel storage where deposition would likely occur. Following the freshwater pulse, suspended-sediment concentrations were greater in Honker Bay than in the adjacent deep channel, due to the larger supply of erodible sediment on the bed. However, the tidal variability of suspended-sediment concentrations in both Honker Bay and in the adjacent channel was greater after the freshwater pulse than before. During wind events, suspended-sediment concentrations in the channel were not affected; however, wind played a crucial role in the resuspension of sediments in the shallows. Despite wind-wave sediment resuspension in Honker Bay, tidally averaged suspended-sediment flux was controlled by the flood-dominated currents.

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USGS2004

Floodtide pulses after low tides in shallow subembayments adjacent to deep channels

In shallow waters surface gravity waves (tides) propagate with a speed proportional to the square root of water depth (c=g(h+η)). As the ratio of free surface displacement to mean depth (η/h) approaches unity the wave will travel noticeably faster at high tide than at low tide, creating asymmetries in the tidal form. This physical process is explained analytically by the increased significance of friction and the nonlinear terms in the continuity and momentum equations. In a tidal system comprising a shallow bay adjacent to a deeper channel, tidal asymmetries will be more prevalent in the shallow bay. Thus strong barotropic gradients can be generated between the two, producing rapid accelerations of currents into the bay (relative to other bay tidal processes) and create a maximum peak in the flood tide that we describe as a floodtide pulse. These floodtide pulses can promote a landward flux of suspended-sediment into the bay. In Grizzly Bay (part of northern San Francisco Bay, USA), field observations verify the occurrence of floodtide pulses during the lowest low tides of the year. No pulses were observed in neighboring Honker Bay, which has an average depth ~30 cm greater than Grizzly Bay. Numerical simulations of northern San Francisco Bay using realistic bathymetry demonstrated that floodtide pulses occurred in Grizzly Bay but not in Honker Bay, consistent with the observations. Both observations and numerical simulations show that floodtide pulses promote a landward flux of sediment into Grizzly Bay. Numerical simulations of an idealized bay-channel system quantify the importance of mean depth and friction in creating these floodtide pulses.

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USGS2004

Shifting shoals and shattered rocks: How man has transformed the floor of west-central San Francisco Bay

San Francisco Bay, one of the world's finest natural harbors and a major center for maritime trade, is referred to as the 'Gateway to the Pacific Rim.' The bay is an urbanized estuary that is considered by many to be the major estuary in the United States most modified by man's activities. The population around the estuary has grown rapidly since the 1850's and now exceeds 7 million people. The San Francisco Bay area's economy ranks as one of the largest in the world, larger even than that of many countries. More than 10 million tourists are estimated to visit the bay region each year. The bay area's population and associated development have increasingly changed the estuary and its environment. San Francisco Bay and the contiguous Sacramento-San Joaquin Delta encompass roughly 1,600 square miles (4,100 km2) and are the outlet of a major watershed that drains more than 40 percent of the land area of the State of California. This watershed provides drinking water for 20 million people (two thirds of the State's population) and irrigates 4.5 million acres of farmland and ranchland. During the past several decades, much has been done to clean up the environment and waters of San Francisco Bay. Conservationist groups have even bought many areas on the margins of the bay with the intention of restoring them to a condition more like the natural marshes they once were. However, many of the major manmade changes to the bay's environment occurred so long ago that the nature of them has been forgotten. In addition, many changes continue to occur today, such as the introduction of exotic species and the loss of commercial and sport fisheries because of declining fish populations. The economy and population of the nine counties that surround the bay continue to grow and put increasing pressure on the bay, both direct and indirect. Therefore, there are mixed signals for the future health and welfare of San Francisco Bay. The San Francisco Bay estuary consists of three subembayments--north bay (San Pablo and Suisun Bays), central bay, and south bay--each characterized by a central area of open water surrounded by intertidal mudflats and marshes. Central bay includes Alcatraz and Angel Islands and also a number of submerged bedrock knobs that protrude through the sediment of the bay floor and rise to within about 40 feet (12 m) of the water surface. The most prominent of these are Harding, Shag, Arch, and Blossom Rocks. These rocks have been lowered by blasting several times in the past, but they remain a potential hazard to shipping because newer cargo vessels are designed with increasingly deeper drafts. Central bay's location adjacent to two major population and commerce centers, San Francisco and Oakland, subjects it to greater human influences than less developed parts of the estuary. The western part of central San Francisco Bay is adjacent to the Golden Gate, the estuary's outlet to the Pacific Ocean. The changing submarine topography of the west-central bay, as well as its geology, form the main focus of this book.

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USGS2004

Deposition, erosion, and bathymetric change in South San Francisco Bay: 1858-1983

Since the California Gold Rush of 1849, sediment deposition, erosion, and the bathymetry of South San Francisco Bay have been altered by both natural processes and human activities. Historical hydrographic surveys can be used to assess how this system has evolved over the past 150 years. The National Ocean Service (NOS) (formerly the United States Coast and Geodetic Survey (USCGS), collected five hydrographic surveys of South San Francisco Bay from 1858 to 1983. Analysis of these surveys enables us to reconstruct the surface of the bay floor for each time period and quantify spatial and temporal changes in deposition, erosion, and bathymetry. The creation of accurate bathymetric models involves many steps. Sounding data was obtained from the original USCGS and NOS hydrographic sheets and were supplemented with hand drawn depth contours. Shorelines and marsh areas were obtained from topographic sheets. The digitized soundings and shorelines were entered into a Geographic Information System (GIS), and georeferenced to a common horizontal datum. Using surface modeling software, bathymetric grids with a horizontal resolution of 50 m were developed for each of the five hydrographic surveys. Prior to conducting analyses of sediment deposition and erosion, we converted all of the grids to a common vertical datum and made adjustments to correct for land subsidence that occurred from 1934 to 1967. Deposition and erosion that occurred during consecutive periods was then computed by differencing the corrected grids. From these maps of deposition and erosion, we calculated volumes and rates of net sediment change in the bay. South San Francisco Bay has lost approximately 90 x 106 m3 of sediment from 1858 to 1983; however within this timeframe there have been periods of both deposition and erosion. During the most recent period, from 1956 to 1983, sediment loss approached 3 x 106 m3/yr. One of the most striking changes that occurred from 1858 to 1983 was the conversion of more than 80% of the tidal marsh to salt ponds, agricultural, and urban areas. In addition, there has been a decline of approximately 40% in intertidal mud flat area. Restoration of these features will require a detailed understanding of the morphology and sediment sources of this complex system.

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USGS2004

Earthquakes and faults in the San Francisco Bay area (1970-2003)

The map depicts both active and inactive faults and earthquakes magnitude 1.5 to 7.0 in the greater San Francisco Bay area. Twenty-two earthquakes magnitude 5.0 and greater are indicated on the map and listed chronologically in an accompanying table. The data are compiled from records from 1970-2003. The bathymetry was generated from a digital version of NOAA maps and hydrogeographic data for San Francisco Bay. Elevation data are from the USGS National Elevation Database. Landsat satellite image is from seven Landsat 7 Enhanced Thematic Mapper Plus scenes. Fault data are reproduced with permission from the California Geological Survey. The earthquake data are from the Northern California Earthquake Catalog.

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USGS2004

Specific conductance and water temperature data for San Francisco Bay, California, for Water Year 2003

This article presents time-series graphs of specific-conductance and water-temperature data collected in San Francisco Bay during water year 2003 (October 1, 2002, through September 30, 2003). 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, CA. (BEN) (site # 11455780) • Carquinez Strait at Carquinez Bridge, near Crockett, CA. (CARQ) (site # 11455820) • Napa River at Mare Island Causeway, near Vallejo, CA. (NAP) (site # 11458370) • San Pablo Strait at Point San Pablo, CA. (PSP) (site # 11181360) • San Pablo Bay at Petaluma River Channel Marker 9, CA. (SPB) (site # 380519122262901) • San Francisco Bay at Presidio Military Reservation, CA. (PRES) (site # 11162690) • San Francisco Bay at San Mateo Bridge, near Foster City, CA. (SMB) (site # 11162765) Suspended-sediment-concentration data also were collected at most of these sites during water year 2003. Specific-conductance and water-temperature data from PSP, PRES, and SMB were recorded by the CA Department of Water Resources (DWR) before 1988, by the USGS National Research Program from 1988 to 1989, and by the USGS-DWR cooperative program since 1990. BEN, CARQ, NAP, and SPB were established in 1998 by USGS. The monitoring station at PRES was discontinued on November 12, 2002, due to shoaling at the site.

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