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At least 271 records · Page 15Linked to original sources
USGS2000

Recent research on the hydrodynamics of the Sacramento - San Joaquin River Delta and north San Francisco Bay

This article presents an overview of recent findings from hydrodynamic research on circulation and mixing in the Sacramento-San Joaquin Delta (Delta) (Figure 1) and North San Francisco Bay (North Bay) (Figure 2). For the purposes of this article, North Bay includes San Pablo Bay, Carquinez Strait, and Suisun Bay. The findings presented are those gained from field studies carried out by the U.S. Geological Survey (USGS), as part of the Interagency Ecological Program (IEP), and Stanford University beginning about 1993. The premise behind these studies was that a basic understanding of circulation and mixing patterns in the Bay and Delta is an essential part of understanding how biota and water quality are affected by natural hydrologic variability, water appropriation, and development activities. Data collected for the field studies described in this article have significantly improved our understanding of Bay and Delta hydrodynamics. Measured flows ,in the Delta have provided valuable information on how water moves through the Delta's network of channels and how export pumping affects flows. Studies of the shallows and shallow-channel exchange processes conducted in Honker Bay have shown that the water residence time in Honker Bay is much shorter than previously reported (on the order of hours to several tidal cycles instead ofweeks). Suisun Bay studies have provided data on hydrodynamic transport and accumulation mechanisms that operate primarily in the channels. The Suisun Bay studies have caused us to revise our understanding of residual circulation in the channels of North Bay and of "entrapment" mechanisms in the low salinity zone. Finally, detailed tidal and residual (tidally averaged) time-scale studies of the mechanisms that control gravitational circulation in the estuary show that density-driven transport in the channels is governed by turbulence time-scale (seconds) interactions between the mean flow and stratification. The hydrodynamic research summarized in this article spans a range of estuarine environments (deep water channels to shallow water habitats and brackish water to freshwater) at time scales that range from seconds to years.

California↗
USGS1989

Potamocorbula amurensis discovered in San Francisco Bay

The small Asian clam, Potamocorbula amurensis , is now a major component of benthic communities in most areas of northern San Francisco Bay and some areas of South Bay. Because of its wide tolerance of salinity and other environmental variables and its high abundance in many areas, benthic ecologists believe this recent invasion may represent a major and permanent change in the bay system.

California↗
USGS2001

Simplified conversions between specific conductance and salinity units for use with data from monitoring stations

The U.S. Geological Survey, Bureau of Reclamation, and the California Department of Water Resources maintain a large number of monitoring stations that record specific conductance, often referred to as “electrical conductivity,” in San Francisco Bay Estuary and the Sacramento-San Joaquin Delta. Specific conductance units that have been normalized to a standard temperature are useful in fresh waters, but conversion to salinity units has some considerable advantages in brackish waters of the estuary and Delta. For example, salinity is linearly related to the mixing ratio of freshwater and seawater, which is not the case for specific conductance, even when values are normalized to a standard temperature. The Practical Salinity Scale 1978 is based on specific conductance, temperature, and pressure measurements of seawater and freshwater mixtures (Lewis 1980 and references therein). Equations and data that define the scale make possible conversions between specific conductance and salinity values. This article presents a simplified conversion to salinity units for use with specific conductance data from monitoring stations that have been normalized to a standard temperature of 25 °C and an equation for the reverse calculation. Although these previously undocumented methods have been shared with many IEP agencies over the last two decades, the sources of the equations and data are identified here so that the original literature can be accessed.

Interagency Ecological Program Newsletter↗
USGS1997

The spring runoff pulse from the Sierra Nevada

A spring runoff pulse is identified in the Merced River record from the Sierra Nevada, that makes the transition from low streamflow conditions in winter to the high streamflow conditions in the later spring-early summer period. The timing of the pulse is delayed with greater seasonal accumulation of snow pack in the Yosemite region. Also, the runoff pulse is triggered by a regional weather fluctuation that establishes a warm high pressure ridge over the California region during the spring (mid-March to Mid-May) period. Since this ridge often blankets the entire western United States, it is found that a simultaneous pulse occurs over a broad collection of high-elevation streams in the region.

California↗
USGS1995

Sierra Nevada runoff into San Francisco Bay - Why has it come earlier recently?

By the time most of the Sierra Nevada snowpack has melted each summer, freshwater outflows from the Sacramento-San Joaquin Delta to San Francisco Bay are typically small, even after the wettest winters. These small delta outflows during the warm months (in comparison with the large flows of winter and spring) are overwhelmed by salty coastal waters, and the bay becomes more and more salty as summer progresses. Because longer lowflow seasons allow the bay to'become saltier, timing of the Sierra Nevada snowmelt and runoff, which are the source of the delta flows, has a profound influence on the salinity 0 the bay and, thus/ can affect its ecosystems (Peterson et al 1995).

Newsletter of the Interagency Ecological Program f↗
USGS2001

Droughts, epic droughts and droughty centuries - lessons from a California paleoclimatic record: a PACLIM 2001 meeting report

During the early 1990s (but echoing studies by S.T. Harding at the University of California, from as early as the 1930s), several lines of paleoclimate evidence in and around the Sierra Nevada Range have provided the water community in California with some real horror stories. By studying ancient tree stumps submerged in Lake Tahoe and Tenaya Lake, stumps that were emerging from Mono Lake during its recent decline, and stumps that were exhumed in the Walker River bed during the floods of 1997, paleoclimatologists like Scott Stine of California State University, Hayward, assembled a picture of epic droughts in the central Sierra Nevada during the medieval period. These droughts had to be severe to drop water levels in the lakes and rivers low enough for the trees to grow in the first place, and then had to last for hundreds of years to explain tree-ring counts in these sizeable stumps. Worse yet, the evidence suggested at least two such epic droughts, one ending close to 1100 and the other close to 1350. These epic droughts challenged paleoclimatologists, as well as modern climatologists and hydrologists, to understand and, ultimately, to determine the likelihood that such droughts might recur in the foreseeable future. The first challenge, however, was to verify that such droughts were more than local events and as extreme as suggested. At this year’s Pacific Climate (PACLIM) Workshop, held March 18–21, 2001, at Asilomar (Pacific Grove, Calif.), special sessions brought together scientists to compare paleoclimatic reconstructions of ancient droughts and pluvial (wet) epidodes to try to determine the nature of decadal and centennial climate fluctuations in western North America, with emphasis on California. A companion session brought together modern climatologists to report on the latest explanations (and evidence) for decadal climate variations during the instrumental era of the 20th century.

Interagency Ecological Program Newsletter↗
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?

California↗
USGS1997

Optimum sampling strategy for sediment-associated pesticides in Suisun Bay

The purpose of this study was to develop a twice-a-day sampling strategy for suspended solids concentration at Mallard Island that best reproduces the residual (tidally averaged) near-surface suspended solids concentration computed using the entire time series (96 sampling times per day) for high delta discharge conditions and to use this stratgy for sampling sediment-associated pesticides vvaried in a similar manner to suspended solids concentration would also be the optimum sampling strategy for sediment-associated pseticides.

California↗
USGS2005

Preliminary results from a shallow water benthic grazing study

The nutrient-rich, shallow waters of San Francisco Bay support high rates of primary production, limited not by nutrients but by light availability and benthic grazing (Alpine and others 1992; Cloern 1982). Phytoplankton blooms are an important food source for upper trophic levels. Consequently animal populations, such as fish, may suffer under conditions of high benthic bivalve grazing. It has been hypothesized that several species of fish are suffering as a result of severe decreases in available phytoplankton since the introduction of Potamocorbula amurensis into San Francisco Bay (Feyrer 2003). The extent of reduction in phytoplankton biomass by benthic bivalves is dependent on both physical and biological factors in addition to their spatial and temporal variability. Physical factors identified as important include: (1) vertical mixing rates, which are a function of wind velocity, currents, and bottom roughness; (2) suspended sediment concentrations; and (3) phytoplankton settling rates. The biological factors controlling the extent of phytoplankton grazing include animal density and organism size, pumping rate, food type and concentration, metabolic demands, assimilation efficiency, and behaviour (Wildish and Kristmanson 1997). Several laboratory studies involving model and live clams have shown that benthic grazers can deplete phytoplankton in the water column (for example, Cole and others 1992). Initially, these studies assumed that the water column remained well mixed above benthic suspension feeders; therefore, parameters measured in the bulk water column were believed to be representative of available particle concentration. For this reason many relationships describing the influence of the bulk flow and bulk seston concentration on benthic grazers physiological processes exist (for example, Levinton 1991). Laboratory measurements using live animals have shown that filtration rates vary with free stream velocity (for example, Levinton 1991). Increases in current speed lead to an increase in filtration rate; however, several studies have shown that filtration may cease at some critical current speed. It has been suggested that resuspension, occurring as a result of high current speeds, may be a factor that negatively affects uptake (Cloern 1987; Levinton 1991). Several mechanisms have been invoked to explain the effects of low speed on growth rates of active suspension feeders. These mechanisms include the formation of a concentration boundary layer and the limiting horizontal flux of seston. It is now accepted that a combination of these factors dictates the growth success of benthic grazers in a particular area. Several field studies have shown that concentration boundary layers can form over benthic ecosystems (for example, Frechette and others 1989, Dolmer 2000); however, many of these studies have failed to measure the hydrodynamics needed to calculate benthic grazing rates. Furthermore, calculating benthic grazing rates with vertical measurements at a single point is problematic due to lack of knowledge of the horizontal gradients in seston (Thompson and others, forthcoming). Despite great improvements in our knowledge on the effects of benthic grazers on seston concentrations in water columns, the effects of different hydrodynamic conditions on grazing rates has not been formulated. This makes it difficult to assess the system-wide effect of the benthic ecosystem on phytoplankton concentrations. Furthermore, it affects our ability to predict the potential success of a benthic species, such as the invasive clams Corbicula fluminea and Potamocorbula amurensis. This paper presents the preliminary results of a control volume approach to elucidate the effect of different hydrodynamic conditions on the grazing rates of Corbicula fluminea.

California↗
USGS1995

Ecosystem responses to phytoplankton blooms - examples from south San Francisco Bay

In 1968, USGS began a program of basic research in San Francisco Bay that has complemented the research and monitoring elements of the Interagency Program. Although the USGS program ranges its focus of study. From year to year, it has elements of continuity because some measurements have been made routinely for decades. One of these elements has been a study of the spring phytoplankton bloom in South San Francisco Bay. Here I present data from multiple sources to explain why such emphasis has been placed on this biological phenomenon.

California↗
USGS1999

A CALFED-supported study of the Delta’s foodweb base

Scientists from six universities and the US Geological Survey (USGS) have begun a new project to characterize the food resource which supports secondary production in different habitats of the Sacramento-San Joaquin Delta. The project is supported by CALFED Category III, USGS, and the IEP; it is designed to answer basic questions about the organic matter which supports biological production at the lowest trophic levels. We know, from the excellent long-term records of IEP agencies, that the abundance of zooplankton (especially native species) has declined dramatically in the past three decades. We do not understand the underlying mechanisms of these declines, but it is likely that they are the result of multiple, interacting stressors. One potential limitation of secondary production could be a sub-optimal food resource, manifested either as low quantity or poor nutritional quality of the available pools of organic matter. Some past studies support this possibility, especially for the case of benthic macroinvertebrates. The project was conceived to do the following: Identify the potential sources of organic matter (for example, phytoplankton, vascular plants, agricultural sources) in different habitats; Determine the relative food quality of each of these different sources for secondary producers, either directly or after microbial processing; and Assess the habitats and environmental conditions that provide the maximum food resources for secondary producers.

Interagency Ecological Program Newsletter↗
USGS2001

Droughts, epic droughts and droughty centuries - lessons from a California paleoclimatic record: a PACLIM 2001 meeting report

During the early 1990s (but echoing studies by S.T. Harding at the University of California, from as early as the 1930s), several lines of paleoclimate evidence in and around the Sierra Nevada Range have provided the water community in California with some real horror stories. By studying ancient tree stumps submerged in Lake Tahoe and Tenaya Lake, stumps that were emerging from Mono Lake during its recent decline, and stumps that were exhumed in the Walker River bed during the floods of 1997, paleoclimatologists like Scott Stine of California State University, Hayward, assembled a picture of epic droughts in the central Sierra Nevada during the medieval period. These droughts had to be severe to drop water levels in the lakes and rivers low enough for the trees to grow in the first place, and then had to last for hundreds of years to explain tree-ring counts in these sizeable stumps. Worse yet, the evidence suggested at least two such epic droughts, one ending close to 1100 and the other close to 1350. These epic droughts challenged paleoclimatologists, as well as modern climatologists and hydrologists, to understand and, ultimately, to determine the likelihood that such droughts might recur in the foreseeable future. The first challenge, however, was to verify that such droughts were more than local events and as extreme as suggested. At this year’s Pacific Climate (PACLIM) Workshop, held March 18–21, 2001, at Asilomar (Pacific Grove, Calif.), special sessions brought together scientists to compare paleoclimatic reconstructions of ancient droughts and pluvial (wet) epidodes to try to determine the nature of decadal and centennial climate fluctuations in western North America, with emphasis on California. A companion session brought together modern climatologists to report on the latest explanations (and evidence) for decadal climate variations during the instrumental era of the 20th century. PACLIM is an annual workshop that, since 1983, has brought together specialists from diverse fields, including physical, social, and biological sciences, to discuss and investigate climate and climate effects in the eastern Pacific and western America. This year’s PACLIM was sponsored by the U.S. Geological Survey, NOAA Office of Global Programs, California Department of Water Resources, and, for the first time, the CALFED Science Program. In addition to the presentations summarized here, sessions at this year’s PACLIM covered topics as varied as the North American monsoon system; recent economic and political effects of California’s climate variations, including a presentation on climate and CALFED by Sam Luoma (U.S. Geological Survey, Menlo Park); and research into daily-to-seasonal weather variations.

Interagency Ecological Program Newsletter↗
USGS2006

Riparian willow restoration at Arapaho National Wildlife Refuge

Riparian willow communities along the Illinois River at Arapaho National Wildlife Refuge in North Park near Walden, Colorado, provide important habitat for a number of wildlife species, including neotropical migratory birds. Existing stands in the northern (downstream) portion of the refuge are sparse and discontinuous (Photo 1) compared to upstream portions of the Illinois River and the parallel Michigan River.

The Green Line, Colorado Riparian Association News↗
USGS1995

Modeling and predicting intertidal variations of the salinity field in the Bay/Delta

San Francisco Bay and the Sacramento/San Joaquin Delta have challenged estuarine modelers for some years. Accurate, broad-scale models of this estuary have been in demand by those concerned with its ecological health and the development of sound management policies. A description and better understanding of the dynamics that govern the bay/delta are complicated by the system's complexity, requiring models that are sophisticated enough to capture the subtle physical processes involved. One approach to simulating daily to monthly variability in the bay is the development of intertidal model using tidally-averaged equations and a time step on the order of the day. An intertidal numerical model of the bay's physics, capable of portraying seasonal and inter-annual variability, would have several uses. Observations are limited in time and space, so simulation could help fill the gaps. Also, the ability to simulate multi-year episodes (eg, an extended drought) could provide insight into the response of the ecosystem to such events. Finally, such a model could be used in a forecast mode wherein predicted delta flow is used as model input, and predicted salinity distribution is output with estimates days and months in advance. This note briefly introduces such a tidally-averaged model (Uncles and Peterson, in press) and a corresponding predictive scheme for baywide forecasting.

California↗