Geology topics

Research about Suisun Bay

Source-linked reports with geographic coverage including Suisun Bay.

5 recordsLinked to original sources

USGS2016

Bivalve grazing can shape phytoplankton communities

The ability of bivalve filter feeders to limit phytoplankton biomass in shallow waters is well-documented, but the role of bivalves in shaping phytoplankton communities is not. The coupled effect of bivalve grazing at the sediment-water interface and sinking of phytoplankton cells to that bottom filtration zone could influence the relative biomass of sinking (diatoms) and non-sinking phytoplankton. Simulations with a pseudo-2D numerical model showed that benthic filter feeding can interact with sinking to alter diatom:non-diatom ratios. Cases with the smallest proportion of diatom biomass were those with the fastest sinking speeds and strongest bivalve grazing rates. Hydrodynamics modulated the coupled sinking-grazing influence on phytoplankton communities. For example, in simulations with persistent stratification, the non-sinking forms accumulated in the surface layer away from bottom grazers while the sinking forms dropped out of the surface layer toward bottom grazers. Tidal-scale stratification also influenced vertical gradients of the two groups in opposite ways. The model was applied to Suisun Bay, a low-salinity habitat of the San Francisco Bay system that was transformed by the introduction of the exotic clam Potamocorbula amurensis . Simulation results for this Bay were similar to (but more muted than) those for generic habitats, indicating that P. amurensis grazing could have caused a disproportionate loss of diatoms after its introduction. Our model simulations suggest bivalve grazing affects both phytoplankton biomass and community composition in shallow waters. We view these results as hypotheses to be tested with experiments and more complex modeling approaches.

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USGS2011

Discontinuous hindcast simulations of estuarine bathymetric change: A case study from Suisun Bay, California

Simulations of estuarine bathymetric change over decadal timescales require methods for idealization and reduction of forcing data and boundary conditions. Continuous simulations are hampered by computational and data limitations and results are rarely evaluated with observed bathymetric change data. Bathymetric change data for Suisun Bay, California span the 1867–1990 period with five bathymetric surveys during that period. The four periods of bathymetric change were modeled using a coupled hydrodynamic-sediment transport model operated at the tidal-timescale. The efficacy of idealization techniques was investigated by discontinuously simulating the four periods. The 1867–1887 period, used for calibration of wave energy and sediment parameters, was modeled with an average error of 37% while the remaining periods were modeled with error ranging from 23% to 121%. Variation in post-calibration performance is attributed to temporally variable sediment parameters and lack of bathymetric and configuration data for portions of Suisun Bay and the Delta. Modifying seaward sediment delivery and bed composition resulted in large performance increases for post-calibration periods suggesting that continuous simulation with constant parameters is unrealistic. Idealization techniques which accelerate morphological change should therefore be used with caution in estuaries where parameters may change on sub-decadal timescales. This study highlights the utility and shortcomings of estuarine geomorphic models for estimating past changes in forcing mechanisms such as sediment supply and bed composition. The results further stress the inherent difficulty of simulating estuarine changes over decadal timescales due to changes in configuration, benthic composition, and anthropogenic forcing such as dredging and channelization.

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USGS2009

Hindcasting of decadal‐timescale estuarine bathymetric change with a tidal‐timescale model

Hindcasting decadal-timescale bathymetric change in estuaries is prone to error due to limited data for initial conditions, boundary forcing, and calibration; computational limitations further hinder efforts. We developed and calibrated a tidal-timescale model to bathymetric change in Suisun Bay, California, over the 1867–1887 period. A general, multiple-timescale calibration ensured robustness over all timescales; two input reduction methods, the morphological hydrograph and the morphological acceleration factor, were applied at the decadal timescale. The model was calibrated to net bathymetric change in the entire basin; average error for bathymetric change over individual depth ranges was 37%. On a model cell-by-cell basis, performance for spatial amplitude correlation was poor over the majority of the domain, though spatial phase correlation was better, with 61% of the domain correctly indicated as erosional or depositional. Poor agreement was likely caused by the specification of initial bed composition, which was unknown during the 1867–1887 period. Cross-sectional bathymetric change between channels and flats, driven primarily by wind wave resuspension, was modeled with higher skill than longitudinal change, which is driven in part by gravitational circulation. The accelerated response of depth may have prevented gravitational circulation from being represented properly. As performance criteria became more stringent in a spatial sense, the error of the model increased. While these methods are useful for estimating basin-scale sedimentation changes, they may not be suitable for predicting specific locations of erosion or deposition. They do, however, provide a foundation for realistic estuarine geomorphic modeling applications.

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USGS1998

Results from the hydrodynamic element of the 1994 entrapment zone study in Suisun Bay

The entrapment zo as long been considered an important region of the San Francisco estuary. It has been the subject of several previous studies, and its location has been suggested as an index of condition of the estuarine ecosystem.A close correlate of this location, X2 1, is now used as a management objective on the basis that X2 is correlated with the abundance or survival of several estuarine-dependent species. X2 is a crude tool to use for this purpose, but it can be refined only through improved understanding of the various mechanisms underlying these correlations. These mechanisms probably differ among species, but for species resident in and near the entrapment zone, the correlation with X2 may be due to variations in intenSity oftrapping mechanisms with pOSition of the entrapment zone. Therefore, it is worthwhile to investigate these trapping mechanisms, the nature of the entrapment zone as habitat, and the responses of the entrapment zone to changes in X2 or outflow from the Sacramento-San Joaquin Delta. Studies ofthe entrapment zone ofthe San Francisco estuary have been conducted in springs of 1994, 1995, and 1996. These studies have been funded by the Interagency Ecological Program and conducted by scientists from IEP member agencies, the Romberg Tiburon Center for Environmental Studies, Bodega Marine Laboratory, and the University of California at Santa Cruz. This report presents results from 1994, a low-flow year. Subsequent reports will describe results from 1995 and 1996 and highlight differences among years. This report is organized in chapters that comprise more-or-Iess independent papers, with an introductory chapter for the entire study. This Executive Summary presents highlights of the overall study plan and summarizes the major findings.

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USGS1984

Trace metals in Suisun Bay, California: A preliminary report

A 5-month partial study (February to July 1983) was completed in Suisun Bay, a shallow embayment of San Francisco Bay, Calif., to determine characteristic heavy metal concentrations present in sediments and organisms (Corbicula clams) prior to possible discharge of San Luis Drain irrigation tile return water. Preliminary results show sediments are typical of other San Francisco Bay study sites, ranging from coarse sands to fine silt-clays. The sediments are enriched in manganese and low in organic carbon; iron is moderately enriched, with acid-extractable iron concentrations of 162-3,521 micro-g/g. Sediment concentrations of silver, zinc, lead, and cadmium measured between April and July are reported. Previous area studies have shown increased concentrations during autumn and winter, a period not covered in the data set. Due to insufficient data, interpretations are incomplete. Clam-tissue burdens for silver and zinc are similar to those found in Corbicula from pristine areas. Lead concentrations are typically below the 2-micrograms/g detection level. Corbicula do show indications of more tissue enrichment for cadmium and copper at estuarine stations than at riverine stations.

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