North San Francisco Bay bathymetry through time

A series of illustrations showing water depth in a bay are shown in sequence to show how depth changed over time.

Detailed Description

Sedimentation maps of San Francisco Bay from different years are combined to produce an animation of sedimentation. This animation gives an overall view of the system in time and space. We can see that, in the more active channels of Suisun Bay, surface sediment is deposited and erodes quickly in response to changing flows (floods/drought) and modifications (such as dredging the southern channel or long term mooring of the mothball fleet).

We assume:

  1. the sediment deposited in North San Francisco Bay between 1856 and 1887 was dominated by hydraulic mining debris;
  2. erosion observed in subsequent surveys was not re-deposited locally; and
  3. material deposited after 1887 was not mining debris.

Making these assumptions, we can predict the location and thickness of the original hydraulic mining debris. It is especially notable that the mercury employed in gold mining in the Sierra Nevada was refined liquid quicksilver or elemental mercury; this is a form of mercury much more likely to foster net methylation than is cinnabar, the form of mercury in most mercury mines. Approximately 10,000 tonnes of refined mercury were lost to the watershed during the Gold Rush mining era. Much of the mercury consumed by gold mining could have been incorporated into the 12 billion cubic meters of sediments extracted by the mining activities and released to the rivers of the Bay-Delta watershed. The mercury-laced hydraulic mining debris was ultimately transported to the bay-delta; it is known that large deposits of hydraulic mining debris remain in bay sediments. These wastes formed marshes, islands, or filled or diked marsh, or were deposited in shallow waters. Under the right circumstances this mercury contamination is transported through the food chain and concentrated in some commercial and sport fish. Human consumption of fish caught in the Bay is restricted because of mercury contamination.

Details

Image Dimensions: 634 x 357

Location Taken: San Francisco, CA, US

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