Methyl Mercury Concentrations and Loads in the Delta http:mercury.mlml.calstate.edulinks

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Methyl Mercury Concentrations and Loads in the
Deltahttp//mercury.mlml.calstate.edu/links/

• Mark Stephenson, Chris Foe, Gary Gill, and Wes
  Heim
• Central Valley Regional Water Quality Control
  Board
• and Department of Fish and Game

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Outline

• Background
• Study Design
• Methyl Mercury Concentrations
• Sources
• Biomagnification
• Sinks
• Methyl Mercury Loads
• Losses
• Seasonal Box Models
• Conclusions

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Sampling Locations
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Methyl Mercury Concentrations in primary Delta
water sources.
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Methyl mercury concentrations in juvenile
silverside fish and in water in the San Joaquin
River at Vernalis. The silverside data are from
Slotton et al. (2008)
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Predicted and observed methyl mercury
concentrations at Mallard Island
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Outline

• Background
• Study Design
• Methyl Mercury Concentrations
• Sources
• Biomagnification
• Sinks
• Methyl Mercury Loads
• Losses
• Seasonal Box Models
• Conclusions

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Ratio of the sum of monthly methyl mercury export
loads divided by the sum of incoming loads as a
function of tributary inflow. The five squares
represent dates when the Yolo Bypass and/or San
Joaquin River were flooding. These five data
were not included in the regression.
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A
(A) Methyl mercury mass balance for the Delta in
January 2005. (B) Same mass balance for August
2005. Note changes in the relative magnitude of
the various processes
B
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Conclusions

• Methyl mercury concentrations were measured in
  all major water inputs and exports to Delta for
  45 months.
• Tributary inputs were the major source of
  methyl mercury.
• Positive correlations between methyl mercury
  concentrations in water and in juvenile
  silverside fish during an upstream flooding event
  in the San Joaquin River shows small fish can
  capture pulses of methyl mercury. These results
  are similar to those showing correlations between
  large fish and methyl mercury concentrations

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Conclusions

• The Delta is a net methyl mercury sink. The
  loss of methyl mercury is an inverse function of
  net Delta inflow.
• Box models demonstrate that Central Valley
  rivers are the major sources of methyl mercury to
  the Delta. Particle settling and exports to
  southern California and to San Francisco Bay are
  the major sinks in winter while photo degradation
  and exports to southern California are major
  sinks in summer.

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Conclusions

• Given input MMHg concentrations we can predict
  export concentrations
• With the particle tracking model we can predict
  flow patterns between inputs and exports, the
  losses that occur in those flow paths, the
  processes responsible and where in the flow paths
  the losses occur.