Spatial and temporal patterns in food web accumulation of Hg

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Spatial and temporal patterns in food web
accumulation of Hg

• Project Update
• RMP Contaminant Fate Work Group Jan. 15, 2008

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RMP Organizational Structure
Program Review Panel
Mike Stenstrom Barbara Mahler Eric Stein
Joel Baker Frank Gobas Keith Stolzenbach Rob Mason
Steve Weisberg Don Weston Harry Ohlendorf Michael
Fry Dan Schlenk
David Sedlak Derek Muir Jen Fields
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Talk outline

• Results update
• Review workplan

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Results updatePreliminary results from 2005 and
2006

• Spatial patterns
• Interannual trends
• Focusing on topsmelt and Mississippi silverside
  (most complete spatial coverage)

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Spatial patterns
Hg wet weight (?g/g)

• 2006 elevated in Pt. Isabel (significant)

• 2005 elevated in southern stations (significant)

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Spatial patterns including salt pond data
Includes data provided by C. Eagles-Smith and J.
Ackerman
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• 2005 elevated in southern stations (not
  significant)

• 2006 elevated in southern stations, Pt. Isabel,
  and Tiburon (significant)

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• Potential explanations for spatial patterns
• High sediment MeHg in southern stations, Tiburon
• Suggests linkage fish vs. sediment MeHg
• Suggests spatial gradient

Source RMP
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Sediment MeHg may be correlated with topsmelt Hg

• Topsmelt 2006 data
• RMP and Calfed
• sediment data within 1.5 km disk of fish
• R2 0.61

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Interannual trendsMississippi silverside

• Station effect
• Year effect
• Interaction term not significant

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Station effect
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Interannual trendsTopsmelt

• Station effect
• Year effect

2006 higher than 2005!
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Relative importance of station vs. year effect
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Results update summary

• Ability to detect significant spatial variation
• South Bay, Tiburon, Pt. Isabel appear elevated
• Salt pond stations higher than Bay stations
  (silverside)
• Substantial interannual variation
• Topsmelt and silverside seeing different MeHg
  signals
• Subtle treatment effects likely missed
• Biosentinels sensitive to changes

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Workplan Specific questions to address

• Where is mercury entering the Bay food web?
• What habitats, conditions, or factors help to
  identify hotspots of food web accumulation in Bay
  margins?
• Are there interannual trends in MeHg
  bioaccumulation resulting from wetland and margin
  restoration activities?
• What are the best biomonitoring tools for
  characterizing hotspots of MeHg bioaccumulation?

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Recent survey decisions

• Regional Board Requests
• Hypothesis testing approach
• Coordinate sampling with South Bay Mercury
  Project
• Focus more on spatial analysis than long-term
  trend detection
• Add a seasonal variation component

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Approach Hg in small fish

• Spatial survey of about 40 stations
• 75 of effort
• Annual monitoring at 8 stations to determine
  trends
• 10 of effort
• Monthly monitoring at 2 stations to determine
  seasonal variation
• 10 of effort
• Comparison of biosentinel tools (pending first
  year results)
• Fish vs. bivalves vs. sediment vs. diffusive
  gradient thin film devices
• 5 of effort

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Spatial survey

• Targeting 40 locations
• Multiple interrelated factors
• Land use, land cover, and Hg sources
• Spatial location in Bay
• Subtidal hydrology and bathymetry
• Sediment physical and chemical parameters

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Spatial survey potential design

• Focus on four types of location test hypothesis
  of effect
• Include spatial gradient from North to South Bay
• Also consider subtidal bathymetery/hydrology
• Focus on topsmelt and Mississippi silverside

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Potential sampling locations

• E.g., POTW outfalls
• Fairfield-Suisun
• Palo Alto
• Sunnyvale
• San Jose

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Coordinate with SBMP sites Improve
understanding of wetland Bay linkages
Topsmelt Silversides
Marsh fish Brine flies Song sparrows
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Trend analysis a multiple station BACI design
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Trend Sampling Locations
Hamilton
Benicia Park
China Camp
Control
Point Isabel
Impact (Restoration)
Oakland Middle Harbor
Candlestick Point
Eden Landing
Bird Island/ Steinberger Slough
Newark Slough
Alviso Slough
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Trend Sampling Locations
Hamilton
Benicia Park
China Camp
Control
Point Isabel
Impact (Restoration)
Oakland Middle Harbor
Candlestick Point
Eden Landing
Bird Island/ Steinberger Slough
Newark Slough
Alviso Slough
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Monthly sampling locations
Additional North Bay Station Sampled by USFWS
Martin Luther King Shoreline
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MLK Shoreline Location
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Collection of additional parameters

• Aimed at better understanding mechanisms for
  spatial variation in bioavailable Hg
• GIS spatial parameters
• Sediment parameters

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GIS spatial parameters
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Sediment parameters

• Sediment parameters redox, TON, grain size,
  total and methyl Hg
• Duplicate sediment samples at subset of 20
  stations

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Sediment MeHg lt 1 ng/g 1 2 ng/g
gt 2 ng/g
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Sediment MeHg may be correlated with topsmelt Hg

• Topsmelt 2006 data
• RMP and Calfed
• sediment data within 1.5 km disk of fish
• R2 0.61

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Questions for the Workgroup

• Is the general approach appropriate?
• Indicators selected
• Allocation of effort to spatial vs. interannual
  vs. monthly vs. tool comparison
• Spatial survey design
• Hypothesis testing approach
• Sampling sites (wetlands, POTWs)
• Trend sampling
• Annual sampling sites
• Monthly sampling sites
• Additional parameters
• Sediment parameters

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Annual monitoring of trend stations
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