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Spatial and temporal patterns in food web accumulation of Hg

Update on project results focusing on spatial and temporal patterns of mercury accumulation in the food web, including station effects and interannual trends. Discusses potential explanations for variation and outlines a five-year workplan. Details approach, sampling locations, and parameters for monitoring.

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Spatial and temporal patterns in food web accumulation of Hg

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  1. Spatial and temporal patterns in food web accumulation of Hg Project Update RMP Technical Review Committee Dec. 18, 2007

  2. Talk outline • Results update • Review workplan

  3. Results updatePreliminary results from 2005 and 2006 • Spatial patterns • Interannual trends • Focusing on topsmelt and Mississippi silverside (most complete spatial coverage)

  4. Spatial patterns • 2005 elevated in southern stations (significant) Hg wet weight (g/g) • 2006 elevated in Pt. Isabel (significant)

  5. Spatial patterns including salt pond data Includes data provided by C. Eagles-Smith and J. Ackerman

  6. 2005 elevated in southern stations (not significant) • 2006 elevated in southern stations, Pt. Isabel, and Tiburon (significant)

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

  8. Interannual trendsMississippi silverside • Station effect • Year effect • Interaction term not significant

  9. Station effect

  10. Year effect and interaction 2006 generally lower than 2005

  11. Interannual trendsTopsmelt • Station effect • Year effect 2006 higher than 2005!

  12. Relative importance of station vs. year effect

  13. 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

  14. Five Year 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?

  15. 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

  16. Approach: Hg in small fish • Spatial survey of about 40 stations • 75% of effort • Annual monitoring at 6 - 10 stations to determine trends • 10% of effort • 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

  17. 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

  18. Spatial survey potential design • Focus on four types of location – test hypothesis of effect • Include spatial gradient from North to South Bay • Include explicit consideration of subtidal bathymetery/hydrology • Focus on topsmelt and Mississippi silverside

  19. Coordinate with SBMP sites: Improve understanding of wetland – Bay linkages Topsmelt Silversides Marsh fish Brine flies Song sparrows

  20. Trend analysis – a multiple station BACI design

  21. 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

  22. 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

  23. Collection of additional parameters • Aimed at better understanding mechanisms for spatial variation in bioavailable Hg • Potential parameters: • Sediment parameters: redox, TOC, grain size, MeHg • Water parameters: TSS, nutrients, chlorophyll • Bathymetry and hydrology: use GIS to characterize bathymetric profile and water retention time • MeHg via Diffusive Gradient Thinfilm devices • Proposing to collect ancillary parameters for subset of 20 - 30 stations

  24. Annual monitoring of trend stations

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