Spatial and temporal patterns in food web accumulation
Spatial and temporal patterns in food web accumulation of Hg San Francisco Mercury Coordination Meeting February 20, 2008
Questions addressed • Spatial patterns: Where is most bioavailable mercury in the Bay? – Using small fish as biosentinels – Comparing with sediment Me. Hg data – Regions – Habitat types and conditions • Temporal patterns: How does mercury vary in small fish from year to year?
Spatial patterns: Bay margins vs. open waters
Spatial patterns: Bay margins vs. open waters
Spatial patterns: Organized by species habits Wetlands/margins Open waters
Hg wet weight ( g/g) Spatial patterns: Regional patterns across Bay • 2005 elevated in southern stations (significant) n 2006 elevated in Pt. Isabel (significant)
Spatial patterns including salt pond data Includes data provided by C. Eagles-Smith and J. Ackerman
• 2005 elevated in southern stations (not significant) n 2006 elevated in southern stations, Pt. Isabel, and Richardson Bay (significant)
• Potential explanations for spatial patterns: – High sediment Me. Hg in southern stations, Richardson Bay – Suggests linkage: fish vs. sediment Me. Hg – Suggests spatial gradient Source: RMP
Sediment Me. Hg may be correlated with topsmelt Hg • Topsmelt 2006 data • RMP and Calfed sediment data within 1. 5 km disk of fish • R 2 = 0. 61
Sediment Me. Hg higher in shallow/nearshore sites Sediment Me. Hg: < 1 ng/g 1 – 2 ng/g > 2 ng/g
Me. Hg Hotspots in Sediment Concentrations highest close to shoreline and surrounded by land < 2 ng/g > 2 ng/g
Hypothesis: Importance of enclosed areas like Pt. Isabel and Richardson Bay
Temporal Patterns
How Hg varies from year to year? Mississippi silverside • Station effect • Year effect • Interaction term not significant • Disconnect from patterns seen in Delta/Suisun Bay (Slotton et al. )
Topsmelt • Station effect • Year effect • Similar to Slotton et al. 2006 higher than 2005!
Relative importance of station vs. year effect
Summary New • Interannual variation differs among species (habitat types) • Elevated in some salt ponds • Apparent association between sediment and biosentinel Me. Hg Q 1 • Hg entering food web at Bay margins, tributaries, wetlands, salt ponds • South Bay and nearshore or enclosed hotspots (Pt. Isabel, Richardson Bay) Q 2 • Sediment net methylation may be locally important process for food web accumulation
Next step: more intensive survey • Spatial survey of about 40 stations/yr (3 years) • Annual monitoring at 8 stations to determine trends • Monthly monitoring at 2 stations to determine seasonal variation • External collaborations – Combining efforts with UC Davis team – Diffusive Gradient in Thinfilm Devices, Bivalves (Hintelmann and Best) – Stable Hg isotopes in fish (Blum)
Collaboration/Data Sharing… Andy Jahn Mark Sandheinrich Kristen Cayce Collin Eagles-Smith Josh Ackerman Wes Heim SF Bay Regional Board Field/Lab Work and Site Access… Katie Harrold Aroon Melwani John Oram Carrie Austin Max Delaney Fred Hetzel Richard Looker April Robinson Meg Sedlak SF Bay National Wildlife Refuge USFWS Stockton USGS BRD California State Parks CA Department Fish & Game Interagency Ecological Program
SUPPORTING INFORMATION:
Spatial survey • • Targeting 40 locations Multiple interrelated factors A. B. C. D. Land use, land cover, and Hg sources Spatial location in Bay Subtidal hydrology and bathymetry Sediment physical and chemical parameters
Workplan: Specific questions to address 1. Where is mercury entering the Bay food web? 2. What habitats, conditions, or factors help to identify hotspots of food web accumulation in Bay margins? 3. Are there interannual trends in Me. Hg bioaccumulation resulting from wetland margin restoration activities? 4. What are the best biomonitoring tools for characterizing hotspots of Me. Hg bioaccumulation?
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 Land Use/Land Cover Wetlands Urban outfall POTW into slough/marsh N Bay 5 sites S Bay 5 sites Control (upland, residential, no discharges) 5 sites
Potential sampling locations – • E. g. , POTW outfalls: – Fairfield-Suisun – Palo Alto – Sunnyvale – San Jose
Coordinate with SBMP sites: Improve understanding of wetland – Bay linkages Topsmelt Silversides Marsh fish Brine flies Song sparrows
Trend analysis – a multiple station BACI design
Trend Sampling Locations Hamilton Benicia Park China Camp Control Point Isabel Candlestick Point Impact (Restoration) Oakland Middle Harbor Eden Landing Bird Island/ Steinberger Slough Newark Slough Alviso Slough
Trend Sampling Locations Hamilton Benicia Park China Camp Control Point Isabel Candlestick Point Impact (Restoration) Oakland Middle Harbor Eden Landing Bird Island/ Steinberger Slough Newark Slough Alviso Slough
Monthly sampling locations Additional North Bay Station Sampled by USFWS Martin Luther King Shoreline
MLK Shoreline Location
Collection of additional parameters • Aimed at better understanding mechanisms for spatial variation in bioavailable Hg • GIS spatial parameters • Sediment parameters
GIS spatial parameters Parameter Type Hypothesized mechanism of influence Water residence time Water dilution and replacement and sediment advective transport may cause net loss of Hg or Me. Hg, and redox conditions Distance to nearest POTW and nearest storm drain discharge Loading of Hg and Me. Hg, as well as nutrients, fine particulates, influencing methylation potential Number of storm drains feeding into inlet (for urban stormwater outfall sites) As above. Distance to creeks and tributaries As above. Also, movement of fish upstream to conditions favoring methylation. Latitude Longer residence time in South Bay favoring reduced conditions and consequent methylation. Average depth near site High biotic activity and repeated wetting and drying at shallow sites favoring bacterial methylation activity. Abundance of intertidal mudflat near site As above. Nearby Land Cover/Land Uses Multiple potential mechanisms
Sediment parameters • Sediment parameters: redox, TON, grain size, total and methyl Hg • Duplicate sediment samples at subset of 20 stations
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
Annual monitoring of trend stations
Station effect
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