Spatial and temporal patterns in food web accumulation of Hg

San Francisco Mercury Coordination MeetingFebruary 20, 2008

Questions addressed

• Spatial patterns: Where is most bioavailable mercury in the Bay?

– Using small fish as biosentinels– Comparing with sediment MeHg 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

Total Length (mm)

0 20 40 60 80 100 120

Hg

(g/

g w

et)

0.01

0.1 ARROW GOBYCHEEKSPOT GOBYMISSISSIPPI SILVERSIDESHIMOFURI GOBYTOPSMELTYELLOWFIN GOBYBAY GOBYSTRIPED BASSNORTHERN ANCHOVYPACIFIC HERRING

0.4

0.003

Spatial patterns: Bay margins vs. open waters

Total Length (mm)

0 20 40 60 80 100 120

Hg

(g/

g w

et)

0.01

0.1 ARROW GOBYCHEEKSPOT GOBYMISSISSIPPI SILVERSIDESHIMOFURI GOBYTOPSMELTYELLOWFIN GOBYBAY GOBYSTRIPED BASSNORTHERN ANCHOVYPACIFIC HERRING

0.4

0.003

Wetlands/margins

Open waters

Spatial patterns: Organized by species habits

0 20Miles

Mississippi silverside 2005

Hg

(ug/

g w

et)

0.05

0.1

0.15

0.2

Hg

wet

weig

ht

(g

/g)

Mississippi Silverside 2006

0 20Miles

Hg

(ug/

g w

et)

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

• 2005 elevated in southern stations (significant)

2006 elevated in Pt. 2006 elevated in Pt. Isabel (significant)Isabel (significant)

Spatial patterns: Regional patterns across Bay

Spatial patterns including salt pond data

Includes data provided by C. Eagles-Smith and J. Ackerman

0 20Miles

Topsmelt 2005

Hg

(ug/

g w

et)

0.028

0.03

0.032

0.034

0.036

0.038

0.04

0.042

0.044

0.046

0.048

Topsmelt 2006

0 20Miles

Hg

(ug/

g w

et)

0.025

0.03

0.035

0.04

0.045

0.05

0.055

• 2005 elevated in southern stations (not significant)

2006 elevated in 2006 elevated in southern stations, southern stations, Pt. Isabel, and Pt. Isabel, and Richardson Bay Richardson Bay (significant)(significant)

• Potential explanations for spatial patterns:– High sediment

MeHg in southern stations, Richardson Bay

– Suggests linkage: fish vs. sediment MeHg

– Suggests spatial gradient

Source: RMP

Sediment MeHg may be correlated with topsmelt Hg

0.5 1.0 1.5 2.0 2.53.03.5

MeHg in sediment (ng/g)

0.02

0.03

0.04

0.05

0.06

0.070.08

Hg

in f

ish

(u

g/g

)

•Topsmelt 2006 data

•RMP and Calfed sediment data within 1.5 km disk of fish

•R2 = 0.61

-122.6 -122.3 -122.0 -121.7Longitude

37.4

37.5

37.6

37.7

37.8

37.9

38.0

38.1

38.2La

titud

e

-3-2-1012

LOGMEHG

0.00.51.01.52.02.5

MEHG_HIGH1

Sediment MeHg: < 1 ng/g 1 – 2 ng/g > 2 ng/g

Sediment MeHg higher in shallow/nearshore sites

MeHg Hotspots in SedimentSediment MeHg Hotspots

0.2 0.4 0.6 0.8 1.0Proportion Land Within 2 KM Buffer

1000

2000

3000

40005000600070008000

Dis

tanc

e F

rom

Nea

r est

Sho

reli n

e (m

)

10

HIGHMEHG

Concentrations highest closeto shoreline and surrounded by land

< 2 ng/g> 2 ng/g

Hypothesis: Importance of enclosed areas like Pt. Isabel and Richardson Bay

Temporal Patterns

ALVSL

BENPK

CHINA

EDENL

NEWSL

STATION

0.0

0.1

0.2

0.3H

GW

W

20062005

YEAR

•Station effect•Year effect•Interaction term not significant•Disconnect from patterns seen in Delta/Suisun Bay (Slotton et al.)

How Hg varies from year to year?Mississippi silverside

ALVSL

BIRDI

EDENL

NEWSL

OMHEA

STATION

0.02

0.03

0.04

0.05

0.06

0.07

0.08H

GW

W

20062005

YEAR

•Station effect•Year effect•Similar to Slotton et al.

2006 higher than 2005!

Topsmelt

Relative importance of station vs. year effect

Species Station R2 Year R2Station/Year

Topsmelt 0.30 0.43 0.7Mississippi Silverside 0.58 0.05 11.6

Summary

New • Interannual variation differs among species (habitat types)

• Elevated in some salt ponds• Apparent association between sediment and

biosentinel MeHg

Q1

Q2

• Hg entering food web at Bay margins, tributaries, wetlands, salt ponds

• South Bay and nearshore or enclosed hotspots (Pt. Isabel, Richardson Bay)

• 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)

Field/Lab Work and Site Access…Katie HarroldAroon MelwaniJohn OramCarrie AustinMax DelaneyFred HetzelRichard LookerApril RobinsonMeg SedlakSF Bay National Wildlife RefugeUSFWS StocktonUSGS BRDCalifornia State ParksCA Department Fish & GameInteragency Ecological Program

Collaboration/Data Sharing…Andy JahnMark SandheinrichKristen CayceCollin Eagles-SmithJosh AckermanWes HeimSF Bay Regional Board

SUPPORTING INFORMATION:

Spatial survey• Targeting 40 locations

• Multiple interrelated factorsA. Land use, land cover, and Hg sources

B. Spatial location in Bay

C. Subtidal hydrology and bathymetry

D. 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 MeHg bioaccumulation resulting from wetland and margin restoration activities?

4. What are the best biomonitoring tools for characterizing hotspots of MeHg 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 N Bay S Bay

Wetlands 5 sites 5 sites

Urban outfall 5 sites 5 sites

POTW into slough/marsh 5 sites 5 sites

Control (upland, residential, no discharges)

5 sites 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

Marsh fishBrine fliesSong sparrows

TopsmeltSilversides

Trend analysis – a multiple station BACI design

0

0.05

0.1

0.15

0.2

0.25

0.3

1 2 3 4 5 6 7 8 9

Year

Mer

cury

Con

cent

ratio

ns Control 1

Impact 1

Control 2

Impact 2

Control 3

Impact 3

Control 4

Impact 4

Trend Sampling Locations

Alviso Slough

Newark Slough

Bird Island/Steinberger Slough

Eden Landing

China Camp

Benicia Park

Control

Impact (Restoration)Point Isabel

CandlestickPoint

Hamilton

Oakland Middle Harbor

Trend Sampling Locations

Alviso Slough

Newark Slough

Bird Island/Steinberger Slough

Eden Landing

China Camp

Benicia Park

Control

Impact (Restoration)Point Isabel

CandlestickPoint

Hamilton

Oakland Middle Harbor

Monthly sampling locations

Martin Luther King Shoreline

Additional North Bay Station Sampled by USFWS

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 parametersParameter Type Hypothesized mechanism of influence

Water residence time Water dilution and replacement and sediment advective transport may cause net loss of Hg or MeHg, and redox conditions

Distance to nearest POTW and nearest storm drain discharge

Loading of Hg and MeHg, 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

0.5 1.0 1.5 2.0 2.53.03.5

SEDIMENT

0.02

0.03

0.04

0.05

0.06

0.070.08

FIS

H

SQ

Pt Isabel

Tiburon

Alviso

Newark

Oakland Harb

Treasure Isl

China Camp

Least Squares Means

ALVSL

BENPKCHIN

A

EDENL

NEWSL

STATION

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

LOG

HG

DW

Station effect