Spatial and temporal patterns in food web accumulation of Hg

Project UpdateRMP Contaminant Fate Work Group Jan. 15, 2008

S o u rce s,P a th w a ys,

a n d L o a d in gsW o rkg ro up

C o n ta m in a n tF a te

W o rkg ro up

E xp o su rea n d E ffe c tsW o rkg ro up

E m e rg ingC o n ta m in a n ts

W o rkg ro up

M e rcu ryG ro up

T e ch n ica l R e v ie wC o m m ittee

S te e ring C o m m ittee

RMP Organizational Structure

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

Program Review Panel

Talk outline

• Results update

• Review workplan

Results updatePreliminary results from 2005 and 2006

• Spatial patterns

• Interannual trends

• Focusing on topsmelt and Mississippi silverside (most complete spatial coverage)

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

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 Tiburon Tiburon (significant)(significant)

• Potential explanations for spatial patterns:– High sediment

MeHg in southern stations, Tiburon

– 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

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

Interannual trendsMississippi silverside

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

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 effect2006 higher than 2005!

Interannual trendsTopsmelt

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

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

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?

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

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

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

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

-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 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

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