Mercury and Methylmercury Processes in North SF Bay Tidal Wetland EcosystemsSan Francisco Estuary InstituteUSGS BRD WERC Vallejo, CA USGS WRD Menlo Park, CAUSGS WRD Middleton, WIAvocet Research Associates

Background: The Good?Tidal wetland restoration plans

Adding 12,000+ acres North Bay

Tidal wetlandsHabitat for threatened & other wildlife

Wetland restoration = good

but…

The Bad?Mercury (Hg) already in Bay-Delta biota @ levels of concern

human & wildlife health

Hg in biota correlates to watershed % wetlands

Mostly freshwater systemsSimilar in tidal marshes?

Attractive nuisance?Wildlife check in, but …? x

Species

Cal

iforn

ia H

alib

ut

Jack

smel

t

Leop

ard

Sha

rk

Shi

ner

Sur

fper

ch

Str

iped

Bas

s

Whi

te C

roak

er

Whi

te S

turg

eon

Hg

(ug/

g w

et

wei

ght)

0.0

0.5

1.0

1.5

2.0

2.5

The Ugly?Not just a matter of reducing Hg…

0.0

0.5

1.0

1.5

2.0

2.5

0.00 0.20 0.40 0.60 0.80 1.00

Hg mg/kg dw

MeH

g µ

g/k

g d

w

2002

2003

2004 y = 1.06x + 0.23

R2 = 0.067

What (Me)Hg Worry? Not just Hg, need to worry about reducing methylmercury (MeHg)

Most bioaccumulative formFormed by sulfate reducing bacteria under reducing conditions

But is subject to degradation- MicrobialAbiotic (photolytic)

Ask Questions First(Me)Hg in wetlands: where, when, how much?What influences (Me)Hg distribution & production?How does (Me)Hg accumulate in tidal wetland food webs?How does (Me)Hg get there: wetlands to bay (or vice versa)?

Approach: GeneralSpatial distribution of (Me)Hg (water, sediments, biota)

Differences in (Me)Hg concentrationsDifferences in (de)methylation processes

Temporal distributionSeasonal differences in methylation rates and concentrations

Spatial Distribution3 wetlands along Petaluma River

Gambinini Ranch(Mid-)Petaluma MarshBlack John Slough

Salinity gradient along Petaluma main stem

Petaluma Marsh North

Black John Slough

Gambonini Ranch

Petaluma Marsh North

Black John Slough

Gambonini Ranch

Spatial DistributionWithin wetlands: habitat elements

Medium channels (2nd-3rd order)High marsh plain

Transect composites (some grabs)Replicates of habitat elements

Food WebCharismatic Critter: California Black Rail (USGS-BRD CA) - capture, tag, track

Identify distribution, habitat use, range, diet

BioaccumulationExamine (Me)Hg in biota:

High marsh food web:Hg in California Black Rails (blood, feathers)(Me)Hg in probable/potential diet items

Channel biota food webChannel fish and invertebrates to compare

MeHg Processes Sediment processes (USGS-Menlo Park CA)

(De)Methylation rates in channel and high marsh

Lab incubations of sediment composites

Microbially available (reactive) HgSediment quality (sulfur, carbon)

Water processes (USGS-Middleton WI)

Demethylation ratesPhoto-incubation experiments

Results: Hg DistributionSediment Hg similar @ all sites

>>ancient Hg levelscomparable to Bay sediments

High marsh < channel

0

50

100

150

200

250

300

350

400

BJS MP GAM

Hg

(ng/

g)

High Marsh

Slough

Sediment MeHg DistributionHigh marsh

Highest at mid-Petaluma

Channel MeHgOpposite of salinity gradient< high marsh

0

1

2

3

4

5

6

7

8

9

BJS MP GAM

MeH

g (n

g/g)

High Marsh

Slough

Vertical MeHg DistributionMeHg highest in high marsh surface layers

0

2

4

6

8

10

12

14

16

18

20

0-2

5-1

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5-1

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15

-20

2-5

10

-15

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-15

2-5

10

-15

0-2

5-1

0

15

-20

Depth (cm)

Co

nc

(n

g/g

dry

) BJS-HM1

BJS-HM2

GAM-HM1

GAM-HM2

MP-HM1

MP-HM2

Black John

Gambinini

MidPetaluma

MeHg in SedimentsNet = methylation - demethylationSediment MeHg parallels sulfate reductiony = 0.0009x + 1.1511

R2 = 0.67

0

2

4

6

8

10

0 1 2 3 4 5 6 7 8 9

SRR (mol/g dry sed/d)

Me

Hg

(ng

/g d

ryse

d)

MPGAMBJS

Figure 2. The positive relationship between microbial sulfate reduction rate (SRR) and methylmercury (MeHg) concentration during April 2005 for the three wetland regions studied. SRR data from August 2005 is pending. The best fit linear regression equation and associated r2 value is given.

y = 0.0009x + 1.1511

R2 = 0.67

0

2

4

6

8

10

0 1 2 3 4 5 6 7 8 9

SRR (mol/g dry sed/d)

Me

Hg

(ng

/g d

ryse

d)

MPGAMBJS

y = 0.0009x + 1.1511

R2 = 0.67

0

2

4

6

8

10

0 1 2 3 4 5 6 7 8 9

SRR (mol/g dry sed/d)

Me

Hg

(ng

/g d

ryse

d)

MPGAMBJS

Figure 2. The positive relationship between microbial sulfate reduction rate (SRR) and methylmercury (MeHg) concentration during April 2005 for the three wetland regions studied. SRR data from August 2005 is pending. The best fit linear regression equation and associated r2 value is given.

What Drives Sediment MeHg?Sulfate reducing bacteria need food!

% LOI versus % Total as MethylmercuryTop 2 cm of Sediment

R2 = 0.7452

0

5

10

15

20

25

30

0 1 2 3 4 5 6 7 8

% Total as Methyl

% L

OI

(Me)Hg in WaterWater MeHg similar to channel sediments

MeHg lowest near Bay end of PetalumaMeHg & Hg mostly (80%+) in particulate phase

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

BJS MP GM

Filt

ere

d H

g n

g/L

2005-Apr

2005-Aug

0

0.05

0.1

0.15

0.2

0.25

BJS MP GM

Pa

rtic

ula

te M

eH

g (

ng

/L)

0

5

10

15

20

25

30

Pa

rticula

te H

g (n

g/L

)

MeHg

HgT

Where do Biota Fit?Are black rails in areas w/ high MeHg?

Small ranges (avg .24ha) in spring

Black John Slough Mid Petaluma

Habitat UsagePrimarily in high marsh pickleweed

0.0

0.1

0.2

0.3

0.4

0.5

0.6

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0.8

Salicornia Scirpus Distichlis Grindelia Other Bare

Pe

rcen

t co

ver

Black John Slough

Petaluma Marsh

Gambonini Marsh

Does It Add Up?

0

1

2

3

4

5

6

7

8

9

BJS MP GAM

MeH

g (n

g/g)

High MarshSlough

High Marsh sediment MeHg ~2x higher Mid-PetalumaMeHg is bioaccumulative form of Hg

Black Rail (Feather) HgBlack rails reside and feed in high marsh,

therefore…Rail Hg differs among wetlands (Mid-Petaluma

~2x)

0

2

4

6

8

10

12

Black John Slough Petaluma Marsh Gambinini Marsh

[TH

g]

(mg

/kg

)

Implications for ManagementMP feather Hg up to 10ng/g, is it bad?

Other birds “background” in feather ~1-5ng/g

Can we do anything about it?Less (or more) reducing conditions?Less organic matter?

Other goals and priorities?(Me)Hg not the only factorNewer marsh Hg < ancient marsh (problem in 2000 years?)

Closing CreditsFunding: CBDA Ecosystem Restoration Program grant

ERP-02D-P62Site Access: CDFG, the PhelansProject Partners:

SFEI: (Don Yee), Josh Collins, Letitia Grenier, S. PearceUSGS WRD-CA: Mark Marvin-DiPasquale, Jennifer Agee, Le Kieu, Nick Ladizinski, Lisa WindhamUSGS WRD-WI: Dave Krabbenhoft, Shane Olund, Tom SabinUSGS BRD- John Takekawa, Isa Woo, Danika Tsao-MelcerAvocet Associates: Jules Evens