From Micro to Macro: A view from downstreamA synthesis of MeHg science from the Yolo Bypass and SFB-Delta

Lisa Windham-Myers9/26/13 EPA Workshop, San Francisco, CA

Modified from Parks et al. Science 2013

TributaryMeHg

Surface

Sediments

Pore WaterExchange &

Diffusion

bacterial methylation

Hg MeHg

MeHg

OpenChannel

Wetlands

Urban & WWTPs

Agricultural Lands /Delta Islands

Where can we control MeHg loading to delta?

Figure from Michelle Wood, CVRWQCB

Managed Wetlands (85% seasonal)

Agriculture Type

Where can we control MeHg loading to delta?

What Controls MeHg Production?

HighLowHg(II)bio Concentration

Hig

hLo

w

Hg(

II)-m

ethy

latin

g ba

cter

ia

activ

ity (k

met

h)

LowMPP

ModerateMPP

ModerateMPP

HighMPP

MeHg Production Potential (MPP) = kmeth x Hg(II)bio

MeHg Production Potential (MPP) = kmeth x Hg(II)bio

• Periodically Periodically floodedflooded

• VegetatedVegetated

Seasonal Wetlands

Wetland Mercury CyclingWetland Mercury Cycling

ProductionProduction

TransportTransportBioaccumulationBioaccumulation

Key findings of synthesis(Windham-Myers and Ackerman, 2012)

1. Hydrologic Control• Slowing water flow increases rates of storage and degradation of MeHg more than production.BUT• Slowing water concentrates surface water MeHg and enhances in situ bioaccumulation in fish.

2. Permanent Wetlands• Rates of MeHg storage and degradation may exceed processes of MeHg production (net sink).BUT• High soil carbon (peat) may produce more MeHg than they remove (net source).

3. Seasonal Wetlands1. Rewetting of dried wetlands regenerates biogeochemical species that enhance MeHg production.

• reactive Hg• ferric iron (FeIII)• sulfate (SO4)• labile carbon

2. Flood-up of dried wetlands can generate an initial pulse of MeHg from sediment to surface waters.4. TEMPORAL VARIABILITY in matrix concentrations can be orders of magnitude

• “Hot moments” drive annual patterns of MeHg production and export in seasonal wetlands.• Diel patterns in surface water – lower concentrations during daylight, higher concentrations at

night – may be important in shallow vegetated habitats, due to dominant effects of photodemethylation and/or downward advective storage of MeHg through transpiration..

• Biota MeHg concentrations vary over time, and breeding season is when wildlife is most vulnerable.5. SPATIAL VARIABILITY can relate to different initial conditions or management practices.

• Total Hg concentrations are often poorly correlated with MeHg concentrations. • Soil organic matter is associated with MeHg in wetlands and irrigated agriculture.• Wetlands can be a MeHg sink or source based on the relative loads of sourcewater and tailwater.

Yolo Bypass: Pulse of MeHg in surface water upon flood up

Alpers et al. 2013

Yolo Bypass: Pulse of MeHg in surface water upon flood up

Alpers et al. 2013

MeHg export rates

-195

31

-38

22

-10

100

-20

41

140161

310

21

68

24

-9-22

3524

81

119 13

-13

-200

-100

0

100

200

300

400

F20 F66 R31 R64 W32 W65 SW PW

Me

Hg

(u

g/h

a/d

ay

)

summer (irrigated) winter (non-flood) annual avg

Yolo Bypass: Wetlands are all MeHg sources in winter except Permanent Wetland (which is a sink year-round).

Bachand et al. (b) 2013

Source

Sink

Yolo Bypass: Seasonal wetlands discharge dissolved Hg (0.45 m)

Alpers et al. 2013

Yolo Bypass: Seasonal wetlands primarily discharge dissolved MeHg (0.45 mm)

Alpers et al. 2013

See Fleck et al. 2013

Surface water concentrations change over 24hour diel cyclePhotodemethylation and Transpirative Demand

Effects are greatest during summer, leaf-on conditions

Temporal Variability

Loads: “we need movies, not snapshots”. Browns Island: Continuous monitoring using FDOM (Bergamaschi et al. 2011)

Temporal Variability

JUNEJUNE(newly seeded)(newly seeded)

JULYJULY

AUGUSTAUGUST DECEMBER (post harvest)DECEMBER (post harvest)

Seasonality Matters!!Seasonality Matters!!Seasonality Matters!!Seasonality Matters!! Temporal VariabilityTemporal Variability

Yolo Bypass: Sediment MeHg concentrations range Yolo Bypass: Sediment MeHg concentrations range 6-fold annually within a given rice field6-fold annually within a given rice field

Caged mosquitofish

[TH

g] (

µg

g-1d

w)

A

0.0

0.5

1.0

1.5

2.0

0 30 60

White riceWild ricePermanent wetlands

Increase in 60 Days12 X higher

6 X higher

3 X higher

Ackerman and Eagles-Smith 2010, ES&TAckerman and Eagles-Smith 2010, ES&T

Yolo Bypass: Seasonally decoupled MeHg cyclingYolo Bypass: Seasonally decoupled MeHg cyclingSummer- High bioaccumulation, medium production, and low exportSummer- High bioaccumulation, medium production, and low export

Temporal VariabilityTemporal Variability

• Export in Winter• Storage in Summer• Decouples periods of production and export

Bachand et al., in review, bBachand et al., in review, b

SummerSummer WinterWinter

Yolo Bypass: Plant bio-physics – E vs TYolo Bypass: Plant bio-physics – E vs T• Evaporation concentrates constituents in placeEvaporation concentrates constituents in place• Transpiration Transpiration transportstransports constituents into soil constituents into soil

Temporal VariabilityTemporal Variability

Bachand et al. (a) 2013

SanFrancisco

SacramentoRiver

San Joaquin River

CALIFORNIA

• Cinnabar + elemental HgCinnabar + elemental Hg• THg = 200-500 ng/gTHg = 200-500 ng/g

• Clayey soils, OM=2-10%Clayey soils, OM=2-10%• SOSO44 = 10 – 300 mg/L = 10 – 300 mg/L• Conventional (white) rice/Conventional (white) rice/ wild rice/ fallow rotationwild rice/ fallow rotation

Yolo Bypass Wildlife Area: YWA

• Elemental HgElemental Hg• THg = 50-400 ng/gTHg = 50-400 ng/g

• Silty soils, OM = 5 -10%Silty soils, OM = 5 -10%• SOSO44 = 1 – 20 mg/L = 1 – 20 mg/L• Organic (white) riceOrganic (white) rice

Cosumnes River Preserve: CRP

• Elemental Hg Elemental Hg • THg = 50-150 ng/gTHg = 50-150 ng/g

• Organic soils, OM=10-40%Organic soils, OM=10-40%• SOSO44 = 20 – 500 mg/L = 20 – 500 mg/L• Conventional (white) riceConventional (white) rice

Twitchell Island: TR

All rice fields flooded in All rice fields flooded in summer AND winter summer AND winter (2 flood periods)(2 flood periods)

Fleck (USGS) 2013

Spatial Variability (Rice)Spatial Variability (Rice)

CRP YWA TR

Me

Hg

exp

ort

(ug

ha-1

d-1

)

-100

0

100

200

300

N = number of rice fieldsn = number of years* =rice systemcontaining 5 - 20 fields

N = 9n = 2

N = 9n = 1

N = 6n = 1

N = 6n = 1

N = 1*n = 3

N = 1*n = 3

SummerWinter

Fleck (in preparation)

Seasonal net MeHg export from rice fields

Source

Sink

Spatial Variability (Rice)Spatial Variability (Rice)

Marvin-DiPasquale Marvin-DiPasquale et al., 2013, STOTENet al., 2013, STOTEN

Seasonal Export not a function of MeHg productionSeasonal Export not a function of MeHg productionSpatial Variability (Rice)Spatial Variability (Rice)

YWA MPP rates by season

Ag summer Ag winter

MP

P(p

g/g/d

ay)

0

20

40

60

80

100

www.kevinstewartfishing.com

We still have many science gaps to address for MeHg TMDL.We still have many science gaps to address for MeHg TMDL.

To get from micro to macro, one must consider•Production (Hg, carbon, redox)•Transport (“plumbing”, degradation)•Bioaccumulation (season, sensitivity)

Thank you. lwindham-myers@usgs.govYolo Bypass papers (n=8), in press, STOTEN special section (2013)

Key findings of synthesis(Windham-Myers and Ackerman, 2102)

1. Hydrologic Control• Slowing water flow increases rates of storage and degradation of MeHg more than production.BUT• Slowing water concentrates surface water MeHg and enhances in situ bioaccumulation in fish.

2. Permanent Wetlands• Rates of MeHg storage and degradation may exceed processes of MeHg production (net sink).BUT• High soil carbon (peat) may produce more MeHg than they remove (net source).

3. Seasonal Wetlands1. Rewetting of dried wetlands regenerates biogeochemical species that enhance MeHg production.

• reactive Hg• ferric iron (FeIII)• sulfate (SO4)• labile carbon

2. Flood-up of dried wetlands can generate an initial pulse of MeHg from sediment to surface waters.4. TEMPORAL VARIABILITY in matrix concentrations can be orders of magnitude

• “Hot moments” drive annual patterns of MeHg production and export in seasonal wetlands.• Diel patterns in surface water – lower concentrations during daylight, higher concentrations at

night – may be important in shallow vegetated habitats, due to dominant effects of photodemethylation and/or downward advective storage of MeHg through transpiration..

• Biota MeHg concentrations vary over time, and breeding season is when wildlife is most vulnerable.5. SPATIAL VARIABILITY can relate to different initial conditions or management practices.

• Total Hg concentrations are often poorly correlated with MeHg concentrations. • Soil organic matter is associated with MeHg in wetlands and irrigated agriculture.• Wetlands can be a MeHg sink or source based on the relative loads of sourcewater and tailwater.