From Micro to Macro: A view from downstream A synthesis of MeHg science from the Yolo Bypass and SFB-Delta Lisa Windham-Myers 9/26/13 EPA Workshop, San Francisco, CA Modified from Parks et al. Science 2013

Tributary MeHg Surface Sediments Pore Water Exchange & Diffusion bacterial methylation HgMeHg Open Channel 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? High Low Hg(II) bio Concentration High Low Hg(II)-methylating bacteria activity (k meth ) Low MPP Moderate MPP Moderate MPP High MPP MeHg Production Potential (MPP) = k meth x Hg(II) bio MeHg Production Potential (MPP) = k meth x Hg(II) bio Periodically floodedPeriodically flooded VegetatedVegetated Seasonal Wetlands

Wetland Mercury Cycling Production Transport Bioaccumulation

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 Wetlands 1.Rewetting of dried wetlands regenerates biogeochemical species that enhance MeHg production. reactive Hg ferric iron (FeIII) sulfate (SO 4 ) 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

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 Surface water concentrations change over 24hour diel cycle Photodemethylation 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

JUNE (newly seeded) JULY AUGUST DECEMBER (post harvest) Seasonality Matters!! Temporal Variability Yolo Bypass: Sediment MeHg concentrations range 6-fold annually within a given rice field

Increase in 60 Days 12 X higher 6 X higher 3 X higher Ackerman and Eagles-Smith 2010, ES&T Yolo Bypass: Seasonally decoupled MeHg cycling Summer- High bioaccumulation, medium production, and low export Temporal Variability

Export in Winter Storage in Summer Decouples periods of production and export Bachand et al., in review, b SummerWinter Yolo Bypass: Plant bio-physics – E vs T Evaporation concentrates constituents in place Evaporation concentrates constituents in place Transpiration transports constituents into soil Transpiration transports constituents into soil Temporal Variability Bachand et al. (a) 2013

Cinnabar + elemental HgCinnabar + elemental Hg THg = ng/gTHg = ng/g Clayey soils, OM=2-10%Clayey soils, OM=2-10% SO 4 = 10 – 300 mg/LSO 4 = 10 – 300 mg/L Conventional (white) rice/Conventional (white) rice/ wild rice/ fallow rotation wild rice/ fallow rotation Yolo Bypass Wildlife Area: YWA Elemental HgElemental Hg THg = ng/gTHg = ng/g Silty soils, OM = 5 -10%Silty soils, OM = 5 -10% SO 4 = 1 – 20 mg/LSO 4 = 1 – 20 mg/L Organic (white) riceOrganic (white) rice Cosumnes River Preserve: CRP Elemental HgElemental Hg THg = ng/gTHg = ng/g Organic soils, OM=10-40%Organic soils, OM=10-40% SO 4 = 20 – 500 mg/LSO 4 = 20 – 500 mg/L Conventional (white) riceConventional (white) rice Twitchell Island: TR All rice fields flooded in summer AND winter (2 flood periods) Fleck (USGS) 2013 Spatial Variability (Rice)

Fleck (in preparation) Seasonal net MeHg export from rice fields Source Sink Spatial Variability (Rice)

Marvin-DiPasquale et al., 2013, STOTEN R31 R64 whiterice W32 W65 wildrice F20 F66 fallowfields Seasonal Export not a function of MeHg production Spatial Variability (Rice)

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. Yolo 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 Wetlands 1.Rewetting of dried wetlands regenerates biogeochemical species that enhance MeHg production. reactive Hg ferric iron (FeIII) sulfate (SO 4 ) 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.