DOC and THMP loads from a restored wetland in the Delta DWR RD1601 CALFED CBDA staff USGS staff Jacob A Fleck Steven J. Deverel Roger Fujii

Wetland restoration Many thousands acres of wetland restoration Many thousands acres of wetland restoration All native wetland types: Tidal, non-tidal, mudflat All native wetland types: Tidal, non-tidal, mudflat Benefits Benefits Provide habitat for native species Provide habitat for native species Improve ecosystem function Improve ecosystem function Flood protection Flood protection Subsidence mitigation on organic soils Subsidence mitigation on organic soils Engineering difficulties (deep subsidence) Engineering difficulties (deep subsidence) Island in-fill Island in-fill Setback levees Setback levees Impounded, flow-through wetlands Impounded, flow-through wetlands

USGS/DWR wetland restoration demonstration project Initially established in 1997 Initially established in 1997 Use of wetland restoration as subsidence mitigation technique on deeply subsided islands Use of wetland restoration as subsidence mitigation technique on deeply subsided islands Impounded, flow-through system Impounded, flow-through system This study established in 2000 This study established in 2000 To determine the effects that wetland restoration will have on DOC and THMP loads from subsided peat islands. To determine the effects that wetland restoration will have on DOC and THMP loads from subsided peat islands.

Demo pond setting: Twitchell Island

Twitchell Island Deeply subsided Deeply subsided As much as 20 ft As much as 20 ft Peat soils dominate Peat soils dominate >10 ft remain >10 ft remain ~35% OM ~35% OM Primarily agriculture Primarily agriculture srsr corn srsr corn Water upwelling Water upwelling

Twitchell Island drainage

Demonstration pond

Soils/drainage Peat soil high in C Peat soil high in C Two layers Two layers Zone of drain influence Zone of drain influence Well-decomposed peat Well-decomposed peat High hydraulic conductivity High hydraulic conductivity Deep peat Deep peat Unaltered peat Unaltered peat Low hydraulic conductivity Low hydraulic conductivity

Twitchell pumping station

WQ Effects?

HCX 3 OH X O HOOC O HCCl 2 Trihalomethanes HaloaceticAcids MX Halophenols C CX n O= OH C CX n O= CR 3 Haloketones Haloacetonitriles O OH H3CH3C O=C O OH COOH OH C C C O= OH O C O= OH C=O CH 3 CH 2 DOC - OCl - OBr CX 3 CN DBPs Drinking water concern

Study design Collect samples of surface and subsurface waters for DOC and THMFP analyses Collect samples of surface and subsurface waters for DOC and THMFP analyses Combine with water flux data to calculate loads Combine with water flux data to calculate loads

Monitoring plan Surface inflow and outflow Surface inflow and outflow Continuously monitored for water flux Continuously monitored for water flux Weekly sampling for DOC and THMFP Weekly sampling for DOC and THMFP Piezometers Piezometers Sampled soil water 2x/yr for seasonal extremes in 2 depths at 3 piers Sampled soil water 2x/yr for seasonal extremes in 2 depths at 3 piers Shallow soils (0.5-2 ft) Shallow soils (0.5-2 ft) Deep peat (8-10 ft) Deep peat (8-10 ft)

Water flux out of the pond

Water flux ( )

Demo pond surface water DOC

DOC concentrations in soil water underlying the pond

DOC loads ( )

THMP loads ( )

Compare net loads to ag

Temporal trends Surface water fluxes show strong seasonal trend Surface water fluxes show strong seasonal trend Subsurface DOC concentrations are decreasing over time in some shallow soil water ( ) Subsurface DOC concentrations are decreasing over time in some shallow soil water ( )

DOC concentrations in surface water ( )

Net DOC flux out of the pond (surface waters, )

THMFP (surface water)

Net THMP flux from the pond (surface waters, )

Subsurface trends

Subsurface fluxes (estimated) Seepage governed by hydraulic head Seepage governed by hydraulic head ~240 m3/day ~240 m3/day Concentration in shallow soils declined over time Concentration in shallow soils declined over time Pier H (2001) = 60 mg/L ~ 200 g/m 2 -yr Pier H (2001) = 60 mg/L ~ 200 g/m 2 -yr Pier H (2004) = 25 mg/L ~ 85 g/m 2 -yr Pier H (2004) = 25 mg/L ~ 85 g/m 2 -yr Pier K ~ 160 mg/L ~ 440 g/m 2 -yr Pier K ~ 160 mg/L ~ 440 g/m 2 -yr

Temporal trend summary Wetland net surface fluxes are seasonal Wetland net surface fluxes are seasonal Higher in summer and lower in winter Higher in summer and lower in winter Opposite trend of ag operations Opposite trend of ag operations Subsurface fluxes Subsurface fluxes No apparent seasonal trend (lack of data?) No apparent seasonal trend (lack of data?) Concentration (fluxes) have been decreasing over time for soils in flow path Concentration (fluxes) have been decreasing over time for soils in flow path

DOC quality? DOC quality differs in source of DOC and processing in the environment DOC quality differs in source of DOC and processing in the environment We would expect ag, wetland soil, and surface water DOC to differ in quality We would expect ag, wetland soil, and surface water DOC to differ in quality Food source vs drinking water problem? Food source vs drinking water problem? Different carbon structures react differently in DBP formation Different carbon structures react differently in DBP formation Some DOC structures are tasty some are not Some DOC structures are tasty some are not

DOC quality

Conclusions Demo pond contributes more DOC and THMPs to Delta waters than nearby ag fields (>10x) Demo pond contributes more DOC and THMPs to Delta waters than nearby ag fields (>10x) Most of demo pond loads derived from seepage through the shallow soils Most of demo pond loads derived from seepage through the shallow soils If contribution from shallow soils minimized… If contribution from shallow soils minimized… Demo pond loads would be more comparable to ag operations (DOC ~2x, THMPs ~4x) Demo pond loads would be more comparable to ag operations (DOC ~2x, THMPs ~4x) Timing of loads would be different from ag operations (benefits?) Timing of loads would be different from ag operations (benefits?) Demo pond surface water DOC is more reactive, but also more likely beneficial for food web (?) Demo pond surface water DOC is more reactive, but also more likely beneficial for food web (?)

Implications Design of large-scale wetland restoration sites need to consider shallow soil contributions to drain flow Design of large-scale wetland restoration sites need to consider shallow soil contributions to drain flow Need to consider the effect changing the DOC load timing from converted fields will have on Delta ecosystems and drinking water facilities? Need to consider the effect changing the DOC load timing from converted fields will have on Delta ecosystems and drinking water facilities? Need to balance potential benefits for subsidence mitigation, habitat restoration and food web dynamics with potential threats to drinking water supply Need to balance potential benefits for subsidence mitigation, habitat restoration and food web dynamics with potential threats to drinking water supply

Future and ongoing work Twitchell South pond Twitchell South pond Using lessons from demo ponds to monitor loads before, during, and after conversion Using lessons from demo ponds to monitor loads before, during, and after conversion Expand studies to include other priorities (ie: MeHg) Expand studies to include other priorities (ie: MeHg) Rice project Rice project Using water management lessons to help determine BMPs for reducing DOC loads from rice fields in Delta Using water management lessons to help determine BMPs for reducing DOC loads from rice fields in Delta Compare conversion of corn fields to rice with conversion to wetland Compare conversion of corn fields to rice with conversion to wetland

Questions?