Overview: Diagnosis and prognosis of effects of changes in lake and wetland extent on the regional carbon balance of northern Eurasia Ted Bohn Princeton Workshop, December 4-6, 2006

Outline Project Details Motivation –Carbon, Water, and Climate –High-latitude Wetlands –Lakes Science Questions Strategies –Modeling –Remote Sensing –Validation: In-Situ Data Preliminary Results Future Work (Freeman et al., 2001)

Project Details Part of Northern Eurasia Earth Science Partnership Initiative (NEESPI) Personnel: PI: –Dennis Lettenmaier (University of Washington, Seattle, WA, USA) Co-PIs: –Kyle MacDonald (NASA/JPL, Pasadena, CA, USA) –Laura Bowling (Purdue University, Lafayette, IN, USA) Collaborators: –Gianfranco De Grandi (EU Joint Research Centre, Ispra, Italy) –Reiner Schnur (Max Planck Institut fur Meteorologie, Hamburg, Germany) –Nina Speranskaya and Kirill V. Tsytsenko (State Hydrological Institute, Russia) –Daniil Kozlov and Yury N. Bochkarev (Moscow State University) –Martin Heimann (Max Planck Institut fur Biogeochemie, Jena, Germany) –Ted Bohn (University of Washington, Seattle, WA, USA) –Erika Podest (NASA/JPL, Pasadena, CA, USA) –Ronny Schroeder (NASA/JPL, Pasadena, CA, USA) –KrishnaVeni Sathulur (Purdue University, Lafayette, IN, USA)

NEESPI Region Forest Grass/Shrub/TundraCrops Wetlands

Carbon, Water, and Climate Human impact since 1750 –Emissions of Gt C (as CO 2 ) Burning of fossil fuels: 280 Gt C Land-use change: Gt C –Atmosphere’s C pool has only increased by 190 Gt C (~ 40% of emissions) –Land and ocean have taken up the remainder (roughly 150 Gt C, or 30%, each) Ability of land/ocean to continue absorbing C is limited and depends on climate Hydrology plays a major role (Keeling et al., 1996)

Terrestrial Carbon Stocks (IPCC 2001) Wetland soils store the most carbon per unit area Wetland extent depends on hydrology Wetland behavior depends on hydrology

High-Latitude Wetlands – Boreal Peatlands Dual role in terrestrial carbon cycle Methane Source –Saturated soil → anaerobic respiration –46 TgCyr -1 (Gorham 1991; Matthews & Fung 1987) very uncertain –Roughly 10 % of global methane emissions –Methane is a very strong greenhouse gas (Wieder, 2003) Carbon Sink –cold T & saturated soil for most of year –NPP > Rh and other C losses –70 TgCyr -1 (Clymo et al 1998) - very uncertain –Current storage: 455 Pg C (1/3 of global soil C, ¼ of global terrestrial C) (Gorham 1991) Balance of these effects depends on climate –Climate feedback

Peatland H 2 O Budget Water Table Living Biomass Acrotelm Catotelm Subsurface Flow (Q sb ) Precipitation (P) Evaporation (E) Water Table = f(P, E, Tr, Q s, Q sb ) Transpiration (Tr) From Upslope Surface Runoff (Q s ) Groundwater To Ocean Streams

Peatland C Budget* Water Table Living Biomass Acrotelm Catotelm Fire Outgassing DOC Aerobic R h NPP CO 2 (25-40 Tg C/y) Streams CO 2 Org C Anaerobic R h CH 4 (45 Tg C/y) CO 2 (25-50 Tg C/y) DOC Litter Carbon balance = f(NPP, T, water table, fire, DOC export) To Ocean Subsurface Flow (Q sb )From Upslope (25 Tg C/y) (NPP – Rh ≈ Tg C/y) * Extremely crude estimates! DOC

West Siberian Lowlands (Gorham, 1991) Peatland Distribution in N. Eurasia Belt of major peat accumulation overlaps with: boreal forest (taiga) permafrost (mostly peatlands) Majority of world’s peatlands are in Eurasia

High-Latitude Lakes Accumulate large amounts of carbon –Lakes worldwide accumulate 42 Gt C/yr in their sediments (Dean and Gorham, 1998) Vent terrestrial carbon to the atmosphere –Respiration > Productivity in most lakes (Kling et al., 1991, Cole et al., 1994) –R:P correlates with DOC (del Giorgio et al., 1994) –DOC is imported from surrounding terrestrial ecosystems (especially true near wetlands) –Some Arctic terrestrial ecosystems may become net sources of atmospheric carbon when DOC loss is taken into account NE Siberian thaw lakes are strong methane sources (Walter et al., 2006) –Decomposition of “fresh” carbon in newly-thawed soil under lakes –Substantial amounts of C could be liberated as methane if all permafrost were to thaw

Lake H 2 O Budget Streams Streams, Surface Runoff, Groundwater To Ocean Evaporation (E)Precipitation (P) Balance: P + Q in = E + Q out

Lake C Budget Streams Streams, Surface Runoff, Groundwater Dis- solution Evasion To Ocean Sediment Deposition Anaerobic Rh CO 2 CO 2, CH 4 POC NPP CO 2 Algae DOC POC Aerobic Rh DOC Balance: TOC in + NPP = Rh + TOC out (~30%) 42 Gt C/yr

High-Latitudes Have Experienced Change Thawing of permafrost (Turetsky et al., 2002) Increased outgassing of methane (Walter et al., 2006) Increasing precipitation (Serreze et al., 2000) Increasing river discharge (Peterson et al., 2002) Growing/shrinking lakes (Smith et al., 2005)

DOC Export DOC export from Arctic land into Arctic Ocean: 25.1 Tg C/y (Opsahl et al. 1999) Peatlands supply most of this (Pastor et al. 2003) Higher DOC in streams can drive outgassing of CO2 (evasion) Fry and Smith, 2005: Permafrost zone: DOC export small Permafrost-free zone: DOC export large (Opsahl et al., 1999)

Main Science Issues High-latitude lakes and wetlands are potentially large sources of CO2 and CH4 Fluxes and extent are sensitive to climate (especially hydrology) Lake/wetland extent is underrepresented by low-resolution remote sensing Long time series of high-resolution remote sensing data not available

Science Questions Overarching Science Questions: –How have changes in lake and wetland extent in northern Eurasia over the last half-century affected the region’s carbon balance? –What will the effects be over the next century? Sub-Topics: –What areas within the region have been/will be affected by changes in lake/wetland extent? –How are ongoing changes in the tundra region affecting the dynamics of wetlands? Changes in permafrost active layer depth –How are/will these changes affect the carbon balance of the region? –How well can current sensors (MODIS, SAR) detect changes in wetland extent? –Can high-resolution SAR products be used to provide seasonal and interannual variations in lake/wetland extent? Extend the rapid repeat cycle of lower-resolution products like MODIS

Modeling Strategy Integrate several models: VIC – hydrology (incl. frozen soil, water table, explicit lake/wetlands model) BETHY – fast ecosystem processes on sub-daily timescale (photosynthesis, respiration) Walter-Heimann (WHM) methane model – methane emissions on daily timescale –CH4 flux = f(water table, soil T, NPP) LPJ – slow ecosystem processes on yearly timescale (change in plant assemblage, fire)

VIC: Large-scale Hydrology Inputs Meteorology: –Gridded ERA-40 reanalysis Soil parameters: –FAO soil properties –Calibration parameters Soil layer depth Infiltration Baseflow Vegetation parameters: –Observed veg cover fractions (AVHRR) –Veg properties from literature Outputs Moisture and energy fluxes and states Hydrograph (after routing) Typically 0.5- to degree grid cells Water and energy balance Daily or sub-daily timesteps Mosaic of veg tiles; Penman-Monteith ET Non-linear baseflow Heterogeneous infiltration/runoff Multi-layer soil column

VIC Lake/Wetland Algorithm soil saturated land surface runoff enters lake evaporation depletes soil moisture lake recharges soil moisture Lake drainage = f(water depth, calibration parameter)

Model Integration Obs Met Data or Climate Model BETHY Photosynthesis Respiration C storage VIC Hydrology LPJ Species distribution Fire Walter-Heimann Methane Model Methane emissions Soil moisture, evapotranspiration C fluxes Plant functional types Water table, Soil temperature NPP Precipitation, Air temperature, Wind, Radiation Obs or Projected [CO 2 ] (Completed)

Validation: Remote Sensing JERS: 100m SAR imagery 1 mosaic, acquired 1997/1998

Validation: In-Situ Data Landcover classifications: –5-yearly landcover summaries (SHI) 1950s- 1990s Hydrological observations: –Soil moisture (SHI) 1960s-1980s –Evaporation (pan & actual) (SHI) 1960s- 1990s Carbon fluxes: –TCOS towers (hourly, )

soil moisture and T evap flux tower

Preliminary Results Valdai/Fyodorovskoye SitesOb Site

Hydrology at Valdai

Estimated Methane Emissions at Valdai

g C/m 2 d Date Net CO 2 Emissions Productivity and Respiration Carbon Fluxes at Fyodorovskoye Tower

Future Work Remote Sensing: –Validation of remote sensing classifications In-situ data Other remote-sensing products –Extension of classifications back in time via relationships with other remote sensing or in-situ products Models: –Finish integration of models Add photosynthesis, respiration, etc. to VIC Take into account decomposition of carbon formerly locked up in permafrost (specifically: yedoma)? DOC leaching from terrestrial systems Take into account C cycling in lakes Add long-term vegetation dynamics

Future Work –Validate models against historical observations Landcover timeseries (from remote sensing/in situ data) –Lake extent (seasonal) –Wetland extent –Vegetation cover Hydrological fluxes and storage –soil moisture and temperature –evaporation –runoff –water table –snow depth and cover Carbon fluxes and storage –CO2 –CH4 –standing biomass –soil carbon profiles –DOC in soil, streams, lakes –C accumulation rates in soils, lake sediments –Expand from point estimates to regional estimates –Use climate models to predict changes over next century

Thank You (Corradi et al., 2005)

Peatlands: Long-term C Sink but Initial Greenhouse Source Friborg et al., 2003 Adding 1 m 2 of peatland produces the equivalent CO 2 emissions: 6 g CO 2 /m 2 day over next 20 years 1 g CO 2 /m 2 day over next 100 years 0 net greenhouse effect over next 149 years Net greenhouse sink thereafter Removing 1 m 2 of peatland is initially a greenhouse sink, then a source Methane Greenhouse Warming Potential (GWP): 62 (20 years) 23 (100 years) 7 (500 years) Compared to CO2, CH4 is a stronger, but shorter-lived, greenhouse gas

Modeling Strategy Previous Studies: –Coarse statistical relationships between soil moisture and methane emissions –Some used explicit ecosystem C-cycling –Some handled frozen soils –None used explicit lake/wetland formulations –Large disagreement on magnitude of future emissions