Overview: Diagnosis and prognosis of effects of changes in lake and wetland extent on the regional

carbon balance of northern Eurasia

Ted BohnPrinceton 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 460-480 Gt C (as

CO2)• Burning of fossil fuels: 280 Gt C• Land-use change: 180-200 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 H2O Budget

Water Table

Living Biomass

Acrotelm

Catotelm

Subsurface Flow (Qsb)

Precipitation (P) Evaporation (E)

Water Table = f(P, E, Tr, Qs, Qsb)

Transpiration (Tr)

From Upslope

Surface Runoff (Qs)

Groundwater

ToOcean

Streams

Peatland C Budget*

Water Table

Living Biomass

Acrotelm

Catotelm

Fire

Outgassing

DOC

Aerobic Rh

NPP

CO2 (25-40 Tg C/y)

Streams

CO2 CO2

Org C

Anaerobic Rh

CH4 (45 Tg C/y)

CO2 (25-50 Tg C/y)

DOC

Litter

Carbon balance = f(NPP, T, water table, fire, DOC export)

ToOcean

Subsurface Flow (Qsb)From Upslope

(25 Tg C/y)

(NPP – Rh ≈ 200-300 Tg C/y)

* Extremely crude estimates!

DOC

West SiberianLowlands

(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 H2O Budget

Streams

Streams, Surface Runoff,Groundwater

ToOcean

Evaporation (E)Precipitation (P)

Balance: P + Qin = E + Qout

Lake C Budget

Streams

Streams, Surface Runoff,Groundwater

Dis-solution

Evasion

ToOcean

Sediment Deposition

Anaerobic Rh

CO2CO2, CH4

POC

NPP

CO2

Algae

DOCPOC

AerobicRhDOC

Balance: TOCin + NPP = Rh + TOCout

(~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 ExportDOC 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 0.125-degree grid cells• Water and energy balance• Daily or sub-daily timestepsMosaic of veg tiles;Penman-Monteith ET

Non-linear baseflow

Heterogeneous infiltration/runoff

Multi-layer soil column

VIC Lake/Wetland Algorithm

soilsaturated

land surface runoff enters

lake

evaporation depletes soil

moisture

lake recharges

soil moisture

Lake drainage = f(water depth, calibration parameter)

Model IntegrationObs Met Data orClimate 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 [CO2]

(Completed)

Validation: Remote SensingJERS: 100m SAR imagery1 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, 1998-2002)

soil moisture

soil moistureand T

evap

flux tower

Preliminary Results

Valdai/Fyodorovskoye Sites Ob Site

Hydrology at Valdai

Estimated Methane Emissions at Valdai

g C

/m2 d

g C

/m2 d

Date

Net CO2 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 butInitial Greenhouse Source

Friborg et al., 2003

Adding 1 m2 of peatland producesthe equivalent CO2 emissions:

6 g CO2/m2day over next 20 years

1 g CO2/m2day over next 100 years

0 net greenhouse effectover next 149 years

Net greenhousesink thereafter

Removing 1 m2 of peatlandis initially a greenhouse sink,then a source

Methane GreenhouseWarming Potential (GWP):•62 (20 years)•23 (100 years)•7 (500 years)

Compared to CO2, CH4 isa 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