overview: diagnosis and prognosis of effects of changes in lake and wetland extent on the regional...
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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