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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 Bohn Princeton Workshop, December 4-6, 2006. Outline. Project Details Motivation Carbon, Water, and Climate High-latitude Wetlands Lakes

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slide1
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
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
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)
slide4
NEESPI Region

Wetlands

Forest

Crops

Grass/Shrub/Tundra

carbon water and climate
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
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
High-Latitude Wetlands – Boreal Peatlands
  • 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)

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)

  • Balance of these effects depends on climate
    • Climate feedback
peatland h 2 o budget
Peatland H2O Budget

Precipitation (P)

Evaporation (E)

Transpiration (Tr)

Living Biomass

Surface Runoff (Qs)

Acrotelm

To

Ocean

Water Table

Streams

From Upslope

Subsurface Flow (Qsb)

Groundwater

Catotelm

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

peatland c budget
Peatland C Budget*

(NPP – Rh ≈ 200-300 Tg C/y)

CO2

CH4 (45 Tg C/y)

CO2

CO2 (25-40 Tg C/y)

Fire

NPP

Living Biomass

CO2 (25-50 Tg C/y)

Litter

Acrotelm

Outgassing

Aerobic Rh

Org C

To

Ocean

Water Table

DOC

DOC

Streams

(25 Tg C/y)

Anaerobic Rh

DOC

From Upslope

Subsurface Flow (Qsb)

Catotelm

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

* Extremely crude estimates!

slide10
Peatland Distribution in N. Eurasia

West Siberian

Lowlands

Majority of world’s peatlands are in Eurasia

(mostly peatlands)

  • Belt of major peat accumulation overlaps with:
  • boreal forest (taiga)
  • permafrost

(Gorham, 1991)

high latitude lakes
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
Lake H2O Budget

Precipitation (P)

Evaporation (E)

Streams, Surface Runoff,

Groundwater

Streams

To

Ocean

Balance: P + Qin = E + Qout

lake c budget
Lake C Budget

CO2

CO2, CH4

CO2

Dis-

solution

Evasion

NPP

Algae

Aerobic

Rh

DOC

Streams, Surface Runoff,

Groundwater

POC

DOC

POC

(~30%)

Streams

Sediment Deposition

To

Ocean

42 Gt C/yr

Anaerobic Rh

Balance: TOCin + NPP = Rh + TOCout

high latitudes have experienced change
High-Latitudes Have Experienced Change
  • Increasing precipitation (Serreze et al., 2000)
  • Increasing river discharge (Peterson et al., 2002)
  • Growing/shrinking lakes (Smith et al., 2005)
  • Thawing of permafrost (Turetsky et al., 2002)
  • Increased outgassing of methane (Walter et al., 2006)
doc export
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
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
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
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
VIC: Large-scale Hydrology
  • Typically 0.5- to 0.125-degree grid cells
  • Water and energy balance
  • Daily or sub-daily timesteps

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)

Mosaic of veg tiles;

Penman-Monteith ET

Heterogeneous infiltration/runoff

Non-linear baseflow

Multi-layer soil column

vic lake wetland algorithm
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
(Completed)Model Integration

Obs Met Data or

Climate Model

Precipitation,

Air temperature,

Wind, Radiation

Obs or Projected [CO2]

  • VIC
  • Hydrology
  • BETHY
  • Photosynthesis
  • Respiration
  • C storage
  • LPJ
  • Species distribution
  • Fire

Soil moisture,

evapotranspiration

C fluxes

Plant functional types

Water table,

Soil temperature

NPP

  • Walter-Heimann Methane Model
  • Methane emissions
validation remote sensing
Validation: Remote Sensing

JERS: 100m SAR imagery

1 mosaic, acquired 1997/1998

validation in situ data
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)
slide24
soil moisture

soil moisture

and T

evap

flux tower

preliminary results
Preliminary Results

Valdai/Fyodorovskoye Sites

Ob Site

slide30
Carbon Fluxes at Fyodorovskoye Tower

Productivity and Respiration

g C/m2d

Net CO2 Emissions

g C/m2d

Date

future work
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 work1
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
Thank You

(Corradi et al., 2005)

peatlands long term c sink but initial greenhouse source
6 g CO2/m2day over next 20 years

1 g CO2/m2day over next 100 years

0 net greenhouse effect

over next 149 years

Net greenhouse

sink thereafter

Peatlands: Long-term C Sink butInitial Greenhouse 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

Adding 1 m2 of peatland produces

the equivalent CO2 emissions:

Removing 1 m2 of peatland

is initially a greenhouse sink,

then a source

Friborg et al., 2003

modeling strategy1
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
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