Transcript Impacts of leaf phenology and water table on interannual

Impacts of leaf phenology and
water table on interannual
variability of carbon fluxes in
subboreal uplands and wetlands
Implications for regional fluxes in the
upper Midwest USA
Ankur R Desai, Benjamin N Sulman
University of Wisconsin-Madison
D. Scott Mackay
State University of New York-Buffalo
Ameriflux/ChEAS PIs
Ameriflux Meeting 2008
Motivation
• Interannual variation (IAV) in carbon fluxes
from land to atmosphere is significant at
most flux sites
• Key to understanding how climate affects
ecosystems comes from modeling IAV
• IAV (years-decade) is currently poorly
modeled, while hourly, seasonal, and even
successional (century) are better
Predicting NEE (Ricciuto et al)
Climate Drivers of Carbon Flux
•Temperature
•Precipitation
•Radiation
•[CO2]
Interannual
Climate Drivers of ^Carbon Flux
•Temperature -> Phenology
•Precipitation -> Drought
•Radiation
-> Light Quality
•[CO2]
-> Acclimation
Interannual NEE at ChEAS
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Questions
• What controls IAV of NEE in subboreal uplands?
– Hypothesis: Phenology -> Growing season start, end, or
length affects GPP
– Piao et al (2008) -> Autumn warming and Rh
• What controls IAV of NEE in subboreal wetlands?
– Hypothesis: Phenology + Water table affects ER
– Ise et al (2008) -> Decomposition and moisture
• What controls IAV of regional NEE in subboreal North
America?
• Can a very simple model be constructed to explain
IAV?
– Can we make do a parameter opimization more attuned to
IAV?
– Hypothesis: MCMC overfits to hourly data
Optimization
HOURLY
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IAV
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Phenology
• Five sites with 5-8 years of data
– 1 regional (LEF), 1 wetland (LCR), 3 uplands (SYL,
UMB, WCR)
– Assimilate 1st 4 years of data
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Phenology Model
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Twice daily model, annually resetting pools
Driven by PAR, Air and Soil T, VPD
LUE based GPP model f(PAR,T,VPD)
Three respiration pools f(Air T, Soil T, GPP)
Model 1. NOLEAF
– Constant leaf on and leaf off days
• Model 2. LEAF (Phenology)
– Sigmoidal Threshold GDD (base 10) function for leaf on
– Sigmoidal Threshold Daily Mean Soil Temp function for leaf
off
• 17 parameters, 3 are fixed
– Output: NEE, ER, GPP, LAI
HOURLY NOLEAF
Hourly
HOURLY LEAF
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IAV NOLEAF
IAV LEAF
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Interannual
HOURLY NOLEAF
HOURLY LEAF
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IAV NOLEAF
IAV LEAF
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Quic kTime™ and a
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Quic kTime™ and a
dec ompr es sor
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Quic kTime™ and a
dec ompres sor
are needed to s ee this pic tur e.
Quic kTime™ and a
dec ompres sor
are needed to s ee this pic tur e.
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NEE-Leaf
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GPP ER Leaf
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Precipitation and Water Table
• Sulman et al (in prep) Biogeosciences see Ameriflux poster
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Shrub Wetland Flux Response
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Three Wetlands
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Three Wetlands
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Regional NEE
• See NACP poster in Feb.
Annual flux (NEE)
1997
1998
1999
2000
2001
2002
2003
2004
0
gC m-2 yr-1
-50
-100
Flux towers
FIA model
ABL Budget
-150
-200
-250
Year
Conclusions
• Autumn soil temperature appears to be a major
control on interannual variability in subboreal upper
Midwest USA flux tower site annual NEE
– Due mainly to effect of growing season length for GPP
– Only detectable using a modified MCMC cost function that
penalizes for poor fit to cumulative annual NEE
• Additionally, growing season average water table
strongly affects ER in wetlands
– GPP effect in both uplands and wetlands -> related to
precipitation deficits?
• Regional NEE is messy
• Thanks: DOE NICCR, DOE TCP, NASA CC, NOAA CPO,
USDA/USFS NRS, NSF, UW Foundation, ChEAS