impacts of leaf phenology and water table on interannual variability of carbon fluxes in subboreal...
TRANSCRIPT
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
USAAnkur R Desai, Benjamin N SulmanUniversity of Wisconsin-Madison
D. Scott MackayState 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]
Climate Drivers of Carbon Flux
•Temperature -> Phenology
•Precipitation -> Drought•Radiation -> Light Quality
•[CO2] -> Acclimation
Interannual
^
Interannual NEE at ChEAS
QuickTime™ and a decompressor
are needed to see this picture.
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
QuickTime™ and a decompressor
are needed to see this picture.
QuickTime™ and a decompressor
are needed to see this picture.
HOURLY
IAV
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
QuickTime™ and a decompressor
are needed to see this picture.
Phenology Model• 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
QuickTime™ and a decompressor
are needed to see this picture.
HOURLY NOLEAF
IAV NOLEAF
HOURLY LEAF
IAV LEAF
QuickTime™ and a decompressor
are needed to see this picture.
Interannual
QuickTime™ and a decompressor
are needed to see this picture.
HOURLY NOLEAF
IAV NOLEAF
HOURLY LEAF
IAV LEAF
QuickTime™ and a decompressor
are needed to see this picture.
QuickTime™ and a decompressor
are needed to see this picture.
QuickTime™ and a decompressor
are needed to see this picture.
QuickTime™ and a decompressor
are needed to see this picture.
QuickTime™ and a decompressor
are needed to see this picture.
QuickTime™ and a decompressor
are needed to see this picture.
NEE-Leaf
QuickTime™ and a decompressor
are needed to see this picture.
GPP ER Leaf
QuickTime™ and a decompressor
are needed to see this picture.
QuickTime™ and a decompressor
are needed to see this picture.
Precipitation and Water Table
• Sulman et al (in prep) Biogeosciences - see Ameriflux poster
QuickTime™ and a decompressor
are needed to see this picture.
Shrub Wetland Flux Response
QuickTime™ and a decompressor
are needed to see this picture.
Three Wetlands
QuickTime™ and a decompressor
are needed to see this picture.
Three Wetlands
QuickTime™ and a decompressor
are needed to see this picture.
Regional NEE
• See NACP poster in Feb.Annual flux (NEE)
-250
-200
-150
-100
-50
0
1997 1998 1999 2000 2001 2002 2003 2004
Year
gC m-2 yr-1
Flux towers
FIA model
ABL Budget
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