Climatic Controls on Carbon Exchange in the US Mountain West at Multiple Scales (1 pages)

AGU Fall 2010 B31E 351 Climatic Controls on Carbon Exchange in the US Mountain West at Multiple Scales A R Desai W Ahue B Brooks D J Moore T L Quaife R K Monson S De Wekker T L Campos B B Stephens P Wilkes D Schimel Questions Peak uptake in June is strongly a function of timing of snowmelt Hu et al 2010 Fig 1 20 mm 15 10 5 0 100 200 Day of Year e 20 b Precipitation Figure 2 Daily a average temperature and b total precipitation at the flux tower site Carbon uptake occurs when T 0 C Mid summer drought is evident mol m 2 s 1 c SiP d CT 0 20 Aug 09 Aug 03 Aug 01 Jul 18 Jun 21 Jun 15 C1 C2 C3 C4 C5 C6 C7 Jun 1 Aug 09 Aug 03 Aug 01 Jul 18 Jun 21 Jun 15 C1 C2 C3 C4 C5 C6 C7 Jun 1 30 AC ME 07 Answers Pattern of primary and secondary uptake is seen at site and regional scale across central Rockies less apparent in airborne subregional budget or in subcontinental inversion where monsoon rains are less important gC m 2 day 1 T Higher carbon uptake is seen at high elevations with most methods with later peaks in timing of the uptake as might be expected Quantifying NEE in mountain areas is difficult to achieve but the four methods do reveal the importance of moisture stress and elevation in determining NEE magnitude and timing Significant sinks of carbon do exist in the Mountain West Citations Desai A R et al in prep Seasonal patterns of regional carbon balance in the Airborne Carbon in the Mountain Experiment 2007 Journal of Geophysical Research Biogeosciences Hu J et al 2010 Longer growing seasons lead to less carbon sequestration by a subalpine forest Global Change Biology 16 771 783 doi 10 1111 j 1365 2486 2009 01967 x Monson R K et al 2002 Carbon sequestration in a high elevation subalpine forest Global Change Biology 8 459 478 Peters et al 2007 An atmospheric perspective on North American carbon dioxide exchange Carbontracker Proceedings of the National Academy of Sciences 104 48 18925 18930 Sacks et al 2007 Coupling between carbon cycling and climate in a high elevation subalpine forest a model data fusion analysis Oecologia 151 54 68 Temporal pattern shows a later peak uptake than SipNET and lack of secondary peak uptake suggesting climate sensitivity of uptake varies across the Rockies Fig 7 Figure 7 Temporal pattern of mountain west NEE black line and SipNET red line Peak uptake is larger in magnitude than SipNET Note that SipNET shows carbon sources circa day 150 200 while the larger region does not become a carbon source until after day 200 and a lacks a secondary peak ker rac onT 10 120 100 50 0 50 gC m 2 mo 1 Figure 5 Spatial map of SipNET NEE in July 2007 shows high uptake shaded green and blue at high elevation across central Colorado and carbon sources throughout much of W Colorado E Utah Spatial patterns show strongest July sinks in northern Rockies though discrepancies exist with SipNET over Colorado Fig 6 b Car nt 10 Figure 3 Comparison of daytime NEE 10 14 LT at a airborne boundary layer budget BLB b flux tower NWR c ecosystem model SiP and d atmospheric inversion CT for 7 flight days of the ACME07 experiment Error bars reflect propagation of uncertainties of BLB and spatiotemporal variability for the others The primary and secondary carbon uptake peaks are captured by NWR SipNET and possibly BLB however at the regional scale the secondary uptake peak vanishes for CT 300 CarbonTracker atmospheric inversion Peters et al 2007 best represents continental scale NEE ine 20 on 10 b R egi 0 2 S u b NWR Figure 4 2007 mean daily NEE from SipNET for Western Colorado region black line compared to NWR flux tower red line Pattern is similar though magnitudes and timing differ given mix of deciduous conifer and grassland Late August drought stress is strong leading to a three peak pattern SipNET Ecosystem model Sacks et al 2006 was paramterized against representative flux towers and spatialized with remotely sensed leaf area and interpolated meteorology July NEE shows a strong SE to NW gradient of increasing NEE nt Co ub a BLB Sip NE Four approaches compared at the scale they best 3 2 1 represent processes 1 flux tower 2 airborne budget 3 ecosystem model and 4 atmos pheric inversion Daily NEE for each was computed for 2007 Maps are for July 4 S 10 200 Day of Year 4 Airborne Carbon in the Mountains Experiment 2007 used University of Wyoming King Air to construct paired upwind downwind boundary layer budgets on 7 days in north central Colorado Desai et al in prep Compared to models at same space and time scale and the flux tower daytime uptake from aircraft is similar if slightly higher in magnitude and drought stress effect is less clear Fig 3 100 Daily NEE pattern Fig 4 is similar to flux tower but peak uptake is shifed earlier in time and much smaller in magnitude while relative drought stress is smaller Methods Drought stress in July is followed by period of additional uptake in August coincident with return of North American monsoon with reduced uptake in late August Fig 2 300 3 Where are the major sources and sinks of NEE in the US Mountain West 2 1 0 1 2 3 4 gC m 2 day 1 10 on 0 idg degrees C a Temperature 2 How similar are relationships between patterns of seasonal NEE and climate at each scale ot R Niw 10 Niwot Ridge eddy covariance tower samples footprint of subalpine forest in Colorado Monson et al 2002 1 What is the magnitude of regional NEE at each scale ite 20 100 1 S 200 300 Day of Year Figure 1 Daily NEE at flux tower site in 2007 shows a primary and secondary peak uptake typical of most years Complex terrain adds challenges to measuring regional net ecosystem exchanges NEE of carbon dioxide The U S Mountain West is experiencing significant climatic changes and abiotic and biotic stresses To better understand impacts to carbon cycling we compare sub regional left and regional right NEE at four different scales and ask egi 2 1 0 1 2 3 4 3 R gC m 2 day 1 Corresponding author Ankur R Desai Dept of Atmospheric Oceanic Sciences University of Wisconsin Madison desai aos wisc edu http flux aos wisc edu 2 1 0 1 2 3 4 120 100 50 0 50 gC m 2 mo 1 Figure 6 Spatial map of Carbontracker NEE in July 2007 similar to Fig 5 showing pattern of high uptake at high elevation while much of western U S is carbon neutral with largest sinks in Northern Rockies 100 200 Day of Year 300 Acknowledgments We acknowledge support of the various teams that collected these data for the Niwot Ridge Ameriflux tower ACME07 field campaign SipNET modeling team and NOAA ESRL CarbonTracker inverse modeling