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Keith Paustian 1,2 , Steven Ogle 2 , Scott Denning 3 and Erandi Lokupitiya 3

Estimating the contribution of agricultural land use to terrestrial carbon fluxes in the continental US. Keith Paustian 1,2 , Steven Ogle 2 , Scott Denning 3 and Erandi Lokupitiya 3 1 Dept. of Soil and Crop Sciences, Colorado State University

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Keith Paustian 1,2 , Steven Ogle 2 , Scott Denning 3 and Erandi Lokupitiya 3

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  1. Estimating the contribution of agricultural land use to terrestrial carbon fluxes in the continental US Keith Paustian1,2, Steven Ogle2, Scott Denning3 and Erandi Lokupitiya3 1Dept. of Soil and Crop Sciences, Colorado State University 2Natural Resource Ecology Lab, Colorado State University 3Dept. of Atmospheric Sciences, Colorado State University

  2. Outline • Agriculture’s role in the US C balance • Bottom-up ‘inventory’ modeling of C dynamics in cropland and grassland • Agricultural influences on process-based CO2 flux and transport modeling

  3. The (familiar) overarching ?s • What is the current C balance and magnitudes of sources and sinks in the US? • Will sinks decrease in the future with LU changes and/or with CC? • Can sinks be increased by management? How much? How fast?

  4. What is agriculture’s role in all of the above? • Responsible for ~ 7% of US GHG emissions (mostly from non-CO2) • C balance on agricultural land dominated by soil carbon stock changes (and commodity exports) • Policy needs • National inventory reporting (UNFCCC) • National (and market-based) GHG mitigation efforts (50-250 Tg C/yr potential) • Resource conservation policies (national, state, local) • Biofuel development the new ‘wildcard’

  5. Bottom-up modeling framework Environmental Conditions Model Inputs Database Management Activity Point Scale Data (NRI Survey) PDF Results Database Structural Uncertainty Estimator Database Management Run Control Simulation Model: Century

  6. Data sources • National Resource Inventory (NRI) • Statically-based sample of ca. 800,000 points since 1979 • LU, soils, crop rotations/vegetation • Most land management practices NOT collected • County-, state- and regional survey data of management practices • E.g. tillage, fertilization, manuring, irrigation • Regional-level land use practices (pre-1980)

  7. Totals for US Croplands (1990s) 1990-1994: -62.0 ± 22% Tg CO2 eq. yr-1 1995-2000: -64.0 ± 16% Tg CO2 eq. yr-1

  8. Current status – bottom-up efforts • At national level, estimates of average soil C stock changes are relatively well constrained. • However, at subregional & local levels uncertainties are high • Current efforts focus on: • Reducing finer scale uncertainty • Improving estimates of NPP and C inputs • Obtaining bench-mark data on soil C stocks under field conditions

  9. Approach • Adapting MODIS/EVI-based production estimates from NASA-CASA into Century • Testing NPP and yield estimates at field-scale experiments • Field-scale observation of soil C stocks and establishment of a pilot monitoring system • Applying the new model to NRI inventory points

  10. MODIS Enhanced Vegetation Index (EVI) • Frequent (10 d) return interval • Low cost (primary data free) • Better resolution (250m) than previous imagery (e.g. AVHRR) often used for regional crop modeling • But still challenges dealing with mixed pixels and using traditional LTEs for ground-truthing.

  11. MODIS Enhanced Vegetation Index (EVI) - May 2004 Spatial Resolution: 250 meter Farm boundaries and production patterns begin to emerge in details of landscape at 250-m resolution CASA CQUEST Courtesy Chris Potter – NASA-Ames

  12. Courtesy Chris Potter – NASA-Ames

  13. Agricultural influences on process-based CO2 flux and transport modeling • What’s the interannual variability in C fluxes from croplands and how does it influence interannual variability in cropland soil C stocks? • Capturing within-season dynamics of cropland C fluxes.

  14. Cropland NPP the mid-continent region in a dry year (1988) and a wet year (1997)

  15. Variability in residue C inputs 1982-1997 Permanent area for major crops (90 Mha) Tg C yr-1 Lokupitiya et al. 2007

  16. Annual anomalies in residue C and SOC stocks (all land use and management changes are excluded) Lokupitiya et al. in prep

  17. Measured and modeled (SIB3-RAMS) CO2 concentrations at WLEF tower (400 m) in Wisconsin Courtesy Scott Denning

  18. Cropland modifications to SIB3 Revised phenology and leaf area development algorithms Lokupitiya et al. unpubl.

  19. b. now Results from testing SIB3 for maize-soybean flux site – Bonneville, IL a. before Lokupitiya et al. unpubl.

  20. Midcontinent Intensive (MCI) Focus for initial inter-comparisons and synthesis of bottom-up approaches and bottom-up/top-down estimates within NACP Field-campaign 2007-2008

  21. Conclusions • Soil C on US ag. land are currently a small sink • Estimates relatively well constrained at national level thanks to abundant activity data and LTEs • But, uncertainties high at local scale – where management decisions are implemented. • Broad-based soil monitoring network and better fine-scale estimates of C additions to soil needed to reduce uncertainties at local scales. • Large short-term C fluxes and large interannual variability associated with agricultural crops pose challenges for flux/transport based estimates of long-term C balance in agriculturally dominated ecosystems

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