Rapid Assessment and Trajectory Modeling of Soil Carbon

Rapid Assessment and Trajectory Modeling of Soil Carbon Across a Southeastern Landscape Sabine Grunwald

Project Goals: Modeling of soil carbon along pedo -climatic trajectories across diverse ecosystems in Florida PD: S. Grunwald Co-PIs: W. G. Harris, N. B. Comerford and G. L. Bruland Post-Docs: D. B. Myers and D. Sarkhot Graduate students: G. M. Vasques, X. Xiong and W. C. Ross Field and lab staff: A. Stoppe, L. Stanley, A. Comerford and S. Moustafa Core Project of the North American Carbon Program Funding source: National Research Initiative Competitive Grant no. 200735107 -18368 USDA NIFA - AFRI

Rationale and Significance Global issues & priorities Global estimates of terrestrial carbon stocks UNEP-WCMC. http: //www. carbon-biodiversity. net/Global. Scale/Map Scharlemann et al. (2009): Harmonized World Soil Database (2009)-SOC values up to 1 m depth (1 km spatial resolution) & Ruesch and Gibbs (2008): Biomass carbon map using IPCC Tier 1 methodology and GLC 2000 land cover data. Crutzen, 2002. Nature; Steffen et al. , 2005. Global Change and the Earth System; Rockström et al. , 2009. Nature; Grunwald et al. , 2011. Soil Sci. Soc. Am. J. • Lack in understanding of soil carbon (C) variability • Assessments rely on historic/ legacy soil C data • Soil C – a sink or source ? • Soil C – linkages to processes ? • Total soil C – C pools ?

• Resampling of 453 historic SOC Observations (FL) sites (out of 1, 288 historic pedons – FL Soil Database); 1965 -1996 (Soil and Water Science Dept. , UF & NRCS) • In 2008/2009 soil sampling at 1014 sites (0 -20 cm) based on stratified-random sampling design (land use – soil suborder strata): - TC - SOC - IC - HC - RC - BD - TN and TP Historic and current within ≤ 30 m Historic and current within ≤ 300 m Current (2008/2009)

Modeling of Historic SOC (1 m) – FL <5 5 – 10 10 – 15 15 – 20 20 – 50 > 50 Not mapped SSURGOSoil Data Mart (NRCS) 1: 24, 000 Block Kriging N: 1, 099 Data source: Florida Soil Characterization Database (FSCD) STATSGO 2 Soil Data Mart (NRCS) 1: 250, 000 Class Pedotransfer function (PTF) SOC = f {LU, order} Block size: 250 x 250 m Target: Ln-SOC kg m-2 Nugget: 0. 61 Sill: 0. 86 Range: 101, 088 m ME: -0. 0040 ln[kg m-2] (~ 0. 10 kg m-2) Vasques G. M. and S. Grunwald. 201_. Global Env. Change J. (in prep. ) Presented at the World Congress of Soil Sciences (2010)

Florida Map unit Estimates of SOC stocks to 1 m in Florida based on different data/methods was 4. 110 ± 1. 01 Pg (mean ± std. error) SOC statistic (depth to 1 m) SSURGO STATSGO 2 FSCD observations FSCD block kriging FSCD PTF Map unit 655, 155 map units 2, 823 map units 1, 099 points 2, 282, 843 250 -m cells 7 soil orders Minimum (kg m-2) 0. 67 4. 01 0. 13 2. 82 7. 70 Maximum (kg m-2) 291. 77 264. 32 207. 98 116. 19 144. 17 Median (kg m-2) 7. 90 27. 05 6. 32 9. 00 14. 75 Mean (kg m-2) 24. 17 58. 44 12. 85 13. 95 32. 84 Std. dev. (kg m-2) 39. 31 62. 67 23. 69 12. 28 45. 63 Total mapped area (km 2) 128, 788 142, 681 N/A 142, 678 142, 626 Total stock (Pg) 3. 518 6. 820 N/A 1. 990 4. 112 Mean stock (kg m-2) 27. 32 47. 80 N/A 13. 95 28. 83 Vasques G. M. and S. Grunwald. 201_. Global Env. Change J. (in prep. )

Conceptual Modeling Framework: STEPAWBH (“STEP-UP”) • Predicts the spatially-explicit evolution and behavior of Soil Pixels / Voxels • Explicitly incorporates anthropogenic forcings • Incorporates bio-, topo-, litho-, pedo- and hydrosphere • Provides temporal context to account for ecosystem processes and forcings • Fuses empirical and process-based knowledge Soil pixel (SA): Grunwald S. , J. A. Thompson & J. L. Boettinger. 2011. SSSAJ. In press.

Spatially & temporally explicit environmental matrix (FL): ~2 TB of data STEP variables: • Soil • Topographic • Ecological / geographic • Parent material + AWBH variables: • Atmosphere / climate • Water • Biota: LU/LC • H(uman) + Soil observations N: 200+ variables …. . Model development: • PLSR • CART • Ensemble regression trees • … and others Predict soilenvironmental properties: • TC • SOC seq. • Carbon pools • TN, TP • … and more Model validation: Uncertainty assessment

Soil Taxonomic Classes – FL Net Primary Productivity – FL Histosol Spodosol Data source: NRCS-USDA, Soil Geographic Database / Soil Data Mart. Time period: 2000 – 2005; data source: MODIS satellite data

Climatic Data – FL Avg. Monthly Precipitation (mm) [1971 -2000] 35 – 55 33 – 75 75 – 55 55 – 75 75 – 95 95 – 115 – 135 – 155 – 175 – 195 – 215 – 235 Data source: PRISM December January March September October February November April August July June May

Climatic Data – FL Time frame: 1971 – 2000 Data source: PRISM

Land Use Change (1970 – 2003) Based on Satellite Data 2003 1995 ? 1990 1970 to 2003: ↑ Urbanization (5. 4% - 12. 1% - 11. 0% ↓ Agriculture (21. 9% - 7. 4% - 8. 6%) ↓ ↑ Rangeland (8. 8% - 4. 7% - 8. 2%) ↓ ↑ Forest (29. 9% - 23. 2% - 26. 2%) ↓ Wetland (21. 7% - 4. 4% - 5. 8%) Data sources: Land use / land cover 1970: USGS; 1990 and 1995: Water Management Districts & FL Department of Transportation 2003: Florida Fish and Wildlife Conservation Commission

Modeling of Current SOC (0 -20 cm) – FL Methods: Ensemble regression trees (RT) and other data mining methods Inputs (predictor variables): STEP-AWBH environmental variables Predict SOC stocks

Modeling of Current (2009) SOC Stocks (0 -20 cm) – FL Validation results – STEP-AWBH Modeling (kg C m-2) R 2 RMSE RPD Regression trees (RT) 0. 49 3. 2 1. 34 Bootstrapped RT 0. 63 2. 6 1. 64 Boosted RT 0. 61 2. 7 1. 59 Random Forest 0. 64 2. 6 1. 66 Support Vector Machine 0. 60 2. 8 1. 55 Total N: 1, 014; Randomized 70/30 calibration/validation split of dataset Myers D. B. , S. Grunwald et al. 201_. Global Change Biology J. (in prep. )

Modeling of Current (2009) SOC Stocks (kg m-2) (0 -20 cm) – FL Predictor variables of importance: • Available water capacity 50 cm • Soil Great Group • Land cover / land use (NLCD) • Land cover / land use (FFWC, 2003) • Ecologic region • Soil Order • Soil Suborder 1. 0 0. 85 0. 83 0. 74 0. 50 0. 25 0. 22 • … and more Method: Random Forest Independent validation (N: 304) Myers D. B. , S. Grunwald et al. 201_. Global Change Biology J. (in prep. )

Modeling of Current (2009) SOC Stocks (20 cm) – FL SOC (kg m-2) Spatial resolution: 30 m Myers D. B. , S. Grunwald et al. 201_. Global Change Biology J. (in prep. )

SOC Sequestration in Florida (1965 – 2009) Historic & current sites ≤ 30 m (N: 194) SOC sequestration (g C m-2 yr-1) • Mean: 11. 6; Median: 17. 7 • STDev: 93. 3 • Max: 511. 3 Time frame of sequestration (yrs) • Mean: 30. 3; Median: 29. 6 • STDev: 5. 3 • Max: 43. 5 Grunwald et al. , 201_. Front Ecol. Env. J. (in prep. )

Modeling of SOC Sequestration Rates (g C m-2 yr-1) (0 -20 cm) – FL Predictor variables of importance: • Surficial geology 100 • Land use 1995 75. 4 • Long-term max. temp. May 75. 4 • Long-term max. temp. March 62. 9 • Long-term max. temp. April 35. 9 • Soil Great Group 27. 3 • Land use 1970 25. 9 • MODIS EVI (day 137) 22. 8 • MODIS EVI (day 169) 22. 7 • Landsat Bd. 3 20. 6 • Forest canopy cover 17. 5 • …. and more Methods: Ensemble trees (bagging mode) 10% V-fold cross-validation STEP-AWBH model evaluation (g C m-2 yr-1): MSE = 85. 93 MAD = 47. 61 Grunwald et al. , 201_. Front Ecol. Env. J. (in prep. )

Significance of research: • Predict high-resolution soil C pixels across large landscapes • Reduce the uncertainty of soil C assessment • Model spatial variability of soil C (C pools and nutrients) along climate and land use trajectories • Model soil change in dependence of anthropogenic induced stressors

Rapid and cost-effective sensing of Soil C and Pools using visible/near-infrared (VNIR) diffuse reflectance spectroscopy Spectral soil C modeling Soil attributes = f (VNIR) Soil attributes = f (VNIR; MIR)

Research Results VNIR & MIR Authors Spectra Type Area N Properties R 2 Cal. R 2 Val. Vasques et al. 2008. Geoderma VNIR SFRW 554 TC 0. 98 0. 86 Vasques et al. 2009. SSSAJ VNIR SFRW 102 TC RC SC HC MC 0. 93 0. 89 0. 92 0. 87 0. 86 0. 82 0. 40 0. 70 0. 65 Vasques et al. 2010. JEQ VNIR FL (hist. ) 7120 SOC 0. 97 0. 79 Myers et al. 2011. in prep. VNIR FL (2009) 1014 SOC (RC, HC) 0. 93 0. 89 Mc. Dowell et al. 2011. in prep. VNIR & MIR Hawaii 306 SOC 0. 93 (VNIR) 0. 97 (MIR) V-fold cross -validation Sarkhot et al. , 2011. Geoderma VNIR TX 514 TC HC SOC IC 0. 94 0. 96 0. 95 0. 93 0. 85 0. 77 0. 86 0. 81 (Ahn et al. , 2009. Ecosystems)

Follow-up Research Project (NRCS, Grunwald – UF & Mc. Bratney – U Sydney) • Rapid soil C assessment across the U. S. • Soil C ↔ Land use/land cover, ecoregion, climate, … • Soil C ↔ VNIR Apply research methodology tested in FL to U. S. FL

http: //soils. ifas. ufl. edu/faculty/grunwald sabgru@ufl. edu