Dependence of Sorption of Dissolved Organic Carbon on Soil Order Classification Melanie A
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Dependence of Sorption of Dissolved Organic Carbon On Soil Order Classification Melanie A. Mayes1 Katherine Rose Heal2, Craig Brandt1, Sindhu Jagadamma1, Philip M. Jardine3 1Environmental Science Division, Oak Ridge National Laboratory, Oak Ridge, TN, 2Colorado College, Colorado Springs, CO, 3Department of Biosystems Engineering and Soil Science, University of Tennessee, Knoxville, TN [email protected] Fig. 1 from Trumbore et al. 1997 Motivation Results Ultisol Soil carbon is the largest terrestrial sink. The top The average sorption Ultisols Ultisols dominate the meter of soils contain about several times the mass of capacities for the soils Alfisol Southeast US (Figure 7b) carbon in standing biomass. DOC (dissolved organic 3.8 with deep, acidic profiles ) were similar(Figure 5). g k 3.6 / carbon) is the most mobile fraction of soil carbon. We g rich in clay and iron content m These three orders of soils 3.4 y t i are interested in the mechanisms and properties that c 3.2 (Figure 7a). DOC sorption a dominate the eastern US. p Mollisol a C 3.0 dictate how DOC is sorbed and stabilized onto mineral onto subsurface Ultisols can n o i 2.8 t p Fig 7b*(above): soils, transforming it to a passive pool of C (Figure 1). r 2.5 be predicted by textural clay o 2.6 S 2.0 ( ) 2 g 2.4 1.5 y Distribution of Ultisols highlighted). o a content and iron content (r l l Many mineral soils are not 2.2 1.0 C % Fig 5. Typical isotherm shapes for three 1.6 0.5 ( g 141.4 o = 0.554, Figg)ure 6b). These saturated with DOC (Jardine 1.2 0.0 l major soil orders 1.0 log ( 0.8 results suggest that both et al. 1989). Certain Fe g/kg Fig 7a*: ) anthropogenically altered soils have demonstrated the ability to ligand exchange are Typical sustain large quantities of soil organic carbon in mineral soils Fig 7c : Observed and model fitted data , where important mechanisms for Mollisols Ultisol profile (Figure 2). The objective of this project is to quantify the log Qmax = 2.141 + 0.403log (%clay) + 0.439log (Fe) DOC sorption onto Ultisols. 6000 ) relationship between dissolved organic carbon sorption capacity g k / g 5000 m and physical and geochemical properties of subsoils. ( y t Alfisols dominate the land around the i 4000 Alfisols c Fig. 2 from Sombroek et al. 1993 a 4.0 p a ) c Great Lakes and Mississippi River 3000 g n k / o i g t 3.5 p 2000 (Figure 8c) with deep, clayey profiles m r 14000 o y s t 12000 i c C 1000 10000 ) a rich in iron and aluminum (Figure 8a). O m 3.0 8000 p p D 0 (p a 6000 C Methods C DOC sorption onto subsurface Alfisols 50 4000 O n o 40 T o 2.5 i 30 2000 t 20 Fig 6 c* : Di str ibut ion p 10 0 r 2.2 can bdidbllbe predicted by textural clay % o 2.0 Clay S 2.0 SilSlSoil Select ion: ( 1.8 ) 2 of Mollisols g 1.6 y content and pH (r = 0.251, Figure 6b). o a l 1.4 l An area-weighted sampling of 1.5 C 1.2 % 8 ( 7 1.0 g These results suggest that ion exchange series in the US with coverage to Fig 6b: Observed and model fitted data, where 6 0.8 lo 5 0.6 is an important mechanism for DOC the great group level in the Fig 6a*: Typical Qmax = -206.452 + 0.127*TOC) - 46.880*%clay) pH 4 sorption onto Alfisols. eastern US (Figure 3). B and C Mollisol profile Fig 8b (above): Observed and model horizons were obtained from the Mollisols dominate the Great Plains (Figure 6c) with deep, often basic profiles fitted data , where: Natural Resource Conservation rich in organic carbon (Figure 6a). DOC sorption onto subsurface Mollisols Fig 8a*: Typical Log Qmax = 2.662 + 0.572 log (%clay) – 0.0602 log (pH) Service (NRCS). 250 samples can be predicted by clay and TOC (r2 = 0.321, Figure 6b), suggesting that Alfisol profile have been analyzed from 73 organic-organic interactions was important for DOC sorption. series and 5 orders. Fig 8c*: Evidence for Preferential Sorption Distribution of Alfisols * Figures of soil order distribution and profiles from the NRCS Fig 3: Distribution of selected Overall, a trend in different isotherm shapes has implications in preferential representative soils at the great group level sorption. Although it has been shown that soils sorb DOC with respect to DOC Analysis of Samples structure, it seems as if Mollisols and Ultisols have very different preferential Conclusions Soil samples were oven-dried, ground, and sieved in the standard manner. The sorption. 1. 3 The empirical equations here can be used to some extent to predict DOC sorption capacity on subsoil chemical following properties were analyzed in all samples: pH in water and CaCl2, total organic and inorganic carbon, iron oxide content, and particle size analysis. 1.1 and physical properties. 0.9 This predictive power can now be coupled with readily available databases (ie: NRCS) for subsurface DOC Ultis o ls sorption potential with minimal effort. DOC 0.7 k Qmax X f Mo llis o l RE -b Although other literature has shown that soils preferentially adsorb DOC based on its chemical structure, our Sorption 0.5 1 k X f data show that this preferential sorption is different between soil orders, most notably Mollisols and Ulitsols. Capacity Equation 1: Langmuir isotherm, where RE is amount of 0.3 DOC sorbed or desorbed in mg/kg, Xf is the final 0.1 Sorption isotherms equilibrium concentration of DOC in pm, k is binding Further Studies were conducted using affinity, Q is maximum adsorption capacity (in mg/kg), -0.1 050100150 max A spatial representation of the “hot spots” for subsurface carbon sequestration will identify regions and field a natural DOC source and b, the desorption potential in mg/kg, was found -0.3 Eq uilib rium DOC Co ncentratio n (p p m) (0-100 ppm) with a experimentally. sites that exhibit greatest potential for enhanced subsurface organic carbon storage and thus most deserving of solid solution ration of -0.5 manipulation or improved management. 1:60 over 48 h. Blanks 1000 1200 Figure 9: Equilibrium DOC concentration vs Extent of Sorption (defined as DOC More experiments are needed to understand how differences in the organic C-mineral structure contribute to were used to 800 1000 sorbed/modeled DOC sorption capacity). the observed preferential sorption differences between Mollisols and Ultisols. 600 determine the 800 rbed (mg/kg) (mg/kg) 400 oo maximum additional 600 DOC sorbed by 200 400 Acknowledgements 0 This work was funded by the US Department of Energy Student Undergraduate Laboratory Internship References optimizing a Langmuir 200 equation (Eq 1), and sorbed DOC -200 (DOE SULI) through the Oak Ridge Science Semester (administered by Denison University), and is P.M. Jardine, N.L. Weber, and J.F. McCarthy, “Mechanisms of dissolved organic carbon adsorption on soil,” Soil Science Society of America Journal, vol 0 part of ORNL’s Climate Mitigation Science Focus Area funded through DOE’s Office of Environmental -400 S DOC Additional 53, pp 1378-1385, 1989. overall maximum 0 20406080 0 20406080 and Biological Research, Climate and Environmental Sciences Division. We would like to Equilibrium DOC Concentration acknowledge Larry West and Thomas Reinsch from the Natural Resource Conservation Service for S. Trumbore, “Potential responses of soil organic carbon to global environmental change,” Proc. Natl. Acad. Sci. USA, vol 94, pp 8284-8291, 1997. DOC sorption capacity providing many of the samples used in the study. Oak Ridge National Laboratory is managed by the was found by Fig 4: Example of isotherm fitting. Left is raw data, right University of Tennessee-Battelle, LLC, under contract DE-AC05-00OR22725 with the US DOE. The W.G. Sombroek, F.O. Nachtergaele, and A. Hebel, “Amounts, dynamics and sequestering of carbon in tropical and subtropical soils,” Ambio, vol 22, pp work has been authored by a contractor of the U.S. Government under contract DE-AC05- 417-427, 1993 . subtracting the with blank subtraction and Langmuir fit. Solid lines 00OR22725. Accordingly, the U.S. Government retains a nonexclusive, royalty-free license to publish amount of desorption represent maximums modeled, with standard errors or reproduce the published form of this contribution, or allow others to do so, for U.S. Government D.M. Kothawala, T.R. Moore, and W.H. Hendershot. Soil properties controlling the adsorption of dissolved organic carbon to mineral soils. Soil Sci. Soc. (Kothawala et al., purposes. Am. J. vol 73, pp1831-1842, 2009. 2009) (Figure 4)..