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Potential Contribution of Combined Atmospheric Ca2+ and Mg2+ Wet Deposition Within the Continental U.S. to Soil Inorganic Carbon Sequestration
Pedosphere 23(6): 808–814, 2013 ISSN 1002-0160/CN 32-1315/P c 2013 Soil Science Society of China Published by Elsevier B.V. and Science Press
Potential Contribution of Combined Atmospheric Ca2+ and Mg2+ Wet Deposition Within the Continental U.S. to Soil Inorganic Carbon Sequestration∗1 E. A. MIKHAILOVA1,∗2 , M. A. GODDARD1 , C. J. POST1 , M. A. SCHLAUTMAN2 and J. M. GALBRAITH3 1 School
of Agricultural, Forest, and Environmental Sciences, Clemson University, Clemson SC 29634 (USA) of Environmental Engineering and Earth Sciences, Clemson University, Anderson SC 29625 (USA) 3 Department of Crop and Soil Environmental Sciences, Virginia Tech, Blacksburg VA 24061 (USA) 2 Department
(Received July 4, 2013; revised September 25, 2013)
ABSTRACT Soil inorganic carbon (SIC) stocks continuously change from the formation of pedogenic carbonates, a process requiring inputs of Ca2+ and Mg2+ ions. This study ranked the soil orders in terms of potential inorganic carbon sequestration resulting from wet Ca 2+ and Mg2+ deposition from 1994 to 2003 within the continental United States. The analysis revealed that average annual atmospheric wet deposition of Ca2+ and Mg2+ was the highest in the Central Midwest-Great Plains region, likely due to soil particle input from loess-derived soils. The soil orders receiving the highest total average annual atmospheric wet Ca 2+ and Mg2+ deposition, expressed as potential inorganic carbon formation (barring losses from erosion and leaching), were: 1) Mollisols (1.1 × 108 kg C), 2) Alfisols (8.4 × 107 kg C), 3) Entisols (3.8 × 107 kg C), and 4) Aridisols (2.8 × 107 kg C). In terms of area-normalized result, the soil orders were ranked: 1) Histosols (73 kg C km−2 ), 2) Alfisols and Vertisols (64 kg C km−2 ), 3) Mollisols (62 kg C km−2 ), and 4) Spodosols (52 kg C km−2 ). The results of this study provide an estimate of potential soil inorganic carbon sequestration as a result of atmospheric wet Ca2+ and Mg2+ deposition, and this information may be useful in assessing dynamic nature of soil inorganic carbon pools. Key Words:
calcite, carbon cycle, dolomite, pedogenic
Citation: Mikhailova, E. A., Goddard, M. A., Post, C. J., Schlautman, M. A. and Galbraith, J. M. 2013. Potential contribution of combined atmospheric Ca2+ and Mg2+ wet deposition within the continental U.S. to soil inorganic carbon sequestration. Pedosphere. 23(6): 808–814.
INTRODUCTION Global soil carbon (C) reservoirs are composed of soil organic and inorganic (pedogenic) carbon. In contrast to soil organic carbon, soil inorganic carbon (SIC) is poorly quantified and understood (Mi et al., 2008). Global soil inorganic carbon estimates are of various ranges: 695–748 Pg (Batjes, 1996), 720 Pg (Sombroek et al., 1993), 780–930 Pg (Schlesinger, 1982) and 940–1 738 Pg (Eswaran et al., 1995; Eswaran et al., 2000) of carbonate C in the top 1 m soil depth. Guo et al. (2006a) estimated the soil inorganic carbon inventory (226 to 937 × 108 Mg of SIC) for the continental U.S. using the State Soil Geographic Database (STATSGO) in the upper 2 m of soil by soil order and state. Rasmussen (2006) used STATSGO and SSURGO (Soil Survey Geographic Database) to analyze SIC pools by biome and soil taxa in Arizona. ∗1 Supported
Rawlins et al. (2011) analyzed the importance of inorganic carbon in soil carbon databases and stock estimates in England. In the context of environmental change, soil inorganic carbon has the potential to sequester atmospheric carbon dioxide as pedogenic carbonate (Manning, 2008). Carbonates (calcite, aragonite, dolomite and siderite) present in soils generally have been formed as a result of lithogenic or pedogenic processes or some combination of these two (Ming, 2002; Schlesinger, 2002). While lithogenic carbonates result from the debris of carbonate parent materials and thus have no impact on the net carbon budget, pedogenic carbonates represent a pathway by which atmospheric CO2 can be sequestered. Atmospheric CO2 sequestration via formation of new carbonate minerals in soils requires outside Ca2+ and Mg2+ sources such as wet deposition, fertilizer addition and irrigation (Monger
by the National Science Foundation of USA (No. 0340534) and the U.S. Department of Agriculture (Nos. SC-1700278, SC-1700452, and SC-1700462). ∗2 Corresponding author. E-mail: [email protected].
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and Gallegos, 2000). In general, precipitation of carbonates in soils is favored by increasing Ca2+ and Mg2+ concentrations, increasing pH, and/or increasing alkalinity (Sposito, 1989; Stumm and Morgan, 1996; Chadwick and Graham, 2000). Therefore, because elevated atmospheric CO2 concentration is of increasing concern, terrestrial carbon sequestration strategies based on carbonate storage require conditions that favor and maintain pedogenic carbonate precipitation, associated with minimal leaching and soil erosion. Atmospheric additions as a source of pedogenic carbonate were investigated by numerous studies. The desert project (Gile et al., 1966; Gile and Grossman, 1979) measured water-soluble calcium loadings in dust traps and reported a yield ranging from 0.35 to 1.3 g m−2 year−1 . Junge and Werby (1958) reported that calcium from rainwater can produce an estimated CaCO3 equivalent of 1.5 g m−2 year−1 based on 200 mm annual rainfall. Guo et al. (2006b) analyzed the effects of average annual precipitation, and average annual temperature on SIC in the continental U.S. and concluded that there was no relation between SIC and average annual precipitation until average annual precipitation exceeded 1 000 mm. Their analysis, however, did not include evaluation of the wet deposition chemistry in relation to SIC sequestration. Goddard et al. (2007) analyzed Mg2+ wet deposition in relation to potential soil inorganic carbon sequestration as dolomite in the continental U.S. and determined that Mollisols, Alfisols and Ultisols received the highest average annual atmospheric deposition of Mg2+ from 1994 to 2003. Precipitation, wind erosion and subsequent dustfall also can be significant sources of Ca2+ , and together contribute to atmospheric Ca2+ wet deposition, and SIC redistribution and sequestration (Goddard et al., 2009). Rabenhorst et al. (1991) reported that the Ca2+ content contained in dust traps from the limestone bedrock Edwards Plateau of Texas was the same as the amount expected from rainfall alone, and thus concluded that the amount of Ca2+ from particulate carbonates was negligible. However, their study also revealed that the dust originated from multiple sources and therefore redistribution was regional in nature rather than being derived only from local soils and rocks. Guo et al. (2006a) showed with maps that a vast majority of pedogenic carbonates in the western U.S. formed in igneous alluvium. A question remains whether the source of calcium was from the soil parent material or was windblown (e.g., loess). Net sequestration of SIC depends on inputs of calcium and magnesium for each soil minus losses. Maps
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of potential SIC accumulation and storage based on wet Ca2+ and Mg2+ deposition can be useful in understanding terrestrial ecosystem inorganic carbon dynamics and the way it can be manipulated to decrease carbon dioxide concentrations in the atmosphere (Blasing et al., 2005). For example, Chang et al. (2012) examined the effects of afforestation on soil organic and inorganic carbon in the Loess Plateau of China, and reported the decrease in SIC in afforested top soil (due to biological activity and leaching) and subsequent increase in SIC in the afforested subsoil due to decrease in water content and root biomass. Previous research (Goddard et al., 2007, 2009) was limited in scope with respect to soil inorganic carbon sequestration potential. As noted above, Goddard et al. (2007) only studied the wet deposition of magnesium and the possible formation of dolomite as the inorganic carbonate mineral and found that the highest deposition of magnesium occurred in Oregon, Washington, parts of California, and the coastal areas of East Coast states due to magnesium enrichment of atmospheric deposition from sea salt. In Goddard et al. (2009), only the wet deposition of calcium was evaluated and the possible formation of inorganic carbon was limited to the formation of calcite. They reported that the wet deposition of calcium varied spatially within the continental United States, being highest in the central Midwest–Great Plains region as a result of Ca-rich dust from loess-derived soil particles and relatively low rainfall. The objectives of the present study were to: i) analyze the combined atmospheric wet Ca2+ and Mg2+ deposition within the continental U.S., ii) rank the twelve major soil orders in terms of average annual potential inorganic carbon sequestration due to both Ca2+ and Mg2+ deposition, and iii) compare our findings with the reported results of Guo et al. (2006a) who estimated the SIC inventory in the continental United States for the upper two meters of soil by soil order and state using STATSGO, which is the soils database also used in this study. The procedures used here were adapted from those reported previously by Goddard et al. (2007, 2009) MATERIALS AND METHODS Data were acquired from national datasets available from U.S. government agencies/sources and are summarized in Table I. Annual trends in average combined Ca2 + and Mg2 + wet deposition (1994–2003) Average annual wet deposition of Ca2+ and Mg2+
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TABLE I Sources and descriptions of the data acquired from national datasets available from U.S. government agencies/sources Data layer
Description
Sources
Wet Ca2+ , Mg2+ deposition
Isopleth maps in ArcGIS Grid format—2 500 m resolution
http://nadp.sws.uiuc.edu/isopleths/
Loess
Gridded 0.1◦ × 0.1◦ from maps from the U.S. Geologic Survey
Kohfeld and Harrison, 2001; U.S. Geological Survey
Precipitation
Isopleth maps in ArcGIS Grid format—2 500 m resolution
http://nadp.sws.uiuc.edu/isopleths/
Soil order
Derived from the State Soil Geographic Database
Soil Survey Staff, 1998
was downloaded for 253 stations from the National Atmospheric Deposition Program (NADP)/National Trends Network (NTN) (NADP, 2005). The Ca2+ and Mg2+ deposition values, available from NADP as kg ha−1 , were then summed using all available stations for each year of the study after first converting from kg mass units to units of moles which was necessary because of the different atomic weights for Ca2+ and Mg2+ . After summing, moles of the cations were converted to potential inorganic carbon sequestration based on stoichiometry and reported as kg C km−2 . Statistical analyses of these summarized data were used to see if depositional trends were evident over the ten-year time period of this study. Combined atmospheric Ca2 + and Mg2 + wet deposition (1994–2003) Annual atmospheric Ca2+ and Mg2+ wet deposition isopleth maps were downloaded from the NADP web site (NADP, 2005) in ArcGIS (Environmental Systems Research Institute, Redlands, CA) Grid format. These files were created using spatial interpolation of combined annual atmospheric Ca2+ and Mg2+ wet deposition data measured at the NADP/NTN sites. Isopleth maps were created by NADP from weekly precipitation samples taken at each NADP/NTN site using their standardized procedures (NADP, 2005). Precipitation-weighted average annual Ca2+ and Mg2+ concentrations were determined from these weekly samples and the atmospheric Ca2+ and Mg2+ wet deposition for each site was calculated by multiplying the total annual precipitation for a site by the precipitation-weighted average of Ca2+ and Mg2+ concentrations. Inverse distance weighting was used to spatially interpolate these data using sites that met the data completeness criteria downloaded from the web site (NADP, 2005). Finally, the Ca2+ and Mg2+ wet deposition values were summed as described above. Precipitation (1994–2003)
Annual precipitation maps, in ArcGIS
Grid for-
mat, were downloaded from the web site (NADP, 2005). These files were created using spatial interpolation of annual precipitation data from the NADP/NTN sites using similar methods to those previously described for Ca2+ and Mg2+ wet deposition. Soil order map The State Soil Geographic Database (Soil Survey Staff, 1998) was used to create the soil order data layers used in this analysis. This national spatial soils database was developed at a scale of 1:250 000 and consists of map units averaging between 2 800 and 24 200 hectares in size. The STATSGO database has a minimum mapping unit of 628 hectares and is designed for management uses at the state, regional, and multi-state scale (USDA-NRCS, 1995; Soil Survey Staff, 1998) and is therefore appropriate for use within this study. A vector map of dominant soil orders for the continental U.S. was created by querying the STATSGO soil component and classification tables (Goddard et al., 2007). Loess distribution Loess-derived soils often contain pedogenic carbonates (Chang et al., 2012), and therefore it is important to incorporate the map of loess distribution in this study. A general loess thickness map of the contiguous U.S. was developed using grids of 0.1 × 0.1 from U.S. Geological Survey (USGS) maps by Kohfeld and Harrison (2001). This data set contains loess deposit boundaries downwind of source regions. Loess thicknesses are greatest in regions that are near their original dust sources, including areas along rivers, at the southern edge of the Late Wisconsin ice sheet and directly downwind of the Rocky Mountains. Loess thicknesses tend to rapidly decrease east of these source regions (Kohfeld and Harrison, 2001). Data analyses ArcGIS v. 9.0 geographic information systems (GIS) software (ESRI, 2004) was used for all spatial
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layer development and data analysis. Geoprocessing steps were automated using ArcGIS ModelBuilderTM within the ArcGIS software package. A cell statistics function within ArcGIS was used to combine yearly Ca2+ and Mg2+ deposition layers to create an average combined Ca2+ and Mg2+ data layer. ArcGIS zonal statistics function was used to create an attribute table of the values for average combined Ca2+ and Mg2+ deposited in each area. Spatial data layers from January 1994 to December 2003 were averaged using the ArcGIS Spatial Analyst ‘Cell Statistics’ tool and an average statistical overlay to create a map layer showing total combined Ca2+ and Mg2+ wet deposition in terms of potential inorganic carbon sequestration in kg C km−2 . This process used the average of each cell within the data layer to create a final data layer. This averaged combined Ca2+ and Mg2+ data layer was multiplied by the cell size (625 ha) to derive combined Ca2+ and Mg2+ deposition/sequestration. The final map of average precipitation for the same time period was also created using the cell statistics tool. The total combined Ca2+ and Mg2+ wet deposition/sequestration per soil order was calculated using ArcGIS zonal statistics by combining the final combined average Ca2+ and Mg2+ data layer with the generalized soil order data layer as previously described (Goddard et al., 2007, 2009). RESULTS AND DISCUSSION Summarized data of average annual potential inorganic carbon sequestration due to Ca2+ and Mg2+ wet deposition showed no consistent increasing or decreasing trend over the ten-year period from January 1994 through December 2003 (Fig. 1). Statistical techniques including ANOVA and regression analysis conducted on the results also established that no discernible trends existed. Projections for climate change across the United States (Grundstein, 2009; Elguindi and Grundstein, 2013) predicted a recession of cold climate zones across the eastern U.S. and northern part of the country. In general, projections indicate that U.S. will become drier, particularly in the Midwest (Elguindi and Grundstein, 2013). Rawlins et al. (2011) reported that magnitude of precipitation events, their frequency, seasonality, and evaporation could play an important role in the formation of secondary pedogenic carbonates. A map of average annual area-normalized potential inorganic carbon sequestration due to combined atmospheric Ca2+ and Mg2+ wet deposition for the years 1994 to 2003 shows that the highest potential occurs
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Fig. 1 Temporal trend in average annual potential inorganic carbon sequestration in the U.S. due to combined Ca2+ and Mg2+ wet deposition (1994–2003).
in the Central Midwest-Great Plains region of the U.S. (Fig. 2). Comparing these findings to those previously reported by Goddard et al. (2007, 2009), one can surmise that Ca2+ dominates the overall trend and that its enrichment in rainwater results from wind-blown loess soils, intensive agriculture, and occurrence of dust storms in this region (Junge and Werby, 1958; Berner and Berner, 1996). Rawlins et al. (2011) reported that historic climatic data and soil inorganic carbon baseline maps provide an opportunity to further investigate the dynamic nature of pedogenic carbonates. The soil orders receiving the highest total average annual atmospheric wet Ca2+ and Mg2+ deposition expressed as potential inorganic carbon sequestration (barring losses from erosion and leaching) are: 1) Mollisols (1.1 × 108 kg C), 2) Alfisols (8.4 × 107 kg C), 3) Entisols (3.8 × 107 kg C), and 4) Aridisols (2.8 × 107 kg C), as shown in Table II. Mollisols and Alfisols are typical soils found in the loess dominant regions of the U.S. (Fig. 2), and much of the Ca2+ and Mg2+ present in the rainwater over these regions is likely derived from soil dust (Berner and Berner, 1996). In addition, Mollisols and Alfisols are the soil orders typically located in the highly arable regions of the U.S. and thus are subject to extensive cultivation and potential fertilization with Ca2+ and Mg2+ (West and McBride, 2005). Aridisols and Entisols are the soil orders most prevalent in the arid zones of the Southwest U.S., where total and effective precipitation is low. Calcium-bearing parent materials and calcium carbonates are major constituents of the topsoil in the Southwest U.S. due to its formation from intense evaporation of soil water at the ground surface (Berner and Berner, 1996).
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Fig. 2 Average annual potential soil inorganic carbon sequestration in the U.S. due to combined Ca 2+ and Mg2+ wet deposition (1994–2003). TABLE II Average annual potential inorganic carbon (IC) sequestration due to combined Ca2+ and Mg2+ wet deposition by soil orders in the U.S. for 1994–2003a) Soil order
Total area of soil orderb)
Annual potential IC sequestration Average
Alfisols Andisols Aridisols Entisols Histosols Inceptisols Mollisols Spodosols Ultisols Vertisols Total
km2 1.3 × 5.9 × 7.8 × 9.2 × 6.8 × 6.0 × 1.8 × 2.6 × 9.1 × 1.5 × 6.9 ×
106 104 105 105 104 105 106 105 105 105 106
(2)d) (10) (5) (3) (9) (6) (1) (7) (4) (8)
kg C 8.4 × 2.9 × 2.8 × 3.8 × 5.0 × 2.7 × 1.1 × 1.4 × 1.7 × 9.7 × -
107 106 107 107 106 107 108 107 107 106
Total area of soil orderc)
Area-normalized average (2) (10) (4) (3) (9) (5) (1) (7) (6) (8)
kg 64 49 35 42 73 44 62 52 19 64 50
C km−2 (3) (6) (9) (8) (1) (7) (4) (5) (10) (2)
km2 1.3 × 6.9 × 8.1 × 1.1 × 1.1 × 7.9 × 2.0 × 2.5 × 8.6 × 1.3 × 7.4 ×
106 104 105 106 105 105 106 105 105 105 106
(2) (10) (5) (3) (9) (6) (1) (7) (4) (8)
Mean total soil ICc) Storage
Content
× 106 Mg C 5 461 (3) 2 (9) 12 890 (2) 5 112 (4) 260 (7) 4 006 (5) 23 181 (1) 149 (8) 0 (10) 3 075 (6) 54 136
kg C m−2 4.3 (6) 0.0 (9) 15.9 (2) 4.8 (5) 2.4 (7) 5.1 (4) 11.5 (3) 0.6 (8) 0.0 (10) 23.2 (1) 7.4
a) Total
areas and thus subsequent calculated values for Oxisols and Gelisols were negligible and therefore are not shown in the table. from Goddard et al., 2007. c) Source from Guo et al., 2006a. d) Numbers in parentheses indicate the relative ranking among soil orders for each column. b) Source
In terms of area-normalized potential inorganic carbon sequestration, the soil orders are ranked: 1) Histosols (73 kg C km−2 ), 2) Alfisols and Vertisols (64 kg C km−2 ), 3) Mollisols (62 kg C km−2 ), and 4) Spodosols (52 kg C km−2 ) (Table II). The soil orders receiving the lowest average annual atmospheric Ca2+ and Mg2+ wet deposition from 1994 to 2003 were Andisols, Histosols and Vertisols (Table II). These orders are found in highly effective rainfall areas in the U.S. (Goddard et al., 2007, 2009) where high water tables
and leaching are common. A majority of previous studies of carbonates in soil have focused their attention on Aridisols and Entisols, i.e., the soils that tend to be dominant in deserts and arid/semi-arid environments (e.g., Schlesinger, 1982, 1985; Marion et al., 1985; Khademi and Mermut, 1999; Singh et al., 2007). Presumably, this attention, at least in part, has been based on a belief that these soils/environments have the largest pools of soil carbonates (Schlesinger, 1982; Khademi and Mermut,
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1999; Lal, 2004; Singh et al., 2007). However, because caliches and other carbonates tend to accumulate in the top 1 m of the soil profile in these particular soils and environments, their collection and study is greatly simplified (Schlesinger, 1982). Pedogenic carbonates may become soluble in soil solutions and their depth of formation or accumulation in a soil will likely be a function of rainfall, soil texture, permeability, land use and many other factors (Royer, 1999; D´ıaz-Hern´andez et al., 2003; Nordt et al., 2006; Mikhailova and Post, 2006; Mikhailova et al., 2006). More attention needs to be given to the potential formation of pedogenic carbonates in other soil orders, particularly Mollisols and Alfisols. The same conclusion can be drawn from the report by Guo et al. (2006a), which ranked Mollisols and Alfisols 1st and 3rd with regard to soil inorganic carbon storage among soils in the U.S. while on a surface area basis Mollisols and Alfisols ranked 3rd and 6th for average total soil inorganic carbon content (Table II). Although Guo et al. (2006a) ranked Aridisols 2nd in both total inorganic carbon stored and inorganic carbon content, our Ca2+ and Mg2+ wet deposition results (i.e., Aridisols ranked 4th and 9th for total and area-based carbon sequestration potentials, respectively; Table II) revealed that Aridisols might not be as important in the sequestration of atmospheric CO2 by pedogenic carbonate formation as it was previously thought. For example, as noted by Schlesinger (1997), despite the large amount of carbonates in desert soils the exchange of carbon between them and the atmosphere is slow with an estimated residence time of 85 000 years. Schlesinger (1997) also argues that it is the annual movements of carbon and not the amounts stored in various reservoirs that are most important for the global carbon cycle. It is important to remember, however, that the calculated soil inorganic carbon sequestration estimates reported in Table II are not the same as net SIC sequestration potentials because not all of the Ca2+ and Mg2+ wet deposition on soils will lead to pedogenic carbonate formation and sequestration. Instead, some fraction of the Ca2+ and Mg2+ will be utilized by plants while other fractions may remain in the upper soil, erode, or be leached completely out of the soil (West and McBride, 2005). CONCLUSIONS The combined wet deposition of Ca2+ plus Mg2+ varies spatially within the continental U.S. It is highest in the Central Midwest-Great Plains region as a result of enrich dust from loess-derived soil particles and relatively low rainfall (e.g., average annual precipitation <
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1 200 mm). Some fraction of the deposited Ca2+ and Mg2+ will be available to form pedogenic carbonate minerals which, upon their formation, can sequester carbon in a form that is more stable than organic matter. Of the different soil orders, Mollisols (1.1 × 108 kg C) and Alfisols (8.4 × 107 kg C) were ranked first and second with regard to the highest total amounts of carbon that could potentially be sequestered as carbonate from the wet deposition of Ca2+ and Mg2+ . Histosols (highest) and Alfisols and Vertisols (second highest) are ranked high with regard to normalizing the potential carbon sequestration on an area basis. Calculating global terrestrial carbon pools and fluxes requires an understanding of the dynamic nature of soil inorganic carbon and its relationship to atmospheric Ca2+ and Mg2+ wet deposition. REFERENCES Batjes, N. H. 1996. Total carbon and nitrogen in the soils of the world. Eur. J. Soil Sci. 47: 151–163. Berner, E. K. and Berner, R. A. 1996. Global environment: Water, Air, and Geochemical Cycles. Prentice Hall, Inc., Upper Saddle River, NJ, USA. Blasing, T. J., Broniak, C. T. and Marland, G. 2005. The annual cycle of fossil-fuel carbon dioxide emissions in the United States. Tellus. 57B: 107–115. Chadwick, O. A. and Graham, R. C. 2000. Pedogenic processes. In Sumner, M. E. (ed.) Handbook of Soil Science. CRC Press, Boca Raton, FL, USA. pp. E-41–75. Chang, R. Y., Fu, B. J., Liu, G. H., Wang, S. A. and Yao, X. L. 2012. The effects of afforestation on soil organic and inorganic carbon: A Case study of the Loess Plateau of China. Catena. 95: 145–152. D´ıaz-Hern´ andez, J. L., Fern´ andez, E. B. and Gonz´ alez, J. L. 2003. Organic and inorganic carbon in soils of semiarid regions: a case study from the Guadix-Baza basin (Southeast Spain). Geoderma. 114: 65–80. Elguindi, N. and Grundstein, A. 2013. An integrated approach to assessing 21st century climate change over the contiguous U.S. using the NARCCAP RCM output. Climatic Change. 117: 809–827. Eswaran, H., Reich, P. F., Kimble, J. M., Beinroth, F. H., Padmanabhan, E. and Moncharoen, P. 2000. Global carbon stocks. In Lal, R., Kimble, J. M. and Stewart, B. A. (eds.) Global Climate Change and Pedogenic Carbonates. Lewis Publishers, Boca Raton, FL. pp. 15–26. Eswaran, H., Van den Berg, E., Reich, P. and Kimble, J. 1995. Global soil carbon resources. In Lal, R., Kimble, J., Levine, E. and Stewart, B. A. (eds.) Soils and Global Change. Advances in Soil Science. CRC Press, Boca Raton, FL. pp. 27– 44. Environmental System Research Institute (ESRI). 2004. ArcGIS 9.0. Environmental System Research Institute, Redlands, CA. Gile, L. H. and Grossman, R. B. 1979. The Desert Project Soil Monograph. Document No. PB80-135304. National Information Service, Springfield, VA. Gile, L. H., Peterson, F. F. and Grossman, R. B. 1966. Morphological and genetic sequences of carbonate accumulation in desert soils. Soil Sci. 101: 347–360.
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Goddard, M. A., Mikhailova, E. A., Post, C. J. and Schlautman, M. A. 2007. Atmospheric Mg2+ wet deposition within the continental United States and implications for soil inorganic carbon sequestration. Tellus. 59B: 50–56. Goddard, M. A., Mikhailova, E. A., Post, C. J., Schlautman, M. A. and Galbraith, J. M. 2009. Continental United States atmospheric wet calcium deposition and soil inorganic carbon stocks. Soil Sci. Soc. Am. J. 73: 989–994. Grundstein, A. 2009. Evaluation of climate change over the continental United States using a moisture index. Climatic Change. 93: 103–115. Guo, Y. Y., Amundson, R., Gong, P. and Yu, Q. 2006a. Quantity and spatial variability of soil carbon in the conterminous United States. Soil Sci. Soc. Am. J. 70: 590–600. Guo, Y. Y., Gong, P., Amundson, R. and Yu, Q. 2006b. Analysis of factors controlling soil carbon in the conterminous United States. Soil Sci. Soc. Am. J. 70: 601–612. Junge, C. E. and Werby, R. T. 1958. The concentration of chloride, sodium, potassium, calcium, and sulfate in rain water over the United States. J. Meteorol. 15: 417–425. Khademi, H. and Mermut, A. R. 1999. Submicroscopy and stable isotope geochemistry of carbonates and associated palygorskite in Iranian Aridisols. Eur. J. Soil Sci. 50: 207–216. Kohfeld, K. E. and Harrison, S. P. 2001. DIRTMAP: the geological record of dust. Earth-Sci. Rev. 54: 81–114. Lal, R. 2004. Soil carbon sequestration to mitigate climate change. Geoderma. 123: 1–22. Manning, D. A. C. 2008. Biological enhancement of soil carbonate precipitation: passive removal of atmospheric CO2 . Mineral. Mag. 72: 639–649. Marion, G. M., Schlesinger, W. H. and Fonteyn, P. J. 1985. CALDEP: A regional model for soil CaCO3 (caliche) deposition in southwestern deserts. Soil Sci. 139: 468–481. Mi, N., Wang, S. Q., Liu, J. Y., Yu, G. R., Zhang, W. J. and Jobb´ agy, E. 2008. Soil inorganic carbon storage pattern in China. Glob. Change Biol. 14: 2380–2387. Mikhailova, E. A. and Post, C. J. 2006. Effects of land use on soil inorganic carbon stocks in the Russian Chernozem. J. Environ. Qual. 35: 1384–1388. Mikhailova, E. A., Post, C. J., Magrini-Bair, K. and Castle, J. W. 2006. Pedogenic carbonate concretions in the Russian Chernozem. Soil Sci. 171: 981–991. Ming, D. W. 2002. Carbonates. In Lal, R. (ed.) Encyclopedia of Soil Science. Marcel Dekker, New York. pp. 139–141. Monger, H. C. and Gallegos, R. A. 2000. Biotic and abiotic processes and rates of pedogenic carbonate accumulation in the Southwestern United State—relationship to atmospheric CO2 sequestration. In Lal, R., Kimble, J. M. and Stewart, B. A. (eds.) Global Climate Change and Pedogenic Carbonates. CRC Press LLC, Boca Raton, FL, USA. pp. 273–289. National Atmospheric Deposition Program (NADP). 2005. NRSP-3 Data. NADP Program Office, Illinois State Water Survey, Champaign, IL, USA. Available online at http://nadp.
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sws.uiuc.edu/ (verified on April 18, 2008). Natural Resources Conservation Service, United States Department of Agriculture (USDA-NRCS). 1995. Soil Survey Geographic (SSURGO) Database: Data Use Information. U.S. Government Printing Office, Washington DC. Nordt, L., Orosz, M., Driese, S. and Tubbs, J. 2006. Vertisol carbonate properties in relation to mean annual precipitation: Implications for paleoprecipitation estimates. J. Geol. 114: 501–510. Rabenhorst, M. C., West, L. T. and Wilding, L. P. 1991. Genesis of calcic and petrocalcic horizons in soils over carbonate rocks. In Nettleton, W. D. (ed.) Occurrence, Characteristics, and Genesis of Carbonate, Gypsum, and Silica Accumulations in Soils. SSSA Special Publication, Vol. 26. Soil Science Society of America, Madison, USA. pp. 61–74. Rasmussen, C. 2006. Distribution of soil organic and inorganic carbon pools by biome and soil taxa in Arizona. Soil Sci. Soc. Am. J. 70: 256–265. Rawlins, B. G., Henrys, P., Breward, N., Robinson, D. A., Keith, A. M. and Garcia-Bajo, M. 2011. The importance of inorganic carbon in soil carbon databases and stock estimates: A case study from England. Soil Use Manage. 27: 312–320. Royer, D. L. 1999. Depth to pedogenic carbonate horizon as a paleoprecipitation indicator? Geology. 27: 1123–1126. Schlesinger, W. H. 1982. Carbon storage in the caliche of arid soils: A case study from Arizona. Soil Sci. 133: 247–255. Schlesinger, W. H. 1985. The formation of caliche in soils of the Mojave Desert, California. Geochim. Cosmochim. Ac. 49: 57–66. Schlesinger, W. H. 1997. Biogeochemistry: An Analysis of Global Change. 2nd Edition. Academic Press, San Diego, CA, USA. Schlesinger, W. H. 2002. Inorganic carbon and the global carbon cycle. In Lal, R. (ed.) Encyclopedia of Soil Science. Marcel Dekker, Inc., New York, USA. pp. 706–708. Singh, S. K., Singh, A. K., Sharma, B. K. and Tarafdar, J. C. 2007. Carbon stock and organic carbon dynamics in soils of Rajasthan, India. J. Arid Environ. 68: 408–421. Soil Survey Staff. 1998. U.S. General Soil Map (STATSGO2). Natural Resources Conservation Service, United States Department of Agriculture. Available online at http://soildatamart.nrcs.usda.gov (verified on July 26, 2005). Sombroek, W. G., Nachtergaele, F. O. and Hebel, A. 1993. Amounts, dynamics and sequestering of carbon in tropical and subtropical soils. Ambio. 22: 417–426. Sposito, G. 1989. The Chemistry of Soils. Oxford University Press, New York, USA. Stumm, W. and Morgan, J. J. 1996. Aquatic Chemistry. 3rd Edition. John Wiley & Sons, New York. West, T. O. and McBride, A. C. 2005. The contribution of agricultural lime to carbon dioxide emissions in the United States: dissolution, transport, and net emissions. Agr. Ecosyst. Environ. 108: 145–154.
Potential Contribution of Combined Atmospheric Ca2+ and Mg2+ Wet Deposition Within the Continental U.S. to Soil Inorganic Carbon Sequestration∗1 E. A. MIKHAILOVA1,∗2 , M. A. GODDARD1 , C. J. POST1 , M. A. SCHLAUTMAN2 and J. M. GALBRAITH3 1 School
of Agricultural, Forest, and Environmental Sciences, Clemson University, Clemson SC 29634 (USA) of Environmental Engineering and Earth Sciences, Clemson University, Anderson SC 29625 (USA) 3 Department of Crop and Soil Environmental Sciences, Virginia Tech, Blacksburg VA 24061 (USA) 2 Department
(Received July 4, 2013; revised September 25, 2013)
ABSTRACT Soil inorganic carbon (SIC) stocks continuously change from the formation of pedogenic carbonates, a process requiring inputs of Ca2+ and Mg2+ ions. This study ranked the soil orders in terms of potential inorganic carbon sequestration resulting from wet Ca 2+ and Mg2+ deposition from 1994 to 2003 within the continental United States. The analysis revealed that average annual atmospheric wet deposition of Ca2+ and Mg2+ was the highest in the Central Midwest-Great Plains region, likely due to soil particle input from loess-derived soils. The soil orders receiving the highest total average annual atmospheric wet Ca 2+ and Mg2+ deposition, expressed as potential inorganic carbon formation (barring losses from erosion and leaching), were: 1) Mollisols (1.1 × 108 kg C), 2) Alfisols (8.4 × 107 kg C), 3) Entisols (3.8 × 107 kg C), and 4) Aridisols (2.8 × 107 kg C). In terms of area-normalized result, the soil orders were ranked: 1) Histosols (73 kg C km−2 ), 2) Alfisols and Vertisols (64 kg C km−2 ), 3) Mollisols (62 kg C km−2 ), and 4) Spodosols (52 kg C km−2 ). The results of this study provide an estimate of potential soil inorganic carbon sequestration as a result of atmospheric wet Ca2+ and Mg2+ deposition, and this information may be useful in assessing dynamic nature of soil inorganic carbon pools. Key Words:
calcite, carbon cycle, dolomite, pedogenic
Citation: Mikhailova, E. A., Goddard, M. A., Post, C. J., Schlautman, M. A. and Galbraith, J. M. 2013. Potential contribution of combined atmospheric Ca2+ and Mg2+ wet deposition within the continental U.S. to soil inorganic carbon sequestration. Pedosphere. 23(6): 808–814.
INTRODUCTION Global soil carbon (C) reservoirs are composed of soil organic and inorganic (pedogenic) carbon. In contrast to soil organic carbon, soil inorganic carbon (SIC) is poorly quantified and understood (Mi et al., 2008). Global soil inorganic carbon estimates are of various ranges: 695–748 Pg (Batjes, 1996), 720 Pg (Sombroek et al., 1993), 780–930 Pg (Schlesinger, 1982) and 940–1 738 Pg (Eswaran et al., 1995; Eswaran et al., 2000) of carbonate C in the top 1 m soil depth. Guo et al. (2006a) estimated the soil inorganic carbon inventory (226 to 937 × 108 Mg of SIC) for the continental U.S. using the State Soil Geographic Database (STATSGO) in the upper 2 m of soil by soil order and state. Rasmussen (2006) used STATSGO and SSURGO (Soil Survey Geographic Database) to analyze SIC pools by biome and soil taxa in Arizona. ∗1 Supported
Rawlins et al. (2011) analyzed the importance of inorganic carbon in soil carbon databases and stock estimates in England. In the context of environmental change, soil inorganic carbon has the potential to sequester atmospheric carbon dioxide as pedogenic carbonate (Manning, 2008). Carbonates (calcite, aragonite, dolomite and siderite) present in soils generally have been formed as a result of lithogenic or pedogenic processes or some combination of these two (Ming, 2002; Schlesinger, 2002). While lithogenic carbonates result from the debris of carbonate parent materials and thus have no impact on the net carbon budget, pedogenic carbonates represent a pathway by which atmospheric CO2 can be sequestered. Atmospheric CO2 sequestration via formation of new carbonate minerals in soils requires outside Ca2+ and Mg2+ sources such as wet deposition, fertilizer addition and irrigation (Monger
by the National Science Foundation of USA (No. 0340534) and the U.S. Department of Agriculture (Nos. SC-1700278, SC-1700452, and SC-1700462). ∗2 Corresponding author. E-mail: [email protected].
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and Gallegos, 2000). In general, precipitation of carbonates in soils is favored by increasing Ca2+ and Mg2+ concentrations, increasing pH, and/or increasing alkalinity (Sposito, 1989; Stumm and Morgan, 1996; Chadwick and Graham, 2000). Therefore, because elevated atmospheric CO2 concentration is of increasing concern, terrestrial carbon sequestration strategies based on carbonate storage require conditions that favor and maintain pedogenic carbonate precipitation, associated with minimal leaching and soil erosion. Atmospheric additions as a source of pedogenic carbonate were investigated by numerous studies. The desert project (Gile et al., 1966; Gile and Grossman, 1979) measured water-soluble calcium loadings in dust traps and reported a yield ranging from 0.35 to 1.3 g m−2 year−1 . Junge and Werby (1958) reported that calcium from rainwater can produce an estimated CaCO3 equivalent of 1.5 g m−2 year−1 based on 200 mm annual rainfall. Guo et al. (2006b) analyzed the effects of average annual precipitation, and average annual temperature on SIC in the continental U.S. and concluded that there was no relation between SIC and average annual precipitation until average annual precipitation exceeded 1 000 mm. Their analysis, however, did not include evaluation of the wet deposition chemistry in relation to SIC sequestration. Goddard et al. (2007) analyzed Mg2+ wet deposition in relation to potential soil inorganic carbon sequestration as dolomite in the continental U.S. and determined that Mollisols, Alfisols and Ultisols received the highest average annual atmospheric deposition of Mg2+ from 1994 to 2003. Precipitation, wind erosion and subsequent dustfall also can be significant sources of Ca2+ , and together contribute to atmospheric Ca2+ wet deposition, and SIC redistribution and sequestration (Goddard et al., 2009). Rabenhorst et al. (1991) reported that the Ca2+ content contained in dust traps from the limestone bedrock Edwards Plateau of Texas was the same as the amount expected from rainfall alone, and thus concluded that the amount of Ca2+ from particulate carbonates was negligible. However, their study also revealed that the dust originated from multiple sources and therefore redistribution was regional in nature rather than being derived only from local soils and rocks. Guo et al. (2006a) showed with maps that a vast majority of pedogenic carbonates in the western U.S. formed in igneous alluvium. A question remains whether the source of calcium was from the soil parent material or was windblown (e.g., loess). Net sequestration of SIC depends on inputs of calcium and magnesium for each soil minus losses. Maps
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of potential SIC accumulation and storage based on wet Ca2+ and Mg2+ deposition can be useful in understanding terrestrial ecosystem inorganic carbon dynamics and the way it can be manipulated to decrease carbon dioxide concentrations in the atmosphere (Blasing et al., 2005). For example, Chang et al. (2012) examined the effects of afforestation on soil organic and inorganic carbon in the Loess Plateau of China, and reported the decrease in SIC in afforested top soil (due to biological activity and leaching) and subsequent increase in SIC in the afforested subsoil due to decrease in water content and root biomass. Previous research (Goddard et al., 2007, 2009) was limited in scope with respect to soil inorganic carbon sequestration potential. As noted above, Goddard et al. (2007) only studied the wet deposition of magnesium and the possible formation of dolomite as the inorganic carbonate mineral and found that the highest deposition of magnesium occurred in Oregon, Washington, parts of California, and the coastal areas of East Coast states due to magnesium enrichment of atmospheric deposition from sea salt. In Goddard et al. (2009), only the wet deposition of calcium was evaluated and the possible formation of inorganic carbon was limited to the formation of calcite. They reported that the wet deposition of calcium varied spatially within the continental United States, being highest in the central Midwest–Great Plains region as a result of Ca-rich dust from loess-derived soil particles and relatively low rainfall. The objectives of the present study were to: i) analyze the combined atmospheric wet Ca2+ and Mg2+ deposition within the continental U.S., ii) rank the twelve major soil orders in terms of average annual potential inorganic carbon sequestration due to both Ca2+ and Mg2+ deposition, and iii) compare our findings with the reported results of Guo et al. (2006a) who estimated the SIC inventory in the continental United States for the upper two meters of soil by soil order and state using STATSGO, which is the soils database also used in this study. The procedures used here were adapted from those reported previously by Goddard et al. (2007, 2009) MATERIALS AND METHODS Data were acquired from national datasets available from U.S. government agencies/sources and are summarized in Table I. Annual trends in average combined Ca2 + and Mg2 + wet deposition (1994–2003) Average annual wet deposition of Ca2+ and Mg2+
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TABLE I Sources and descriptions of the data acquired from national datasets available from U.S. government agencies/sources Data layer
Description
Sources
Wet Ca2+ , Mg2+ deposition
Isopleth maps in ArcGIS Grid format—2 500 m resolution
http://nadp.sws.uiuc.edu/isopleths/
Loess
Gridded 0.1◦ × 0.1◦ from maps from the U.S. Geologic Survey
Kohfeld and Harrison, 2001; U.S. Geological Survey
Precipitation
Isopleth maps in ArcGIS Grid format—2 500 m resolution
http://nadp.sws.uiuc.edu/isopleths/
Soil order
Derived from the State Soil Geographic Database
Soil Survey Staff, 1998
was downloaded for 253 stations from the National Atmospheric Deposition Program (NADP)/National Trends Network (NTN) (NADP, 2005). The Ca2+ and Mg2+ deposition values, available from NADP as kg ha−1 , were then summed using all available stations for each year of the study after first converting from kg mass units to units of moles which was necessary because of the different atomic weights for Ca2+ and Mg2+ . After summing, moles of the cations were converted to potential inorganic carbon sequestration based on stoichiometry and reported as kg C km−2 . Statistical analyses of these summarized data were used to see if depositional trends were evident over the ten-year time period of this study. Combined atmospheric Ca2 + and Mg2 + wet deposition (1994–2003) Annual atmospheric Ca2+ and Mg2+ wet deposition isopleth maps were downloaded from the NADP web site (NADP, 2005) in ArcGIS (Environmental Systems Research Institute, Redlands, CA) Grid format. These files were created using spatial interpolation of combined annual atmospheric Ca2+ and Mg2+ wet deposition data measured at the NADP/NTN sites. Isopleth maps were created by NADP from weekly precipitation samples taken at each NADP/NTN site using their standardized procedures (NADP, 2005). Precipitation-weighted average annual Ca2+ and Mg2+ concentrations were determined from these weekly samples and the atmospheric Ca2+ and Mg2+ wet deposition for each site was calculated by multiplying the total annual precipitation for a site by the precipitation-weighted average of Ca2+ and Mg2+ concentrations. Inverse distance weighting was used to spatially interpolate these data using sites that met the data completeness criteria downloaded from the web site (NADP, 2005). Finally, the Ca2+ and Mg2+ wet deposition values were summed as described above. Precipitation (1994–2003)
Annual precipitation maps, in ArcGIS
Grid for-
mat, were downloaded from the web site (NADP, 2005). These files were created using spatial interpolation of annual precipitation data from the NADP/NTN sites using similar methods to those previously described for Ca2+ and Mg2+ wet deposition. Soil order map The State Soil Geographic Database (Soil Survey Staff, 1998) was used to create the soil order data layers used in this analysis. This national spatial soils database was developed at a scale of 1:250 000 and consists of map units averaging between 2 800 and 24 200 hectares in size. The STATSGO database has a minimum mapping unit of 628 hectares and is designed for management uses at the state, regional, and multi-state scale (USDA-NRCS, 1995; Soil Survey Staff, 1998) and is therefore appropriate for use within this study. A vector map of dominant soil orders for the continental U.S. was created by querying the STATSGO soil component and classification tables (Goddard et al., 2007). Loess distribution Loess-derived soils often contain pedogenic carbonates (Chang et al., 2012), and therefore it is important to incorporate the map of loess distribution in this study. A general loess thickness map of the contiguous U.S. was developed using grids of 0.1 × 0.1 from U.S. Geological Survey (USGS) maps by Kohfeld and Harrison (2001). This data set contains loess deposit boundaries downwind of source regions. Loess thicknesses are greatest in regions that are near their original dust sources, including areas along rivers, at the southern edge of the Late Wisconsin ice sheet and directly downwind of the Rocky Mountains. Loess thicknesses tend to rapidly decrease east of these source regions (Kohfeld and Harrison, 2001). Data analyses ArcGIS v. 9.0 geographic information systems (GIS) software (ESRI, 2004) was used for all spatial
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layer development and data analysis. Geoprocessing steps were automated using ArcGIS ModelBuilderTM within the ArcGIS software package. A cell statistics function within ArcGIS was used to combine yearly Ca2+ and Mg2+ deposition layers to create an average combined Ca2+ and Mg2+ data layer. ArcGIS zonal statistics function was used to create an attribute table of the values for average combined Ca2+ and Mg2+ deposited in each area. Spatial data layers from January 1994 to December 2003 were averaged using the ArcGIS Spatial Analyst ‘Cell Statistics’ tool and an average statistical overlay to create a map layer showing total combined Ca2+ and Mg2+ wet deposition in terms of potential inorganic carbon sequestration in kg C km−2 . This process used the average of each cell within the data layer to create a final data layer. This averaged combined Ca2+ and Mg2+ data layer was multiplied by the cell size (625 ha) to derive combined Ca2+ and Mg2+ deposition/sequestration. The final map of average precipitation for the same time period was also created using the cell statistics tool. The total combined Ca2+ and Mg2+ wet deposition/sequestration per soil order was calculated using ArcGIS zonal statistics by combining the final combined average Ca2+ and Mg2+ data layer with the generalized soil order data layer as previously described (Goddard et al., 2007, 2009). RESULTS AND DISCUSSION Summarized data of average annual potential inorganic carbon sequestration due to Ca2+ and Mg2+ wet deposition showed no consistent increasing or decreasing trend over the ten-year period from January 1994 through December 2003 (Fig. 1). Statistical techniques including ANOVA and regression analysis conducted on the results also established that no discernible trends existed. Projections for climate change across the United States (Grundstein, 2009; Elguindi and Grundstein, 2013) predicted a recession of cold climate zones across the eastern U.S. and northern part of the country. In general, projections indicate that U.S. will become drier, particularly in the Midwest (Elguindi and Grundstein, 2013). Rawlins et al. (2011) reported that magnitude of precipitation events, their frequency, seasonality, and evaporation could play an important role in the formation of secondary pedogenic carbonates. A map of average annual area-normalized potential inorganic carbon sequestration due to combined atmospheric Ca2+ and Mg2+ wet deposition for the years 1994 to 2003 shows that the highest potential occurs
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Fig. 1 Temporal trend in average annual potential inorganic carbon sequestration in the U.S. due to combined Ca2+ and Mg2+ wet deposition (1994–2003).
in the Central Midwest-Great Plains region of the U.S. (Fig. 2). Comparing these findings to those previously reported by Goddard et al. (2007, 2009), one can surmise that Ca2+ dominates the overall trend and that its enrichment in rainwater results from wind-blown loess soils, intensive agriculture, and occurrence of dust storms in this region (Junge and Werby, 1958; Berner and Berner, 1996). Rawlins et al. (2011) reported that historic climatic data and soil inorganic carbon baseline maps provide an opportunity to further investigate the dynamic nature of pedogenic carbonates. The soil orders receiving the highest total average annual atmospheric wet Ca2+ and Mg2+ deposition expressed as potential inorganic carbon sequestration (barring losses from erosion and leaching) are: 1) Mollisols (1.1 × 108 kg C), 2) Alfisols (8.4 × 107 kg C), 3) Entisols (3.8 × 107 kg C), and 4) Aridisols (2.8 × 107 kg C), as shown in Table II. Mollisols and Alfisols are typical soils found in the loess dominant regions of the U.S. (Fig. 2), and much of the Ca2+ and Mg2+ present in the rainwater over these regions is likely derived from soil dust (Berner and Berner, 1996). In addition, Mollisols and Alfisols are the soil orders typically located in the highly arable regions of the U.S. and thus are subject to extensive cultivation and potential fertilization with Ca2+ and Mg2+ (West and McBride, 2005). Aridisols and Entisols are the soil orders most prevalent in the arid zones of the Southwest U.S., where total and effective precipitation is low. Calcium-bearing parent materials and calcium carbonates are major constituents of the topsoil in the Southwest U.S. due to its formation from intense evaporation of soil water at the ground surface (Berner and Berner, 1996).
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Fig. 2 Average annual potential soil inorganic carbon sequestration in the U.S. due to combined Ca 2+ and Mg2+ wet deposition (1994–2003). TABLE II Average annual potential inorganic carbon (IC) sequestration due to combined Ca2+ and Mg2+ wet deposition by soil orders in the U.S. for 1994–2003a) Soil order
Total area of soil orderb)
Annual potential IC sequestration Average
Alfisols Andisols Aridisols Entisols Histosols Inceptisols Mollisols Spodosols Ultisols Vertisols Total
km2 1.3 × 5.9 × 7.8 × 9.2 × 6.8 × 6.0 × 1.8 × 2.6 × 9.1 × 1.5 × 6.9 ×
106 104 105 105 104 105 106 105 105 105 106
(2)d) (10) (5) (3) (9) (6) (1) (7) (4) (8)
kg C 8.4 × 2.9 × 2.8 × 3.8 × 5.0 × 2.7 × 1.1 × 1.4 × 1.7 × 9.7 × -
107 106 107 107 106 107 108 107 107 106
Total area of soil orderc)
Area-normalized average (2) (10) (4) (3) (9) (5) (1) (7) (6) (8)
kg 64 49 35 42 73 44 62 52 19 64 50
C km−2 (3) (6) (9) (8) (1) (7) (4) (5) (10) (2)
km2 1.3 × 6.9 × 8.1 × 1.1 × 1.1 × 7.9 × 2.0 × 2.5 × 8.6 × 1.3 × 7.4 ×
106 104 105 106 105 105 106 105 105 105 106
(2) (10) (5) (3) (9) (6) (1) (7) (4) (8)
Mean total soil ICc) Storage
Content
× 106 Mg C 5 461 (3) 2 (9) 12 890 (2) 5 112 (4) 260 (7) 4 006 (5) 23 181 (1) 149 (8) 0 (10) 3 075 (6) 54 136
kg C m−2 4.3 (6) 0.0 (9) 15.9 (2) 4.8 (5) 2.4 (7) 5.1 (4) 11.5 (3) 0.6 (8) 0.0 (10) 23.2 (1) 7.4
a) Total
areas and thus subsequent calculated values for Oxisols and Gelisols were negligible and therefore are not shown in the table. from Goddard et al., 2007. c) Source from Guo et al., 2006a. d) Numbers in parentheses indicate the relative ranking among soil orders for each column. b) Source
In terms of area-normalized potential inorganic carbon sequestration, the soil orders are ranked: 1) Histosols (73 kg C km−2 ), 2) Alfisols and Vertisols (64 kg C km−2 ), 3) Mollisols (62 kg C km−2 ), and 4) Spodosols (52 kg C km−2 ) (Table II). The soil orders receiving the lowest average annual atmospheric Ca2+ and Mg2+ wet deposition from 1994 to 2003 were Andisols, Histosols and Vertisols (Table II). These orders are found in highly effective rainfall areas in the U.S. (Goddard et al., 2007, 2009) where high water tables
and leaching are common. A majority of previous studies of carbonates in soil have focused their attention on Aridisols and Entisols, i.e., the soils that tend to be dominant in deserts and arid/semi-arid environments (e.g., Schlesinger, 1982, 1985; Marion et al., 1985; Khademi and Mermut, 1999; Singh et al., 2007). Presumably, this attention, at least in part, has been based on a belief that these soils/environments have the largest pools of soil carbonates (Schlesinger, 1982; Khademi and Mermut,
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1999; Lal, 2004; Singh et al., 2007). However, because caliches and other carbonates tend to accumulate in the top 1 m of the soil profile in these particular soils and environments, their collection and study is greatly simplified (Schlesinger, 1982). Pedogenic carbonates may become soluble in soil solutions and their depth of formation or accumulation in a soil will likely be a function of rainfall, soil texture, permeability, land use and many other factors (Royer, 1999; D´ıaz-Hern´andez et al., 2003; Nordt et al., 2006; Mikhailova and Post, 2006; Mikhailova et al., 2006). More attention needs to be given to the potential formation of pedogenic carbonates in other soil orders, particularly Mollisols and Alfisols. The same conclusion can be drawn from the report by Guo et al. (2006a), which ranked Mollisols and Alfisols 1st and 3rd with regard to soil inorganic carbon storage among soils in the U.S. while on a surface area basis Mollisols and Alfisols ranked 3rd and 6th for average total soil inorganic carbon content (Table II). Although Guo et al. (2006a) ranked Aridisols 2nd in both total inorganic carbon stored and inorganic carbon content, our Ca2+ and Mg2+ wet deposition results (i.e., Aridisols ranked 4th and 9th for total and area-based carbon sequestration potentials, respectively; Table II) revealed that Aridisols might not be as important in the sequestration of atmospheric CO2 by pedogenic carbonate formation as it was previously thought. For example, as noted by Schlesinger (1997), despite the large amount of carbonates in desert soils the exchange of carbon between them and the atmosphere is slow with an estimated residence time of 85 000 years. Schlesinger (1997) also argues that it is the annual movements of carbon and not the amounts stored in various reservoirs that are most important for the global carbon cycle. It is important to remember, however, that the calculated soil inorganic carbon sequestration estimates reported in Table II are not the same as net SIC sequestration potentials because not all of the Ca2+ and Mg2+ wet deposition on soils will lead to pedogenic carbonate formation and sequestration. Instead, some fraction of the Ca2+ and Mg2+ will be utilized by plants while other fractions may remain in the upper soil, erode, or be leached completely out of the soil (West and McBride, 2005). CONCLUSIONS The combined wet deposition of Ca2+ plus Mg2+ varies spatially within the continental U.S. It is highest in the Central Midwest-Great Plains region as a result of enrich dust from loess-derived soil particles and relatively low rainfall (e.g., average annual precipitation <
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1 200 mm). Some fraction of the deposited Ca2+ and Mg2+ will be available to form pedogenic carbonate minerals which, upon their formation, can sequester carbon in a form that is more stable than organic matter. Of the different soil orders, Mollisols (1.1 × 108 kg C) and Alfisols (8.4 × 107 kg C) were ranked first and second with regard to the highest total amounts of carbon that could potentially be sequestered as carbonate from the wet deposition of Ca2+ and Mg2+ . Histosols (highest) and Alfisols and Vertisols (second highest) are ranked high with regard to normalizing the potential carbon sequestration on an area basis. Calculating global terrestrial carbon pools and fluxes requires an understanding of the dynamic nature of soil inorganic carbon and its relationship to atmospheric Ca2+ and Mg2+ wet deposition. REFERENCES Batjes, N. H. 1996. Total carbon and nitrogen in the soils of the world. Eur. J. Soil Sci. 47: 151–163. Berner, E. K. and Berner, R. A. 1996. Global environment: Water, Air, and Geochemical Cycles. Prentice Hall, Inc., Upper Saddle River, NJ, USA. Blasing, T. J., Broniak, C. T. and Marland, G. 2005. The annual cycle of fossil-fuel carbon dioxide emissions in the United States. Tellus. 57B: 107–115. Chadwick, O. A. and Graham, R. C. 2000. Pedogenic processes. In Sumner, M. E. (ed.) Handbook of Soil Science. CRC Press, Boca Raton, FL, USA. pp. E-41–75. Chang, R. Y., Fu, B. J., Liu, G. H., Wang, S. A. and Yao, X. L. 2012. The effects of afforestation on soil organic and inorganic carbon: A Case study of the Loess Plateau of China. Catena. 95: 145–152. D´ıaz-Hern´ andez, J. L., Fern´ andez, E. B. and Gonz´ alez, J. L. 2003. Organic and inorganic carbon in soils of semiarid regions: a case study from the Guadix-Baza basin (Southeast Spain). Geoderma. 114: 65–80. Elguindi, N. and Grundstein, A. 2013. An integrated approach to assessing 21st century climate change over the contiguous U.S. using the NARCCAP RCM output. Climatic Change. 117: 809–827. Eswaran, H., Reich, P. F., Kimble, J. M., Beinroth, F. H., Padmanabhan, E. and Moncharoen, P. 2000. Global carbon stocks. In Lal, R., Kimble, J. M. and Stewart, B. A. (eds.) Global Climate Change and Pedogenic Carbonates. Lewis Publishers, Boca Raton, FL. pp. 15–26. Eswaran, H., Van den Berg, E., Reich, P. and Kimble, J. 1995. Global soil carbon resources. In Lal, R., Kimble, J., Levine, E. and Stewart, B. A. (eds.) Soils and Global Change. Advances in Soil Science. CRC Press, Boca Raton, FL. pp. 27– 44. Environmental System Research Institute (ESRI). 2004. ArcGIS 9.0. Environmental System Research Institute, Redlands, CA. Gile, L. H. and Grossman, R. B. 1979. The Desert Project Soil Monograph. Document No. PB80-135304. National Information Service, Springfield, VA. Gile, L. H., Peterson, F. F. and Grossman, R. B. 1966. Morphological and genetic sequences of carbonate accumulation in desert soils. Soil Sci. 101: 347–360.
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