Chemically stabilized soil organic carbon fractions in a reclaimed minesoil chronosequence: implications for soil carbon sequestration

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  • ORIGINAL ARTICLE

    Chemically stabilized soil organic carbon fractions in a reclaimedminesoil chronosequence: implications for soil carbonsequestration

    Sriroop Chaudhuri Louis M. McDonald

    Eugenia M. Pena-Yewtukhiw Jeff Skousen

    Mimi Roy

    Received: 21 March 2012 / Accepted: 15 January 2013

    Springer-Verlag Berlin Heidelberg 2013

    Abstract With adoption of appropriate reclamation

    strategies, minesoils can sequester significant amount of

    soil organic carbon (SOC). The objective of this study was

    to isolate different SOC fractions and coal-C in a reclaimed

    minesoil chronosequence and assess effects of increasing

    time since reclamation on each SOC fraction and selected

    soil properties. The chronosequence was comprised of four

    minesoils with time since reclamation ranging between 2

    and 22 years. Total SOC (TSOC, summation of all SOC

    fractions), ranged between 20 and 8 g kg-1, respectively,

    at the oldest (Mylan Park) and youngest (WVO1) minesite,

    indicating increasing SOC sequestration along the chron-

    osequence. The humin fraction accounted for about 43 and

    7 % of TSOC, respectively, at Mylan Park and WVO1,

    indicating increasing humification and biochemical stabil-

    ization of SOC with increasing time since reclamation. At

    WVO1,[60 % of TSOC was apportioned among the acid-hydrolysable (labile) and mineral-bound SOC fractions.

    Total soil carbon (TSC, TSOC ? coal-C) were signifi-

    cantly (p \ 0.05) related to the humin fraction in olderminesoils, whereas with the acid-hydrolysable (labile)

    fraction in the younger minesoils indicating that C stabil-

    ization mechanisms differed substantially along the

    chronosequence. Coal-C was unrelated to any SOC fraction

    at all minesites indicating that SOC sequestration estima-

    tions in this chronosequence was unaffected by coal-C. Soil

    cation exchange capacity and electrical conductivity were

    significantly (p \ 0.05) related to the humin fraction atMylan Park while to the acid-hydrolysable and mineral-

    bound SOC fractions at WVO1 indicating that the relative

    influences of different SOC fractions on soil quality indi-

    cators differed substantially along the chronosequence.

    Keywords Soil organic carbon sequestration Reclaimedminesoil Humin Coal Sequential fractionation Cationexchange capacity

    Abbreviations

    AHSOC 65 % HNO3 Hydrolysable soil organic carbon

    ARSC Residual soil carbon after 65 % HNO3hydrolysis

    BHSOC Base (0.5 M NaOH) hydrolysable soil organic

    carbon

    CEC Cation exchange capacity

    EC Electrical conductivity

    FBHSOC Final base (0.5 M NaOH) hydrolysable soil

    organic carbon

    FBRSC Residual soil carbon after final base hydrolysis

    HFSOC 10 % HF Hydrolysable soil organic carbon

    HFRSC Residual soil carbon after 10 % HF hydrolysis

    RSC Residual soil carbon after each step of

    sequential fractionation

    SOC Soil organic carbon

    SOM Soil organic matter

    TSC Total soil carbon

    TSOC Total soil organic carbon

    S. Chaudhuri (&)Texas A&M AgriLife Research and Extension Center,

    P.O. Box 1658, Vernon, TX 76385, USA

    e-mail: schaudhuri@ag.tamu.edu

    L. M. McDonald E. M. Pena-Yewtukhiw J. SkousenDivision of Plant and Soil Sciences, West Virginia University,

    1102 Agricultural Sciences Building, P.O. Box 6108,

    Morgantown, WV 26506-6108, USA

    M. Roy

    Department of Agronomy and Soils, Auburn University,

    Auburn, AL 36849, USA

    123

    Environ Earth Sci

    DOI 10.1007/s12665-013-2256-8

  • Introduction

    Surface mining for coal in the Appalachian region leads to

    drastic perturbation of soil systems and alters ecosystem

    processes (Shrestha and Lal 2007; Chatterjee et al. 2009).

    Environmentally adverse consequences of mining include

    degradation of hydrologic systems and loss of aquatic

    habitat, destruction of soil structure, increased soil erosion,

    loss of soil organic matter (SOM), stunted plant growth,

    and restricted nutrient cycling (Johnson and Skousen 1995;

    Lal and Ussiri 2005). However, with the adoption of

    appropriate reclamation strategies, minesoils can sequester

    significant amounts of soil organic carbon (SOC) and

    contribute to terrestrial C sequestration efforts (Akala and

    Lal 2000, 2001; Lal 2004; Shukla et al. 2004, 2005;

    Shrestha and Lal 2006; Ussiri et al. 2006). Researches have

    shown that within 2050 years of reclamation, SOC can

    increase by 1050 % with substantial improvement in

    overall soil quality (Shukla et al. 2004; Ussiri et al. 2006;

    Shrestha and Lal 2007; Chatterjee et al. 2009). Significance

    of reclaimed minesoils in terrestrial greenhouse gas miti-

    gation effort was shown by a recent estimate that indicated

    that US minelands can sequester up 0.501.00 MgC

    ha-1 year-1 through reclamation which in turn could

    incorporate about 1.603.20 TgC year-1 into the soils and

    counterbalance about 5.811.2 Tg CO2 year-1 emerging

    from coal combustion (Lal 2004). Accumulation of SOC also

    has beneficiary effects on several agro-ecological and envi-

    ronmental processes (Stevenson 1994; Trumbore 1997).

    Soil organic carbon (SOC) sequestration ensues from

    SOC stabilization via: (i) soil aggregation (Six et al. 2004),

    (ii) organo-mineral complex formation (Guggenberger and

    Kaiser 2003) and (iii) inherent biochemical recalcitrance of

    SOC (Tan et al. 2004; Paul et al. 2006). A variety of

    chemical, isotopic, and molecular techniques have been

    used to elucidate SOC stabilization patterns. Chemical

    methods mainly include acid hydrolytic (Paul et al. 2006;

    Helfrich et al. 2007), oxidative (Eusterhues et al. 2003;

    Helfrich et al. 2007), and demineralization techniques

    (Eusterhues et al. 2007; Helfrich et al. 2007) to isolate

    different SOC fractions. Isotopic methods (14C) distinguish

    between SOC fractions based on their mean residence

    times (MRT) and turnover rates (Trumbore 2000; Bruun

    et al. 2005). Molecular methods rely upon the structural

    and compositional differences among the organic moieties

    associated with SOM (Kogel-Knabner 2000; Fontain et al.

    2007; Solomon et al. 2005, 2007).

    Owing to extreme biochemical heterogeneity of SOM,

    fractions isolated by different extractants, however, are

    considered operationally defined (Herbert and Bertsch

    1995). The dimensions and characteristics of SOC fractions

    vary widely depending on soil physico-chemical charac-

    teristics, biological processes, geographic location, climate,

    and land management practices. For example, base

    hydrolysis with 0.5 M NaOH fractionation can isolate up to

    80 % of SOM, with higher fractionation efficiencies gen-

    erally achieved for coarser textural classes (Stevenson

    1994). Helfrich et al. (2007) found that demineralization

    (10 % HF) followed by oxidation (sodium hypochlorite,

    NaOCl) can isolate about 4060 % of SOC. The oxidisable

    SOC fraction can account for as much as 72 % of total

    SOC (Siregar et al. 2005). Lee et al. (2009) found that

    organo-mineral association stabilized [70 % of total SOCwhile soil aggregation stabilized about 817 % of SOC.

    Zimmerman et al. (2007) showed that about 6391 and

    3566 % of total SOC, respectively, was isolated by oxi-

    dation with sodium hypochlorite (NaOCl) and acid

    hydrolysis (6 N HCl). Although no consensus exists

    regarding the amount of SOC that can be isolated by acid

    hydrolyses, in general, the acid-resistant (acid non-hydro-

    lysable, NHC) carbon constitutes about 3080 % of total

    SOC, depending upon soil type, texture, and land man-

    agement practices (Paul et al. 2006). The authors analyzed

    about 1,100 records obtained from literature and found that

    NHC accounted for about 48, 56, 55, and 56 % of total

    SOC, respectively, under conventional tillage, no tillage,

    forests, and grassland soils. Tan et al. (2004) found that

    NHC constituted about 53, 37, and 39 % of total SOC,

    respectively, in forest, conventional, and no till soils. Jen-

    kinson and Rayner (1977) have shown that NHC could

    represent 2050 % of total SOC in the upper horizons in

    the temperate zones. The NHC fraction in agricultural soils

    in the US Midwest accounted for about 3565 % of the

    total SOC and was about 1,3001,800 years older than the

    bulk soil (Leavitt et al. 1996; Paul et al. 1997, 2001).

    Unlike native soils, chemical isolation studies of different

    SOC fractions are relatively rare in reclaimed minesoils.

    Lorenz and Lal (2007) used oxidative (disodium perox-

    odisulphate, Na2S2O8) removal of carbon followed by

    demineralization (10 % HF) in minesoils reclaimed to

    forest and pasture ecosystem. Results indicated that the

    highest amounts of both SOC fractions were found at older

    minesites while the least at the youngest. However, the

    study did not account for coal-C and a rigorous chrono-

    sequence based approach was recommended to identify

    temporal changes in the dimensions of SOC fractions.

    Although reclaimed minesoils can sequester significant

    amount of SOC, quantification of SOC sequestration in

    these disturbed ecosystems, however, is challenged by

    presence of coal-C (Rumpel et al. 1998; Dick et al. 2006).

    Distinction between coal-C and SOC has been achieved by

    stable isotopic (d13C) (Ussiri and Lal 2007), radiocarbon(14C) (Rumpel et al. 2005; Ussiri and Lal 2007) and ther-

    mogravimetric (Siewert 2004; Maharaj et al. 2007a, b)

    methods. Such methods, however, are expensive and

    require significant amount of resources (Bruun et al. 2005).

    Environ Earth Sci

    123

  • In addition, studies documenting the relative contribution

    of different SOC fractions to overall soil C budget and/or

    SOC dynamics and temporal changes therein are still

    lacking for reclaimed minesoils. The main objective of this

    study was to isolate and quantify different SOC fractions in

    a reclaimed minesoil chronosequence and assess their rel-

    ative effects on selected soil quality parameters. We used

    relatively inexpensive and easy-to-use chemical fraction-

    ation scheme to (i) isolate different SOC fractions and

    characterize temporal trends along a well-established

    chronosequence, (ii) quantify coal-C, and (iii) evaluate

    interrelationships between different SOC fractions and

    selected soil quality parameters such as soil cation

    exchange capacity (CEC) and electrical conductivity (EC).

    Materials and methods

    Study area

    A chronosequence comprising four reclaimed minesoil

    namely, Mylan Park (MP), New Hill (NH), WVSK, and

    WVO1, was identified in Monongalia County (393704500N,795702200W), West Virginia. Details of the minesoilcharacteristics and reclamation methods are described

    elsewhere (Chaudhuri et al. 2011, 2012a). The minesoils

    had similar soil forming conditions except for time since

    reclamation which ranged from 2 to 22 years along the

    chronosequence (Table 1). At the time of sampling mine-

    soil ages were 2, 4, 5 and 22 years for WV01, WVSK, New

    Hill, and Mylan Park, respectively. Initial reclamation

    work at WVSK was performed in the mid-1990s. However,

    in 2004, the topsoil (03 cm) was scraped and pushed back

    to the high wall situated along the rear margin which

    effectively established its time since reclamation as

    4 years. The minesoils were reclaimed to mixed grass

    legume pasture ecosystem. The predominant species were

    orchard grass (Dactylis glomerata), alfalfa (Medicago

    sativa), red clover (Trifolium pratense), white clover

    (Trifolium repens), timothy (Phleum pratense L.), tall

    fescue (Festuca arundinacea), and birds foot trefoil (Lotus

    corniculatus). The reclaimed sites were owned by the same

    company and were mined and reclaimed in similar manner

    (Table 1), following the protocols established by the 1977

    Surface Coal Mining Reclamation Act. Minesoils were

    compacted and graded to adjoining contours so as to merge

    uniformly with the regional topography. The regional

    geology consisted of interbedded, limy and acidic gray

    shale, siltstone, sandstone, coal, limestone, and thin beds of

    limy red shale. The region is characterized by temperate

    climate with average winter and summer temperatures

    around 0 and 22 C respectively. Thirty year averageannual precipitation amounts to about 104 cm.

    Soil sampling and analysis

    Each minesite was sampled over approximately 0.5 ha area

    in the early summer (MayJune) of 2008. Soil cores were

    collected from the upper 6 cm using site-specific irregular

    grids (7 9 5 m) based on the previous knowledge of spa-

    tial variability of SOC (Chaudhuri et al. 2011). A total of

    64, 83, 79, and 74 soil cores were collected from WVO1,

    WVSK, New Hill, and Mylan Park, respectively. Soils

    were air dried for 48 h, ground and passed through\2 mmsieve before performing chemical analysis.

    Before performing the SOC fractionation method, soil

    samples were treated with 1M HCl to remove inorganic

    carbonates (Midwood and Boutton 1998; Harris et al. 2000;

    Komada et al. 2008). In brief, 10 g of soil was shaken with

    40 mL of 1M HCL for 8 h (Midwood and Boutton 1998).

    Following acid treatment, the soil slurries were centrifuged

    and supernatants were decanted. Soil residues were rinsed

    twice with deionized water (DI), freeze-dried for 48 h, and

    gently ground to pass through \2 mm sieve. Soil carbonin the acid-treated and untreated soil was determined by

    complete combustion using an elemental analyzer unit. The

    difference between pre- and post-acid treatment yielded the

    amount of soil inorganic carbon. Residual carbon left in

    soil after inorganic carbonate removal represented organic

    carbon and was subjected to sequential fractionation using

    acid and base hydrolyses reaction followed by thermal

    oxidation to isolate different SOC fractions.

    The complete combustion was performed with LECO

    CNS-2000 analyzer, a non-dispersive, infrared, micro-

    computer-based facility designed to measure total carbon,

    nitrogen, and sulfur in solid samples (soil, plant tissue,

    fertilizers, meat products, dairy products, seeds, food, res-

    ins, and environmental wastes) with a nominal sample

    requirement (200 mg). The instrument has a detection limit

    of 0.02 mg C with a precision of about 0.4 % relative

    standard deviation (RSD). The combustion involves oxi-

    dation of SOM at 950 C, in the presence of ultra-high pure(UHP) helium, oxygen and low-moisture compressed air.

    Oxidation of SOM yields CO2 gas which is detected by an

    infrared sensor and expressed as %C on a soil dry weight

    basis. Before carbon analysis, 10 blanks and five desic-

    cated, pure primary standards were used to determine the

    calibration factor and correct for drift in SOC estimates.

    Quality control tests were performed by using (1) three

    replicates and (2) one each of a primary standard and blank

    after 15 unknowns (soil samples).

    The detail of the sequential fractionation method is

    available in Ussiri and Lal (2007). In brief, 2 g of car-

    bonate-free soil was subject to sequential treatment with

    0.5M NaOH (1:10 soil:solution ratio; 15 h shaking; twice),

    followed by 60 % HNO3 (1:10 soil:solution ratio shaking;

    15 min), 10 % HF (1:10 soil:solution ratio shaking; 4 h),

    Environ Earth Sci

    123

  • 0.5M NaOH (1:10 soil:solution ratio; 30 min shaking;

    twice) and thermal oxidation in muffle furnace (340 C;3 h) (Fig. 1). Following each fractionation step, soil resi-

    dues were rinsed twice with DI, freeze-dried for 48 h, and

    gently ground to pass through \2 mm sieve. Residual so...

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