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Soil Biology & Biochemistry 69 (2014) 251e264

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Soil Biology & Biochemistry

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Review

Soil burial contributes to deep soil organic carbon storage

Nina T. Chaopricha a,*, Erika Marín-Spiotta a,b

aNelson Institute for Environmental Studies, University of WisconsineMadison, 550 North Park Street, Madison, WI 53706, USAbDepartment of Geography, University of WisconsineMadison, 550 North Park Street, Madison, WI 53706, USA

a r t i c l e i n f o

Article history:Received 14 August 2013Received in revised form16 October 2013Accepted 13 November 2013Available online 2 December 2013

Keywords:Soil organic carbonPaleosolSubsoilDeep soilSoil burialDepositionErosion

* Corresponding author. Present address: Cornell InAgriculture and Development, B75 Mann Library, Ith607 342 4793.

E-mail address: ntc24@cornell.edu (N.T. Chaoprich

0038-0717/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.soilbio.2013.11.011

a b s t r a c t

Understanding the source of soil organic carbon (SOC) in deep soil horizons and the processes influ-encing its turnover is critical for predicting the response of this large reservoir of terrestrial C to envi-ronmental change and potential feedbacks to climate. Here, we propose that soil burial is a globallyimportant but greatly underestimated process contributing to the delivery and long-term persistence ofsubstantial SOC stocks to depths beyond those considered in most soil C inventories. We draw fromexamples in the paleosol and geomorphology literature to identify the effects of soil burial by volcanic,aeolian, alluvial, colluvial, glacial, and anthropogenic depositional processes on soil C storage. Wedescribe how the state factors affecting soil formation affect the persistence and decomposition of SOC inburied soils. Organic horizons and surface mineral soils that become buried under layers of sediment canstore C several meters below the earth’s surface for millennia or longer. Buried SOC concentrations canrival those of surface soils, and soils buried under volcanic deposits generally contain higher concen-trations of SOC than those under alluvial or non-permafrost loess deposits. The dearth of quantitativeresearch on buried SOC specifically, and on deep C pools in general, makes it difficult to estimate theglobal importance of burial as a terrestrial C storage mechanism on contemporary time scales. Thehandful of studies that provide data on soil C stocks in buried horizons and estimate their spatial extentsuggest that buried soils can contain significant regional OC reservoirs that are currently ignored ininventories and biogeochemical models. Recent research suggests that these buried SOC stocks may cyclebiologically on annual-to-decadal time scales if the processes contributing to their protection fromdecomposition are altered. We discuss the vulnerability of buried SOC pools to disturbance from climatechange and human activities that may reconnect these deep SOC pools with the atmosphere. We alsoprovide recommendations on how burial processes can be incorporated into soil biogeochemical modelsto more accurately predict dynamics of deep SOC pools under different landscapes and environmentalconditions.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Soils hold one of the largest terrestrial reservoirs of organiccarbon (OC), and while most of this pool cycles on very slow timescales (centuries to millennia), climate change and landscapedisturbance can affect the proportion of soil organic carbon (SOC)with the potential for more rapid exchange with the atmosphere(Houghton et al., 2001; Trumbore, 2009). Most of our under-standing of the processes affecting C storage and release from soilscomes from studies of the top 30 cm of soil, which has been thefocus of agricultural studies concerned with nutrient cycling

ternational Institute for Food,aca, NY 14853, USA. Tel.: þ1

a).

All rights reserved.

(Richter and Mobley, 2009; Zabowski et al., 2011). The long-heldassumption that SOC with old radiocarbon (14C) ages is notresponsive to changes in environmental conditions has alsocontributed to underestimates of the amount and dynamics of Cstored in deep soils (cf. Fontaine et al., 2007). Evidence that modern14C is incorporated into subsurface soils (Koarashi et al., 2012) andthat ancient SOC can respond to disturbances on annual to decadaltime scales (Paul et al., 2006), in conjunctionwith reinterpretationsof relationships between age and reactivity (Torn et al., 2009),provide new insights into the role of deep SOC in the contemporaryglobal C cycle. A growing number of studies report a dynamicresponse of SOC pools that are located at and below 1 m depth tochanges in land use and land cover (Devine et al., 2011; Harrisonet al., 2011; Veldkamp et al., 2003).

Recent investigations of deep SOC have focused on belowgroundroot inputs and the vertical transport of particulate and dissolvedorganic matter through bioturbation, physical mixing, gravity, and

N.T. Chaopricha, E. Marín-Spiotta / Soil Biology & Biochemistry 69 (2014) 251e264252

preferential flowpaths as the main modes of delivery of OC to thesubsoil (Chabbi et al., 2009; Lorenz and Lal, 2005; Marín-Spiottaet al., 2011; Rumpel and Kögel-Knabner, 2011; Tonneijck andJongmans, 2008; Wilkinson et al., 2009). Depositional processeshave received considerable attention in the context of long-rangesoil erosion and sedimentation on land (Berhe and Kleber, 2013;Berhe et al., 2012, 2007; Quinton et al., 2010; Van Oost et al.,2007). The role of soil burial in the sequestration of C photo-synthesized in situ at depositional sites has been largely ignored indiscussions of deep SOC dynamics. Burial can disconnect a soil fromatmospheric conditions and slow or inhibit the microbial decom-position of native or transported SOC. Buried soil horizons, or sur-face soils that have been buried through various depositionalprocesses, can storemore SOC thanwould exist at such depths fromroot inputs and leaching from upper horizons (Gurwick et al.,2008a; Hoffmann et al., 2013; VandenBygaart et al., 2012).

Here, we propose that soil burial processes are important con-tributors to the accumulation and long-term persistence ofconsiderable quantities of SOC at depths beyond those consideredby global soil C inventories. While the USDA Soil Taxonomy placesthe lower limit of soil at 2 m below the surface (Soil Survey Staff,2010), we expand our consideration of soil to include materialabove weathered rock that is biologically active and plays animportant role in biogeochemical cycling, sensu Richter andMarkewitz (1995). Organic matter makes up the bulk of the soilmany meters in depth in peatlands (Tarnocai et al., 2009; Ellery etal., 2012) and in permafrost soils (Bockheim and Hinkel, 2007;Johnson et al., 2011; Schuur et al., 2008). Most recent reviews ondeep SOC have focused on the top 1 m of soil, whereas here, wefocus on SOC in deeper buried soils to highlight the large stores ofpotentially biologically active C beyond depths commonlymeasured. Our review excludes very deep paleosols that may havebeen subjected to metamorphism and behave more like sedimen-tary rocks.

We review the contributions of geomorphic, pedogenic, andanthropogenic depositional processes to deep SOC storage anddescribe how environmental conditions or state factors (sensuJenny, 1941) influence SOC persistence in buried soils, both duringand since burial. Understanding the mechanisms contributing tothe stabilization or mobilization of SOC from deep buried soils isimportant for predicting the response of soil C pools to changes inenvironmental conditions. Buried soils have been studied histori-cally for information about past environments (Valentine andDalrymple, 1976; Zech et al. 2013) and can also serve as casestudies for understanding both the sensitivity of landscape pro-cesses to future environmental change and the mechanismscontributing to soil organic matter stabilization (Chaopricha, 2013;Marín-Spiotta et al., in review) Where specific information onfactors affecting soils buried below 1 m is scarce, we cite studies ofshallower buried soils. Building upon what is known about theprocesses contributing to the stabilization of deep SOC in buriedsoils, we discuss vulnerability of these underestimated C pools tolandscape and climatic disturbances thatmay reconnect potentiallyancient OC with the atmosphere. Finally, we propose that burialprocesses and landscape disturbance be incorporated into soilbiogeochemical models to better predict the response of below-ground OC pools to global change.

2. Buried soils as deep SOC reservoirs

A buried soil is defined by the National Resources Conserva-tion Service as a soil that is “covered with a surface mantle ofnew soil material that either is 50 cm or more thick or is 30e50 cm thick and has a thickness that equals at least half the totalthickness of the named diagnostic horizons that are preserved in

the buried soil” (NRCS, 2013). Soil layers underlying a plaggenepipedon, an anthropogenic surface layer with thickness of 50 cmor greater resulting from long-continued manuring, also areconsidered to be a buried soil. Much of what is known aboutburied soils comes from the study of paleosols in the geo-morphology and Quaternary paleopedology literature (Jacobs andSedov, 2012). While the term paleosol is sometimes used todescribe any soil that developed under different climatic orenvironmental conditions than today and was once buried, evenwhen overlying material has eroded and it is now exposed at thesurface, we use the term here to refer only to currently buriedsoils (Johnson, 1998). Depositional processes leading to soil burialare certainly not limited to the distant past. Current environ-mental changes driven or influenced by human activities alsolead to landscape disturbances that can result in the rapid burialof recently fixed organic C on land.

Buried SOC can be highly variable spatially and thus challengingto quantify due to the strong dependence of buried soils on land-scape geomorphology and climate history (Johnson et al., 2011;Rosenbloom et al., 2006). Furthermore, most studies of buriedsoils report point locations and do not quantify SOC stocks withinthe soil profile or across the landscape. Here, we report on a handfulof studies that provided either SOC stocks or soil bulk density andOC concentration data, which allowed us to calculate stocks giventhe thickness of the horizons. Only two studies we found reportedestimates of spatial coverage for buried soils, which allowed for thequantification of reservoir size.

Buried soil horizons can contain large SOC content, comparableto surface soils. One of the few studies on SOC dynamics in deepburied soil horizons, which also reported soil bulk density values, isthat of Basile-Doelsch et al. (2005) about a volcanic paleosolsequence on the island of La Réunion. Extrapolating between depthintervals for which specific data were reported, we estimated thatthe two deepest buried soil horizons sampled (90e276 cm) con-tained a total of 512 Mg C/ha, or 72% of the whole soil profile SOC tothat depth, including surface horizons. Volcanic paleosol sequencesbelow 1 m and up to 3 m depths on substrates of varying age inMexico contained between 216 and 565 Mg C/ha, 23e50% of wholesoil profile SOC (Peña-Ramírez et al., 2009). These soils are locatedin the Sierra del Chichinautzin Volcanic Field, an area of ca.2400 km2 covered by volcanic deposits with ages between 50,000and 1670 years B.P. The high SOC densities of these buried soilhorizons (with average values of 2.1 � 0.4 kg/m2) suggest thatburial in volcanic deposits contributes to storage of significant SOCstocks deep below the surface. Organic-rich volcanic paleosolsburied 3 m below the surface on the slopes of Mt. Kilimanjaro wereestimated to contribute a regionally important C “hotspot” of82 Mg C (Zech et al., 2014).

Buried soils can amount to significant C reservoirs evenwith lowSOC concentrations due to the vast volumes of soil resulting fromdeep profiles with compacted bulk densities, as well as extensivegeographic distributions, especially where buried soils are repre-sentative of regional-scale geomorphic processes, as is commonwith loess deposition (Miao et al., 2007). In the U.S. central GreatPlains, a 1-m thick paleosol buried in loess deposits 6 m below themodern surface could contain a maximum of 2.7 Pg C, assuminghomogeneous coverage over the large area across multiple stateswhere the soil has been identified (Marín-Spiotta et al., in review).Even if the loess paleosol covered only one tenth of that area, itwould still amount to a considerable stock of 0.27 Pg C. These largeSOC stocks are located at depths below those accounted for inglobal C inventories and models and can become exposed to themodern surface through geologic or human disturbances includinglandslides, road construction, and mining (Chaopricha, 2013;Karlstrom et al., 2008).

N.T. Chaopricha, E. Marín-Spiotta / Soil Biology & Biochemistry 69 (2014) 251e264 253

In addition to their role in sequestering C from the atmosphere,buried soils can provide important ecosystem services. Deep buriedsoil horizons with higher SOC concentrations than overlying loessmay reduce groundwater contamination by retaining contaminantsand inhibiting their downward flow (Duffy et al., 1997). In riparianwetlands, deep buried SOC can influence denitrification potentialand thus regulate nitrogen losses (Hill and Cardaci, 2004).

3. Soil burial processes contributing to deep SOC

Storage of SOC at depth results from multiple pedogenic, biotic,and geomorphic factors that contribute to the delivery, accumula-tion, and persistence of organic matter in the subsurface of soils.Soil burial processes occur in different types of environments andcan occur repeatedly over centuries to millenia, resulting in verticalsequences of multiple buried soil horizons (Fig. 1). Soil burial isrecognized to be important in the buildup of permafrost throughsuccessive cryoturbation events (Becher et al., 2013; Bockheim,2007). SOC in surface organic and mineral soil horizons also canbecome buried, for example, under lava flows and other volcanic

Fig. 1. Example of different soil burial processes (top panel) and the paleosol sequences they2006); b) aeolian burial at the Old Wauneeta Roadcut in southwestern Nebraska, USA (photoRiver in central Nebraska, USA (photo by Joseph Mason).

deposits (Basile-Doelsch et al., 2005; Zech, 2006), aeolian loess(Antoine et al., 2013; Mason et al., 2008), flood and alluvial sedi-ments (Blazejewski et al., 2009; Carter et al., 2009), colluvial ma-terial landslides and other mass wasting processes (Mayer et al.,2008; VandenBygaart et al., 2012), glacial sediments (Harris et al.,1987; Mahaney et al., 2001), or multiple types of depositionalmaterials (Rawling et al., 2003; Schirrmeister et al., 2013). Humanactivities can influence the rate and geographic extent of most ofthese depositional processes as well as contribute to the burial ofSOC under impervious surfaces in urbanized or constructedlandscapes.

Environmental conditions pre- and post-burial and specific todifferent depositional processes can influence the types of organicmatter that persist in deep buried soils. Not all SOC currently inburied horizons was there at the time of burial. Roots and bur-rowing animals can extend down into deep horizons and penetratethrough multiple paleosols in a soil profile (Gocke et al., 2010) sothat it may be difficult to isolate residual SOC from new inputs afterthe burial process. Disturbance events subsequent to burial can alsoresult in the delivery of more recent C into buried soil horizons. For

form (bottom panel): a) volcanic burial at Mt. Kilimanjaro, Tanzania (photo from Zech,modified from Feggestad et al., 2004); and c) alluvial burial at Pressey Park, South Loup

Table 1Examples of soil organic carbon (SOC) stocks in volcanically buried soil horizons below 1mdepth. Numbers (1, 2) indicate buried soils from different profiles or sites reported in the same study.We report mean and standard error(SE) SOC stocks for buried soils in cases when vertical sequences of multiple buried soils were reported by the authors. Total SOC stocks were calculated by summing SOC stocks for all buried soil layers within a soil profile. Burialtimes/soil ages are based on dates of the burial deposits or buried horizons as reported by the authors. YBP ¼ years before present; m.a.s.l. ¼ meters above sea level.

Buried soil Depthrange (cm)

Mean SOCstocks(kg C/m2)

SE SOCstocks(kg C/m2)

Total SOCstocks(Mg C/ha)

Burial time or soil age (y) Location Current vegetation MAT (�C) MAP (mm) Altitude(m.a.s.l.)

Reference

1) Tlaloc P 95e142 1.6 0.5 62.0 6200 � 85 Mexico Pine forest 10e14 1000e1200 3100 Peña-Ramírezet al., 2009

2) Chautzin P 79e270 3.7 1.3 256.6 1835 � 55 Mexico Pine forest 10e14 1000e1200 31003) Pelado P1 82e200 1.9 1.1 77.8 9620 � 160 to 10,900 � 280 Mexico Pine forest 10e14 1000e1200 31004) Pelado P2 88e180 3.0 1.8 89.7 9620 � 160 to 10,900 � 280 Mexico Pine forest 10e14 1000e1200 31005) Malacatepetl P 95e290 0.8 0.5 41.5 30,500 � 1160 Mexico Pine forest 10e14 1000e1200 31006) Malacatepetl A 75e293 2.4 0.3 143.8 30,500 � 1160 Mexico Fir forest 10e14 1000e1200 3200

1) 1750 N 100e210 0.4 0.0 48.7 55,000 YBP to early Holocene Tanzania Up tow1800 m.a.s.l.:savannah/cultivatedland. Abovew1800 m:sub-montane andmontane forests

Max 3000mm/yearbetween 2000and 2400 m.a.s.l.,much less aboveand belowthose elevations

1750 Zech et al., 20142) 1850 N 100e250 0.5 0.0 53.7 18503) 1400 W 100e130 0.6 0.0 18.2 14004) 1700 N 100e200 0.8 0.1 40.0 17005) 2800 N 100e300 2.3 0.5 411.1 28006) 2200 N 100e160 3.9 0.9 117.9 22007) 2600 N 100e210 5.7 0.8 627.4 26008) 1700 100e160 1.8 0.2 105.7 17009) 2350 100e200 3.6 0.6 285.4 235010) 1750 100e215 3.2 0.7 319.0 175011) 2140 100e215 10.3 4.5 413.4 214012) 2450 100e230 4.7 1.6 282.1 245013) 2250 100e235 6.6 0.7 463.9 225014) 750 100e300 0.4 0.1 28.5 75015) 1430 100e300 2.1 0.1 213.8 143016) 2750 115e160 8.1 2.1 242.8 275017) 2550 115e213 4.1 0.8 122.5 2550

1) Tephra ash 90e276 3.2 1.0 511.6 31,700 YBP and earlier La Réunion Forest 13 1700 1720 Basile-Doelschet al., 2005

1) Sandy loam 560e590 1.2a 0.1 36.1 79 AD Pompeii, Italy Urban 5.7 Vogel andMärker, 2011

2) Sandy loam 640e670 1.0a 0.3 30.2 Urban 6.13) Sandy loam 550e600 0.5a 0.1 27.3 Urban 7.64) Sandy loam 610e670 1.2a 0.2 70.7 Urban 7.75) Silty loam 610e670 2.2a 0.1 130.8 Urban 8.9

a Estimated using mean soil bulk density (0.6 g/cm3) for volcanic paleosols from Zech et al. (2014) and Basile-Doelsch et al. (2005).

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N.T. Chaopricha, E. Marín-Spiotta / Soil Biology & Biochemistry 69 (2014) 251e264 255

example, in the Rocky Mountains, the accumulation of black C indeep buried soil horizons was attributed to the incorporation ofnew inputs from recent surface burning that were transporteddownwards during clay translocation (Leopold et al., 2011).

In the following sections, we examine different burial processesand discuss how differences in the time scales, geographic extent,and properties of the sediment and depositional environmentaffect the amount and persistence of SOC. We provide generaliza-tions on the relative amounts of SOC buried under differentdepositional processes and the frequency and spatial occurrence ofspecific burial processes with the awareness that geographic biasesby researchers investigating buried soils could very well contributeto some of these observed differences. We report values for SOCconcentrations (mg C/g soil) for different depositional processes inTables 1e4 as provided by the authors. For volcanic and loess soils(Tables 1 and 2), we also estimated SOC content (kg/m2) using bulkdensity values for similar buried soils.

3.1. Volcanic deposits

Tephra and lava flows have buried soils around the world inregions with currently or formerly active volcanoes under widelyvarying climates and vegetation types. Volcanic events oftenoccur repeatedly over geologic and historic periods of time,resulting in multiple layers of vertical paleosol sequences such asthose found on the southern slopes of Mt. Kilimanjaro inTanzania (Zech et al., 2014) and near the Nevado de Toluca vol-cano in Central Mexico (Sedov et al., 2003, 2001). The globalextent of soil buried through volcanic deposition tends to beconcentrated in specific regions under the influence of paleo oractive volcanism, unlike other depositional events with muchwider geographic footprints.

Volcanic deposition typically occurs very rapidly, burying livevegetation and organic residues in soils under flows of lava, ash,pumice, or debris avalanches. The properties of the volcanic de-posits are likely to affect the rate of burial, the depth of the deposits,and the potential transformations of organic matter. During certaincombustion conditions, plant and soil organic matter can be con-verted into condensed aromatic structures known as black C, whichcan persist in some soil environments for thousands of years(Spokas, 2010). Burial by volcanically-derived dust during cold andarid glacial periods is thought to have contributed to the accumu-lation of SOC-rich (100 mg/g soil) paleosol sequences up to 3 mdeep on the slopes of Mt. Kilimanjaro in Tanzania (Zech et al., 2014).

Soils developing on weathered lava tend to accumulate highamounts of organic C due to the abundance of noncrystalline oramorphous minerals (Basile-Doelsch et al., 2005; Torn et al., 1997).The high sorptive capacity of most volcanic soils and the presenceof black C can lead to the long-term persistence of high amounts ofSOC. In a tephra-soil sequence in central Japan, the oldest buriedsoil layer at a depth of 4 m from a ca. 29 cal ka BP eruption wasfound to contain the highest C concentrations (>60 mg/g soil)(Inoue et al., 2011).

In the literature surveyed, volcanic paleosols showed a widerange of mean SOC contents, from a low of 0.4 � 0.1 kg C/m2 to ahigh of 10.3 � 4.5 kg C/m2 (Table 1), which could reflect the di-versity of current and past climates where volcanic activity wascommon. There are no consistent trends between depth of buriedsoil and SOC stocks. The different types of volcanic sediments,from ash to pumice to lava, are expected to affect the permeabilityof overlying deposits, the isolation of buried SOC from surfaceconditions, and the rate of weathering. The amount of SOC involcanic soil profiles that include multiple buried horizons isaffected by soil age and mineral composition (Basile-Doelsch et al.,2005), although the specific mechanisms influencing SOC

persistence may differ for modern surface soils and paleosols(Peña-Ramírez et al., 2009).

3.2. Loess deposits

Aeolian deposits formed from the accumulation of windblowndust tend to exist in currently or formerly arid areas with a dustsource, wind, and minimal vegetative cover. Such conditions havedeveloped through the wind erosion of deserts and during degla-ciation as glacial meltwater decreased and floodplains dried up,exposing glacial silts and clays to erosional winds. Loess depositioncan cover very large geographic areas such as the U.S. Great Plains(Bettis et al., 2003) and plateaus in western China (Lu and Sun,2000). The resulting soil building process tends to occur gradu-ally, sometimes over thousands of years, as dust accumulates andsoil thickness increases over time. In the U.S. Great Plains, grasslandMollisols aggraded throughout the Holocene as loess accrued inmultiple events due to changes in climate and vegetative cover,resulting in sequences of A horizons that developed at the end ofthe Pleistocene and today are buried up to several meters below themodern soil surface (Jacobs and Mason, 2005).

Our review of the literature revealed that many paleosols inloess deposits tend to have low SOC concentrations (Table 2), whichin part may be related to the formation of these soils during rela-tively brief periods of slower loess deposition in environments withlow primary production. Episodes of dune mobilization and winderosion can be associated with periods of aridity and increasing firefrequency, leading to the accumulation of black C in buried soilsoverlain by loess sediments (Marín-Spiotta et al., in review; Wanget al., 2005). The highest SOC stocks found in paleosols werethose in Siberian yedoma loess permafrost (Table 2), which formswhen wind-blown sediments bury roots and other organic matterthat then become incorporated into deeper permafrost. Loesspermafrost can contain consistently large SOC content down 20 or30 m (Zimov et al., 2006a). Freezing temperatures protect yedomaSOC from decomposition, making these buried soils highlyvulnerable to changes in climate.

3.3. Alluvial and colluvial deposits

Sediment deposited in stream terrace fill, alluvial fans, andoverbank floodplain deposits can also bury and stabilize SOC. Thick,dark A horizons buried in alluvial deposits were found in U.S.Central Plains stream valleys as deep as 11 m below ground, wherethey have been buried for approximately 10,000 years (Mandel,2008). Floodplain sediments can bury peat, as they have in theMkuze coastal floodplain of South Africa, protecting organic matterfrom threats to currently exposed peatlands for approximately6000 years (Ellery et al., 2012). In Venezuela, a sequence of severalpeat paleosols was found buried under alluvium, and one buriedpeat layer at a depth of 13 m from an interglacial period 60e70,000years ago contained approximately 150e750 mg SOC/g soil(Mahaney et al., 2001).

Riparian zone soils store considerable SOC in buried organic-rich soil horizons. In the Pawcatuck River watershed of Rhode Is-land, 17 of 22 sites studied contained OC-rich material buried informer surface horizons or lenses beneath alluvial deposits at depthbelow 1 m and up to 3.5 m (Blazejewski et al., 2009). Buried SOC insaturated riparian areas can take thousands of years to decomposedue to low oxygen availability (Blazejewski et al., 2009, 2005) butmay become vulnerable to decomposition if drained through hu-man or geomorphic alterations to hydrologic flow. In some areas,riparian zone alluvial and outwash areas have high rates of mi-crobial activity, indicating that buried soils in riparian areas can be

Table

2Ex

amplesof

soilorga

nic

carbon

(SOC)stoc

ksin

aeolian-buried

soilhorizon

sbe

low

1m

dep

th.N

umbe

rs(1,2

)indicatebu

ried

soils

from

differentprofilesor

sitesreportedin

thesamestudy.W

ereportmea

nan

dstan

darderror

(SE)

SOCstoc

ksforbu

ried

soils

incaseswhen

vertical

sequ

encesof

multiple

buried

soils

werereportedby

theau

thors.To

talS

OCstoc

kswerecalculatedby

summingSO

Cstoc

ksforallb

uried

soillaye

rswithin

asoilprofile.B

urial

times/soilag

esareba

sedon

dates

ofthebu

rial

dep

ositsor

buried

horizon

sas

reportedby

theau

thors.YBP¼

yearsbe

fore

present;

m.a.s.l.

¼metersab

ovesealeve

l.

Buried

soil

Dep

thrange

(cm)

Mea

nSO

Cstoc

ks(kgC/m

2)

SESO

Cstoc

ks(kgC/m

2)

TotalSO

Cstoc

ks(M

gC/ha)

Burial

timeor

soilag

e(y)

Location

Curren

tve

getation

MAT(�C)

MAP

(mm)

Altitude

(m.a.s.l.)

Referen

ce

Minusinsk

7.15

e8.00

3.9a

2.1

118.4

Upper

Pleistoc

ene

to38

,900

YBP

Western

Sibe

ria,

Russia

Biryu

kova

etal.,20

081)

Buried

soil2

1.70

e1.90

0.73

7.26

2580

�15

0to

6600

�40

0Neb

raska,

USA

Shortgrass

prairie

9.7

495

Fegg

estad

etal.,20

042)

Buried

soil3

2.60

e3.10

0.61

6.05

6600

�40

03)

Bradysoil

5.50

e6.75

1.05

0.34

42.05

10,250

�65

0Nan

guan

zhuan

g1.25

e3.55

5.3a

0.9

263.8

3100

e11

,500

calYBP

S.Lo

essPlatea

u,C

hina

Agriculture

1262

960

0e75

0Huan

get

al.,20

02Milfordloess

2.05

e4.90

2.6a

1.5

105.0

Tallg

rass

prairie

19.3

843

360

Karlstrom

etal.,20

081)

Yeo

dem

a1

1.00

e16

.052

.9b

11.5

8465

Pleistoc

ene

NorthestSibe

ria,

Russia

Forest

tundra

Zimov

etal.,20

06a,b

2)Yeo

dem

a2

3.00

e37

.055

.08.3

8250

Forest

tundra

aEstimated

usingsoilbu

lkden

sity

(1.21g/cm

3)forloesspaleo

sols

from

Marín-Spiottaet

al.(in

review

)bEstimated

usingsoilbu

lkden

sity

(1.65g/cm

3)forye

odem

aloesspaleo

sols

from

Schuuret

al.(20

08).

N.T. Chaopricha, E. Marín-Spiotta / Soil Biology & Biochemistry 69 (2014) 251e264256

important hotpots of C mineralization and of denitrification(Gurwick et al., 2008a, 2008b).

Typical SOC values of paleosols in alluvial sediments reportedin the literature range from 3 to 35 mg/g at depths commonly upto 4 m but also as deep as 8 m (Table 3). Our review found thatSOC stored under alluvial deposits tended to be more recentlyburied, within the Holocene, than SOC under volcanic and loessdeposits, possibly because soils buried under alluvial sedimentsare prone to continued disturbance, exposure, and reburial inareas where fluvial processes continue to operate.

Colluvium, or the accumulation of loose, eroded materialdropped at the base of hillslopes by mass wasting processes, canquickly bury vegetation and soils. In landscapes prone to frequentsuccessive debris flows such as areas above the treeline or otherhigh-altitude ecosystems, buried soils are characterized by thinorganic layers, as they do not have time to accumulate betweensedimentary events (Matthews et al., 1999). Colluvial paleosolsare often prone to disturbance after burial due to subsequenterosion by the same processes that created them in the first place(Temme et al., 2012). The rate of burial by colluvial activities canbe a lot faster than that by other depositional processes, partic-ularly those driven by wind erosion.

3.4. Glacial deposits

Soil burial rates by alpine and mountain glacier depositionalprocesses operate on a range of time scales due to the diversity ofdelivery mechanisms and types of sediments deposited, rangingfrom glacial till to meltwater. Burial can be instantaneous on oc-casions when a proglacial lake ice dam ruptures and sendssediment-laden waters flooding downstream. Soils buried bysediment from a proglacial lake in Norway that drained 200e300years ago showed SOC values of 77e6mg/g between 1.5 and 1.8 mdepth (Harris et al., 1987). Soils buried under glacial deposits canexist at the edge of currently glaciated landscapes as well as inmuch wider geographic regions with a diversity of temperaturesbut with a common glacial history. Till, glaciofluvial, and glacio-lacustrine deposits from up to 60 kyr BP have buried paleosols atmultiple depths containing very high SOC contents of 150e750 mg/g (Mahaney et al., 2001). Sometimes, multiple deposi-tional processes bury soils at one site (Table 4).

3.5. Anthropogenic deposits and structures

The field of archeology has focused on buried soils to facilitatethe discovery of cultural artifacts and provide insight into pasthuman environments. Some information on SOC buried by pre-historic human constructions exists from burial mounds and theirunderlying soils in remains from the Bronze Age in Denmark(Thomsen et al., 2008) and from steppe kurgans in the centralRussian Plain (Demkina et al., 2010). Studies of buried soils fromthe Neolithic settlement region in the Lower Rhine area in Ger-many have contributed to reinterpretations of ancient humanland use and history of soil erosion (Gerlach et al., 2012).

Humans move massive amounts of soil and sediment that canrival the effect of geologic events (Haff, 2010; Wilkinson andMcElroy, 2007). Human activities such as tillage during soilcultivation, soil movement during construction, and direct andindirect alterations to geomorphic processes can lead to the burialof SOC transported with the eroding material as well as photo-synthesized in situ at the depositional site. The effects of agri-cultural practices on local erosional transport and burial of C arebetter quantified than the effects of other types of human activ-ities, although uncertainties still exist in the spatial and temporalextent of C losses versus gains at the landscape and regional scales

Table 3Examples of soil organic carbon (SOC) concentrations of alluvially-buried soil horizons below 1 m depth. Numbers (1, 2) indicate buried soils from different profiles or sites reported in the same study. Letters (a, b) indicatemultiple buried soil horizons within a vertical profile. Burial times and soil ages are based on dates of the burial deposits or buried horizons as reported by the authors. YBP¼ years before present; m.a.s.l.¼meters above sea level.

Buried soil horizon(s) Depth (m) SOC (mg C/g soil) Burial timeor soil age

Location Currentvegetation

MAT (�C) MAP (mm) Altitude (m.a.s.l.) Reference

1a) Ab3 2.3e3.4a 4.5e7a Late Holocene Southern Plains,Oklahoma, U.S.:1) Carnegie Canyon2) Lizard Site

Prairie (Carter et al., 2009)1b) ABb3 3.4e3.5a 3a

1c) Bkb3 3.5e4.0a 1e2a

1d) Cb3 4.1a 0.5a

2a) A2b 1.3e1.8a 7e8a

2b) Btssb2/Btb2 1.8e2.5a 3e8a

2c) BCb2 2.5e3.3a 2e3a

Four buried A horizonsunder coarse overbankdeposits in karst area

2e3.3a 15e35a,b Late Holocene Rio Indio floodplain,Vega Baja, Puerto Rico

(Clark et al., 2003)

1a) 2Bkb1 1.07e1.35 5.13 Late Holocene Upper Prairie 500 (Daniels, 2003)1b) 2Bkb2 1.35e1.60 4.99 Republican River

Basin, CentralGreat Plains, U.S.1) Nichols Site2) State Site

1c) 2Bkb3 1.60e2.25 7.221d) 2Bw 2.25e3.25 4.041e) 2BC 3.25e4.00 1.01

2a) 4Akb1 0.95e1.12 8.822b) 4Akb2 1.12e1.41 10.122c) 4ABkb 1.41e1.70 7.222d) 4Ckb1 1.70e1.95 7.222e) 4Ckb2 1.95e2.15 5.122f) 4Ckb3 2.15e2.40 4.16Interbedded sand and mud

stream channel sediments(river channel migration)

1.6e2.7 21.9 Near Toronto, Ontario,Canada

Mixed forest,marsh

205a (Hill and Cardaci, 2004)

Buried Mollisols in floodplains 1.0e5.1a 5e40 Since 735 B.C. Platte River system,Southwestern Wisconsin(Hinderman Site 1)

Agriculture (Knox, 2001)

Floodplain soil 1e5.3a (core AKIII) 2e13a 1250e2900 cal YBP Adigrat, Tigray Plateau,Ethiopia & Eritrea

Grassland 619 2493 (Terwilliger et al., 2011)

1) Ab 1.975 83 Pawcatuck Watershed,Rhode Island, USA

Riparian forests (Gurwick et al., 2008a,b)2) Ab 1.005 1263) Ab 2.025 94

a Values were approximated from figures.b Values were obtained from organic matter amounts using the formula OC ¼ OM/2.

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Table 4Examples of soil organic carbon (SOC) concentrations in soil horizons buried below 1 m depth under glacial, erosional, and multiple types of deposits. Letters (a, b) indicate multiple buried soil horizons within a vertical profile.Numbers (1, 2) indicate buried soils from different profiles or sites reported in the same study. Burial times and soil ages are based on dates of the burial deposits or buried horizons as reported by the authors. YBP ¼ years beforepresent; m.a.s.l. ¼ meters above sea level.

Burial processes Buried soil horizon(s) Depth (m) SOC(mg C/g soil)

Burial time or soil age Location Current vegetation MAT (�C) MAP (mm) Altitude (m.a.s.l.) Reference

Till, glaciofluvial,and glaciolacustrinedeposition

Vertical sequenceof sandy peat paleosolswithout clay transformationor aeolian deposition

8.6e13.9a 0e750a Wisconsinan/WeichselianGlaciation(up to 60,000 YBP)

Northern VenezuelanAndes

Agriculture:potatoes, grazing

10 100 3550 (Mahaneyet al., 2001)

Colluvium fromhillslope erosionin intermontane basin

a) Bkb3 1.05e1.35 1 Holocene Middle Park,Colorado, USA

Big sagebrush,grasses

12.9 to �5.7(max/min)

255 2350 (Mayeret al., 2008)b) 2Brkb3 (dark

carbonate-rich horizons)1.35e1.85þ 1

Colluvium (erosionalsediment) deposition

Aggraded sandy loamcropland soil below plowline (Orthic Humo-FerricPodzol): B horizon

1a 10a Since 1955 Grand Falls, NewBrunswick, Canada

Agriculture:potatoes, forage

(VandenBygaartet al., 2012)

Loess, fluvial, andvolcanic tephradeposition

a) Paleosol 4 1.0a 6.9 3000e7000 YBP Stampede site,Cypress Hills, Alberta,Canada with thin,weakly developedpaleosols

Aspen forest 1238 (Klassen, 2004)b) Paleosol 5A 1.3a 24.8c) Paleosol 6 1.6a 11.1d) Paleosol 7 1.7a 16.0e) Paleosol 8 1.75a 6.1f) Paleosol 10 2a 11.1g) Paleosol 11/12 2.1a 7.1h) Paleosol 13 2.35a 9.0i) Paleosol 14 2.9a 3.2j) Paleosol 15 3.1a 9.1k) Paleosol 16 3.45a 10.7

Loess, fluvial,and colluvialdeposition inaeolian cliff-topdeposits

a) Cumulic Ab1 1.00e1.47 7 1263 YBP2003e2036 YBP2355 YBP4152e4219 YBP6665e8588 YBP

S. Dakota WhiteRiver Badlands, USA

Semi-arid mixedgrass ecosystem

10.3 400 950 (Rawlinget al., 2003)b) Ab1 (darker) 1.47e1.52 8

c) Cb1 1.52e1.62 7d) Ab2 1.62e1.80 7e) Cb2 1.80e1.90 5f) Ab3 1.90e2.05 6g) Cb3 2.05e2.15 5h) ABb4 2.15e2.70 4i) BCb4 2.70e2.80 3j) Gravel 2.80e2.98 2k) Sand 2.98e3.20 1

a Values were approximated from figures.

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(Quinton et al., 2010). The redistribution of SOC by agriculturalactivities is significant: during the last 50 years, an estimated 16e21 Pg C of SOC are thought to have been buried on agricultural lands(Van Oost et al., 2007). While much of this erosion leads to shallowburial, repeated events over time can lead successive layers ofsediment. In Belgian croplands under continuous cultivation for atleast 250 years, up to 2.5 m of soil accumulated in depositionalareas on the landscape, contributing to up to 6 times greater SOCstocks than in eroding areas (Doetterl et al., 2012). Landscapedestabilization by human removal of vegetation or alteration ofriver channels and floodplains can also trigger or magnify the ef-fects of other geomorphic processes (Knox, 2001). A recent analysisof OC burial in soil sediments in agricultural landscapes fromCentral Europe reported mean OC stocks of 3.1 � 1.0 kg C/m2 and5.0 � 1.3 kg C/m2 for hillslope and floodplain soils, respectively(Hoffmann et al., 2013).

Few studies have quantified SOC storage under urban environ-ments. One calculation of C storage in U.S. urban soils down to 1 massumed that SOC pools were negligible below that depth, despiterecognizing that this method ignored the SOC in buried A horizonsin fill soils (Pouyat et al., 2006). A study of the U.K. city of Leicester,which is 15% covered by pavement, buildings, and other imperviouscapped surfaces, found no significant difference in SOC stocks incapped vs. greenspace soils at equivalent depths down to 1 m andfound higher SOC under capped soils than in nearby arable fields(Edmondson et al., 2012). The authors conclude that soils in urbanenvironments may continue to be influenced by vegetation andlose less SOC over time while conventional agricultural practicestend to deplete soils of OC. It is unknown how construction andother soil disturbance events that are common practice in urban-ized environments contribute to the long-term preservation of SOCin soils under anthropogenic impervious surfaces.

4. State factors affecting SOC accumulation and stability inburied soils

The preservation of undecomposed wood dated tens of 1000s ofyears old in deep buried soils (e.g., Orlova and Panychev, 2006)provides supporting evidence that burial can contribute to long-term persistence of OC and is consistent with current perspec-tives on the importance of environmental conditions in regulatingSOC turnover time (Schmidt et al., 2011). The specific processescontributing to slow turnover times and old radiocarbon ages ofSOC in deep soils have been the subject of numerous reviews(Rumpel and Kögel-Knabner, 2011; Salomé et al., 2010; Schmidtet al., 2011; Torn et al., 2009; Trumbore, 2009): depressed micro-bial biomass and activity due to low rates of oxygen diffusivity, lowsoil moisture and nutrient availability; the microbial recycling ofaged C compounds; and aging during the slow, downward migra-tion of C that escapes mineralization from upper soil horizons. Thefirst two mechanisms contribute to the long-term persistence ofSOC present in the soil at the time of burial, while the third affectsincorporation of OC following burial. Processes that contribute toslow turnover times for SOC in surface soils and prevent its lossfrom the soil profile, such as the incorporation of OC into soil ag-gregates and associations with mineral surfaces, cations or metals(Lorenz et al., 2011; Six et al., 2002; Torn et al., 2009; Von Lützowet al., 2006), also apply to buried mineral soils. Here, we focus onhow the state factors of soil formationdclimate, organisms, relief,parent material, and time, sensu Jenny (1941)daffect the potentialof different burial processes to contribute to the accumulation andlong-term persistence of deep SOC. The stability of SOC in a buriedhorizon is directly influenced by the burial process as well as by theproperties of both the buried soil and the overlying depositionalmaterial.

4.1. Effects of climate on buried SOC

Climate during soil pedogenesis and at the time of burial canhave an important influence on the content, composition, andpersistence of OC in deep buried horizons. Climate can affect themagnitude and frequency of specific burial processes; forexample, extremely wet and dry periods promote alluvial andaeolian deposition, respectively. In the U.S. Central Great Plains,higher accumulations of SOC in a paleosol of a multiple sequencehave been attributed to periods of higher primary production atthe time of soil formation during the PleistoceneeHolocenetransition, while subsequent increasing aridity led to its burialunder successive events of loess deposition (Feggestad et al.,2004). Changes in climate that lead to multiple freezeethaw cy-cles are known to influence the rate of incorporation of surfaceSOC into deeper permafrost layers by vertical mixing (Becheret al., 2013; Koven et al., 2009). In buried permafrost loess andpeat soils, frozen temperatures currently preserve deep SOC, butthawing due to future atmospheric temperature are predicted toaccelerate microbial decomposition and lead to large OC loss(Schuur et al., 2008; Tarnocai et al., 2009; Zimov et al., 2006a,2006b).

Deep soils in well-drained profiles tend to have a smaller rangeof temperatures and lower levels of moisture than surface horizons,which commonly leads to low microbial activity (Rumpel andKögel-Knabner, 2011; Salomé et al., 2010). Low soil moistureinhibited respiration rates of buried soils in arid loess deposits inthe U.S. Central Great Plains (Chaopricha, 2013) and of paleosolscollected under burial mounds in the dry Russian steppe (Demkinaet al., 2010). The response of paleosols buried 1700 and 4000 yearsto moisture treatments did not differ, but the magnitude of theirresponse was lower than that of modern surface soils (Demkinaet al., 2010). In contrast, waterlogging within a 3330-year-oldburial mound in Denmark resulted in marked differences in themicrobial biomass and chemical composition of SOC in anaerobicand aerobic microsites (Thomsen et al., 2008).

The depth and structure of overlying deposits affect the rate ofgas exchange with the atmosphere as well as the transport ofwater, nutrients, and microorganisms down to a buried horizon.Most paleosols can be influenced by current surface conditionsthrough slow leaching and translocation. Preferential flow-pathscan deliver particulate and dissolved OC from surface organichorizons to mineral subsoils in shrink-swell soils (Marín-Spiottaet al., 2011), and aquifer advection can transport young, surface-derived OC to soil horizons as deep as 11 m (Mailloux et al.,2013). Post-burial changes in groundwater levels can transformpaleosols, as evidenced by redoximorphic features in Romanpaleosols in the ancient ruins of Pompeii (Vogel and Märker, 2011).These changes in redox can accelerate pedogenesis as well as themobility of SOC (Hall and Silver, 2013). Future changes in precip-itation projected with climate change for many regions of theworld can alter current hydrologic patterns that can both recon-nect or disconnect buried soil horizons from surface biologicalprocesses (Holden, 2005).

4.2. Biotic controls on buried SOC

Plants and soil micro- and macroorganisms, such as animals,bacteria, and fungi, affect the quantity of SOC in soils before andafter burial by influencing rates of OC inputs, decomposition andmobilization. High rates of primary production during periods ofwarming and increased precipitation resulted in the buildup of SOCin soils that were subsequently buried by loess during periods oflow vegetative cover that destabilized dune sources (Feggestadet al., 2004). High amounts of SOC in buried volcanic soils can

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also be attributed to high fertility soils typical of many volcanicparent materials (Torn et al., 1997).

Bioturbation by cicadas, earthworms, and small mammals cantransport fresh OM to the mineral subsoil (Don et al., 2008;Wilkinson et al., 2009), where the potential for stabilization in-creases. Bioturbation can also increase the exchange of soil gasesand water through the promotion of preferential flow paths, thuspotentially reducing the stability of deep SOC by reconnectingburied soils with modern surface conditions. Post-burial additionsof OC from plant roots extending into deep soils (Davidson et al.,2011) can facilitate microbial decomposition of ancient SOC(Fontaine et al., 2007) and alter the composition of buried soils(Gocke et al., 2010).

The activity of microbial decomposers in deep and buried soils ispoorly understood. Isolation from fresh OC inputs, low nutrientconcentrations, and the great spatial patchiness of substrates canlead to reduced microbial biomass and a decrease in functionaldiversity with increasing soil depth (Ekschmitt et al., 2008; Fiereret al., 2003). Microbial biomass from soils deep within BronzeAge burial mounds and an underlying paleosol several metersbelow the surface were 10e20 times lower than those in a nearbyarable topsoil (Thomsen et al., 2008). Respiration rates of incubatedsoils from burial mounds responded to addition of a labile C sub-strate (glucose) with a two to three week lag compared to modernsurface soils (Thomsen et al., 2008).

Microbial transformations of SOC post-burial can alsocontribute to the persistence of buried SOC. The role of microbialprocessing in the formation of stable SOC, through preferentialsorption of microbial products to mineral surfaces or through oc-clusion within micropores, is increasingly being recognized(Knicker, 2011; Miltner et al., 2012; Schmidt et al., 2011), especiallyin deep soils (Liang and Balser, 2008). A study of burial mounds inthe central Russian Plain steppe found that the contribution ofmicrobial biomass lipids to the bulk SOC pool increased withburied soil depth and age of the burial mound (Khomutova et al.,2011).

4.3. Influence of topographic relief on soil C burial processes

A landscape’s geomorphology and erosional patterns affect thedistribution of deep SOC as sediment accumulates in differentlandscape positions, creating spatial variability in SOC distribution(Rosenbloom et al., 2006; VandenBygaart et al., 2012). Erosionremoves C from surface soils and buries it in another locationwhereit may become stabilized (Berhe and Kleber, 2013; Berhe et al.,2007). Studies of SOC in erosional and depositional sites alongtopographic gradients report differences in the distribution of SOCpools associated with clay surfaces and with soil aggregates, sug-gesting geomorphic and pedogenic controls on the physical pro-tection of residual and accumulating SOC (Berhe et al., 2012;Doetterl et al., 2012).

Topography can also affect the relative frequency and extentof different burial processes. Steep topographic regions tend tohave more erosion, leading to soil burial under colluvium.Different types of buried soils are likely to be found in specificlandscape positions, such as volcanic soils downslope of volcanicpeaks (Zech, 2006), loess deposits downwind of regional sourceareas (Feggestad et al., 2004), alluvial soils in old river banks(Knox, 2006), colluvial soils in downslope topographic positionswhere eroded material is deposited (Mayer et al., 2008), andglacial deposits at high elevations or northern latitudes nearcurrently or formerly glaciated landscapes (Mahaney et al.,2001). The spatial distribution and thickness of loess sedimentsoverlying buried soils is affected by landform type and slope(Jacobs et al., 2012).

4.4. Effects of parent material on SOC persistence in buried soils

Buried SOC content and persistence are affected by the type ofparent material of the buried soil and of the overlying and under-lying layers within a profile. A soil’s sourcematerial andmineralogyaffect its particle size distribution and texture-related mechanismsfor SOC stabilization (Fabrizzi et al., 2008; Hassink et al., 1997;Jenny, 1941; Krull et al., 2003). Clay content is strongly correlatedwith SOC storage in deep soil layers (Jobbágy and Jackson, 2000).SOC content and radiocarbon age are strongly influenced by type ofmineral composition, which can vary with parent material as wellas weathering stage (Torn et al., 1997). Buried tropical volcanic ashsoil horizons with poorly crystallineminerals storedmore SOCwithslower turnover rates than similar horizons containing more crys-talline minerals, such as feldspars and gibbsite (Basile-Doelschet al., 2005).

The depth, structure, and composition of material above andbelow buried soils can affect the diffusivity of oxygen and soilmoisture conditions. Soil texture also affects water retention ofdeep soils (Sotta et al., 2007), influencing soil CO2 efflux and mi-crobial activity. The presence of an impermeable Fe layer under apaleosol buried under a 7-m tall 3330-year-old burial mound inDenmark led to the formation of a water-logged basin within itsinterior, affecting the decomposition of buried SOC (Thomsen et al.,2008). Soil development of overlying sediment over time, espe-cially in coarser sediments such as loess deposits, can alter soilhydraulic properties (Beerten et al., 2012) and the connectivity ofthe underlying buried soil with the atmosphere.

4.5. Timescale effects on buried SOC

SOC storage in buried soils is affected by the timescale of theburial process as well as the amount of time since burial. The burialof a surface soil by a depositional material can happen instanta-neously, such as during a volcanic eruption or glacial lake damrupture. Soil burial can occur repeatedly over long periods of time,such as with sequences of volcanic eruptions (Sedov et al., 2001),gradual loess deposition over thousands of years (Feggestad et al.,2004; Zech et al. 2013), and river overbank deposits fromrepeated floods (Daniels and Knox, 2005).

The rate of sediment accumulation can affect the number ofburied horizons in a profile. Very slow deposition rates are morelikely to contribute to the formation of thicker surface soil A hori-zons (Daniels, 2003), while soil burial is more likely to occur whenrates of sediment aggradation exceed that of soil development. Avertical sequence of multiple buried soils is representative of in-termediate frequency of sediment deposition, which allow forpedogenesis in between burial events.

The type of burial process can also affect the time scales of SOCpersistence and preservation. A study comparing the reliability ofradiocarbon dating of buried SOC concluded that risk of OCcontamination was greatest in loess deposits due to more gradualaccumulation than in alluvial and flood deposits where burial canoccur relatively quickly and where an individual event will tend todeposit thicker sediments (Orlova and Panychev, 2006). In a studyof Japanese Andisols, estimates of past OC inputs based on phyto-liths and other SOCmeasurements suggested that the high levels ofC buried by successive tephra deposits had not substantiallydecreased over the thousands of years since burial (Inoue et al.,2000).

5. Vulnerability of buried SOC to environmental change

Alteration or disruption of the specific mechanisms contributingto the protection of buried SOC frommineralization or from loss via

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leaching can lead to the reduction of SOC pools in buried soils.Changes in environmental properties regulating the decompositionand persistence of SOC in buried soils can occur through changes inthe structure of overlying horizons that alter some of the mecha-nisms that had previously isolated the buried soil from surfaceconditions or by exposure to the atmosphere through lateral andvertical erosion. Gully erosion in the Drakensberg escarpmentfoothills in South Africa has revealed a sequence of paleosols incolluvial sediment (Temme et al., 2012). The existence of multiplesequences of buried horizons in loess deposits extending across alarge area of the U.S. Central Great Plains (Miao et al., 2007) becameknown to researchers through exposure from road construction.

The sensitivity of buried SOC to changing environmental con-ditions varies with the properties of the mineral matrix and theorganic matter, but recent research suggests that deep, ancient SOCcan respond to disturbance on annual to decadal time-scales(Devine et al., 2011; Harrison et al., 2011; Veldkamp et al., 2003).In buried soils where OC has been preserved due to isolation fromconditions favorable for microbial respiration, exposure to the at-mosphere and inoculation with microbial biomass is expected tolead to large losses of SOC.Wetting of paleosols collected below 1munder 4000-year old burial mounds resulted in comparable respi-ration rates to those of modern surface soils in the arid Russiansteppe (Demkina et al., 2010). Deep SOC pools have been shown tobe more responsive to increased temperature during experimentalmanipulations than surface soil horizons (Schwendenmann andVeldkamp, 2006). On the other hand, buried SOC that may havebeen biochemically altered before or during the burial process(such as during a fire) or since burial may not respond to envi-ronmental change as rapidly (Chaopricha, 2013).

The effects of climate change on buried SOC are complex andpoorly understood. Changing precipitation patterns coupled withlandscape disturbance could alter hydrologic flowpaths and in-crease soil erosion. These processes can reconnect deep SOC withbiologically active surface soil horizons and lead to the exposure ofburied SOC to the atmosphere. Buried peatlands, which storeconsiderable amounts of OC, are vulnerable to changes in drainagethat accelerate decomposition and increase susceptibility to fire,especially in areas where fire is used to clear vegetation (Limpenset al., 2008). Changes in hydrologic processes or erosion ratesthat disrupt the accumulation of clastic sediments on floodplainpeat can also minimize the protection of buried peats to fire (Elleryet al., 2012).

The effect of rising temperatures on buried and deep permafrostC pools has received great attention. Zimov et al. (2006b) estimatethat rising temperatures threaten 500 Pg of SOC in Siberian andAlaskan loess permafrost. Estimates of C release from thawingnorthern permafrost vary widely, partly due to uncertainties in SOCstocks, thawing rates, and the temperature sensitivity of decom-position (Tarnocai et al., 2009). Some authors estimate thatpermafrost SOC, which has accumulated over tens of 1000s ofyears, may be released to the atmosphere within a century (Zimovet al., 2006b). Others suggest that increased cryoturbation inthawing permafrost could lead to greater stabilization of SOC, inpart by transporting OC to deeper, colder layers with depressedmicrobial activity (Bockheim, 2007; Kaiser et al., 2007).

Less is known about the response of buried SOC to changes inland management or land use, although recent work suggests thatdeep SOC stocks are more sensitive than previously thought andcan show opposite responses than surface horizons (Baker et al.,2007; Li et al., 2010; Veldkamp et al., 2003). The conversion ofconventionally tilled agricultural land to managed successionalforests in the U.S. state of Georgia affected total SOC content only inthe top 5 cm of soil but resulted in an accumulation of C in par-ticulate form in soils up to 2 m depth (Devine et al., 2011). Changes

in land use and agricultural practices or hydrology that distributefresh C down the soil profile can prime microbial activity andstimulate the decomposition and release of deep ancient SOC(Fontaine et al., 2007). Buried soil horizons, where microbes areoften C-starved, may show greater responses to priming thanmodern surface soils (Zhuravleva et al., 2012). More research isneeded on how land use and other environmental changes affectdeep and buried SOC under different ecosystems (Harper andTibbett, 2013).

6. Implications of soil C burial for modeling and management

A more explicit incorporation of processes contributing to thedelivery, accumulation, and turnover of SOC in the subsoil isfundamental for improving predictions of belowground SOC poolsto environmental change (Schmidt et al., 2011). A growing body ofevidence suggests that SOC in deep and buried soils can become alarge source of ancient C to the atmosphere if reconnected to theatmosphere, and some of it may already be cycling more activelythan previously considered (Devine et al., 2011; Fontaine et al.,2007; Gurwick et al., 2008b; Trumbore, 1997). Despite the largestocks of OC in deep soils and their potential sensitivity to climateand land use change, most biogeochemical models include onlysurface or shallow soil C dynamics. Recent improvements tobiogeochemical process models include a vertical dimension to Cpools and transformations, the consideration of vertical mixingsuch as bioturbation, and the input of OC at various depths, ratherthan the trickle down of OC from surface horizons (Koven et al.,2013).

Given the importance of burial to long-term SOC storage, theincorporation of depositional processes across the landscape intomodels of SOC should improve predictions of whole-soil profile Cdynamics as well as regional C budgets. In Central Europe, rates ofSOC burial at the landscape level caused by post-Neolithic agri-cultural erosion were estimated to be about 170 times greater thanregional OC storage in lake and reservoir sediments, but theseprocesses are not included in continental C budgets (Hoffmannet al., 2013).

Our understanding of geomorphic controls on SOC has beengreatly improved due to recent research quantifying lateral andvertical C fluxes during erosion across topographic sequences inboth cultivated and non-cultivated landscapes and measuringprocesses leading to the release and protection of C at erosional anddepositional sites (Berhe et al., 2012; Doetterl et al., 2012; Van Oostet al., 2012; VandenBygaart et al., 2012) coupled with models ofsediment transport (Pelletier et al., 2011; Yoo et al., 2005). Toaccurately represent buried SOC dynamics, the following additionalinformation should be incorporated into vertically-resolved soilbiogeochemistry models: the type of depositional process (e.g.,alluvial, colluvial, volcanic, aeolian, anthropogenic, etc.), the rate ofburial, the amount of time since burial, the amount of SOC trans-ported in the sediment, the mineral and particle-size compositionof the aggrading sediment, and depths of the soil and sedimentlayers. This information provides a first approximation of the typesof mechanisms contributing to the accumulation or loss of SOC atdifferent depths. Inclusion of a process-based understanding ofhow environmental properties affect SOC decomposition and sta-bilization in different soil layers in soil C models (Schmidt et al.,2011) will improve predictions of the response of deep andburied SOC to future landscape disturbances driven by changes inclimate or human activities. The incorporation of physical mixing ofSOC into deeper soil horizons simulating cryoturbation in a landsurface model improved estimates of high-latitude SOC stocksdown to 3 m (Koven et al., 2009). Even still, lower model pre-dictions than other permafrost pool estimates (Tarnocai et al.,

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2009) were attributed by the authors to the exclusion of alluvialand loess depositional processes which lead to the accumulation ofsubstantial deep SOC (Koven et al., 2009). Burial processes arebetter represented in biogeochemical models of oceans, whereenvironmental conditions play an important role in the fate oforganic matter deposited in marine sediments (Kriest and Oschlies,2013).

From a management perspective, buried SOC pools can beprotected through practices that inhibit their exposure to the at-mosphere. Alternatives to soil tillage and drainage processes thatthreaten currently buried SOC pools and that are less disruptive tothe soil profile may prevent mobilization and losses of deep andburied SOC. Soil micro-environmental conditions and hydrologycould also be managed to stabilize SOC by considering crop choice,rooting depths, and crop residue retention. Assessments of man-agement practices on SOC need to consider the potential presenceof large buried SOC pools and the likelihood that the mechanismscontributing to their persistence could be disrupted under differentland use and climatic scenarios. The inclusion of geomorphic pro-cesses into knowledge of a site’s history can help predict the po-tential for the presence of buried soils at depth in a landscape.

While exposure of buried soils can result in SOC losses to theatmosphere initially from increased microbial respiration(Demkina et al., 2010), exposed organic horizons can become animportant source of nutrients for local primary production. Theestablishment of vegetation on the exposed soil surfaces can lead toSOC retention, following the successional model of Vitousek andReiners (1975). The economic importance of paleosols and therole of Quaternary history in shaping soil functional properties thatmake up the terroir concept are very well recognized (Costantiniet al., 2012). More in-depth investigations of soil landscape his-tory are expected to reveal important contributions of buried soilsto agricultural productivity and terrestrial C storage.

7. Conclusions

Buried soils have historically been studied to provide insightsinto past climate change and human environments and to recon-struct landscape evolution. Deeper understanding into thegeomorphic, pedogenic, and biological processes that contribute tothe accumulation and persistence of SOC in buried soils can alsoshed light into mechanisms regulating the response of SOC pools toenvironmental change. Few studies have quantified SOC stocks inpaleosols and buried modern soils; however, those that do revealthat substantial SOC stocks, comparable to those of surface soils,may exist in deeply buried soil horizons beyond depths included inmost regional or global C inventories. Deep buried soils store SOC ofdifferent ages and depths around the world in a variety of differentlandscapes, climates, and vegetation and altitudinal zones. Organicmatter can be buried through a variety of volcanic, aeolian, alluvial,colluvial, glacial, and anthropogenic processes acting indepen-dently or in combination. These burial processes differ in theirgeographic extent, the rate of burial, and their effects on thequantity and turnover of SOC transported in sediment and photo-synthesized at the depositional site.

The incorporation of depositional processes and landscapedisturbance events, as well as process-based understanding of howstate factors influence the fate of buried SOC, into biogeochemicalmodels coupled to land surface models will improve predictions ofthe response of large terrestrial OC reservoirs to environmentalchange and of feedbacks to climate change. There is a rich literatureon paleosols, which is primarily descriptive in nature. Increaseddata on the bulk density of buried horizons and estimates of theirgeographic extent can improve quantification of the contribution ofgeomorphic processes to C storage.

Soil burial can isolate OC from the atmosphere, creating envi-ronmental conditions unfavorable to microbial decomposition,such as low moisture or low oxygen, which can lead to thepersistence of SOC relatively unchanged for thousands of years.Once exposed to ambient conditions, soil microbial activity canrecover to rates comparable to surface soils. In other buried soils,biochemical transformations from fire before burial or microbialprocessing post burial lead to the accumulation of SOC with oldradiocarbon ages.

Accelerated landscape disturbance by climate change and hu-man activities can increase the vulnerability of SOC that has beenprotected from mineralization in deep horizons and increase Closses to the atmosphere. At the same time, increases in erosion andshifts in depositional patterns, resulting from changing climatesand extreme weather patterns, could bury higher amounts of OC inthe future. Our results highlight the need for landscape-levelevaluations on the effects of geomorphic processes on mecha-nisms of SOC stabilization and incorporation of soil burial processesinto soil biogeochemical models.

Acknowledgments

The authors would like to thank Joe Mason, Steve Ventura,Randy Jackson, Rob Beattie, Michelle Haynes, and three anonymousreviewers for providing helpful feedback on earlier versions of thismanuscript; Patrick Chaopricha for sketching the figure illustra-tions; and the Wisconsin Alumni Research Foundation for sup-porting research on a buried soil that led to the writing of thisreview.

References

Antoine, P., Rousseau, D.-D., Degeai, J.-P., Moine, O., Lagroix, F., kreutzer, S.,Fuchs, M., Hatté, C., Gauthier, C., Svoboda, J., Lisá, L., 2013. High-resolution re-cord of the environmental response to climatic variations during the LastInterglacialeGlacial cycle in Central Europe: the loess-palaeosol sequence ofDolní V�estonice (Czech Republic). Quat. Sci. Rev. 67, 17e38.

Baker, J.M., Ochsner, T.E., Venterea, R.T., Griffis, T.J., 2007. Tillage and soil carbonsequestrationdwhat do we really know? Agric. Ecosyst. Environ. 118, 1e5.

Basile-Doelsch, I., Amundson, R., Stone, W.E.E., Masiello, C.A., Bottero, J.Y., Colin, F.,Masin, F., Borschneck, D., Meunier, J.D., 2005. Mineralogical control of organiccarbon dynamics in a volcanic ash soil on La Reunion. Eur. J. Soil Sci. 56, 689e703.

Becher, M., Olid, C., Klaminder, J., 2013. Buried soil organic inclusions in non-sortedcircles fields in northern Sweden: age and Paleoclimatic context. J. Geophys.Res. Biogeosci. 118, 104e111.

Beerten, K., Deforce, K., Mallants, D., 2012. Landscape evolution and changes in soilhydraulic properties at the decadal, centennial and millennial scale: a casestudy from the Campine area, northern Belgium. CATENA 95, 73e84.

Berhe, A.A., Harden, J.W., Torn, M.S., Kleber, M., Burton, S.D., Harte, J., 2012.Persistence of soil organic matter in eroding versus depositional landformpositions. J. Geophys. Res. Biogeosci. 117.

Berhe, A.A., Harte, J., Harden, J.W., Torn, M.S., 2007. The significance of the erosion-induced terrestrial carbon sink. Bioscience 57, 337e346.

Berhe, A.A., Kleber, M., 2013. Erosion, deposition, and the persistence of soil organicmatter: mechanistic considerations and problems with terminology. Earth Surf.Process. Landf. 38, 908e912.

Bettis, E.A., Muhs, D.R., Roberts, H.M., Wintle, A.G., 2003. Last Glacial loess in theconterminous USA. Quat. Sci. Rev. 22, 1907e1946.

Biryukova, O.N., Orlov, D.S., Biryukov, M.V., 2008. Humus status of buried soils inloess deposits of the Minusinsk intermontane trough. Eurasian Soil Sci. 41, 471e480.

Blazejewski, G.A., Stolt, M.H., Gold, A.J., Groffman, P.M., 2005. Macro- and micro-morphology of subsurface carbon in riparian zone soils. Soil Sci. Soc. Am. J. 69,1320e1329.

Blazejewski, G.A., Stolt, M.H., Gold, A.J., Gurwick, N., Groffman, P.M., 2009. Spatialdistribution of carbon in the subsurface of riparian zones. Soil Sci. Soc. Am. J. 73,1733e1740.

Bockheim, J.G., 2007. Importance of cryoturbation in redistributing organic carbonin permafrost-affected soils. Soil Sci. Soc. Am. J. 71, 1335e1342.

Bockheim, J.G., Hinkel, K.M., 2007. The importance of “deep” organic carbon inpermafrost-affected soils of arctic Alaska. Soil Sci. Soc. Am. J. 71, 1889e1892.

Carter, B.J., Kelley, J.P., Sudbury, J.B., Splinter, D.K., 2009. Key aspects of A horizonformation for selected buried soils in Late Holocene alluvium; Southern Prai-ries, USA. Soil Sci. 174, 408e416.

N.T. Chaopricha, E. Marín-Spiotta / Soil Biology & Biochemistry 69 (2014) 251e264 263

Chabbi, A., Kögel-Knabner, I., Rumpel, C., 2009. Stabilised carbon in subsoil horizons islocated in spatially distinct parts of the soil profile. Soil Biol. Biochem. 41, 256e261.

Chaopricha, N.T., 2013. The Importance, Origin, Composition, and Stability of DeeplyBuried Soil Organic Matter. University of Wisconsin-Madison, Madison, WI.

Clark, J.J., Walker, J., Ramos, R.R., 2003. Depositional history and evolution of thePaso del Indio site, Vega Baja, Puerto Rico. Geoarchaeology 18, 625e648.

Costantini, E.A.C., Bucelli, P., Priori, S., 2012. Quaternary landscape history de-termines the soil functional characters of terroir. Quat. Int. 265, 63e73.

Daniels, J.M., 2003. Floodplain aggradation and pedogenesis in a semiarid envi-ronment. Geomorphology 56, 225e242.

Daniels, J.M., Knox, J.C., 2005. Alluvial stratigraphic evidence for channel incisionduring the Mediaeval Warm Period on the central Great Plains, USA. Holocene15, 736e747.

Davidson, E., Lefebvre, P.A., Brando, P.M., Ray, D.M., Trumbore, S.E., Solorzano, L.A.,Ferreira, J.N., Bustamante, M.M. da C., Nepstad, D.C., 2011. Carbon inputs andwater uptake in deep soils of an Eastern Amazon forest. Forest Sci. 57, 51e58.

Demkina, T.S., Borisov, A.V., Demkin, V.A., 2010. Production of CO2 by surface andburied soils of the steppe zone under native and moistened conditions.Eurasian Soil Sci. 43, 1030e1035.

Devine, S., Markewitz, D., Hendrix, P., Coleman, D., 2011. Soil carbon change through2m during forest succession alongside a 30-year agroecosystem experiment.Forest Sci. 57, 36e50.

Doetterl, S., Six, J., Van Wesemael, B., Van Oost, K., 2012. Carbon cycling in erodinglandscapes: geomorphic controls on soil organic C pool composition and Cstabilization. Global Chang. Biol. 18, 2218e2232.

Don, A., Steinberg, B., Schöning, I., Pritsch, K., Joschko, M., Gleixner, G., Schulze, E.-D., 2008. Organic carbon sequestration in earthworm burrows. Soil Biol. Bio-chem. 40, 1803e1812.

Duffy, C.C., McCallister, D.L., Renken, R.R., 1997. Carbon tetrachloride retention bymodern and buried soil A horizons. J. Environ. Qual. 26, 1123e1127.

Edmondson, J.L., Davies, Z.G., McHugh, N., Gaston, K.J., Leake, J.R., 2012. Organiccarbon hidden in urban ecosystems. Sci. Rep. 2.

Ekschmitt, K., Kandeler, E., Poll, C., Brune, A., Buscot, F., Friedrich, M., Gleixner, G.,Hartmann, A., Kästner, M., Marhan, S., Miltner, A., Scheu, S., Wolters, V., 2008.Soil-carbon preservation through habitat constraints and biological limitationson decomposer activity. J. Plant Nutr. Soil Sci. 171, 27e35.

Ellery, W.N., Grenfell, S.E., Grenfell, M.C., Humphries, M.S., Barnes, K., Dahlberg, A.,Kindness, A., 2012. Peat formation in the context of the development of theMkuze floodplain on the coastal plain of Maputaland, South Africa. Geo-morphology 141e142, 11e20.

Fabrizzi, K.P., Rice, C.W., Amado, T.J.C., Fiorin, J., Barbagelata, P., Melchiori, R., 2008.Protection of soil organic C and N in temperate and tropical soils: effect ofnative and agroecosystems. Biogeochemistry 92, 129e143.

Feggestad, A.J., Jacobs, P.M., Miao, X., Mason, J.A., 2004. Stable carbon isotope recordof Holocene environmental change in the central Great Plains. Phys. Geogr. 25,170e190.

Fierer, N., Schimel, J.P., Holden, P.A., 2003. Variations in microbial communitycomposition through two soil depth profiles. Soil Biol. Biochem. 35, 167e176.

Fontaine, S., Barot, S., Barré, P., Bdioui, N., Mary, B., Rumpel, C., 2007. Stability oforganic carbon in deep soil layers controlled by fresh carbon supply. Nature450, 277e280.

Gerlach, R., Fischer, P., Eckmeier, E., Hilgers, A., 2012. Buried dark soil horizons andarchaeological features in the Neolithic settlement region of the Lower Rhinearea, NW Germany: formation, geochemistry and chronostratigraphy. Quat. Int.265, 191e204.

Gocke, M., Kuzyakov, Y., Wiesenberg, G.L.B., 2010. Rhizoliths in loess e evidence forpost-sedimentary incorporation of root-derived organic matter in terrestrialsediments as assessed from molecular proxies. Org. Geochem. 41, 1198e1206.

Gurwick, N.P., Groffman, P.M., Yavitt, J.B., Gold, A.J., Blazejewski, G., Stolt, M., 2008a.Microbially available carbon in buried riparian soils in a glaciated landscape.Soil Biol. Biochem. 40, 85e96.

Gurwick, N.P., McCorkle, D.M., Groffman, P.M., Gold, A.J., Kellogg, D.Q., Seitz-Rundlett, P., 2008b. Mineralization of ancient carbon in the subsurface of ri-parian forests. J. Geophys. Res. Biogeosci. 113.

Haff, P.K., 2010. Hillslopes, rivers, plows, and trucks:mass transport on Earth’s surfaceby natural and technological processes. Earth Surf. Process. Landf. 35,1157e1166.

Hall, S.J., Silver, W.L., 2013. Iron oxidation stimulates organic matter decompositionin humid tropical forest soils. Global Chang. Biol. 19, 2804e2813.

Harper, R.J., Tibbett, M., 2013. The hidden organic carbon in deep mineral soils.Plant Soil 368, 641e648.

Harris, C., Caseldine, C.J., Chambers, W.J., 1987. Radiocarbon dating of a palaeosolburied by sediments of a former ice-dammed lake, Leirbreen, Southern Norway.Norsk Geogr. Tidsskr. e Norweg. J. Geogr. 41, 81e90.

Harrison, R.B., Footen, P.W., Strahm, B.D., 2011. Deep soil horizons: contribution andimportance to soil carbon pools and in assessing whole-ecosystem response tomanagement and global change. Forest Sci. 57, 67.

Hassink, J., Whitmore, A.P., Kubát, J., 1997. Size and density fractionation of soilorganic matter and the physical capacity of soils to protect organic matter. In:Perspectives for Agronomy e Adopting Ecological Principles and ManagingResource Use. Elsevier, pp. 245e255.

Hill, A.R., Cardaci, M., 2004. Denitrification and organic carbon availability in ri-parian wetland soils and subsurface sediments. Soil Sci. Soc. Am. J. 68, 320e325.

Hoffmann, T., Schlummer, M., Notebaert, B., Verstraeten, G., Korup, O., 2013. Carbonburial in soil sediments from Holocene agricultural erosion, Central Europe.Global Biogeochem. Cycl. 27, 828e835.

Holden, J., 2005. Peatland hydrology and carbon release: why small-scale processmatters. Phil. Trans. R. Soc. A 363, 2891e2913.

Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., Van der Linden, P.J., Dai, X.,Maskell, K., Johnson, C.A., 2001. Climate Change 2001: the Scientific Basis.Contribution of Working Group I to the Third Assessment Report of the Inter-governmental Panel on Climate Change.

Huang, C.C., Pang, J., Huang, P., 2002. An early Holocene erosion phase on the loesstablelands in the southern Loess Plateau of China. Geomorphology 43, 209e218.

Inoue, Y., Nagaoka, S., Sugiyama, S., 2011. Late Pleistocene buried humic soils withina tephra-soil sequence near Unzen volcano, Kyushu, Japan. Quat. Int. 246, 233e238.

Inoue, Y., Sugiyama, S., Nagatomo, Y., 2000. Organic carbon content and phytolith ina cumulative Andisols in Miyakonojo Basin, Japan. Jpn. Soc. Pedol. 44, 109e123.

Jacobs, P., Sedov, S., 2012. Paleosols in soilscapes of the past and present. Quat. Int.265, 1e2.

Jacobs, P.M., Mason, J.A., 2005. Impact of Holocene dust aggradation on A horizoncharacteristics and carbon storage in loess-derived Mollisols of the Great Plains,USA. Geoderma 125, 95e106.

Jacobs, P.M., Mason, J.A., Hanson, P.R., 2012. Loess mantle spatial variability and soilhorizonation, southern Wisconsin, USA. Quat. Int. 265, 43e53.

Jenny, H., 1941. Factors of Soil Formation, p. 146. New York.Jobbágy, E.G., Jackson, R.B., 2000. The vertical distribution of soil organic carbon and

its relation to climate and vegetation. Ecol. Appl. 10, 423e436.Johnson, D.L., 1998. Paleosols are buried soils. Quat. Int. 51e52, 7.Johnson, K.D., Harden, J., McGuire, A.D., Bliss, N.B., Bockheim, J.G., Clark, M., Net-

tleton-Hollingsworth, T., Jorgenson, M.T., Kane, E.S., Mack, M., O’Donnell, J.,Ping, C.-L., Schuur, E.A.G., Turetsky, M.R., Valentine, D.W., 2011. Soil carbondistribution in Alaska in relation to soil-forming factors. Geoderma 167e168,71e84.

Kaiser, C., Meyer, H., Biasi, C., Rusalimova, O., Barsukov, P., Richter, A., 2007. Con-servation of soil organic matter through cryoturbation in arctic soils in Siberia.J. Geophys. Res. 112.

Karlstrom, E.T., Oviatt, C.G., Ransom, M.D., 2008. Paleoenvironmental interpretationof multiple soileloess sequence at Milford Reservoir, northeastern Kansas.CATENA 72, 113e128.

Khomutova, T.E., Kashirskaya, N.N., Demkin, V.A., 2011. Assessment of the living andtotal biomass of microbial communities in the background chestnut soil and inthe paleosols under burial mounds. Eurasian Soil Sci. 44, 1373e1380.

Klassen, J., 2004. Paleoenvironmental interpretation of the paleosols and sedimentsat the Stampede site (DjOn-26), Cypress Hills, Alberta. Can. J. Earth Sci. 41, 741e753.

Knicker, H., 2011. Soil organic N e an under-rated player for C sequestration in soils?Soil Biol. Biochem. 43, 1118e1129.

Knox, J.C., 2001. Agricultural influence on landscape sensitivity in the Upper Mis-sissippi River Valley. CATENA 42, 193e224.

Knox, J.C., 2006. Floodplain sedimentation in the Upper Mississippi Valley: naturalversus human accelerated. Geomorphology 79, 286e310.

Koarashi, J., Hockaday, W.C., Masiello, C.A., Trumbore, S.E., 2012. Dynamics of dec-adally cycling carbon in subsurface soils. J. Geophys. Res. Biogeosci. 117 n/aen/a.

Koven, C., Friedlingstein, P., Ciais, P., Khvorostyanov, D., Krinner, G., Tarnocai, C.,2009. On the formation of high-latitude soil carbon stocks: effects of cry-oturbation and insulation by organic matter in a land surface model. Geophys.Res. Lett. 36 n/aen/a.

Koven, C.D., Riley, W.J., Subin, Z.M., Tang, J.Y., Torn, M.S., Collins, W.D., Bonan, G.B.,Lawrence, D.M., Swenson, S.C., 2013. The effect of vertically-resolved soilbiogeochemistry and alternate soil C and N models on C dynamics of CLM4.Biogeosci. Discuss. 10, 7201e7256.

Kriest, I., Oschlies, A., 2013. Swept under the carpet: the effect of organic matterburial in global biogeochemical ocean models. Biogeosci. Discuss. 10, 10859e10911.

Krull, E.S., Baldock, J.A., Skjemstad, J.O., 2003. Importance of mechanisms andprocesses of the stabilisation of soil organic matter for modelling carbonturnover. Funct. Plant Biol. 30, 207e222.

Leopold, M., Völkel, J., Dethier, D., Huber, J., Steffens, M., 2011. Characteristics of apaleosol and its implication for the Critical Zone development, Rocky MountainFront Range of Colorado, USA. Appl. Geochem. 26, S72eS75.

Li, C., Li, Y., Tang, L., 2010. Soil organic carbon stock and carbon efflux in deep soils ofdesert and oasis. Environ. Earth Sci. 60, 549e557.

Liang, C., Balser, T.C., 2008. Preferential sequestration of microbial carbon in subsoilsof a glacial-landscape toposequence, Dane County, WI, USA. Geoderma 148,113e119.

Limpens, J., Berendse, F., Blodau, C., Canadell, J.G., Freeman, C., Holden, J., Roulet, N.,Rydin, H., Schaepman-Strub, G., 2008. Peatlands and the carbon cycle: fromlocal processes to global implications e a synthesis. Biogeosciences 5, 1475e1491.

Lorenz, K., Lal, R., 2005. The depth distribution of soil organic carbon in relation toland use and management and the potential of carbon sequestration in subsoilhorizons. In: Advances in Agronomy. Elsevier, pp. 35e66.

Lorenz, K., Lal, R., Shipitalo, M.J., 2011. Stabilized soil organic carbon pools in sub-soils under forest are potential sinks for atmospheric CO2. Forest Sci. 57, 19e25.

Lu, H., Sun, D., 2000. Pathways of dust input to the Chinese Loess Plateau during thelast glacial and interglacial periods. CATENA 40, 251e261.

Mahaney, W.C., Russell, S.E., Milner, M.W., Kalm, V., Bezada, M., Hancock, R.G.V.,Beukens, R.P., 2001. Paleopedology of Middle Wisconsin/Weichselian paleosolsin the Mérida Andes, Venezuela. Geoderma 104, 215e237.

N.T. Chaopricha, E. Marín-Spiotta / Soil Biology & Biochemistry 69 (2014) 251e264264

Mailloux, B.J., Trembath-Reichert, E., Cheung, J., Watson, M., Stute, M., Freyer, G.A.,Ferguson, A.S., Ahmed, K.M., Alam, M.J., Buchholz, B.A., 2013. Advection ofsurface-derived organic carbon fuels microbial reduction in Bangladeshgroundwater. Proc. Natl. Acad. Sci. 110, 5331e5335.

Mandel, R.D., 2008. Buried paleoindian-age landscapes in stream valleys of thecentral plains, USA. Geomorphology 101, 342e361.

Marín-Spiotta, E., Chadwick, O.A., Kramer, M., Carbone, M.S., 2011. Carbon deliveryto deep mineral horizons in Hawaiian rain forest soils. J. Geophys. Res. 116,G03011.

Marín-Spiotta, E., Chaopricha, N.T., Plante, A.F., Diefendorf, A.F., Müller, C.W.,Grandy, S., Mason, J.A., 2013. Rapid climate change leads to millennial stabili-zation of soil carbon by fire and burial. Nat. Geosci. (in review).

Mason, J.A., Miao, X., Hanson, P.R., Johnson, W.C., Jacobs, P.M., Goble, R.J., 2008.Loess record of the Pleistocene-Holocene transition on the northern and centralGreat Plains, USA. Quat. Sci. Rev. 27, 1772e1783.

Matthews, J.A., Shakesby, R.A., McEwen, L.J., Berrisford, M.S., Owen, G., Bevan, P.,1999. Alpine debris-flows in Leirdalen, Jotunheimen, Norway, with particularreference to distal fans, intermediate-type deposits, and flow types. ArcticAntarct. Alpine Res. 31, 421e435.

Mayer, J.H., Burr, G.S., Holliday, V.T., 2008. Comparisons and Interpretations ofCharcoal and Organic Matter Radiocarbon Ages from Buried Soils in North-central Colorado. In: Late Quaternary Landscape Evolution, EnvironmentalChange, and Paleoindian Geoarchaeology in Middle Park, Colorado, pp. 331e346.

Miao, X., Mason, J.A., Swinehart, J.B., Loope, D.B., Hanson, P.R., Goble, R.J., Liu, X.,2007. A 10,000 year record of dune activity, dust storms, and severe drought inthe central Great Plains. Geology 35, 119e122.

Miltner, A., Bombach, P., Schmidt-Brücken, B., Kästner, M., 2012. SOM genesis:microbial biomass as a significant source. Biogeochemistry 111, 41e55.

NRCS, 2013. Buried Soils and Their Effect on Taxonomic Classification.Orlova, L.A., Panychev, V.A., 2006. The reliability of radiocarbon dating buried soils.

Radiocarbon 35, 369e377.Paul, E.A., Morris, S.J., Conant, R.T., Plante, A.F., 2006. Does the acid hydrolysisein-

cubation method measure meaningful soil organic carbon pools? Soil Sci. Soc.Am. J. 70, 1023.

Pelletier, J.D., McGuire, L.A., Ash, J.L., Engelder, T.M., Hill, L.E., Leroy, K.W., Orem, C.A.,Rosenthal, W.S., Trees, M.A., Rasmussen, C., Chorover, J., 2011. Calibration andtesting of upland hillslope evolution models in a dated landscape: Banco Bonito,New Mexico. J. Geophys. Res. Earth Surf. 116.

Peña-Ramírez, V.M., Vázquez-Selem, L., Siebe, C., 2009. Soil organic carbon stocksand forest productivity in volcanic ash soils of different age (1835e30,500 yearsB.P.) in Mexico. Geoderma 149, 224e234.

Pouyat, R.V., Yesilonis, I.D., Nowak, D.J., 2006. Carbon storage by urban soils in theUnited States. J. Environ. Qual. 35, 1566.

Quinton, J.N., Govers, G., Van Oost, K., Bardgett, R.D., 2010. The impact of agricul-tural soil erosion on biogeochemical cycling. Nat. Geosci. 3, 311e314.

Rawling, J.E., Fredlund, G.G., Mahan, S., 2003. Aeolian cliff-top deposits and buriedsoils in the White River Badlands, South Dakota, USA. Holocene 13, 121e129.

Richter, D. deB., Mobley, M.L., 2009. Monitoring Earth’s critical zone. Science 326,1067e1068.

Richter, D.D., Markewitz, D., 1995. How deep is soil? BioScience 45, 600e609.Rosenbloom, N.A., Harden, J.W., Neff, J.C., Schimel, D.S., 2006. Geomorphic control of

landscape carbon accumulation. J. Geophys. Res. 111.Rumpel, C., Kögel-Knabner, I., 2011. Deep soil organic matterda key but poorly

understood component of terrestrial C cycle. Plant Soil 338, 143e158.Salomé, C., Nunan, N., Pouteau, V., Lerch, T.Z., Chenu, C., 2010. Carbon dynamics in

topsoil and in subsoil may be controlled by different regulatory mechanisms.Global Chang. Biol. 16, 416e426.

Schirrmeister, L., Froese, D., Tumskoy, V., Grosse, G., Wetterich, S., 2013. Yedoma:Late Pleistocene Ice-rich Syngenetic Permafrost of Beringia. In: Encyclopedia ofQuaternary Science.

Schmidt, M.W.I., Torn, M.S., Abiven, S., Dittmar, T., Guggenberger, G., Janssens, I.A.,Kleber, M., Kögel-Knabner, I., Lehmann, J., Manning, D.A.C., Nannipieri, P.,Rasse, D.P., Weiner, S., Trumbore, S.E., 2011. Persistence of soil organic matter asan ecosystem property. Nature 478, 49e56.

Schuur, E.A.G., Bockheim, J., Canadell, J.G., Euskirchen, E., Field, C.B.,Goryachkin, S.V., Hagemann, S., Kuhry, P., Lafleur, P.M., Lee, H., Mazhitova, G.,Nelson, F.E., Rinke, A., Romanovsky, V.E., Shiklomanov, N., Tarnocai, C.,Venevsky, S., Vogel, J.G., Zimov, S.A., 2008. Vulnerability of permafrost carbon toclimate change: implications for the global carbon cycle. BioScience 58, 701e714.

Schwendenmann, L., Veldkamp, E., 2006. Long-term CO2 production from deeplyweathered soils of a tropical rain forest: evidence for a potential positivefeedback to climate warming. Global Chang. Biol. 12, 1878e1893.

Sedov, S., Solleiro-Rebolledo, E., Gama-Castro, J.E., Vallejo-Gómez, E., González-Velázquez, A., 2001. Buried palaeosols of the Nevado de Toluca: an alternativerecord of Late Quaternary environmental change in central Mexico. J. Quat. Sci.16, 375e389.

Sedov, S., Solleiro-Rebolledo, E., Morales-Puente, P., Arias-Herreıa, A., Vallejo-Gòmez, E., Jasso-Castañeda, C., 2003. Mineral and organic components of theburied paleosols of the Nevado de Toluca, Central Mexico as indicators ofpaleoenvironments and soil evolution. Quat. Int. 106, 169e184.

Six, J., Conant, R.T., Paul, E.A., Paustian, K., 2002. Stabilization mechanisms of soilorganic matter: implications for C-saturation of soils. Plant Soil 241, 155e176.

Soil Survey Staff, 2010. Keys to Soil Taxonomy, 11th ed. USDA-Natural ResourcesConservation Service, Washington, DC.

Sotta, E.D., Veldkamp, E., Schwendenmann, L., GuimarãEs, B.R., PaixãO, R.K.,Ruivo, M. de L.P., LOLA da COSTA, A.C., Meir, P., 2007. Effects of an induceddrought on soil carbon dioxide (CO2) efflux and soil CO2 production in anEastern Amazonian rainforest, Brazil. Global Chang. Biol. 13, 2218e2229.

Spokas, K.A., 2010. Review of the stability of biochar in soils: predictability of O:Cmolar ratios. Carbon Manag. 1, 289e303.

Tarnocai, C., Canadell, J.G., Schuur, E.A.G., Kuhry, P., Mazhitova, G., Zimov, S., 2009.Soil organic carbon pools in the northern circumpolar permafrost region. GlobalBiogeochem. Cycl. 23.

Terwilliger, V.J., Eshetu, Z., Huang, Y., Alexandre, M., Umer, M., Gebru, T., 2011. Localvariation in climate and land use during the time of the major kingdoms of theTigray Plateau in Ethiopia and Eritrea. CATENA 85, 130e143.

Temme, A.J.A.M., Schaap, J.D., Sonneveld, M.P.W., Botha, G.A., 2012. Hydrologicaleffects of buried palaeosols in eroding landscapes: a case study in South Africa.Quat. Int. 265, 32e42.

Thomsen, I.K., Kruse, T., Bruun, S., Kristiansen, S.M., Knicker, H., Petersen, S.O.,Jensen, L.S., Holst, M.K., Christensen, B.T., 2008. Characteristics of soil carbonburied for 3300 years in a Bronze Age burial mound. Soil Sci. Soc. Am. J. 72, 1292.

Tonneijck, F.H., Jongmans, A.G., 2008. The influence of bioturbation on the verticaldistribution of soil organic matter in volcanic ash soils: a case study in northernEcuador. Eur. J. Soil Sci. 59, 1063e1075.

Torn, M.S., Swanston, C.W., Castanha, C., Trumbore, S.E., 2009. Storage and Turnoverof Organic Matter in Soil. In: Biophysico-chemical Processes Involving NaturalNonliving Organic Matter in Environmental Systems, pp. 219e270.

Torn, M.S., Trumbore, S.E., Chadwick, O.A., Vitousek, P.M., Hendricks, D.M., 1997.Mineral control of soil organic carbon storage and turnover. Nature 389,170e173.

Trumbore, S., 2009. Radiocarbon and soil carbon dynamics. Annu. Rev. Earth Planet.Sci. 37, 47e66.

Trumbore, S.E., 1997. Potential responses of soil organic carbon to global environ-mental change. Proc. Natl. Acad. Sci. 94, 8284e8291.

Valentine, K.W.G., Dalrymple, J.B., 1976. Quaternary buried paleosols: a critical re-view. Quat. Res. 6, 209e222.

Van Oost, K., Quine, T.A., Govers, G., Gryze, S.D., Six, J., Harden, J.W., Ritchie, J.C.,McCarty, G.W., Heckrath, G., Kosmas, C., Giraldez, J.V., Silva, J.R.M. da, Merckx, R.,2007. The impact of agricultural soil erosion on the global carbon cycle. Science318, 626e629.

Van Oost, K., Verstraeten, G., Doetterl, S., Notebaert, B., Wiaux, F., Broothaerts, N.,Six, J., 2012. Legacy of human-induced C erosion and burial on soil-atmosphereC exchange. Proc. Natl. Acad. Sci. 109, 19492e19497.

VandenBygaart, A.J., Kroetsch, D., Gregorich, E.G., Lobb, D., 2012. Soil C erosion andburial in cropland. Global Chang. Biol. 18, 1441e1452.

Veldkamp, E., Becker, A., Schwendenmann, L., Clark, D.A., Schulte-Bisping, H., 2003.Substantial labile carbon stocks and microbial activity in deeply weathered soilsbelow a tropical wet forest. Global Chang. Biol. 9, 1171e1184.

Vitousek, P.M., Reiners, W.A., 1975. Ecosystem succession and nutrient retention: ahypothesis. BioScience 25, 376e381.

Vogel, S., Märker, M., 2011. Characterization of the pre-AD 79 Roman paleosol southof Pompeii (Italy): correlation between soil parameter values and paleo-topography. Geoderma 160, 548e558.

Von Lützow, M., Kögel-Knabner, I., Ekschmitt, K., Matzner, E., Guggenberger, G.,Marschner, B., Flessa, H., 2006. Stabilization of organic matter in temperatesoils: mechanisms and their relevance under different soil conditions e a re-view. Eur. J. Soil Sci. 57, 426e445.

Wang, X., Peng, P.A., Ding, Z.L., 2005. Black carbon records in Chinese Loess Plateauover the last two glacial cycles and implications for paleofires. Palaeogeogr.Palaeoclimatol. Palaeoecol. 223, 9e19.

Wilkinson, B.H., McElroy, B.J., 2007. The impact of humans on continental erosionand sedimentation. Geol. Soc. Am. Bull. 119, 140e156.

Wilkinson, M.T., Richards, P.J., Humphreys, G.S., 2009. Breaking ground: pedological,geological, and ecological implications of soil bioturbation. Earth Sci. Rev. 97,257e272.

Yoo, K., Amundson, R., Heimsath, A.M., Dietrich, W.E., 2005. Erosion of uplandhillslope soil organic carbon: coupling field measurements with a sedimenttransport model. Global Biogeochem. Cycl. 19.

Zabowski, D., Whitney, N., Gurung, J., Hatten, J., 2011. Total soil carbon in the coarsefraction and at depth. Forest Sci. 57, 11e18.

Zech, M., 2006. Evidence for Late Pleistocene climate changes from buried soils onthe southern slopes of Mt. Kilimanjaro, Tanzania. Palaeogeogr. Palaeoclimatol.Palaeoecol. 242, 303e312.

Zech, R., Zech, M., Markovic, S., Hambach, U., Huang, Y., 2013. Humid glacials, aridinterglacials? Critical thoughts on pedogenesis and paleoclimate based onmulti-proxy analyses of the loess-paleosol sequence Crvenka, Northern Serbia.Paleogeogr. Paleoclimatol. Paleoecol. 387, 165e175.

Zech,M.,Hörold,C., Leiber-Sauheitl, K., Kühnel,A.,Hemp,A., Zech,W.,2014.Buriedblacksoils on the slopes ofMt. Kilimanjaro as a regional carbon storage hotspot. CATENA112, 125e130. ISSN 0341-8162, http://dx.doi.org/10.1016/j.catena.2013.05.015.

Zhuravleva, A.I., Yakimov, A.S., Demkin, V.A., Blagodatskaya, E.V., 2012. Minerali-zation of soil organic matter initiated by the application of an available sub-strate to the profiles of surface and buried podzolic soils. Eurasian Soil Sci. 45,435e444.

Zimov, S.A., Davydov, S.P., Zimova, G.M., Davydova, A.I., Schuur, E.A.G., Dutta, K.,Chapin, F.S., 2006a. Permafrost carbon: stock and decomposability of a globallysignificant carbon pool. Geophys. Res. Lett. 33.

Zimov, S.A., Schuur, E.A.G., Chapin, F.S., 2006b. Permafrost and the global carbonbudget. Science 312, 1612e1613.