Mayas Cultivaron Maiz Guatemala

7/30/2019 Mayas Cultivaron Maiz Guatemala

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Soil Science Society of America Journal

Soil Sci. Soc. Am. J.

doi:10.2136/sssaj2010.0224Received 2 June 2012.*Corresponding author ([email protected]).

Soil Science Society o America, 5585 Guilord Rd., Madison WI 53711 USAAll rights reserved. No part o this periodical may be reproduced or transmitted in any orm or byany means, electronic or mechanical, including photocopying, recording, or any inormation storage

and retrieval system, without permission in writing rom the publisher. Permission or printing and orreprinting the material contained herein has been obtained by the publisher.

Upland and Lowland Soil Resources ofthe Ancient Maya at Tikal, Guatemala

Pedology

ikal National Park, Guatemala, was established in 1955 to protect the ru-

ins o one o the largest ancient Maya sites. Population o the ancient cityat its height (Late Classic, 600850 CE) is estimated to have been 60,000

or more inhabitants (Culbert et al., 1990; Dickson, 1980; urner, 1990). Giventhe large population o ikal, agricultural productivity and sustainability wouldhave been important concerns.

Te current understanding o ancient Maya agriculture suggests that slash andburn (swidden) agriculture was not the sole method o crop production (urner,1978). While this practice may have been used throughout Maya history, it is likelythat as populations grew, swidden agriculture was modifed and augmented with ad-ditional agriculture practices designed to maintain and increase yields (Dunning et al.,1998; Dunning and Beach, 2000). Te agricultural strategies employed by the Mayato support their vast populations likely varied over time and space, depending on many

environmental and cultural actors (Dunning et al., 1998; Dunning and Beach, 2000).Te landscape o northern Guatemalas Department o Petn where ikal is lo-

cated is dominated by karst uplands and both seasonal and perennial wetlands in

Richard L. BurnettRichard E. Terry*Ryan V. Sweetwood

Dep. o Plant and Wildlie SciencesBrigham Young Univ.Provo, UT 84602USA

David WebsterDep. o AnthropologyPennsylvania State Univ.University Park, PA 16802USA

Tim MurthaDep. o Landscape ArchitecturePennsylvania State Univ.University Park, PA 16802USA

Jay SilversteinIntelligence and GIS Section

Joint POW/MIA Accounting CommandHickam AFB, HI 96853-5530USA

Debate over agricultural methods and productivity during the Preclassic andClassic Maya period (1000 BCE to 900 CE) ocuses on the agronomic utilityo both upland and lowland soil resources o the karst topography character-istic o northern Guatemala and much o the Yucatan peninsula. In settingswhere direct evidence o agriculture is sparse, stable carbon (C) isotope evi-dence rom soil organic matter (SOM) provides inormation on past vegetationchanges related to ancient maize agriculture. Areas o ancient sustained maizecultivation can be identifed in an ecosystem dominated by C3 orest vegeta-tion because o the unique C4 photosynthetic pathway o maize. The decompo-sition o plant materials with divergent photosynthetic mechanisms (C3 versusC4) results in SOM with correspondingly distinct stable C isotope ratios (

13C).Such dierences are preserved and detectable within the reractory humin rac-tion o the SOM. This study analyzes the physical and chemical soil propertiesincluding stable C isotopes o soils collected rom upland and lowland locations

near Tikal, Guatemala. Toeslope soils contained strong isotopic evidence o C4vegetation likely the result o ancient maize agriculture, while the evidencerom shallow soils o the summit and backslopes was less conclusive. In bothupland and lowland contexts, however, the stronger evidence o ancient veg-etation shits associated with maize agriculture was ound in the deeper fne-textured soils in the ootslopes and toeslopes. Examination o soils on toeslopesrevealed evidence o deposition rom erosional processes upslope that mayhave been related to the spread o agriculture to less productive soils over time.

Abbreviations: COLE, coefcient o linear extensibility; DEM, digital elevation model;SOM, soil organic matter.


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6 Soil Science Society of America Journal

the lowlands. Te low-lying wetlands are locally known as bajosand there has been substantial debate on the agricultural utility othe bajos; a debate usually ramed in an uplands versus lowlandsconstruct (Baker, 2007). While this construct is useul, the varia-tion within the lowlands category should be accounted or whenreconstructing and interpreting ancient agriculture and its impacts(Beach et al., 2006; Dunning et al., 2006). While it is likely that thekarst uplands were used or agriculture (Fedick and Ford, 1990;Pope and Dahlin, 1989), questions remain as to whether, and to

what extent, the lowlands (karst depressions, seasonal bajos, bajomargins, and toeslopes) were cultivated (Kunen et al., 2000).

Evidence rom some bajos has revealed paleosols buried bythe deposition o eroded soils rom the surrounding uplands.Erosion rates were accelerated by human activities related to de-orestation and agriculture. Te initial erosion acceleration beganduring the Preclassic period (2200 BCE to 300 CE) beore pop-ulation pressure reached a maximum. Some o these depositedsoils, usually described as Maya clay (600800 g kg1 clay; color

values 6), overlie buried A horizons (Beach et al., 2008; Beachet al., 2006, able 3). Te newly aggraded soils on the margins

o the bajos were probably agricultural resources or the Maya(Dunning and Beach, 2010; Dunning et al., 2002; Gunn et al.,2002; Hansen et al., 2002; Kunen et al., 2000). Moreover, recentstudies have shown the perennial wetlands o nearby northernBelize hold similar evidence or aggradation and Classic Maya

wetland agriculture borne out by carbon isotopic evidence withoverlapping, multiple ancient land use proxies such as charcoal,

pollen, phytoliths, and others (Beach et al., 2009, 2011).An extensive settlement survey o ikal was conducted in

the 1960s along 12-km long transects oriented in each o thecardinal directions. Te survey did not reveal agricultural ter-races, but an extensive ditch and parapet earthwork system was

discovered on the north and east sides o the park (Puleston andCallender, 1967; Puleston, 1983). It was thought that the earth-

works enclosed and were used to deend at least a portion o i-kals agricultural hinterland. Sustainability at ikal has puzzledresearchers because evidence o terraces and other agriculturalintensifcation eatures such as drainage ditches or raised feldshas not been identifed (Pope and Dahlin, 1989; Puleston, 1973,1978; Webster et al., 2007a, 2007b).

Te analysis o 13C values o soil and sediment organicmatter as indicators o past vegetation changes have been sum-marized by Wright et al. (2009). Most pertinent to this study isthe isotope research that has been conducted in Central America

and the Caribbean Basin, including the analyses o lake sedi-ments, cave sediments, and soils. Lane et al. (2004, 2008) docu-mented 13C values associated with pollen and charcoal analy-ses as evidence o prehistoric orest clearance and crop (maize)cultivation in Dominican Republic and in Costa Rica. Polk etal. (2007) analyzed 13C values o cave sediments rom the VacaPlateau, Belize, and identifed sediments with enriched 13C

values that corresponded with periods o Preclassic and ClassicMaya agriculture. Webb et al. (2004) examined the 13C valueso humic ractions o SOM rom terraced soils at Caracol, Belize,

as a method to indicate evidence o ancient maize agriculture.Similar approaches have been used at various Maya sites acrossthe region (Beach et al., 2008; Fernandez et al., 2005; Johnsonet al., 2007a, 2007b; Sweetwood et al., 2009; Webb et al., 2007;

Wright et al., 2009).Te unctional use o SOM 13C values as an indicator o

past vegetation change is based on the derivation o SOM romdetritus o distinctive plant communities with unique photo-synthetic pathways. Many tropical grasses including maize uti-lize the C4 HatchSlack photosynthetic pathway while other

plants like trees, shrubs, vines, and many grasses use the C3 Cal-vinBenson cycle or photosynthesis. Both categories o plantsdiscriminate against the heavier 13C isotope when incorporat-ing CO2 into their plant tissue through photosynthesis, but C3

plants are signifcantly more discriminatory. Te result is that C4plants are relatively enriched in 13C as compared to C3 plants(Smith and Epstein, 1971). On average, C3 plants have a stableC isotope (13C) value o27, and C4 plants have an averageo12 (Ehleringer, 1991; Liu et al., 1997). Te characteristic13C values o the respective C3 and C4 plant communities are

maintained as SOM orms rom the decomposition o both sur-ace and subsurace vegetative matter.Te SOM consists o nondiscrete pools o organic sub-

stances, including recent detritus that is labile to urther de-composition and an older, nonlabile pool o humic materialsthat is recalcitrant to decomposition (Hsieh, 1992). Te labile

pool has a hal-lie that typically does not exceed a ew decades(Balesdent et al., 1988), while the reractory nonlabile pool mayhave a mean age ranging rom hundreds to thousands o years de-

pending on climatic conditions (Balesdent et al., 1988; Bowmanet al., 2007; Hsieh, 1992, 1996; Janssen, 1984; Jenkinson andRayner, 1977). Te increased longevity o the nonlabile pool is

associated with its stable physical and chemical properties as wellas interactions with the fne clay ractions o soils (Powers andSchlesinger, 2002; Sollins et al., 1996; Veldkamp, 1994). As thereractory portion o the SOM is recalcitrant to decomposition,its associated stable C isotope ratios are preserved or centuries.Changes in 13C values within a given soil reveal the past veg-etative history o an area. Such changes can be prominent when

plant communities have shied over time rom dominantly C3to C4 assemblages or vice versa. Deorestation o a tropical C3orest ollowed by the growth o C4 maize and associated weeds,is an example o a vegetation shi that would be reected in thestable C isotopes within soils.

Te majority o the SOM derived rom long-term maize pro-duction originates rom root decomposition and rhizodepositiono sloughed cells and biologic compounds released rom live roots.Nearly twice the amount o SOM developed under maize cultiva-tion results rom these belowground processes as opposed to thedecay o aboveground plant detritus (Balesdent and Balabane,1996; Molina et al., 2001). Tus, changes in the 13C values ohumin rom soils in ancient maize felds results rom both detri-tus deposited to the soil surace and deposition within the rootingzone. Another important actor involving the interpretation o soil


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www.soils.org/publications/sssaj 6

13C values concerns the naturally occurring isotopic ractionationo carbon isotopes by microbial diagenesis o the SOM (Blair et al.,1985). Te metabolic pathways o microbial decomposition causemoderate isotopic ractionation that result in 13C increases o 1to 2.5 in deeper soil horizons (Agren et al., 1996; Balesdent andMariotti, 1987; Boutton, 1996; Cerri et al., 1985). Heightenedmicrobial activity in certain tropical soils can cause microbial in-duced increases as high as 3 to 4 (Martinelli et al., 1996). Tus,increases in 13C values greater than ~3.5 within a soil are attrib-uted to C3/C4 vegetation changes whereas smaller increases could

potentially be accounted or by microbial ractionation (Boutton,1996; Cerri et al., 1985; Webb et al., 2004).

Te objectives o this study were twoold: (i) characterizesoil resources available to the ancient Maya and (ii) use 13C val-ues o SOM to identiy areas and landscape eatures associated

with past vegetative changes reective o ancient orest clearanceand subsequent maize agriculture at ikal.

MATERIALS AND METHODSGeneral Soil Properties

A survey o the upland soils at the site center o ikal (Ol-son, 1977) indicated that most soils all in the USDA soil tax-onomy order Mollisols and the suborder Rendolls. Tey havedark, organic-rich mollic epipedons and neutral pH levels. Tesoils are inherently ertile (Olson and Puleston, 1972) but havesignifcant limitations. Some o the soils o the bajo areas are clas-sifed as Vertisols. While these soils are comparable in ertility tothe upland soils, their high clay content would make them di-fcult to cultivate. Te bajo soils shrink, swell, crack, and heavedepending on moisture conditions. Tey are sticky when wet and

very hard when dry.

Field MethodsTe soil samples were collected by ho-rizon rom pedons in the summit, shoul-der, backslope, ootslope and toeslope othe uplands, and seasonal bajos o lowlanddepressions during the reevaluation o theikal earthworks (Webster et al., 2007b).Lowland soils were collected rom Bajo An-tonio north o the site center and rom BajoEl Grande in the northwest vicinity o theearthworks (Fig. 1). Both o these bajos arerelatively small seasonal wetlands, and Bajo

Antonio is best characterized as an uplanddepression. Te upland soils were sampledat a variety o locations, including topose-quences associated with the ikal Northand West ransects (Coe and Haviland,1982; Puleston, 1983). Other upland soils

were rom ancient settlement mound groupsand rom the area surrounding the ancientreservoir, Aguada El Duende (Fig. 1).

Surace lea litter was removed (approximately 5 cm) andsoil samples were collected with an 8-cm diameter bucket au-ger at 15-cm depth increments. Te soil samples were placedin sterilized polyethylene plastic bags (Whirl-pak, Nasco) andtransported to the Brigham Young University Soils Laboratory(Provo, U) or analysis. Te slope o the soil locations was mea-sured on site using a clinometer and a digital elevation model(DEM) generated rom data collected by Airborne SyntheticAperture Radar (AIRSAR) and Shuttle Radar opography Mis-sion (SRM). Te same DEM data were used to determine thelandscape position o each soil. Te Universal ransverse Merca-tor (UM) coordinates o each soil sampled were recorded inthe feld. Te horizon separations were confned to the 15-cmdepth increments and were initially based on soil color and tex-ture. Aer chemical and physical analyses, horizon designations

were fnalized and subscript modifers were added.

Laboratory AnalysisSamples were air-dried and aggregates were crushed to pass

a 2-mm (10 mesh) sieve. Five-gram subsamples were urther

ground to pass a 250-

m (60 mesh) sieve in preparation or totalC, total nitrogen (N) determinations, and stable C isotope anal-yses. Soil texture was determined using the hydrometer method(Gee and Bauder, 1986). Te coe cient o linear extensibility(COLE) was determined or the B horizons (Schaer and Singer,1976). Te pH o each A and buried A horizon was determinedon a 1:2 soil/water mixture by glass electrode. Te extractable

phosphorus (P) and potassium (K) levels were also measured orthose same horizons using the Olsen bicarbonate method (Olsenand Sommers, 1982). otal C and N were measured by dry com-bustion with an elemental analyzer (Costech EA, Valencia, CA).

Fig. 1. Map o Tikal National Park, Guatemala, with the soil pedon locations identifed withcrosses. Elevation shades are in meters above mean sea level.


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Te calcium carbonate equivalent o each horizonwas determined by titration (United States Salin-ity Laboratory Sta, 1954).

Carbonates were removed rom 60-meshsamples by reaction with excess HCl and rinsing,beore C isotope analysis. Researchers have raisedconcern that some preanalysis acidifcation proce-dures or removal o carbonates cause signifcant,nonsystematic bias in the isotope analysis (Brodieet al., 2011). o address these concerns, samples

were centriuged at high speed (>30,000 gormore than 1 h) aer acidifcation and aer rinsing

with water. On the basis o the fndings o Webbet al. (2004) that the humin raction would bethe most sensitive detector o ancient C4 vegeta-tion in this type o environment, the humic acidand ulvic acid ractions were removed by alka-line pyrophosphate extraction (Webb et al., 2004,2007; Wright et al., 2009). Te stable C isotoperatios o the humin raction o the SOM o each

soil horizon were determined in duplicate using anisotope ratio mass spectrometer (Termo Finni-gan, Waltham, MA) coupled with an elementalanalyzer (EAIRMS) (Costech, Valencia, CA).Te standard deviation o six replicate analyses o13C was 0.27. Te stable C isotope values othe humin ractions were reported as 13C in permil notation ().

Te absolute value o the largest shi in 13Cvalues between surace and subsurace horizons wasreported or each soil as the change in 13C. Tis

value represents the amount o 13C enrichment

in each soil and was the primary indicator used tomeasure the eects o past vegetation changes onthe SOM o each soil.

RESULTSBajo Soils

Selected physical and chemical properties othe soils rom Bajo Antonio and Bajo El Grandeare listed in able 1. A complete listing o soil

physical properties and the USDA taxonomic sub-groups o the sampled pedons are reported else-

where (Burnett, 2009). All o the Bajo Antonio

A horizon textures were clay or clay loam with theexception o soil 6 (sandy clay loam). Te suracehorizons were dark in color (value < 3, chroma 900 g kg1).

Te eight soils rom Bajo El Grande (512) were sampled inthe ootslope and toeslope landscape positions. Tese soils weredeep (>137 cm) and clayey (>660 g kg1, able 1). Four o thesesoils possessed buried A horizons with thick, lighter colored (val-ue < 7, chroma < 1) deposition layers above the Ab horizon. Teshrinkswell potentials o these soils were low (COLE: high value= 0.14, mean 0.06 (able 1)). Te surace horizons were just aboveneutral pH, and the extractable P levels were generally medium to

high or crop growth (Havlin et al., 2005, ables 913). otal Nand organic C in the surace horizons ranged rom 1.3 to 7.0 g kg1and rom 15.8 to 84.3 g kg1, respectively. Te 13C values o thehumin in the surace horizons were in the range o28 to30(Fig. 3a and 3b), and the average change in 13C with depth was4.49 (able 1). Six o the eight Bajo El Grande soils exceeded4 enrichment, indicative o ancient C4 vegetation. Only soils 5and 6 lacked evidence o a C4 vegetative history with enrichment

values o 1.53 and 1.68.

Fig. 2. The change in 13C o the humin raction with depth o soils inBajo Antonio near Tikal.

Fig. 3. The change in 13C o the humin raction with depth o pedonsin Bajo El Grande near Tikal.


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Upland Soils

Te 52 upland soils were collected rom rural house moundgroups near the earthwork, the North ransect, the West ransect,and rom the Aguada El Duende (Fig. 1). Selected physical andchemical properties o the upland soils are listed in able 2. Teupland soils include pedons rom the rural mound groups iden-tifed by archaeologists as Operation 12, Group 30, West Group19, and Group 41. Te mound group soils (sampled on summit,shoulder, backslope, and ootslope) were dark (value < 3, chroma< 2), shallow (


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Ta

ble2

.Se

lec

tedpropert

ieso

fre

presen

tativeup

lan

dso

ilsa

longsurvey

transec

tsan

dnearanc

ien

tse

ttlemen

ts.

Pedon

Hillslope

D

epth

Horizon

SoilColor

Dry

Texture

COLE

Slope

pH

P

K

TotalN

TotalC

Organic

C

CCE

Changein

13C#

Clay

Class

cm

g/kg

%

mg/kg

mg/kg

g/kg

NorthTransect1

SU

01

5

A

10YR3/1

430

C

1

7.9

3.1

107.3

15.8

250.7

179.0

597.7

0.5

2

152

8

A/Cr

2.5

Y5/1

360

CL

8.0

213.9

118.8

792.4

NorthTransect2

BS

01

5

A1

10YR2/1

470

C

4

7.7

2.8

95.3

19.2

182.5

145.1

37.4

0.6

9

152

5

A2

10YR3/1

480

C

12.4

178.6

114.3

64.3

NorthTransect3

FS

01

5

A1

10YR3/1

720

C

2

7.8

4.1

231.7

16.1

157.2

131.1

26.1

1.9

2

153

0

A2

10YR3/1

730

C

8.4

113.9

77.1

36.8

NorthTransect4

TS

01

5

A

10YR3/1

790

C

1

8.0

5.3

230.7

10.5

108.6

84.9

197.5

5.2

5

156

0

Bk1

10YR3/1

730

C

0.1

1

3.4

117.2

58.1

492.7

607

5

Bk2

10YR3/1

800

C

0.1

1

2.0

90.0

43.9

384.2

751

30

Btk

10YR3/1

920

C

0.2

2

0.7

71.5

28.3

360.3

1301

75

Ab

10YR3/1

980

C

8.2

1.2

99.2

2.3

28.7

13.8

124.3

1752

00

BC

2.5

Y4/1

810

C

0.1

8

2.4

65.2

27.4

315.3

NorthTransect8

BS

01

5

A

10YR3/1

530

C

2

7.8

7.1

185.3

10.0

162.7

97.3

544.8

0.4

6

152

4

A/Cr

2.5

Y5/1

490

C

6.0

149.0

65.2

698.1

NorthTransect10

FS

02

0

A

10YR5/1

420

C

4

8.0

5.7

135.2

8.3

175.8

88.0

731.3

0.6

6

203

0

A

10YR6/1

420

C

6.8

169.5

77.0

770.5

304

2

Cr

10YR6/1

450

C

4.5

157.0

59.5

812.3

NorthTransect11

FS

02

0

A

10YR3/1

620

C

3

7.9

6.3

177.1

8.6

107.8

80.4

228.2

2.3

7

204

0

Bk

10YR3/1

600

C

0.0

5

3.4

74.8

18.3

470.8

407

0

Bt

10YR3/1

920

C

0.1

8

2.6

15.3

7.5

65.3

707

8

BC

10YR4/2

760

C

1.9

56.4

16.9

329.2

WestTransect1

FS

01

5

A

10YR3/1

860

C

2

7.7

4.4

39.6

3.6

34.1

32.3

14.6

2.1

5

156

0

Bw

7.5

YR3/1

910

C

0.0

4

1.3

11.6

10.0

13.5

608

0

Cr

10YR8/1

410

C

0.6

96.8

0.7

800.6

WestTransect2

BS

01

5

A1

10YR3/1

90

SiL

3

7.9

5.1

95.4

8.9

92.1

71.7

170.0

0.1

4

152

9

A2

7.5

YR4/1

130

L

4.7

94.1

35.0

492.8

WestTransect3

BS

01

4

A

10YR3/1

700

C

3

7.8

2.0

176.3

6.8

70.1

64.2

49.3

0.9

9

143

0

Bw

10YR3/1

760

C

0.0

8

4.6

38.8

32.9

49.2

WestTransect8

BS

01

5

A

10YR3/1

820

C

4

7.8

1.9

248.5

6.4

60.2

57.9

19.3

2.9

9

153

0

Bw1

10YR3/1

780

C

0.1

6

4.8

44.5

42.3

18.1

305

4

Bw2

7.5

YR2/1

840

C

0.0

9

3.2

40.5

26.9

113.7

WestTransect9

FS

01

5

A

10YR3/1

880

C

2

6.3

1.6

310.4

15.0

234.1

165.2

574.1

3.4

6

153

0

Bw1

7.5

YR3/1

930

C

0.1

1

307

5

Bw2

7.5

YR3/1

980

C

0.1

2

8.3

166.3

93.9

603.2

751

05

Bw3

10YR6/1

980

C

0.1

1

34.6

534.4

510.7

197.5

WestTransect12

BS

01

5

A

10YR4/1

560

C

3

7.9

2.6

70.8

0.7

136.7

58.7

650.0

0.2

1

152

1

A/Cr

7.5

YR4/1

430

C

12.7

196.5

141.9

454.6

WestTransect13

FS

01

5

A

10YR3/1

920

C

3

6.5

2.0

79.9

9.7

182.4

120.0

519.7

3.3

5


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Pedon

Hillslope

D

epth

Horizon

SoilColor

Dry

Texture

COLE

Slope

pH

P

K

TotalN

TotalC

Organic

C

CCE

Changein

13C#

Clay

Class

153

0

Bw1

10YR4/1

950

C

0.1

1

14.7

188.0

141.1

390.7

301

18

Bw2

2.5

Y3/1

980

C

0.0

8

10.0

150.8

97.1

447.5

AguadaElDuende1

FS

02

0

A

10YR4/1

330

CL

3

7.8

4.7

214.6

1.7

133.3

57.7

75.6

AguadaElDuende2

FS

03

6

A

10YR3/1

600

C

2

7.7

6.9

155.1

12.2

193.2

129.7

529.4

1.5

4

364

8

Cr

7.5

YR6/1

530

C

7.4

164.3

83.9

669.9

AguadaElDuende3

TS

04

6

O

10YR2/1

920

C

2

4.5

153.1

59.3

781.3

0.8

5

466

4

A

10YR3/1

960

C

7.5

11.4

98.3

10.4

159.1

117.7

344.9

461

10

Bw

10YR2/1

970

C

0.1

9

4.0

126.7

51.0

630.6

AguadaElDuende4

FS

01

7

A

7.5

YR3/1

950

C

8

7.0

6.6

127.4

8.4

144.9

85.7

493.5

6.7

8

173

1

Bw1

7.5

YR3/1

980

C

0.1

9

3.1

139.8

46.6

777.0

317

5

Bw2

7.5

YR4/1

0.1

0

3.4

88.0

38.3

414.3

751

80

Bw3

7.5

YR4/1

950

C

0.1

6

0.3

48.6

37.0

97.0

1802

00

Bw4

7.5

YR5/1

980

C

0.1

1

0.1

19.4

9.9

79.5

AguadaElDuende5

BS

02

0

A

7.5

YR3/1

440

C

16

7.8

5.5

98.9

8.3

116.3

81.0

293.8

0.3

2

204

0

A

7.5

YR4/1

8.0

4.1

71.3

Group41Soil1

FS

02

0

A

10YR2/1

490

C

1

7.8

9.1

130.4

15.0

228.6

151.2

645.0

Group41Soil2

FS

02

0

A

10YR2/1

540

C

2

7.8

10.5

302.5

23.0

292.2

263.4

239.7

0.9

8

204

0

Cr

7.5

YR5/1

520

C

7.5

195.3

96.5

823.3

Group41Soil3

BS

02

0

A

10YR2/1

510

C

3

7.6

9.8

200.8

26.8

362.9

329.9

275.0

0.0

8

202

5

Cr

7.5

YR5/1

Group41Soil4

BS

01

9

A

10YR2/1

410

C

4

7.8

9.3

123.1

19.0

280.8

218.1

522.3

0.5

6

193

9

Cr

10YR7/1

470

C

4.2

194.4

84.5

915.8

Group41Soil5

FS

02

0

A

10YR2/1

590

C

1

8.0

6.6

88.7

11.0

173.3

100.4

607.1

0.4

5

204

3

Cr

7.5

YR5/1

470

C

5.5

177.2

81.2

800.2

Group41Soil9

BS

01

9

A1

10YR2/1

540

C

4

7.9

9.1

177.8

14.8

231.9

159.9

599.9

0.1

4

192

5

A2

10YR3/1

Group30

BS

01

5

A

10YR3/1

750

C

7

7.7

7.7

77.0

10.6

123.5

113.0

87.9

1.5

5

153

0

Bt

10YR6/2

840

C

3.2

84.6

68.7

132.4

304

5

Cr1

10YR7/2

750

C

0.9

121.0

33.5

729.2

455

8

Cr2

10YR8/1

680

C

0.7

136.7

58.7

650.0

WestGroup19Soil1

SU

01

5

A

10YR2/1

460

C

2

7.8

9.6

207.3

12.7

196.5

141.9

454.6

0.4

4

153

0

Cr

10YR7/1

520

C

9.7

182.4

120.0

519.7

WestGroup19Soil2

SU

01

5

A

10YR2/1

510

C

2

7.9

10.9

282.3

14.7

188.0

141.1

390.7

0.6

8

153

0

Cr

10YR7/1

460

C

10.0

150.8

97.1

447.5

Operation12Soil1

SH

01

8

A

10YR2/1

210

SCL

3

7.8

6.2

247.0

12.2

193.2

129.7

529.4

0.8

1

182

7

A/Cr

10YR7/1

260

SCL

7.4

164.3

83.9

669.9

273

3

Cr

10YR2/1

460

C

4.5

153.1

59.3

781.3

Operation12Soil2

BS

02

0

A

10YR3/1

550

C

3

7.7

4.2

235.1

10.4

159.1

117.7

344.9

1.9

5

203

1

Cr

7.5

YR4/1

510

C

4.0

126.7

51.0

630.6

SlopePosition:SU,summit;SH,sho

ulder;BS,backslope;FS,

ootslope;TS,toeslope.

Textureclass:SiL,siltloam;SCL,sandyclayloam;CL,clayloam;C,clay.

COLE,

Coefcientolinearextensib

ility.

CCE,calciumcarbonateequivalent.

#Thechangein13Cromsuracehorizontoahorizonatdepth.


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Fig. 4. The change in 13C o the humin raction with depth o soilsalong the North Transect o Tikal.

Fig. 5. The change in 13C o the humin raction with depth o pedonsalong the West Transect o Tikal.

El Grande Soil 8, sampled at the ootslope lacked a distinct bur-ied horizon at depth but does have the white C horizon (10YR8/1) characteristic o the other soils in the group. Te darker bur-ied horizons occurred at greater depths and thicknesses in eachsoil moving down in elevation. Te overlying depositional lay-ers ollowed the same pattern. One possible explanation is thatagriculture was ocused near the center o the depression and

spread outward and upward to slightly steeper slopes over time.Cultivated surace soils rom upslope locations may have erodedcreating buried horizons, deposition layers, and increasingly C4-enriched 13C values in soils at lower landscape positions. Maizecultivation and rhizodeposition were more likely the sources o13C enrichment in the El Grande soils, however.

Contemporary vegetation diered between the two ba-jos. Bajo Antonio had more escoba palm (Crysophilia argentesBartlett), with little to no tintal (Haematoxylum campechianumL.), while Bajo El Grande had escoba and tintal vegetation withthe tintal dominating the lower, atter regions o the bajo. Tese

vegetation and soil dierences would potentially have had an

impact on isotope values, i substantial 13C dierences existedbetween these two plant species. Tereore, we collected fve

plant specimens or C isotopic analysis. Both escoba palm andtintal were identifed as C3 plants with

13C values o33.9and31.4, respectively. Tree unidentifed grass species werecollected in the wetlands o ikal and 13C values ranged rom31.9 to 28.5, indicating that they were also C3 plants. Itis interesting that both the plant tissue and the surace horizon13C values rom bajos were very negative, oen below29(able 1). Tis is likely the result o greater soil moisture and

high relative humidity in the bajos. Under these conditions thestomata o C3 plant leaves remained open allowing or greaterdiscrimination against the heavier 13CO2 (Wright et al ., 2009).

Other bajo and grass species sampled rom the Departmento Petn were also identifed as C3 plants (Johnson et al., 2007b)as were all but two species sampled rom the nearby perennial

wetlands o northern Belize (Beach et al., 2011). Furthermore,some o the aquatic pollen types that dominated the pollen as-semblage o a buried soil in a bajo near La Milpa were classifedas C3 plants (Dunning et al., 2002). Tus, the isotopic evidencerom La Milpa may actually suggest maize agriculture instead o,or in addition to, herbaceous wetland vegetation common to pe-rennial or seasonal wetlands. Te data rom Nakbe (Jacob, 1995)show that the majority o species sampled rom the perennially

wet civales were also C3, indicating that the isotopic shi in the

buried bajo soils may have resulted rom maize agriculture.Te change in 13C values with depth o Bajo El Grande

soils 9, 10, and 11 were all greater than 5. Te highest 13Cvalues o El Grande soil 9 were within the buried horizons, withthe greatest in the lower portion o the buried Akb horizon(22.84 at 125145 cm) (able 1 and Fig. 3b). A slightlyless enriched 13C value was located in a mixed CAb horizondeposited above the ancient surace. Tis mixed horizon likelyconsisted o soil eroded rom upslope locations, providing ur-ther evidence o the proposed scenario where agriculture spread


11/14


outward and upward away rom the best soils tomarginal soils more susceptible to erosion.

Bajo El Grande Soils 10 and 11 lacked Abhorizons, yet still had strong C isotope evidenceo ancient agriculture (able 1 and Fig. 6). Tesetwo soils were located arther away rom settle-ment and the earthworks and appear to havebeen agriculturally important, indicated by thelarge change with depth in the 13C values (5.65and 5.90). Soil 11 shows a more sustained pe-riod o ancient C4 vegetation with

13C valuesranging rom 24.90 to 23.21 below the30-cm depth (Fig. 3b).

Bajo El Grande Soil 12 was located near theearthworks and close to ancient settlements (Fig.6). Te soil had a distinct buried Ab horizon withassociated 13C values indicating strong evidenceo ancient agriculture. Te change in 13C valueso 6.18 associated with the large 13C value o22.61 at 125 to 158 cm was the greatest o

any soil rom Bajo El Grande (Fig. 3b).

Upland SoilsTe upland soils were divided into three groupings: mound

group soils, transect soils, and soils rom near Aguada El Duende(Fig. 6, 8, and 9). Te mound groups including Operation 12,

West Group 19, Group 30 and Group 41 soils were typicallyshallow (


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West ransect soil W9 located approximately100 m outsidethe earthwork had a 13C enrichment o 3.46, the greatest oany o the West ransect soils (Fig. 9). Te other deeper soils romthe West ransect had shis in 13C values o 2.15 (soil W1)and 3.35 (soil W13). While not as deep, soil W8 had anenrichment o 2.99. Tese enrichment values provide only weakevidence o ancient C4 vegetation, but examination o the trends

o the 13C values indicates the possibilityo ancient agriculture (Fig. 5b). Excludingsoil W8, each o these soils exhibited in-creasing13C values with depth, ollowedby a return to more negative, C3-like valuesat the greatest depths o the soils. While achange o 4 was not met, the trend (Fig.5a and 5b) inherently hints at a C3C4 C3shi caused by past vegetation changes thatcould be attributed to agriculture.

Te area around Aguada El Duendecould have been agriculturally importantgiven its location with respect to the earth-

works and because o the water the aguadawould have stored (Fig. 6) (Silverstein et al.,2009; Webster et al., 2007b). Te 13C datao soil horizons in and around the aguadaare shown in Fig. 7. Te shallow ootslopeand backslope soils urthest rom the agua-da showed little to no evidence o ancient

C4 vegetation associated with maize agri-culture. Aguada El Duende Soil 4, adjacentto the aguada, exhibited a large enrichmento 6.78. Soil 4 stands in contrast to soil

3 rom the center o the aguada which had an enrichment o only0.85. Aguada El Duende Soil 4, at least, provided evidence thatthe area was agriculturally important. Aguada El Duende Soil 3ormed rom sediments near the center o the aguada, thereore itcould be considered a control because maize would not have beengrown at this ooded location. Soil 3 exhibited small increases in13C values consistent with natural isotopic ractionation rom

microbial processes.

CONCLUSIONSStable C isotope ratios in soils rom

peripheral areas surrounding ikal providedinormation on both the current and past

vegetation assemblages o the area. Signif-cant shis in 13C values o greater than 4

within certain soils indicated ancient vegeta-tion changes associated with C4 maize agri-culture. Te evidence o such changes was

preserved in the humin raction o SOMrom soils located within both upland and

lowland topography.Te evidence o ancient maize agri-

culture in the upland soils was not strong.Tose ew upland soils that exhibited stron-ger stable C isotope enrichment, indicativeo past maize agriculture, were confnedmostly to deeper ootslope and toeslopesoils with properties similar to bajo soils.Lower locations within uplands such asdrainages, localized depressions, and areasFig. 9. Map o the West Transect and West Group 19 with the change in

13C with soil depth indi-cated as 13C enrichment (). Elevation contours are in meters above mean sea level.

Fig. 8. Map o Bajo Antonio and the North Transect with the change in 13C with depth indicatedas 13C enrichment (). Elevation contours are in meters above mean sea level.


13/14


near aguadas were those where the evidence o past vegetationchanges associated with agriculture was strongest.

Although great variation exists among bajos in the Petn,the stable C isotope evidence suggests that the two bajos exam-ined in this study were avored or ancient agriculture. Te datarom Bajo El Grande and Bajo Antonio imply that these season-ally wet depressions were initially cultivated beore the steeperupland slopes immediately enclosing the bajos. Ten, as needed,agriculture spread to the more erodible steeper slopes that sur-rounded these depressions. Substantial soil erosion and deposi-tion ollowed, burying some o the prime agricultural land o thedepressions. Te deposits may have been subsequently cultivatedas at other sites (Beach et al., 2006, 2009, 2011). Tis series oevents likely began during the Preclassic period.

ACKNOWLEDGMENTSTis portion o the Re-evaluation o the Earthworks at ikal,Guatemala, project was unded by the National Science Foundation(grant BCS-0443280) and by Brigham Young University. Te Institutode Antropologa e Historia, the Consejo Nacional de Areas Protegidas,and the Parque Nacional ikal o Guatemala granted permission

or this research to take place. Te Re-evaluation o the Earthworksat ikal, Guatemala, project thanks all those who assisted with thecollection, preparation, and analysis o the soil samples. Special thanksgo to Horacio Martinez, Walter Alvarado, and Kirk Straight or theircontributions to this study. We acknowledge the work o the anonymousreviewers who helped to improve this paper.

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Mayas Cultivaron Maiz Guatemala

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