Environmental and Cultural Changes in Highland Guatemala Inferred from Lake Amatitlán Sediments

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Maria I. Velez,1,* Jason H. Curtis,2 Mark Brenner,2 Jaime Escobar,2, 3 Barbara W. Leyden,4 and Marion Popenoe de Hatch5 1Department of Geology, University of Regina, Regina, Saskatchewan S4S 0A2, Canada 2Department of Geological Sciences, and Land Use and Environmental Change Institute (LUECI), University of Florida, Gainesville, FL 32611 3Center for Tropical Paleoecology and Archaeology, Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Panama 4Deceased 5Departamento Arqueología, Universidad del Valle de Guatemala, Apartado Postal No. 82, Guatemala 01901, Guatemala

We inferred the late Holocene environmental history of the Guatemala highlands from multiple lines of evidence in a sediment core from Lake Amatitlán. Inferred environmental changes are generally synchronous with archaeologically documented highland Maya cultural shifts. Population increases in the Middle Preclassic, Early Classic, and Late Postclassic are associated with deforestation and soil erosion. Land abandonment in the Late Preclassic, Late Classic, and Early Postclassic is associated with evidence for reforestation and soil stabilization. Diatoms indicate relatively lower lake level and greater trophic status at times of reduced human impact, from ca. 250 B.C. to A.D. 125 and from ca. A.D. 875 to 1375. Decreased water levels were probably due to drier climate, to reforestation, or both. Lake eutrophication was caused by reduced water volume combined with a legacy of long-term agricultural activity. Our data contribute to the understanding of relations among ancient Maya culture, climate, and environment. © 2011 Wiley Periodicals, Inc.

INTRODUCTION Investigations of lake sediment cores have been conducted in the Maya lowlands since the late 1950s to shed light on relationships between paleoclimate, past environmental conditions, and ancient Maya culture (Brenner et al., 2002; Neff et al., 2006). Early studies on lake sediments explored the impact of Maya agricultural and engineering activities on lowland karst watersheds of the Yucatán Peninsula, from ca. 3000 to 1000 cal yr B.P., with a focus on human-induced deforestation and soil

*Corresponding author; E-mail: [email protected].

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erosion (Cowgill et al., 1966; Deevey et al., 1979; Brenner, 1983; Vaughan, Deevey, & Garret-Jones, 1985). By the 1970s, attention had turned to inferring past climate in the Maya Lowlands (Covich & Stuiver, 1974). High-resolution stable oxygen isotope and geochemical records from lakes in the Mexican region of the Yucatán Peninsula indicated that moisture availability fluctuated appreciably throughout the late Holocene (Hodell, Curtis, & Brenner, 1995; Curtis, Hodell, & Brenner, 1996; Hodell, Brenner, & Curtis, 2005). Pronounced droughts, identified paleolimnologically (Hodell, Curtis, & Brenner, 1995; Curtis, Hodell, & Brenner, 1996; Hodell et al., 2001) and by speleothem studies (Webster et al., 2007), were invoked as a possible con- tributing factor to the Terminal Classic Maya cultural collapse of the 9th century A.D. More recent studies of regional lake sediment cores addressed quantitative anthropogenic soil loss from a catchment in Petén, Guatemala (Anselmetti et al., 2007), as well as climate and environmental conditions leading up to, during, and following the protracted period of sedentary Maya settlement in the lowlands (Müller et al., 2009, 2010). Whereas studies at low-elevation sites in Guatemala and other selected regions of Central America have yielded abundant information about past climate and environmental conditions in the Maya region, little has been done in the Guatemalan highlands (Popenoe de Hatch et al. 2002; Marcus 2003). There have, however, been several attempts to obtain lake sediment cores from high-elevation areas for paleoenvironmental study. Newhall et al. (1987) retrieved cores up to 9.8 m long from Lake Atitlán, but serious concerns about “14C reservoir effects” in this caldera lake made radiocarbon ages suspect, compromising the sediment chronology. Sediments were ultimately “dated” by palynological correlation with records from lowland sites (Higuera-Diaz, 1983), assuming that vegetation changes in both regions were con- temporaneous. Other issues also made paleolimnological study of Lake Atitlán chal- ϳ 2 ϭ lenging. First, the lake is large ( 130 km ) and deep (zmax 340 m), with some 70% of its area (ϳ91 km2) deeper than 100 m (Deevey, 1957), posing logistical challenges for recovering long cores. Furthermore, sediment pore waters are gas-rich and the stratigraphy of deep-water cores is locally complicated by massive turbidity flows and slumping (Newhall et al., 1987). Poppe et al. (1985) studied Lake Ayarza, another ϭ caldera system that also presents problems. It too is very deep (zmax 240 m) and the uppermost 9 m of sediment consist mainly of turbidites. The best candidate for paleolimnological study in the Guatemalan highlands is Lake Amatitlán. With an area of 15.35 km2 and a maximum depth of ϳ33 m, suitable sediment cores can be obtained with hand-coring technology. The lake’s morphom- etry, and the well-documented archaeological history of the watershed, which extends back Ͼ3000 years (Borhegyi, 1959) prompted Tsukada and Deevey (1967) to retrieve a core from a relatively shallow area (ϳ16 m) of the lake. The undated 4.25-m-long sediment column was studied palynologically. The base of the section was inferred to be ca. 3000 years old by pollen correlation with lowland records, suggesting that settlement in the catchment dated back to the earliest Formative period, 1500 B.C.–600 B.C. The bottom ϳ2.0 m of the core contained pollen evidence of substantial human disturbance, with low arboreal and high non-arboreal percentages,

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abundant Ambrosia and other Compositae, large amounts of chenopod, amaranth, and Zea pollen, and abundant carbonized fragments. From approximately 2.0 m to 0.75 m depth, there was evidence for declining human impact, with only spotty presence of maize, declines in relative abundance of composites and “cheno-ams,” greater proportions of tree pollen, and lower abundance of carbonized fragments. The uppermost ϳ75 cm reflected a new cycle of human disturbance that continues to the present, with abundant charcoal, high relative abundance of weedy species and low forest pollen types, and large amounts of maize pollen. The work of Tsukada and Deevey (1967) suggested that the sediments from Lake Amatitlán could yield valuable paleoenvironmental information about the Guatemalan highlands. In 2000, a collaborative project between the University of Florida and Universidad del Valle de Guatemala was initiated to understand the past dynamics among climate, environment, and Maya culture in the highlands (Popenoe de Hatch et al., 2002). Several cores were recovered from extinct Lake Miraflores and from extant Lake Amatitlán. Lake Miraflores was of particular interest because it dried out completely by ϳA.D. 100 and it is not known if its desiccation was due to human impact or to natural climatic variability (Popenoe de Hatch et al., 2002). The core from Lake Amatitlán was dated using accelerator mass spectrometry 14C measurements on terrestrial macrofossils. The core was analysed for pollen, diatoms, and sediment geochemical variables (magnetic susceptibility, C/N ratio, and d15N) to infer past environmental changes in the lake and its watershed. Overall, our goal was to pro- vide a paleoenvironmental context for archaeologists, against which they could inter- pret cultural development in the Guatemalan highlands over the last three millennia. Here we present the results of that investigation.

STUDY SITE Lake Amatitlán (14°27'23''N, 90°33'58''W) lies at 1186 meters above sea level (masl), ca. 25 km southwest of Guatemala City in the mountains of southern Guatemala (Figure 1). The area contains four major active volcanoes that lie within 30 km of Lake Amatitlán: Agua (3760 masl), Acatenango (3976 masl), Fuego (3766 masl), and Pacaya (2544 masl). Volcanic activity contributed to the formation and fertility of soils in the area (Sanders & Murdy, 1982). The lake owes its origin to combined volcanic and tectonic processes. Mean direct rainfall on the lake is ϳ1220 mm/yr. The main hydrologic input to the lake is the Rio Villalobos, which drains a watershed of ϳ313 km2 and today carries a substantial suspended sediment load and pollutants from Guatemala City. Other smaller inlets include surface streams and groundwater inflow from hot springs. Excess water exits the lake via the Rio Michatoya. Combined annual hydrologic inputs exceed yearly evapotranspiration (ϳ830 mm/yr). A railroad bridge constructed across a nar- row constriction now divides the lake into two subbasins (Figure 1). Lake Amatitlán has displayed high nutrient concentrations since at least 1950 (Deevey, 1957), when total phosphorus concentrations in surface waters approached 60 mg L–1. By 1988, total phosphorus concentration displayed a mean annual value of

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Figure 1. Map of the Lake Amatitlán study area (A–B) and coring sites (C). Lake depths are in meters.

440 mg L–1 (International Lake Environment Committee, 2009). Present lake water quality is, in part, attributable to human activities in the catchment, such as agriculture and urbanization. The lake also receives sewage and industrial waste from Guatemala City. Despite its hypereutrophic status, the lake remains a popular site for recreation. The lake is also exploited for thermoelectric and hydroelectric power.

METHODS In March 2000, sediment cores were collected at three locations in Lake Amatitlán. For this study, we analyzed core Amatitlán 15-III-00 from Station 3, in the northwest area of the lake (Figure 1). Water depth, measured with a Secchi disk on a metered rope at Station 3, was ϳ13.8 m. The uppermost 85 cm of the sediment were collected with a large- diameter piston corer (Fisher, Brenner, & Reddy, 1992). Deeper sections, below 50 cm sediment depth, were collected in approximately 1-m increments using a modified Livingston piston corer with a locking piston and polycarbonate core tubes. The total

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Table I. Radiocarbon results for core Amatiltán 15-III-2000. Samples were analyzed at the Center for Accelerator Mass Spectrometry (CAMS) at the Lawrence Livermore National Laboratories. Depth Oxcal (INTCAL04) Oxcal (INTCAL04) Size CAMS# (cm) Age 14C yr B.P. Age cal. yr B.P. Age (B.C./A.D.) Material (mg C)

71623 240 710 Ϯ 50 652 Ϯ 48 1298 Ϯ 48 A.D. charcoal 0.27 71624 340* 2910 Ϯ 130 3076 Ϯ 159 1127 Ϯ 159 B.C. charcoal 0.04 71625 440 1530 Ϯ 190 1467 Ϯ 202 483 Ϯ 202 A.D. charcoal 0.03 71626 540 2010 Ϯ 100 1985 Ϯ 130 36 Ϯ 130 B.C. charcoal 0.06 71627 610 2340 Ϯ 110 2408 Ϯ 169 459 Ϯ 169 B.C. charcoal 0.05 71628 690 2570 Ϯ 40 2663 Ϯ 83 714 Ϯ 83 B.C. charcoal 0.42 * Not included in age model.

length of the recovered sediment profile was 7.01 m. The sediment/water interface core (0–85 cm) was extruded and sampled at 4-cm intervals. Deeper, consolidated sediment sections were transported in their core barrels to the University of Florida, where they were kept at 4°C. Deeper sediments (0.50–7.01 m) were measured for magnetic susceptibility and gamma ray attenuation (density) on complete core sections, with a Geotek Multisensor core logger. Next, the sections were split lengthwise. Working halves of each core section were subsampled at 5-cm intervals for total carbon (TC), total nitrogen (TN), and d15N analysis. Selected samples were measured for inorganic ϭ carbon content by coulometry using a UIC CO2 coulometer. Samples for pollen (n 30) and diatom analyses (n ϭ 40) were taken throughout the core at depths above and below observed changes in the sediment lithology. Six samples of charcoal were dated using accelerator mass spectrometry (AMS) 14C (Table I); calibrated ages are based on the INTCAL04 data set. Calibrated B.C./A.D. sediment ages at depths in the profile were derived by linear interpolation between the midpoint calendar age ranges (Figure 2). The 14C date at 340 cm sediment depth was out of sequence (Table I) and was excluded from the age model. Samples for total carbon and total nitrogen were freeze-dried and ground with a mortar and pestle. Percent total carbon (%TC) and percent total nitrogen (%TN) were measured using a Carlo Erba NA 1500 C/N/S analyzer. Stable isotope (d15N) analyses were carried out with the Carlo Erba NA 1500 CNS elemental analyzer and a VG PRISM II series mass spectrometer. Nitrogen isotopes are expressed as the per mil deviation from air, that is, d15N ϭ 0. Pollen samples were prepared using standard chemical extraction techniques (Whitehead, 1981). Grains were stained and mounted in silicone oil on microscope slides. Counts for most levels exceeded 200 pollen grains from terrestrial taxa. Pollen results include some algae and exclude grains from taxa that occurred only once or

twice. Diatom frustules were extracted by digestion of organic matter with 30% H2O2. Digested samples were washed three times with distilled water. Permanent slides were mounted in Zrax (R.I. ϳ1.7ϩ). At least 350 diatom frustules were counted per slide. Diatom identification and ecology were based on Patrick and Reimer (1966), Foged (1978), Gasse (1980, 1986), Krammer and Lange-Bertalot (1991, 1997), and Moro and Fürstenberger (1997). Raw diatom and pollen counts were transformed into

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Figure 2. Calibrated 14C ages versus depth for core Amatitlán 15-III-2000.

percentages and plotted against depth using Tilia and Tiliagraph. Core zonation was done using CONISS (Grimm, 1987) within Tiliagraph.

RESULTS

Sediment Geochemistry Percentages of total nitrogen (%TN) and carbon (%TC) display similar trends over the length of the core (Figure 3). Amatitlán sediments have very low inorganic carbon content and extremely low abundance of calcium carbonate microfossils, consisting mostly of ostracods belonging to the species Candona lactea and C. angu- lata. Percent TN varies between 0.07 and 0.35 and %TC values fluctuate between 0.33 and 8.07. Values are relatively constant from ϳ600 B.C. to ϳA.D. 875. Thereafter, both TN and TC concentrations show increases and high variability, with a decrease to new lows ϳA.D. 1500. In the subsequent few centuries, values remain relatively constant, until they display general increases in the last ϳ100 years. The C/N ratio varies from ca. 4.5 to 28.9 over the length of the core, and fluctuates in concert with

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Figure 3. Total C, total N, and C/N (mass) values versus age in calibrated years B.C./A.D. for core Amatitlán 15-III-2000.

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Figure 4. d15N and magnetic susceptibility values versus age for core Amatitlán 15-III-2000.

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Figure 5. Diatom relative abundance (%) diagram for core Amatitlán 15-III-2000.

TN and TC values. The C/N ratio displays such variation because TC displays a much broader range of values (24ϫ) than does TN (5ϫ). Nitrogen isotope (d15N) values are fairly constant, with most values between 4 and ϳ6‰, from the base of the core up to ϳA.D. 1875 (Figure 4). Thereafter, d15N values display an increase to Ͼ10‰ near the core top. Magnetic susceptibility (MS) values show dramatic fluctuations between ca. 700 and 500 B.C., with lows near 200 SI ϫ 10–6, and three peaks of 800–1000 SI ϫ 10–6. Thereafter, values are generally lower (Ͻ200) from ϳ500 B.C. to ϳA.D. 125, except for small peaks at ϳ475 B.C. and ϳ250 B.C. Between ϳA.D. 125 and A.D. 525, MS values are generally higher, between ϳ200 SI ϫ 10–6 and ϳ400 SI ϫ 10–6. MS values in the measured remainder of the core, from ϳA.D. 600 to A.D. 1800, are typically lower, around 200 SI ϫ 10–6, except for several small peaks, the most pronounced at ϳ A.D. 1225.

Diatoms Three main diatom assemblages were identified in the sediment core (Figure 5). Assemblage 1 is dominated by the planktonic species Aulacoseira granulata, with varying proportions of the planktonic–littoral Cyclotella species. Assemblage 1 char- acterizes the periods ϳ500 B.C. to ϳ160 B.C., ϳA.D. 120 to ϳA.D. 890, and ϳA.D. 1370 to present. Assemblage 2 is dominated by Nitzschia amphibia, N. palea, and Fragilaria

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delicatissima, and is the principal assemblage between ϳ160 B.C. and ϳA.D. 120. Assemblage 3 is dominated by the littoral/epiphytic species N. amphibia f. rostrata and N. palea. This assemblage dominates between ϳA.D. 890 and ϳA.D. 1370.

Pollen Three main pollen zones were identified in the Amatitlán core (Figure 6). Zone I, from ϳ650 B.C. to ϳA.D. 600 is divided into to subzones (Ia and Ib). Subzone Ia, from ϳ600 B.C. to ϳA.D. 125, is dominated by herbs, mainly grasses (Poaceae, 15%), composites (Asteraceae, 15%) and maize (Zea, 10%). Trees and shrubs are also represented, mainly by pines (Pinus, 10%) and oaks (Quercus, 15%). Aquatic taxa are represented by the duckweed Lemna that peaks at ϳ360 B.C. (22%) and the alga Botryococcus. Between ϳ360 B.C. and ϳA.D. 100, the proportions of Zea and Asteraceae decrease (Ͻ5%) and the proportions of Pinus and Quercus increase to 15% and 25%, respectively. Lemna decreases, whereas Potamogeton and unknown alga-3 increase. Subzone Ib, from ϳA.D. 125 to ϳA.D. 600, shows an increase in Asteraceae (from 10 to 20%), fern spores (from Ͻ5% to 5%), and Zea (Ͻ5% to 10%). Poaceae, Pinus, and Quercus maintain about the same abundances, while aquatic elements decrease (Ͻ2%). Zone II, from ϳA.D. 600 to ϳA.D. 1600, is dominated mainly by trees. It shows an increase in Quercus and Pinus. Other tree genera such as bayberry (Myrica) and gumbo-limbo (Bursera), and shrubs such as Acalypha, increase during this time period. There is no change in Poaceae abundance, but Zea and Asteraceae decrease markedly. Aquatic taxa display low relative abundance during this time, except for Botryococcus, which increases slightly. Zone III, from ϳA.D. 1600 to the present, shows a decrease in trees and shrubs, particularly Quercus, from 25% to 10%, and Pinus, from 25% to 20%. A slight increase in Pinus, Alnus, Eugenia, and Trema is recorded after ca. A.D. 1900. Herbs and aquatic taxa, including Lemna, unknown alga-1, and Pediastrum, increase.

ENVIRONMENTAL HISTORY

Sediment Indicators of Environmental Change Lake Amatitlán sediments are composed largely of inorganic material, containing variable amounts of organic matter (Figure 3). The ratio of total (organic) carbon to total nitrogen (TC/TN) in the sediment was used as an indicator of the relative con- tributions of organic matter from terrestrial versus aquatic sources. Terrestrial organic matter typically possesses TC/TN values Ͼ20, whereas algal organic matter generally displays TC/TN values from ca. 4 to 10 (Meyers & Ishiwatari, 1993). Stratigraphic changes in d15N of sediment organic matter (Figure 4) were used to infer past productivity and identify sources of nitrogen accumulating on the lake bottom (Hodell & Schelske, 1998; Brenner et al., 1999; Das et al. 2009), including sewage (d15N values of 3–12‰) (Rosenmeier et al., 2004). Magnetic susceptibility (MS) can be used to identify periods of soil erosion from watersheds (Lowe & Walker, 1997). In the Lake

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Figure 6. Pollen relative abundance (%) diagram for core Amatitlán 15-III-2000. GEA_20352.qxd 3/24/11 12:45 PM Page 12

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Amatitlán core, however, high values also indicate input of volcanic ash. In our record, isolated MS peaks were used to identify episodic volcanic eruptions, whereas sustained high MS values were used to identify periods of higher transport of ash-rich soils into the lake over time (Figure 4). Consistently low values were interpreted to reflect periods of lower volcanic activity and minimal erosion. Diatom frustules in the Lake Amatitlán core were used to infer past water levels, nutrient concentrations (trophic status), and ion concentrations (conductivity) in the lake water (Figure 5). Assemblage 1, with high relative abundances of planktonic Aulacoseira granulata, and fluctuating percentages of the planktonic–littoral Cyclotella spp., was interpreted to reflect relatively high lake levels, high pH, and low conductivity. Periods with higher abundances of Cyclotella species may reflect slight decreases in water level. Assemblage 2, with its littoral Nitzschia spp., indicates relatively lower lake level and eutrophic water, but deeper-water conditions are indicated during times with greater percentages of planktonic Fragilaria delicatissima. Assemblage 3, also composed of Nitzschia spp., lacks the planktonic component and is indicative of uniformly low water levels and higher productivity. Presence of maize (Zea) and abundant herbs, especially Asteraceae, is indicative of agriculture (Figure 6). Times of relatively low proportions of forest elements indicate land clearance (Figure 6). High water-column nutrient concentrations are inferred from aquatic elements such as the alga Botryococcus, and Lemna, which is a floating plant that derives its nutrients directly from the water column (Goldsborough, 1993). We identified six major periods of environmental change in the Amatitlán sediment core using multiple sediment variables (Figure 7). Shifts in paleoenvironmental indicators generally correspond with known changes in the Maya prehistory of the region, identified archaeologically. Below, we characterize the environmental conditions during each episode, using a suite of paleoenvironmental proxies, and indicate the approximate corresponding archaeological or historic period.

ϳ625 B.C. to ϳ250 B.C. (Middle Preclassic) At the beginning of this period until ϳ360 B.C., agriculture expanded at the expense of forest. Sustained soil erosion occurred from the beginning of the period until ϳ500 B.C., as indicated by the highest values in MS in the record (Figure 4). Presence of charcoal particles (2–3 mm) in this interval suggests fire was used fre- quently to clear forest for agriculture. High lake levels prevailed, with high planktonic productivity. From ϳ360 B.C. until the end of the period, agriculture decreased, the forest recovered, and lake level may have decreased slightly. Soil erosion also decreased. During this period, the highlands were subject to increas- ing Maya population densities and land use intensification, and numerous satellite villages arose (Murdy, 1996; Borhegyi 1965). A sociocultural change dated at ϳ400 B.C. in the nearby city of Kaminaljuyu is represented by the Providencia to Verbera phase change, identified by a shift in ceramic styles (Popenoe de Hatch et al., 2002; Murdy 1996). Another change, dated at ϳ400 B.C., was the construction of

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Figure 7. Inferred environmental changes compared to local Maya cultural chronology; calendar ages pre- sented as A.D./B.C.

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a new canal (Canal San Jorge) in Lake Miraflores that was built parallel to the abandoned Canal Miraflores. Canals were used primarily to irrigate vegetable crops (Popenoe de Hatch et al., 2002). The reforestation recorded by our pollen data at ϳ360 B.C. probably reflects land abandonment, as more people moved to the grow- ing urban site of Kaminaljuyu.

ϳ250 B.C. to ϳA.D. 125 (Late Preclassic) Water level declined and the lake became eutrophic during this period, as evidenced by an increase in the accumulation of terrestrial organic matter. Land use that characterized the previous period, as indicated by the pollen record, with decreas- ing agriculture and forest expansion, continued until ϳ100 B.C. Thereafter, the pollen record indicates that agriculture increased once again at the expense of forest. The peak in magnetic susceptibility at the beginning of this period most likely indicates a volcanic event. Soil erosion remained low until ϳA.D. 50, after which it increased, supporting pollen evidence for a change in land use. Population continued to grow and many people migrated to the northern city of Kaminaljuyu, which was established as an important political and cultural center during this period (Sanders & Murdy, 1982; Sharer & Sedat, 1987). There was approximately a 40% decline in population around Lake Amatitlán during the Terminal Formative, possibly as a consequence of migration to urbanized Kaminaljuyu (Murdy, 1996). Canal San Jorge was used until ϳA.D. 100, when Lake Miraflores desiccated completely (Popenoe de Hatch et al., 2002). At Kaminaljuyu, cultural changes are documented by ceramics, with a phase change from Verbena to Arenal ϳA.D. 200 (Popenoe de Hatch et al., 2002).

ϳA.D. 125 to ϳA.D. 875 (Late Preclassic–Late Classic) At the beginning of this period, agriculture continued to expand and there was increased deforestation and sustained soil erosion. Lake water level increased relative to the previous period and maintained high levels throughout. At ϳA.D. 600, however, the pollen record indicates forest expansion and a decrease in agriculture. The organic matter that accumulated in the lake changed from algal-derived (low C/N) to terrestrial-derived (high C/N), reflecting sustained erosion and input of organic matter from the watershed, resulting from deforestation at the beginning of the period. Culturally, the rural population continued to decrease while urban Kaminaljuyu grew and became more powerful (Sanders & Murdy, 1982). Pyramids were built at Kaminaljuyu (Sharer & Sedat, 1987) and there is evidence of lowland Maya and Mexican influence, such as glyphic inscriptions (Borhegyi, 1965; Sanders & Murdy, 1982). Cultural changes are reflected in the different archaeological phases identified during this period, including Arenal, Santa Clara, Aurora, Esperanza, Amatle, and Pamplona (Popenoe de Hatch et al., 2002). In the Middle Classic, however, the distribution of population changed as people emigrated from Kaminaljuyu and resettled in rural areas. Eventually, in the Late Classic, a provincial center was established

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near Lake Amatitlán (Murdy, 1996). Increased erosion in the region during this time is consistent with archaeological evidence suggesting intensive land use practices, including agriculture (Sanders & Murdy, 1982).

ϳA.D. 875 to ϳA.D. 1375 (Terminal Classic–Postclassic) This period was characterized by forest expansion and very little agriculture. Lake levels were low, the littoral zone was extensive, and the lake was eutrophic. The proportion of terrestrial organic matter in the sediments was high. Although this seems at odds with the pollen data, which indicate land abandonment and forest recovery, greater input of high-C/N material may have resulted from continued human clearance of regrowing, successional vegetation. Eutrophic conditions under relaxed anthropogenic impact may have been, in part, a consequence of reduced lake volume, which concentrated nutrients. Lower lake levels may have been due to regional drying or possibly a result of reforestation, as regrowing vegetation captured greater amounts of incoming rainfall, limiting runoff to the lake. In the Maya Lowlands, dry conditions prevailed between A.D. 750 and 1050, with episodes of pronounced drought (Hodell et al., 2001; Brenner et al., 2002; Hodell, Brenner, & Curtis, 2005). Droughts are also reported for the Guatemalan Pacific Lowlands (Neff et al., 2006), and dated at ϳA.D. 780, and A.D. 910, 1074, and 1139 in Belize (Webster et al., 2007). Archaeological excavations indicate that large ceremonial centers in the Guatemalan highlands were abandoned in the Late Classic, as were most highland valley sites (Borhegyi, 1965). Likewise, the population at Kaminaljuyu decreased markedly (Sanders & Murdy, 1982). The provincial center established in Amatitlán in the Late Classic was reduced to a small village in the Terminal Classic (Murdy, 1996), and the population that lived on the slopes moved to the valley (Borhegyi, 1965; Murdy, 1996). According to Murdy (1996), this was probably due to land degradation and soil loss. Land abandonment and population reduction were also recorded in the Pacific Lowlands and along the boundary between Guatemala and Mexico (Gill, 2000). Archaeological phases during this time included Ayampic and part of Chanautla (Popenoe de Hatch et al., 2002). Two volcanic events occurred at A.D. 989 and A.D. 1225.

ϳA.D. 1375 to ϳA.D. 1875 (Late Postclassic) This period was characterized by increased lake water levels and low nutrient concentrations. Forest surrounding the lake expanded, and there was considerably less agriculture prior to the 17th century. However, at ϳA.D. 1600 conditions changed, as pollen evidence for deforestation and increased agriculture indicates the return of people to the previously abandoned land. This period corresponds to the Maya Late Postclassic and the arrival of the Spanish. Borhegyi (1965) mentions that movement of populations to mountain slopes and hilltops during the Late Classic continued until the Early Postclassic, and that people from the isolated satellite villages created during the Classic period returned to a Preclassic mode of subsistence, in which villages were economically independent but still culturally affiliated with the primary

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settlement. One volcanic eruption occurred at A.D. 1400, and Kaminaljuyu was abandoned. Sociocultural changes are reflected in the Chinautla phase (Popenoe de Hatch et al., 2002).

ϳA.D. 1875 to Present (Modern Era) Conditions similar to the previous period prevailed, except for a slight change in forest composition, with more variety in trees, such as Alnus, Eugenia, and Myrica. This period corresponds to the establishment of Guatemala City as the capital (A.D. 1775) and very rapid urban expansion over the last ϳ50 years. After ϳA.D. 1875, Lake Amatitlán started to receive greater nitrogen inputs, almost certainly from sewage, as indicated by the high d15N values (Ͼ10). Today, Amatitlán receives a substantial nutrient load and other contaminants from Guatemala City via the Rio Villalobos, and despite its hypereutrophic condition, it is considered by some to be “a dead lake.”

CONCLUSIONS The paleoenvironmental history of the Guatemala highlands was inferred using multiple lines of sedimentological, chemical, and biogenic evidence in a sediment core from Lake Amatitlán. Results reflect the dynamic relations among human activities, climate, and the environment. The main environmental changes we identified in the lake core are synchronous with archaeologically documented periods in Maya prehistory. Periods of reforestation and soil stabilization, inferred from pollen, geochemistry, and magnetic susceptibility of the sediments, coincide with times of population decrease and/or land abandonment evidenced by the archaeological record. Likewise, paleolimnological evidence for deforestation and soil erosion coincides with periods of population growth and increased land use. Two periods of low lake level and eutrophic conditions, inferred from diatom analyses, were identified between ϳ250 B.C. and ϳA.D. 125 and from ϳA.D. 875 to ϳA.D. 1375. These periods occurred at times when pollen and archaeological data suggest forest expansion and minimal human impact in the area. The lower lake stage may be explained by two possible processes which could have operated independently, or in combination: (1) foresta- tion, with increased vegetation cover intercepting rainfall and reducing runoff to the lake; and (2) climate drying, that is, increased evaporation to precipitation ratio. During the first low-stage period, Lake Miraflores at the nearby site of Kaminaljuyu dried completely by ϳA.D. 100. Although this argues for regional drying, the lake’s demise could also have been caused by human-mediated drainage for agricultural pur- poses. During the second low-stage episode, there is ample evidence of dry conditions at sites in the Maya Lowlands, again supporting the notion that climate accounted for the drop in water level. We propose that the nutrient enrichment inferred during times of low lake level was caused by reduced lake water volume and resultant concentration of nutrients delivered to the basin as a consequence of centuries of widespread agriculture. Additional paleolimnological studies from the region

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will enable comparisons with the data from Lake Amatitlán and shed further light on the paleoecology of the highland Maya.

We thank Drs. Huckleberry and Woodward and two anonymous reviewers for helpful comments on the manuscript. Dr. Jason Cosford is thanked for his comments on an earlier version of the manuscript. Natalia Hoyos kindly produced Figure 1. The Instituto de Antropología e Historia (Dirección General del Patrimonio Cultural y Natural de Guatemala) and the Universidad del Valle de Guatemala supported the fieldwork. We thank AMSA (Autoridad para el Manejo Sustentable de la Cuenca y del Lago de Amatitlán) for facilitating access to the lake.

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Received 10 August 2010 Accepted for publication 9 January 2011 Scientific editing by Nicholas Dunning

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