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Long-Term Geomorphic Change in the Maya Lowlands of Central America
Abstract
Prehispanic societies transformed large areas of tropical forest in Mexico and Central America, a region now known as the Maya lowlands, into highly engineered urban and agricultural landscapes, over a period of more than two millennia. This chapter provides an overview of the impacts of the ancient Maya on their environment, with a focus on the history of Maya modification of local and regional geomorphic systems during the late Holocene. An overview of the geomorphology of the Maya lowlands is provided, with key examples of Maya interactions with and modifications of the landscape. The Maya converted natural ecosystems into vast urban and rural infrastructure with locally attuned water management systems that included reservoirs, wetland fields and canals, terraces, field ridges and water temples. Evidence for increasing Maya deforestation, carried out for urbanization and agriculture, is preserved in the form of deep sequences of anthropogenic sediments that cascaded through catchments, buried Maya infrastructure and paleosols, silted in reservoirs, waterways, floodplains and wetlands, and accumulated on lake bottoms. The use of proxies for ancient Maya land-use intensity, such as inorganic and organic geochemistry and stable carbon isotopes, soil organic matter and mineral magnetism, are briefly reviewed. The Maya geomorphic impacts were sufficiently severe that centuries of erosion left a region-wide anthropogenic chronostratigraphic marker known as the ‘Maya Clay’ across much of the southern Maya lowlands. The greatest geomorphic impacts of the Maya in the region began to diminish by c. 1000 BP, in response to social and political upheavals that have been referred to as the ‘Maya Collapse.’ Geomorphological, geoarcheological, and paleoenvironmental investigations have provided data that can be used to quantify Maya-mediated environmental impacts and test hypotheses about climate and environmental drivers of societal ‘Collapse.’
... The sediments of the delta and the broader lower Usumacinta-Grijalva River Basin come mostly from the materials eroded from the Sierra Madre de Chiapas and Altos de Chiapas, mainly composed of diorites and granites belonging to a Paleozoic batholith (Cros et al., 1998;Morán-Zenteno et al., 1999; Figures 1 and 2(a)), and in lesser amounts, from the volcanic ejecta of the El Chichón and Tacaná volcanoes (Solís-Castillo et al., 2014;Figures 1 and 2(b)), from different volcanoes located in the Central American Volcanic Arc (Figure 1), and even lesser amounts from Saharan dusts. The highland regions of the basin have high relief and heavy precipitation (up to 3 m per annum), leading to high rates of denudation (Cook et al., 2022). The coastal plain geology includes a sequence of seaward-dipping Pleistocene terraces and Holocene deltaic deposits that partially cover the Pleistocene terraces (Thom, 1967;West et al., 1969;Solís-Castillo et al., 2013). ...
... La Venta arose contemporaneously with many Middle Preclassic Olmec and Maya sites in the Gulf Coast region that mark a new phase of environmental history, featuring the hallmark Mesoamerican organization and architecture of formal complexes of plazas and pyramids as well as extensive land clearance, agriculture, and urbanization (Inomata et al., 2021). (Beach et al., 2015;Cook et al., 2022). Rivers were an integral aspect of the Maya environment, with many key cities established along the Usumacinta-Grijalva River system, allowing the Maya to take advantage of floodplain soils, riverine resources, and transportation. ...
... Rivers were an integral aspect of the Maya environment, with many key cities established along the Usumacinta-Grijalva River system, allowing the Maya to take advantage of floodplain soils, riverine resources, and transportation. Rivers were a primary form of transport and communication through some parts of the Maya lowlands, though peripheral coastal transport and overland transport prevailed through the karst in Yucatan that has only underground water flow (Cook et al., 2022;Velázquez, 1994) (Figure 1). ...
The lower Usumacinta–Grijalva River Basin contains one of the richest biodiversity landscapes of the Maya region. Our research is based on (1) an integrative literature review of the geomorphological and archaeological papers published about the lower Usumacinta–Grijalva River Basin and (2) topographic analysis of digital elevation models using a geographical information system to explore the relationship between past human settlement and landscape accessibility along the coastal plain of Tabasco. This work provides a new synthesis of previous research and proposes new models for the geomorphic evolution of the lower Usumacinta–Grijalva River Basin in the context of four millennia of human land use and settlement. For the evolution of the strand-plain of the Usumacinta and Grijalva rivers, there are two published geochronological models that provide different chronologies. We discuss here how both geochronological models encompass Pre-Columbian human settlement in the delta. Interestingly, we notice that one of them overlaps a possible high-magnitude flood event (or events) that drove large geomorphic change around 750 CE (1200 BP), with implications for settlement patterns and chronology. Based on topographical analysis of the eastern-distal sector of the Usumacinta–Grijalva delta, we propose a new model for the evolution of this area with implications for the human occupation during the Mesoamerican Terminal Classic and Early Postclassic on the delta. As one of the main conclusions, we propose that the Pom–Atasta water bodies predate much of the Usumacinta–Grijalva delta and the most recent phase of delta building overlays the original lagoon barriers, resulting in a geomorphic setting more attractive to local human occupation after the Terminal Classic period. According to one of the geochronological models of the delta, this dates to ca. 900 CE, preceding the establishment of nearby settlements such as Atasta.
... Focusing on the present, this includes very little research dedicated to understanding the environmental consequences of mercury use and deposition in antiquity. To expand on the archaeological data sets on ancient cinnabar and elemental mercury use, multidisciplinary teams working on Maya archaeological projects in recent decades have undertaken geochemical studies of excavated Maya occupation areas and environmental materials (mainly soils) (Cook et al., 2022). We may turn to the growing body of mercury data collected during these investigations as a means of quantifying the environmental legacy of ancient mercury use by the Maya. ...
... This is an important consideration given the propensity for heavy metal concentrations to generally increase with decreasing particle size, with the highest particle-size effect often seen in the silt fraction (for example, in the <45 μm fraction in Wang et al., 2006). Most of the studies in this review reported Hg values determined on the <2 mm soil fraction (from Chunchucmil, Tikal, Lake Petén Itza, Piedras Negras, Cancuén, Cerén), but we note that most Maya lowland region soils are dominated by much finer clay-rich (<2 μm) material (Beach et al., 2015;Cook et al., 2022). The Hg data from La Corona, Chan b'i and Actuncan are from samples that were not sieved, but instead pulverized prior to analysis. ...
... While just at the TET, this concentration of Hg is 24 times greater than the maximum upper limit for background samples at the site p. 638). Along with the anthropogenic geochemical enrichment processes previous detected across the Maya world, elevated Hg in soils and sediment from pre-Columbian cinnabar mining and use may be considered one of the "golden spikes" of an early Anthropocene (or "Mayacene"); an enduring and distinct region-wide geochemical marker of pre-Columbian landscape modification (Beach et al., 2015;Wagreich and Draganits, 2018;Penny and Beach, 2021;Cook et al., 2022). ...
The Mexico and Central American region has a history of mercury use that began at least two millennia before European colonisation in the 16th century. Archaeologists have reported extensive deposits of cinnabar (HgS) and other mercury materials in ancient human settlements across the region. However, there has been no consideration to date of the environmental legacy of this long history of anthropogenic mercury use. This review begins by synthesising our knowledge of the history and nature of anthropogenic mercury in ancient Mesoamerica based on archaeological data, with a particular focus on the Maya culture of lowland Guatemala, Belize, the Yucatan of Mexico, El Salvador, and Honduras. The Classic Period Maya used mercury for decorative and ceremonial (including funerary) purposes: Cinnabar (HgS) predominantly, but the archaeological record also shows rare finds of elemental mercury (Hg0) in important burial and religious contexts. In this review, we have located and summarised all published data sets collected from (or near) ancient Maya settlements that include environmental mercury measurements. Comparing mercury determinations from pre-Columbian Maya settlements located across the region confirms that seven sites from ten have reported at least one location with mercury concentrations that equal or exceed modern benchmarks for environmental toxicity. The locations with elevated mercury are typically former Maya occupation areas used in the Late Classic Period, situated within large urban settlements abandoned by c. 10th century CE. It is most likely that the mercury detected in buried contexts at Maya archaeological sites is associated with pre-Columbian mercury use, especially of cinnabar. In more complex contexts, where modern biological or specifically anthropogenic inputs are more probable, legacy mercury in the environment will have a more complex, and time transgressive input history. This review identifies current research gaps in our understanding of the long history of Maya mercury use and in the collection of robust total mercury datasets from the Maya world. We identify important areas for future research on the environmental persistence and legacy of mercury, including the need to interpret environment mercury data in the context of mercury exposure and human health at Maya archaeological sites.
Elevated concentrations of total mercury (THg) are found in the surface soils and flanking wetland sediments at the Classic Maya coastal site of Marco Gonzalez, Belize. Significant concentrations (up to 1.3 µg·g−1 dry mass) of THg occur in leaf litter‐rich soils, as well as in the artefact‐rich anthrosol spread over the vegetated mound site of structures and occupation debris. The abundance and spatial pattern of major and trace elements measured in the surface soils indicate both site‐scale controlling factors of topography, structures and vegetation on soil geochemistry as well as local highs in concentration compared with background, due to human activity. Geochemical stratigraphy of wetland sediment cores shows that a shift from carbonate‐reef sediments to mangrove peat in the 13th century AD was attended by an input of allogenic (mineral) elements, including mercury. A THg concentration peak (0.8 μg·g−1) in brackish pool sediment is 210Pb‐dated to 1960–1970 AD, but the incorporation of mercury in multiple cores adjacent to the site shows increasing mercury inputs to have occurred before, during Classic‐period Maya occupation and following the sites abandonment. Analysis of element values from site‐scale soil sampling, combined with results from off‐site cores, provides a numerical framework upon which outlier values of THg and other element spatial patterns can be assessed, especially the spatial co‐association of elements related to differences in soil–sediment matrices. Geochemical results from active soils developing from occupation deposits (anthrosols) and sediment cores open up questions concerning contemporary and past mercury accumulation at coastal Mayan sites, and the wider interaction of human and natural biogeochemical processes that occur in human‐modified soils and coastal wetland sediments.
In this paper, we present the highest-resolution-available (10 m) national map of the mangrove ecosystems of Belize. These important ecosystems are increasingly threatened by human activities and climate change, support both marine and terrestrial biodiversity, and provide critical ecosystem services to coastal communities in Belize and throughout the Mesoamerican Reef ecoregion. Previous national- and international-level inventories document Belizean mangrove forests at spatial resolutions of 30 m or coarser, but many mangrove patches and loss events may be too small to be accurately mapped at these resolutions. Our 10 m map addresses this need for a finer-scale national mangrove inventory. We mapped mangrove ecosystems in Belize as of 2020 by performing a random forest classification of Sentinel-2 Multispectral Instrument imagery in Google Earth Engine. We mapped a total mangrove area of 578.54 km2 in 2020, with 372.04 km2 located on the mainland and 206.50 km2 distributed throughout the country’s islands and cayes. Our findings are substantially different from previous, coarser-resolution national mangrove inventories of Belize, which emphasizes the importance of high-resolution mapping efforts for ongoing conservation efforts.
Ancient Maya societies experienced a period of reorganisation and change in settlement patterns associated with social and climate instability at the end of the Classic period (750-1000 CE) and the subsequent Postclassic period (1200-1500 CE). Although it has been proposed that severe droughts and the breakdown of Classic political systems caused a migration of populations towards the coast, we have little evidence of the nature of land-use at coastal sites. Our understanding of subsistence on islands has been shaped by archaeological research indicating marine-based diets, with maize imported from the mainland. Here we provide, for the first time, palaeoecological proxy data that inform on ancient Maya land-use on an island site, located on Ambergris Caye, Belize. Using pollen and charcoal proxies, we present over 6000 years of environmental change and land-use history. Our reconstruction reveals evidence of cultivation, beginning at 2900 BCE and culminating during the Postclassic Period. We demonstrate that periods of higher land-use intensity correlate with climate instability, which corroborates archaeological evidence of migration to coastal locations. We hypothesize that the diverse marine and terrestrial environments of the island provided sustainable resources for the mainland Maya to use during times of both political and climatic stress.
The analysis of faecal stanols in lake sediment cores offers a novel opportunity to reconstruct human population change, assuming that variability in faecal stanol concentration is a reliable proxy for relative human populations. The ancient lowland Maya of Mesoamerica represents an important ancient society whose demographic dynamics in many locations remain uncertain. We apply the faecal stanol proxy to a sediment core retrieved from a lake adjacent to the archaeological site of Itzan, an ancient population centre in the southwestern Maya lowlands. The sedimentary faecal stanol record from Laguna Itzan implies substantial centennial-and millennial-scale changes in local human populations from 3300 cal years BP to the present. Variability in faecal stanol concentrations is broadly consistent with archaeological evidence for regional societal change across the Maya lowlands, but also implies an earlier presence of humans at this site than is currently indicated in the Itzan archaeological record. We find evidence for high-frequency variability in coprostanol concentrations during the Maya Preclassic period, which we infer represents centennial-scale shifts in settlement patterns associated with changes in agricultural and land use patterns. Given Preclassic-period faecal peak stanol concentrations, we observe lower-than-expected Classic-period faecal peak stanol concentrations, and these may partly be a result of either use of human waste for fertiliser or reduced soil erosion or both. Three periods of inferred population decline are associated with palaeoclimate evidence for a drying climate, specifically during the Terminal Classic (1220-1050 cal yr BP) and the Protoclassic 2 (1860-1670 cal yr BP), as well as the less well-studied drought between 3330 and 2900 cal yr BP during the Early to Middle Preclassic periods. An additional decline and hiatus in coprostanol input coincides with a period of anomalously wet climate in the Late Preclassic. These linkages suggest that climatic change and variability could have played a role in demographic change at multiple points in the evolution of Maya civilisation. Our work shows that faecal stanols are valuable proxies for past human population dynamics, and their relation to climatic change, in Mesoamerica.
The Coupled Model Intercomparison Project Phase 6 (CMIP6) dataset is used to examine projected changes in temperature and precipitation over the United States (U.S.), Central America and the Caribbean. The changes are computed using an ensemble of 31 models for three future time slices (2021–2040, 2041–2060, and 2080–2099) relative to the reference period (1995–2014) under three Shared Socioeconomic Pathways (SSPs; SSP1-2.6, SSP2-4.5, and SSP5-8.5). The CMIP6 ensemble reproduces the observed annual cycle and distribution of mean annual temperature and precipitation with biases between − 0.93 and 1.27 °C and − 37.90 to 58.45%, respectively, for most of the region. However, modeled precipitation is too large over the western and Midwestern U.S. during winter and spring and over the North American monsoon region in summer, while too small over southern Central America. Temperature is projected to increase over the entire domain under all three SSPs, by as much as 6 °C under SSP5-8.5, and with more pronounced increases in the northern latitudes over the regions that receive snow in the present climate. Annual precipitation projections for the end of the twenty-first century have more uncertainty, as expected, and exhibit a meridional dipole-like pattern, with precipitation increasing by 10–30% over much of the U.S. and decreasing by 10–40% over Central America and the Caribbean, especially over the monsoon region. Seasonally, precipitation over the eastern and central subregions is projected to increase during winter and spring and decrease during summer and autumn. Over the monsoon region and Central America, precipitation is projected to decrease in all seasons except autumn. The analysis was repeated on a subset of 9 models with the best performance in the reference period; however, no significant difference was found, suggesting that model bias is not strongly influencing the projections.
The northern Yucatan peninsula is prone to coastal flooding and erosion owing to its low-land elevation and high exposure to storms. Therefore, it is important to assess the capability of the beach-dune system to resist, recover, and adapt from storms in the context of coastal development and climate change. This work aims to investigate the role of human impacts on the spatiotemporal evolution of the Coastal Resilience Index (CRI) in the area. The study is conducted on a prograding micro-tidal beach located on the vicinity of coastal structures. Beach and dune morphometrics, characteristic beach parameters, and maximum shoreline recession were determined from the analysis of beach profiles undertaken along a 2-km straight of coastline during the 2015-2020 period. Moreover, the maximum extreme water levels were estimated using in situ data and numerical models. This information is employed to assess the alongshore and temporal variability of the beach resilience. The results suggest that the beach and dune morphology present alongshore and temporal variability due to the human impacts associated to the dune degradation and the presence of coastal structures. The analysis shows that coastal resilience has been increasing over the past years but present significant alongshore variations. High CRI values were found at beach transects presenting low anthropogenic impact, whereas low resilience was observed at transects with a degraded dune or located in the vicinity of coastal structures regardless of presenting high progradation rates. The observed beach response during the passage of recent tropical storms is consistent with the CRI values.
Changes in land-use and land-cover, including both agricultural expansion and the establishment of protected areas, have altered the landscape pattern and extent of forest and wetland cover in the tropics. In Central America, land-use and land-cover change is also threatening the cultural resources of the region’s ancient Maya heritage since many ancient sites have been degraded by burning, deforestation, and plowing. In this study of Orange Walk District of northern Belize, from the 1980s to the present, we used multitemporal Landsat data with a random forest classifier to reveal trends in land-use and land-cover change and the increasing loss of forest and wetlands. We develop a random forest classifier that is time-generalized to map land-use and land-cover across the entire Landsat record, including Landsat 4, 5, 7, and 8, with a single algorithm. Including multiyear and seasonal composites was important for obtaining cloud-free coverage and distinguishing between different land-use and land-cover types. Early deforestation (1984–1987) was in small patches scattered across the landscape and likely driven by small scale agriculture such as milpa and smaller area tractor and horse-drawn plowing. The establishment of protected areas in the late 1980s and early 1990s allowed for forest regrowth in these areas, while wetland losses were high at 15%. The transition to industrial agriculture in the 2000s, however, drove a 43.6% expansion of agriculture and a 7.5% loss of forest and a 28.2% loss of wetlands during the ~15 years. Protected areas initiated in the 1980s led to a nearly 100 km2 decrease in agriculture from 1984–1987 to 1999–2001, and they became essential refugia for habitat and maintaining ecosystem services.
Central America is a region susceptible to natural disasters and climate change. We reviewed the literature on the main atmospheric and oceanographic forces and climate modulators affecting Central America, for different spatial and time scales. We also reviewed the reported correlation between climate variability, natural hazards and climate change aspects (in the past and future). In addition, we examined the current state of seasonal prediction systems being applied to the region. At inter-annual scales, El Niño/Southern Oscillation is the main climate modulator; however, other indices such as the Tropical North Atlantic, Atlantic Multi-Decadal Oscillation and Pacific Decadal Oscillation, have shown a correlation with precipitation anomalies in the region. Current seasonal forecast systems in the region have shown a constant development, including incorporation of different approaches ranging from statistical to dynamical downscaling, improving prediction of variables such as precipitation. Many studies have revealed the need of including –in addition to the climatic information– socio-economic variables to assess the impact of natural disasters and climate change in the region. These studies highlight the importance of socio-economic and human life losses associated with the impacts caused by natural hazards for organizations and governments. Rev. Biol. Trop. 66(Suppl. 1): S153-S175. Epub 2018 April 01.
Evidence for the oldest known zeolite water purification filtration system occurs in the undisturbed sediments of the Corriental reservoir at the Maya city of Tikal, in northern Guatemala. The Corriental reservoir was an important source of drinking water at Tikal during the Late Preclassic to Late Classic cultural periods. X-ray diffraction analysis (XRD) and six AMS radiocarbon ages show that between ~ 2185 and 965 cal yr B.P. the drinking water in the Corriental reservoir water was filtered through a mixture of zeolite and coarse, sand-sized crystalline quartz. Zeolite is a non-toxic, three-dimensionally porous, crystalline, hydrated aluminosilicate with natural adsorbent and ion exchange properties, which removes harmful microbes as well as dispersed insoluble and soluble toxins from drinking water. The occurrence of zeolite in Corriental reservoir sediments expands our understanding of the earliest history of water purification and the long-term sustainability of an ancient Maya city.
Climate reconstructions for the Common Era are compromised by the paucity of annually-resolved and absolutely-dated proxy records prior to medieval times. Where reconstructions are based on combinations of different climate archive types (of varying spatiotemporal resolution, dating uncertainty, record length and predictive skill), it is challenging to estimate past amplitude ranges, disentangle the relative roles of natural and anthropogenic forcing, or probe deeper interrelationships between climate variability and human history. Here, we compile and analyse updated versions of all the existing summer temperature sensitive tree-ring width chronologies from the Northern Hemisphere that span the entire Common Era. We apply a novel ensemble approach to reconstruct extra-tropical summer temperatures from 1 to 2010 CE, and calculate uncertainties at continental to hemispheric scales. Peak warming in the 280s, 990s and 1020s, when volcanic forcing was low, was comparable to modern conditions until 2010 CE. The lowest June–August temperature anomaly in 536 not only marks the beginning of the coldest decade, but also defines the onset of the Late Antique Little Ice Age (LALIA). While prolonged warmth during Roman and medieval times roughly coincides with the tendency towards societal prosperity across much of the North Atlantic/European sector and East Asia, major episodes of volcanically-forced summer cooling often presaged widespread famines, plague outbreaks and political upheavals. Our study reveals a larger amplitude of spatially synchronized summer temperature variation during the first millennium of the Common Era than previously recognised.
Investigations in the now-submerged cave systems on the Yucatán Peninsula continue to yield evidence for human presence during the Pleistocene-Holocene transition. Skeletal remains are scattered throughout the caves of Quintana Roo, most representing individuals who died in situ. The reasons why they explored these underground environments have remained unclear. Here, we announce the discovery of the first subterranean ochre mine of Paleoindian age found in the Americas, offering compelling evidence for mining in three cave systems on the eastern Yucatán over a ~2000-year period between ~12 and 10 ka. The cave passages exhibit preserved evidence for ochre extraction pits, speleothem digging tools, shattered and piled flowstone debris, cairn navigational markers, and hearths yielding charcoal from highly resinous wood species. The sophistication and extent of the activities demonstrate a readiness to venture into the dark zones of the caves to prospect and collect what was evidently a highly valued mineral resource.
Understanding civilizations of the past and how they emerge and eventually falter is a primary research focus of archaeological investigations because these provocative data sets offer critical insights into long-term human behavior patterns, especially in regard to land use practices and sustainable environmental interactions. The ancient Maya serve as an intriguing example of this research focus, yet the details of their spectacular emergence in a tropical forest environment followed by their eventual demise have remained enigmatic. Tikal, one of the foremost of the ancient Maya cities, plays a central role in this discussion because of its sharp population decline followed by abandonment during the late 9th century CE. Our results, based on geochemical and molecular genetic assays on sediments from four of the main reservoirs, reveal that two of the largest reservoirs at Tikal, essential for the survival of the city during the dry seasons, were contaminated with high levels of mercury, phosphate and cyanobacteria known to produce deadly toxins. Our observations demonstrate severe pollution problems at a time when episodes of climatic aridity were prevalent. This combination of catastrophic events clearly threatened the sustainability of the city and likely contributed to its abandonment.
Archaeologists have traditionally thought that the development of Maya civilization was gradual, assuming that small villages began to emerge during the Middle Preclassic period (1000–350 bc; dates are calibrated throughout) along with the use of ceramics and the adoption of sedentism¹. Recent finds of early ceremonial complexes are beginning to challenge this model. Here we describe an airborne lidar survey and excavations of the previously unknown site of Aguada Fénix (Tabasco, Mexico) with an artificial plateau, which measures 1,400 m in length and 10 to 15 m in height and has 9 causeways radiating out from it. We dated this construction to between 1000 and 800 bc using a Bayesian analysis of radiocarbon dates. To our knowledge, this is the oldest monumental construction ever found in the Maya area and the largest in the entire pre-Hispanic history of the region. Although the site exhibits some similarities to the earlier Olmec centre of San Lorenzo, the community of Aguada Fénix probably did not have marked social inequality comparable to that of San Lorenzo. Aguada Fénix and other ceremonial complexes of the same period suggest the importance of communal work in the initial development of Maya civilization.
AimsWe studied how soils vary between cohune palm and non-cohune forests and assessed whether the forests differed in soil fertility.Methods
We sampled soil profiles from six cohune palm forests and eleven non-cohune forests. Our laboratory analyses included soil organic matter (SOM), extractable phosphorous, and the total concentration of 10 elements. Each soil characteristic was subjected to a mixed-effects model with depth, forest type, and the interaction between the two as factors that were grouped by excavation.ResultsTotal phosphorous, sulfur, and SOM differed significantly between the two forest types, with higher values in non-cohune forests, on average. SOM, extractable phosphorous, and nine elements showed statistically significant changes with depth. The interaction between depth and forest type was significant for eight elements and SOM. The elemental concentrations were consistently maintained with depth in the cohune forests. Meanwhile, the elemental concentrations in non-cohune forest soils decreased with depth for all elements except calcium and magnesium, which increased concentration with depth.Conclusions
Cohune forest soils and non-cohune forest soils differ in distinct ways but these differences do not relate to key measures of soil fertility. Cohune palm forest soils exhibit consistent elemental concentrations with depth, which suggests bioturbation or another phenomenon that redistributes nutrients.
Human presence on the Yucatán Peninsula reaches back to the Late Pleistocene. Osteological evidence comes from submerged caves and sinkholes (cenotes) near Tulum in the Mexican state of Quintana Roo. Here we report on a new skeleton discovered by us in the Chan Hol underwater cave, dating to a minimum age of 9.9±0.1 ky BP based on ²³⁰Th/U-dating of flowstone overlying and encrusting human phalanges. This is the third Paleoindian human skeleton with mesocephalic cranial characteristics documented by us in the cave, of which a male individual named Chan Hol 2 described recently is one of the oldest human skeletons found on the American continent. The new discovery emphasizes the importance of the Chan Hol cave and other systems in the Tulum area for understanding the early peopling of the Americas. The new individual, here named Chan Hol 3, is a woman of about 30 years of age with three cranial traumas. There is also evidence for a possible trepanomal bacterial disease that caused severe alteration of the posterior parietal and occipital bones of the cranium. This is the first time that the presence of such disease is reported in a Paleoindian skeleton in the Americas. All ten early skeletons found so far in the submerged caves from the Yucatán Peninsula have mesocephalic cranial morphology, different to the dolicocephalic morphology for Paleoindians from Central Mexico with equivalent dates. This supports the presence of two morphologically different Paleoindian populations for Mexico, coexisting in different geographical areas during the Late Pleistocene-Early Holocene.
Significance
Understanding agricultural subsistence is vital for understanding past complex societies. Lidar data are indicating widespread ancient Maya infrastructure. Wetland agriculture was crucial to ancient cultures, but no previous study coupled lidar with multiproxy evidence to demonstrate the extent and uses of Maya wetland fields. We conducted a lidar survey around wetlands that multiple use proxies established were ancient Maya polycultural systems. Lidar indicated the Birds of Paradise (BOP) wetland field complex was five times larger than we had previously mapped and identified an even larger wetland agroecosystem. We ground-verified the BOP fields through excavations and dating, creating a study to couple these multiproxy data with lidar, thereby demonstrating widespread ancient Maya wetland agroecosystems.
A synthetic history of human land use
Humans began to leave lasting impacts on Earth's surface starting 10,000 to 8000 years ago. Through a synthetic collaboration with archaeologists around the globe, Stephens et al. compiled a comprehensive picture of the trajectory of human land use worldwide during the Holocene (see the Perspective by Roberts). Hunter-gatherers, farmers, and pastoralists transformed the face of Earth earlier and to a greater extent than has been widely appreciated, a transformation that was essentially global by 3000 years before the present.
Science , this issue p. 897 ; see also p. 865
Now somewhat aging given its original 1987 SAA presentation and 1992 publication dates, this article retains its value and interest as one of the very first, pioneering applications of this methodology in the Maya lowlands. It had been previously employed successively and extensively both in the upper Midwest (especially Wisconsin) and in southern California, where the authors had become familiar with it. Exploratory as it was, it yielded excellent data and information regarding the circumambient Buenavista settlement zone of Guerra de Buenavista.
This paper presents the results of a multiproxy approach to the ancillary activities which supported the ancient Maya royal court of the center of La Corona (750–900 CE). This approach sampled both the plaster floors and their overlaying soil matrix from areas of the palace of La Corona, resulting in a data set comprised of inductively coupled plasma mass spectrometry geochemical, soil‐flotation derived microartifactual, and macrobotanical data. These data complemented the architectural and artifactual record, documenting elusive aspects of the economic, ancillary functions of the Northwest Group of the La Corona regal palace. Specifically, this approach revealed that distinct portions of this architectural group were regularly used for preparing foods and craft objects, carrying products and items, discarding ash, using and/or grinding cinnabar‐based pigments, and illuminating nighttime activities. These results not only revealed activity areas in patios, but also provided evidence regarding the functions of adjacent buildings. This paper significantly contributes to our understanding of the pragmatic economic functions of ancient Maya royal courts. In addition, the presented data sets are methodologically valuable for students of archaeological activity areas.
This paper responds to and supports the earlier ‘Three Flaws’ paper by William Ruddiman (this journal, 2018). It builds upon his critique of the method used by the Anthropocene Working Group (AWG) in determining the start date of the Anthropocene. While chronostratigraphy is acknowledged as the best means of establishing a framework for the division of deep time - on geological timescales of millions of years – it is argued that the method is unsuitable for use on archaeological and historical timescales. Close proximity in time between the chronostratigraphic observer and the stratigraphic boundary in question renders placement of a precisely defined globally synchronous timeline onto highly time-transgressive evidence inappropriate on these scales of analysis. Application of the method hinders rather than helps understanding of the role of human impact on Earth system change. It leads to loss of the bigger picture and to relative neglect of the crucial evidence provided by humanly-modified ground – the missing strata in most chronostratigraphic accounts of the Anthropocene start. A more ground-up approach is called for. Recognition of humans as geological agents needs to be accompanied by recognition of the distinctive traces of human agency in the ground, which are unprecedented in the stratigraphic records of earlier geological time periods.
The Caribbean is a complex region that heavily relies on its rainfall cycle for its economic and societal needs. This makes the Caribbean especially susceptible to hydro-meteorological disasters (i.e. droughts and floods). Previous studies have investigated the seasonal cycle of rainfall in the Caribbean with monthly or longer resolutions that often mask the seasonal transitions and regional differences of rainfall. This has resulted in inconsistent findings on the seasonal cycle. In addition, the mechanisms that shape the climatological rainfall cycle in the region are not fully understood. To address these problems, this study conducts: (i) a principal component analysis of the annual cycle of precipitation across 38 Caribbean stations using daily observed precipitation data; and, (ii) a moisture budget analysis for the Caribbean, using the ERA-Interim Reanalysis. This study finds that the seasonal cycle of rainfall in the Caribbean hinges on three main facilitators of moisture convergence: the Eastern Pacific ITCZ, the Atlantic ITCZ, and the western flank of the North Atlantic Subtropical High (NASH). The Atlantic Warm Pool and Caribbean Low-Level Jet modify the extent of moisture provided by these main facilitators. The expansion and contraction of the western flank of NASH generate the bimodal pattern of the precipitation annual cycle in the northwestern Caribbean, central Caribbean, and with the Eastern Pacific ITCZ the western Caribbean. This study identifies the Atlantic ITCZ as the major source of precipitation for the central and southern Lesser Antilles, which is responsible for their unimodal rainfall pattern. Convergence by sub-monthly transients contributes little to Caribbean rainfall.
We present new global maps of the Köppen-Geiger climate classification at an unprecedented 1-km resolution for the present-day (1980–2016) and for projected future conditions (2071–2100) under climate change. The present-day map is derived from an ensemble of four high-resolution, topographically-corrected climatic maps. The future map is derived from an ensemble of 32 climate model projections (scenario RCP8.5), by superimposing the projected climate change anomaly on the baseline high-resolution climatic maps. For both time periods we calculate confidence levels from the ensemble spread, providing valuable indications of the reliability of the classifications. The new maps exhibit a higher classification accuracy and substantially more detail than previous maps, particularly in regions with sharp spatial or elevation gradients. We anticipate the new maps will be useful for numerous applications, including species and vegetation distribution modeling. The new maps including the associated confidence maps are freely available via www.gloh2o.org/koppen.
Large, low-density settlements of the tropical world disintegrated during the first and second millennia of the CE. This phenomenon, which occurred in South Asia, Southeast Asia, and Mesoamerica, is strongly associated with climate variability and extensive landscape transformation. These profound social transformations in the tropical world have been popularized as “collapse,” yet archaeological evidence suggests a more complex and nuanced story characterized by persistence, adaptation, and resilience at the local and regional scales. The resulting tension between ideas of climate-driven collapse and evidence for diverse social responses challenges our understanding of long-term resilience and vulnerability to environmental change in the global tropics. Here, we compare the archetypal urban collapse of the Maya, in modern Belize, Guatemala, Honduras, and Mexico, during the 8th to 11th centuries CE, and the Khmer in modern Cambodia, Laos, Thailand, and Vietnam during the 14th to 15th centuries CE. We argue that the social response to environmental stress is spatially and temporally heterogenous, reflecting the generation of large-scale landesque capital surrounding the urban cores. Divergences between vulnerable urban elite and apparently resilient dispersed agricultural settlements sit uncomfortably with simplistic notions of social collapse and raise important questions for humanity as we move deeper into the Anthropocene.
Wetlands epitomize all forms of the proposed Anthropocene era because they record both past and recent human environmental interaction and because of their abundant resources. This is especially true for tropical wetlands, and a growing body of research demonstrates their important connections with past and Indigenous societies. Maya culture, for example, provides an extraordinary example of wetland use in the “Early Anthropocene”. Through excavations and lidar survey, we demonstrate that ancient Maya farmers managed riparian wetlands in northwestern Belize to a much greater spatial extent than previous estimates. This paper provides new evidence from soil geomorphic and palaeoecological excavations within the Birds of Paradise wetland in Belize. We focus on the timing, extent, and intensity of human management as well as soil pedogenesis and ecological changes over the last c. 2000 years. Bayesian modelling of radiocarbon dates show the transformation of the wetland from a natural to an agricultural system, starting as early as c. 2100 BP. The Maya were constructing berms on the margin of the wetland by c. 1600 BP, and widespread clearing and canal construction began by c. 1350-1290 BP. These periods coincide with population growth and decline and urban construction and abandonment in this region. This clearing, farming, and channelization ended as late as c. 690-620 BP based on canal sedimentation, pollen evidence reflecting tropical forest replacing cultivars like maize, and soil carbon isotope ratios that reflect C4 plants like maize shifting to more mixed and C3 plants. We demonstrate the complexity and scale of human engineering and modification of soil and water resources, provide a new chronology for ancient wetland use, and present new evidence for the farming of economic plants as well as the succession of tropical wetlands after intensive anthropogenic manipulation ceased.
Soils are a pivot of sustainable development. Yet, urban planning decisions persist in compromising the usability of the urban soils resource. Urban land cover expansion to accommodate an increasing population results in soil sealing. Concealment of and physical obstructions to soils prevent urban populations from engaging with their soil dependency. The concept of soil connectivity recognises that nurturing mutually beneficial soil–society relations is an essential dimension for achieving soil security. The concentrated populations of urban environments acutely require productive soil–society relations and offer the greatest potential for enhancing soil connectivity. Soil connectivity remains notably under-researched, however, resulting in deficient evidence to substantiate exactly how soil connectivity can contribute to sustaining urban life. The entanglement of soil and urban development has been critical throughout history, but seldom recognised in soil security discourse. We review the manifestation of effective soil connectivity in Precolumbian lowland Maya tropical urbanism. Archaeological evidence reveals, first, that lowland Maya urban settlement patterns largely preserved the availability, proximity, and accessibility of soils in the subdivision and configuration of urban open space. Second, Maya urban life included practices that proactively contributed to the formation of soils by adding to the stock of soils and improving beneficial soil properties of the thin and often nutrient-poor soils resulting from the regionally dominant karstic lithology. Third, a range of Maya landscape modifications and engineering practices enabled the preservation and protection of soils within urban environments. We derive evidence-based insights on an urban tradition that endured for well over two millennia by incorporating intensive soil–society relationships to substantiate the concept of soil connectivity. Inspiring urban planning to stimulate soil connectivity through enhancing the engagement with soils in urban life would promote soil security.
Anthropogenic erosion and sedimentation are critical components of global change that involve life-sustaining natural resources of soil and water. Many geomorphic systems have responded to intense land use disturbance with episodic erosion and sedimentation, often orders of magnitude greater than background geological rates in the Holocene. Accelerated sedimentation is a metric for land use change and provides evidence of geomorphic change in fans, floodplains, terraces, deltas, lakes, karst sinks, estuaries, and coastal marine deposits. This review describes high variability in the timing of alluvial sedimentation and the value of bottomland stratigraphy with emphasis on records and heterogeneity of anthropogenic change. Although floodplain sedimentary evidence might be ill-suited for defining the proposed Anthropocene epoch boundary based on stratigraphic boundary criteria, sedimentology and stratigraphy provide rich evidence for long-term human activities that measures buildups of human environmental alterations long before the proposed mid-twentieth-century onset of the Anthropocene. Anthropogenic sedimentation is globally widespread but is too time-transgressive to serve as a stratigraphic indicator for onset of the proposed Anthropocene epoch. The emphasis here is on an example of longue durée; that is, the long record of anthropogenically accelerated sedimentation and the valuable evidence that it provides of human-induced environmental change. A conceptual tripartite model summarizes the evolution of anthropogeomorphic change. Anthropogenic sediments preserve geoarchaeological evidence and other important contextual information in buried landscapes that include human infrastructure, fields, material culture, contaminants, and paleosols. Geomorphic change can threaten food production, flooding, water quality, and so on. Understanding erosion and sedimentation dynamics is a vital concern for humanity.
Of multiple ways to assess the geography of the early Anthropocene, three ongoing efforts are establishing the extent, intensity, and chronology of human impacts on landscapes and connecting impacts to global change through greenhouse gas (GHG) fluxes. Landscapes interact with GHGs, and these have global climate implications. LiDAR, capable of precisely mapping through forest gaps, has revolutionized our ability to characterize and quantify humanized landscapes. In many cases, though, LiDAR is only as good as its accompanying ground verification. This article forges these together to compare a mature literature on wetland contributions to the early Anthropocene in Asia through methane from paddy rice agriculture with the growing literature on a large area of wetland agriculture in the Americas, focusing on the newest discoveries in Central America. Several studies have linked the ∼20 ppm rise in atmospheric CO2 from ∼7000 to 1000 BP with deforestation for global farming; the 100 ppb rise in CH4 from ∼5000 to 1000 BP with wetland farming; and the 7 to 10 ppm decline in CO2 in the sixteenth century CE with reforestation and population collapses of the Americas after the European Conquest. We synthesize the evidence for the onset, duration, and impacts of wetland agriculture in the Maya Lowlands of Mesoamerica to compare their impacts on GHGs and, thus, their contributions to global impacts on climate. This article builds from three decades of studying neotropical humanized landscapes and wetland agroecosystems and more recent quantification from ground-verified LiDAR imagery and synthesizes this growing research and the challenges ahead to gauge the early Anthropocene.
A common property regime was established at the founding of the Maya site of Actuncan, Belize, in the Terminal Preclassic period (175 BC–AD 300), which governed access to land until the Terminal Classic period (AD 780–1000). This interpretation is based on urban settlement patterns documented through household excavation and remote-sensing programs. Excavations of all visible patio-focused groups in the urban core provided data to reconstruct residential histories, and a 60,621 m ² gradiometer survey resulted in a magnetic gradient map that was used to document buried constructions. Twenty ground-truth testpits correlated types of magnetic signatures to buried patio-focused groups and smaller constructions, including walled plots in agricultural field systems that were later exposed more fully through large-scale excavations. Combined, these methods provided data to reconstruct four correlates of land tenure systems: (1) the spatial proximity of residential units to land and resources, (2) diachronic changes in community settlement patterns, (3) land subdivision and improvements, and (4) public goods. Spatial analyses documented that houselots did not cluster through time, but instead became gradually improved, lending evidence to suggest the transgenerational inheritance of property rights in the Late and Terminal Classic periods.
The Holocene (<11.7 kyr BP) is characterized by several periods of distinct climate changes. Some of these climate variations had extensive effects on mankind and coincided with demises of extinct high civilizations. Annually-resolved climate reconstructions will certainly play an increasingly important role in public perception, when applying these past patterns to the recent climate debate. The future consequences of the ongoing climate crisis are still challenging to predict, due to the lack of comprehensive, annually-resolved and continuous sea-surface temperature (SST) data. Our 8.55 m long sediment core from the bottom of the Great Blue Hole (Lighthouse Reef, Belize) provides an annually-resolved, continuous and unique southwestern Caribbean climate record for the last 1885 years. The varved, "lake-like" sinkhole successions of marine carbonates encompass approximately the entire Common Era (0 CE-modern), a time window, which is key for studying climatic variations and their effects on human society. Our SST record is based on stable isotopes (d 18 O) and molecular proxy applications (TEX 86). Throughout the Common Era, oxygen isotopes (d 18 O) and TEX 86 data imply a general SST rise of 0.5 C and 1.3 C, respectively, within the southwestern Caribbean. The modulation of SST within the Common Era time series likely operated on two different time levels: (1) Solar (e.g., "Gleissberg Cycles") and volcanic activity triggered climate changes, which in turn induced responses of the Atlantic Multidecadal Oscillation (AMO), the North Atlantic Oscillation (NAO) and the El-Niño-Southern Oscillation (ENSO). Their changing mode of action has been identified as a likely origin of the primary, i.e., centennially scaled SST variability. We suspect long-term positive AMO and NAO modes as the primary key control mechanisms of the Dark Ages Cold and Medieval Warm Period SST patterns. ENSO mode modulation likely exerted primary control on regional SST variability during the Little Ice Age and the Modern Global Warming. (2) Our d 18 O data further indicate a striking secondary control on multi-decadal time scales: d 18 O variations occur with 32e64 years periodicity. This signal is clearly evidence of SST modulation controlled by AMO phase changes (50e70 years) over almost the entire Common Era. Our carbon isotope record (d 13 C) exhibits two remarkable negative anomalies and a long-term up-core decreasing trend. The first excursion (drop of 0.5‰) occurred with the onset of the Medieval Warm Period, which is reconstructed to be a peak time in southwestern Caribbean tropical cyclone (TC) activity. This overlap is stressing a potential context between TC activity, enhanced coastal runoff and increased soil-erosion reflected by 13 C-depleted carbon isotopes. A second anomaly (>1900 CE) is more likely the result of the "Suess Effect" (anthropogenic impact of the Industrial Revolution on carbon isotopes composition) than another reflection of a TC peak activity interval.
Mercury was widely used in the art and rituals of the pre-Columbian Maya. A large amount (>6 kg) of documented liquid mercury has been recovered in Maya cultural deposits at Copan, Honduras. The Copan Acropolis also contains abundant evidence of cinnabar (mercury sulfide) use in ritual practice: sprinkled over tomb surfaces; coating the bones of the dead; and covering offerings. Discovering the specific source of cinnabar and liquid mercury used in Copan will contribute to further interpretations of economic networks utilized by the Copan Maya. The geology of the Copan Valley supports the hypothesis that mercury could be mined locally. To test it we designed a geochemical survey on the stream network within the Copan watershed basin using portable X-ray Fluorescence Spectrometry (pXRF) analysis. Results of the survey confirmed data from previous geologic mapping, indicating the presence of mercury in the valley. However, its concentrations are extremely low, sporadic and do not support its potential as a mining source. Therefore, it is very likely that mercury found in Copan ritual contexts was brought from elsewhere either as tribute or through trading.
Just as geomorphology evolved from a predominantly descriptive science to largely quantitative, a new framework for geomorphology is again required as rapidly increasing human population pushes anthropic-geomorphic processes to a dominant role in the Anthropocene. Understanding these processes requires new conceptual frameworks, interdisciplinarity, and a strong technology-assisted approach. We propose a focus on the Critical Zone as a useful conceptual framework in studies of Anthropocene geomorphology. Prior studies have assessed the Anthropocene with a focus on soils, which are generally considered the unifying thread of the Critical Zone. The Critical Zone in its entirety, however, extends from the top of the canopy to the base of the groundwater system. This concept thus permits a systems approach to geomorphology across scales, addressing the extensive role of human impact on Earth surface processes. Changing climatic conditions impact the delivery of water to the Critical Zone, causing an expansion of arid lands. Land-cover alteration is decreasing infiltration, armoring surfaces, increasing surface runoff, enhancing erosion rates, and is expected to expand in the future. Thus, the benefit of using the Critical Zone as a lens to study geomorphology will result in a broad, unified interdisciplinary study of the Anthropocene. These studies can be aided by modern technology, including drones and machine-learning applications. The trend toward technology-driven studies will continue throughout the geosciences, and geomorphology will be well-aided by its use. We present a comprehensive review of the concept of the Anthropocene and the Critical Zone making a case for the necessity of a Critical Zone-approach to anthropogeomorphology.
The protection of landscape is a matter of priority in this Anthropocene epoch, as explained in Chap. 25. If we agree that humanity has become the dominant driver of environmental change then figuring out the intellectual and social relevance of geomorphology is a topic that requires equally urgent attention. Classical geomorphology pays scant attention to the social, cultural and political factors that provoke geomorphic change. A modest proposal to recast geomorphology as both a landscape science and a geoscience is a suggested preferred first step. If that step is taken, the contested status of ‘landscape’ will make broader philosophical and methodological approaches possible in geomorphology. In particular, both the intrinsic and utilitarian value of geomorphology could be assessed more realistically. The net result could be more careful consideration of human well-being in geomorphological research.
Climate change projections have identified the Yucatan Peninsula as being vulnerable to increasing drought. Understanding spatial and temporal precipitation variability and drought occurrence are therefore important. Drought monitoring in Mexico has been carried out only relatively recently and often without considering the long‐term variability in both droughts and precipitation. This research explores the spatio‐temporal variability of precipitation and occurrence of droughts at a much finer spatial resolution and over a longer temporal period than previous studies. Using statistical (cluster analysis and standardised precipitation index) and geostatistical (kriging) techniques, maps of precipitation and droughts are generated for the period 1980–2011. These show that while many previous studies have regarded the Yucatan Peninsula as a homogenous region with respect to precipitation, there are actually four distinctive clusters of precipitation amount, showing climatic variability across the Peninsula. The analyses also show that droughts in the Peninsula are regionalised. Twelve‐month Standardised Precipitation Indices (SPI), calculated for individual stations and for precipitation surfaces, reveal distinct patterns of spatial and temporal variability. SPI surfaces indicate the occurrence of major droughts in 1981, 1986–87, 1994, 1996, 2003, 2004 and 2009, but these rarely affect the whole Yucatan Peninsula uniformly. Wetter years, such as 1983, 1984, 1988, 1992, 1995, 2002 and 2005 sometimes reflect the impact of individual extreme events, such as hurricane Isidore in 2002. Our results show that drought can be regionalised, thus enhancing the quality of information about droughts in the area and providing evidence and support for future drought mitigation and environmental protection. These methods could usefully be applied elsewhere. This article is protected by copyright. All rights reserved.
Ilopango volcano (El Salvador) erupted violently during the Maya Classic Period (250–900 CE) in a densely-populated and intensively-cultivated region of the southern Maya realm, causing regional abandonment of an area covering more than 20,000 km². However, neither the regional nor global impacts of the Tierra Blanca Joven (TBJ) eruption in Mesoamerica have been well appraised due to limitations in available volcanological, chronological, and archaeological observations. Here we present new evidence of the age, magnitude and sulfur release of the TBJ eruption, establishing it as one of the two hitherto unidentified volcanic triggers of a period of stratospheric aerosol loading that profoundly impacted Northern Hemisphere climate and society between circa 536 and 550 CE. Our chronology is derived from 100 new radiocarbon measurements performed on three subfossil tree trunks enveloped in proximal TBJ pyroclastic deposits. We also reassess the eruption magnitude using terrestrial (El Salvador, Guatemala, Honduras) and near-shore marine TBJ tephra deposit thickness measurements. Together, our new constraints on the age, eruption size (43.6 km³ Dense Rock Equivalent of magma, magnitude = 7.0) and sulfur yield (∼9–90 Tg), along with Ilopango's latitude (13.7° N), squarely frame the TBJ as the major climate-forcing eruption of 539 or 540 CE identified in bipolar ice cores and sourced to the tropics. In addition to deepening appreciation of the TBJ eruption's impacts in Mesoamerica, linking it to the major Northern Hemisphere climatic downturn of the mid-6th century CE offers another piece in the puzzle of understanding Eurasian history of the period.
Underlying Mexico's Yucatan Peninsula is one of the world's most extensive flooded cave systems. Humans and non-humans can enter this aquifer via water-sinkholes - known locally as cenotes. Cenotes for the Maya of the Peninsula are the entrances to the Xibalba, a mythological underworld. Fostered by technological innovations since the 20th century, this underworld has become a site of explorative calculation. Cave divers travel to the Peninsula for a chance to explore the region's subterranean frontier, to potentially ‘find’ a place where no human has been before. However, it is not just about the destination; for many cave divers, it is about the affect of the watery subterranean; an experience that defies most basic (physical and social) human functions: breathing underwater, timeless space, total darkness, no natural orientation, floating, and no talking (efficiently). As one cave diver noted “once you have swum, snorkelled or dived in a cenote, you have been infected by thrill and curiosity”. In this paper, drawing from interviews with cave divers as well as land and cenote owners, I analyse how caving explorations contributed to processes that socially construct and physically modified the Yucatan Peninsula's subterranean. In particular, I analyse how the embodied conditions of being a cave diving ‘explorer’ have become commodified into an experience that is sold into the region's booming tourism industry. Cenotes have been transformed into a tourism product through the entanglement of diving technologies, emotive exploration narratives and a sacred Maya underworld.
1.Leaf‐cutter ants are a prominent feature in Neotropical ecosystems but a comprehensive assessment of their effects on ecosystem functions is lacking. We reviewed the literature and used our own recent findings to identify knowledge gaps and develop a framework to quantify the effects of leaf‐cutter ants on ecosystem processes.
2.Leaf‐cutter ants disturb the soil structure during nest excavation changing soil aeration and temperature. They mix relatively nutrient‐poor soil from deeper layers with the upper organic rich layers increasing the heterogeneity of carbon and nutrients within nest soils.
3.Leaf cutter ants account for about 25% of all herbivory in Neotropical forest ecosystems, moving 10‐15% of leaves in their foraging range to their nests. Fungal symbionts transform the fresh, nutrient rich vegetative material to produce hyphal nodules to feed the ants. Organic material from roots and arbuscular mycorrhizal fungi enhance carbon and nutrient turnover in nest soils and creates biogeochemical hot spots. Break down of organic matter, microbial and ant respiration, and nest waste material decomposition result in increased CO2, CH4, and N2O production, but the build‐up of gases and heat within the nest is mitigated by the tunnel network ventilation system. Nest ventilation dynamics are challenging to measure without bias, and improved sensor systems would likely solve this problem.
4.Canopy‐gaps above leaf‐cutter ant nests change the light, wind, and temperature regimes which affects ecosystem processes. Nests differ in density and size depending on colony age, forest type and disturbance level and change over time resulting in spatial and temporal changes of ecosystem processes. These characteristics remain a challenge to evaluate rapidly and non‐destructively.
5.Addressing the knowledge gaps identified in this synthesis will bring insights into physical and biological processes driving biogeochemical cycles at the nest and ecosystem scale and will improve our understanding of ecosystem biogeochemical heterogeneity and larger‐scale ecological phenomena. This article is protected by copyright. All rights reserved.
Concern with the human impact in Geomorphology has a long history. What is new is that since 1969 a number of developments have taken place that have led to an increasing realisation of its importance. These developments are in four main areas: (i) intellectual and policy-related; (ii) technological developments that alter geomorphological processes; (iii) demographic trends; and (iv) the proliferation of techniques for the study of landform and process change. There has been a realisation of the role of humans in landscape transformation in ancient times. The human impact has developed through time, but particularly notable are the potential early effects of fire, extinctions and deforestation on geomorphological processes. The spread of European agriculture, particularly in the nineteenth century, transformed erosion and sedimentation rates in many parts of the world. Notwithstanding the importance of some of these changes in prehistoric and historic times, recent researches have demonstrated that humans have become an increasingly important agent of geomorphological change during the period of the Great Acceleration of the past five or six decades. The interest in global warming that has developed since the early 1980s has created considerable interest in its consequences for a range of geomorphological phenomena. It is also becoming apparent that anthropogenic geomorphological change is having an impact on the Earth System as a whole. Finally, Geomorphologists have taken an increasing interest in how they can make an impact in the field of landscape conservation.