Environmental legacy of pre-Columbian Maya mercury

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

Ancient Maya wetland fields revealed under tropical forest canopy from laser scanning and multiproxy evidence

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.We report on a large area of ancient Maya wetland field systems in Belize, Central America, based on airborne lidar survey coupled with multiple proxies and radiocarbon dates that reveal ancient field uses and chronology. The lidar survey indicated four main areas of wetland complexes, including the Birds of Paradise wetland field complex that is five times larger than earlier remote and ground survey had indicated, and revealed a previously unknown wetland field complex that is even larger. The field systems date mainly to the Maya Late and Terminal Classic (∼1,400–1,000 y ago), but with evidence from as early as the Late Preclassic (∼1,800 y ago) and as late as the Early Postclassic (∼900 y ago). Previous study showed that these were polycultural systems that grew typical ancient Maya crops including maize, arrowroot, squash, avocado, and other fruits and harvested fauna. The wetland fields were active at a time of population expansion, landscape alteration, and droughts and could have been adaptations to all of these major shifts in Maya civilization. These wetland-farming systems add to the evidence for early and extensive human impacts on the global tropics. Broader evidence suggests a wide distribution of wetland agroecosystems across the Maya Lowlands and Americas, and we hypothesize the increase of atmospheric carbon dioxide and methane from burning, preparing, and maintaining these field systems contributed to the Early Anthropocene.Office of the VP for Researc

Comparison and evaluation of ground water quality in Surprise Valley and Alturas Basin using Thornthwaite's evapotranspiration model

A quarter of a century ago, the California Department\ud of Water Resources undertook an investigation of ground\ud water basins in northeastern California. For more than\ud two decades, California Department of Water Resources\ud Bulletin 98, Northeastern Counties Ground Water Investigation,\ud 1 was the major source of information on the area. At\ud the same time, ground water quality studies2 were also\ud completed for both the Surprise Valley and Alturas Basin\ud in Modoc County, California. Twenty years later three investigations of northeastern\ud California's ground water were conducted by the Department\ud of Water Resources to update and supplement the\ud original reports. These were Northeast Counties Ground\ud Water Update, 1982, Alturas Basin Ground Water Quality\ud Study, 1986, and Surprise Valley Ground Water Quality\ud Study, 1986. These reports were spawned from concern\ud over then-recent increases in ground water pumping in\ud the areas, declining water levels in wells, and possible impacts\ud on water quality

Stability and instability on Maya lowlands tropical hillslope soils

Substantial lake core and other evidence shows accelerated soil erosion occurred in the Maya Lowlands of Central America over ancient Maya history from 3000 to 1000 years ago. But we have little evidence of the wider network of the sources and sinks of that eroded sediment cascade. This study begins to solve the mystery of missing soil with new research and a synthesis of existing studies of tropical forest soils along slopes in NW Belize. The research aim is to understand soil formation, long-term human impacts on slopes, and slope stability over time, and explore ecological implications. We studied soils on seven slopes in tropical forest areas that have experienced intensive ancient human impacts and those with little ancient impacts. All of our soil catenas, except for one deforested from old growth two years before, contain evidence for about 1000 years of stable, tropical forest cover since Maya abandonment. We characterized the physical, chemical, and taxonomic characteristics of soils at crest-shoulder, backslopes, footslopes, and depression locations, analyzing typical soil parameters, chemical elements, and carbon isotopes (δ13C) in dated and undated sequences. Four footslopes or depressions in areas of high ancient occupation preserved evidence of buried, clay-textured soils covered by coarser sediment dating from the Maya Classic period. Three footslopes from areas with scant evidence of ancient occupation had little discernable deposition. These findings add to a growing corpus of soil toposequences with similar facies changes in footslopes and depressions that date to the Maya period. Using major elemental concentrations across a range of catenas, we derived a measure (Ca + Mg) / (Al + Fe + Mn) of the relative contributions of autochthonous and allochthonous materials and the relative age of soil catenas. We found very low ratios in clearly older, buried soils in footslopes and depressions and on slopes that had not undergone ancient Maya erosion. We found high (Ca + Mg) / (Al + Fe + Mn) values on slopes with several lines of evidence that suggest relative youth, soils possibly formed since Maya abandonment. Carbon isotopes (δ13C) also provide some evidence of past vegetation change on slopes. We found strong evidence for maize or other alien C4 species in an ancient terrace soil and additional evidence in buried footslopes but only evidence for C3 species (like tropical trees) on the backslopes and other crest-shoulders. The fact that steep slopes preserved no evidence of C4 species inputs may mean that the ancient Maya maintained forests here. Alternatively, ancient Maya land uses eroded slopes, with the δ13C signatures detected today being the result of more recent soil development under forest over the last millennium. Additional evidence that these soils are recent in age includes elevated (Ca + Mg) / (Al + Fe + Mn) values, skeletal soil profiles, and low soil magnetic susceptibility. Besides the evidence for truncating backslopes and aggrading footslopes, the ancient Maya built agricultural terraces that accumulated soils and altered drainage. All these ancient Maya slope alterations would have influenced modern tree distributions, because many tree species in the modern forest show strong preferences for different soil types and topographic situations that the ancient Maya changed

Economic feasibility of integrating solar energy into water utility operations in Ciudad Juárez, Mexico

We perform an economic feasibility analysis for installing grid-connected solar arrays with batteries to power ten water supply, distribution, and treatment stations in Ciudad Juárez in tandem with the existing local grid. This article covers detailed results from the four stations that represent the topographical and geographical variability of the city and the variable electricity demand across sites. Using data from the city’s water utility and calculations from the HOMER and RETScreen models, we find contrasting results. The HOMER model finds that solar arrays with or without batteries are economically viable while RETScreen reaches the opposite conclusion. One key reason for this is the two models’ differing predictions on the amount of electricity the proposed solar arrays would supply. Further, having reliable battery storage is paramount to overcoming grid outages and the intermittent availability of solar power to ensure the success of solar projects. Global scientific consensus recognizes the need for more renewable energy. With a sunny-climate and its status as a manufacturing hub on the US-Mexico border, Ciudad Juárez has the potential to lead the way forward in promoting solar energy. The comparative results of the HOMER and RETScreen models provide a more complete understanding of the feasibility of solar power for Ciudad Juárez’s water infrastructure as well as vital insight into the factors that shape the success of solar projects

Archaeologic Machine Learning for Shipwreck Detection Using Lidar and Sonar

The objective of this project is to create a new implementation of a deep learning model that uses digital elevation data to detect shipwrecks automatically and rapidly over a large geographic area. This work is intended to apply a new methodology to the field of underwater archaeology. Shipwrecks represent a major resource to understand maritime human activity over millennia, but underwater archaeology is expensive, misappropriated, and hazardous. An automated tool to rapidly detect and map shipwrecks can therefore be used to create more accurate maps of natural and archaeological features to aid management objectives, study patterns across the landscape, and find new features. Additionally, more comprehensive and accurate shipwreck maps can help to prioritize site selection and plan excavation. The model is based on open source topo-bathymetric data and shipwreck data for the United States available from NOAA. The model uses transfer learning to compensate for a relatively small sample size and addresses a recurring problem that associated work has had with false positives by training the model both on shipwrecks and background topography. Results of statistical analyses conducted—ANOVAs and box and whisker plots—indicate that there are substantial differences between the morphologic characteristics that define shipwrecks vs. background topography, supporting this approach to addressing false positives. The model uses a YOLOv3 architecture and produced an F1 score of 0.92 and a precision score of 0.90, indicating that the approach taken herein to address false positives was successful

Four millennia of geomorphic change and human settlement in the lower Usumacinta–Grijalva River Basin, Mexico

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

Long-Term Geomorphic Change in the Maya Lowlands of Central America

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.

Machine learning for cave entrance detection in a Maya archaeological area

Machine learning can offer an efficient method to identify and map caves, sinkholes, and other cave-like features (i.e. sinkholes, rockshelters, voids) using remotely sensed imagery. While there exists a body of work applying machine learning for sinkhole identification, little work exists for caves. In the densely forested and rugged Maya Lowlands, developing such a methodology can help archaeologists to identify previously unknown caves that may contain important archaeological materials. Here, we introduce a proof-of-concept project that uses random forest and lidar-derived landscape morphometrics to map caves and other cave-like features in northwest Belize. Several undocumented caves and cave-like features were identified in our study area based on model results. Next steps towards making a more robust version of this model include the addition of more training data and integration of a larger number of morphologic parameters. Based on the results described here as well as those in cited works focused on caves, we proposed machine learning as a first step in cave and cave-like feature identification, followed then by fieldwork and ground-truthing