Assessing nutrient inputs, sediment organic matter sources, and the potential for cyanobacteria in ancient water reservoirs at the Maya city of Ucanal, Guatemala: A glimpse at sustainable water management practices Jean D. Tremblay a,* , Peter M.J. Douglas b , Christina T. Halperin a , Christian von Sperber c , Jean-François H´elie d , Laurianne Gauthier a a Department of Anthropology, Universit´e de Montr´eal, Montr´eal, QC H3T 1N8, Canada b Department of Earth and Planetary Sciences and Geotop Research Center, McGill University, Montr´eal, QC H3A 0E8, Canada c Department of Geography, McGill University, Montr´eal, QC H3A 0B9, Canada d Geotop Research Centre, D´epartement des sciences de la Terre et de l’atmosph`ere, Universit´e du Qu´ebec ` a Montr´eal, Montr´eal, QC H2X 3Y7, Canada A R T I C L E INFO Keywords: Maya Cyanobacteria Water reservoirs Ucanal Stable isotopes Nutrients ABSTRACT Although water storage infrastructure was crucial to ancient Maya society, relatively little is known about their potential contamination by biological pathogens and nutrient pollution within ancient Maya cities. At the site of Ucanal, Guatemala, inhabitants created an extensive water infrastructure landscape to manage both supply and drainage. Archaeological, geochemical and paleolimnological data were compiled from stratigraphically exca- vated and chronologically controlled dried sediments from 3 ancient water reservoirs in Ucanal to investigate potential cyanobacteria contamination from the Late Preclassic to the Terminal Classic periods. Elemental and isotopic analyses of carbon, nitrogen, and phosphorus reveal that none of the 3 reservoirs exhibited nutrient or organic carbon rich environments indicative of or conducive to cyanobacteria or eutrophication, regardless of time period. In addition, δ 13 C data show a common pattern of C 4 /CAM plants usage throughout the city core from the Preclassic to Terminal Classic periods, similar to settlement zones and agricultural fields identified elsewhere in the Maya area. These results suggest that inhabitants of Ucanal managed a sustainable water landscape system that remained relatively stable and without excessive nutrient inputs despite population in- creases at the end of the Classic period. 1. Introduction Pre-Columbian peoples, including the Maya, regularly constructed water reservoirs, drainage canals, dams, terraces, and other features to more effectively access and manage water resources (Chase 2016; Chase and Cesaretti 2019; Chase and Chase 2017; Dunning et al. 1999; Lucero 2002; Lucero et al. 2011; Luzzadder-Beach et al. 2016; Scarborough 1998; Scarborough et al. 2012). These water reservoirs may have been in danger of being polluted due to increases in population, urban densities, intensive agriculture, and other anthropogenic environmental changes. For example, an aDNA study of ancient reservoirs at the large urban site of Tikal, Guatemala, revealed evidence of cyanobacteria or blue-green algae during periods of heavy occupation of the site (Lentz et al. 2020), and geochemical analyses of the western arm of Lake Pet´en Itz´ a revealed deteriorated aquatic ecological conditions during the Preclassic period (ca. 800 BCE – 300 CE), corresponding to a period of agricultural intensification and urban development at the nearby site of Nixtun- Ch’ich’, Guatemala (Birkett et al. 2023) (Fig. 1). Nonetheless, the study of cyanobacteria blooms (Lentz et al. 2020; Waters et al. 2021) in ancient Maya reservoirs is relatively rare, and the available studies do not encompass the diverse range of cities and regional ecosystems found throughout the Maya area. Here we report on the study of three water reservoirs from the medium-sized ancient Maya city of Ucanal located in eastern Pet´en, Guatemala (Fig. 2). The water infrastructure system at Ucanal included monumental-scale reservoirs, smaller reservoirs or water collection zones, and large-scale open-air canals, which were integrated with public plazas, roads, and civic-ceremonial buildings to drain excess rainwater to the nearby Mopan River to prevent flooding and erosion in residential areas of the ancient city (Halperin et al. 2019). Excavations of * Corresponding author. E-mail address: jean.tremblay.2@umontreal.ca (J.D. Tremblay). Contents lists available at ScienceDirect Journal of Archaeological Science: Reports journal homepage: www.elsevier.com/locate/jasrep https://doi.org/10.1016/j.jasrep.2025.105389 Received 29 May 2025; Received in revised form 22 August 2025; Accepted 4 September 2025 Journal of Archaeological Science: Reports 67 (2025) 105389 Available online 11 September 2025 2352-409X/© 2025 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.