Short communication: Estimating radiocarbon reservoir effects in Bolivian Amazon freshwater lakes

Abstract. The Llanos de Moxos, in the Bolivian Amazon, preserves a remarkable archaeological record, featuring thousands of forest islands. These anthropogenic sites emerged as a result of activities of the earliest inhabitants of Amazonia during the Early and Middle Holocene. Excavations conducted to date on the forest islands have revealed that many assemblages contain a high number of ancient freshwater snail remains. In these shell middens, the most represented mollusc taxon, and in most cases the sole one, is Pomacea spp., a genus that inhabits inland shallow lakes and wetlands. Although human burials and faunal remains are typically recovered from these sites, their collagen is often not preserved or is of poor quality, and shell carbonates from Pomacea shells, along with carbonised plant remains, are often used for 14C measurements. However, it remains undetermined if these measurements are subject to radiocarbon reservoir effect (RRE). To determine if a freshwater RRE could affect the age estimations of Amazonian archaeological and other paleoecological deposits, we collected modern coeval Pomacea shells and tree leaves from four locations across the Llanos de Moxos area for AMS radiocarbon dating. The radiocarbon results combined with the environmental history of Llanos de Moxos during the Holocene, do not reveal any significant RREs, and support the continued use of freshwater molluscs as viable material for radiocarbon dating in the region.