Reconstructing Holocene landscape and environmental changes at Lago Rogaguado, Bolivian Amazon

Walter Finsinger,Heinz Veit,Umberto Lombardo,Alena Giesche

doi:10.1007/s10933-020-00164-8

Abstract

We performed geochemical analyses of two lake sediment cores (1.25 and 1.5 m long) from Lago Rogaguado, which is a large (315 km2) and shallow lake in the Llanos de Moxos, Bolivian Amazon, to investigate Holocene environmental changes based on a multi-proxy dataset (XRF, density, grain size, C:N, and macrocharcoal). One of the two cores provides a history of environmental changes in the Llanos de Moxos from 8100 cal BP until present, which supplements previously published pollen and microscopic charcoal records. Our analyses indicate lake expansion at 5800 cal BP, which may relate to tectonic activity. This was followed by further increasing lake levels, peaking at approximately 1050–400 cal BP, which supports increasingly wetter conditions in the Llanos de Moxos after the mid-Holocene. A fourfold increase in macroscopic charcoal accumulation rate and a more than fivefold increase in sedimentation rates supports anthropogenic fire activity at around 1450 cal BP (500 CE), suggesting that pre-Columbian populations used fire to actively manage the landscape during a period of maximum lake levels around Lago Rogaguado. From 400–100 cal BP, higher C:N, larger grain sizes and peaks in macroscopic charcoal accumulation rates suggest increased watershed erosion associated with increased biomass burning, possibly related to intensified land use.

Highlights

Palaeoenvironmental reconstructions can reveal important information about past interactions between climate, the environment, and humans (Messerli et al 2000)
The two lowermost radiocarbon dates of core LR-400 reached an age of ca. 11,300 calendar years before present (cal BP) (ESM Table S1)
The depth-age model of core LR-400–12 revealed a shift in sedimentation rate after 36 cm depth (1050 cal BP)

Summary

Introduction

Palaeoenvironmental reconstructions can reveal important information about past interactions between climate, the environment, and humans (Messerli et al 2000). Besides contributing to the growing collection of palaeoenvironmental reconstructions from the Southern Hemisphere (de Souza et al 2019), such studies are highly relevant to the ongoing debate concerning the extent and impact of human occupation in Amazonia (Bush and Silman 2007). Instead of an untouched, unchanged landscape, it is widely accepted that Amazonia has experienced climate change and natural ecosystem shifts, and the significant impact of pre-Columbian people throughout the Holocene (Neves 2008; Schaan 2008; Arroyo-Kalin et al 2009; Parssinen et al 2009; Lombardo and Prumers 2010; Whitney et al 2013). The debate has shifted to precisely how densely populated Amazonia may have been and where these populations were centered (Koch et al 2019), with some researchers pointing to domesticated landscapes (Levis et al 2017) that would have supported a preColumbian population of several millions (Erickson 2008; Clement and Junqueira 2010; Denevan 2012; Clement et al 2015), whereas others found little evidence of large, widespread populations in the palaeoecological records (McMichael et al 2012)

Methods

Results

Discussion

Conclusion