Holocene environmental changes inferred from an oxbow lake in a Mauritia palm swamp (aguajal) in the Madre de Dios region, southeastern Peru

Mauritia peatland palm swamps (locally called aguajales) are typical ecosystems in Madre de Dios River floodplains in southeastern Peru. We investigated a sediment core from an oxbow lake in Los Amigos Aguajal to reconstruct paleoclimatic changes, vegetation dynamics on a regional scale, and human impact using multi-proxy analysis. The results show that the oxbow lake was part of Madre de Dios River's active meandering system and cut off at ca. 1760 cal yr BP. X-Ray Fluorescence results combined with stratigraphy suggest that since the cutting off, the recorded climate was humid until 540 cal yr BP excepting a shortly drier period of 640–610 cal yr BP, but after 540 cal yr BP the climate became less wet until the present. Pollen results show a stable terra firme forest composed primarily by Moraceae/Urticaceae throughout the record. The dense aguajal surrounding the oxbow lake developed from 1240 cal yr BP until the present, but canopy was more open during 780–180 cal yr BP. Hedyosmum became consecutively abundant since 270 cal yr BP until the present. Charcoal analysis indicated almost no human activity in the study area throughout the record. Comparison of the oxbow lake record and the previously studied palm swamp record both from Los Amigos Aguajal shows that: (1) main environmental changes in the palm swamp may correspond to moisture changes; (2) vegetation composition and dynamics on local aguajal and more regional scales are similar, except for the missing period of marsh in the oxbow lake. Furthermore, the oxbow lake record shows less wet conditions during the Little Ice Age and relatively wet in the Medieval Climate Anomaly, which is contrary to many records from the Peruvian Andes. This might be related to elevational differences (lowland vs. mountain) and/or non-climate factors and will need further investigation.