Late Quaternary Isoëtes megaspores as a proxy for paleolimnological studies of the southeastern Amazonia

Abstract

Isöetes have higher diversity in South America, with two endemic species (I. serracarajensis and I. cangae) recently discovered in the Carajás Mountain Range (CMR), southeastern Amazonia. I. serracarajensis is observed in upland oligotrophic to eutrophic swamps and ponds, while I. cangae is restricted to a single oligotrophic upland and active lake (Amendoim) the CMR since it is very sensitive to algal blooms and the eutrophication process. In this study, a species level identification and quantification of Isöetes megaspores were carried out for the first time in sediment cores of upland lakes of the CMR during the last 50k cal yr BP, and the main factors influencing population dynamics and conservation status were discussed. Generally, during millennial-scale drier hydroclimate conditions, swamps and ponds mostly dehydrated, and I. serracarajensis were restricted to active lakes, which became eutrophicated due to the increase in nutrient production from the remineralization of organic matter deposited in bottom sediments triggered by the decrease in water levels. On the other hand, the highly-sensitive population of I. cangae contracted since the Amendoim Lake become eutrophicated. During wetter climate, these species reappeared in their preferred habitats. However, the CMR is currently under climate and hydrological stress mainly due to an intense land use–land cover changes during the last four decades, with a worst-case scenario for the next 30 years, according to recent hydrological models. This may strongly impact the natural habitats of Isöetes and further increase pressure on already endangered populations.