Holocene vegetation and environmental changes of peat ecosystems in southwestern and northeastern Amazonia

Abstract

Amazonia plays a significant role in the global climate change, hydrological cycle, biodiversity conservation, especially in the carbon (C) cycle. Amazonia likely contains the most extensive peat C stock in the tropics. Easily degraded, these Amazonian peat ecosystems are at risk of changing from representing a large C sink to a major C source, impacting global cycles. Thus, it is essential to understand how the peat ecosystems in Amazonia developed and the past drivers of changes. Most palaeoecological research on these peat ecosystems has focused on the northwestern Amazonia. Although the representative peat ecosystems in southwestern (SW) and northeastern (NE) Amazonia have been investigated for vegetation dynamics, peat and organic C accumulation, climate, human activities, hydrology, and geomorphology, our knowledge of peat ecosystem evolution is still insufficient. Therefore, in this paper, we first summarize the recently published palaeoecological studies for representative peat ecosystems in SW and NE Amazonia, and the modern and Holocene regional climate. We reconsider the mechanisms of the representative peat ecosystems combined with other related palaeoecological studies under the regional climate framework. Finally, we compare the conditions of peat ecosystems in SW and NE Amazonia. Through the present comparison, we find that the development of peat ecosystems depends on local settings in Amazonia. The onset of the peat ecosystem is mainly driven by river dynamics in SW Amazonia, but is strongly influenced by the Atlantic sea level in low-lying areas in NE Amazonia. The local factors also include geomorphology, fluvial dynamics, local climate, and human activities. Various influencing factors cause diverse processes in peat ecosystems, whether in vegetation successions or peat and C accumulation rates. It is worth noting that regional human activities may indirectly play an important role in peat ecosystem development in both SW and NE Amazonia. This study helps to further understand the mechanism of the development of tropical peat ecosystems, which is important for the modeling, conservation, and management of tropical peat ecosystems.