Plant wax n-alkane distributions, concentrations, carbon and hydrogen isotope compositions in modern plants from the central Congo peatlands

The central Congo Basin in central Africa hosts the world largest tropical peatland complex, which is covered by tropical swamp forest. Understanding the factors that determine the nature and dynamics of the peatland vegetation cover is an important issue in the face of climate change and ongoing/planned human activities in the region.

Studying lipid biomarkers preserved in environmental archives and peat, such as plant wax n-alkanes, allows the reconstruction of past vegetation changes and environmental conditions. Long-chain n-alkanes are recalcitrant molecules not affected by low temperature decomposition processes of organic matter and represent robust palaeo-environmental and palaeo-climatic proxies.

However, there is little information on how the production of plant waxes by different plant types may influence the abundance and isotopic composition of sedimentary n-alkanes in peat and sediment archives in the Congo Basin. A sound interpretation of the sedimentary data requires knowledge of the distribution, concentration, stable carbon isotope composition (δ¹³C) and hydrogen isotope composition (δD) of plant wax n-alkanes from the current vegetation in the region. Therefore, calibration studies of these proxies in the central Congo Basin region are needed.

To fill this knowledge gap, we sampled the dominant plant types (trees, shrubs, herbs) in the peatlands from the Cuvette Department, Republic of the Congo. In total, 53 samples were collected from 13 families, 27 species and across five different environments. Environmental meteoric waters (e.g., river waters, channels, standing ponds) were also sampled for their isotopic composition to identify the isotopic composition of hydrogen used during lipid biosynthesis. In this study we assess the variation of plant wax n-alkane δ¹³C and δD values according to photosynthetic pathways (C₃ vs. C₄), plant types (dicots, monocots) and source water δD values. It provides a framework for detailed paleo-environmental and paleo-climatic reconstructions in the central Congo Basin.