Temporal Evolution and Spatial Distribution of Lake Productivity in the Amazon Basin During the Holocene

Abstract:

There are few studies about the paleoecology of the tropical and equatorial regions, places that play a key role in climate change. Researches show that non-disturbed forests of the Amazon Basin are important carbon sinks, however, little is known about the functioning of its continental aquatic systems and its role in the carbon storage and relationship with paleoclimate changes. Organic matter provides important paleoenvironmental information, being an indispensable tool for understanding these areas. Here we evaluated the paleoproductivity, over the Holocene, of nine lakes distributed over the north, the center and the south/southwest ecotones areas in the Amazon Basin, by analyzing organic matter TOC, δ13C, chlorophyll derivatives, and C/N ratio in nine sediment cores, correlating it to past environmental changes by determining the nutrient apport to the lakes from the surrounding drainage area, the main sources of the sedimentary organic matter and lake levels changes. Our data are in agreement with the dry and wet phases of the Holocene in the Amazon Basin, already known by other previous works. This was observed mainly by the chlorophyll derivatives values, which are generated mainly in an autochthonous way, that presented its lowest values during the early and middle Holocene (dry phases) and its highest on the upper Holocene (wet phase), indicating lowest and highest water levels, respectively. δ13C and C/N ratio are parameters used to distinguish the sources of organic matter, the highest values of both of the parameters were found during the dry phases, indicating the presence of C4 plant species, while during the upper Holocene higher values were found, indicating, predominantly, the presence of C3 species and phytoplankton. In general, the parameters responded according to the expected results, some differences from the expected can be found due to the distinct features of each lake and the surrounding drainage area.