CARBON ACUMULATION IN AMAZON LAKES AS INDICATORS OF ANTROPIC AND PALEOCLIMATIC EVENTS

Abstract

Land biota is regarded as a natural sink for atmospheric carbon. Tropical forests have an important role in this assimilation, but little is known about the role of continental aquatic systems in the process of carbon sequestration and its relationship with paleoclimatic changes. The objective of the present article is to bring together the main studies with Amazon lakes in order to highlight the participation of aquatic systems in the local accumulation of carbon and the participation of human-made and paleoclimatic changes in the Amazon in different time scales. Three different lake systems were analysed: the lowland lakes of Santa Ninha and Acarabixi, which are respectively directly influenced by the hydrological cycles of Amazon and Negro rivers, and some lakes that are isolated from the effects of the dynamics of Amazon rivers (which despite their little size play an important role in understanding the local palaeoclimatic processes). Records from the following locations were addressed: lake Pata (Amazon), lake Caracarana (Roraima), lake CSN N4 Carajas (Pará), and a lake over a flooded field at Humaita (Amazon). As an example of a system under anthropogenic influence, a dam in a region of intense alternate land usage at Alta Floresta (Mato Grosso) was studied. The past environmental conditions and their effect over the way the different Amazon river ecosystems work nowadays were estimated using a number of palaeoenvironmental indicators: chronological analyses by 210Pb and 14C, organic carbon concentration, C/N ratio, determination of chlorophyll derivates, analysis of the deposition of charcoal particles, 15N and 13C, and accumulation rates of mercury, minerals , and carbon. The lowland lakes Santa Ninha and Acarabixi presented high carbon accumulation rates of over 400g/m2/yr, while the isolated lakes presented lower carbon accumulation rates, records rarely exceeding 20g/m2/yr. carbon accumulation rates between 10580 to 10550cal.yr. B.P. in lake Acarabixi lake were the highest, reaching 462g/ m2/yr, being its peak restricted to a brief period that dis not coincide with the peaks of Varzea of Curuai. The carbon accumulation rate of Acarabixi is similar to the maximum carbon accumulation rate of the artificial barrier in the intense land use change area in Alta Floresta (MT). These data indicate that the different Amazon lake environments are important in the carbon accumulation rates, which may have altered because of the climate changes of the recent millennia.