Acumulação de carbono e interpretações paleohidrológicas do lago do Boto – Arquipélago de Anavilhanas, durante o Holoceno Superior

Abstract

The studies on carbon accumulation and paleohydrological conditions in lake environments are important for understanding the carbon cycle in inland water systems and to help predict how these environments can react to future climate changes. Therefore, this work had as objective to make notes on the accumulation of carbon and the paleohydrological conditions of Boto Lake (Anavilhanas Archipelago) during the Upper Holocene. In order to characterize the present hydrological dynamics of the lake systems of the archipelago and identify the alterations associated with the landscape, two images of the Landsat 08 satellite, obtained in the period of high and low waters of the Rio Negro, as well as hydrological data were used. To determine carbon accumulation in Lake Boto, 1 m of sedimentary record was analyzed. The core was dated with 14C accelerator mass spectrometry (AMS) and described; subsequently were measured bulk density, grain size analysis and total organic carbon (TOC) contents. With these results, sedimentation rates, accumulation and stock carbon were determined for each centimeter of the depth of 1 m. For the current conditions, it has been observed that the Anavilhanas Archipelago is subject to a large range of seasonal variation, even under regular conditions (interannual daily fluviometric averages). This seasonality causes a series of changes in the landscape over these periods that impact differently on the lakes. A variation of around 10% in the exposed water surface of the archipelago was observed between periods of low and high water and for lacustrine systems and "dead water" areas was 17%. For 447 lakes identified, 46% are lakes connected to the archipelago canals during the low water period, including the Boto Lake, area of this study, and 54% are isolated during this period. The results indicate that since 1880 cal cal AP the lake of Boto has presented conditions of a lake environment with predominance of low river influence, however, with some variations and a tendency to increase in carbon accumulation and sedimentation rates towards the top. . Between 1880 to 854 years cal AP sedimentation rates were 0.03 cm.year-¹ and average carbon accumulation rates 94.84 g.m-².year-¹. Between 854 years cal AP at present, sedimentation rates were 0.07 cm.year-¹ and average carbon accumulation rates of 148.85 g.m-².year-¹. In total, a stock of about 230,987 tonnes of TOC was estimated for the 1 meter depth of this lake. The results highlight the importance of the Amazonian lake environments in carbon accumulation and highlight the need for further studies in this perspective.