Distribuição temporal da matéria orgânica depositada no limite de ocorrência dos manguezais na Costa Oeste do Atlântico Sul

Abstract

Considering the ecological functions performed by mangroves, their social and economic importance and the dependence on oceanographic/climatic factors and human activities, it is essential to have a greater understanding of the transformations that took place in bordering regions. This assessment can be done by analyzing the behavior of organic matter (OM) deposited in mangroves through the determination of organic molecular markers, as n-alkanes. These are saturated aliphatic hydrocarbons produced mainly by primary producers, such as higher plants and phytoplankton. The objective of this thesis is to evaluate, through the analysis of n-alkanes in sedimentary cores, the temporal changes in the deposition of organic matter in the southern limit of occurrence of mangroves on the west coast of the South Atlantic. Two sedimentary cores were collected in the Santo Antônio lagoon (LSA, Santa Catarina – Brazil). Data for 14C dating, particle size, total organic carbon (TOC) and total nitrogen (NT) are published. The analysis of n-alkanes occurred every 5 cm from collected cores, using a Gas Chromatography coupled with a Flame Ionization Detector (GC-FID). The concentrations of COT, NT and total n-alkanes ranged from 0.15 to 3.79%, 0.02 to 0.22%, 520 to 14,107 µg g-1 and from 292 to 17,757 µg g-1 in dry weight, respectively. The lowest values of them were found at the base of the testimonies and the highest at the top. The diagnostic reasons applied to the concentrations of n-alkanes identified the domain in the supply of OM by macrophytes and vegetation of type C3 in the oldest samples and in the most recent samples, the domain of mangrove vegetation, superior plants of type C4 in the OM present in the region. The climate, human activities and hydrodynamics of the region being the main responsible for the results found.