Evolução da deposição de matéria orgânica na Baía da Ilha Grande, RJ

Abstract

Coastal environments have been suffering impacts due to the human occupation, one main effect is the alteration of organic matter (OM) cycling within the coastal zone. In order to investigate the most important OM sources and how human influence has shaped the composition of sedimentary organic matter in Ilha Grande Bay (IGB), four sediment cores (Abraão, Saco do Céu, TEBIG and Marina Piratas) were taken, aged and analysed for organic carbon, total nitrogen, fine-grained content, sterols and n-alcohols. Results indicate great contributions of allochthonous in Abraão’s core and specially in Saco do Céu’s, these cores are enriched in organic carbon, fine-grained sediments in comparison with sediments deposited in the vicinities of TEBIG and Marina Piratas. During the 1950’s some alterations, such as the increase in phytoplanktonic contribution, are observed as pointed by the Principal Component Analysis (PCA), at the same period of time an abrupt change has occurred in granulometry for Marina Piratas’ core. These changes are man-made indirect effects, caused by the enhanced population growth, that is responsible for polluting water bodies and destroys highly important ecosystems such as mangroves. Nevertheless, sewage-derived tracers showed very little influence of fecal OM to sediments, additionally, it has low growing importance through the last decades. Along with dense vegetal cover, the elevated pluviometric records help carrying large amounts of terrigenous material to IGB sediments as indicated by abundant long-chain n-alcohols