Alexandre Barreto Costa

Characterization of organic matter in sediment cores of the Todos os Santos Bay, Bahia, Brazil, by elemental analysis and 13C NMR.

The impact of human activity on the sediments of Todos os Santos Bay in Brazil was evaluated by elemental analysis and 13C Nuclear Magnetic Resonance (13C NMR). This article reports a study of six sediment cores collected at different depths and regions of Todos os Santos Bay. The elemental profiles of cores collected on the eastern side of Frades Island suggest an abrupt change in the sedimentation regime. Autoregressive Integrated Moving Average (ARIMA) analysis corroborates this result. The range of depths of the cores corresponds to about 50 years ago, coinciding with the implantation of major onshore industrial projects in the region. Principal Component Analysis of the 13C NMR spectra clearly differentiates sediment samples closer to the Subaé estuary, which have high contents of terrestrial organic matter, from those closer to a local oil refinery. The results presented in this article illustrate several important aspects of environmental impact of human activity on this bay.

Characterization of organic matter in a sediment Core near the Mataripe refinery, Bahia-Brazil.

A sediment core was taken from the Todos os Santos Bay, near the Mataripe Bahia-Brazil refinery. The results of dating, (210)Pb and (137)Cs methods, combined with organic indicators, Polycyclic aromatic hydrocarbons (PAHs), n-alkanes and total organic carbon (TOC), showed significant change with the start of production of the oil fields of Aratu, Itaparica and Dom João (1939-1947) and the construction of the Mataripe refinery (1949-1950). This event was marked by a series of significant changes, including an abrupt increase in TOC and the growth of PAH concentrations and the presence Unresolved/Resolved ratio (UR/R)>4 in n-alkanes fraction, which indicated that the contamination was of petrogenic origin. The δ(13)C of specific n-alkanes compounds showed gradual deplete with the depth.

Aplicação de isótopos estáveis de carbono orgânico e nitrogênio e relações C/N como indicadores de fontes de matéria orgânica no complexo estuarino de Nova Viçosa-Caravelas, sul da Bahia, Brasil

This study characterized the elementary ratio and isotopes (δ13C, δ15N and C/N) of surface sediments and suspended solids in surface water of 20 sample points in the estuarine complex of Nova Vicosa-Caravelas, southern Bahia, Brazil . The d13C DIC of the dissolved inorganic carbon (DIC), the δ18O and δD and physico-chemical parameters of water was analyzed to estimate the contribution of continental sources, marine and anthropogenic interference in the study area. The area is characterized by the influence of adjacent coastal area through the main channel of Caravelas Estuary entrance and the Peruipe River in Nova Vicosa Estuary, as the main freshwater intake. The highest values of δ13C in sediment and DIC in water were found in the Caravelas bar and higher values of total organic carbon and C/N ratio found within the two channels that interconnect the estuaries of Caravelas and Nova Vicosa. The isotope ratios of carbon and nitrogen indicate that the analyzed organic matter has terrestrial origin with strong signature of mangroves, characteristic of estuarine regions. Although the values of C/N indicate an anthropogenic contribution at some sampling points, the δ15N found, compared with the literature, suggests that processes of N series cycling in the estuary are sufficient to keep the impact of human activity in the region at low levels. The results may serve as a baseline for future monitoring and environmental studies in estuarine complex of Nova Vicosa-Caravelas.

Geochemical markers of sedimentary organic matter in Todos os Santos Bay, Bahia – Brazil. Indicators of sources and preservation

Natural stable isotopes, such as carbon (C) and nitrogen (N), are modern tools to assess geochemical processes. C and N in organic matter can carry fingerprints of their hydrologic flows and sedimentary processes, including any anthropogenic modification on the natural system. This study focuses on the determination of aliphatic and polycyclic aromatic hydrocarbons and isotopic ratio in the sediment of Todos os Santos Bay (TSB). The isotopic results of the total organic matter indicate varied contribution marine and terrigenous. Typical rates of PAHs mainly indicate a pyrogenic source and mixture between pyrogenic and petrogenic sources. Typical ratios for the n-alkanes indicate the presence of petroleum hydrocarbons. The isotopic composition of n-alkanes suggests a mixture of sources, with the possible contribution of petrogenic.