Renato S. Carreira

Changes in the sedimentary organic carbon pool of a fertilized tropical estuary, Guanabara Bay, Brazil: an elemental, isotopic and molecular marker approach

Sediments from Guanabara Bay, sampled as short-cores (50–60 cm) from eight stations, were analysed for the elemental (C and N), isotopic (δ13C and δ15N) and molecular composition (steroids) of the organic matter. The objective of this study was to examine whether there are changes in the sources of sedimentary organic matter pool due to increasing N, P and particulate loads to the bay over the last 100 years. On average, we found a 10-fold increase in the flux of organic matter to the sediments with a maximum of 41.7 mol C m−2 year−1. C/N and δ13C time–space distribution and mass balance calculations indicate that the organic material results from a mixture of marine, terrestrial and estuarine sources, with a growing predominance of autochthonous inputs in recent years. Dinosterol was predominant in most samples (>50% of all measured sterols). Concentrations of dinosterol increased significantly in the last two decades and reached values as high as 150 μg g−1 dry sediment. Net increases in concentration were estimated using the first-order decay rate constants derived from experimental data. There are strong indications that an increase in carbon storage occurred in response to growing eutrophic conditions. In spite of the high respiration rates occurring in the water column, fast sedimentation rates result in the transfer of a significant carbon fraction to the anoxic sediments. Further decomposition proceeds only in the first 10 cm of sediment as indicated by the decay rates.

Speciation of sewage derived phosphorus in coastal sediments from Rio de Janeiro, Brazil

Abstract Phosphorus speciation was performed in sediments and waters from an area of 20 km2 under the influence of untreated sewage released via a submarine outfall. Results showed that the pool of organic and non-apatite P made up the major fraction of sewage derived P. A good correlation between Pnapat and FeDBC indicated that sorption on iron oxides is an important mechanism for removal of P to the sediments. Mass balances revealed that most of the sewage derived P had been exported from the observation area but, in spite of this, concentrations of labile forms of P reaching 1900 μg P g−1 were amongst the highest reported for polluted estuarine sediments. The supply over 20 yr of high nutrient loads would have been sufficient to produce 500 000 t of fixed carbon, of which 2% lies presently in the sediments of the surveyed area.

Sedimentary sterols as indicators of environmental conditions in Southeastern Guanabara Bay, Brazil

The interconnected Icarai and Jurujuba embayments, set within the lower south-eastern portion of Guanabara Bay, SE-Brazil, have been subject to the direct input of domestic effluents and other associated contaminants from human activities in their watersheds. This study addresses the composition of carbon, nitrogen and molecular steroid markers of surface sediments (n = 24) and a short core (L = 47 cm), in order to evaluate the impact by sewage, the contribution between allochthonous and autochthonous derived organic matter and eutrophication of the embayments. Coprostanol concentrations revealed, when compared to other regions in Guanabara Bay, high contamination by sewage close to the point of sewage discharge in Icarai embayment. In contrast, the more enclosed and eutrophic Jurujuba embayment exhibited a larger contribution of autochthonous organic matter, as shown by the combination of cholesterol, dinosterol and, partially, also brassicasterol. The presence of stigmasterol and b-sitosterol also indicated a minor contribution of organic matter from terrestrial plants, as revealed by principal component analysis. The sedimentary record of the Jurujuba embayment exhibited highest concentrations of all sterol markers in the top layer, corroborating the recent increase in the accumulation of sewage, plankton derived organic carbon and also eutrophication. Trend in degradation of organic matter was evidenced by sterol/stanol ratios and the behavior of dinosterol indicated that the embayment has been dominated by the accumulation of phytoplankton derived organic matter since earlier times.

Regional assessment of PAHs contamination in SE Brazil using brown mussels (Perna perna Linnaeus 1758)

Cultured and native brown mussels (Perna perna Linnaeus 1758) were used to evaluate the contamination by PAHs in the SE Brazilian coastal zone. Mean concentrations of total PAH (38 parental and alkylated compounds) and cluster analysis revealed that: (i) mussel farms (32.7-70.1 ng g(-1)) are located in uncontaminated areas; (ii) coastal rockyshore areas (89.7 ± 25.8 ng g(-1)) have low level of contamination; and (iii) the Guanabara Bay (760.9 ± 456.3 ng g(-1)) is chronically contaminated by hydrocarbons, which is consistent with previous results. PAH profiles and diagnostic ratios suggested mixed petrogenic and pyrolitic sources for group (ii) and petrogenic sources for group (iii). The levels of PAH in the cultured and native mussels are below threshold values for safe food, even in Guanabara Bay, and thus in such cases other contaminants and pathogens should be considered in order to evaluate the quality of shellfish for human consumption.

Distribuição de coprostanol (5beta(H)-colestan-3beta-ol) em sedimentos superficiais da Baía de Guanabara: indicador da poluição recente por esgotos domésticos

A critical evaluation is presented on the use of faecal sterols for the identification of sewage contamination in Guanabara Bay. Sediments were collected from 8 stations in the bay selected as representative of different contamination levels. GC/MS determination of faecal sterols gave: coprostanol, 335 - 40000 ng g-1; coprostanone, 112-4136 ng g-1; cholesterol, 1407-7800 ng g-1; cholestanol, 2011 - 10900 ng g-1 and cholestanone, 655-7954 ng g-1. The observed concentration is in accordance with the presence of known pollution sources, however, concentration ratios of different sterols species produced unclear results evidently influenced by primary production and microbial processes.

A comparison between faecal sterols and coliform counts in the investigation of sewage contamination in sediments

In September 2002, nine sediment samples (0-2 cm) were collected from Botafogo Cove (southwestern part of Guanabara Bay) in order to compare the use of chemical (coprostanol) and biological markers (E. coli and total coliforms) in identifying faecal contamination. The values found (organic carbon - 6.0 to 64.8 mg g-1; coprostanol - 1.4 to 105 µg g-1; E. coli - < 30 to 2400 NMP/10g and total coliforms - 40 to 9300 NMP/10g) were similar to or even higher than those observed in other contaminated areas of Guanabara Bay. In stations close to the shoreline, both coprostanol concentration and bacteria count confirmed that domestic sewage had accumulated in the cove. Coprostanol concentrations were still relatively high in the stations furthest from contamination sources, although faecal material represented a smaller fraction of the total organic carbon originated by dilution in waters containing algae. Reduction was proportionately higher by virtue of the use of the colimetric assessment method. This result may be associated with the effect that environmental variables (light, salinity, temperature) may have on the survival of bacteria during transport and deposition of sewage particles. Consequently, based on these results, coprostanol may be considered the better indicator of the faecal contamination level in Botafogo Cove sediments.

Hidrocarbonetos e esterois como indicadores de fontes e destino de matéria orgânica em sedimentos da Baía de Sepetiba, Rio de Janeiro

The inputs of organic matter derived from natural and anthropogenic sources to Sepetiba Bay were investigated by using aliphatic hydrocarbons and sterols in superficial sediments. Concentrations ranged from 0.26 to 2.65 μg g-1, <0.01 to 17.41 μg g-1 and 0.77 and 9.24 μg g-1 for n-alkanes, UCM (unresolved complex mixture) and total sterols, respectively. The selected markers and ratios among individual compounds showed the major contribution of terrestrial sources to the total pool of sedimentary organic matter in the bay, but the accumulation of autochthonous organic matter increased with distance from the shoreline. The input of petroleum hydrocarbons and sewage (coprostanol in the range 0.01 to 0.43 μg g-1) were also detected, especially in the more urbanized regions of the bay, but at lower levels of contamination when compared to estuaries in other Brazilian coastal regions.

Characterization of organic matter in cross-margin sediment transects of an upwelling region in the Campos Basin (SW Atlantic, Brazil) using lipid biomarkers

Lipid biomarkers [fatty acids (FAs), sterols and alcohols] and total organic carbon (TOC) were analyzed in 48 surface (0–2xa0cm) sediment samples collected twice (winter 2008/2009 and summer/2009) in two transects ranging from 25 to 3,000xa0m depths. This sampling array encompassed the major upwelling region in the southeastern Brazilian continental margin, where the river influence is probably minimal. The objectives were (1) to evaluate the sources, transport and major areas of organic matter (OM) accumulation in the continental margin and (2) to identify the fraction of OM that is potentially available to secondary benthic producers. As expected from the regional oceanographic characteristics, lipids derived from primary and secondary autochthonous producers (0.073–5.3xa0mgxa0gTOC−1) made the major fraction of the sedimentary OM, whereas lipids from allochthonous sources (0.043–0.40xa0mgxa0gTOC−1) and from bacteria (<0.01–0.43xa0mgxa0gTOC−1) were of relatively less importance. The accumulation of OM in the sediments was highly dependent on the coupling of physical (hydrodynamics) and biological (response to upwelling) factors. It was found that while some restricted areas in the shelf was a sink of labile OM, the export of this material to the upper and middle slope (400–1,000xa0m depths) can represent an important source of bioavailable OM to the deep sea benthic community.

Black carbon contents and distribution in sediments from the southeastern Brazilian coast (Guanabara Bay)

The concentration of black carbon (BC), as well as the relative contribution of BC to total organic carbon, was determined for the first time in sediments from Guanabara Bay. BC was quantified by a thermal oxidation method (CTO-375) and total organic carbon by dry oxidation. Sedimentary organic carbon showed a large range in concentrations (0.82 to 10.3%), but it was possible to define distinct regions of the Bay accordingly to variations in sediment grain size, location and magnitude of allochthonous and autochthonous sources of organic matter and hydrodynamic features. Low concentrations of BC were observed (0.03 to 0.31%, with a mean of 0.19 ± 0.07%, n = 25) when considering the large spectrum of possible sources on land and at sea. However, in some stations levels are sufficiently high as to influence the fate of pollutants of concern, such as PAH and dioxins. The space distribution of BC concentrations in Guanabara Bay cannot be fully understood at this stage since further information on contributions from various sources and on natural dispersion processes are required.

Esterois como indicadores do acúmulo de esgotos domésticos em sedimentos de um sistema estuarino-lagunar tropical (Mundaú-Manguaba, AL)

The history of sewage contamination in the Mundau-Manguaba estuarine lagoon system (NE Brazilian coastal zone) was evaluated through the concentration of sterols in sediment cores. The concentration of coprostanol increased towards the surface sediments, with the maximum of 5.65 µg g-1 at 0-2 cm sediment layer in Mundau. Manguaba exhibited a lower level of contamination. The ratio cholestanol/cholesterol suggested degradation of coprostanol only before the burial of organic matter in the sediment. This feature, together with information of population growth in the watershed, allowed the estimation of a sedimentation rate of 0.90 cm year-1 to the Mundau lagoon.