Renato Campello Cordeiro

Evaluating levoglucosan as an indicator of biomass burning in Carajás, amazônia: a comparison to the charcoal record

Abstract We report the use of levoglucosan, a novel molecular marker, to trace contributions from vegetation combustion to sediments. Unlike other indicators used for the same purpose (e.g., retene, polynuclear aromatic hydrocarbons) levoglucosan is source specific and emitted in dominant amounts during the burning of any fuel containing cellulose. The combustion of other materials (i.e., fossil fuels) or biodegradation and hydrolysis of cellulose do not produce levoglucosan. In order to validate the application of this novel marker, levoglucosan was analyzed in a sediment core from a lake in Carajas (southeastern Amazonia). This region presents a unique record of forest fires over the last 7,000 years as indicated by charcoal analysis. The fires, which occurred in that area, could be characterized by using levoglucosan as a molecular marker. Similar reconstruction was possible by using charcoal as an indicator, which validates the application of levoglucosan for tracing vegetation combustion in sediments. Both indicators enabled the recognition of major fires that occurred 700, 1200, 5000, and 7,000 years ago.

Variations of the Amazonian rainforest environment: a sedimentological record covering 30,000 years

Abstract Two cores (CSS 2 and CSS 10) were collected from two lakes situated in the Carajas area (6°35′S, 49°30′W) that show different stages of silting up. The results of geochemical and petrographic organic analyses, backed up by 14 C radiometric dating, lead to a reconstruction of the variations in the hydrological regime of these lakes over the last 30,000 years. Evidence is revealed for a period of drying up, characterized by a sedimentary hiatus between 22,000 and 13,000 14 C years BP, followed by a period of refilling between 13,000 and 11,000 14 C years BP. (15,400–12,900 cal years BP). The latter interval is primarily characterized by a mainly clastic sedimentary input rich in quartz, kaolinite and iron hydroxides, leading on to the authigenic formation of siderite. This type of sedimentation implies the erosion of the small catchment basin during periods of transition between arid and humid climatic regimes. From 8000 to 4000 14 C years BP (8900–4500 cal years BP), as well as from 2700 to 1500 14 C years BP (2780–1360 cal years BP), special hydrological conditions prevailed. They are characterized in the sedimentary record by the presence of micro-laminae containing wood charcoal interlayered with sponge spicule material. This interlamination reflects the rapid alternation of dry and humid periods. A comparison with the results obtained by pollen analysis shows that sedimentological indicators, once filtered for strictly local effects, can provide a full record of the regional-scale variations in the environment.

A 21 000 cal years paleoclimatic record from Caçó Lake, northern Brazil: evidence from sedimentary and pollen analyses

Abstract Sedimentological studies including seismic profiles, mineralogy and organic geochemistry on two cores from the center and margin of Caco Lake, Maranhao State, northern Brazil, revealed variable climatic and environmental conditions during the last 21 cal kyr BP. Between 21 and 17 cal kyr BP, during the Late Glacial Maximum, regional climate was predominantly dry, interrupted by short humid phases, as reflected by a succession of very thin layers of sand and organic matter. The Late Pleistocene climate was relatively wet as is suggested by rapid lake-level rise and forest expansion. The Late Pleistocene humid climate differed significantly from present conditions. We suggest that Late Glacial humid conditions were the consequence of intensification of the Inter-Tropical Convergence Zone or shifts of its position, resulting in Antarctic cold-front occurrences. The abrupt climatic changes during this period were marked by siderite deposition into Caco Lake, which appears to be related to regional hydrologic changes linked to global/Northern Hemisphere events. The Holocene was characterized by lower moisture availability and a distinct dry period until 7 cal kyr BP, in response to South American insolation conditions.

Accumulation of organic carbon in five Brazilian lakes during the Holocene

Abstract A comparative study was made of organic carbon accumulation in five lacustrine environments in Brazil (large open water lake, ponds with floating meadows and marshes). The most representative cores were used to calculate the accumulation of total organic carbon (TOC) in the sediment over the past 12,000 cal years BP. Carbon accumulation rates were determined using the TOC concentration, sediment «in situ» density, 14 C calibrated ages and the interpolated sedimentation rate (cm year −1 ) or sediment accumulation rate (g m −2 year −1 ). The C/N ratio and microscopic observations were used to characterise the sedimentary organic matter. Recent TOC accumulation in the lakes was estimated at 7–41 g m −2 year −1 by averaging the last 500 years. This variation roughly correlated with the present-day ratio of watershed area vs. lake area, indicating that nutrient input is important for the modern accumulation of organic matter. The accumulation rates were greatest in lakes with floating macrophytes. The largest lake (Dom Helvecio), with a strong thermal stratification, low primary production and low carbon accumulation, had relatively well preserved organic matter when its low watershed area/lake area ratio was considered. The general increase in carbon accumulation during the Holocene followed the expansion of lakes and the development of a wetter climate, due to a growing penetration of the Atlantic and Amazonian wet air mass over Brazil driven by insolation changes. This change in carbon accumulation was not controlled by the higher water and nutrient inputs alone, more organic matter was decomposed when lake levels were low at the beginning of the Holocene. Some lakes were also influenced by higher inputs of allochthonous organic matter during the early and middle Holocene. These inputs included high concentrations of charcoal fragments. Lake morphology and its changes as the lake level rose, as well as the nature of primary producers, strongly influenced the carbon accumulation rates. Our understanding of how climate changes are linked to changes in the lacustrine environment should not be based on measuring organic matter alone, but requires a good description of the organic matter and other limnological parameters.

Carbon storage in Amazonia during the Last Glacial Maximum: secondary data and uncertainties

The Amazonian forest is, due to its great size, carbon storage capacity and present-day variability in carbon uptake and release, an important component of the global carbon cycle. Paleo-environmental reconstruction is difficult for Amazonia due to the scarcity of primary palynological data and the mis-interpretation of some secondary data. Studies of lacustrine sediment records have shown that Amazonia has known periods in which the climate was drier than it is today. However, not all geomorphological features such as dunes, and slope erosion, which are thought to indicate rainforest regression, date from the time of the Late Glacial Maximum (LGM) and these features do not necessarily correspond to episodes of forest regression. There is also uncertainty concerning LGM carbon storage due to rainforest soils and biomass estimates. Soil carbon content may decrease moderately during the LGM, whereas rainforest biomass may change considerably in response to changes in the global environment. Biomass per unit area in Amazonia has probably been reduced by the cumulative effects of low CO2 concentration, a drier climate and lower temperatures. As few paleo-vegetation data are available, there is considerable uncertainty concerning the amount of carbon stored in Amazonia during the LGM, which may have corresponded to 44-94% of the carbon currently stored in biomass and soils.

Mass balance in the monitoring of pollutants in tidal rivers of the Guanabara Bay, Rio de Janeiro, Brazil.

This study addressed the identification and monitoring of pollution sources of terrestrial origin in rivers (domestic sewage and industrial effluents) and critical fluvial segments in highly polluted environments under tidal influence (mixing marine and continental sources) from Guanabara Bay Basin, Rio de Janeiro, Brazil. The mass balance of contaminants was determined in conditions of continuous flow (low tide) during dry season (lower dilution capability). The results allowed the evaluation of the potential of contaminant mass generation by the different river segments and the estimation of their natural and anthropogenic components. The water quality of Iguaçú and Sarapuí Rivers were evaluated for metals and biochemical oxygen demand. The method gave an excellent response, including the possibility of sources identification and contaminated river segments ranking. The approach also offers fast execution and data interpretation, being highly efficient.

Ecological risk evaluation of sediment metals in a tropical Euthrophic Bay, Guanabara Bay, Southeast Atlantic.

Surface sediments were collected from Guanabara Bay, at 14 stations distributed in five sectors, over three sampling campaigns. Analyses of metals, grain size fractions and total organic carbon analyses were performed. The geo-accumulation index and the enrichment factor were estimated to assess contamination status based on background values. Additionally, the sediment quality guidelines were applied to evaluate the adverse biological effects. Results show that there was no seasonal variation in sediment quality based on any methodology, and all methods utilized showed that NW sector and HRJ sector were the worst affected and that the NE sector had the best conditions. The sediments of GB are polluted mainly by Cr, Pb and Zn. According to ΣSEM/AVS, these metals are not available to the biota, although toxicity tests dispute this. Among the various methods employed, those using background values for the area seem to best reflect the local historical contamination.

Use of the digestive gland of the oyster Crassostrea rhizophorae (Guilding, 1828) as a bioindicator of Zn, Cd and Cu contamination in estuarine sediments (south-east Brazil)

This study demonstrates the accumulation of Zn, Cd and Cu in the digestive gland of the oyster Crassostrea rhizophorae in response to the contamination of sediments and discusses the potential use of this specific organ in monitoring metal contamination in tropical areas. Sediment and oyster samples were collected from coastal Rio de Janeiro sites with different levels of human impact: Sepetiba Bay, Guanabara Bay and the Paraty coast. Metal concentrations were measured using inductively coupled plasma optical emission spectrometry (ICP OES). Significant statistical differences (p<0.001; p<0.05) were observed for Zn and Cd concentrations in the digestive gland; the highest Zn concentrations were found at Sepetiba, followed by Guanabara and Paraty. The highest digestive gland Cd concentrations were found at Paraty, followed by Sepetiba and Guanabara. These concentrations were proportional to those found in the sediments. There was no significant difference (p>0.05) in Cu among the sampling sites. The highest digestive-gland Cu concentration was also found at Sepetiba, followed by Guanabara. The biosediment accumulation factor indicated a gradient of sediment contamination for Zn and Cd. The digestive gland of C. rhizophorae can be a potential indicator of trace metal contamination in sediments from tropical estuarine environments.

Uso dos fenóis da lignina no estudo da matéria orgânica na Várzea do Lago Grande Curuái, Pará e no Lago do Caçó, Maranhão, Brasil

Este estudo tem por objetivo caracterizar os sedimentos superficiais, quanto ao seu teor e qualidade dos fenois da lignina, em dois sistemas lacustres distintos: a Varzea do Lago Grande Curuai (PA) e o Lago do Caco (MA). A Varzea do Lago Grande Curuai e localizada na margem direita do Rio Amazonas, aproximadamente 850 km da foz e e caracterizada pela presenca de lagos de aguas brancas e pretas. O Lago do Caco esta localizado no Maranhao, na borda do ecossistema amazonico. Foram realizadas analises da concentracao de lignina (λ), carbono orgânico total (COT), nitrogenio e isotopos do carbono (δ13C). Os resultados indicam que os sedimentos superficias de lagos de aguas brancas apresentam baixos valores de COT (1,5 a 3,6%), baixa concentracao de λ (0,73 a 1,28 mg.100mg CO-1) e alto indice de degradacao (0,29 a 2,01). Os sedimentos superficiais de lagos de aguas pretas apresentam maiores valores de COT (6,0 a 12,1%) e de λ (1,44 a 1,93 mg.100mg CO-1) em relacao aos sedimentos de lagos de aguas brancas, porem baixos em comparacao com os sedimentos do Lago do Caco (7,2 ~ 15,3% e 1,83 ~ 4,64 mg .100mg CO-1, respectivamente). Atraves das analises realizadas foi possivel identificar diferentes contribuicoes de fontes assim como diferentes estados de preservacao da materia orgânica sedimentada nos dois sistemas apresentados.

Palaeohydrological controls on sedimentary organic matter in an Amazon floodplain lake, Lake Maracá (Brazil) during the late Holocene

In order to understand the impact of hydrological changes of the Amazon River on sedimentary organic matter (OM) composition in Amazonian floodplain lakes, three sediment cores were collected from Lake Maracá (eastern Amazonia) along a transect from the Amazon River main channel to inland. The cores were dated with 14C accelerator mass spectrometry (AMS) and studied by x-ray, mineralogical composition, total organic carbon (TOC) and total nitrogen (TN) contents, stable isotopic composition of TOC and TN (δ13COC and δ15N) and glycerol dialkyl glycerol tetraether (GDGT) distributions. Two distinctive sedimentary depositional phases were identified based on the mineralogical composition and the geochemical characteristics of sedimentary OM. During the early–mid Holocene (~13,000–3200 cal. yr BP), low values of TOC followed by a break in sedimentation suggest a complete drying of the lake caused by drier climatic conditions. Between 3600 and 3200 cal. yr BP, this lake received a reduced influence of the Amazon River main stem. This induced a predominant deposition of C3-plant-derived OM supplied by surface erosion and runoff of acidic soil. A distinct connection of Lake Maracá to the Amazon River began after 3200 cal. yr BP and became permanently established, with its modern characteristics, at 1880 cal. yr BP. This change provoked an increased contribution of phytoplankton and semi-aquatic C4 macrophytes as well as C3 plant derived more alkaline soil OM to the sedimentary OM pool. Consequently, our study demonstrates that the source of sedimentary OM in the Amazon floodplain lakes was strongly linked to the Amazon River hydrodynamics during the late Holocene.