The structure of food webs is a fundamental attribute of ecosystems, and their characterization provides an intrinsic knowledge of the trophic interactions among organisms and of nutrient and energy transfer within ecosystems. Over the last few decades, several chemical and biogeochemical approaches have been proposed to explore different aspects of food webs. In this sense, this study reviews the application of stable isotopes and mercury as main auxiliary tools to the characterization and modeling of aquatic food webs, including analytical and modeling advances, strengths and limitations. The metanalysis performed showed that the most used tools for trophic ecology studies are stable isotopes, and that they can provide better results when combined with mercury and specific chemical molecules such as amino and fatty acids. In addition, the statistical methods applied in the interpretation of results, such as isotope mixing models, have witnessed significant advances in the last two decades. All approaches have premises and limitations when applied to aquatic ecosystems, which must be well understood prior to results interpretation. The use of multiple tracers in trophic studies provides complementary information and in many cases is an appropriate alternative to overcome some limitations, allowing to expand the knowledge of the food webs. ecosystems decades sense acids addition models

Este estudo foi realizado no lago Puruzinho (Humaitá, AM) considerando os períodos de cheia e seca para investigar a importância do pulso de inundação na deposição, remobilização e distribuição das concentrações de mercúrio e matéria orgânica nos sedimentos de fundo no lago da bacia do rio Madeira, na Amazônia brasileira. As amostras de sedimentos e solos foram analisadas para mercúrio total e matéria orgânica. As concentrações mercúrio no sedimento de fundo variaram entre 32,20 e 146,40 ng g-1 e as porcentagens de matéria orgânica variaram de 3,5 a 18,0%. A principal região de acumulação de mercúrio e de matéria orgânica foi na área central e mais profunda do lago. Na estação chuvosa ocorreu maior distribuição de Hg e de matéria orgânica controlada principalmente pelo pulso de inundação do rio Madeira, enquanto que no período de seca predominam os processos de remobilização de mercúrio devido a resssuspensão do sedimento de fundo

The study was conducted in Puruzinho lake (Humaitá, AM) considering seasonal periods of rainy and dry in way to elucidate the flood pulse importance in the deposition, remobilization and distributions of mercury and organic matter in bottom sediments in the Madeira River Basin (Brazilian Amazon). Bottom sediments and soils samples were analyzed for total mercury and organic matter. Mercury concentrations obtained in bottom sediment were 32.20-146.40 ng g-1 and organic matter values were 3.5 - 18.0%. The main region for accumulation of mercury and organic matter was in the central and deepest lake area In the rainy season there was a greater distribution of Hg and organic matter, mainly controlled by means of income of the Madeira river water during flooding, while the predominant process in the dry season was the remobilization of total Hg due to the resuspension of bottom sediments.

Emission factors of natural processes and anthropogenic activities were used to estimate nutrients and metal loads for the lower Macaé river basin, which hosts the operational base for the offshore oil and gas exploration in the Campos Basin. The estimates indicated that emissions from anthropogenic activities are higher than natural emissions. Major contributing drivers include husbandry and urbanization, whose effluents receive no treatment. The increasing offshore oil exploration along the Brazilian littoral has resulted in rapid urbanization and, therefore might increase the inshore emission of anthropogenic chemicals in cases where effective residue control measures are not implemented in fluvial basins of the region.

Emission factors of anthropogenic activities and natural processes were used to estimate nutrients and metals loads to the Contas River lower basin, Southern Bahia, Brazil. Among natural sources, emission from soil leaching is larger for N, Cu and Pb. Atmospheric deposition is the major natural source of P, Zn, Cd and Hg. Among anthropogenic sources, agriculture is the major source of N, Cu and P. Urban sources are the major contributors to the other elements. Present anthropogenic land uses are already responsible for 78 and 99% of total N and P loads and about 50% of total Cu and Hg.

This paper analyses the scientific contribution of chemists and of the Brazilian Chemical Society (SBQ) and its publications to the development of Oceanography in Brazil, as well as major drivers of this participation. A total of 528 articles were analyzed. Most articles (72%) originated in research groups not associated with graduate programs in oceanography. Nearly 50% dealt with the contamination of the marine environment, followed by chemical process studies (32%) and analytical methods development (15%). SBQ journals contributed with 78 articles (14.7% of the total), and rank 1st (QN) and 2nd (JBCS) among scientific journals publishing the analyzed articles.

O processo de contaminação por mercúrio em ecossistemas aquáticos é discutido, levando-se em consideração as características biogeoquímicas atuantes nesses sistemas que resultam em uma maior mobilização e biodisponibilidade do mercúrio para incorporação na cadeia alimentar, eventualmente aumentando a exposição humana ao metal. Traça-se um paralelo entre sistemas aquáticos amazônicos e estuários, ambientes que, pela elevada capacidade de complexação do mercúrio por compostos orgânicos dissolvidos, tendem a manter esse elemento sob formas biodisponíveis, aptas a sofrerem metilação e biomagnificação por meio da cadeia alimentar.

Mercury contamination in aquatic ecosystems in Brazil is discussed by comparing the biogeochemical characteristics resulting in increasing mobilization and bioavailability to food chains and eventually increasing human exposure to mercury. We compare key Amazonian systems and some estuaries, which due to the high complexing capacity of Hg by dissolved organic matter; maintain elevated concentrations of mercury under readily bioavailable forms, able to undertake methylation and biomagnification through food chains.

Increasing natural gas use in Brazil triggered a discussion of its role as a Hg source. We show that Hg emissions to the atmosphere from fossil fuel combustion for power generation in Brazil contribute with 6.2% (4.2 t yr-1) to the total anthropogenic Hg atmospheric emissions, with coal combustion and biomass burning as major sources. Natural gas contributes with 0.04 t yr-1, mostly from electricity generation (88%) and industrial uses (7.6%). Preliminary results on Hg concentrations in natural gas suggest that a large fraction of it is trapped during refining and transport, which may create Hg point sources between extraction and consumption.

Mudanças regionais no uso da terra no estuário do Rio Pacoti, Estado do Ceará, NE do Brasil resultaram em um aumento de duas vezes na área original de manguezais presente neste estuário entre 1958 (0,71 km²) e 2004 (1,44 km²). A maior parte desta expansão ocorreu através da colonização de áreas anteriormente cobertas por vegetação de salgado, mas também ao longo de praias alargadas do rio e em ilhas recém formadas. A diminuição do fluxo de água doce e a acumulação de sedimentos devidos à construção de barragens foram as principais causas deste aumento, embora alterações resultantes de mudanças climáticas globais não possam ser descartadas.

Regional land use changes at the Pacoti River basin, Ceará State, NE Brazil resulted in doubling the mangrove area from 1958 (0.71 km²) to 2004 (1.44 km²). Most of the increase was due to the replacing of salt marsh vegetation inland, but also along newly formed islands and enlarged river banks. Drastic reduction in freshwater supply and sediment accumulation due to river damming were probably the major drivers of the increased mangrove cover. However, changes due to global climate changes can not be ruled out.

The monitoring of the pollution status of the Brazilian coast is hampered by the lack of a consistent environmental indicator. We propose Hg as an environmental proxy to anthropogenic pollution of coastal regions due to its absence in the Brazilian geology, its ubiquity in anthropogenic effluents, and its toxicity. Available data suggest Hg "backgrounds" in coastal sediments of 1-10 ng g-1, in the East and 15-30 ng g-1 in the South. We suggest short sediment cores to establish these values estimating a geo-accumulation index to compare all areas. The distribution of index values showed the majority of southern coast at least moderately contaminated whereas many eastern areas are still pristine.

As matas formadoras do Parque Nacional da Tijuca, Rio de Janeiro, apresentaram em sua serrapilheira um teor médio de chumbo de 16,2 µg/g ao longo de um ano. A entrada do metal no sistema via queda da serrapilheira foi de 140 g/ha/ano. O Pb atinge o sistema florestal pela deposição atmosférica, e tem origem provável na queima de combustíveis (gasolina e petróleo)

Analysis of the litter layer of the Tijuca National Park rainforest revealed an average annual lead concentration of 16.2 µg/g. Rate of lead in the litter fall was 140 g/ha/yr. Lead en ters the forest ecosystem by way of the atmosphere, gasoline usage and petroleum combustion being the most probable causes