Marcelo Gomes de Almeida

The impacts of land use changes in the mercury flux in the Madeira River, Western Amazon

Changes in hydrochemistry and Hg distribution in the Madeira River from Porto Velho to the confluence with the Amazon River were studied in two cruises in 1997 and 2002. Water conductivity was similar in both periods, but the pH was significantly higher in 2002, in particular along the middle reaches of the river. Total suspended matter concentrations also increased from 1997 to 2002 along the same river portion, which is a result of forest conversion to other land uses, in particular pastures and agriculture accelerated during the interval between the cruises. Dissolved Hg concentrations were similar along the river in both cruises, but particulate Hg concentrations increased significantly along the middle portion of the river, although the suspended matter from 2002 was relatively poorer in Hg compared to that from 1997. Since particulate Hg represents more than 90% of the total Hg present in the river water, there was a significant increase in the total Hg transport in the Madeira River. Although gold mining has nearly ceased to exist in the region, the remobilization of Hg from forest soils through conversion to other land uses is responsible for maintaining relatively high Hg content in the Madeira River environment.

Mercury degassing from forested and open field soils in Rondônia, Western Amazon, Brazil

A Teflon dynamic flux chamber was used to characterize Gaseous Elemental Mercury (GEM) flux from forested and open field soils in a highly changing environment in Rondônia State, western Amazon. We simultaneously analyzed meteorological parameters at the soil level relating GEM fluxes to soil temperature, air humidity, soil moisture, solar radiation, and speed and wind direction. We also examined variations of atmospheric GEM concentration. GEM fluxes during the day and night in the open field site were significantly different (17+/-14ngm(-2) h(-1) and 0.9+/-1.9ngm(-2)h(-1), for day and night, respectively), but were similar within the forest site (4.8+/-1.4ngm(-2)h(-1) and 4.4+/-1.8ngm(-2) h(-1) for day and night periods, respectively). A comparison between 24-h periods averages in the two sites showed much larger emission from the open field site. GEM fluxes at the open field site were positively correlated with soil moisture, solar irradiation and soil temperature and inversely correlated with air humidity. At the forest site GEM fluxes showed no correlation with meteorological variables. At the open field site GEM concentrations significantly correlated with GEM flux, at least during the day. At night in the open field site and during the day and night at the forest site no correlation was found between GEM fluxes and GEM concentrations in the ambient air. Higher emissions from the open field site support earlier studies showing larger Hg remobilization following forest conversion to pasture.

Mercury speciation changes in waters of the sepetiba Bay, SE Brazil during tidal events and different seasons

This work describes changes in Hg speciation in water along the transport from Sepetiba Bay, SE Brazil, to the adjacent continental platform during tide events and in different seasons. The chemical evaluation of Sepetiba Bay waters showed that the bay exports suspended particulate material (SPM) impoverish in organic carbon to adjacent continental platform areas, mainly during the wet season and imports SPM enriched in organic carbon from the ocean, probably of phytoplanktonic origin, during the dry season. The chemical speciation of Hg during the study period showed that Hg0 production can be controlled by primary productivity and that the bay acts as a producer and exporter of organic species of Hg to adjacent areas, since the highest non-reactive Hg concentrations were observed during the ebb tide. No significant correlations were found between non-reactive Hg and dissolved or particulate organic matter concentrations. In general the particulate Hg, non-reactive Hg and reactive Hg fractions represents 55%, 35.5% and 9.5% of the total Hg content in Sepetiba Bay waters, respectively.

Methodology optimization and application for measurement of gaseous elemental mercury in the amazon atmosphere

The aim of this study was to optimize a semi-automatic methodology using commercial pure gold cartridges (Tekran Inc.) to quantify gaseous elemental mercury (GEM) in the Amazon atmosphere. The detection limit was 0.020 ± 0.006 ng Hg. This corresponds to detection limits varying from 0.2 to 0.4 ng Hg m-3, for field sample volumes ranging between 0.1 and 0.05 m3. The similarity between the 9 tested cartridges was evaluated. Under sampling flow rates varying between 0.4 and 2.0 L min-1 no difference among cartridges was observed. The maximum retention capacity of the cartridge (breakthrough) was not reached in experiments with flow rates of 1 or 2 L min-1, and with Hg concentration of 25 ng m-3 and maximum air volume of 150 L. Water condensation on the gold surface showed to be a problem, but that was solved by heating the sample cartridge at 60 oC during sampling.

9 – A COMPOSIÇÃO FÍSICA E ELEMENTAR DOS SEDIMENTOS MARINHOS ENTRE A REGIÃO COSTEIRA E O OCEANO PROFUNDO NA BACIA DE CAMPOS*

RESUMO Neste estudo esta sendo apresentada a composicao fisica (granulometria) e quimica (carbonato, carbono orgânico, enxofre total, nitrogenio total, fosforo total, aluminio, ferro, manganes, bario, vanadio, zinco, cromo, arsenio, niquel, chumbo, cobre e mercurio) dos sedimentos superficiais (0 a 2 cm) da plataforma e margem continental da Bacia de Campos entre 25 e 3.000 m, e dos cânions Almirante Câmara (CANAC) e Grussai (CANG), entre 400 e 1.350m. Com base nos teores de carbonato e granulometria, o ambiente de plataforma continental e um ambiente heterogeneo com sedimentos variando de lama a cascalho e, de acordo com os teores de carbonato, de Litoclastico/Bioclastico e Biolitoclasticos/clasticos. Na margem continental ate a regiao mais profunda temos um ambiente mais homogeneo, tipicamente lamoso, com areas areno-lamosas, e sendo um dominio sedimentar composto por materiais tipicamente bioclasticos e biolitoclasticos. As concentracoes dos metais e metaloides foram determinadas quanto as suas concentracoes totais, reativas em solucao de HCl 1,0 mol L−1, e Pb, Zn, Ni e Cu foram determinados atraves dos metais simultaneamente extraidos (SEM) com sulfetos volateis em acido (AVS). A abundância absoluta dos metais e metaloides seguiu um padrao geral com as menores concentracoes na faixa de isobata ate 150 m, aumentando entre 400 e 1.000 m (meio da margem continental) e diminuindo ate 3.000 m. A distribuicao dos elementos determinados neste estudo nos anos de 2008 e 2009 apresentou a mesma distribuicao, nao sendo encontradas diferencas significativas interanuais. Os cânions representaram ambientes deposicionais importantes, mostrando diferencas marcantes quando comparadas com as regioes adjacentes da margem continental. As concentracoes de AVS e SEM estiveram abaixo do limite de deteccao para a maioria das estacoes amostradas na plataforma e margem continental, assim como nos cânions. Estes resultados mostram que os sulfetos nao sao suportes geoquimicos relevantes nestes ambientes que sao predominantemente oxidantes, porem em algumas estacoes no Cânion Grussai (700 m) os sulfetos representam um importante suporte geoquimico para os elementos estudados. As concentracoes totais dos elementos analisados estao abaixo de outras regioes e tipos de sedimentos, exceto para Mn, As e Hg que estao acima do folhelho medio. As concentracoes relativas dos elementos determinados nas fracoes reativas apontam para uma grande variabilidade dependente dos elementos e das regioes ao longo da plataforma e margem continental sendo o Cu e o Al os menos reativos, enquanto os demais elementos podem chegar a ate 98%, como o caso do Mn; os demais elementos chegaram ao maximo de 60 a 70%, principalmente nas regioes onde ha predominância da fracao silte e argila. O As apresentou concentracoes acima dos limites maximos estabelecidos pelo National Oceanic and Atmospheric Administration (NOAA) de incorporacao biologica sem promover danos aos organismos, enquanto algumas estacoes estiveram proximas a estes limites para o Cu, Ni e Cr. Os principais suportes geoquimicos da regiao sao carbonatos e oxi-hidroxidos de Fe e Mn, responsaveis majoritariamente pela fracao de metais fracamente associada aos sedimentos, seguidos pela materia orgânica e, em algumas estacoes menos oxidantes, ha participacao dos sulfetos como esta funcao.

Barium and its Importance as an Indicator of (Paleo)Productivity

Barium (Ba) is a trace element which occurs predominantly as barite mineral (BaSO4) in the marine environment. Previous work suggests that barite concentrations are related to the organic carbon flux and marine biological debris in the water column suggesting a direct or indirect involvement in the marine biological cycling. In addition, barite has a high preservation rate (~30%) in sediments and it is less affected by early diagenesis than other proxies for productivity such as carbonates (~10%) and organic carbon (~1%), for example. Therefore, Ba is considered an excellent proxy for ocean (paleo)productivity. However, correlating barite to productivity involves some caveats. Specifically, the post-depositional formation of barite in oxic sediments can lead to Ba release into porewaters under anoxic conditions, which can form barite again under oxic conditions. This diagenetic formation is not correlated to export production as the seawater authigenic barite formed with decaying organic matter in the water column. Therefore, the main goal of this work is to briefly review the marine Ba cycle and highlight its importance for (paleo)productivity research.