Pré-concentração em linha para a determinação simultânea de ácidos carboxílicos de baixo peso molecular e ânions inorgânicos em amostras de rios da Amazônia empregando cromatografia de íons com detecção por condutividade elétrica

An ion chromatography procedure, employing an IonPac AC15 concentrator column was used to investigate on line preconcentration for the simultaneous determination of inorganic anions and organic acids in river water. Twelve organic acids and nine inorganic anions were separated without any interference from other compounds and carry-over problems between samples. The injection loop was replaced by a Dionex AC15 concentrator column. The proposed procedure employed an auto-sampler that injected 1.5 ml of sample into a KOH mobile phase, generated by an Eluent Generator, at 1.5 mL min-1, which carried the sample to the chromatographic columns (one guard column, model AG-15, and one analytical column, model AS15, with 250 x 4mm i.d.). The gradient elution concentrations consisted of a 10.0 mmol l-1 KOH solution from 0 to 6.5 min, gradually increased to 45.0 mmol l-1 KOH at 21 min., and immediatelly returned and maintained at the initial concentrations until 24 min. of total run. The compounds were eluted and transported to an electro-conductivity detection cell that was attached to an electrochemical detector. The advantage of using concentrator column was the capability of performing routine simultaneous determinations for ions from 0.01 to 1.0 mg l-1 organic acids (acetate, propionic acid, formic acid, butyric acid, glycolic acid, pyruvate, tartaric acid, phthalic acid, methanesulfonic acid, valeric acid, maleic acid, oxalic acid, chlorate and citric acid) and 0.01 to 5.0 mg l-1 inorganic anions (fluoride, chloride, nitrite, nitrate, bromide, sulfate and phosphate), without extensive sample pretreatment and with an analysis time of only 24 minutes.A metodologia analítica foi desenvolvida empregando coluna pré-concentradora AC15 em linha na cromatografia iônica na determinação simultânea de ânions orgânicos e inorgânicos, com uso de coluna de guarda AG15 e analítica AS15, 250 x 4 mm i.d. (Dionex Corp.). O gradiente de concentração do eluente foi fixo em 10,0 mmol.l-1 KOH nos tempos de retenção de 0 até 6,5 min, seguido do aumento da concentração até 45,0 mmol.l-1 KOH a 21 min, imediatamente retornando e mantendo a concentração inicial até o tempo total de análise de 24 min. Os compostos foram separados com boa resolução e deslocados para uma cela de detecção de condutividade elétrica acoplada a um detector eletroquímico. O emprego da coluna pré-concentradora em linha apresentou vantagens analíticas na determinação de rotina dos íons na faixa linear de 0,01 até 1,0 mg l-1 (r=0,9989) de ácidos orgânicos (acético, propiônico, fórmico, butírico, glicólico, pirúvico, tartárico, ftálico, metanossulfônico, valérico, maleico, oxálico e cítrico) e 0,01 até 5,0 mg.l-1 (r=0,9987) de ânions inorgânicos (fluoreto, cloreto, nitrito, brometo, nitrato, sulfato, clorato e fosfato) sem pré-tratamento da amostra. Um tempo de análise de 24 min e limite de detecção de 5 µ.l-1 foram obtidos para os ânions orgânicos ácido ácetico, ácido fórmico, ácido butírico, ácido glicólico, ácido valérico, ácido cítrico e de 10 µg.l-1 para ácido propiônico, piruvato, ácido tartárico, ácido ftálico, ácido metasulfônico e ácido maleico. Para os ânions inorgânicos 2 µg.l-1 de fluoreto, cloreto, nitrato, brometo, sulfato e 10 µg.l-1 de clorato, nitrito e fosfato foram estimados, segundo metodologia sugerida por IUPAC.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The Large Scale Biosphere Atmosphere Experiment in Amazoni

Perspectivas de pesquisas na relação entre clima e o funcionamento da Floresta Amazônica

Pesquisas recentes do programa LBA (Programa de\ud Grande Escala da Biosfera‑Atmosfera na Amazônia)\ud demonstram ligações entre o clima e o uso da terra\ud na Amazônia e o funcionamento do bioma (1). A\ud vegetação tem uma estreita relação com a atmosfera,\ud controlando uma série de processos físico‑químicos que influenciam\ud a taxa de formação de nuvens, quantidade de núcleos de condensação\ud de nuvens, quantidade de vapor de água, balanço de radiação, emissão\ud de gases biogênicos e de efeito estufa entre tantas outras propriedades.\ud A Amazônia, por sua localização tropical e grande área (Figura 1), é\ud uma importante fonte de vapor de água para nosso planeta. Ela também\ud contém o maior reservatório de carbono entre os ecossistemas\ud terrestres, e tem um papel fundamental na mitigação das mudanças\ud climáticas em curso. A mobilização de pequena fração do carbono\ud acumulado na biomassa da floresta pode perturbar o ciclo de carbono\ud global. A Amazônia também é parte do mais intenso ciclo hidrológico\ud de nosso planeta, com um sofisticado processamento e reciclagem de\ud vapor de água, que alimenta a maior bacia hidrológica. Estes aspectos\ud fazem da região amazônica uma questão central em pesquisas de clima\ud e nas mudanças globais. Desde seu início, o programa LBA focou no\ud relacionamento entre clima, ciclos biogeoquímicos e o papel da mudança\ud de uso do solo em curso, alterando o funcionamento do bioma

Dinâmica do Carbono Inorgânico Dissolvido nos Rios Teles Pires e Cristalino na Bacia Amazônica

The rivers are extremely important in the carbon cycle, either inthe CO2 out gassing flows or carbon exporters to the oceans. Directmeasuring of CO2 exchanges between the terrestrial ecosystems and theatmosphere should consider the aquatic systems flows, not overestimatingthe carbon terrestrial accumulation. The Amazon basin has the largest andmore complex system of fresh water in the world, so that it holds animportant in the global carbon cycle. The objective of this work was toevaluate, during the period between September 2004 to August 2005, thedynamics of the Total Dissolved Inorganic Carbon (DIC) and fractions(dissolved CO2 + HCO3 - + CO32 -), in the waters of Teles Pires andCristalino rivers, components of the Amazon basin, in the district of AltaFloresta, MT. Fortnightly were determined DIC concentration, pH andtemperature of the rivers. Based in those results and applying thethermodynamic balance equations, it was possible to estimate the pCO2and the carbonate system fractions. The rivers presented a seasonal variationin the pH values, being closer to the neutrality in the drought period. Theconcentration of HCO3- was significantly larger in the drought than duringthe flood season. Both studied rivers were oversaturated in CO2 related tothe atmosphere.Os rios têm importante papel no ciclo do carbono, seja nos fluxosevasivos de CO2 ou como exportadores de carbono para os oceanos. Medidasdiretas de trocas de CO2 entre os ecossistemas terrestres e a atmosferadevem considerar os fluxos dos sistemas aquáticos, para não superestimaro acúmulo terrestre de carbono. A bacia Amazônica forma o maior e maiscomplexo sistema de água doce do mundo, tendo conseqüentemente umimportante papel no ciclo global de carbono. O objetivo deste trabalho foiavaliar, no período compreendido entre os meses de setembro de 2004 aagosto de 2005, a dinâmica do carbono inorgânico dissolvido total (CID) esuas frações (CO2 dissolvido + HCO3- + CO32-) nas águas dos rios TelesPires e Cristalino, componentes da bacia amazônica, no município de AltaFloresta, MT. Quinzenalmente foram determinadas as concentrações deCID, pH e temperatura dos rios. Com base nessas determinações e aplicandoas equações de equilíbrio termodinâmico, estimou-se a pCO2 e asfrações do sistema de carbonatos. Os rios apresentaram variação sazonalnos valores de pH, sendo estes mais próximos da neutralidade no períododa seca. A concentração de HCO3- foi significativamente maior no perío116Ciência e Natura, UFSM, 29(2): 115 - 127, 2007do da seca do que no período da cheia. Ambos os rios estudados apresentaram-se sempre supersaturados de CO2 em relação atmosfera

Dissolved carbon in an urban area of a river in the Brazilian Amazon

The main objective of this study was to evaluate dissolved organic and inorganic carbon dynamics along upstream and downstream reaches of the Acre River draining the city of Rio Branco, in the state of Acre, Brazil. Dissolved organic carbon (DOC) concentrations in the Acre River were significantly higher during the wet season, ranging from 385 +/- A 160 to 430 +/- A 131 mu M among the stations, with no difference in upstream and downstream concentrations. Dissolved inorganic carbon (DIC) showed an inverse pattern, with higher concentrations in the dry season, ranging from 816 +/- A 215 to 998 +/- A 754 mu M among the stations, as well as no difference in upstream and downstream DIC concentrations. Bicarbonate was the dominant DIC fraction and was mainly observed during the dry season. Due to lower pH values during the wet season, CO(2) partial pressure (pCO(2)) in the Acre River was higher in the wet season, with values ranging from 4,567 +/- A 1,813 to 4,893 +/- A 837 ppm among the stations. Our results indicate that, although the Acre River drains a large city with significant sewage disposal into the river, seasonal hydrological processes are the main driver of dissolved carbon dynamics, even in the downstream study reach directly influenced by urbanization.Milenio-2 Project[420199/2005-5]Large-Scale Biosphere Atmosphere (LBA) project[CD-06

Water Quality Monitoring in Large Reservoirs Using Remote Sensing and Neural Networks

Water quality monitoring in lakes and reservoirs using water samples and laboratorial analysis is expensive and time consuming. The use of artificial neural networks to predict water quality using satellite images shows great potential to make this process faster and at lower costs. This article discusses an indirect method to estimate the concentration of pigments (chlorophyll-a), an optically active parameter in water quality. A model based on artificial neural networks, using radial base functions architecture, was developed to predict Tucurui’s Reservoir chlorophyll-a concentrations. As input to the neural networks spectral information from Landsat imagery was used, while pigment concentration were used as output information. To train and validate the model we used data from the years 1987, 1988, 1995, 1999, 2000 and 2004. The tested model showed a correlation coefficient of 0.92 for the estimation of pigment (chlorophyll-a) concentrations, indicating its applicability to predict this water quality parameter.ALMEIDA, A. C. Universidade Federal do Par

The Role of Rivers in the Regional Carbon Balance

Through the evolution of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia, fluvial systems evolved from being regarded as ecologically interesting, but not necessarily relevant to the carbon budget, to important systems outgassing a volume of CO2 roughly equal to the carbon sequestered by the forest. Resolving the role of fluvial systems in the carbon balance of the Amazon basin is a problem in scaling, from small seeps and springs to streams to larger rivers. Groundwater discharge of CO2 and its subsequent evasion is a significant conduit for terrestrially respired carbon in tropical headwater catchments. Hydrologic transport of dissolved CO2 was equivalent to nearly half the gaseous CO2 contributions from deep soil (>2 m) to respiration at the soil surface. At larger scales, the dominant feature was a clear relation between discharge and biogeochemical concentrations, with systematic variance among sites. Seasonal distributions of pCO2 rose and fell almost exactly with the discharge hydrograph, while pH decreased and dissolved organic carbon increased. This suggests a constancy of processes across systems. Gas exchange is greater than previously thought, primarily due to greater outgassing in smaller streams than expected. No single organic matter source consistently fuels respiration; instead, the δ13C of respiration-derived CO2 varies with time and space. Photochemical production of labile bioavailable compounds would appear to be limited to clear water conditions. Based on these results, the original Richey et al. (2002) estimate of outgassing of 1.2 ± 0.3 Mg C ha-1 a-1 is conservative; the true value is likely higher. © 2009 by the American Geophysical Union. All rights reserved

The role of rivers in the regional carbon balance

Through the evolution of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia, fluvial systems evolved from being regarded as ecologically interesting, but not necessarily relevant to the carbon budget, to important systems outgassing a volume of CO2 roughly equal to the carbon sequestered by the forest. Resolving the role of fluvial systems in the carbon balance of the Amazon basin is a problem in scaling, from small seeps and springs to streams to larger rivers. Groundwater discharge of CO2 and its subsequent evasion is a significant conduit for terrestrially respired carbon in tropical headwater catchments. Hydrologic transport of dissolved CO2 was equivalent to nearly half the gaseous CO2 contributions from deep soil (>2 m) to respiration at the soil surface. At larger scales, the dominant feature was a clear relation between discharge and biogeochemical concentrations, with systematic variance among sites. Seasonal distributions of pCO2 rose and fell almost exactly with the discharge hydrograph, while pH decreased and dissolved organic carbon increased. This suggests a constancy of processes across systems. Gas exchange is greater than previously thought, primarily due to greater outgassing in smaller streams than expected. No single organic matter source consistently fuels respiration; instead, the δ13C of respiration-derived CO2 varies with time and space. Photochemical production of labile bioavailable compounds would appear to be limited to clear water conditions. Based on these results, the original Richey et al. (2002) estimate of outgassing of 1.2 ± 0.3 Mg C ha -1 a-1 is conservative; the true value is likely higher. © Copyright 2009 by the American Geophysical Union