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

A mathematical and experimental model of the phosphorus cycle in Castle Lake, California

A study of the phosphorus dynamics in castle Lake, California, is presented. The approach is (1) to identify the important phosphorus parameters, (2) to develop and apply methods measuring the parameters in the field and (3) to develop a computer model of the phosphorus cycle. This model will be used to test hypotheses concerning the functioning of the phosphorus cycle and to suggest future research. The cellular metabolism of phosphorus and its different forms and flows in lakes are discussed to identify the important parameters needed to build a model. The method for measuring these parameters involves determining chemically the size of the phosphorus pools and using the tracer 32p to measure the fluxes. Bioassays and stoichiometric approximations provide further data. The concentrations of phosphorus in Castle fake from 14 August to 18 September 1972 were extremely low: in µg l⁻¹, dissolved inorganic 0.1, total dissolved 1-3, and total 1-4, with a maximum 0.5 m off the sediments of 10. There was no measurable polyphosphate, but there was a detectable increase in alkaline phosphatase activity with depth. The rate of 32p uptake was constant over depth and time, with an increase under conditions of high photosynthesis. The rate of evolution of 32DOP was quite variable, being the greatest under high photosynthesis and decreasing with depth. Phosphorus was no limiting in bottle bioassays and was even inhibitory on occasion at additions as low as 1 µg l⁻¹. The model of the phosphorus cycle was derived from expected rates of phosphorus flux and pool size derived from stoichiometric calculations of phytoplankton, bacteria and zooplankton carbon masses and fluxes and functions derived from the literature or experimentation. Model output was compared against the field-measured values and good agreement was found. A steady-state model was modified to include the case of a sudden addition of phosphorus fertilizer under different conditions. The lessons learned from and the shortcomings of the model are discussed. The direction for future research into phosphorus dynamics is outlined

Andean contributions to the biogeochemistry of the Amazon river system

Contributions from Andean rivers may play a significant role in determining the basin-wide biogeochemistry integrated into the mainstem Amazon River of Brazil. Concentration data for organic C, NO3-, and PO43- in Andean rivers are highly variable and reveal no clear spatial or altitudinal patterns. Concentrations measured in Andean rivers are similar to those reported in the mainstem Amazon river and its major tributaries. Explanations of processes which alter Andean-derived particulates and solutes as they exit the Cordillera are only speculative at this time, but their net effect is to diminish Andean signals through decomposition and dilution by lowland inputs. The 13C of particulate and dissolved organic matter in the mainstem Amazon provides evidence that some fraction of Andean derived material persists within the river system, ultimately to be discharged to the Atlantic Ocean. In 1994 a new collaborative research program was launched to further characterize the biogeochemistry of Andean rivers.La contribution andine à la biogéochimie de l'Amazone Les fleuves andins ont vraisemblablement un rôle déterminant sur la biogéochimie de l'Amazone au Brésil. Les données disponibles sur le C organique, le NO3-, et le PO43- des fleuves andins montrent des concentrations très variables et ne révèlent aucune relation avec leur altitude ou leur position dans le bassin. En général, les concentrations des fleuves andins sont semblables à celles du chenal principal et de ses principaux affluents. L'explication des phénomènes d'altération du matériel provenant des Andes ne peut être que spéculative. Cependant, l'atténuation du signal andin est liée à la décomposition et à l'ajout de matériel en aval des Andes. Les analyses de 13C sur la matière organique particulaire ou soluble du chenal principal de l'Amazone mettent en évidence qu'une fraction andine persiste dans le système fluvial qui se jette dans l'océan Atlantique. En 1994, un nouveau programme international de recherche a commencé pour mieux caractériser la biogéochimie des fleuves andins.Contribución andina a la biogeoquímica del Río Amazonas. Los ríos andinos podrían ejercer una influencia significativa sobre la biogeoquímica del Río Amazonas. Las concentraciones en C orgánico, NO3-, and PO43- de los ríos andinos son altamente variables y no presentan claros patrones geográficos o altitudinos. En general, las concentraciones presentan valores similares a aquéllos observados en el Río Amazonas. Actualmente sólo existen explicaciones especulativas de los procesos que modifican el material de origen andino ; sin embargo, la atenuación de la señal andina es una consecuencia del proceso de descomposición y de la añadidura de materiales provenientes de las planicies bajas. El contenido de 13C en el material orgánico del Río Amazonas constituye una evidencia concreta de que cierta fracción del material andino persiste y es transportado hacia el Atlántico. Un nuevo programa colaborativo de investigación se inició en 1994 con el propósito de caracterizar de una manera más completa la biogeoquímica de los ríos andinos.Mcclain Michael E., Richey Jeffrey Edward, Victoria Reynaldo l. Andean contributions to the biogeochemistry of the Amazon river system. In: Bulletin de l'Institut Français d’Études Andines, tome 24, N°3, 1995. Eaux, glaciers & changements climatiques dans les Andes tropicales. pp. 425-437