In the coastal multilayer aquifer system of a highly urbanized southern city (Recife, Brazil), where groundwaters are affected by salinization, a multi-isotope approach (Sr, B, O, H) was used to investigate the sources and processes of salinization. The high diversity of the geological bodies, built since the Atlantic opening during the Cretaceous, highly constrains the heterogeneity of the groundwater chemistry, e.g. Sr isotope ratios, and needs to be integrated to explain the salinization processes and groundwater pathways. A paleoseawater intrusion, most probably the 120 kyB.P. Pleistocene marine transgression, and cationic exchange are clearly evidenced in the most salinized parts of the Cabo and Beberibe aquifers. All (87)Sr/(86)Sr values are above the past and present-day seawater signatures, meaning that the Sr isotopic signature is altered due to additional Sr inputs from dilution with different freshwaters, and water-rock interactions. Only the Cabo aquifer presents a well-delimitated area of Na-HCO3 water typical of a freshening process. The two deep aquifers also display a broad range of B concentrations and B isotope ratios with values among the highest known to date (63-68.5‰). This suggests multiple sources and processes affecting B behavior, among which mixing with saline water, B sorption on clays and mixing with wastewater. The highly fractionated B isotopic values were explained by infiltration of relatively salty water with B interacting with clays, pointing out the major role played by (palaeo)-channels for the deep Beberibe aquifer recharge. Based on an increase of salinity at the end of the dry season, a present-day seawater intrusion is identified in the surficial Boa Viagem aquifer. Our conceptual model presents a comprehensive understanding of the major groundwater salinization pathways and processes, and should be of benefit for other southern Atlantic coastal aquifers to better address groundwater management issues.

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RESUMODevido aos grandes problemas de eutrofização de lagos e reservatórios, a identificação de áreas fornecedoras de fósforo possui grande importância no planejamento de medidas de controle da poluição hídrica por atividades agrícolas. Neste trabalho, aplicou-se uma metodologia denominada P-Index, para identificar áreas com potencial de fornecimento de fósforo de ecossistemas terrestres para os corpos d'água, cujo método está baseado no cruzamento de planos de informações referentes à disponibilidade de fósforo no solo e dos processos de transferência deste nutriente, para os cursos de água. Tal procedimento foi aplicado na bacia contribuinte do Sistema de Reservatório Salto, no município de São Francisco de Paula, RS. Com o cruzamento dos planos de informação, obteve-se um mapa de classes de contribuição de fósforo para os reservatórios, verificando-se que a quase totalidade desta área da bacia foi classificada como tendo baixo potencial de fornecimento. As pequenas áreas consideradas com maior potencial de contribuição representam áreas situadas próximas aos corpos d'água e sob cultivo de culturas como batata e alho, nos quais são aplicadas doses elevadas de fertilizantes. Palavras-chave: eutrofização, uso da terra, Sistema de Informações GeográficasUse of P-Index in a waterbasin by geoprocessing techniques ABSTRACT Due to problems caused by eutrophication of lakes and reservoirs, the identification of phosphorus source areas is important for planning the control of agriculture-related water pollution. This study applied a method designed to identify these phosphorus source areas, called P-Index, which is based on combining data layers related to soil phosphorus availability and phosphorus transport processes. The method was used for studying the Salto Reservoir waterbasin, in São Francisco de Paula, in the State of Rio Grande do Sul, Brazil. Data related to phosphorus availability, intensity of transport processes, and distance to waterways were combined to yield a map of phosphorus contribution classes, which showed that almost the entire study area was considered to have low phosphorus contribution potential. A few small areas, corresponding to potato and garlic fields that received heavy chemical fertilization, were classified as having high phosphorus contribution potentials.

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[1] In order to understand mechanical processes likely to be occurring on the surfaces of asteroids, we have performed experiments with mineral mixtures on NASA's KC-135 microgravity facility. The behavior of sand and iron filing mixtures, the sand and metal being in the proportions and with grain sizes of ordinary chondrite meteorites, was observed with digital cameras as gas was flowed upward through the mixtures and the plane went through cycles of positive, zero, negative and normal gravity. Partial separation of gas and sand occurred readily under gas flow and microgravity conditions and sometimes survived subsequent turbulence. This behavior is consistent with predictions of the Ergun equation derived from terrestrial experiments. The data have implications for understanding chondrite genesis, for understanding the spectra of asteroid surfaces, and for the design of equipment to function on asteroid surfaces.

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[1] We report here experiments on NASA's KC-135 microgravity facility aimed at investigating metal-silicate fractionation in chondrites. Metal and sand particle mixtures, with sizes and relative proportions approximating chondritic values, were allowed to undergo density and aerodynamic sorting as air was passed through 310, ten-centimeter long 2.54 cm diameter columns under microgravity conditions. Metal and silicate fractionation was found to occur when gases passed through the mixtures and when the particle diameter ratio was large ($3.0), with sand being enriched near the surface of the beds. This is contrary to experiments performed under terrestrial gravity and the semi-empirical Ergun equation. While the reason for this discrepancy is not well understood, the present results do suggest that separation of metal and silicates will readily occur under microgravity conditions on the surface of asteroids.