ABSTRACT. An estuary is a transition zone between freshwater and marine ecosystems, resulting in dilution of seawater. Estuaries are also considered environments of intense biological activity related to the processes of nutrient cycling. The aim of this study was to evaluate the microbial community composition along a salinity gradient in the estuary of the Cachoeira River, located in southern Bahia, Brazil. The analysis of bacterial and yeast communities was performed by determining the denaturing gradient gel electrophoresis band richness. Formation of zones with similar profiles of bands was observed, and the increasing richness at the intermediate zone demonstrated a clear spatial distinction of communities depending DGGE for detection of bacterial and yeast communities on salinity. In addition, the dissolved oxygen content, temperature, pH, salinity, and dissolved inorganic nutrient contents (NH 3 + , NO 2 -, NO 3 -, PO 4 -) were determined. Nutrients were distributed in similar patterns, with decreasing concentrations as the salinity increases.
The main Permian Reservoirs in Central Saudi Arabia have presented an evaluation challenge because of the presence of fresh-brackish water encountered directly below the hydrocarbon accumulations. If this water is used in the evaluation of the oil zone then high connate water saturation is obtained which is inconsistent with generally initial water free oil production observed in the field. Early field development evaluation pragmatism assumed a dual salinity model. Higher salinity formation water was used for the evaluation of the oil zone and fresher water used for evaluation of the underlying water zone. The oil zone formation water was assumed to be the original depositional water present at the time of oil migration. High salinity can be typical for an Arid Fluvial-Estuarine system with high evaporation. Oil migration trapped this water in place. Post-hydrocarbon migration, Paleozoic rain water from higher elevations of the Arabian Shield recharged and flushed the original water beneath the oil. Practical issues have limited confirmation of this assumption and no measurements have been taken to confirm the oil zone water salinity or the dual salinity model. A new technique is being explored that involves extraction and analysis of small quantities of fluid from core plugs sampled at the rig site. Invasion is quantified using mud doping. Initial results show that there is indeed evidence for higher salinity water present in the hydrocarbon zone compared with fresher water in the aquifer, consistent with the proposed dual salinity model. Extended testing of the technique has been conducted which shows that it can be used to measure water salinities in even very tight rock (~micro Darcy). The potential of the technique is to provide a more reliable fluid discriminator, both in these low relief difficult to evaluate formations, and in exploration and unconventional areas.
Tropical streams are among the most threatened ecosystems in the world. As such, studies carried out and compiled over spatial and temporal scales can provide useful information to examine patterns of species diversity and threats to their survival. Here we conducted a systematic review of published research on biological and ecological aspects of stream fish fauna found in the Piracicaba-Capivari-Jundiaí Basin, an industrial watershed of São Paulo State. We aimed to detect main patterns, trends and gaps in studies related to species composition, distribution, spatial and temporal scales, as well as in the covered topics. Results were related to main land uses, biomes and Conservation Units. A constant increase in published articles occurred from 2003 until 2016 with an average of 1.8 articles/year. Twenty-six publications were considered for the present study, reporting on fish samples obtained in 67 sites and resulting in 89 species. A high proportion of studies were concentrated in the Corumbataí sub-basin, and rarefaction curves indicated that stream fish richness in the PCJ Basin may be considerably higher than that shown by the actual numbers. Basin studies were unevenly distributed and did do not include such highly preserved areas as the Camanducaia, Jaguari and Jundiaí sub-basins. We emphasize the importance of further surveys in these regions, as well as in high priority conservation areas, which may lead to new insights for developing appropriate conservation strategies for this basin.
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