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Pore-water and solid-phase analysis was undertaken to study the effects of different environmental conditions on redox processes in mangrove soils on the southern coast of Brazil. Three Rhizophora mangle (L.) mangrove forests were studied in different physiographic positions-riverine, fringe, and basin forest-and substrate compositions. Our results indicate different geochemical conditions in soils from different physiographic positions. In the fringe soils, the low acid-volatile sulfide and pyrite Fe contents, associated with high values of Fe2+ in pore water, indicate oxic and suboxic conditions in surface layers (0-10 cm). Below this depth, anoxic conditions prevail and sulfate reduction becomes the dominant process of organic matter decay, as indicated by higher concentrations of dissolved HS and pyrite Fe. In the basin forest, long periods of tidal flooding and low rates of litter export maintained anoxic conditions and high organic matter contents, necessary for anoxic respiration to take place, as shown by the low Fe2+ and HS- concentrations in pore water, along with high degree of Fe pyritization values and high concentrations of pyrite Fe. In the riverine soils, the lowest concentrations of pyrite Fe and the highest concentrations of HSin pore water were obtained in response to low availability of reactive Fe (0-10cm, 31.8 ± 8.0 mmol kg-1; 20-30 cm, 43.2 ± 32.3 mmol kg-1) due to its sandy texture, which limits pyrite synthesis. Our results indicate that the participation and intensity of each process may vary within different physiographic positions because of the effects on the frequency and duration of tidal flooding and soil composition. Our results also show that R. mangle is present on substrates with different geochemical conditions (oxic, suboxic, and anoxic). [ABSTRACT FROM AUTHOR]

The determination of optical properties of organic matter using spectroscopic techniques is a powerful tool for the characterization of humic substances (HS) in soils and sediments because of sensitivity, specificity and sample throughput. However, basic spectroscopic techniques have practical limitations because of the similarity in the optical properties of many HS. To improve resolution, the combination of excitation-emission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC) was applied for characterizing fulvic acid (FA) and humic acid (HA) fractions from soils and sediments of two estuarine environments in Spain. Five fluorescent components were identified by EEM-PARAFAC and were found in both FA and HA fractions, consistent with the new paradigm of HS as supramolecular associations as well as the ubiquity of the HS components in the environment. Their contribution was, however, different between the FA and HA fractions. Two different, humic-like, fluorescent components were representative of FA and HA fractions, respectively. The spectral characteristics of these components were similar to previously reported PARAFAC components in dissolved organic matter (DOM) in a wide range of environments, suggesting their applicability in assessing OM quality and environmental dynamics. A microbial humic-like component was much more abundant in FA than in HA fractions. Furthermore, principal component analysis clarified that the two identified protein-like components, were enriched in sediment HA compared to soil HA, suggesting a larger contribution of refractory algaenan in sediment HA. The results of the present study demonstrate that EEM-PARAFAC is a useful technique for the biogeochemical characterization of soil and sedimentary HS. [ABSTRACT FROM AUTHOR]

Due to the limited number of studies on phytoremediation using native tree species in tropical soils, the aim was to identify new phytoremediator species from tropical climate with the purpose of promoting an increase in the diversity of tropical native trees used in phytoremediation projects. Seven native tree species from Brazil were selected: Cedrela fissilis, Handroanthus serratifolius, Copaifera langsdorffii, Hymenaea courbaril, Mimosa caesalpiniifolia, Cecropia sp. and Myracrodruon urundeuva. Seedlings of these species were planted in pots with an unpolluted Arenosol, and then spiked with 60, 100 and 500 mg kg−1 Cu. Height and stem diameters were measured over 60 days. Biomass and total Cu concentration were determined in leaves, stem and roots. Copper in bulk soils and rhizospheres was analyzed by a sequential extraction method. All species accumulated high concentration of Cu in roots (>300 mg kg−1), so they could be used as phytostabilizators for this metal. Copper mobilization increased in the rhizospheres, but it was mostly absorbed by roots. Cecropia sp., M. urundeuva and C. langsdorffii are hyperaccumulators of Cu (>300 mg kg−1 in shoots), so they are potential phytoextractor species. This study evidence the potential of seven tree species native from tropical regions for phytostabilizing copper-polluted soils. [ABSTRACT FROM AUTHOR]

The minerals of the clay fraction in estuarine plains are mainly detrital, being a mixture of marine and continental sediments, but can also be authigenic. Because of the importance of mangrove ecosystems in tropical estuarine areas and the relatively few existing studies of the mineralogical composition of soils in these environments, the aim of this study was to determine the mineralogical assemblage and identify potential contrasts along the coast of the State of São Paulo. Soils from 11 mangroves distributed along the coastal plain of the State of São Paulo were sampled at depths of 0 to 20 and 60 to 80 cm, and samples of suspended sediments from the Ribeira do Iguape River were collected for analysis. Mineralogical analyses were performed on the clay and silt fractions by x-ray diffraction (XRD) and transmission electron microscopy, and fresh soil samples were analyzed by scanning electron microscopy-energy dispersive spectrometry and suspended sediments by XRD. The silt fraction contained quartz, feldspars, gibbsite, kaolinite, illite, and vermiculite, and the clay fraction contained smectite, kaolinite, illite, gibbsite, quartz, and feldspars. Locally, vermiculite, biotite, anatase, halloysite, and goethite may occur because of recent transport of sediments to the system. Pyrite was identified in fresh samples. The allochthonous minerals found either were terrestrial and transported by rivers or had originated from the continental platform by past transgressive events. We suggest that the neoformation of smectite and kaolinite occurs in mangrove soils. Different geomorphological settings along the São Paulo coast appear to regulate mineral distribution in mangrove soils. [ABSTRACT FROM AUTHOR]