Distribution and behavior of manganese in the Alto do Paranapanema Basin

This paper reports manganese (Mn) fractionation in samples collected from the water column and sediments in an environmental protection area in the Alto do Paranapanema Basin (Sao Paulo State, Brazil). The three locations studied showed equivalent Mn levels, with moderate seasonal differences (p < 0.05). The sediment samples contained five Mn species (p < 0.05): iron and manganese (hydr)oxides > Mn bound to carbonates approximate to exchangeable Mn approximate to Mn bound to silicates > Mn bound to organic matter (p < 0.05). The water samples contained three species (p < 0.05): particulate Mn > labile Mn approximate to non-labile Mn. The data suggest that Mn has a natural origin (Enrichment Factor EF < 2; Geoaccumulation Index I(geo) < 0) and moderate environmental risk (Risk Assessment Code RAC similar to 30%). At the same time, under certain conditions some manganese species could be present in a state of equilibrium between the water column and sediment. These results could provide a basis for Mn management in the Alto do Paranapanema Basin.

Analysis of foraminifera assemblages and sediment geochemical properties to characterise the environment near Araca and Saco da Cape la domestic sewage submarine outfalls of Sao Sebastiao Channel, Sao Paulo State, Brazil

Superficial bottom samples were collected near diffusers of domestic sewage submarine outfalls at Araca and Saco da Capela, Sao Sebastiao Channel, Brazil. The goal of this study was to investigate the distribution and composition of live benthic foraminifera assemblages and integrate the results obtained with geochemical analyses to assess human-induced changes. According to the results obtained no environmental stress was observed near the Saco da Capela submarine outfall diffusers. The foraminifera assemblage is characterised by species typical of highly hydrodynamic environments, with well-oxygenated bottom waters and low nutrient contents. In contrast, near Araca submarine outfall, organic enrichment was denoted by high phosphorus, sulphur and, to a lesser extent, total organic carbon content. Harmful influences on foraminifera could be identified by low richness and specific diversity, as well as the predominance of detritivore feeder species, which are associated with higher organic matter flux and low oxygen in the interstitial pore water. (C) 2009 Elsevier Ltd. All rights reserved.

Grain size and heavy minerals of the Late Quaternary eolian sediments from the Imbituba-Jaguaruna coast, Southern Brazil: Depositional controls linked to relative sea-level changes

The stratigraphic subdivision and correlation of dune deposits is difficult, especially when age datings are not available. A better understanding of the controls on texture and composition of eolian sands is necessary to interpret ancient eolian sediments. The Imbituba-Jaguaruna coastal zone (Southern Brazil, 28 degrees-29 degrees S) stands out due to its four well-preserved Late Pleistocene (eolian generation 1) to Holocene eolian units (eolian generations 2, 3, and 4). In this study, we evaluate the grain-size and heavy-mineral characteristics of the Imbituba-Jaguartma eolian units through statistical analysis of hundreds of sediment samples. Grain-size parameters and heavy-mineral content allow us to distinguish the Pleistocene from the Holocene units. The grain size displays a pattern of fining and better sorting from generation 1 (older) to 4 (younger), whereas the content of mechanically stable (dense and hard) heavy minerals decreases from eolian generation 1 to 4. The variation in grain size and heavy-mineral content records shifts in the origin and balance (input versus output) of eolian sediment supply attributable mainly to relative sea-level changes. Dunefields submitted to relative sea-level lowstand conditions (eolian generation 1) are characterized by lower accumulation rates and intense post-depositional dissection by fluvial incision. Low accumulation rates favor deflation in the eolian system, which promotes concentration of denser and stable heavy minerals (increase of ZTR index) as well as coarsening of eolian sands. Dissection involves the selective removal of finer sediments and less dense heavy minerals to the coastal source area. Under a high rate of relative sea-level rise and transgression (eolian generation 2), coastal erosion prevents deflation through high input of sediments to the coastal eolian source. This condition favors dunefield growth. Coastal erosion feeds sand from local sources to the eolian system. including sands from previous dunefields (eolian generation 1) and from drowned incised valleys. Therefore, dunefields corresponding to transgressive phases inherit the grain-size and heavy-mineral characteristics of previous dunefields, leading to selective enrichment of finer sands and lighter minerals. Eolian generations 3 and 4 developed during a regressive-progradational phase (Holocene relative sea level highstand). The high rate of sediment supply during the highstand phase prevents deflation. The lack of coastal erosion favors sediment supply from distal sources (fluvial sediments rich in unstable heavy minerals). Thus, dunefields of transgressive and highstand systems tracts may be distinguished from dunefields of the lowstand systems tract through high rates of accumulation (low deflation) in the former. The sediment source of the transgressive dunefields (high input of previously deposited coastal sands) differs from that of the highstand dunefields (high input of fluvial distal sands). Based on this case study, we propose a general framework for the relation between relative sea level, sediment supply and the texture and mineralogy of eolian sediments deposited in siliciclastic wet coastal zones similar to the Imbituba-Jaguaruna coast (C) 2009 Elsevier B.V. All rights reserved.