Estuarine sediments represent important pools of trace metals, released from both anthropogenic and natural sources. Fluctuations in the water column physicochemical conditions, on the other hand, may transfer metals from solid to liquid compartment and resulting in contamination of the surrounding environment. The present research was carried out to evaluate the weakly bounded heavy metal levels in tropical hypersaline and positive estuaries, in order to quantify its potentially availability. The monitoring includes five metals (Cd, Cr, Cu, Pb, Zn) and cover nine estuaries in Rio Grande do Norte state/Brazil, including four hypersaline and five true estuaries. 50 surface sediment samples were collected in each estuary. At the same time, organic matter concentrations were evaluated in order to help explaining possible local variations in heavy metal levels. Organic matter results (0.7% -7.3%) suggest the positive Potengi estuary as the most critical environmental quality situation. On the other hand, according to heavy metals levels, both Conchas and Potengi estuaries registered the higher concentrations of Cr. The highest concentrations were observed in the hyper-saline estuaries, with the exception of the Zn. The present study revealed that the watershed occupation has significantly influenced the heavy metal concentrations in the estuaries.
The short-term variability of the benthic macrofauna community in the shallow coastal area off the Brazilian Antarctic Station Comandante Ferraz (EACF) was investigated during the austral summer of 2008. Three replicates of sediment samples were obtained by a van Veen grab (0.0275 m²) at 20 m depth, in six periods from 1 st February to 7 th March. Macrofaunal densities and sediment composition varied during this period and were correlated to the wind field. Annelids (Polychaeta and Oligochaeta) were the most abundant group with density values ranging from 202 ind.0.0275m-² to 330 ind.0.0275m-² followed by Mollusca and Crustacea. The Principal Component Analysis (PCA) showed that the main sediment components that distinguish the samples were the percentage of gravel, silt and clay. These variations may be influenced by many factors and the climatic conditions play an important role in the local hydrodynamics that affect the benthic community, mainly the organisms with swimming capacity. Meteorological events may influence differently the sediment composition and the macrofauna community. Additional analysis is ongoing to better understand the short-term variability of the macrofauna, including the identification of the polychaetes. Moreover, studies concerning the local hydrodynamics and the interaction between wind, water and sediment in Admiralty Bay are needed.
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