Factors that control the spatial and temporal distributions of phosphorus, nitrogen, and carbon in the sediments of a tropical reservoir.

The impacts of anthropic activities have had profound effects on the nitrogen (N) and phosphorus (P) cycles in many aquatic ecosystems. We investigated the spatial and temporal distributions of carbon (C), N, and P in the sediments of a tropical Paiva Castro Reservoir (São Paulo, Brazil), as well as their release and retention in the system. In 2010, surface sediments were collected at nine sites in the reservoir, and a core was obtained in the limnetic zone, in 2010. The core was dated using the 210Pb technique. The organic C content was estimated from organic matter concentration, which was measured by the loss-on-ignition method, and the concentrations of P and N were determined by spectrophotometry. Marked spatial heterogeneity in the Paiva Castro sediments associated with both natural variations in the water body and variations induced by human impacts was observed. Heterogeneity was evidenced by a decrease in the allochthonous contribution of organic matter (C/N) in the upstream-downstream direction and increases of N and P, mainly associated with water flows in the different compartments of the reservoir. In the core, C and N concentrations display significant positive correlations with increases in population and agricultural activities in the drainage basin through time. The C/P molar ratios in surface sediments are indicative of human impacts in the region, as C:P ratios in the sediment are low (7.8:1) compared to the Redfield ratio (C:P = 108:1). Predominance of oxic conditions at the sediment surface and particles sizes < 63 µm provided favorable conditions for P retention in the sediments, which helps prevent eutrophication. Approaches used in this research should be extended to other locations, especially in mesotrophic and oligotrophic reservoirs, to provide information on historical impacts in such aquatic ecosystems.

Use of a chemometric tool to establish the regional background and assess trace metal enrichment at Baixada Santista - southeastern Brazil.

The trace metals in sediments consist of two components, anthropogenic and lithogenic or natural, which can cause misinterpretations for what actually exists in sediments. Normally, to investigate trace metal background levels, indices are applied in order to normalize the values and reduce natural variability, but it is well known that using the average shale or crust content is not the best choice and vertical sediment profiles are not always available. The purpose of this study is to use a prediction interval to assess metal enrichment without a reference level and to assess a regional background level using the same tool. The levels of eight elements were submitted to a partial digestion technique and analyzed by ICP-OES. The enrichment factor results suggested that using background values from the prediction interval and using values from vertical sediment profiles yield statistically similar results. Furthermore, the background equations present more realistic data than other methods because they consider the mud content of the samples. Thus, a prediction interval can be a useful tool to establish a regional background and assess trace metal enrichment.

Spatial distribution and enrichment assessment of heavy metals in surface sediments from Baixada Santista, Southeastern Brazil.

The Baixada Santista, besides being an important estuarine system, is responsible for most of the international trade and economic development in the region because of the Santos Port and the Cubatão Industrial Complex. The aim of this study is to assess heavy metal contamination of the Santos São Vicente Estuary using enrichment factors (EFs) and sediment quality guidelines (SQGs). Thus, superficial sediment samples were subjected to acid digestion and analyzed (Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Sc, V, and Zn) by inductively coupled plasma optical emission spectrometry (ICP-OES). The results indicated an absence of contamination, with the EFs indicating moderate enrichment. As and Pb presented higher enrichment probably due to the natural processes of weathering and sedimentation, and the influence of human activity. This conjoint analysis showed that potentially polluting activities are of concern as the highest values converge near the Cubatão Industrial Complex, which correspond to intense urbanization and industrial activity.

Bioaccumulation of potentially toxic trace elements in benthic organisms of Admiralty Bay (King George Island, Antarctica).

Data about the concentration, accumulation and transfer of potentially toxic elements in Antarctic marine food webs are essential for understanding the impacts of these elements, and for monitoring the pollution contribution of scientific stations, mainly in Admiralty Bay due to the 2012 fire in the Brazilian scientific station. Accordingly, the concentration of As, Cd, Cu, Ni, Pb and Zn was measured in eight benthic species collected in the 2005/2006 austral summer and the relationship between concentration and trophic position (indicated by δ(15)N values) was tested. A wide variation in metal content was observed depending on the species and the element. In the studied trophic positions, it was observed bioaccumulation for As, Cd and Pb, which are toxic elements with no biological function. In addition, Cd showed a positive relationship between concentration and trophic level suggesting the possible biomagnification of this element.

137Cs in marine sediments of Admiralty Bay, King George Island, Antarctica.

The radionuclide cesium-137 ((137)Cs) is produced exclusively by anthropogenic processes and primarily by nuclear explosions. This study determined the reference inventory that is (137)Cs associated with the element's original input, and utilized the levels of activity of this radionuclide previously measured in five sediment profiles collected from Admiralty Bay, Antarctica, to investigate the mobility of this element in the environment. (137)Cs has a half-life of 30 years. Because of this, it is environmentally persistent and has been shown to accumulate in marine organisms. The mean reference inventory of this radionuclide in Admiralty Bay sediments, determined using high resolution gamma ray spectrometry, was 20.23±8.94 Bq m(-2), and within the ambient (137)Cs activity range. A model of (137)Cs diffusion-convection was applied to data collected from 1cm intervals in sediment cores with the aim of providing insights with respect to this element's behavior in sediments. Model results showed a significant correlation between measured and modeled values using the concentrations of (137)Cs, and estimated input into the system from the global fallout of past nuclear tests and expected values based on local sedimentation rates. Results highlight the importance of accounting for the vertical diffusion of (137)Cs in marine sediments when used as a tracer for environmental processes and for assessing potential bioavailability.