Inputs of organic carbon from Ria de Aveiro coastal lagoon to the Atlantic Ocean

Land/ocean boundaries constitute complex systems with active physical and biogeochemical processes that affect the global carbon cycle. An example of such a system is the mesotidal lagoon named Ria de Aveiro (Portugal, 40°38′N, 08°45′W), which is connected to the Atlantic Ocean by a single channel, 350 m wide. The objective of this study was to estimate the seasonal and inter-tidal variability of organic carbon fluxes between the coastal lagoon and the Ocean, and to assess the contribution of the organic carbon fractions (i.e. dissolved organic carbon (DOC) and particulate organic carbon (POC)) to the export of organic carbon to the Ria de Aveiro plume zone. The organic carbon fractions fluxes were estimated as the product of the appropriate fractional organic carbon concentrations and the water fluxes calculated by a two-dimensional vertically integrated hydrodynamic model (2DH). Results showed that the higher exchanges of DOC and POC fractions at the system cross-section occurred during spring tides but only resulted in a net export of organic carbon in winter, totalling 85 t per tidal cycle. Derived from the winter and summer campaigns, the annual carbon mass balance estimated corresponded to a net export of organic carbon (7957 = 6585 t yr⁻¹ POC + 1372 t yr⁻¹ DOC). On the basis of the spring tidal drainage area, it corresponds to an annual flux of 79 g m⁻² of POC and 17 g m⁻² of DOC out of the estuary.     

Adsorption of methylene blue and crystal violet on low-cost adsorbent: waste fruits of <Emphasis Type="Italic">Rapanea ferruginea</Emphasis> (ethanol-treated and H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-treated)

This study assesses the ability of two low-cost adsorbents made from waste of Rapanea ferruginea treated with ethanol (WRf) and its H₂SO₄-treated analog (WRf/H₂SO₄) for the removal of two cationic dyes methylene blue (MB) and crystal violet (CV) from aqueous solutions. The adsorbent was characterized by scanning electron microscopy, Fourier transform infrared spectrometry, thermogravimetric analysis, point of zero charge (pH_pzc), specific surface, and functional groups. The adsorption of dye onto the adsorbents was studied as a function of pH solution (2–12), contact time (up to 120 min) and initial concentration (20–120 mg/L), and temperature (25, 35, and 55 °C). The influence of these parameters on adsorption capacity was studied using the batch process. The response surface methodology (RSM) was used in the experimental design, modeling of the process, and optimizing of the variables and was optimized by the response involving Box–Behnken factorial design (15 runs). The results show that the data correlated well with the Sips isotherm. The maximum adsorption capacities of MB and CV onto WRf were found to be 69 and 106 mg/g, and onto WRf/H₂SO₄, the adsorption capacities were 33 and 125 mg/g, respectively. The kinetic data revealed that adsorption of cationic dyes onto the adsorbents closely follows the pseudo-second-order kinetic model. Regression analysis showed good fit of the experimental data to the second-order polynomial model, with coefficient of determination (R²) values for MB (R²?=?0.9685) and MB (R²?=?0.9832) for WRf and CV (R²?=?0.9685) and CV (R²?=?0.9832) for WRf/H₂SO₄ indicated that regression analysis is able to give a good prediction of response for the adsorption process in the range studied. The results revealed that waste from R. ferruginea is potentially an efficient and low-cost adsorbent for adsorption of MB and CV.     

Use of radon isotopes,gamma radiation and dye tracers to study water interactions in a small stream in Brazil

In this study, natural (²²²Rn) and fluorescent (uranin) tracers were used to investigate the interactions between surface and subsurface waters in a small hydrographical basin located in the southeast region of Brazil. Levels of ²²²Rn were measured in 117 water samples with the use of an alpha solid-state detector. After the identification of the probable discharge sections along the stream, a measurement of the natural flows, upstream and downstream of these sections, was done with the use of a fluorimeter and fluorescent tracers. Also, scanning was done to verify a correlation between the natural gamma radiation and the ²²²Rn in the areas where its activity was higher. The results showed some sections where the ²²²Rn activity is more significant and contributed to the growth of the flows along the stream. It was possible to confirm a correlation between the discharge sections and the natural gamma radiation, what can be used as a preliminary approach to finding these sections in scenarios similar to the one studied here.     

Selection criteria for linear regression models to estimate individual tree biomasses in the Atlantic Rain Forest,Brazil

Background

Biomass models are useful for several purposes, especially for quantifying carbon stocks and dynamics in forests. Selecting appropriate equations from a fitted model is a process which can involves several criteria, some widely used and others used to a lesser extent. This study analyzes six selection criteria for models fitted to six sets of individual biomass collected from woody indigenous species of the Tropical Atlantic Rain Forest in Brazil. Six models were examined and the respective fitted equations evaluated by the residual sum of squares, adjusted coefficient of determination, absolute and relative estimates of the standard error of estimate, and Akaike and Schwartz (Bayesian) information criteria. The aim of this study was to analyze the numeric behavior of these model selection criteria and discuss the ease of interpretation of them. The importance of residual analysis in model selection is stressed.

Results

The adjusted coefficient of determination (\( R^{2}_{adj.} \)) and the standard error of estimate in percentage (Syx%) are relative model selection criteria and are not affected by sample size and scale of the response variable. The sum of squared residuals (SSR), the absolute standard error of estimate (Syx), the Akaike information criterion and the Schwartz information criterion, in turn, depend on these quantities. The best fit model was always the same within a given data set regardless the model selection criteria considered (except for SSR in two cases), indicating they tend to converge to a common result. However, such criteria are not always closely related across different data sets. General model selection criteria are indicative of the average goodness of fit, but do not capture bias and outlier effects. Graphical residual analysis is a useful tool to this detection and must always be used in model selection.

Conclusions

It is concluded that the criteria for model selection tend to lead to a common result, regardless their mathematical formulation and statistical significance. Relative measures of goodness of fitting are easier to interpret than the absolute ones. Careful graphical residual analysis must always be used to confirm the performance of the models.

     

Recent effects of tidal and hydro‐meteorological changes on coastal plains near the mouth of the Amazon River

The goal of this work was to understand the main hydrodynamic processes acting on tidal flats of the coast of Amapá near the mouth of the Amazon River, and how they change over the short term (~ 20 years). The analysis of morphological and geobotanical units was carried out by applying processing and interpretation methods to optical and synthetic aperture radar (SAR) images, combined with data on water salinity, maximum flood height, sedimentary facies data, rainfall and river discharge. The temporal analysis of morphological and geobotanical units suggests the relative stabilization of savannah, ‘várzea’ and mangrove areas during the drier period and increasing tidal amplitude between 1987 to 1997. The wetter period and decreasing tidal amplitude between 1997 to 2008 led to an increase in the area of ‘várzea’ and lakes over savannah, and the expansion of mangroves mainly over the inundated field and tidal mud/mixed flats. Therefore, the decrease in rainfall index during the drier period is well‐correlated with the reduction of the Calçoene River discharge and jointly with increasing tidal amplitude favored the increase of migration rate of the mud bank and erosion profile along the littoral. It was followed by the increase of the Calçoene River discharge and jointly with decreasing tidal amplitude during the wetter period, favoring the development of mangroves on muddy substrates near the coastline. Copyright © 2013 John Wiley & Sons, Ltd.     

Cytotoxic and genotoxic evaluation and chemical characterization of sewage treated using activated sludge and a floating emergent-macrophyte filter in a municipal wastewater treatment plant: a case study in Southern Brazil

This study was conducted to evaluate the chemical parameters and the cytotoxic and genotoxic potential of raw domestic sewage and effluents from treatment with activated sludge and a floating emergent-macrophyte filter from a domestic wastewater treatment plant in the city of Novo Hamburgo, Rio Grande do Sul, Brazil. The physicochemical analysis revealed that both treatment systems achieved the legal emission pattern for biochemical oxygen demand, chemical oxygen demand, and suspended solids, but ammoniacal nitrogen and E. coli values were above the limits in the macrophyte treatment effluent. Phosphorous values were above the maximum permitted for both treatments. The results obtained from the Allium cepa test and the micronuclei test in fish did not demonstrate any significant differences in both cytotoxicity (mitotic index) and genotoxicity (chromosome aberration and micronucleus) endpoints between the negative control group and the exposed groups. However, the comet assay in fish revealed a DNA damage increase in animals exposed to the 30 % concentration of the macrophyte effluent and two concentrations of the activated sludge treatment effluent (10 and 75 %), which suggests that these two treatment systems may increase wastewater genotoxicity.     

Geochemical tracers of northern Portuguese estuarine sediments on the shelf

The northern Portuguese coastal zone is drained by large Iberian rivers, along which there is intensive industrial, agricultural and urban activity. Offshore of the two main river basins of the Douro and Minho, two fine-grained sedimentary formations can be characterised. A geochemical study of this sediment cover has been performed focussing in particular on the fine deposits and the adjacent estuaries. The chemical composition of superficial sediments collected from the northern Portuguese shelf and from the river basins of the Minho and Douro rivers was determined for major, minor and trace elements; the rare earth elements (REE) composition was also determined in selected samples. Statistical analyses of these data for the shelf sediments allow us to identify elements with similar behaviours and the different sediment types along the shelf, and to evaluate of their origins. Downcore profiles of the chemical composition of the fine sediments reveal no evidence for changes induced by recent human activities. To assess the influence of the rivers on the fine sedimentary formations, the elemental distribution patterns of selected sediments have been compared with the estuarine sediments. Lithogenic elements composition normalised to Al and the shale normalised REE distributions showed there are similarities between the Douro River sediments and the sediment composition of the Douro and Galicia mud patches. However, the Galicia mud field showed no relationship in its chemical composition to sediments derived from the Minho River. Nor was any evidence for heavy metal contamination originating from the Douro estuary detected in anthropogenic element/Al ratios in the shelf sediments. This may be because of processes associated with resuspension, complexation and bioturbation that occur during sediment transport and deposition. Nevertheless, the Douro River seems to be the main continental source of fine sediments being deposited on the northern Portuguese shelf.     

Recent sedimentation and sedimentary budgets on the western Iberian shelf

Thus study is based on 31 box-core samples collected mainly from the mud-patches of the Galician and North-Portuguese shelf. Each of these cores, some decimetres in length, have been described, radiographied and sampled each centimetre for grain-size analysis and measurement of the particulate organic carbon (C_org) content. ²¹⁰Pb excess profiles have been measured using gamma spectrometry, which, combined with the analysis of the vertical variations of the sedimentary facies, have allowed estimates of sedimentation rates. These rates were found to vary between 0.05 and 0.40 cm yr⁻¹. Considering the latitudinal variation of sedimentation rates around the 100m contour, we note that the maximum rates occurred off the Douro estuary in the southern sector and also near the Galician rias to the north. The organic content (C_org) of sediments varied between 0.4 and 2%. Latitudinally C_org showed a decrease from the South to the North. These results coupled with the sedimentary map (see Dias, Gonzalez, Garcia & Diaz del Rio, 2001) have permitted us to establish the detrital mass budget and an inventory of C_org burial.