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The diffusive gradients in thin films (DGT) technique pre-concentrates labile species of trace elements, giving time-integrated in situinformation about their labile concentrations. All previous DGT approaches for simultaneous uptake of cations and anions have used the hazardous polyacrylamide reagent to immobilize the binding phase. The present work proposes a diffusive layer of agarose and a mixed binding layer of ZrO2and Chelex 100 immobilized in an agarose hydrogel to simultaneously determine the labile concentration of cations (Mn, Co, Ni, Cu, Zn and Cd) and anions (V, As, Se, Mo and Sb) in aquatic systems. The use of both layers using agarose instead of carcinogenic polyacrylamide as the hydrogel significantly reduces the costs and simplifies the manufacturing process. The proposed device was evaluated through recovery tests, deployment curves and pH/ionic strength tests. The mixed binding layer was compared with commercially available DGT devices for in situdeployment in river water. The relationships between accumulated mass and time (24 h) was linear (r2> 0.9) for all analytes. The diffusion coefficients obtained were consistent with the literature, ranging from 3.98 to 8.43 × 10−6cm2s−1. Except for Zn at pH 8.0, the obtained values of CDGT/Cbulkwere within the range of 1.00 ± 0.2 for the studied range of pH and for most ionic strengths. However, at low ionic strength, the concentrations of Mn, Co, Ni, Zn, V and Mo were underestimated. The concentrations of trace elements determined in river water using the proposed devices agreed with the labile concentrations determined by using commercial devices.

Located in the Upper Paraguay River Basin (UPRB), the Pantanal is considered the world's largest wetland, being rather pristine although increasingly threatened by development programs. The main objective of this paper is to provide a baseline of water chemistry for this region, which is largely unknown as a result of poor accessibility. We used two datasets (70 and 122 water samples) collected in the Pantanal floodplain and surrounding uplands during the wet season occurring from November to March. From the major‐ion mineral chemistry, dissolved silica, pH, electrical conductivity (EC), and the ionic forms of N, principal components analysis (PCA) treatments were used to identify and rank the main factors of variability and decipher the associated processes affecting the water chemistry. The results revealed that the water mineral concentration was a major factor of variability and it must be attributed first to lithology and second to agricultural inputs from extensive crop cultivation areas that mainly affects sulfate (SO42−) concentration on the eastern edge of the Pantanal. These processes influence the floodplain, where (i) the mixing of waters remains the main process, (ii) the weight of the biological and redox processes increased, and (iii) the chemical signature of the extensive cropping is transferred along the São Lourenço Basin down to its confluence with the Cuiaba River. Optimized parameters based on projections in the main factorial score plots were used for the mapping of lithological and agricultural impacts on water chemistry. Water chemistry baseline and process discrimination in the largest wetland in the world.Original process discrimination through projections on PCA score plots.

Smectite formation in alkaline-saline environments has been attributed to direct precipitation from solution and/or transformation from precursor minerals, but these mechanisms are not universally agreed upon in the literature. The objective of this work was to investigate the mineralogy of smectites in the soils surrounding a representative alkaline-saline lake of Nhecolândia, a sub-region of the Pantanal wetland, Brazil, and then to identify the mechanisms of their formation. Soils were sampled along a toposequence and analyzed by X-ray diffraction, transmission electron microscopy-energy dispersive X-ray analysis, and inductively coupled plasma-mass spectrometry. Water was collected along a transect involving the studied toposequence and equilibrium diagrams were calculated using the databases PHREEQC and AQUA. The fine-clay fraction is dominated by smectite, mica, and kaolinite. Smectites are concentrated at two places in the toposequence: an upper zone, which includes the soil horizons rarely reached by the lake-level variation; and a lower zone, which includes the surface horizon within the area of seasonal lake-level variation. Within the upper zone, the smectite is dioctahedral, rich in Al and Fe, and is classified as ferribeidellite. This phase is interstratified with mica and vermiculite and has an Fe content similar to that of the mica identified. These characteristics suggest that the ferribeidellite originates from transformation of micas and that vermiculite is an intermediate phase in this transformation. Within the lower zone, smectites are dominantly trioctahedral, Mg-rich, and are saponitic and stevensitic minerals. In addition, samples enriched in these minerals have much smaller rare-earth element (REE) contents than other soil samples. The water chemistry shows a geochemical control of Mg and saturation with respect to Mg-smectites in the more saline waters. The REEcontents, water chemistry, and the presence of Mg-smectite where maximum evaporation is expected, suggest that saponitic and stevensitic minerals originate by chemical precipitation from the water column of the alkaline-saline lake.

Since the construction of the anti - salting Diama dam , a resumption of aeolian deflation has been observed in the Senegal delta and particularly in Diawling National Park . It results in the formation of many clay dunes with high salt concentrations . The soft powdery structure observed on the soil surface , affected by aeolian defla tion is due to rapid salt crystallization . In order to identify the mineralogy of the salt involved in this environment , the chemistry of soil and groundwater was studied along a transect from a pan to the associated clay dune . Equilibria computation and field and scanning electron microscope (SEM) observations indicated that the changes observed in the chemical facies of the solution were due to the following precipitation sequence: calcite > gypsum > halite . A progressive but significant fixing of Na+ onto the clay particles was observed . The calcite deposition in the soil was limited by exhibition of the potential acidity arising from the former man grove site soils . It resulted in high equilibrating p CO2 . This study intended to test a new extension to the Debye - Huckel law for concentrated chlorurated sodic waters . The relationship between chloride amounts and the residual alkalinity concept con firmed that calcite and gypsum formation and the exchanges between Na and Ca are the main phenomena responsible for the changes observed in the soil solution (r2 =0.99).