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In the northern Pantanal wetlands of Brazil, alkaline sodic soils play a significant role in the ecological functioning of the region, but little is known about their mineralogical equilibria in current flooding dynamics, which is necessary for good management of these areas. This study focused on a transition between sodic and non‐sodic soils, identified by low frequency electromagnetic induction survey. Samples of B horizons from alkaline‐sodic and non‐sodic soils were analyzed via soil solution from saturated paste, decomposition of X‐ray diffraction (XRD) patterns and transmission electron microscopy with X‐ray dispersive energy spectroscopy (TEM‐EDS) analysis. The transition between alkaline‐sodic and non‐sodic soils matches with the transition between flooded and non‐flooded areas. The soil solution shows a concentration factor of about 40 along this transition. The formation of sodic soils results from an accumulation by evaporation of solutions with a positive calcite residual alkalinity (RAcalcite), probably imposed by the chemistry of the São Lourenço River. An increasing Na:Ca ratio caused solonization of the exchange complex. These alkaline‐sodic soils, however, can be interpreted as declining soils in the current context with an evacuation of soluble salts during flood cycles. The detailed investigation of the fine clay fraction (< 0.2 μm) using full profile modelling and decomposition of XRD patterns and TEM‐EDS analysis demonstrates gradual transformations of trioctahedral to dioctahedral smectite by Mg ‐ Al substitutions on octahedral sites, leading to the prevalence of kaolinite‐smectite interstratified minerals when the conditions become more acidic via the solodization process. Highlights: Clay minerals of alkaline‐sodic soil have been altered due to flooding dynamic.Clay minerals are a useful tool for understanding environmental changes.Interstratified clay minerals result from current acidification.The evolution of soil mineral suite is related to the environmental changes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Saline-alkaline lakes are extreme environments that limit the establishment and development of life. The Nhecolândia, a subregion of the Pantanal wetland in Brazil, is characterized by the existence of ~500 saline-alkaline lakes, which support an underexplored and rich diversity of microorganisms. In this study, unicellular and homocytous cyanobacteria from five saline-alkaline lakes were accessed by culture-dependent approaches. Morphological evaluation and analyses of near complete sequences (~1400 nt) of the 16S r RNA genes were applied for phylogenetic and taxonomic placement. This polyphasic approach allowed for the determination of the taxonomic position of the isolated strains into the following genera: Cyanobacterium, Geminocystis, Phormidium, Leptolyngbya, Limnothrix, and Nodosilinea. In addition, fourteen Pseudanabaenales and Oscillatoriales representatives of putative novel taxa were found. These sequences fell into five new clades that could correspond to new generic units of the Pseudanabaenaceae and Phormidiaceae families. [ABSTRACT FROM AUTHOR]