A simple, green and low-cost agarose-based binding layer for simultaneous determination of cations and anions in aquatic systems using DGT.

The diffusive gradients in thin films (DGT) technique pre-concentrates labile species of trace elements, giving time-integrated in situ information 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 ZrO2 and 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 situ deployment 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 × 10-6 cm2 s-1. Except for Zn at pH 8.0, the obtained values of CDGT/Cbulk were 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.

Bioaccumulation and speciation of arsenic in plankton from tropical soda lakes along a salinity gradient.

Uptake and transformation of arsenic (As) by living organisms can alter its distribution and biogeochemical cycles in the environment. Although well known for its toxicity, several aspects of As accumulation and biological transformation by field species are still little explored. In this study, the bioaccumulation and speciation of As in phytoplankton and zooplankton from five soda lakes in the Brazilian Pantanal wetland were studied. Such lakes exhibited contrasting biogeochemical characteristics along an environmental gradient. Additionally, the influence of contrasting climatic events was assessed by collecting samples during an exceptional drought in 2017 and a flood in 2018. Total As (AsTot) content and speciation were determined using spectrometric techniques, while a suspect screening of organoarsenicals in plankton samples was carried out by high-resolution mass spectrometry. Results showed that AsTot content ranged from 16.9 to 62.0 mg kg-1 during the dry period and from 2.4 to 12.3 mg kg-1 during the wet period. The bioconcentration and bioaccumulation factors (BCF and BAF) in phytoplankton and zooplankton were found to be highly dependent on the lake typology, which is influenced by an ongoing evapoconcentration process in the region. Eutrophic and As-enriched lakes exhibited the lowest BCF and BAF values, possibly due to the formation of non-labile As complexes with organic matter or limited uptake of As by plankton caused by high salinity stress. The season played a decisive role in the results, as significantly higher BCF and BAF values were observed during the flooding event when the concentration of dissolved As in water was low. The diversity of As species was found to be dependent on the lake typology and on the resident biological community, cyanobacteria being responsible for a significant portion of As metabolism. Arsenosugars and their degradation products were detected in both phytoplankton and zooplankton, providing evidence for previously reported detoxification pathways. Although no biomagnification pattern was observed, the diet seemed to be an important exposure pathway for zooplankton.

Spatial and seasonal variation of arsenic speciation in Pantanal soda lakes.

The occurrence of high arsenic concentrations (up to 3000 µg L-1) in water of soda lakes of the Pantanal wetland is a remarkable case of natural arsenic contamination in South America. However, little is known about arsenic speciation in this environment, particularly regarding speciation changes related to lake trophic status and seasonal variations. To fill this gap, arsenic speciation analysis was carried out in surface (SW) and subsurface (SSW) waters sampled in five soda lakes with different eutrophication status, in two dry and one wet season. As(V) was the dominant species in these waters, while As(III), DMA, MMA and likely complex organic species were present in lower amounts. The results allow to conclude that the arsenic speciation in SW and SSW varies seasonally according to the regional wet or dry periods and lake water levels. In eutrophic turbid and in oligotrophic vegetated soda lakes, arsenic speciation was also characterized by spatial differences between edge and center or between the SW and SSW. Cyanobacteria or macrophytes/algae are involved in arsenic biotransformation in soda lakes through its metabolic and detoxification processes. Significant variation in surface water arsenic speciation occurs as a result of seasonal primary production fluctuation or water arsenic concentration changes in the soda lakes, increasing organoarsenics in dry periods, whereas in flood periods, As(V) prevails. Spatial distribution of arsenic species is significantly impacted by biogeochemical conditions at the water/sediment interface in soda lakes.

Bacterial Communities Along Environmental Gradients in Tropical Soda Lakes.

Soda lake environments are known to be variable and can have distinct differences according to geographical location. In this study, we investigated the effects of different environmental conditions of six adjacent soda lakes in the Pantanal biome (Mato Grosso do Sul state, Brazil) on bacterial communities and their functioning using a metagenomic approach combined with flow cytometry and chemical analyses. Ordination analysis using flow cytometry and water chemistry data from two sampling periods (wet and dry) clustered soda lakes into three different profiles: eutrophic turbid (ET), oligotrophic turbid (OT), and clear vegetated oligotrophic (CVO). Analysis of bacterial community composition and functioning corroborated this ordination; the exception was one ET lake, which was similar to one OT lake during the wet season, indicating drastic shifts between seasons. Microbial abundance and diversity increased during the dry period, along with a considerable number of limnological variables, all indicative of a strong effect of the precipitation-evaporation balance in these systems. Cyanobacteria were associated with high electric conductivity, pH, and nutrient availability, whereas Actinobacteria, Alphaproteobacteria, and Betaproteobacteria were correlated with landscape morphology variability (surface water, surface perimeter, and lake volume) and with lower salinity and pH levels. Stress response metabolism was enhanced in OT and ET lakes and underrepresented in CVO lakes. The microbiome dataset of this study can serve as a baseline for restoring impacted soda lakes. Altogether, the results of this study demonstrate the sensitivity of tropical soda lakes to climate change, as slight changes in hydrological regimes might produce drastic shifts in community diversity.

In situ fractionation and redox speciation of arsenic in soda lakes of Nhecolândia (Pantanal, Brazil) using the diffusive gradients in thin films (DGT) technique.

In situ fractionation and redox speciation of As in three different saline-alkaline lakes (green, black and crystalline lakes) in the Pantanal of Nhecolândia (Brazil) were performed by using Diffusive Gradients in Thin films (DGT). The results indicated that As is present mainly in dissolved form. Total As concentration was similar when using different filter membranes, demonstrating that the species adsorbed by DGT devices were <10 kDa. Higher concentrations of labile total As were observed in the center of the lakes, indicating that the nature of the organic matter influences the formation of As complexes. Total As concentrations determined by using ZrO2 DGT were consistent with As concentration in ultrafiltered water samples collected in the black lake. However, part of the data about As(III) obtained in grab samples contrasted with DGT results. The differences observed may indicate that alterations in the species occur during the storage period before analysis by ultrafiltration. As(III) concentrations measured by DGT in the black and crystalline lakes were 1-3 µg L-1 and 4-7 µg L-1, respectively, accounting for only 4%-8% of the total DGT inorganic As. In the green lake, As(III) concentrations were significantly higher at the center (217 µg L-1). Both the phytoplankton community and the dissolved organic carbon influence the As speciation and bioavailability in the lakes of Nhecolândia. The DGT approach used in the present work was able to perform As speciation and demonstrates that in situ sampling analytical techniques are essential in understanding As speciation and its behavior in complex natural aquatic systems.

In situ arsenic speciation at the soil/water interface of saline-alkaline lakes of the Pantanal, Brazil: A DGT-based approach.

Arsenic (As) is a naturally occurring element in the Earth's crust, exhibiting toxicity towards a wide range of living organisms. Its properties and environmental dynamics are strongly regulated by its speciation, and the species As(III) and As(V) are the most commonly found in environmental systems. Recently, high concentrations of As were found in saline-alkaline lakes of the Pantanal (Brazil), which is the largest wetland area in the world. Therefore, we evaluated As contamination and its redox speciation (As(III) and As(V)) at the soil/water interface of biogeochemically distinct saline-alkaline lakes of Pantanal wetlands (Brazil). Both conventional sampling and in situ diffusive gradients in thin films (DGT) technique were employed. Zirconium oxide and 3-mercaptopropyl were used as ligand phases in DGT to selectively bind As species. High concentrations of total dissolved As in a shallow water table were found (<2337.5 µg L-1), whereas levels in soils were up to 2.4 µg g-1. Distinct scenarios were observed when comparing speciation analysis through spot sampling and DGT. Considering spot sampling, As(V) was the main species detected, whereas As(III) was only detected in only a few samples (<4.2 µg L-1). Conversely, results obtained by DGT showed that labile As(III) dominated arsenic speciation at the soil/water interface with levels up to 203.0 µg L-1. Coupling DGT data and DGT induced fluxes in sediments and soils model allowed obtaining kinetic data, showing that the soil barely participated in the arsenic dynamics on the shore of the lakes, and that this participation depends on the evapoconcentration process occurring in the region. Therefore, soil acts like a nonreactive matrix depending on the natural concentration process. In addition, our results reinforced the different geochemical characteristics of the studied saline-alkaline lakes and highlights the importance of robust passive sampling techniques in the context of metal/metalloid speciation in environmental analysis.

Dissolved arsenic in the upper Paraguay River basin and Pantanal wetlands.

Although high levels of dissolved arsenic were detected in surface and ground waters of Nhecolândia, a sub-region of the vast Pantanal wetlands in Brazil, the possible sources have not been clearly identified and the potential release from the wetland to the draining rivers has not been investigated. In this study we measured the dissolved As content in all the rivers and small streams that supply the southern Pantanal region, as well as in the two main rivers draining the wetland, i.e., the Cuiaba and Paraguay rivers and tributaries. In addition, Arsenic in surface waters, perched water-table, soils and sediments from 3 experimental sites located in the heart of Nhecolândia were compared. On the one hand, the results show the absence of As contamination in rivers that supply the Pantanal floodplain, as well as a lack of significant release from the floodplain to the main drains. The As contents in the rivers are <2 µg L-1, with variations that depend on the lithology and on the geomorphology at the collection point (uplands or floodplain). On the other hand, they confirm the regional extension of As contamination in Nhecolândia's alkaline waters with some values above 3 mg L-1. Arsenic is mainly in the arsenate form, and increases with the evaporation process estimated from sodium ion concentrations. The pH of soil solution and surface water increases rapidly during evapo-concentration up to values above 9 or 10, preventing adsorption processes on oxides and clay minerals and promoting the retention of dissolved arsenic in solution. Solutions from organic soil horizons show higher As contents in relation to Na, attributed to the formation of ternary complex As-(Fe/Al)-OM. In this alkaline pH range, despite high levels of dissolved As, soil horizons and lake sediments in contact with these waters show As values that correspond to uncontaminated environments.

Biogeochemical diversity, O2-supersaturation and hot moments of GHG emissions from shallow alkaline lakes in the Pantanal of Nhecolândia, Brazil.

Nhecolândia is a vast sub-region of the Pantanal wetland in Brazil with great diversity in surface water chemistry evolving in a sodic alkaline pathway under the influence of evaporation. In this region, >15,000 shallow lakes are likely to contribute an enormous quantity of greenhouse gas to the atmosphere, but the diversity of the biogeochemical scenarios and their variability in time and space is a major challenge to estimate the regional contribution. From 4 selected alkaline lakes, we compiled measurements of the physico-chemical characteristics of water and sediments, gas fluxes in floating chambers, and sedimentation rates to illustrate this diversity. Although these lakes have a similar chemical composition, the results confirm a difference between the black-water and green-water alkaline lakes, corresponding to distinct biogeochemical functioning. This difference does not appear to affect lake sedimentation rates, but is reflected in gas emissions. Black-water lakes are CO2 and CH4 sources, with fairly constant emissions throughout the seasons. Annual carbon dioxide and methane emissions approach 0.86molm-2y-1 and 0.07molm-2y-1, respectively, and no clear trend towards N2O capture or emission was observed. By contrast, green-water lakes are CO2 and N2O sinks but important CH4 sources with fluxes varying significantly throughout the seasons, depending on the magnitude of the phytoplankton bloom. The results highlight important daily and seasonal variations in gas fluxes, and in particular a hot moments for methane emissions, when the O2-supersaturation is reached during the afternoon under extreme bloom and sunny weather conditions, provoking an abrupt O2 purging of the lakes. Taking into account the seasonal variability, annual methane emissions are around 10.2molm-2y-1, i.e., much higher than reported in previous studies for alkaline lakes in Nhecolândia. Carbon dioxide and nitrous oxide consumption is estimated about 1.9molm-2y-1 and 0.73mmolm-2y-1, respectively. However, these balances must be better constrained with systematic and targeted measurements throughout the seasons.

Contrasting the Genetic Patterns of Microbial Communities in Soda Lakes with and without Cyanobacterial Bloom.

Soda lakes have high levels of sodium carbonates and are characterized by salinity and elevated pH. These ecosystems are found across Africa, Europe, Asia, Australia, North, Central, and South America. Particularly in Brazil, the Pantanal region has a series of hundreds of shallow soda lakes (ca. 600) potentially colonized by a diverse haloalkaliphilic microbial community. Biological information of these systems is still elusive, in particular data on the description of the main taxa involved in the biogeochemical cycling of life-important elements. Here, we used metagenomic sequencing to contrast the composition and functional patterns of the microbial communities of two distinct soda lakes from the sub-region Nhecolândia, state of Mato Grosso do Sul, Brazil. These two lakes differ by permanent cyanobacterial blooms (Salina Verde, green-water lake) and by no record of cyanobacterial blooms (Salina Preta, black-water lake). The dominant bacterial species in the Salina Verde bloom was Anabaenopsis elenkinii. This cyanobacterium altered local abiotic parameters such as pH, turbidity, and dissolved oxygen and consequently the overall structure of the microbial community. In Salina Preta, the microbial community had a more structured taxonomic profile. Therefore, the distribution of metabolic functions in Salina Preta community encompassed a large number of taxa, whereas, in Salina Verde, the functional potential was restrained across a specific set of taxa. Distinct signatures in the abundance of genes associated with the cycling of carbon, nitrogen, and sulfur were found. Interestingly, genes linked to arsenic resistance metabolism were present at higher abundance in Salina Verde and they were associated with the cyanobacterial bloom. Collectively, this study advances fundamental knowledge on the composition and genetic potential of microbial communities inhabiting tropical soda lakes.

Organic Control of Dioctahedral and Trioctahedral Clay Formation in an Alkaline Soil System in the Pantanal Wetland of Nhecolândia, Brazil.

Recent studies have focused on the formation of authigenic clays in an alkaline soil system surrounding lakes of the Nhecolândia region, Pantanal wetland. The presence of trioctahedral Mg-smectites (stevensite and saponite types), which requires low Al and Fe contents in the soil solution for its formation, contrasts with the neoformation of dioctahedral Fe-mica (glauconite, and Fe-illite), which instead requires solutions relatively enriched in Al and Fe. This study aims to understand the conditions of co-existence of both, Mg-smectite and Fe-mica a common clay association in former or modern alkaline soil systems and sediments. The study was carried out along an alkaline soil catena representative of the region. The soil organization revealed that Mg-smectite occur in top soil close to the lake, whereas Fe-mica dominate in the clay fraction of deeper greenish horizons a few meters apart. We propose here that this spatial distribution is controlled by the lateral transfer of Fe and Al with organic ligands. Alkaline organic rich solutions (DOC up to 738 mg L-1) collected in the watertable were centrifuged and filtered through membranes of decreasing pore size (0.45 µm, 0.2 µm, 30 KDa, 10 KDa, 3 KDa) to separate colloidal and dissolved fractions. Fe, Al, Si, Mg and K were analysed for each fraction. Although the filtration had no influence on Si and K contents, almost 90% of Fe (up to 2.3 mg L-1) and Al (up to 7 mg L-1) are retained at the first cutoff threshold of 0.45µm. The treatment of the same solutions by oxygen peroxide before filtration shows that a large proportion of Fe and Al were bonded to organic colloids in alkaline soil solution at the immediate lake border, allowing Mg-smectite precipitation. The fast mineralization of the organic matter a few meters apart from the lake favors the release of Fe and Al necessary for Fe-mica neoformation. In comparison with chemical and mineralogical characteristics of alkaline environments described in the literature, the study suggests that the co-existence of trioctahedral Mg-smectite and dioctahedral Fe-mica should be regarded as a standard occurrence in alkaline soil systems with organic rich waters.

Impacts of Lithological and Anthropogenic Factors Affecting Water Chemistry in the Upper Paraguay River Basin.

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 (SO) 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.

Pantanalinema gen. nov. and Alkalinema gen. nov.: novel pseudanabaenacean genera (Cyanobacteria) isolated from saline-alkaline lakes.

The genus Leptolyngbya Anagnostidis & Komárek (1988) was described from a set of strains identified as 'LPP-group B'. The morphology within this group is not particularly informative and underestimates the group's genetic diversity. In the present study, two new pseudanabaenacean genera related to Leptolyngbya morphotypes, Pantanalinema gen. nov. and Alkalinema gen. nov., are described under the provisions of the International Code of Nomenclature for Algae, Fungi and Plants, based on a polyphasic approach. Pantanalinema gen. nov. (type species Pantanalinema rosaneae sp. nov.) has sheaths and trichomes with slight gliding motility, which distinguish this genus from Alkalinema gen. nov. (type species Alkalinema pantanalense sp. nov.), which possesses trichomes arranged in an ornate (interwoven) pattern. 16S rRNA gene sequences of strains of Pantanalinema and Alkalinema exhibited low identity to each other (≤91.6 %) and to other sequences from known pseudanabaenacean genera (≤94.3 and 93.7 %, respectively). In a phylogenetic reconstruction, six sequences from strains of Pantanalinema and four from strains of Alkalinema formed two separate and robust clades (99 % bootstrap value), with the genera Oculatella and Phormidesmis, respectively, as the closest related groups. 16S-23S rRNA intergenic spacer sequences and secondary structures of strains of Pantanalinema and Alkalinema did not correspond to any previous descriptions. The strains of Pantanalinema and Alkalinema were able to survive and produce biomass at a range of pH (pH 4-11) and were also able to alter the culture medium to pH values ranging from pH 8.4 to 9.9. These data indicate that cyanobacterial communities in underexplored environments, such as the Pantanal wetlands, are promising sources of novel taxa.

Nonheterocytous cyanobacteria from Brazilian saline-alkaline lakes.

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 rRNA 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.

Dissolved organic matter fluorescence as a water-flow tracer in the tropical wetland of Pantanal of Nhecolândia, Brazil.

The Nhecolândia is a sub-region of the Brazilian Pantanal wetland, where saline and freshwater lakes coexist in close proximity. Measurements of dissolved organic carbon (DOC) content and analysis of fluorescence excitation-emission matrices (EEM) were conducted in an effort to characterize spatial variability in concentration and source of dissolved organic matter (DOM) and to further understand the hydrochemical functioning of this complex environment. Increasing pH under the influence of evaporation resulted in an increasing DOC solubility ranging from 50 to over 300 mgC L(-1) in surface water. Spectrofluorescence characterisation indicates the presence of several families of dissolved organic matter (fulvic and humic-type and proteinaceous materials), which are related to the type of lake and its hydro-bio-geochemical functioning. Moreover, the fluorescence signatures from lake water DOM and from surrounding soil-water-extracted organic matter (WEOM) show strong similarities although some labile proteinaceous compounds disappeared during humification. Results from the characterisation of DOM and WEOM not only suggest that spectrofluorescence is a reliable technique for the tracing of water flows, but also for the marking of the origin of organic horizons in this environment.