Long-term impacts on estuarine benthic assemblages (2015-2020) after a mine tailing spill in SE Brazil.

The Rio Doce estuary was critically impacted in 2015 by the world's largest mining tailing spill, with still unclear long-term effects on the aquatic biota. Here we present a long-term (2015 to 2020) assessment of estuarine benthic assemblages, where we demonstrate that despite a decline in the absolute concentrations of potentially toxic elements; sediment contamination is still above pre-impact conditions. The presence of these contaminants is likely responsible for a continued low habitat quality for the benthic fauna, characterized by a reduction of 96 % of the macroinvertebrate density and persistent change in the benthic assemblage composition. Our study supports previous work indicating the long-term nature of pollution impacts in estuaries, and demonstrate that although water quality levels were quickly adequate under regulatory terms, they largely lack significance to the overall ecosystem health assessment, as they are not related to the recovery of bottom- dwelling assemblages in estuarine ecosystems.

Degraded mangroves as sources of trace elements to aquatic environments.

Mangrove forests have been reported as sinks for metals because of the immobilization of these elements in their soils. However, climate change may alter the functioning of these ecosystems. We aimed to assess the geochemical dynamics of Mn, Cu, and Zn in the soils of a mangrove forest dead by an extreme weather event in southeastern Brazil. Soil samples were collected from dead and live mangroves adjacent to each other. The physicochemical parameters (total organic carbon, redox potential, and pH), total metal content, particle size, and metal partitioning were determined. Distinct changes in the soil geochemical environment (establishment of suboxic conditions) and a considerable loss of fine particles was caused by the death of the mangroves. Our results also showed a loss of up to 93 % of metals from soil. This study highlights the paradoxical role of mangroves as potential metal sources in the face of climate change.

Iron hazard in an impacted estuary: Contrasting controls of plants and implications to phytoremediation.

Due to its abundance and role as a micronutrient for plants iron (Fe) is rarely perceived as a contaminant. However, in redox active environments, Fe bioavailability increases sharply representing an environmental risk. In this study, a recent catastrophic mining dam failure is used as a field framework to evaluate the role of wetland plants on Fe biogeochemistry and assess their potential for phytoremediation programs. To achieve these objectives, a Fe geochemical partitioning and the concentration of Fe in different plant compartments (iron plaque on root surfaces, roots, and leaves) were determined in two sites vegetated by different wetland species. Soils exhibited contrasting Fe biogeochemical dynamics. Lower pseudo-total contents and more reactive Fe oxides were observed in the soil vegetated by Typha domingensis. Iron plaque was present on both species but more concentrated in Fe in T. domingensis. T. domingensis showed Fe shoot concentrations (3874 mg kg-1) 10-fold higher than in Hibiscus tiliaceus, which prevented Fe absorption through iron plaque formation and root accumulation. In conclusion, contrasting biogeochemical effects on Fe (e.g., rhizosphere acidification) lead to different phytoremediation abilities. T. domingensis showed a high potential for Fe phytoremediation on sites affected by Fe-enriched wastes and should be tested in assisted phytoremediation approaches.

Litho-climatic characteristics and its control over mangrove soil geochemistry: A macro-scale approach.

Brazil hosts an extensive coastal area, marked by a great diversity of geoenvironments. The present study evaluated the role of geoclimatic factors in the geochemistry of mangrove soils by using wet extractions and several physical and chemical parameters. Soil samples were collected in 11 mangrove forests from NE (n = 94) and SE Brazil (n = 230). Our results show an important effect of the surrounding geology and climate on the geochemistry of the mangrove soils. NE mangroves are dominated by suboxic soils (mean: Eh of +150 ± 174 mV and pH 7.1 ± 0.5, respectively) while anoxic conditions prevail in the SE mangrove soils (mean: Eh -46 ± 251 mV and pH 6.5 ± 0.5). In the NE region, a period of several months without rainfall and high temperatures leads to soil suboxic conditions. Conversely, at the SE coast, the surrounding mountain range contributes to well-distributed rain favoring anoxic conditions. The contrasting geochemical environment caused differences in the geochemistry of elements such as C, Fe, and S. Significantly higher Fe (193 ± 24 µmol g-1) and organic carbon contents (6.9 ± 7.1%) were recorded in the SE coast. The higher organic carbon contents are possibly related to Fe organo-mineral associations. These differences are ultimately associated with the contrasting geological surroundings (crystalline massifs at the SE and the iron poor sedimentary formations at the NE). The higher contents of reactive Fe and organic carbon also triggered more intense pyritization in the SE mangroves (pyritic Fe: 93 ± 63 µmol g-1). Our results demonstrate that climate and geological surroundings create identifiable patterns at a regional level and, thus, studies should take these factors into account on future global modelling approaches.

Benthic bioturbation: A canary in the mine for the retention and release of metals from estuarine sediments.

After the largest mining tailings spill in Brazil, the Rio Doce estuarine ecosystem was severely impacted by metal contamination. In a 28-day laboratory experiment, we examined the effects of the polychaeta Laeonereis sp. on fluxes of oxygen and metal across the sediment-water interface. The density-dependent effect of Laeonereis sp. in the oxygen and metal fluxes was tested at low and high (74 and 222 ind m-2, respectively) densities, and compared with defaunated controls. The higher worm density had an amplified effect on the oxygen flux, sediment uptake of Al and Mn, and Fe oxidation compared with the control, but no significant effects on other metals (Ba, Cd, Co, Cr, Cu, Ni, and Zn). Higher worm density increased the oxidation of Fe phases, but no effect in the solid phase of other metals. Consequently, Laeonereis sp. bioturbation prevents the reduction of Fe phases and the release of metal-bound-contaminants to estuarine systems.

Role of Fe dynamic in release of metals at Rio Doce estuary: Unfolding of a mining disaster.

The role of Fe oxyhydroxides dynamic on metal bioavailability was studied in the Rio Doce estuary after the largest mining disaster in the world. Soon after the disaster in 2015, metals were associated with Fe oxyhydroxides under a redox-active estuarine environment. Our results indicate that organic matter inputs from plant colonization on deposited tailings over estuarine soils led to a reductive dissolution of Fe oxyhydroxides within two years. Soil pseudo-total Fe content decreased by 70% between 2015 and 2017, while the total metal contents (Cr, Cu, Ni, Pb, and Zn) decreased by 79% in the soil. The losses of Fe and metals coupled to changes in Fe oxides crystallinity reveal a future ephemeral control of Fe oxyhydroxides over metal immobilization. Our results suggest a potential chronic contamination at the estuary and points to an aggravating scenario for the following years due to the increasing dominance of poorly crystalline Fe oxyhydroxides.

Manganese: The overlooked contaminant in the world largest mine tailings dam collapse.

Manganese (Mn) is an abundant element in terrestrial and coastal ecosystems and an essential micronutrient in the metabolic processes of plants and animals. Mn is generally not considered a potentially toxic element due to its low content in both soil and water. However, in coastal ecosystems, the Mn dynamic (commonly associated with the Fe cycle) is mostly controlled by redox processes. Here, we assessed the potential contamination of the Rio Doce estuary (SE Brazil) by Mn after the world's largest mine tailings dam collapse, potentially resulting in chronic exposure to local wildlife and humans. Estuarine soils, water, and fish were collected and analyzed seven days after the arrival of the tailings in 2015 and again two years after the dam collapse in 2017. Using a suite of solid-phase analyses including X-ray absorption spectroscopy and sequential extractions, our results indicated that a large quantity of MnII arrived in the estuary in 2015 bound to Fe oxyhydroxides. Over time, dissolved Mn and Fe were released from soils when FeIII oxyhydroxides underwent reductive dissolution. Due to seasonal redox oscillations, both Fe and Mn were then re-oxidized to FeIII, MnIII, and MnIV and re-precipitated as poorly crystalline Fe oxyhydroxides and poorly crystalline Mn oxides. In 2017, redox conditions (Eh: -47 ± 83 mV; pH: 6.7 ± 0.5) favorable to both Fe and Mn reduction led to an increase (~880%) of dissolved Mn (average for 2015: 66 ± 130 µg L-1; 2017: 582 ± 626 µg L-1) in water and a decrease (~75%, 2015: 547 ± 498 mg kg-1; 2017: 135 ± 80 mg kg-1) in the total Mn content in soils. The crystalline Fe oxyhydroxides content significantly decreased while the fraction of poorly ordered Fe oxides increased in the soils limiting the role of Fe in Mn retention. The high concentration of dissolved Mn found within the estuary two years after the arrival of mine tailings indicates a possible chronic contamination scenario, which is supported by the high levels of Mn in two species of fish living in the estuary. Our work suggests a high risk to estuarine biota and human health due to the rapid Fe and Mn biogeochemical dynamic within the impacted estuary.

From sinks to sources: The role of Fe oxyhydroxide transformations on phosphorus dynamics in estuarine soils.

The availability of phosphorus (P) in estuarine ecosystems is ultimately controlled by the nature of interactions between dissolved P and the soil components (e.g., soil minerals), especially iron (Fe) oxyhydroxides. P retention on Fe oxyhydroxides and its subsequent availability depends on mineral crystallinity and susceptibility to dissolution. However, in estuarine soils, geochemical conditions (e.g., redox oscillation and high soil organic matter content) may alter the fate of P and decrease the environmental quality of estuarine waters. The large input of Fe-rich tailings into the Rio Doce Estuary in Brazil in 2015 after a rupture of a Fe ore tailings dam (i.e., "Mariana mine disaster") offers a unique framework to evaluate the Fe oxyhydroxides role in P availability in estuarine soils, their potential effects on the cycling of P and eutrophication. We observed a significant correlation between Fe minerals and the P content in the estuary soils, suggesting that P enrichment was promoted by the deposited Fe-rich tailings. Adsorption isotherm curves indicated that mine tailings had a strong affinity for P due to presence of crystalline Fe oxyhydroxides in the tailings. Significant losses of Fe (62%) and P (56%) from the estuarine soil was observed two years after the initial impact and in response to redox conditions oscillations. Additionally, the content of high crystallinity Fe oxyhydroxides decreased significantly, whereas that of low crystallinity Fe oxyhydroxides showed an increase over time. These changes were associated with the dissimilatory Fe reduction, which led an increase in the concentrations of readily available P (2015: 2.30 ± 0.41 mg kg-1; 2017: 3.83 ± 1.82 mg kg-1; p < 0.001) in the studied soils. Moreover, in 2017, the dissolved P content exceeded the recommended environmental safety limits by five times. Our results indicate that Fe oxyhydroxides are a continuous source of dissolved P for the ecosystem, and Fe-rich tailings deposited in the estuarine ecosystem may be linked to a potential eutrophication.

Nitrogen mineralization and eutrophication risks in mangroves receiving shrimp farming effluents.

Nitrogen (N) inputs originated from shrimp farming effluents were evaluated for potential changes in the net N mineralization for mangrove soils from Northeastern Brazil. Our study provides notable information and assessment for the potential enhancement of N mineralization in preserved and shrimp-impacted semi-arid mangrove soils of the Jaguaribe River estuary, which is one of the largest shrimp producers of Brazil, using an analytical and daily tidal variation experimental approach. Nitrogen-rich effluents promoted a significant (p value < 0.001) increase of the total soil N content (1998 ± 201 mg kg-1 on average) compared with the preserved sites (average: 1446 ± 295 mg kg-1). The effluents also increased the N mineralization in the shrimp-impacted sites (N-min: 86.6 ± 37.5 mg kg-1), when compared with preserved mangroves (N-min: 56.5 ± 23.8 mg kg-1). Over a daily tidal variation experiment, we found that just 30% (36.2 ± 20.6 mg kg-1) of mineralized N remains stored in the soil, whereas 70% (102.9 ± 38.8 mg kg-1) was solubilized in tidal waters. Therefore, the N mineralization process may trigger eutrophication by increasing N inorganic bioavailability in mangrove soils receiving N-rich effluents from shrimp ponds, which in turn might increase primary producers' activity. This approach has not been studied so far in semi-arid mangroves, where the shrimp farming activity is one of the most important economic activities.

Phosphorus enriched effluents increase eutrophication risks for mangrove systems in northeastern Brazil.

Discharge of effluents loaded with phosphorus (P) from anthropogenic activities constitutes serious eutrophication risks in marine and terrestrial ecosystems, including mangroves. Three mangroves in NE-Brazil were studied to evaluate the impact of P-rich-effluents from shrimp farming and domestic sewage, in relation to a control area (natural mangrove). Soil phosphorus fractionation and water chemical analysis were performed to assess potential pollution. We observed the most labile P forms increased gradually and significantly from control to sewage to shrimp farm impacted mangroves as observed by increasingly dissolved orthophosphate (PO43-) content in water and the exchangeable/soluble P (Exch-P) extracted from soils, which is supported by the discriminant analysis. Exch-P results were correlated to Humic-Acid-P, which can release more labile P forms when mineralized. Our results demonstrate a substantial impact of aquiculture and sewage effluents in mangroves at both organic and inorganic P fractions, raising important concerns regarding pollution for these marine ecosystems.

Influence of pO2 on Iron Redox Cycling and Anaerobic Organic Carbon Mineralization in a Humid Tropical Forest Soil.

Ferrous iron (FeII) oxidation is an important pathway for generating reactive FeIII phases in soils, which can affect organic carbon (OC) persistence/decomposition. We explored how pO2 concentration influences FeII oxidation rates and FeIII mineral composition, and how this impacts the subsequent FeIII reduction and anaerobic OC mineralization following a transition from oxic to anoxic conditions. We conducted batch soil slurry experiments within a humid tropical forest soil amended with isotopically labeled 57FeII. The slurries were oxidized with either 21% or 1% pO2 for 9 days and then incubated for 20 days under anoxic conditions. Exposure to 21% pO2 led to faster FeII oxidation rates and greater partitioning of the amended 57Fe into low-crystallinity FeIII-(oxyhydr)oxides (based on Mössbauer analysis) than exposure to 1% pO2. During the subsequent anoxic period, low-crystallinity FeIII-(oxyhydr)oxides were preferentially reduced relative to more crystalline forms with higher net rates of anoxic FeII and CO2 production-which were well correlated-following exposure to 21% pO2 than to 1% pO2. This study illustrates that in redox-dynamic systems, the magnitude of O2 fluctuations can influence the coupled iron and organic carbon cycling in soils and more broadly, that reaction rates during periods of anoxia depend on the characteristics of prior oxidation events.

Eucalyptus urograndis and Pinus taeda enhance removal of chlorobenzene and benzene in sand culture: A greenhouse study.

Contamination of soils and groundwater by chlorobenzene and benzene is a common problem at industrial sites worldwide. Since chemical remediation techniques are rarely completely effective, remnants of these contaminants often persist at levels that can still influence ecosystem health. We evaluated the potential of Pinus taeda and Eucalyptus urograndis to accelerate the removal of these compounds from sand/water systems using a completely randomized block greenhouse experiment with a no-plant control. At 2-day intervals, we added a solution containing both chlorobenzene and benzene with the same concentration of 50 mg L(-1) (25 mg pot(-1)), and we monitored leachate concentrations daily. The planted treatments showed greater decrease of contaminants over time. In the absence of plants, the contaminant mass decreased 50-60% during each 2-day cycle; whereas, in the planted treatments the contaminant mass decreased 91-98%. At the end of the experiment the plant roots, leaves, and the sand-substrate each contained less than 1 mg kg(-1) of contaminants, which is ∼1% of the total contaminant mass added. In addition, we observed no tree mortality even at concentrations exceeding the aqueous solubility limit of both compounds. Our results suggest both trees are good candidates for remediating chlorobenzene and benzene in soils and groundwater.

Comparação de áreas de soja (Glycinemax (L) Merr. ) obtidas por meio da interpretação de imagens TM/Landsat e MODIS/Terra no município de Maracaju (MS) / Comparison of areas of soybean (Glycine max (L) Merr. ) obtained through the interpretation of tm/landsat and modis/terra images in the municipality of Maracaju (MS)

A cultura da soja possui características favoráveis para sua identificação e mapeamento por meio de interpretação de imagens de sensores remotos a bordo de satélites.O presente trabalho teve como objetivo comparar os resultados de mapeamento dessa cultura, por meio da interpretação de imagens TM/Landsat-5 e MODIS/Terra para o ano safra 2010/11. O trabalho foi realizado para o município de Maracaju, Mato Grosso do Sul, maior produtor de soja do Estado. Foram adquiridas oito imagens MODIS/Terra no ano de 2010 e quatro em 2011 e uma do TM/Landsat-5 do ano de 2011, compreendendo o período de cultivo da soja na região. De posse das imagens e dos processamentos foram gerados mapas temáticos de áreas de soja, das quais segue: componentes principais de imagem monotemporal TM, monotemporal MODIS com seus respectivos NDVI´s e EVI´s, por meio do classificador supervisionado MaxVer; além disso foi calculado o índice CEI, que no processo de fatiamento de pixels foram obtidas as áreas de soja. As classificações utilizando bandas do TM/Landasat-5 apresentaram excelentes estimativas de áreas de soja indicadas pelas métricas de validação Kappa e exatidão global. No método do índice CEI, neste caso, apresentou inferioridade perante as demais estimativas obtidas, apenas apresentando-se superior a estimativa de área obtida pela imagem monotemporal NDVI/MODIS.

The soybean has favorable characteristics for its identification and mapping through interpretation of remote sensing images. This paper aims compare the mapping results of this culture by interpretation of TM/Landsat-5 and MODIS/Terra images for the crop-year 2010/11. The study area was the town of Maracaju, Mato Grosso do Sul, Brazil, the larger producer of soybeans in the state. Eight MODIS/Terra images were acquired in 2010, four in 2011 and one TM/Landsat-5 in 2011, comprising the period from soybean cultivation in the region. With ' thematic maps of soybean areas, of which follows: principal components of mono temporal TM image with their respective MODIS NDVI's and EVI's, through the Max Ver classifier; addition we calculated the CEI index, which in the process of slicing the pixel areas were obtained from soybeans. The classifications using TM/Landasat-5 bands showed excellent estimates of soybean areas, indicated by the metrics validation Kappa and overall accuracy. In the method CEI index presented inferiority before the other estimates are they only over area estimation obtained by the mono temporal NDVI/MODIS image.