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Water clarity is a key parameter of aquatic ecosystems impacted by mining tailings. Tracking down tailings dispersion along the river basin requires a regional monitoring approach. The longitudinal fluvial connectivity, river-estuary-coastal ocean, and the lateral connectivity, river-floodplain-alluvial lakes are interconnected by hydrological flows, particularly during high fluvial discharge. The present study aims to track the dispersal of iron ore tailing spill, from the collapse of the Fundão dam (Mariana, MG, Brazil), on November 5, 2015, in the Lower Doce River Valley. A semi-empirical model of turbidity data, as a water clarity proxy, and multispectral remote sensing data (MSI Sentinel-2), based on different hydrological conditions and well-differentiated water types, yielded an accuracy of 92%. Five floods (> 3187m3 s-1) and five droughts (< 231m3 s-1) events occurred from 2013 to 2020. The flood of January 2016 occurred one month after the mining slurries reached the coast, intruding tailings on some alluvial and coastal plain lakes with highly turbid waters (> 400 NTU). A fluvial plume is formed in the inner shelf adjoining the river mouth on high flow. The dispersion of river plume was categorized as plume core (turbidity > 200 NTU), plume core and inner shelf waters (100-199 NTU), other shelf water (50-99 NTU), and offshore waters (< 50 NTU). Fluvial discharge and local winds are the main drivers for river plume dispersion and transport of terrigenous material along the coast. This work provides elements for evaluating the impact of mining tailings and an approach for remote sensing regional monitoring of surface water quality.

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We present an assessment on the sediment flux caused by the tailing dam failure at Mariana, Minas Gerais Estate, Brazil. Field data of water level, water flow, and suspended sediment concentrations (SSCs) were obtained during the period from 21 November to 5 December 2015, when the muddy waters reached the coast. A rating curve of the coastal tidal signal was built, allowing a robust estimate of the flow at the mouth of the Doce River. Together with SSC data, early sediment delivered to the coastal sea was of 15 × 104 t, what may account for only 0.5% of the total material remobilized at the accident site. This accounted for >25 000 t of Fe and between 1 and 4 t of other trace metals, such as Co, Ni, and Zn. Integr Environ Assess Manag 2020;16:661-668. © 2020 SETAC.

É apresentada uma avaliação do fluxo de sedimentos causado pela ruptura da represa de resíduos em Mariana, MG. Dados de campo de nível da água, fluxo e concentração de sedimentos em suspensão (CSS) foram obtidos durante o período de 21-Novembro até 5-Dezezembro, 2015, quando as águas barrentas chegaram na costa. Uma curva chave de descarga resolvendo o nível da maré costeira foi elaborada permitindo uma estimativa robusta da descarga fluvial na desembocadura do Rio Doce. Com valores de descarga e CSS, obtivemos que a exportação inicial de sedimentos para a costa foi de 15 × 104 ton, o que contabiliza por somente 0,5% do total de material remobilizado no local do acidente. Isto contabiliza >25,000 tons de Fe e entre 1 e 4 toneladas de outros metais traço, tais como Co, Ni e Zn. Integr Environ Assess Manag 2020;16:661-668.

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BACKGROUND: Thaumarchaeota are abundant in the Amazon River, where they are the only ammonia-oxidizing archaea. Despite the importance of Thaumarchaeota, little is known about their physiology, mainly because few isolates are available for study. Therefore, information about Thaumarchaeota was obtained primarily from genomic studies. The aim of this study was to investigate the ecological roles of Thaumarchaeota in the Amazon River and the Amazon River plume. RESULTS: The archaeal community of the shallow in Amazon River and its plume is dominated by Thaumarchaeota lineages from group 1.1a, which are mainly affiliated to Candidatus Nitrosotenuis uzonensis, members of order Nitrosopumilales, Candidatus Nitrosoarchaeum, and Candidatus Nitrosopelagicus sp. While Thaumarchaeota sequences have decreased their relative abundance in the plume, Candidatus Nitrosopelagicus has increased. One genome was recovered from metagenomic data of the Amazon River (ThauR71 [1.05 Mpb]), and two from metagenomic data of the Amazon River plume (ThauP25 [0.94 Mpb] and ThauP41 [1.26 Mpb]). Phylogenetic analysis placed all three Amazon genome bins in Thaumarchaeota Group 1.1a. The annotation revealed that most genes are assigned to the COG subcategory coenzyme transport and metabolism. All three genomes contain genes involved in the hydroxypropionate/hydroxybutyrate cycle, glycolysis, tricarboxylic acid cycle, oxidative phosphorylation. However, ammonia-monooxygenase genes were detected only in ThauP41 and ThauR71. Glycoside hydrolases and auxiliary activities genes were detected only in ThauP25. CONCLUSIONS: Our data indicate that Amazon River is a source of Thaumarchaeota, where these organisms are important for primary production, vitamin production, and nitrification.

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The Amazon River watershed and its associated plume comprise a vast continental and oceanic area. The microbial activities along this continuum contribute substantially to global carbon and nutrient cycling, and yet there is a dearth of information on the diversity, abundance, and possible roles of viruses in this globally important river. The aim of this study was to elucidate the diversity and structure of virus assemblages of the Amazon River-ocean continuum. Environmental viral DNA sequences were obtained for 12 locations along the river's lower reach (n = 5) and plume (n = 7). Sequence assembly yielded 29,358 scaffolds, encoding 82,546 viral proteins, with 15 new complete viral genomes. Despite the spatial connectivity mediated by the river, virome analyses and physical-chemical water parameters clearly distinguished river and plume ecosystems. Bacteriophages were ubiquitous in the continuum and were more abundant in the transition region. Eukaryotic viruses occurred mostly in the river, while the plume had more viruses of autotrophic organisms (Prochlorococcus, Synechococcus) and heterotrophic bacteria (Pelagibacter). The viral families Microviridae and Myoviridae were the most abundant and occurred throughout the continuum. The major functions of the genes in the continuum involved viral structures and life cycles, and viruses from plume locations and Tapajós River showed the highest levels of functional diversity. The distribution patterns of the viral assemblages were defined not only by the occurrence of possible hosts but also by water physical and chemical parameters, especially salinity. The findings presented here help to improve understanding of the possible roles of viruses in the organic matter cycle along the river-ocean continuum. IMPORTANCE The Amazon River forms a vast plume in the Atlantic Ocean that can extend for more than 1,000 km. Microbial communities promote a globally relevant carbon sink system in the plume. Despite the importance of viruses for the global carbon cycle, the diversity and the possible roles of viruses in the Amazon are poorly understood. The present work assesses, for the first time, the abundance and diversity of viruses simultaneously in the river and ocean in order to elucidate their possible roles. DNA sequence assembly yielded 29,358 scaffolds, encoding 82,546 viral proteins, with 15 new complete viral genomes from the 12 river and ocean locations. Viral diversity was clearly distinguished by river and ocean. Bacteriophages were the most abundant and occurred throughout the continuum. Viruses that infect eukaryotes were more abundant in the river, whereas phages appeared to have strong control over the host prokaryotic populations in the plume.

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Politicians do not acknowledge the devastating impacts riverine sediments can have on healthy coral reef ecosystems during environmental debates in Caribbean countries. Therefore, regional and/or local decision makers do not implement the necessary measures to reduce fluvial sediment fluxes on coral reefs. The Magdalena River, the main contributor of continental fluxes into the Caribbean Sea, delivers water and sediment fluxes into the Rosario Islands National Park, an important marine protected area in the southwestern Caribbean. Until now, there is no scientific consensus on the presence of sediment fluxes from the Magdalena River in the coral reefs of the Rosario Islands. Our hypothesis is that high sediment and freshwater inputs from the Magdalena have been present at higher acute levels during the last decade than previously thought, and that these runoff pulses are not flashy. We use in-situ calibrated MODIS satellite images to capture the spatiotemporal variability of the distribution of suspended sediment over the coral reefs. Furthermore, geochemical data are analyzed to detect associated sedimentation rates and pollutant dispersion into the coastal zone. Results confirm that turbidity levels have been much higher than previous values presented by national environmental authorities on coral reefs off Colombia over the last decade. During the 2003-2013-period most of the Total Suspended Sediments (TSS) values witnessed in the sampled regions were above 10mg/l, a threshold value of turbidity for healthy coral reef waters. TSS concentrations throughout the analyzed time were up to 62.3mg/l. Plume pulses were more pronounced during wet seasons of La Niña events in 2002-2003, 2007-2008, and 2009-2010. Reconstructed time series of MODIS TSS indicates that coral reef waters were exposed to river plumes between 19.6 and 47.8% of the entire period of analysis (2000-2013). Further analyses of time series of water discharge and sediment load into the coastal zone during the last two decades show temporal increases in water discharge and sediment load of 28% and 48%, respectively. (210)Pb dating results from two cores indicate sedimentation rates of ~0.75 cm/y of continentally exported clastic muddy sediments that are being deposited on the carbonatic shelf. The cores contain sediments with heavy metals and their concentrations are frequently above the ecologically accepted standards. Overall, the last decade has witnessed stronger magnitudes in fluvial fluxes to the coastal region, which probably coincide with associated declines in healthy coral cover and water quality. Our results emphasize the importance of local stressors, such as runoff and dispersion of turbid plumes, as opposed to ocean warming, disease and hurricanes, which have played a larger role on other coral reefs in the Caribbean. Coral reef management across the southwestern Caribbean, a coastal region influenced by continental fluxes of numerous rivers flowing from the Andes, may only be effective when land and marine-based stressors are simultaneously mitigated.

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River-dominated continental shelf environments are active sites of air-sea CO2 exchange. We conducted 13 cruises in the northern Gulf of Mexico, a region strongly influenced by fresh water and nutrients delivered from the Mississippi and Atchafalaya River system. The sea surface partial pressure of carbon dioxide (pCO2) was measured, and the air-sea CO2 flux was calculated. Results show that CO2 exchange exhibited a distinct seasonality: the study area was a net sink of atmospheric CO2 during spring and early summer, and it was neutral or a weak source of CO2 to the atmosphere during midsummer, fall, and winter. Along the salinity gradient, across the shelf, the sea surface shifted from a source of CO2 in low-salinity zones (0≤S<17) to a strong CO2 sink in the middle-to-high-salinity zones (17≤S<33), and finally was a near-neutral state in the high-salinity areas (33≤S<35) and in the open gulf (S≥35). High pCO2 values were only observed in narrow regions near freshwater sources, and the distribution of undersaturated pCO2 generally reflected the influence of freshwater inputs along the shelf. Systematic analyses of pCO2 variation demonstrated the importance of riverine nitrogen export; that is, riverine nitrogen-enhanced biological removal, along with mixing processes, dominated pCO2 variation along the salinity gradient. In addition, extreme or unusual weather events were observed to alter the alongshore pCO2 distribution and to affect regional air-sea CO2 flux estimates. Overall, the study region acted as a net CO2 sink of 0.96 ± 3.7 mol m-2 yr-1 (1.15 ± 4.4 Tg C yr-1).

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Coastal river plumes represent one of the final stages of material transport across the land-sea interface. Most studies, however have focused on the behavior of medium to large sized river plumes of coastal-shelf waters, whereas small sized river plumes acting within estuaries have been neglected. This study addressed the behavior of suspended particulate matter (SPM), dissolved inorganic nutrients (DIN, DIP and DSi) and Chlorophyll a (Chl. a) of a small sized river plume derived from the closely lain São Francisco and Guandú river channels, set in the Sepetiba Bay estuary, SE-Brazil. Two surface water sampling campaigns were conducted, one in January 2003 (humid summer conditions) and the other in June 2003 (dry winter conditions). On both occasions, the plumes dispersed in a SE direction towards the inner portion of the bay. The "wet" event plume was more turbid, nutrient rich and dispersed beyond nearshore waters, whereas the "dry" event plume proliferated as a narrow, less turbid and more nutrient poor film alongshore. Both exhibited a marked degree of patchiness, induced by the differential input of materials from the river sources and resuspension processes from the shallow nearshore bottom. The São Francisco river channel was the main source of freshwater, SPM and nutrients, except for ammonia (NH4+-N) derived from domestic effluents of the Guandú river. The mesohaline portion of the estuarine mixing zone of the plumes behaved as a slight source for SPM, DSi and DIP, due to bottom resuspension processes. N:P molar ratios ranged between 80:1 and 20:1 along the estuarine gradient, being higher in the summer than in the winter event, indicating that DIP was the potential nutrient limiting primary production. Chl. a concentrations increased at the outer premises of the plume, suggesting that the short residence times and turbidity of the plume waters, hampered primary production nearshore, particularly during the summer occasion...

A extensão, forma e as concentrações da matéria das plumas de pequena escala geradas pelos canais dos rios São Francisco e Guandu, se diferenciaram consideravelmente entre os eventos de alta e baixa descarga. A pluma durante o evento de alta descarga apresentou maior potencial de fertilização da parte central interna da Baía de Sepetiba, enquanto a pluma de baixa descarga fluvial reteve materiais próximo da costa em área rasa. As plumas foram impactadas por múltiplas fontes de materiais, incluindo o aporte lateral fluvial e os sedimentos do fundo. A baixa profundidade da área foi responsável pelo acoplamento nítido da água e do sedimento. O bombeamento da maré com, provavelmente, o atrito no fundo gerado pelo fluxo fluvial, foram responsáveis pela ressuspensão de matéria em suspensão e a liberação de nutrientes dos sedimentos superficiais. As plumas apresentaram um desacoplamento nítido entre as zonas de turbidez e a clorofila, e um acoplamento entre as zonas de turbidez e de mistura estuarina, geralmente não observado em plumas de médio a grande porte que se proliferam na costa e plataforma continental.