The microbial profile of rivers and lagoons three years after the impact of the world's largest mining disaster (Fundão dam, Brazil)

Lake Bacterial Communities in North Patagonian Andes: The Effect of the Nothofagus pumilio Treeline

One of the most noticeable environmental discontinuities in mountains is the transition that exists in vegetation below and above the treeline. In the North Patagonian Andean lakes (between 900 and 1950 m a.s.l.), we analyzed the bacterial community composition of lakes in relation to surrounding vegetation (erected trees, krummholz belt, and bare rocks), dissolved organic carbon (DOC), and total dissolved nutrients (nitrogen, TDN and phosphorus, TDP). We observed a decrease in DOC, TDP, and TDN concentrations with altitude, reflecting shifts in the source inputs entering the lakes by runoff. Cluster analysis based on bacterial community composition showed a segregation of the lakes below treeline, from those located above. This first cluster was characterized by the cyanobacteria Cyanobium PCC-6307, while in the krummholz belt and bare rocks, bacterial communities were dominated by Actinobacteria hgcl-clade and Proteobacteria (Sandarakinorhabdus and Rhodovarius), with the presence of pigments such as actinorhodopsin, carotenoids, and bacteriochlorophyll a. The net relatedness index (NRI), which considers the community phylogenetic dispersion, showed that lakes located on bare rocks were structured by environmental filtering, while communities of lakes below treeline were structured by species interactions such as competition. Beta-diversity was higher among lakes below than among lakes located above the treeline. The contribution of species turnover was more important than nestedness. Our study brings light on how bacterial communities may respond to changes in the surrounding vegetation, highlighting the importance of evaluating different aspects of community structure to understand metacommunity organization.

Advancing fluorescence tracing with 3D-2D spectral conversion: A mixed culture on microbial degradation mechanisms of DOM from a large-scale watershed

Fluorescence tracing, known for its precision, rapid application, and cost-effectiveness, faces challenges due to the microbial degradation of dissolved organic matter (DOM) in aquatic environments, altering its original spectral fingerprint. This study conducted a 15-day microcosm experiment to examine the effects of biodegradation on the spectral properties of DOM from various sources: livestock excrement (EXC), urban sewage (URB), industrial wastewater (IND), and riparian topsoil (tDOM). Our findings show that while the spectral structures of DOM from different sources change during 15 days of microbial degradation, these changes do not overlap or interfere with each other. However, distinguishing between tDOM and URB in the presence of both IND and EXC is only possible at high resolution. Spectral index calculations revealed significant fluctuations and interference in FI and BIX indices among samples from different sources due to microbial degradation. In contrast, the HIX index exhibited independent fluctuations and remained a reliable spectral index for tracing. LEfSe (Linear discriminant analysis Effect Size) identified characteristic bio-indicators (CBI) for each DOM source. The CBI for tDOM and URB differed significantly; tDOM showed a marked CBI only within the first four days of microbial degradation, with a sharp decline in abundance thereafter, while URB's CBI remained abundant for 12 days. Similarly, IND's CBI maintained high relative abundance for the first 12 days. EXC's CBI was unique, showing a distinct and stable community only after six days of degradation, likely due to its high bioavailability and initial rapid microbial utilization. This study addresses the temporal variability in spectral tracing techniques caused by pollutant biodegradation. We developed a combined spectral-biological tracing technique using the "three-dimensional to two-dimensional" method along with bio-indicators, enhancing the accuracy and timeliness of spectral tracing.

Mineralogical fingerprint and human health risk from potentially toxic elements of Fe mining tailings from the Fundão dam

In 2015, >50 million cubic meters of Fe mining tailings were released into the Doce River basin from the Fundão dam, raising the question of its consequences on the affected ecosystems. This study aimed to establish a mineralogical-(geo)chemical association of potentially toxic elements (PTEs) from Fe mining tailings from the Fundão dam, collected seven days after the failure, through a multidisciplinary approach combining assessment of the risk to human health, environmental geochemistry, and mineralogy. Thus, eleven tailings samples were collected with the support of the Brazilian Military Police Fire Department. Granulometry, magnetic measurements, optical microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and sequential chemical extraction of PTEs analyses were performed. Contamination indexes, assessment of risk to human health, and Pearson correlation were calculated using the results of sequential chemical extraction of PTEs. The predominance of goethite in Fe oxyhydroxide concentrates from the mud indicates that the major source of hematite may not be from tailings, but from pre-existing soils and sediments, and/or preferential dissolution of hematite in deep flooded zones of the tailings column of the Fundão dam. Moreover, the high correlation of most carcinogenic PTEs with their crystallographic variables indicates that goethite is the primary source of contaminants. Goethites from Fe mining tailings showed high specific surface area and Al-substitution, and due to their greater stability and reactivity, the impacts on PTE sorption phenomena and bioavailability may be maintained for long periods. However, their lower dissolution rate, and the consequent release of heavy metals would promote greater resilience for affected ecosystems, preventing significant PTE inputs under periodic reduction conditions. More specific studies, involving the crystallographic characteristics of Fe oxyhydroxides should be developed since they may provide another critical component of this set of complex and dynamic variables that interfere with the bioavailability of metals in ecosystems.

A conceptual model to establish preventive and corrective actions to guarantee water safety following scenarios of tailing dam failure

One of the impacts related to mining dam failures is the change in water quality downstream of the rupture and a knowledge gap is observed in terms of methodologies aimed at the prognosis of impact in water abstractions, a vulnerability that can be identified before a rupture event. Thus, the present work aims to describe a novel methodological proposal, not currently considered by control agencies, of a standard protocol that enables a comprehensive prognosis of the impacts on water quality impact in scenarios of dam failure. Initially, extensive bibliographic research was carried out on the main disruptions events since 1965 intended to better comprehend the impacts on water quality and to identify mitigatory actions proposed by the time. The information provided a framework to propose a conceptual model for the prognosis of water abstractions, with the suggestion of software and studies to comprehend the different scenarios in the event of dam failure. A protocol was prepared to obtain information on potentially affected inhabitants and a multicriteria analysis was developed using the Geographic Information System (GIS) to suggest the employment of preventive and corrective actions. The methodology was demonstrated in the Velhas River basin considering a hypothetical scenario of tailing dam failure. Changes in water quality would be observed in 274 km of its extension, mainly related to alterations in solids, metals, and metalloids' concentration, in addition to the impact on important water treatment plants. The map algebra and the results suggest the need for structuring actions in cases where the water abstraction is intended for human supply and in populations greater than 100,000 inhabitants. Populations smaller than these, or usages other than human supply, could be supplied by water tank trucks or mixed alternatives. The methodology pointed out the necessity for structuring supply actions with due notice, with the potential to prevent water shortages in scenarios of tailing dam failure and to complement the enterprise resource planning of mining companies.