Dissolved organic matter (DOM) is a crucial component of continental aquatic ecosystems. It plays a vital role in the carbon cycle by serving as a significant source and reservoir of carbon in water. DOM provides energy and nutrients to organisms, affecting primary productivity, organic composition, and the food chain. This study presents empirical bio-optical models for estimating the absorption of colored dissolved organic matter (aCDOM) in the Negro River using in situ remote sensing reflectance (Rrs) data. Physical–chemical data (TSS, DOC, and POC) and optical data (aCDOM and Rrs) were collected from the Negro River, its tributaries, and lakes and empirical relationships between aCDOM at 440 nm, single band, and the ratio bands of Rrs were assessed. The analysis of spectral slope shows no statistically significant correlations with DOC concentration or aCDOM absorption coefficient. However, strong relationships were observed between DOC and aCDOM (R² = 0.72), aCDOM and Rrs at 650 nm (R² > 0.80 and RMSE < 1.75 m⁻¹), as well as aCDOM and the green/red band ratio (R² > 0.80 and RMSE < 2.30 m⁻¹). aCDOM displayed large spatial and temporal variations, varying from 1.9 up to 20.1 m⁻¹, with higher values in rivers of the upper course of the Negro basin and lower values in rivers with total solids suspended > 10 mg·L⁻¹. Environmental factors that influence the production of dissolved organic matter include soil type, dense forest cover, high precipitation, and low erosion rates. This study demonstrated that aCDOM can serve as an indicator of DOC, and Rrs can serve as an indicator of aCDOM in the Negro basin. Our findings offer a starting point for future research on the optical properties of Amazonian black-water rivers.

The objective of this study was to evaluate the zootechnical performance of tambaqui (Colossoma macropomum) for fattening (> 2 kg) under three management strategies on nine fish farms, which were equally distributed as follows: Low Productive Efficiency (LPE) – 6-8 tons year^-1 without aeration; Medium Productive Efficiency (MPE) – 9-14 tons year^-1 with emergency aeration and High Productive Efficiency (HPE) – 15-22 tons year^-1 with supplemental aeration. Tank management data were collected and water quality parameters were monitored. Performance indices were evaluated through monthly biometrics until the end of the cycle; growth curves (von Bertalanffy) and instantaneous growth rate (IGR) were also calculated for comparison. Analysis of variance was applied to test the effect of the productive efficiency of the models on zootechnical performance. There was a difference (p<0,05) between the production strategies in relation to storage, density and productivity. Water quality indicators of oxygen (4.49-4.99 mg L^-1), pH (6.51-6.77), temperature (31.12-33.81 °C), conductivity (43.37-55.63 µS cm^-1), transparency (23.04-26.92 cm), nitrite (0.06-0.08 mg L^-1) and nitrate (0.36-0.42 mg L^-1) were within the cultivation standards. Phosphorus (0.37-0.48 mg L^-1) and TSS (65.85-91.12 mg L^-1) parameters suggest higher nutrient loads promoted by high densities. Differences between systems (p<0,05) demonstrate better overall results for HPE in final weight (2,726.53 ± 136.99 g), weight gain (2,719.98 ± 133.84 g) and apparent feed conversion (1.82 ± 0.02). The growth curves and IGR revealed differences in performances, indicating that production strategies alter the way fish grow. Systems with higher productivity demonstrate, based on their better results, greater care in the management.

Extreme climate events are intensifying in the Amazon Basin, with the 2023 drought marking the most severe on record in the Negro River, exposing extensive sediment banks and raising concerns about geochemical alterations in this acidic, organic-rich blackwater system. Rare earth elements (REEs), increasingly recognized as emerging contaminants and geochemical tracers, were analysed in surface and profile sediments from Anavilhanas Archipelago and from Manaus. Samples from Anavilhanas Archipelago exhibited low ΣREE concentrations and fractionation patterns consistent with natural mafic sources. In contrast, Manaus sediments, particularly those exposed to air, showed elevated ΣREE levels (up to 167.6 mg/kg), enhanced ΣLREE/ΣHREE ratios, and positive cerium anomalies, indicating oxidative processes and potential anthropogenic inputs. Positive europium anomalies across all sites reflected plagioclase retention under variable weathering conditions. Ecological risk assessment using the Potential Ecological Risk Index (PERI), indicated moderate risk, with Eu, Tb, Ho, Tm, and Lu contributing most, elements linked to electronic waste and industrial activity. Expansion of the Manaus Free Trade Zone has increased e-waste generation, much of it improperly discarded into rivers, contributing to REE accumulation. This study provides the first evaluation of REE fractionation and ecological risk in Negro River sediments during an extreme drought, establishing a geochemical baseline and underscoring the need for systematic monitoring and regulatory frameworks to mitigate REE-related risks in climate stressed Amazonian watersheds.

O estudo teve como objetivo desenvolver e caracterizar um sistema de tratamento de água de baixo custo, denominado STAC (Sistema de Tratamento de Água com Carvão Ativado), elaborado a partir do reaproveitamento de caroços de açaí (Euterpe oleracea Mart.), visando sua aplicação como tecnologia social em comunidades ribeirinhas da Amazônia. O sistema foi construído utilizando camadas de cascalho, areia grossa, areia fina e carvão ativado artesanalmente produzido a partir do caroço de açaí ativado com cloreto de zinco (ZnCl₂). Foram realizados ensaios de caracterização físico-química do carvão por MEV, FTIR e DRX, evidenciando estrutura altamente porosa, grupos funcionais oxigenados e caráter amorfo, características que favorecem a adsorção de contaminantes. Testes com amostras de água do rio Negro e soluções contendo ferro total mostraram redução de 88 % na turbidez, 84 % na concentração de ferro total e eliminação completa de coliformes totais e Escherichia coli, atendendo aos padrões de potabilidade estabelecidos pela Portaria GM/MS nº 888/2021. A validação social ocorreu por meio de oficinas participativas, onde os participantes confeccionaram seus próprios filtros e aprenderam o processo de produção do carvão ativado. A ação promoveu autonomia comunitária, educação ambiental e fortalecimento da bioeconomia local ao valorizar um resíduo agroextrativista abundante. Conclui-se que o STAC é uma alternativa eficiente, sustentável e replicável, capaz de garantir acesso à água potável e contribuir para o cumprimento das ODS 3, 5, 6, 12 e 13, integrando ciência, tecnologia e inclusão social na Amazônia.

Coari Lake is a critical area in the Amazon due to the oil exploration that began in the 1980s. The present study evaluates the impact on Coari Lake and the Solimões River in order to identify the origin of the sedimentary organic matter. This research is of great importance as it constitutes a crucial follow-up assessment, conducted 13 years after the initial survey by the same research group. Aliphatic hydrocarbons found in the new collected samples ranged from n-C14 to n-C34, with Cmax at C29–C31 and CPI values between 2.5 and 5.1, suggesting predominantly terrestrial biogenic inputs. Although the total n-alkane concentrations increased from 2012 to 2025, values remained within natural background ranges and as well as those ones associated with contaminated sediments. Aromatic hydrocarbons were strongly dominated by perylene, further supporting a biogenic origin. Monoaromatic and polyaromatic triterpenoids derived from α-amyrin, β-amyrin and lupeol were consistently detected, reflecting contributions from higher-plant material. No petrogenic indicators such as hopanes, steranes or unresolved complex mixtures were identified in any sample. Principal Component Analysis confirmed a temporal increase in hydrocarbon abundance while maintaining stable source signatures. Overall, the results demonstrate that Coari Lake sediments are still dominated by natural organic matter.