Amazon River Research Articles

Unraveling the sedimentation environment of Marajó island: Insights from geochemical studies and implications for the origin of potentially toxic element in soils

Marajó Island, located at the mouth of the Amazon and Tocantins rivers, is the largest fluvial maritime island on Earth. Its unique location within the Amazon biome and its complex sedimentary dynamics makes it a region of great ecological and socio-economic importance. However, the island is facing significant challenges due to climate change, with projections suggesting permanent flooding of its floodplains in the coming decades. Despite numerous studies on soil geochemistry in the Amazon biome, there is a lack of research specifically focused on Marajó Island. Our study aims to investigate the soil's geochemical properties on the major parent materials in the eastern portion of Marajó Island, seeking to unravel the nature of its complex sedimentary environment, elemental relationships, origin and implications of potentially toxic elements. Samples from seven soil profiles representative of the eastern portion island were collected in a chronosequence, to conduct physical and chemical analyzes: selective dissolution of Fe oxides by sodium citrate-bicarbonate-dithionite and ammonium acid oxalate; quantification of major, trace and rare earth elements (REE) performed by multi-acid digestion and determination in ICP-OES/MS; characterization of weathering intensity by the chemical index of alteration (CIA), chemical weathering index (CWI), plagioclase index of alteration (PIA), chemical proxy of alteration (CPA), and index of compositional variability (ICV); and assessment of potentially toxic elements using enrichment factor and geoaccumulation index. The results indicated that the geochemical variation of soils reflected particularities of the parent material influenced by marine transgression events, and by the current conditions of water table oscillation and humid tropical climate. Holocene Sediments (HS) revealed enrichment by light REE. In soils on Post-Barreiras (PB), Laterite Formation (LF) and Lateritic Debris (LD), the main elements were Al, Fe, and Ti. Due to intense weathering and leaching, negative anomalies were observed in nearly all elements, including the REE. Arsenic enrichment in HS soils was due to the past estuarine influence and the current hydromorphic conditions, while soils on PB, LF and LD are naturally enriched by the parent material.

OceanSODA-UNEXE: a multi-year gridded Amazon and Congo River outflow surface ocean carbonate system dataset

Abstract. Large rivers play an important role in transferring water and all of its constituents, including carbon in its various forms, from the land to the ocean, but the seasonal and inter-annual variations in these riverine flows remain unclear. Satellite Earth observation datasets and reanalysis products can now be used to observe synoptic-scale spatial and temporal variations in the carbonate system within large river outflows. Here, we present the University of Exeter (UNEXE) Satellite Oceanographic Datasets for Acidification (OceanSODA) dataset (OceanSODA-UNEXE) time series, a dataset of the full carbonate system in the surface water outflows of the Amazon (2010–2020) and Congo (2002–2016) rivers. Optimal empirical approaches were used to generate gridded total alkalinity (TA) and dissolved inorganic carbon (DIC) fields in the outflow regions. These combinations were determined by equitably evaluating all combinations of algorithms and inputs against a reference matchup database of in situ observations. Gridded TA and DIC along with gridded temperature and salinity data enable the calculation of the full carbonate system in the surface ocean (which includes pH and the partial pressure of carbon dioxide, pCO2). The algorithm evaluation constitutes a Type-A uncertainty evaluation for TA and DIC, in which model, input and sampling uncertainties are considered. Total combined uncertainties for TA and DIC were propagated through the carbonate system calculation, allowing all variables to be provided with an associated uncertainty estimate. In the Amazon outflow, the total combined uncertainty for TA was 36 µmol kg−1 (weighted root-mean-squared difference, RMSD, of 35 µmol kg−1 and weighted bias of 8 µmol kg−1 for n = 82), whereas it was 44 µmol kg−1 for DIC (weighted RMSD of 44 µmol kg−1 and weighted bias of −6 µmol kg−1 for n = 70). The spatially averaged propagated combined uncertainties for the pCO2 and pH were 85 µatm and 0.08, respectively, where the pH uncertainty was relative to an average pH of 8.19. In the Congo outflow, the combined uncertainty for TA was identified as 29 µmol kg−1 (weighted RMSD of 28 µmol kg−1 and weighted bias of 6 µmol kg−1 for n = 102), whereas it was 40 µmol kg−1 for DIC (weighted RMSD of 37 µmol kg−1 and weighted bias of −16 µmol kg−1 for n = 77). The spatially averaged propagated combined uncertainties for pCO2 and pH were 74 µatm and 0.08, respectively, where the pH uncertainty was relative to an average pH of 8.21. The combined uncertainties in TA and DIC in the Amazon and Congo outflows are lower than the natural variability within their respective regions, allowing the time-varying regional variability to be evaluated. Potential uses of these data would be the assessment of the spatial and temporal flow of carbon from the Amazon and Congo rivers into the Atlantic and the assessment of the riverine-driven carbonate system variations experienced by tropical reefs within the outflow regions. The data presented in this work are available at https://doi.org/10.1594/PANGAEA.946888 (Sims et al., 2023).

Are scattered microsatellites weak chromosomal markers? Guided mapping reveals new insights into Trachelyopterus (Siluriformes: Auchenipteridae) diversity.

The scattered distribution pattern of microsatellites is a challenging problem in fish cytogenetics. This type of array hinders the identification of useful patterns and the comparison between species, often resulting in over-limited interpretations that only label it as "scattered" or "widely distributed". However, several studies have shown that the distribution pattern of microsatellites is non-random. Thus, here we tested whether a scattered microsatellite could have distinct distribution patterns on homeologous chromosomes of closely related species. The clustered sites of 18S and 5S rDNA, U2 snRNA and H3/H4 histone genes were used as a guide to compare the (GATA)n microsatellite distribution pattern on the homeologous chromosomes of six Trachelyopterus species: T. coriaceus and Trachelyopterus aff. galeatus from the Araguaia River basin; T. striatulus, T. galeatus and T. porosus from the Amazonas River basin; and Trachelyopterus aff. coriaceus from the Paraguay River basin. Most species had similar patterns of the (GATA)n microsatellite in the histone genes and 5S rDNA carriers. However, we have found a chromosomal polymorphism of the (GATA)n sequence in the 18S rDNA carriers of Trachelyopterus galeatus, which is in Hard-Weinberg equilibrium and possibly originated through amplification events; and a chromosome polymorphism in Trachelyopterus aff. galeatus, which combined with an inversion polymorphism of the U2 snRNA in the same chromosome pair resulted in six possible cytotypes, which are in Hardy-Weinberg disequilibrium. Therefore, comparing the distribution pattern on homeologous chromosomes across the species, using gene clusters as a guide to identify it, seems to be an effective way to further the analysis of scattered microsatellites in fish cytogenetics.

Numerical Simulation of Oil Spills in the Lower Amazonas River

In 2013, a slope slide took place at the Santana-AP channel that links to the Lower Amazon River’s North Channel, resulting in the sudden collapse of a substantial section of the Port of Santana and its infrastructure. This area houses liquid bulk terminals and pipelines with high pollution potential. The objective of the research is to evaluate the potential environmental impacts of an eventual oil spill in the very short term using a numerical hydrodynamic simulation model coupled with that of pollutant dispersion. The SisBaHiA® software, experimentally calibrated using acoustic methods (ADCP), was used to generate hypothetical scenarios in these areas with a substantial risk of landslides. Two hydrological scenarios stand out in the simulations: (a) November S-1 (dry) and (b) May S-2 (rainy). In S-1, the plume dispersion was higher during flood tides S-1a and S-1b, reaching 4 h urban slope areas, river mouths, tributaries (Matapi and Vila Nova), and environmental protection areas. At S-2, the plume spread was greater during the ebb tides S-2c and S-2d, affecting Macapá’s water supply system 12 h after the accident. The scenarios suggest the existence of high risks associated with the study hypotheses. The dispersion of the plume is directly proportional to the flow, indicating that local hydrodynamics is probably the most relevant dispersive factor. We conclude that the mitigation time for more severe effects is critical in the first 4 h because the coastal geographic feature tends to keep the plume in the Santana channel.

Nickel mass balance and isotopic records in a serpentinic weathering profile: Implications on the continental Ni budget

During serpentinite rock weathering, Ni is concentrated in the regolith owing to residual and secondary enrichment, forming a Ni-rich deposit under tropical conditions. This study presents geochemical, isotopic, and mineralogical data for Ni from the Serra do Puma Complex (SPC) weathering profile in Carajas (Brazil). The Ni fluxes, redistribution, and Ni isotopic fractionation magnitudes were quantified along the entire weathering profile: rock, saprock, lower and upper saprolite, and limonite. The results show that chlorite and serpentine are the primary Ni-scavenging phases in saprolite, whereas Fe oxyhydroxides are the main Ni-hosting minerals in the limonite unit. The mass balance model confirmed a global Ni gain at the weathered profile scale, with larger Ni enrichment in the upper saprolite. The isotopic dataset obtained in this study contributes greatly to the knowledge of the current Ni cycle on regional and global scales. The detailed insights into Ni isotopes in the SPC, coupled with chemical and mineralogical composition, allow for the first time a Ni mass balance and Ni isotopic values for an entire weathering profile in an Amazonian context. The Ni isotopic profile agrees with the preferential retention of light Ni isotopes in the residual material relative to the parent rock during weathering processes, with the Δ60Ni limonite-saprock of −0.72‰. In the SPC, major isotopic fractionation was notably recorded during saprolitization, while limonitization was accompanied by an overall Ni loss without significant Ni isotopic fractionation. As already observed in previous studies, heavier Ni isotopes, preferentially leached during weathering processes, can be further mobilized downward and lost from the profile or incorporated in secondary minerals in the saprolite and limonite sections. The Ni isotopic mass balance model indicated that the Ni loss from the weathered serpentinite profile was isotopically heavy, in agreement with the isotopically heavier composition of the dissolved load of Amazonian rivers. The isotopically light Ni pool, associated with the significant Ni gain encountered in the upper saprolite, is notable in the SPC weathering profile and confirms the existence of a light Ni isotope reservoir in the continent.

Composition and Flux of Dissolved and Particulate Carbon and Nitrogen in the Lower Tocantins River

AbstractThe Tocantins River contributes ∼5% of the total flux of water to the Amazon River plume in the Atlantic Ocean. Here, we evaluate monthly variability in the composition and abundance of carbon, nitrogen, and suspended sediment in the lower reaches of the Tocantins River from 2014 to 2016. Dissolved organic carbon concentrations generally increased during periods of high discharge and are ∼1.5 times lower than average concentrations at the mouth of the Amazon River. Dissolved inorganic carbon similarly increased during periods of high discharge. Total dissolved nitrogen and individual nitrogen species followed a similar temporal pattern, increasing during high water. predominated the dissolved inorganic nitrogen pool, followed by , and , characteristic of environments with a relatively low anthropogenic impact. Dissolved fractions represented 92% of the total carbon exported and 78% of the total nitrogen exported. The suspended particulate sediment flux was 2.72 × 106 t yr−1, with fine suspended sediment dominating (71.3%). Concentrations of carbon relative to nitrogen indicate a primarily terrigenous source of organic matter and CO2 derived from in situ respiration of this material during the rainy season and a primarily algal/bacterial source of organic matter during the dry season. Considering past estimates of dissolved carbon and nitrogen fluxes from the Amazon River to the Atlantic Ocean, the Tocantins River contributes 3% and 3.7% to total fluxes to the Amazon River plume region, respectively. While this contribution is relatively small, it may be influenced by future changes to the basin's land use and hydrology.

Dislocating Sounds: The Unsettling Sonorities of the Amazon in William Ospina's El país de la canela

Abstract: In this article, I examine the literary sounds of William Ospina's historical fiction, El país de la canela (2008), which retells the story of the 1541-1542 expedition led by Francisco de Orellana along the Amazon River. Exploring the relationship between aural imagery and space in the novel, I argue that sound contributes to dislocating the outsiders within the jungle, and building an alternative account of history in which senses act as an unstable counterpoint to the lettered archive. I maintain that Ospina re-elaborates the colonial past from a decentered perspective that challenges the primacy of the imperial gaze and rhetoric on the conquest, to criticize the enduring extractivist view of American nature in (neo)colonial discourse. To analyze the narrative's literary soundscape, I study the network of drums, howls, shrieks, rumbles, and silences that can be 'heard' by the mind's ear of its readers in relation to the Amazonian space. Following an interdisciplinary method, I draw on theoretical debates on historical fiction (Menton, Perkowska), eco-critical approaches on the novela de la selva (Marcone, Wylie), and contributions from the sound studies field (Ochoa Gautier, Estévez Trujillo, Kane). This all lends to my claim that the appeal to sounds in the narrative underpins a decolonial retelling of the past ruled by the senses, in which sonic disruptions make the conquistador appear out of place in the rainforest.

Human‐Induced Changes in South American River Sediment Fluxes From 1984 to 2019

AbstractRiver sediment fluxes have been impacted in South America (SA), one of the continents with the highest erosion and sediment transport rates globally. However, the magnitude and spatio‐temporal distribution of the main drivers of changes have been poorly identified and explored. Here, we performed simulations using a hydrological‐hydrodynamic‐sediment model to comprehensively estimate the spatial and temporal sediment changes and trends in SA from 1984 to 2019. We found that 51% of the main SA rivers experienced significant changes in simulated sediment transport (QST) over this period, with 36% due to Amazon deforestation and river damming and 15% due to precipitation changes. We also estimated a 10% reduction in the average sediment delivery to the oceans. Deforestation was responsible for QST changes higher than 80% in some Amazon sites, and hydropower expansion led to a greater reduction of sediment flows (80%–100%) in the Tocantins, Uruguay, Upper Paraná, lower São Francisco, Desaguadero, and Negro rivers. In addition, our results suggest that reservoirs built in the Amazon region in the 2011–2019 period are also affecting sediment transport. Our modeling outputs provide unprecedented information about the status of river sediment dynamics in SA, and a template to develop evidence‐based strategies and transboundary policies related to continental‐wide sediment dynamics and the conservation and restoration of ecosystems.

A new highly apomorphic species of Bujurquina (Teleostei: Cichlidae) from a reverse flowing river in the Peruvian Amazon, with a key to the species in the genus

Bujurquina is the most widely distributed and species-rich genus of cichlids in the western Amazon of South America. In this study we describe a new species from Peru from a hypothesized reverse flowing river system. Prior to the origin of the modern Amazon River at 4.5 Ma, this river system had its headwaters on the Iquitos arch, one of several main structural arches (swells) in the Amazon. Prior to the origin of the modern Amazon these arches formed topographic barriers of drainage basins in lowland Amazonia. For our analyses we use morphological and molecular data, analyzed through multivariate statistics and molecular phylogenies, respectivelly. For all valid species in the genus (except B. cordemadi and B. pardus) we additionally for the first time provide photographs of live specimens. Based on DNA phylogeny and coloration patterns we demonstrate that Bujurquina is divided into two main clades and based on this we provide a dichotomous key for all the species.

Fisheries of the scavenger species Calophysus macropterus: a case study in the Bolivian Amazon

Bolivian Amazon small-scale fisheries traditionally focus on large migratory fish species. However, in the last decade there has been a trend of increased landings of low-value medium-sized migratory species, such as blanquillo, Calophysus macropterus. This scavenger species is captured using chicken and bovine waste as bait, and occasionally carcasses from wild species. This study explores the boom of this specialized fishery in Puerto Villarroel, a small harbor on the Ichilo River, using a combination of historical landing data, fisheries statistics obtained by participatory fisheries monitoring, fish market studies and interviews with local key stakeholders. Additionally, mercury contamination of fish meat was evaluated. Blanquillo fishing started in 2008 and boomed around 2015, representing 30% of landings, after which it decreased to fluctuate around 15%. The capture and landing data suggest that this species is mainly captured by non- organized fishers. The market studies conducted between 2015 and 2018 in Cochabamba city and in lowland middle towns showed that on average more than 20% of consumption of Amazon river fish consisted of blanquillo meat. Mercury is accumulated in the muscle tissue at concentrations near the official limit established by WHO for human consumption, whereas in 15% of fish the concentrations exceeded this limit. The paper pieces together the evolution of the blanquillo fishery in Bolivia, and looks at different aspects, including the diversity of fishers involved, possible impacts on other vulnerable species and public health, and potential impacts and effectiveness of different public policy approaches. In conclusion, the present study shows there is an overall need for more consistent and inclusive fisheries regulations in the Bolivian Amazon, as a way to protect aquatic fauna, avoid environmental contamination and secure human health.

New insights into the Cretaceous evolution of the Western Amazonian paleodrainage system

The geological history of the Amazon River is a complex story driven by geodynamic processes operating in the South American plate. In spite of recent research, the pre-Neogene structure of Amazon paleodrainage is still underconstrained. A recent study has suggested that the western Amazonian paleodrainage system was reversed, cratonic in origin during the Cretaceous. However, the extent and duration of this system are not well-constrained. To add new constraints, we investigated the sources of Cretaceous sedimentary rocks in the Brazilian Acre and Peruvian Madre de Dios basins, based on major and trace element concentrations, Sm–Nd isotopic compositions, and U–Pb detrital zircon dating. The late Cretaceous samples of the Acre Basin have εNd(0) values between −21.2 and −8.4 and zircon grains derived from terranes situated in the easternmost part of the Amazonian Craton: Ventuari–Tapajos (2.0–1.82 Ga) and Rio Negro–Juruena (1.82–1.54 Ga). In contrast, the Madre de Dios Basin samples have εNd(0) values ranging from −15.2 to −7.1 and a wide range of U–Pb zircon age distributions. The samples from the northern part of the basin (MD234 and MD238) are dominated by zircon ages between 0.9 and 1.3 Ga (Grenville/Sunsás, 30 %–43 %) and 0.5 and 0.7 Ga (Brazilian/Pampean, 26 %–16 %) with felsic provenance. The oldest MD234 sample also shows a dominant contribution from Paleozoic zircon (20 %). On the other hand, the samples from the southern part of the Madre de Dios Basin (samples MD-2019-4A; MD-2019-10; MD-2019-13; MD-2019-11D and MD-2019-12A) have U–Pb age distributions dominated by zircon ages between 0.9 and 1.3 Ga (Grenville/Sunsás, 30 %–45 %) and 1.54 and 1.3 Ga (Rondonia–San Ignácio, 16 %–43 %), pointing to a cratonic origin for these sedimentary rocks. To elucidate the distinction in provenance between the samples from the northern and southern parts of the Madre de Dios Basin, we suggest that a structural barrier (the Madidi Arch (?)) was active during the late Cretaceous. In this scenario, the northern part of the Madre de Dios Basin had similar sedimentary sources as the nearby basins like Huallaga, Bagua, Ucayali, and Marañón, whereas, in the southern part of the basin, sedimentation was influenced by local sources. Together with previously published studies, these data indicate that the continent-wide cratonic drainage developed between the Cenomanian and Maastrichtian in response to the Purus Arch uplift was probably driven by a geodynamic process related to the post-rift opening of the Atlantic Equatorial Ocean.

Considerations for hypothetical carbon dioxide removal via alkalinity addition in the Amazon River watershed

Abstract. The Amazon River plume plays a critical role in shaping the carbonate chemistry over a vast area in the western tropical North Atlantic. We conduct a sensitivity analysis of hypothetical ocean alkalinity enhancement (OAE) via quicklime addition in the Amazon River watershed, examining the response of carbonate chemistry and air–sea carbon dioxide flux to the alkalinity addition. Through a series of sensitivity tests, we show that the detectability of the OAE-induced alkalinity increment depends on the perturbation strength (or size of the alkalinity addition, ΔTA) and the number of samples: there is a 90 % chance to meet a minimum detectability requirement with ΔTA>15 µmol kg−1 and sample size >40, given background variability of 15–30 µmol kg−1. OAE-induced pCO2 reduction at the Amazon plume surface would range between 0–25 µatm when ΔTA=20 µmol kg−1, decreasing with increasing salinity (S). Adding 20 µmol kg−1 of alkalinity at the river mouth could elevate the total carbon uptake in the Amazon River plume (15<S<35) by at least 0.07–0.1 Mt CO2 per month, and a major portion of the uptake would occur in the saltiest region (S>32) due to its large size, comprising approximately 80 % of the S>15 plume area. However, the lowest-salinity region (S<15) has a greater drop in surface ocean partial pressure of CO2 (pCO2sw) due to its low buffer capacity, potentially allowing for observational detectability of pCO2sw reduction in this region. Reduced outgassing in this part of the plume, while more uncertain, may also be important for total additional CO2 uptake. Such sensitivity tests are useful in designing minimalistic field trials and setting achievable goals for monitoring, reporting, and verification purposes.

Amazon River Delta Suspended Sediment Analysis

This study focuses on the variation of suspended sediment concentrations in the Amazon River basin near Macapa, Brazil for each season between 2016 and 2020. The suspended sediment concentrations were calculated by spectral analysis of satellite images obtained by Landsat 8-9 OLI/TIRS in the study area. The effects of seasonality, discharge, and precipitation on suspended sediment concentrations in the Amazon Delta were also investigated in conjunction with discharge and precipitation data in the Amazon River basin near Macapa. Findings showed that precipitation was a strong driver of SSC increase, but high SSC lasts longer after high precipitation in autumn. Precipitation, discharge, and SSC were positively correlated with each other, but there was a lag period between their changes.

Food web structure in the Xingu River rapids prior to operation of the Amazon’s largest hydropower plant

The results of recent theoretical studies suggest that food webs are size-structured, with top predators coupling across different energy sources. However, evidence supporting this hypothesis is still scarce, especially in highly diverse tropical rivers. In the present study, we explored the association between body size, trophic position, and the use of allochthonous and autochthonous basal production sources in the Volta Grande rapids of the Xingu River, a major clearwater tributary of the Amazon River, during the period prior to operation of the Belo Monte Hydropower Plant (BMHP). This section of the river contains a maze of channels with rocky shoals that support dozens of endemic fishes, mollusks and other aquatic taxa that may be impacted by flow regulation by the Pimental Dam located upstream. During the low-water season, we surveyed fish, crustaceans, mollusks, sponges, aquatic and terrestrial insects, zooplankton, and basal production sources to obtain tissue samples for analysis of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N). The results indicated that the biomass of most aquatic organisms appears to be largely supported by riparian vegetation, highlighting the importance of the lateral connectivity between aquatic and terrestrial habitats. In contrast to expectation, we did not observe a gradual increase in the coupling of energy pathways with increasing body size and trophic position. These findings provide a baseline for the trophic ecology of this river under the natural flow regime that can be used for future impact assessments, and they also indicate that more complex food web models, potentially including additional functional traits (e.g., gut length) are needed to describe resource and habitat use in highly diverse tropical ecosystems.

Predicting driving transferred energy without needing the hammer efficiency: three case studies

This study presents case studies on the implementation of an innovative method of calculating effective driving energy with no need to account for hammer efficiency. The approach is based on measurements of set and elastic rebound, as well as a site-specific parameter (λ) calibration. The study applied this method to steel piles located in the cities of Santos (SP), Itaguaí (RJ), and Óbidos (PA), with the latter site being built in the Amazon region, near the Amazon River. Following coefficient calibration, the effective driving energy estimation technique exhibited a strong correlation with realistic and accurate energies directly obtained from dynamic loading tests. The method provides a highly accurate means of calculating effectively transferred energy to piles due to hammer blows, without relying on knowledge of the driving system performance. In that way, it can be applied to all the piles at the site (100% of them), including those that are not tested. This optimized and agile approach represents a significant breakthrough in foundation engineering and an enhance of pile foundation quality control.

New records of Pimelodella (Siluriformes, Heptapteridae) from Colombia for the Amazon River basin, and redescription of P. serrata.

We recorded Pimelodella bockmanni and P. serrata for the first time for Colombia, based on specimens collected in tributaries from the main channel of the Amazonas River, in the so-called Trapecio Amazónico, in the southernmost region of this country. We also present morphometric, meristic, and osteological data of the examined material, and provide a complementary morphological description of the poorly known P. serrata, a species known only from the Madeira River drainage in Bolivia and Brazil.

River mouth morphodynamics and deflection over the short term: effects on spit growth and mangrove dynamics

The river mouth shows the influence of the dynamics of sediment deposition and the processes organising the deposits. The river mouths of the Guyana coast, as with other coastal systems in the Guianas, are influenced by the deposition of mud banks from the Amazon River and other rivers. This study analysed and probed the influence of the riverine and marine influences on small river mouth morphological developments. In this study, the morphological dynamics of the system were carried out from satellite images through the comparison of the inter-annual morphodynamics of the river mouths, complemented by data from hydrodynamic processes among others. This study demonstrates that the recent advancement and availability of Synthetic Aperture Radar (SAR), remotely sensed data, allow for the classification of migrating river mouth action and processes; effective monitoring of mudflats development and spit formation; and, the exhibition of river mouth transitioning and infilling. Sentinel-1 images of the Mahaica-Mahaicony river mouth in Guyana were processed and analysed using Google Earth Engine (GEE) and ArcGIS to observe the mud dynamics and its effects on deflecting the river mouth, influencing the development of spit and mangrove dynamics. The results of the analyses show that the dynamics of the mud shoal and river mouth are governed by feedback from various estuarine and hydrodynamic processes resulting from the interactions between the river and ocean. The results have not only highlighted the importance of mud infilling and sediment build-up for spit development and river-mouth deflection but the impact of the sediment morphological dynamics on the ecosystem (mangrove) associated with the river mouth.

Bacterioplankton Communities in Dissolved Organic Carbon-Rich Amazonian Black Water.

The Amazon River basin sustains dramatic hydrochemical gradients defined by three water types: white, clear, and black waters. In black water, important loads of allochthonous humic dissolved organic matter (DOM) result from the bacterioplankton degradation of plant lignin. However, the bacterial taxa involved in this process remain unknown, since Amazonian bacterioplankton has been poorly studied. Its characterization could lead to a better understanding of the carbon cycle in one of the Earth's most productive hydrological systems. Our study characterized the taxonomic structure and functions of Amazonian bacterioplankton to better understand the interplay between this community and humic DOM. We conducted a field sampling campaign comprising 15 sites distributed across the three main Amazonian water types (representing a gradient of humic DOM), and a 16S rRNA metabarcoding analysis based on bacterioplankton DNA and RNA extracts. Bacterioplankton functions were inferred using 16S rRNA data in combination with a tailored functional database from 90 Amazonian basin shotgun metagenomes from the literature. We discovered that the relative abundances of fluorescent DOM fractions (humic-, fulvic-, and protein-like) were major drivers of bacterioplankton structure. We identified 36 genera for which the relative abundance was significantly correlated with humic DOM. The strongest correlations were found in the Polynucleobacter, Methylobacterium, and Acinetobacter genera, three low abundant but omnipresent taxa that possessed several genes involved in the main steps of the β-aryl ether enzymatic degradation pathway of diaryl humic DOM residues. Overall, this study identified key taxa with DOM degradation genomic potential, the involvement of which in allochthonous Amazonian carbon transformation and sequestration merits further investigation. IMPORTANCE The Amazon basin discharge carries an important load of terrestrially derived dissolved organic matter (DOM) to the ocean. The bacterioplankton from this basin potentially plays important roles in transforming this allochthonous carbon, which has consequences on marine primary productivity and global carbon sequestration. However, the structure and function of Amazonian bacterioplanktonic communities remain poorly studied, and their interactions with DOM are unresolved. In this study, we (i) sampled bacterioplankton in all the main Amazon tributaries, (ii) combined information from the taxonomic structure and functional repertory of Amazonian bacterioplankton communities to understand their dynamics, (iii) identified the main physicochemical parameters shaping bacterioplanktonic communities among a set of >30 measured environmental parameters, and (iv) characterized how bacterioplankton structure varies according to the relative abundance of humic compounds, a by-product from the bacterial degradation process of allochthonous DOM.

Nanoparticles containing hazardous elements and the spatial optics of the Sentinel-3B OLCI satellite in Amazonian rivers: a potential tool to understand environmental impacts.

The Amazon River is the longest river in the world. The Tapajós River is a tributary to the Amazon. At their junction, a marked decrease in water quality is evident from negative impacts from the constant activity of clandestine gold mining in the Tapajós River watershed. The accumulation of hazardous elements (HEs), capable of compromising environmental quality across large regions is evident in the waters of the Tapajós. Sentinel-3B OLCI (Ocean Land Color Instrument) Level-2 satellite imagery with Water Full Resolution (WFR) of 300m was utilized to detect the highest potential for the absorption coefficient of detritus and gelbstoff in 443m-1 (ADG443_NN), chlorophyll-a (CHL_NN) and total suspended matter concentration (TSM_NN), at 25 points in the Amazon and Tapajós rivers (in 2019 and 2021). Physical samples of riverbed sediment collected in the field at the same locations were analyzed for NPs and ultra-fine particles to verify the geospatial findings. The riverbed sediment samples collected in the field were studied by Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM), with selected area electron diffraction (SAED), following laboratory analytical procedures. The Sentinel-3B OLCI images, based on the Neural Network (NN) were calibrated by the European Space Agency (ESA), with a standard average normalization of 0.83µg/mg, containing a maximum error of 6.62% applied to the sampled points. The analysis of the riverbed sediment samples revealed the presence of the following hazardous elements: As, Hg, La, Ce, Th, Pb, Pd, among several others. The Amazon River has significant potential to transport ADG443_NN (55.475m-1) and TSM_NN (70.787 gm-3) in sediments, with the possibility of negatively impacting marine biodiversity, in addition to being harmful to human health over very large regions.

Titanium transport and isotopic fractionation in the Critical Zone

Stable Ti isotopes have been applied in the detrital sediment record to reconstruct the bulk composition of Earth’s continental crust due to the relationship between magmatic differentiation and Ti isotopic compositions. However, no study has systematically evaluated the influence of provenance, physical, and chemical weathering on the composition of sediments relative to the protolith they originated from. To test the influence of these processes on Ti isotopic compositions we investigate the Ti isotope composition of 82 surface samples including loess, volcaniclastic rocks, river sediment, and two separate weathering profiles through igneous rocks, collected from a broad geographical area and a range of environmental conditions. Limited but significant Ti isotope fractionation exists in samples subjected to extreme chemical weathering processes, potentially as a result of elemental mobilization. For example, the δ49Ti isotopic composition of bauxites developed on Columbia River basalt varies by up to 0.1‰, becoming isotopically heavier with increasing weathering intensity. However, negligible variation in δ49Ti was found in a second profile of saprolites developed on weathered diabase. Titanium isotope variations in loess do not correlate with chemical weathering intensity or size sorting, but may instead be related to the provenance of the sediment. We find that the δ49Ti of Amazon River sediments is correlated with the Al/Zr ratio, indicating that δ49Ti is impacted by sediment sorting. At our study sites, the river averaged offset between the isotopic composition of the bedload and the suspended sediment fraction is 0.051‰, with the largest offset being + 0.116‰. Our data suggest that during chemical weathering, heavy Ti isotopes are preferentially incorporated into secondary minerals producing higher δ49Ti in intensely weathered soils. During fluvial transport, the Ti isotopic composition of fine-grained sediment is heavier than that of its coarser counterpart. Crustal protolith composition and sorting during transport and sedimentation have a stronger effect on the Ti isotopic composition than chemical weathering. Our results have implications for studies that utilize the Ti elemental concentration to calculate relative enrichment or depletion during chemical weathering and physical transport processes in the Critical Zone and for studies using Ti isotopes in terrigenous sediments to infer the composition of their provenance.