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Abstract Between 2013 and 2017, we carried out nine field missions in the Lago Grande de Curuai floodplain, located in Pará state – North of Brazil – to collect samples for monitoring surface water quality. This site separated from the river by a narrow bank is composed of a network of channels and shallow lakes, a morphology shared by the floodplains of the lower Amazon. A multiparameter probe was used in situ to measure electrical conductivity, temperature, pH, dissolved oxygen, chlorophyll, turbidity, depth and a Secchi disk to estimate transparency. Water grab samples were analysed for suspended material, alkalinity, humic acid, phosphorus, nitrogen, carbon and chlorophyll. Sampling stations were distributed over the seven larger lakes in the floodplain and sampled at different periods of the hydrological cycle. The number of samples varied with the floodplain water level, with a minimum of 25 samples for each field visit. This data set is a collection of water quality data to assist in the limnological or biogeochemical studies of surface waters in Amazonian floodplain lakes, and the product of successive French‐Brazilian projects: (1) the Clim‐FABIAM ‘Climate changes and Floodplain lake biodiversity in the Amazon Basin: how to cope and help the ecological and economic sustainability’ funded by the French Foundation for biodiversity research (FRB), (2) the project Bloom‐ALERT –‘Environmental sensitivity and population health vulnerability to cyanobacteria in the Amazon: towards shared indicators’ funded by the French‐Brazilian research program GUYAMAZON 2014, and the project (3) ‘Ecossistemas das várzeas e biodiversidade: Impactos das mudanças ambientais e climáticas considerando cenários de desenvolvimento sustentáveis’ (Project number 490634/2013‐3) funded by the Brazilian National scientific Research Council CNPq.

Copyright of Environmental & Social Management Journal / Revista de Gestão Social e Ambiental is the property of Environmental & Social Management Journal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Between 2013 and 2017, we carried out nine field missions in the Lago Grande de Curuai floodplain, located in Pará state – North of Brazil – to collect samples for monitoring surface water quality. This site separated from the river by a narrow bank is composed of a network of channels and shallow lakes, a morphology shared by the floodplains of the lower Amazon. A multiparameter probe was used in situ to measure electrical conductivity, temperature, pH, dissolved oxygen, chlorophyll, turbidity, depth and a Secchi disk to estimate transparency. Water grab samples were analysed for suspended material, alkalinity, humic acid, phosphorus, nitrogen, carbon and chlorophyll. Sampling stations were distributed over the seven larger lakes in the floodplain and sampled at different periods of the hydrological cycle. The number of samples varied with the floodplain water level, with a minimum of 25 samples for each field visit. This data set is a collection of water quality data to assist in the limnological or biogeochemical studies of surface waters in Amazonian floodplain lakes, and the product of successive French‐Brazilian projects: (1) the Clim‐FABIAM 'Climate changes and Floodplain lake biodiversity in the Amazon Basin: how to cope and help the ecological and economic sustainability' funded by the French Foundation for biodiversity research (FRB), (2) the project Bloom‐ALERT –'Environmental sensitivity and population health vulnerability to cyanobacteria in the Amazon: towards shared indicators' funded by the French‐Brazilian research program GUYAMAZON 2014, and the project (3) 'Ecossistemas das várzeas e biodiversidade: Impactos das mudanças ambientais e climáticas considerando cenários de desenvolvimento sustentáveis' (Project number 490634/2013‐3) funded by the Brazilian National scientific Research Council CNPq. [ABSTRACT FROM AUTHOR]

In coupled perturbed parameter ensemble (PPE) experiments or for development of a single coupled global climate model (GCM) in general, models can exhibit a slowdown in the Atlantic Meridional Overturning Circulation (AMOC) that can result in unrealistically reduced transport of heat and other tracers. Here we propose a method that researchers running PPE experiments can apply to their own PPE to diagnose what controls the AMOC strength in their model and make predictions thereof. As an example, using data from a 25-member coupled PPE experiment performed with HadGEM3-GC3.05, we found four predictors based on surface heat and freshwater fluxes in four critical regions from the initial decade of the spinup phase that could accurately predict the AMOC transport in the later stage of the experiment. The method, to our knowledge, is novel in that it separates the effects of the drivers of AMOC change from the effects of the changed AMOC. The identified drivers are shown to be physically credible in that the PPE members exhibiting AMOC weakening possess some combination of the following characteristics: warmer ocean in the North Atlantic Subpolar Gyre, fresher Arctic and Tropical North Atlantic Oceans and larger runoff from the Amazon and Orinoco Rivers. These characteristics were further traced to regional responses in atmosphere-only experiments. This study suggests promising potential for early stopping rules for parameter perturbations that could end up with an unrealistically weak AMOC, saving valuable computational resources. Some of the four drivers are likely to be relevant to other climate models so this study is of interest to model developers who do not have a PPE. [ABSTRACT FROM AUTHOR]

Most of our knowledge about the Amazon River plume is limited from the field experiments or modeling due to various challenges for satellite remote sensing, i.e., constant cloud coverage, atmospheric correction, and difficulties to differentiate the Amazon River plume from normal Atlantic Ocean water. In this study, observations of ocean properties from the Visible Infrared Imaging Radiometer Suite (VIIRS) and sea surface salinity (SSS) from the Soil Moisture Active Passive (SMAP) missions in 2021 are used as an example to demonstrate the capability to monitor the Amazon River plume on daily basis and characterize the change of the ocean environment driven by the offshoots and migration of the plume in the western tropical Atlantic Ocean. The start, development, evolvement, dispersion, and dissipation of the Amazon River plume in 2021 in the western tropical Atlantic Ocean were effectively monitored. The extensive influence of the Amazon River runoff mostly occurred between June and November. The water diffuse attenuation coefficient at 490 nm (Kd(490)) and SSS were significantly impacted by the Amazon River plume in the vast region of the western tropical Atlantic Ocean. The routes of the Amazon River plume that flowed into the Atlantic Ocean were highly variable. High turbidity, low salinity plume water with Kd(490) reaching ~1.0 m−1 and SSS ~25 practical salinity unit (psu) was found in a region over 500 km from the Amazon River Estuary. The comparison of the Amazon River plume in 2020 and 2022 further shows the complication of the driving forcing and inter-annual variability of the Amazon River plume. The combination of gap-free satellite ocean color and SSS observations provided a new tool to monitor the short-term variability of the Amazon River plume and assess its seasonal and interannual impact on the ocean environment in the western tropical Atlantic Ocean.

We report, in 15 Ecuadorian mountainous lakes, dissolved concentrations of CO2, CH4, and N2O and a suite of ancillary biogeochemical variables (dissolved inorganic nutrients, oxygen, major cations, dissolved and particulate organic carbon, and the stable isotope composition of dissolved inorganic carbon and water). The sampled lakes were located in the páramos of Salve Facha and Antisana y Mojanda (northern region of Ecuadorian Andes), along an elevational gradient from 2213 to 4361 m above sea level, as well as a gradient of lake surface area (0.003–6.1 km2) and depth (1–74 m). Most lakes were characterized by lower values of the partial pressure of CO2 (pCO2) (644–2152 ppm) than usually attributed to tropical lakes (~ 1900 ppm). Three lakes influenced by volcanic inputs were characterized by the highest pCO2 values (3269–10,069 ppm), while two lakes bordered by large cities were characterized by the lowest pCO2 values (208–254 ppm). Dissolved CH4 concentrations ranged between 170 and 24,908 nmol/L and were negatively correlated to lake area and depth. N2O saturation levels ranged between 64% and 101%. The surface waters were undersaturated in N2O with respect to atmospheric equilibrium, probably due to inputs of soil–water with low N2O levels owing to denitrification in soils. The data obtained in the sampled highland lakes was combined with published data from lowland lakes (elevation < 500 m, n = 17 for CO2 and n = 16 for CH4) to derive relations between CO2 and CH4 and lake surface area, allowing to compute CO2 and CH4 lacustrine emissions at the scale of the Amazon basin using the HydroLAKES spatial data set. The CO2 and CH4 emissions from highland lakes (elevation > 500 m) only represented 0.4% and 2% of the total lacustrine emissions at the scale of the Amazon basin, respectively. Total CO2 and CH4 emissions from lakes represented a small fraction (8.6%) of total lentic and lotic CO2 and CH4 emissions at the scale of the Amazon basin. The lake and river emissions of CH4 represented ~ 3% of total CH4 emissions from all compartments of the Amazon basin, mainly attributable to wetlands. [ABSTRACT FROM AUTHOR]

Copyright of Environmental & Social Management Journal / Revista de Gestão Social e Ambiental is the property of Environmental & Social Management Journal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The content of sediment-forming minerals in two cores from the eastern (ANS45-37) and western (ANS45-48) parts of the valley of the Vema Fracture Zone is studied using semiquantitative XRD analysis of bulk powder sediment samples. The mineral composition of deep-sea sediments from the Amazone Cone is also analyzed for comparison. It appeared that the average composition of the terrigenous component of both cores (according to prevailing quartz, secondary mica, plagioclase and potassium feldspar, as well as smectite, chlorite, kaolinite, illite) is quite similar and approximately corresponds to the composition of sediments from the Amazon Cone. The ratio of four clay minerals suggests supply of terrigenous material to the Amazon and Orinoco due to erosion of the Andes and humid tropical weathering in the lower courses of the rivers with further transport of the suspended load to the ocean. This material was transported to the valley of the Vema Fracture Zone due to interplay between gravitational flows from the South American continental slope and current of Antarctic Bottom Water. In addition, data on biogenic calcite (planktic foraminiferal tests, nannofossils) and opal A (radiolarians, sponge spicules) have been obtained. In the study area, several authigenic (diagenetic) minerals are identified. In particular, siderite and greigite are first found in the sediments from the Vema valley and Amazon Cone, respectively. [ABSTRACT FROM AUTHOR]

A set of maps from the middle of the sixteenth century featuring the New World, such as those by Jean Rotz (1542), Giacomo Gastaldi (1546), and Jean Bellère (1554), presented a peculiarity regarding the delineation of the Amazon River. Instead of having a latitudinal direction, as dictated by modern cartographic conventions, the Amazon had a longitudinal orientation. This is often assumed to be an inaccurate cartographic representation of the river. However, these maps were rather precise insofar as, according to contemporaneous accounts of South America provided by scholars such as Peter Martyr, Gonzalo Fernández de Oviedo, and Francisco López de Gómara, the Amazon had a potential longitudinal course. In this sense, the author aims to explain the accuracy of some of the early modern cartographies of Amazonia by placing these maps in dialogue with geographic and hydrographic descriptions of the river that circulated at that time. Consequently, this work re-evaluates the notion of precision when applied to the study of the early European mapping of the Amazon River. [ABSTRACT FROM AUTHOR]

Over the past several decades, concern has grown over the rising mortality of the Amazon river dolphin ('boto') from increased human–dolphin interactions. Among these interactions are tourist attractions involving up-close feeding encounters with the botos, confrontations with fishers, and an illegal fishing practice that uses dolphin flesh as fish bait. Drawing on original data sourced from in-depth semi-structured interviews and household surveys, existing studies on boto habitat preferences and seasonal movement, and remotely-sensed data, this paper discusses the spatial and temporal overlap between humans and dolphins in a region outside of Manaus, Amazonas in the central Brazilian Amazon. Results suggest that there is considerable spatial overlap between boto habitat and spaces used for fishing and tourism activities; additionally, overall potential for conflict is greatest during the high-water season. [ABSTRACT FROM AUTHOR]

To examine the alteration of river-derived sediments through a large estuary and the implications for elemental cycling and global climate, this study analyses lithium (Li) isotopes and elemental concentrations (e.g., Li, Na, Mg, K, Ca, Fe and Al) of both the dissolved load and different phases of the sediment load (i.e., exchangeable, carbonate, oxide, clay and residue) in the Amazon estuary. The results show that river-derived sediments remove Li from the dissolved load, largely due to cation retention in secondary clays. By modelling the Li mass-balance and isotope fractionation, we estimate that the river-derived sediments gain 3–4 μg/g Li from the dissolved load in the Amazon estuary, with a Li isotope fractionation factor (α clay-solution) of approximately 0.975. Considering the whole Amazon estuary, the river-derived sediments remove around 3.6–4.8 × 109 g/yr of Li from the dissolved load. Specifically, around 1.0–1.7 × 108 g/yr of Li is removed from river water (∼1.8–3.0% of the dissolved Li discharge flux of the Amazon River) and around 3.5–4.7 × 109 g/yr of Li is removed from seawater, which represents a significant sink from the ocean. This estuarine Li sink is likely to be related to continental erosion rates; thus, continental weathering and erosion regimes could influence not only riverine Li input, but could also directly affect the Li sink, leading to a dual control on the Li budget and isotope composition in the ocean. [ABSTRACT FROM AUTHOR]

Little is known about the effect of the polymodal tide of the Amazon estuary on the phenology of palms. We evaluated the effect of climate/flood and biotic factors on the phenology of 80 Attalea phalerata palms over 1‐year period. Bract emission and young leaves percentage were negatively correlated to accumulated rainfall. Inflorescence and leaf production occurred mainly in the dry season. Immature fruit was positively correlated with rainfall, showing that fruit development occurs during the rainy season. The production of flowers, unripe fruit, and young leaves were positively correlated to flooding. The production of infructescence, per palm, varied from 0 to 4 and 18% of the variance was explained by variables of stem diameter, number of new leaves, altitude, and flood amplitude. The number of infructescence increased for large palms and decreased for individuals subjected to high amplitudes of flooding. These findings reveal that phenological patterns of A. phalerata are driven by seasonal variation in rainfall and flooding. Furthermore, infructescence production can be predicted by plant size and this production is sensitive to variations in flood amplitude. Alteration in rainfall and flooding due to climate change may have a negative impact on fruit production if extreme events increase in frequency. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract River rhythmicity refers to the periodic, recurrent phenomena of a riverscape that are synchronized with the rise and fall of river water, creating regimes of river time. River rhythmicity can serve as a lens into the temporal dimension of river formation and socio‐ecological dynamics that are of great interest to many disciplines. In this paper, we introduce river rhythmicity as a conceptual and analytical framework to unify riparian human communities, academic disciplines and water agencies in approaching research and management of rivers. We also explore how the disruptions to riverine rhythms that are experienced by river‐dwelling communities, and are often visible in river discharge data through time, reconfigure, hinder or sever relationships between people and rivers. To ground our discussion in practical, lived experience, we provide brief descriptions of regimes of river time to demonstrate how rhythmic patterns established with rivers in north‐central Canada and Amazonian Colombia shape the lives of two of our co‐authors. By prioritizing holistic accounts of river rhythms, we can elucidate a fuller range of phenomena and their dynamic interactions, revealing riverscape features that are highly valued by local communities yet not often visible to any one discipline. Rhythmicity provides a conceptual framework to help address several challenges facing river conservation and water allocation dilemmas. By emphasizing relationality, it serves to (a) move beyond a biophysical framing of human‐nature connectedness by demonstrating that dynamic processes and relationships are constitutive of rivers, not derivative of them; (b) enhance understanding of how the temporal dimensions of riverine relationships and river dwelling are experienced; (c) highlight the socio‐cultural consequences of changes to river time and (d) centre socially embedded relationships with rivers forged from generations of observations of care and reciprocity. Read the free Plain Language Summary for this article on the Journal blog.

The western tropical North Atlantic (WTNA) is a very complex region, with the influence of intense western boundary currents in connection with equatorial zonal currents, important atmospheric forcings (e.g Intertropical Convergence Zone), mesoscale activities (e.g NBC rings), and the world’s largest river discharge as the Amazon River runoff. The volume discharge is equivalent to more than one-third of the Atlantic river freshwater input, with a plume that spreads over the region reaching the northwestward Caribbean Sea and eastward longitudes of 30°W, and influencing from physical to biological structures. Therefore, in order to enable and encourage more understanding of the region, here we present a dataset based on an idealized scenario of no river runoff of the Amazon River and Par ́a River in the WTNA. The numerical simulations were conducted with a regional oceanic modeling system (ROMS) model and three pairs of files were generated with the model outputs: (i) ROMS-files, with the parameters of the ROMS-outputs raw data in a NetCDF format and monthly and weekly frequencies; (ii) MATLAB-files, which contain oceanographic parameters also in monthly and weekly frequencies; and (iii) NetCDF-files, with oceanographic parameters again in monthly and weekly frequencies. For each file, we present the coordinates and variable names, descriptions, and correspondent units. The dataset is available in the Science Data Bank repository (doi: https://doi.org/10.57760/sciencedb.02145)

The Amazon River plume plays a critical role in shaping the carbonate chemistry over a vast area in the western tropical North Atlantic. We explore a thought experiment of ocean alkalinity enhancement (OAE) via hypothetical 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 μ mol kg-1 and sample size > 40, given background variability of 15–30 μ mol kg-1. OAE-induced p CO2 reduction at the Amazon plume surface would range between 0–25 μ atm when ΔTA = 20 μ mol kg-1, decreasing with increasing salinity. Adding 20 μ mol kg-1 of alkalinity at the river mouth could elevate the total carbon uptake in the Amazon River plume by 0.07–0.1 MtCO2 month-1. Such thought experiments are useful in designing minimalistic field trials and setting achievable goals for monitoring, reporting, and verification purposes. [ABSTRACT FROM AUTHOR]

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The Brazilian North Coast (BNC) encompasses the intersection of multiple oceanographic features such as strong currents, a large continental shelf under the influence of the Amazon River freshwater and sediment outflow, extensive muddy and sand bottom, as well as a mesophotic reef system. As a result, the BNC hosts a diverse fish fauna, consisting of estuarine and freshwater species, including species endemic to the region. These fish species are distributed across a mosaic of megahabitats within the region. Here, we present the first comprehensive effort to understand the distribution patterns of ray-finned fishes and cartilaginous fishes among these different megahabitats. On 1891 samples, we recorded 616 species from 147 families distributed across five distinct megahabitats. The Continental Slope megahabitat had the highest number of families and consisted primarily of pelagic species, indicating its close association with the open sea. The Sand and Mud megahabitats exhibited high species richness and shared similar generalist fish families in terms of habitat use. The Amazon Plume megahabitat was characterized by freshwater and marine euryhaline species, emphasizing the influence of the Amazon River on the BNC's ecological dynamics. The Reef megahabitat had species closely associated with consolidated substrates and shared many species with the Sand megahabitat. This study offers valuable insights into fish species distribution and composition in the BNC, contributing to biodiversity assessments and conservation efforts in the region. • The Brazilian North Coast present a diverse fish fauna which is significantly influenced by the mosaic of megahabitats. • Species exhibit preferences for specific foraging substrates and/or are influenced by environmental factors. • The discharge of freshwater from the Amazon River mouth seems to play a direct role in defining the megahabitats boundaries. • The Amazon Plume megahabitat confirms the existence of a barrier for non-euryhaline species. • Amazon Plume megahabitat presenting the lowest percentage of species and families, which shows the selective character. [ABSTRACT FROM AUTHOR]

ABSTRACT Phytoplankton is formed by photosynthesizing microorganisms that act as primary producers in distinct water bodies. These include microalgae and cyanobacteria. It is essential to know the phytoplankton in water catchment areas intended for drinking water treatment once their excessive density may result in problems, such as taste and odor in the water, toxin production, filter clogging, and other damages. This study investigated the phytoplankton dynamics and the environmental factors that may influence phytoplankton density in the drinking water catchment zone of Macapá, a city located on the Amazon River mouth. The sampling was carried out monthly from April/2015 to March/2016. The study reports the first detailed information on the phytoplankton in the study area since previously published studies regarded only cyanobacteria. The species Limnothrix planctonica and Aulacoseira granulata may substantially influence the water treatment due to their great abundance in the study area, especially in July and November, when their density peaks occur, respectively. Nevertheless, Aulacoseira granulata is the primary constituent of the phytoplankton biovolume. This study provides biological and sanitary information to guide public administration towards improving the quality and safety of water supply services, and also to increase the biodiversity knowledge of Amazonian phytoplankton.

The contamination with arsenic in Santana led to the perception that the brownish waters of the Amazon River carry arsenic, at a rate higher than 235,000 tonnes per year, and it seems important that this arsenic should be studied in detail. The anomaly was caused by the discharge of tailings of a pellet plant in an excavated sump. These tailings were composed of iron- and arsenic-rich minerals, crystallized at above 900°C in the metallurgical process, which become unstable when submersed in fresh water at pH 5.0-6.0. In the sump, iron, arsenic, manganese, and other metals were slowly solubilized from the minerals, entering the groundwater. When iron got in contact with the water organic compounds, it formed a gel, absorbing As, Mn, and other metals, as it normally happens during weathering in the Amazon. The sump has been built in practically impermeable clayey soil, which made the gel move slowly, giving time to form hard concretions of limonite, characteristic of the Amazonian soil. Iron, manganese, arsenic and other metals were retained in the concretions, and the arsenic-bearing iron gels went for a maximum of some hundreds of meters away from the sump. Soon after the identification of the contamination, the water of the sump was, under close control, discharged into the Amazon River, and the tailings were removed to high ground. In sequence, as it was impossible to properly isolate the tailings, they were sold and shipped away. In the meantime, there were complaints that persons have been affected by arsenic-contaminated water that flowed from a broken dam (that never existed) into a small creek that crossed a community, and that people that consumed the water had cancer. A large medical team was called by the local government, thousands of persons were examined, diseases were found, and none related to arsenic. Analysis of blood and hair presented arsenic in limits worldwide accepted as normal. As samples of the Amazon showed a conspicuous presence of arsenic, they led to the study of the river waters for arsenic. Information is presented to correct misunderstandings present in the literature. Two important points are commented on to understand the event. One is the geological affinity of arsenic with iron. The other is that the toxicity of a solid is determined by how much of the toxic element is liberated for contamination; the standards used for the proper definition of toxicity of a solid are presented.

Aim: The Amazon‐Orinoco plume is the major biogeographical barrier between the Great Caribbean and the Brazilian Province. No study has so far addressed the influence of this barrier in a broad chrono‐phylogenetic context. Here, we evaluate the effects of the Amazon‐Orinoco plume barrier on the patterns of diversification of Western Atlantic reef fishes through time. Location: Tropical Western Atlantic. Taxon: Reef Fishes (Percomorpha). Methods: We compiled DNA sequence data of 21 molecular markers from sister species/population pairs across 33 reef‐fish families in the Greater Caribbean biogeographical region and the Brazilian Province. The data included estimated divergence times between sister‐pairs based on previously published phylogenies and 94 newly proposed time‐trees. Divergence dates were compared with variations in the sedimentation discharge rate of the Amazon River and sea‐level fluctuations. To address the hypothesis that fishes with different adult sizes are affected differently by the Amazon‐Orinoco plume, we used a phylogenetic least squares regression to test the relationship between maximum total body length and divergence times between the Caribbean and Brazilian sister‐pairs. Results: We identified an increase in the rates of lineage diversification between sister‐pairs of the Greater Caribbean and Brazilian Province reef fishes in the past 2.4 million years, in accordance with the period of higher sedimentation rates of the Amazon River and the more frequent sea‐level fluctuations in the Pleistocene. A strong relationship between total body length and effectiveness of the barrier through time was confirmed, with smaller species typically diverging earlier in periods when sedimentation rates of the Amazon River were significantly lower. Conclusions: The strong biogeographical signal detected in this study across different lineages of reef fishes clearly indicates that the Amazon‐Orinoco plume played a significant role in the diversification of the Atlantic reef‐fish fauna. The temporal pattern of diversifications indicates a correlation between the permeability of the plume, sea‐level fluctuations, variability in the volume of the discharge and fish body size, with the barrier's influence being weaker on larger fishes. [ABSTRACT FROM AUTHOR]

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This work aims at analyzing the Negro and Solimões rivers' water meeting in the perspective of geoheritage and its geotouristic potential in the Amazon. inventory of places of hydrological interest - hydrosites, adapted from the proposal by Foleto and Costa (2021), and the Negro and Solimões rivers' water meeting's geotouristic potential was based on studies developed by Manosso (2012). The relevance of the theme and the lack of studies on hydrological geopathology, especially in the Amazon, the site of the largest hydrographic basin, the longest river in length and several hydrosites, such as the Negro and Solimões rivers' water meeting. The research showed that despite the aforementioned point having wide visibility and being known, even by name, it does not have legal instruments that actually protect and safeguard it from being impacted. From the point of view of geoheritage, Negro and Solimões rivers' water meeting has a hydrosite for presenting a value of 76.45% for the inventory of places of hydrological interest. And regarding geotourism purposes, its characteristics can be well used for teaching geosciences, since it enables the teaching of geological-geomorphological, hydrological, socio-spatial dynamics and biodiversity phenomena, for students (from basic and higher education) and lay people, like tourists. Therefore, this article is relevant, not only for the advancement of studies related to geodiversity in the Amazon, but also for the popularization of geotourism in this context. [ABSTRACT FROM AUTHOR]

Anablepsoides is a widely distributed Neotropical killifish genus found in shallow streams, in both dense forests and open areas, throughout northern and northeastern South America. The phylogenetic and biogeographic relationships of the genus are here analysed, based on two nuclear and four mitochondrial genes of 26 species and six out‐groups. The origin of Anablepsoides was recovered in Early Miocene in an area corresponding to the Paleo‐Amazon‐Orinoco system. The current analyses indicate that the initial diversification of the genus in two main clades was associated with marine transgressions related to the formation of the Pebas mega‐wetland isolating each MRCA of those main clades in the upper Amazon river basin and river basins of the Guiana Shield. The diversification of the genus and the colonisation of new areas may be associated with Miocene and Pliocene events such as changes in the sea level, formation and extinction of wetlands, rupture of the Purus arch and Amazon river assuming the current flow to the East. Also, the evolution of Anablepsoides could be associated with the diversification of several other Neotropical lineages, so that the present study leads to a better understanding of the evolution of the Neotropical freshwater biota and South American geological history. [ABSTRACT FROM AUTHOR]

Some of the main obstacles to the conquest and colonization of America by European powers were the scarce knowledge of the territory and the hostility of indigenous ethnic groups to its presence. Over the years, remarkable characters played the role of explorers and applying empirical methods began the survey of the territory, using the data collected and with the methods available on that time the first maps were delineated. Nearly two centuries passed and maps of South America with the Amazon River and its hydrographic basin as one of the centrals elements began to be produced by religious and scientific personalities. The purposes were totally different, but the expected result was a reliable representation of the area. Through the use of geographic information system programs and specialized software in map comparison, a temporal and comparative analysis of five old maps of the region published in the eighteenth century was carried out, with which in a graphical way the reader can visualize the updates of the mapped geographic elements and the accuracy of the work. Likewise, the selected area was digitalized and the basic cartography of each map with its respective database was created. In order to visualize the information generated through a virtual environment, a Story Map Journal in ArcGIS Online was created, it includes a summary about the life of each author, a description and the bibliographic reference of the map made, and the map compared to current data. [ABSTRACT FROM AUTHOR]

Some of the main obstacles to the conquest and colonization of America by European powers were the scarce knowledge of the territory and the hostility of indigenous ethnic groups to its presence. Over the years, remarkable characters played the role of explorers and applying empirical methods began the survey of the territory, using the data collected and with the methods available on that time the first maps were delineated. Nearly two centuries passed and maps of South America with the Amazon River and its hydrographic basin as one of the centrals elements began to be produced by religious and scientific personalities. The purposes were totally different, but the expected result was a reliable representation of the area. Through the use of geographic information system programs and specialized software in map comparison, a temporal and comparative analysis of five old maps of the region published in the eighteenth century was carried out, with which in a graphical way the reader can visualize the updates of the mapped geographic elements and the accuracy of the work. Likewise, the selected area was digitalized and the basic cartography of each map with its respective database was created. In order to visualize the information generated through a virtual environment, a Story Map Journal in ArcGIS Online was created, it includes a summary about the life of each author, a description and the bibliographic reference of the map made, and the map compared to current data.

This paper traces the sixteenth-century addition and removal on maps of a bulge on the southern coast of Chile. Abraham Ortelius was primarily responsible for these changes and many cartographers followed his lead. Then, Ortelius rotated the coastline of Chile from northwest to north. Later, he dropped the latitude of the islands of San Pablo and Isla de los Tiburones down six degrees. He named the Amazon River “Río de las amazons.” Finally, he removed the cities with fake Native-American-sounding names along the Pacific coast of North America. The research underlying this paper examined over seven-hundred sixteenth-century maps made by sixdozen cartographers. This paper cites five-dozen maps by four-dozen cartographers. In the traceability section of this paper, this information was condensed into a traceability diagram, which shows the chronological flow of information among a score of cartographers. Using this information, this paper traced the influence of one cartographer on another: it showed who influenced whom. It showed the spread of knowledge. Ortelius was at the center of most of this knowledge explosion. [ABSTRACT FROM AUTHOR]

Understanding the direct and indirect effects of niche and neutral processes in structuring species diversity is particularly challenging because environmental factors are often geographically structured. Here, we used Structural Equation Modeling to quantify direct and indirect effects of geographic distance, the Amazon River's opposite margins, and environmental differences in temperature, precipitation, and vegetation density (Normalized Difference Vegetation Index—NDVI) on ant beta diversity (Jaccard's dissimilarity) across Amazon basin. We used a comprehensive survey of ground-dwelling ant species from 126 plots distributed across eight sampling sites along a broad environmental gradient. We found that geographic distance and NDVI differences were the major direct predictors of ant composition dissimilarity. The major indirect effect was that of temperature through NDVI, whereas precipitation neither had direct or indirect detectable effects on beta diversity. Thus, ant compositional dissimilarity seems to be mainly driven by a combination of isolation by distance (through dispersal limitation) and selection imposed by vegetation density, and indirectly, by temperature. Our results suggest that neutral and niche processes have been similarly crucial in driving the current beta diversity patterns of Amazonian ground-dwelling ants. [ABSTRACT FROM AUTHOR]

Rivers connect the carbon cycle in land with that in aquatic ecosystems by transporting and transforming terrestrial organic matter (TeOM). The Amazon River receives huge loads of TeOM from the surrounding rainforest, promoting a substantial microbial heterotrophic activity and consequently, CO2 outgassing. In the Amazon River, microbes degrade up to 55% of the lignin present in the TeOM. Yet, the main microbial genomes involved in TeOM degradation were unknown. Here, we characterize 51 population genomes (PGs) representing some of the most abundant microbes in the Amazon River deriving from 106 metagenomes. The 51 reconstructed PGs are among the most abundant microbes in the Amazon River, and 53% of them are not able to degrade TeOM. Among the PGs capable of degrading TeOM, 20% were exclusively cellulolytic, while the others could also oxidize lignin. The transport and consumption of lignin oxidation byproducts seemed to be decoupled from the oxidation process, being apparently performed by different groups of microorganisms. By connecting the genomic features of abundant microbes in the Amazon River with the degradation machinery of TeOM, we suggest that a complex microbial consortium could explain the quick turnover of TeOM previously observed in this ecosystem. [ABSTRACT FROM AUTHOR]

Objective: To evaluate two methods to estimate dry matter availability in mixed pastures in the Amazon region, Peru. Materials and Methods: The traditional method and the electronic capacitance method with Grass Master Pro equipment were used. A complete randomized block design was used, with two sources of variation: five pastures, three evaluation periods (20, 40 and 60 days) and the average of 15 observation units per pasture. A variance analysis and multiple comparisons of means were performed using Tukey's test: 5 % probability to compare the existence of significant differences among means. Linear and polynomial regression were also used to estimate the relationship between the two methods. For data processing and analysis, the statistical program R was used. Results: Actual dry matter values were obtained using the quadrat method. The traditional method and the electronic capacitance method showed significant differences (p < 0,05). Dry matter availability by the traditional method was 3 530,3 kg DM/ha and by the capacitance method 3 942,4 kg DM/ha. With the linear regression, a determination coefficient of R² = 0,87 was obtained and with the polynomial regression, of R² = 0,93. Conclusions: The electronic capacitance method reported average dry matter measurements in the pasture, significantly higher than the traditional method, and showed desirable and concordant characteristics for its use in animal husbandry activity. [ABSTRACT FROM AUTHOR]

This article introduces questions about repatriation of archaeological objects from Brazil and presents the project 'Atlas of Lost Finds' as an exploratory methodology to deal with symbolic restitution and open access to archaeological items that are currently invisible in foreign museums. A premise of this project is that Amazonian archaeological objects are vectors of ancestry and cosmological knowledge of indigenous peoples of the present and therefore we must listen to them about the meanings of these objects and implications for their musealization, restitution or repatriation. We then present an interview on the subject with the Guarani Nhandeva curator Sandra Benites, within the scope of the project still in progress. [ABSTRACT FROM AUTHOR]

River flows are an essential component of the water cycle and are directly accessible for human consumption and activities. River water flux (i.e., river discharge) not only can be measured locally at in situ gauges but also can be estimated at larger scales with the river routing models. However, the number of in situ gauges is declining worldwide while emerging river-related products from satellites are becoming more available. Especially, discharge products based on satellite altimetry water elevations are emerging. These altimetry missions provide different spatial and temporal coverages and may not provide the same amount of information. In this study, discharge products from two satellite altimetry missions (ENVISAT and JASON-2) were assimilated into the large-scale hydrologic model Intéractions Sol-Biosphére-Atmosphére-CNRM’s Total Runoff and Integrating Pathways (ISBA-CTRIP) using an ensemble Kalman filter, to correct the simulated discharge. This work investigates whether it is better to assimilate products with a dense spatial coverage but a lower temporal sampling (ENVISAT) or the opposite (JASON-2). Three experiments have been performed: the first two assimilated each product separately, and the last one assimilated the combined product. The open-loop normalized root-mean-square error evaluated against in situ discharge (RMSEn) is 69%. RMSEn is decreased for all experiments. Specifically, it is slightly lower when assimilating ENVISAT-based discharge product (51%) than JASON-2 product (53%) as the ENVISAT-based product spatial coverage is denser. The best results are obtained when both products are assimilated (RMSEn=49%). These results are very encouraging and could be improved when the future Surface Water and Ocean Topography (SWOT) wide swath altimetry mission discharge product will be available. [ABSTRACT FROM AUTHOR]

As the largest river basin on Earth, the Amazon is of major importance to the world's climate and water resources. Over the past decades, advances in satellite‐based remote sensing (RS) have brought our understanding of its terrestrial water cycle and the associated hydrological processes to a new era. Here, we review major studies and the various techniques using satellite RS in the Amazon. We show how RS played a major role in supporting new research and key findings regarding the Amazon water cycle, and how the region became a laboratory for groundbreaking investigations of new satellite retrievals and analyses. At the basin‐scale, the understanding of several hydrological processes was only possible with the advent of RS observations, such as the characterization of "rainfall hotspots" in the Andes‐Amazon transition, evapotranspiration rates, and variations of surface waters and groundwater storage. These results strongly contribute to the recent advances of hydrological models and to our new understanding of the Amazon water budget and aquatic environments. In the context of upcoming hydrology‐oriented satellite missions, which will offer the opportunity for new synergies and new observations with finer space‐time resolution, this review aims to guide future research agenda toward integrated monitoring and understanding of the Amazon water from space. Integrated multidisciplinary studies, fostered by international collaborations, set up future directions to tackle the great challenges the Amazon is currently facing, from climate change to increased anthropogenic pressure. Plain Language Summary: The Amazon basin is the largest river basin in the world, characterized by complex hydrological processes that connect high rates of precipitation, extensive floodplains, dense tropical forests, complex topography, and large variations in freshwater storage and discharge. It plays a key role in the water, energy, and carbon cycles and interacts with the global climate system. Earth observations have played a major role in supporting research in Amazon hydrology, and the characterization of several hydrological processes was only possible with the help of remote sensing data. The basin is now facing great risk under current climate change and increased anthropogenic pressure and the resulting environmental alterations require a better understanding of the overall basin's water cycle across scales. We review the strengths and limitations of observations from satellites in the context of the current and upcoming hydrology‐oriented satellite missions, and we make recommendations for improving satellite observations of the Amazon basin water cycle, along with an interdisciplinary and stepwise approach to guide research for the next decades. Key Points: Integrated view of scientific advances in Amazon hydrology with remote sensingExpected progress to understand the water cycle, aquatic ecosystems, and environmental changes with upcoming hydrology‐oriented missionsNeed to translate advanced knowledge from remote sensing to support water management and environmental governance [ABSTRACT FROM AUTHOR]

Abstract Background The Amazon River is one of the largest in the world and receives huge amounts of terrestrial organic matter (TeOM) from the surrounding rainforest. Despite this TeOM is typically recalcitrant (i.e. resistant to degradation), only a small fraction of it reaches the ocean, pointing to a substantial TeOM degradation by the river microbiome. Yet, microbial genes involved in TeOM degradation in the Amazon River were barely known. Here, we examined the Amazon River microbiome by analysing 106 metagenomes from 30 sampling points distributed along the river. Results We constructed the Amazon River basin Microbial non-redundant Gene Catalogue (AMnrGC) that includes ~ 3.7 million non-redundant genes, affiliating mostly to bacteria. We found that the Amazon River microbiome contains a substantial gene-novelty compared to other relevant known environments (rivers and rainforest soil). Genes encoding for proteins potentially involved in lignin degradation pathways were correlated to tripartite tricarboxylates transporters and hemicellulose degradation machinery, pointing to a possible priming effect. Based on this, we propose a model on how the degradation of recalcitrant TeOM could be modulated by labile compounds in the Amazon River waters. Our results also suggest changes of the microbial community and its genomic potential along the river course. Conclusions Our work contributes to expand significantly our comprehension of the world’s largest river microbiome and its potential metabolism related to TeOM degradation. Furthermore, the produced gene catalogue (AMnrGC) represents an important resource for future research in tropical rivers. Video abstract.

Abstract 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.

The article discusses the devastating effects of the invasive golden mussel Limnoperna fortunei as it spreads through South American rivers including the Amazon basin. Topics include the discovery of the invasive species by biologist Maria Christina Dreher Mansur at the Lake Guaiba in Brazil in the 1990s, how the species invaded lakes, fisheries, hydroelectric dams and the Amazon basin and its tributaries, and the estimated population of golden mussels invading the La Plata River in Argentina.

Urban areas in the Brazilian Amazon have grown at an unprecedented rate during the last years. About 90% of the wastewater produced by these urban areas are discharged untreated into Amazonian freshwater ecosystems, constituting a potential environmental pathway for pharmaceuticals and other chemicals consumed by modern societies (e.g. psychostimulants, personal-care products, hormones). The distribution of these chemicals into the Amazon River and their potential risks for freshwater biodiversity have not been evaluated so far. Here, we show the results of the largest chemical monitoring campaign conducted in the Amazon region. We assessed exposure patterns for 43 pharmaceuticals and other urban contaminants in 40 sampling sites distributed along the Amazon River, three major tributaries (Negro, Tapajós and Tocantins Rivers), and four large cities of the Brazilian Amazon (Manaus, Santarém, Macapá, Belém). We assessed risks for freshwater biodiversity using species sensitivity distributions and mixture toxicity approaches. We found that urban areas constitute important hot-spots for chemical contamination, with mixtures containing up to 40 different compounds and exposure concentrations reaching the world’s maxima for some of them. We show that chemical pollution can result in long-term effects for up to 50–80% of aquatic species next to urban areas. Moreover, we identified several ubiquitous compounds which can be used as tracers of anthropogenic pressure in the Amazon basin. We conclude that the chemical burden created by urbanization significantly contributes to a biodiversity loss in the region and should be further controlled.

We investigated the interaction between surface conditions and precipitating convection by comparing the Amazon River against the surrounding forest. Despite similar synoptic conditions within a few tens of kilometers, the river surface is substantially cooler than the surrounding forest during the day and warmer at night. We analyzed 20 years of high‐resolution satellite precipitation data and confirmed previous findings of daytime rainfall reduction over the river for the whole Amazon Basin. The percentage reduction is strongest during the dry‐to‐wet transition season. In addition, the percentage reduction of individual tributary is significantly correlated with the Laplacian of surface temperature, which causes thermally driven surface divergence and suppresses local convection. Additionally, nighttime rainfall is enhanced over tributaries near the Atlantic coast during the wet season. A regional climate model then simulates the local rainfall anomalies associated with the river. Above the river, moisture diverges near the surface and converges above the surface before the daytime rainfall, partially driven by the horizontal gradient of humidity. Unlike the river, moisture convergence within the boundary layer is more critical for the rainfall above the forest region. Our studies suggest that strong thermal contrast can be important in deriving heterogeneous convection in moist tropical regions. Plain Language Summary: To understand how surface types and surface conditions influence precipitation and cloud processes, we compared rainfall characteristics between the Amazon River and its surrounding rainforest using satellite observations and a regional climate model. With similar large‐scale meteorological conditions, a much cooler river surface is shown to reduce daytime rainfall relative to the forest. By contrast, the warmer river surface at night contributes to higher nighttime rainfall in some tributaries near the coast. The climate model further suggests that daytime rain over the river relies on moisture sources above the surface, whereas above the rainforest most moisture converges near the surface. Key Points: Daytime rainfall is suppressed over the Amazon River compared with the surrounding forestThe reduction of daytime rainfall is inversely correlated with the Laplacian of surface temperatureDaytime rain over the river needs moisture convergence above the surface, while above the forest, most moisture converges near the surface [ABSTRACT FROM AUTHOR]

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As climate‐driven El Niño Southern Oscillation (ENSO) events are projected to increase in frequency and severity, much attention has focused on impacts regarding ecosystem productivity and carbon balance in Amazonian rainforests, with comparatively little attention given to carbon dynamics in fluvial ecosystems. In this study, we compared the wet 2012 La Niña period to the following normal hydrologic period in the Amazon River. Elevated water flux during the La Niña period was accompanied by dilution of inorganic ion concentrations. Furthermore, the La Niña period exported 2.77 Tg C yr−1 more dissolved organic carbon (DOC) than the normal period, an increase greater than the annual amount of DOC exported by the Mississippi River. Using ultra‐high‐resolution mass spectrometry, we detected both intra‐ and interannual differences in dissolved organic matter (DOM) composition, revealing that DOM exported during the dry season and the normal period was more aliphatic, whereas compounds in the wet season and following the La Niña event were more aromatic, with ramifications for its environmental role. Furthermore, as this study has the highest temporal resolution DOM compositional data for the Amazon River to‐date we showed that compounds were highly correlated to a 6‐month lag in Pacific temperature and pressure anomalies, suggesting that ENSO events could impact DOM composition exported to the Atlantic Ocean. Therefore, as ENSO events increase in frequency and severity into the future it seems likely that there will be downstream consequences for the fate of Amazon Basin‐derived DOM concurrent with lag periods as described here. Plain Language Summary: Increases in atmospheric carbon concentrations originate from many sources and pose a serious threat to global ecosystem health and humanity. The Amazon River delivers one‐fifth of global discharge and represents the largest single flux of dissolved organic carbon (DOC) from land to ocean. As climate change is projected to increase precipitation anomalies throughout the Amazon, flooding and droughts will become more frequent and severe, disrupting the natural seasonal rhythm of the Amazon River. We demonstrate that precipitation anomalies in South America (caused by La Niña) exported an additional amount of DOC from the Amazon River to the Atlantic Ocean than the Mississippi River exports annually. Organic compounds mobilized during the La Niña were more aromatic, presumably from terrestrial sources. These compositions, measured near the mouth of the Amazon River, arrived six months after Pacific sea‐surface temperature and pressure anomalies indicated the onset of La Niña, highlighting the lag time that events in the Pacific take to impact the Atlantic Ocean. Key Points: The Amazon River during a La Niña year exports an additional amount of dissolved organic carbon than the Mississippi exports annuallyThe Amazon River dissolved organic matter composition in a La Niña year was more oxidized and aromatic than during a non‐ENSO yearThe dissolved organic matter composition in the Amazon River correlates to a 6‐month lag with La Niña indices [ABSTRACT FROM AUTHOR]

The Manacapuru hydrometric gauge station has been used for more than 30 years by the Brazilian National hydrometric network to provide data on the Solimões-Amazon River. At this place, the Solimões river average water discharge is about 103,000 m³ s-1, the mean width is 3,000 m and the mean depth is 20 m. The gauge station record represents the whole upstream contribution of the total suspended solids (TSS) from the Solimões basin, whose total area is approximately 2 x 106 km2, representing a runoff of 0.48 m³ s-1 km-2. TSS annual flow is approximately 400 x 106 t. The systematic TSS sampling procedures traditionally used at the Brazilian hydrometric network has limitations, some of them being related to local effects affecting the TSS flow. This article aims to study the local variability of TSS flow at Manacapuru station. The study was conducted in the scope of MESASOL and PIATAM IV projects, whose objectives are precisely to consider alternative methods for TSS flow assessment in the Amazon basin. It was identified that local geologic-geomorphologic features are related with the TSS flux spatial variability at the vicinity of the Manacapuru section. This results induce a new interpretation to the general sediment flux for the Solimões river basin, were local flux can’t be see as a total flux from the hole up-stream river basin.

Didiscus Dendy, 1922 and Myrmekioderma Ehlers, 1870 are closely related genera of axinellid sponges, distinguished mainly by the presence of didiscorhabd microscleres in Didiscus and of trichodragmata in Myrmekioderma. Their family-level classification, however, is highly controversial, in part because their specific and morphological diversities are still poorly known. Here, we redescribed Didiscus oxeatus Hechtel, 1983 based on new specimens and revision of the holotype, described two new species of Didiscus and two new species of Myrmekioderma from off the Amazon and São Francisco river mouths in Northern and Northeastern Brazil. These two areas in the Tropical Atlantic (TA) are still understudied, especially when considering their high environmental and economic importance. We observed for the first time the presence of tylostyles in the holotype of D. oxeatus, as well as in the new specimens from Sergipe State. Didiscus pseudoverdensis sp. nov. has thick, strongly spined didiscorhabds with sharp ends; Didiscus raraediscus sp. nov. has small microspined oxeas; Myrmekioderma guajajara sp. nov. has microxeas and verrucose small oxeas; and Myrmekioderma tenax sp. nov. has both raphidiform and sinuous oxeas. The morphological diversities of both genera are expanded by the addition of new spicule types and ornamentations. Morphological data indicated that both Didiscus and Myrmekioderma should be classified in the family Heteroxyidae, in contrast to previous molecular studies, which suggest that they could belong at least in part to Raspailiidae. These two families and the genus Myrmekioderma are probably polyphyletic and need revision. The number of species of Didiscus and Myrmekioderma worldwide is raised to 11 and 13, respectively, of which five species of Didiscus and six of Myrmekioderma occur in the TA. Most species have narrow distributions, probably reflecting the low sampling effort. This study provides a more accurate picture of the biodiversity and distribution of Didiscus and Myrmekioderma in the TA and reinforces the importance of scientific explorations in understudied areas such as off the mouths of the Amazon and São Francisco rivers. [ABSTRACT FROM AUTHOR]

The Amazon River drains a diverse tropical landscape greater than 6 million km2, culminating in the world's largest export of freshwater and dissolved constituents to the ocean. Here, we present dissolved organic carbon (DOC), organic and inorganic nitrogen (DON, DIN), orthophosphate (PO43−), and major and trace ion concentrations and fluxes from the Amazon River using 26 samples collected over three annual hydrographs. Concentrations and fluxes were predominantly controlled by the annual wet season flood pulse. Average DOC, DON, DIN, and PO43− fluxes (±1 s.d.) were 25.5 (±1.0), 1.14 (±0.05), 0.82 (±0.03), and 0.063 (±0.003) Tg yr−1, respectively. Chromophoric dissolved organic matter absorption (at 350 nm) was strongly correlated with DOC concentrations, resulting in a flux of 74.8 × 106 m−2 yr−1. DOC and DON concentrations positively correlated with discharge while nitrate + nitrite concentrations negatively correlated, suggesting mobilization and dilution responses, respectively. Ammonium, PO43−, and silica concentrations displayed chemostatic responses to discharge. Major and trace ion concentrations displayed clockwise hysteresis (except for chloride, sodium, and rubidium) and exhibited either dilution or chemostatic responses. The sources of weathered cations also displayed seasonality, with the highest proportion of carbonate‐ and silicate‐derived cations occurring during peak and baseflow, respectively. Finally, our seasonally resolved weathering model resulted in an average CO2 consumption yield of (3.55 ± 0.11) × 105 mol CO2 km−2 yr−1. These results represent an updated and temporally refined quantification of dissolved fluxes that highlight the strong seasonality of export from the world's largest river and set a robust baseline against which to gauge future change. Key Points: Concentrations/fluxes of dissolved carbon, nitrogen, phosphorus, and major/trace ions were predominantly controlled by annual flood pulseMean Amazon River dissolved organic carbon flux was 25.5 teragrams per yearAnnual carbonate + silicate weathering CO2 consumption yield was 3.55 × 105 moles carbon dioxide per square kilometer [ABSTRACT FROM AUTHOR]