Eastern Amazon Basin Research Articles

A novel post-1950 CE atmospheric 14C record for the tropics using absolutely dated tree rings in the equatorial Amazon

In this study, we present a comprehensive atmospheric radiocarbon (14C) record spanning from 1940 to 2016, derived from 77 single tree rings of Cedrela odorata located in the Eastern Amazon Basin (EAB). This record, comprising 175 high-precision 14C measurements obtained through accelerator mass spectrometry (AMS), offers a detailed chronology of post-1950 CE (Common Era) 14C fluctuations in the Tropical Low-Pressure Belt (TLPB). To ensure accuracy and reliability, we included 14C-AMS results from intra-annual successive cuts of the tree rings associated to the calendar years 1962 and 1963 and conducted interlaboratory comparisons. In addition, 14C concentrations in 1962 and 1963 single-year cuts also allowed to verify tissue growth seasonality. The strategic location of the tree, just above the Amazon River and estuary areas, prevented the influence of local fossil-CO2 emissions from mining and trade activities in the Central Amazon Basin on the 14C record. Our findings reveal a notable increase in 14C from land-respired CO2 starting in the 1970s, a decade earlier than previously predicted, followed by a slight decrease after 2000, signaling a transition towards the fossil fuel era. This shift is likely attributed to changes in reservoir sources or global atmospheric dynamics. The EAB 14C record, when compared with a shorter record from Muna Island, Indonesia, highlights regional differences and contributes to a more nuanced understanding of global 14C variations at low latitudes. This study not only fills critical spatial gaps in existing 14C compilations but also aids in refining the demarcation of 14C variations over South America. The extended tree-ring 14C record from the EAB is pivotal for reevaluating global patterns, particularly in the context of the current global carbon budget, and underscores the importance of tropical regions in understanding carbon-climate feedbacks.

The South American Tropopause Aerosol Layer (SATAL)

Abstract The presence of an aerosol layer in the upper troposphere/lower stratosphere (UT/LS) in South America was identified with the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2). This layer, which we shall refer to as the South American tropopause aerosol layer (SATAL), was identified over the Amazon basin at altitudes between 11 and 14 km. It exhibits a seasonal behavior similar to the Asian tropopause aerosol layer (ATAL) and the North American tropopause aerosol layer (NATAL). The SATAL is observed from October to March, coinciding with the presence of the South American monsoon. It forms first in the eastern Amazon basin in October, then moves to the southern Amazon, where it weakens in December–January and finally dissipates in February–March. We hypothesize that two main factors influence the SATAL formation in the UT/LS: 1) the source of aerosols from Africa and 2) the updraft mass flux from deep convective systems during the active phase of the South American monsoon system that transports aerosols to the UT/LS. Further satellite observations of aerosols and field campaigns are needed to provide useful information to find the origin and composition of the aerosols in the UT/LS during the South American monsoon.

The Complete Mitogenome of Amazonian Hyphessobrycon heterorhabdus (Characiformes: Characidae) as a Valuable Resource for Phylogenetic Analyses of Characidae

Hyphessobrycon heterorhabdus (Ulrey, 1894), popularly known as ‘Flag Tetra’ in English speaking countries, belongs to the genus Hyphessobrycon of the family Characidae, and is widely present in the eastern Amazon basin. Here, using Illumina sequencing, we report the complete mitogenome sequence of H. heterorhabdus. Overall, the mitogenome has 17,021 bp, containing 13 protein-coding, 22 tRNA, and 2 rRNA genes. Non-ambiguous nucleotide compositions of the H. heterorhabdus mitogenome are A: 29.2%, T: 29.4%, G: 15.6%, and C: 25.8%. As recently indicated, the phylogenetic analyses did not support four separate genera (Hemigrammus, Hyphessobrycon, Moenkhausia, and Psalidodon) of Characidae. Understanding the H. heterorhabdus mitogenome is important for taxonomic purposes as well as for the molecular characterization of environmental pollutants. Thus, the mitogenome described here will be a valuable resource for studies on environmental changes, evolutionary genetics, species delimitation, and phylogenetic analyses in Characidae.

Time Ring Data: Definition and Application in Spatio-Temporal Analysis of Urban Expansion and Forest Loss

Remote sensing can provide spatio-temporal continuous Earth observation data and is becoming the main data source for spatial and temporal analysis. Remote sensing data have been widely used in applications such as meteorological monitoring, forest investigation, environmental health, urban planning, and water conservancy. While long-time-series remote sensing data are used for spatio-temporal analysis, this analysis is usually limited because of the large data volumes and complex models used. This study intends to develop an innovative and simple approach to reveal the spatio-temporal characteristics of geographic features from the perspective of remote sensing data themselves. We defined an efficient remote sensing data structure, namely time ring (TR) data, to depict the spatio-temporal dynamics of two common geographic features. One is spatially expansive features. Taking nighttime light (NTL) as an example, we generated a NTL TR map to exhibit urban expansion with spatial and temporal information. The speed and acceleration maps of NTL TR data indicated extraordinary expansion in the last 10 years, especially in coastal cities and provincial capitals. Beijing, Tianjin, Hebei Province, Shandong Province, and Jiangsu Province exhibited fast acceleration of urbanization. The other is spatially contractive features. We took forest loss in the Amazon basin as an example and produced a forest cover TR map. The speed and acceleration were mapped in two 10-year periods (2000–2010 and 2010–2020) in order to observe the changes in Amazon forest cover. Then, combining cropland TR data, we determined the consistency of the spatio-temporal variations and used a linear regression model to detect the association between the acceleration of cropland and forest. The forest TR map showed that, spatially, there was an apparent phenomenon of forest loss occurring in the southern and eastern Amazon basin. Temporally, the speed of forest loss was more drastic between 2000 and 2010 than that in 2010–2020. In addition, the acceleration of forest loss showed a dispersed distribution, except for in Bolivia, which demonstrated a concentrated regional acceleration. The R-squared value of the linear regression between forest and cropland acceleration reached 0.75, indicating that forest loss was closely linked to the expansion of cropland. The TR data defined in this study not only optimized the use of remote sensing data, but also facilitated their application in spatio-temporal integrative analysis. More importantly, multi-field TR data could be jointly applied to explore the driving force at spatial and temporal scales.

The impact of urbanization and domestic waste on a small watercourse in the eastern Amazon basin

The present study shows the physical and chemical parameters collected in an urban river in the Eastern Amazon, they present the characteristics of the waters in the Neblina stream, which has its basin inserted in an urban center, in the city of Araguaína - TO. Therefore, the present study aims to investigate the water quality parameters of that stream, and thus allow deductions about the causes and effects of these changes. In this stream, sampling points were listed that contemplate environments from the springs to its mouth. Being, the quality of its waters, evaluated in two stages that envision two seasons (dry and rainy), respectively, August 2020 and March 2021. Adding a total of six sampling points, systematically visited in both seasons described, making up 12 samples, for all parameters analyzed here. In this way, the samples were explored in order to find values for the parameters: In Situ (Turbidity by turbidimeter; Dissolved oxygen; Electrical conductivity; Water temperature; Air temperature; pH); and Ex Situ (BOD; COD; Nitrogen series; Phosphate series; Fecal coliforms; Chlorophyll-α; Heavy metals). The parameters showed similar variations between the sampling points, with a notable data discrepancy between the mouth and head of the Neblina stream. These results show that there are higher concentrations for these parameters, directly related to the length of the route in the urban environment. Indicating a possible impact on the existing fauna and flora, which may conjecture a plausible toxicity and risks to organisms, as an admissible threat to biodiversity.

Psammothidium elnatanianum sp. nov. (Achnanthidiaceae, Bacillariophyta) a new diatom species found in Holocene sediments (Meghalayan Age) of the Xingu River, Eastern Amazon

ABSTRACT An unknown species of Psammothidium (Achnanthidiaceae) was found in core sediment (~4000 cal yr BP) collected from Xingu ria, located in eastern Amazon Basin (Brazilian Amazon). The detailed morphology of the new species was examined and described using light (LM) and scanning electron (SEM) microscopy. The new species described here is mainly characterized by small valve dimensions, an irregular and expanded central area in rapheless valve (RLV) clearly visible in LM. Under SEM observations, the new species show slightly radiate striae with rectangular to rounded areolae present both on the surface and the valve mantle. Morphology and ecology of the new species is compared to those already described for the genus. Moreover, information about core chronology and the co-occurrence of other diatom species in the sample are also provided.

Density and Abundance Estimation of Amazonian River Dolphins: Understanding Population Size Variability

The dolphins Inia geoffrensis—boto and Sotalia fluviatilis—tucuxi are threatened cetaceans inhabiting river ecosystems in South America; population numbers are still lacking for many areas. This paper provides density and abundance estimations of boto and tucuxi in 15 rivers sampled during the past nine years as part of a multinational research alliance. Visual boat-survey data collection protocols and analyses have been developed since 2012 (based on Distance Sampling methods) and recently reviewed (2019) to improve robustness and comparability. Differences across the sampled rivers and the analyzed river basins (Amazon and Orinoco) pointed to a density/population size gradient with lower densities and abundances observed in the Orinoco basin (0.9–1.5 ind./km²), passing through the eastern Amazon basin (2–5 ind./km²), and the largest numbers found at the central Brazilian Amazon (lower Purus River—2012 (14.5 boto/km², N = 7672; 17.1 tucuxi/km², N = 9238)). However, in other parts of the central Amazon, the density of dolphins was smaller than expected for high productive whitewater rivers (1–1.7 ind./km² in the Japurá and Solimões rivers). We attributed these differences to specific features of the basin (e.g., hydro-geomorphology) as well as to the cumulative effects of anthropogenic activities.

Large and increasing methane emissions from eastern Amazonia derived from satellite data, 2010–2018

Abstract. We use a global inverse model, satellite data and flask measurements to estimate methane (CH4) emissions from South America, Brazil and the basin of the Amazon River for the period 2010–2018. We find that emissions from Brazil have risen during this period, most quickly in the eastern Amazon basin, and that this is concurrent with increasing surface temperatures in this region. Brazilian CH4 emissions rose from 49.8 ± 5.4 Tg yr−1 in 2010–2013 to 55.6 ± 5.2 Tg yr−1 in 2014–2017, with the wet season of December–March having the largest positive trend in emissions. Amazon basin emissions grew from 41.7 ± 5.3 to 49.3 ± 5.1 Tg yr−1 during the same period. We derive no significant trend in regional emissions from fossil fuels during this period. We find that our posterior distribution of emissions within South America is significantly and consistently changed from our prior estimates, with the strongest emission sources being in the far north of the continent and to the south and south-east of the Amazon basin, at the mouth of the Amazon River and nearby marsh, swamp and mangrove regions. We derive particularly large emissions during the wet season of 2013/14, when flooding was prevalent over larger regions than normal within the Amazon basin. We compare our posterior CH4 mole fractions, derived from posterior fluxes, to independent observations of CH4 mole fraction taken at five lower- to mid-tropospheric vertical profiling sites over the Amazon and find that our posterior fluxes outperform prior fluxes at all locations. In particular the large emissions from the eastern Amazon basin are shown to be in good agreement with independent observations made at Santarém, a location which has long displayed higher mole fractions of atmospheric CH4 in contrast with other basin locations. We show that a bottom-up wetland flux model can match neither the variation in annual fluxes nor the positive trend in emissions produced by the inversion. Our results show that the Amazon alone was responsible for 24 ± 18 % of the total global increase in CH4 flux during the study period, and it may contribute further in future due to its sensitivity to temperature changes.

New Ecuadorian records of the eyeless banjo catfish Micromyzon akamai (Siluriformes: Aspredinidae) expand the species range and reveal intraspecific morphological variation.

Two specimens of Micromyzon akamai, an eyeless and miniaturized species previously known only from the deep channels of the eastern Amazon basin in Brazil, are reported from the Curaray River, a tributary of the Napo River in Ecuador. The new specimens are the first records of Micromyzon in the headwaters of the Amazon River and the first records of M. akamai outside Brazil. External morphological characters and a phylogenetic analysis of cytochrome c oxidase I (coI) gene support the identification of the new specimens as M. akamai. Nevertheless, the new specimens also indicate that some features previously hypothesized to be apomorphic for M. akamai are intraspecifically variable.

Hidden biodiversity of Amazonian white-sand ecosystems: two distinctive new species of Utricularia (Lentibulariaceae) from Pará, Brazil.

As deforestation and fire move forward over pristine vegetation in the Amazon, many species remain undiscovered and may be threatened with extinction before being described. Here, we describe two new species of Utricularia (Lentibulariaceae) collected during recent fieldwork in an area of white-sand vegetation in the eastern Amazon Basin named Campos do Ariramba. Further herbarium revision revealed that both species were first collected over 60 years ago in the same area, remaining unnamed until now. The new species, named U. arirambasp. nov. and U. jaramacarusp. nov., are placed in U. sect. Aranella and U. sect. Setiscapella, respectively. We provide full descriptions, illustrations, photographs, a distribution map, and taxonomic discussion for both species. Additionally, we provide a preliminary list of Lentibulariaceae from the Campos do Ariramba. Both new species are assessed as Vulnerable, however, yet known only from a few collections each, highlighting the urgency and importance of fieldwork and taxonomic revisions in the Amazon biogeographic region in order to provide essential data for the conservation of both known and still unknown biodiversity.

Empirical–Statistical Downscaling of Austral Summer Precipitation over South America, with a Focus on the Central Peruvian Andes and the Equatorial Amazon Basin

AbstractPrecipitation is one of the most difficult variables to estimate using large-scale predictors. Over South America (SA), this task is even more challenging, given the complex topography of the Andes. Empirical–statistical downscaling (ESD) models can be used for this purpose, but such models, applicable for all of SA, have not yet been developed. To address this issue, we construct an ESD model using multiple-linear-regression techniques for the period 1982–2016 that is based on large-scale circulation indices representing tropical Pacific Ocean, Atlantic Ocean, and South American climate variability, to estimate austral summer [December–February (DJF)] precipitation over SA. Statistical analyses show that the ESD model can reproduce observed precipitation anomalies over the tropical Andes (Ecuador, Colombia, Peru, and Bolivia), the eastern equatorial Amazon basin, and the central part of the western Argentinian Andes. On a smaller scale, the ESD model also shows good results over the Western Cordillera of the Peruvian Andes. The ESD model reproduces anomalously dry conditions over the eastern equatorial Amazon and the wet conditions over southeastern South America (SESA) during the three extreme El Niños: 1982/83, 1997/98, and 2015/16. However, it overestimates the observed intensities over SESA. For the central Peruvian Andes as a case study, results further show that the ESD model can correctly reproduce DJF precipitation anomalies over the entire Mantaro basin during the three extreme El Niño episodes. Moreover, multiple experiments with varying predictor combinations of the ESD model corroborate the hypothesis that the interaction between the South Atlantic convergence zone and the equatorial Atlantic Ocean provoked the Amazon drought in 2015/16.

Radiocarbon analysis confirms annual periodicity in Cedrela odorata tree rings from the equatorial Amazon

Abstract A Cedrela odorata tree ring width chronology spanning from 1786 to 2016 was developed in the quasi-equatorial eastern Amazon Basin. Annual calendar dates were assigned using dendrochronological techniques at the Federal University of Lavras, Brazil. Due to its strategic location at the edge of the Equator (approximately 0°57′S), an independent confirmation of the annual periodicity of this century-long chronology would be of great value, allowing its future use for climate reconstruction and for filling gaps in upcoming atmospheric radiocarbon (14C) compilations. For reconstruction of atmospheric 14C, high reliability of the dendrochronological calendar dates is a requirement. Here, we used high-precision 14C bomb pulse dating (BPD) of selected C. odorata tree rings as a robust independent method to validate the dendrochronological dates. Eight calendar years from across the pre-to post-bomb period were tested through 14C analysis of α-cellulose extracts (19 targets in total were produced from those 8 calendar years). All dendrochronologically dated tree rings measured produced 14C values in perfect alignment with the Southern Hemisphere 14C bomb curve, further confirming the annual growth of this important record. Extraction of α-cellulose was attained by a recently implemented procedure at the Lamont-Doherty Earth Observatory (LDEO). The method was 14C assessed by high-precision measurements at the Keck Carbon Cycle Accelerator Mass Spectrometer (KCCAMS) at the University of California, Irvine (UCI) by measuring reference materials and unknown samples. High reproducibility of reference materials (within uncertainties) showed that the novel 150-funnel system and protocol developed at LDEO is reliable and can potentially expedite cellulose extractions for 14C analysis.

Four new species of Pristimantis Jiménez de la Espada, 1870 (Anura: Craugastoridae) in the eastern Amazon.

The Pristimantis genus (Anura: Craugastoridae) is the most diverse among all vertebrates with 531 described species. The highest diversity occurs in Ecuador (215 species), followed by Colombia (202), Peru (139), Venezuela (60), Brazil (30), Bolivia (17), Guyana (6) Suriname and French Guiana (5). The genus is divided into 11 species groups. Of these, the P. conspicillatus group (containing 34 species), distributed in extreme southeastern Costa Rica, Isla Taboga (Panama), northern South America (from Colombia to eastern Guyana), south Bolivia, and is the best represented in Brazil (16 species). The main characteristics of this group are the tympanic membrane and tympanic annulus distinct (except in P. johannesdei); dorsum smooth or shagreen; dorsal lateral fold present or absent; usually smooth belly, but may be weakly granular in some species; toe V slightly larger than the toe III. Most of the taxonomic inconsistencies in species of Pristimantis could be due to its much conserved morphology and the lack of comprehensive taxonomic evaluations. Thus, an ongoing challenge for taxonomists dealing with the Pristimantis genus is the ubiquitous abundance of cryptic species. In this context, accurate species delimitation should integrate evidences of morphological, molecular, bioacoustics and ecological data, among others. Based on an integrative taxonomy perspective, we utilize morphological, molecular (mtDNA) and bioacoustic evidence to describe four new species of the Pristimantis conspicillatus group from the eastern Amazon basin. Pristimantis giorgii sp. nov. is known from the Xingu/Tocantins interfluve and can be distinguished from the other Pristimantis species of the region by presenting discoidal fold, dorsolateral fold absent, vocalization composed of three to four notes and genetic distance of 7.7% (16S) and 14.8% (COI) from P. latro, the sister and sympatric species with respect P. giorgii sp. nov.. Pristimantis pictus sp. nov. is known to the northern Mato Grosso state, Brazil, and can be distinguished from the other species of Pristimantis by presenting the posterior surface of the thigh with light yellow patches on a brown background, also extending to the inguinal region, vocalization consisting of four to five notes and a genetic distance of 11.6% (16S) and 19.7% (COI) from P. pluvian sp. nov., which occurs in sympatry. Pristimantis pluvian sp. nov. is known to the northern Mato Grosso state, Brazil, and may be distinguished from the other Pristimantis species by having a posterior surface of the thigh reddish and vocalization composed of two notes. Pristimantis moa sp. nov. is known to the northern Tocantins state and southwestern Maranhão state. This species can be distinguished from the other Pristimantis species by possessing slightly perceptible canthal stripe, external thigh surface with dark yellow spots on brown background, vocalization consisting of three to five notes and genetic distance of 2.3-11.7 (16S) and 10.5-23.1 (COI) for the new Pristimantis species of this study.

Modeling the effects of land cover change on sediment concentrations in a gold-mined Amazonian basin

Land use/land cover change (LUCC) combined with gold mining activity (GMA) have reportedly affected the water quality of Amazonian rivers by intensifying surface soil erosion and increasing rivers’ sediment concentration (SC). However, the role of LUCC on river siltation in comparison to that caused by GMA has not been assessed, and predictions of SC in the rivers accounting for future LUCC are scarce. This study applied a sediment modeling approach on Crepori Basin, located at eastern Amazon Basin, to simulate the impacts of past and future LUCC on SC in the river, comparing their impacts to those caused by GMA. Between 1973 and 2012, the expansion of deforested areas in the region had increased sheet erosion-driven SC in the river, especially during the high-water season, by up to 73.3%. LUCC projections for 2050 suggest future increases in sheet erosion-driven SC during the high-water season by more than three times of that caused by the land cover scenario of 1998–2012. Comparison between SC driven by sheet erosion to that caused by GMA has also shown that during the high-water and the low-water seasons, respectively, only about 14% and 6% of the total SC in the Crepori River resulted from laminar soil erosion, with the remaining proportion resulting from GMA.

Reconstruction of Holocene coupling between the South American Monsoon System and local moisture variability from speleothem δ18O and 87Sr/86Sr records

Investigating controls on past variability of South American hydroclimate is critical to assessing its response to future warming scenarios. δ18O records from South America offer insight into past variability of the South American Monsoon System (SAMS). The controls, however, on precipitation δ18O values can be decoupled from precipitation amount at a given site and, thereby, limit local moisture condition reconstructions. Here we use a principal components analysis to assess the coherence of speleothem and lake core Holocene δ18O records in tropical and subtropical South America to evaluate the extent to which δ18O variability reflects changes in SAMS intensity at different sites across the region. The main mode of variability across Holocene δ18O records (PC1) closely tracks austral summertime insolation, consistent with existing work. Sites towards the periphery of the continent are heavily weighted on PC1, whereas interior sites as not. Further δ18O variability at interior sites bear little similarity to each other and implicate controls, beyond regional monsoon intensity, on these δ18O records. Further, we develop speleothem 87Sr/86Sr records spanning the Holocene from Tamboril Cave (Brazilian Highlands), Paraíso Cave (eastern Amazon Basin), Jaraguá Cave (Mato Grosso do Sul Plateau), and Botuverá Cave (Atlantic coastal plain) to investigate coupling between reconstructed monsoon variability (reflected by PC1) and local moisture conditions (interpreted from 87Sr/86Sr records). We interpret speleothem 87Sr/86Sr variability as a proxy of local moisture conditions, reflecting the degree of water-rock interaction with the cave host rock as driven by variations in water residence time. Speleothem 87Sr/86Sr records from all the sites, except Botuverá cave, do not co-vary with PC1, suggesting that local moisture conditions do not necessarily follow variations in regional monsoon intensity at these interior sites. These speleothem 87Sr/86Sr records generally suggest dry mid-Holocene conditions relative to the early- and late-Holocene, consistent with interpretations of other paleo-moisture records in the region, but timing of wet-dry transitions varies between sites. These results highlight that controls, in addition to SAMS variability, might influence δ18O variability. Further, our results suggest spatially variable local moisture conditions at interior sites that do not uniformly respond to regional monsoon intensity, and stress the need for δ18O-independent reconstructions of moisture conditions.

Population and reproductive parameters of the red-tailed catfish, Phractocephalus hemioliopterus (Pimelodidae: Siluriformes), from the Xingu River, Brazil

ABSTRACT A field study of the sex ratio, length-weight ratio, body size at first gonadal maturation, and the breeding season of the red-tailed catfish, Phractocephalus hemioliopterus, was carried out in the region of the middle Xingu River in the eastern Amazon basin. The fish were sampled quarterly from September 2012 to January 2014 using gillnets and long lines. The sex ratio was balanced, and while males and females were similar in standard length, the females were heavier than the males, on average. The males presented negative allometric growth, and the females, isometric growth. The estimated size at first maturity was 77.8 cm. The variation in the gonadosomatic index and the greater frequencies of mature specimens indicated a reproductive peak at the beginning of the high-water (flood) period. As P. hemioliopterus is an important commercial fish, our findings will contribute to the future development of effective conservation and management strategies, such as minimum catch size and a close season that is appropriate for the region. These data will also provide important insights for the evaluation of potential impacts on the biology of this fish resulting from the construction of Belo Monte dam.

Influence of longer dry seasons in the Southern Amazon on patterns of water vapor transport over northern South America and the Caribbean

Several studies have identified a recent lengthening of the dry season over the southern Amazon during the last three decades. Some explanations to this lengthening suggest the influence of changes in the regional circulation over the Atlantic and Pacific oceans, whereas others point to the influence of vegetation changes over the Amazon rainforest. This study aims to understand the implications of more frequent long dry seasons in this forest on atmospheric moisture transport toward northern South America and the Caribbean region. Using a semi-Langrangian model for water vapor tracking, results indicate that longer dry seasons in the southern Amazon relate to reductions of water vapor content over the southern and eastern Amazon basin, due to significant reductions of evaporation and recycled precipitation rates in these regions, especially during the transition from dry to wet conditions in the southern Amazon. On the other hand, longer dry seasons also relate to enhanced atmospheric moisture content over the Caribbean and northern South America regions, mainly due to increased contributions of water vapor from oceanic regions and the increase of surface moisture convergence over the equatorial region. This highlights the importance of understanding the relative role of regional circulation and local surface conditions on modulating water vapor transport toward continental regions.

Intra‐seasonal rainfall variability in the Amazon basin related to large‐scale circulation patterns: a focus on western Amazon–Andes transition region

ABSTRACTThis study aims to relate the intra‐seasonal rainfall variability over the Amazon basin to atmospheric circulation patterns (CPs), with particular attention to extreme rainfall events in the Amazon–Andes region. The CPs summarize the intra‐seasonal variability of atmospheric circulation and are defined using daily low‐level winds from the ERA‐Interim (1.5° × 1.5°) reanalysis for the 1979–2014 period. Furthermore, observational data of precipitation and high‐resolution TRMM 3B42 (∼25 km), 2A25 PR (∼5 km) and CHIRPS (∼5 km) data products are related to the CPs throughout the Amazon basin. Nine CPs are determined using a hybrid method that combines a neural network technique (self‐organizing maps, SOM) and hierarchical ascendant classification. The CPs are characterized by a specific cycle with alternative transitions and a duration of 14 days on average. This configuration initially results in northerly winds to southerly winds towards the northern or eastern Amazon basin. The related rainfall suggests that it is driven mainly by CP dynamics. In addition, we demonstrate a good agreement amongst the four rainfall data sets: observed precipitation, TRMM 3B42, TRMM 2A25 PR and CHIRPS. Furthermore, special attention is given to the Amazon–Andes transition region. Over this region, two particular CPs (CP4 and CP5) are identified as the key contributors of maximum and minimum daily rainfall, respectively. Thus, during the dry season, 40.8% (11.4%) of the CP5 (CP4) days demonstrate rainfall of less than 1 mm day−1, while during the wet season, 6.2% (14.6%) of the CP5 (CP4) days show rainfall amounts higher than the seasonal 90th percentile (10.4 mm day−1). This study provides additional information concerning the intra‐seasonal circulation variability in Amazonia and demonstrates the value of using remote sensing precipitation data in this region as a tool for forecast in areas lacking observable information.

A New Weed in Florida,Spermacoce latifolia, and the Distinction betweenS. alataandS. latifolia(Spermacoceae, Rubiaceae)

Spermacoce alata Aubl. and Spermacoce latifolia Aubl., frequently referred to as Borreria alata (Aubl.) DC. and Borreria latifolia (Aubl.) K. Schum., were described in the 18th century by Jean Baptiste Christophe Fusee Aublet from French Guiana. They have sometimes been treated as a single species but are two easily distinguished species. Spermacoce alata occurs from Venezuela through the Guianas and in the eastern Amazon basin north of the Rio Amazonas and is not weedy. The New World distribution of S. latifolia is from southern Mexico through Central America and throughout eastern South America to Bolivia and Paraguay, and it is naturalized in the tropical and subtropical regions of the Old World. Spermacoce latifolia is a noxious weed that has frequently been misidentified as S. alata. The first documented reports of S. latifolia in Florida are presented. Given its aggressive colonization elsewhere, prompt consideration should be given to controlling the spread of S. latifolia in the southern USA.

Effects of human disturbance and riparian conditions on Odonata (Insecta) assemblages in eastern Amazon basin streams

Riparian vegetation is an important determinant of the physical, chemical, and biological condition of streams, and odonates are useful indicators of riparian condition. To identify environmental factors that structure Odonata assemblages in tropical forest streams, we collected adult odonate specimens and habitat data from 50 stream sites located in the Brazilian municipality of Paragominas (Pará state). We collected 1769 specimens representing 11 families, 41 genera, and 97 species. Of these species, 56 were Zygoptera, and 41 were Anisoptera. Improved environmental condition was reflected in increased Zygoptera species richness and reduced Anisoptera species richness. Channel shading was strongly and positively related to Zygoptera richness, and negatively to Anisoptera richness. Zygoptera species richness, but not Anisoptera species richness, was related positively to bank angle, quantity of wood in the stream bed, electrical conductivity, and decreased water temperature. Altered riparian vegetation structure was the principal determinant of odonate assemblage structure. Our results indicate that maintaining intact riparian vegetation is fundamental for conserving or re-establishing aquatic odonate assemblage structure.