Amazon River Delta Research Articles

Divergent dynamics of coastal wetlands in the world’s major river deltas during 1990–2019

Coastal wetlands provide vital dynamic ecosystem services. They have become increasingly important after being linked to several sustainable developmental goals, resulting in a focus on their protection, management, and restoration. Therefore, there is an increasing need to detect and compare coastal wetland spatiotemporal dynamics in deltas at a global scale. In this study, we mapped and characterized coastal wetland spatiotemporal patterns for 1990–2019 in the world’s major river deltas using pixel frequency algorithms and Landsat-4/5 (TM), −7 (ETM + ), −8 (OLI), and Sentinel-2 (MSI) time-series imagery obtained from Google Earth Engine (GEE). Our map had a high overall accuracy (91.84 %) for 2019. Tidal flats were primarily distributed in North America (∼6.87 %) and Asia (∼5.91 %), whereas salt marshes were more commonly found in North America (∼45.39 %) and South America (∼10.61 %). Mangroves are more common in South America (∼11.86 %) and Asia (∼5.83 %), primarily because of the Amazon River Delta and tropical and subtropical regions of Asia, which host several large river deltas. South America had the largest coastal delta wetland area (798,569 km2), followed by Asia (640,251 km2), North America (581,977 km2), Africa (181,977 km2), Europe (140,759 km2), and Oceania (15,915 km2). There was a minor difference in the distribution of wetland vegetation and tidal flats in Asian coastal deltas, and the wetland vegetation area in Asia was greater than that in tidal flats on other continents. We found that the coastal wetland areas increased during 1990–2001, decreased during 2001–2012, and steadily increased during 2012–2019. Our study provides a baseline for monitoring the area, status, and health of the coastal wetlands in these river deltas.

Rainfall Influences the Patterns of Diversity and Species Distribution in Sandy Beaches of the Amazon Coast

The Amazon region is one of the Earth’s hotspots of biodiversity and has a pivotal role in climate regulation. Yet, little is known about its coastal biodiversity. Here, we performed the first assessment of macrobenthic diversity and ecological patterns of sandy beaches north of the Amazon River delta, the world’s largest freshwater input into the oceans. By assessing spatial and temporal changes in the soft-bottom biodiversity and environmental variables of three beaches (Goiabal, Nazaré, and Sumaúma) in the northernmost stretch of the Brazilian coast, we found low richness (14 taxa, overall; Goiabal: 3.27 ± 1.78; Nazaré: 2.34 ± 1.29; Sumaúma: 2 ± 0.67) and diversity (Goiabal: 0.72 ± 0.52; Nazaré: 0.62 ± 0.46; Sumaúma: 0.55 ± 0.39) across 2949 individuals with great dominance of estuarine species (notably Nephthys fluviatis and Sphaeromopsis mourei). Abundance was higher during rainy periods, and the same pattern was observed for richness and diversity in comparison to transitional periods, at least on Nazaré Beach. Environmental heterogeneity was reduced during rainy periods, resulting in a higher abundance of dominant species and lower beta diversity. Most species presented aggregated distribution at the upper intertidal zone, and changes in macrobenthic assemblages were linked to variations in rainfall and organic matter content in the sediment. Given the ecological uniqueness and the severe erosional process affecting the northern coast of the Amazon region, our results provide essential baseline knowledge to better understand the patterns and processes influencing its understudied biodiversity. We advocate that further studies expand our findings to support the conservation of this region.

Epipelagic cnidarian fauna in the Western Equatorial Atlantic Ocean off the Amazon River Delta

Epipelagic cnidarian fauna in the Western Equatorial Atlantic Ocean off the Amazon River Delta

Low transmission rates of Equine infectious anemia virus (EIAV) in foals born to seropositive feral mares inhabiting the Amazon delta region despite climatic conditions supporting high insect vector populations

BackgroundMarajó Island, within in the Amazon River Delta, supports numerous bands of feral equids including the genetically distinct Marajoara horses. Approximately 40% of the equids on the island are infected with Equine infectious anemia virus (EIAV). This high seropositivity rate coupled with the need to preserve rare breeds such as the Marajoara horse precludes euthanasia as the primary means for controlling EIAV in this region. In the absence of iatrogenic transmission, spread of this lentivirus is mediated primarily by hematophagous insects, whose year-round prevalence on the island is supported by favorable climatic conditions. In addition, cases of vertical EIAV transmission have been observed suggesting inclusion of seropositive mares in restorative breeding programs could result in their progeny becoming infected with this virus either pre-parturition or post-partum via hematophagous insects. Therefore, the aim of this study was to evaluate EIAV vertical and post-partum insect-mediated transmission rates among foals born to seropositive feral mares until natural weaning. Serum samples from foals born to seropositive feral mares within the Soure municipality, of Marajó Island, were collected to investigate their serological status, using an indirect ELISApgp45, with positive samples confirmed using the classical agar gel immunodiffusion (AGID) assay.ResultsThe serological status of 28 foals were monitored over a 2-year period with some subjects, depending on their date of birth, being sampled up to six times. All foals remained with their respective mares until fully weaned at approximately 10 months of age. Only 2 foals (7.14%) in the study group became seropositive against EIAV.ConclusionThe results demonstrate that in most cases it is possible to obtain seronegative foals born to and eventually weaned by EIA positive mares, even in equatorial regions where substantial rainfall and high temperatures favor the proliferation of insect vectors.

Brazil, Amazon River Delta, Atlantic Coast

Brazil, Amazon River Delta, Atlantic Coast

Sustainable Management, Conservation, and Restoration of the Amazon River Delta and Amazon-Influenced Guianas Coast: A Review

The Amazon River delta may be currently characterized biophysically as a relatively preserved delta compared to the rampant vulnerability of many of the world’s large deltas. This status of relative preservation is reflected in a number of criteria: The still largely free-flowing nature of many of the rivers and the main stem of the Amazon that feed the delta in sediment, exceptional biodiversity, dominant shoreline accretion, and the absence of anthropogenically-generated subsidence. In this review, we show that these relatively reassuring conditions are progressively being called into question by the effects of dams on fluvial sediment supply to the delta, by increasing demographic, urban, and land development pressures in this still largely underpopulated delta, and by problems of governance that underplay aspects of basin-wide and deltaic environmental deterioration. A major challenge is that of bringing together these contrasting demands that are leading to the emergence of zones of environmental stress that test the resilience of this delta. An integral part of the strategy for the analysis of collective action, management, and conservation is that of considering the Amazon delta in terms of interacting socio-ecological systems. Pressures on the delta will be compounded in the future by decreasing fluvial sediment supply and sea-level rise. Although climate change is projected to generate surplus sediment, the rapid growth of dam constructions upstream of the delta will negatively impact the river’s sediment flux. Conservation and management of the Amazon River system aimed at keeping the delta resilient in the context of sea-level rise and reduction of sediment supply will require clear governance and better planning and anticipation, as well as socio-ecological integration. These are also requirements that will need to be implemented in the 1500 km-long coastal zone of the Guianas countries located west of the Amazon delta and the sediment dynamics and stability of which are largely determined by sediment supply from the Amazon.

A multiproxy approach to characterize the sedimentation of organic carbon in the Amazon continental shelf

Surface sediments were collected in a transect from the Amazon river delta to open marine sites in the north Atlantic Ocean in order to characterize spatial contrasts in the deposited organic carbon (OC), allowing to uncover the role of the river plume on the sedimentation of OC. Analysis of isoprenoidal and branched glycerol dialkyl glycerol tetraethers (GDGTs), lignin phenols, fatty acids, n-alkanes and bulk parameters were performed to characterize the sedimentary OC. An end-member approach based on biomarkers (lignin phenols and GDGTs), and the stable carbon isotopic composition of bulk organic carbon (δ13COC), was used to estimate the fraction of marine (OCmar) and continental sources (OCcont) of sedimentary organic carbon. Similar estimates based on lignin phenols were obtained and indicates that the OCcont was on average 30 ± 37%; based on the GDGTs it was 29 ± 35% while based on the δ13COC it was 30 ± 32%. The OC content of the surface sediments remained relatively constant from the delta to the marine sites northward (ca. 0.6%) but the fractions of continental and marine OC were variable. In the deltaic region, OCcont was ca. 84%, while in the open marine sites, OCmar was ca. 86%. In the stations southward the delta, the OC content was about 0.03% with high OCmar and low OCcont, which indicates a low influence of the river plume on this location. The accumulation rates of OCcont and OCmar were estimated and showed that both were higher in the deltaic region in comparison to the marine sites. The results suggested that only 10–15% of the OCcont is deposited offshore and that river plume conditions stimulated primary production and, thus, ultimately the sedimentation of OCmar in the continental shelf and offshore sediments. Finally, our estimates showed that the Amazon River Delta has an accumulation rate above the global average and the material transported horizontally by the river plume fuels the primary production in adjacent areas, which improves the relevance of the Amazon continental shelf to the global carbon budget.

Spatial Issues and Covid-19 Dispersion in Small Cities of The Amazon River Delta

The COVID - 19 virus emerged in China and has spread to all areas in Brazil, including the Amazon River Delta, where the population lacks essential services. Thus, this article aims to characterize the dispersion of COVID-19 in the small municipalities of the Amazon River Delta, which have fewer than 50,000 inhabitants, detailing the towns' situation. Covid-19 data provided by the health departments of the states of Amapá and Pará, and census data from the IBGE, were used to create maps of the disease for the Delta's municipalities. The virus circulated rapidly to the smallest localities, where the health service and sanitary conditions are precarious, leading to a severe contamination rate. Together with other known aspects, this is yet another opportunity to show the regional needs and the importance of public policies for this population.

River body extraction from sentinel-2A/B MSI images based on an adaptive multi-scale region growth method

River networks are important water carriers that provide a multitude of ecosystem services, including freshwater for agriculture, drinking water for cities, and recreational activities. Accurate mapping of river networks from remote-sensing images is important for the study of these systems. Unfortunately, the delineation of river networks is challenging due to the meandering nature of river channels, the often complex and variable features of the surrounding landscape, and the spatial heterogeneity of the river networks. Here, we present an adaptive, multi-scale region growth method (AMRGM) to delineate river networks from sentinel-2A/B MSI images. The method can handle variable river heterogeneous surroundings, multiple spatial scales, and variable curvatures of the river channels. The method includes four steps: (1) a water index (NDWI) is used to provide initial detection of river water pixels in the image; (2) a bias-corrected fuzzy C-means (BCFCM) method alleviates the effects of the variable surrounding landscape; (3) a scale-enhancement algorithm based on the hessian matrix makes full use of scale and direction information to enhance river morphology characteristics (multiple dimensions and variable curvatures), and (4) a regional growth criterion facilitates handling of various river dimensions. Fast-growing and fine-screening strategies are also included in the AMRGM. The method is applied to eight river networks to evaluate its accuracy and reliability with various river morphologies and hydrological conditions. The AMRGM is more widely applicable than four commonly used river-detection methods (i.e., K-means method, maximum likelihood method, iterative self-organizing data analysis technique algorithm, and support vector machine) and outperform these methods when detecting multi-scale river branches. The mean overall accuracy (OA) and kappa coefficients (KC) of the AMRGM exceed 97% and 0.92 across the eight river networks. The most accurate river extractions are obtained for large rivers such as the Amazon River, Mackenzie River, and Ganges River Delta, which have more discernable scale and direction characteristics. Relatively high omission and commission errors are observed in river networks with complex and heterogeneous zonations, such as the river Welland, UK, and the Zagya Zangbo River in the Tibet plateau. The complex geomorphic features of the river Welland reduce OA and KC to 93.8% and 0.86, respectively

Fluvial sand, Amazon mud, and sediment accommodation in the tropical Maroni River estuary: Controls on the transition from estuary to delta and chenier plain

The Maroni River, South America, is a tropical estuary encased in a narrow lower valley with a limited area of estuarine tidal flat development, and displays a channel with large downstream-migrating sandy bedforms linked to a large sand-filled shallow mouth. The sand-rich nature of the lower Maroni River reflects significant fluvial bedload supply, and the Maroni is among rivers with the lowest suspension-sized sediment load in the world. During the dry season, the estuary shows high suspended sediment concentrations near the bottom (several g/l) that are due to the ingress of mud streaming alongshore from the Amazon River delta. However, Amazon mud is expelled from the estuary during the high-discharge rainy-season, and seems to be essentially restricted to this seasonal intrusion along the main channel with little net estuarine sedimentation because of limited channel overbank sediment accommodation space. Sand actively supplied by the Maroni River to the coast has been diverted by wave-generated longshore transport westwards, towards the Suriname coast. This has resulted in the construction of numerous sandy cheniers within a muddy coastal plain built from Amazon mud. This sediment-source dichotomy is an important original feature of the Guiana Shield estuaries. The asymmetric progradation at the mouth of the Maroni fingerprints the westward growth, in the vicinity of river mouths, of the muddy, chenier-studded, coastal plain of the Guianas. The propensity for these rivers to supply sand to the coast, eventually evolving into deltas, depends on the ability of their estuaries to limit westward (downdrift) deflection by long-term updrift coastal sedimentation. The Maroni estuary has tended to evolve towards a delta built from both Maroni river sand and Amazon mud, a stage, among the Guiana Shield Rivers, that only the large Essequibo River estuary in Guyana has achieved. Further studies will be needed in order to constrain the infill pattern of the Maroni River estuary and its mouth.

Identification of Pathogenic Leptospira Species in the Urogenital Tract of Water Buffaloes (Bubalus bubalis) From the Amazon River Delta Region, Brazil.

In the current context of deforestation and fire in the Amazon, buffaloes could be a cost-effective and sustainable alternative for cattle production in the region, as they can convert low-quality foods and be raised in floodplain areas. However, little is known about the reproductive diseases that affect these animals; thus, the purpose of this study was to perform the molecular characterization of Leptospira spp. in the urogenital tract of water buffaloes (Bubalus bubalis) raised in the Amazon River Delta region in Brazil. Samples were collected from 114 kidneys, 204 ovaries, and 160 uterine swabs of slaughtered buffaloes in the Macapá microregion of Amapá State (Brazil) and were subjected to PCR to detect bacterial DNA. Positive amplicons were sequenced to identify Leptospira species. Among the total samples, 11/473 were PCR positive (2.3%), including 10 kidney samples and one uterine swab sample. DNA sequencing identified two pathogenic species from the kidney samples: L. interrogans, accounting for 60.0% (6/10) of these samples, and L. borgpetersenii, accounting for 20.0% (2/10), while 20.0% (2/10) were identified only at the genus level. The bacterium in the uterine swab sample was identified as L. interrogans with genetic proximity to strains belonging to the serovar Hardjo. This is the first report of leptospires species identified in buffaloes from the Amazon River Delta region and revealed that these animals may be carriers of different pathogenic Leptospira species, similar to bovines, including showing genital colonization.

Amazon fluid mud impact on tide- and wave-dominated Pliocene lobes of the Orinoco Delta

The modern Orinoco Delta is a major sink for the world's largest alongshore (littoral) mud dispersal system; it receives some 108 tons/yr from the Amazon river delta. The influence of these huge volumes of Amazon mud on the paleo-Orinoco Delta succession is now investigated for the first time. Abundant fluid-mud deposits are preserved in outcrops from the Pliocene Orinoco Delta deposits (Lower Morne L'Enfer, Manzanilla and Mayaro formations on Trinidad) with different styles in tide-dominated, in tide-dominated and wave-influenced, and in storm wave-dominated delta lobes. Fluid-mud deposits in sandy parasequences (10–20 m thick) of the Lower Morne L'Enfer Formation change from thin layers amalgamating to form mud bedsets (up to 4 cm) or draping across ripple laminae in the lower part, to thick layers (up to 10 cm) occasionally with deformed and load structures at their top, in the upper part. The Manzanilla Formation parasequences (30–40 m thick) exhibit coarsening-to-fining-upward (CUFU) facies successions with fluid-mud deposits located mainly in the middle to upper parts of the parasequences, near the transition between the CU and FU parts of the units. Most of the fluid-mud layers are interbedded with bi-directional, current rippled-sandstones, whereas minor mud layers are associated with erosion-based sandstones with small-scale swaley strata and bi-directional symmetrical ripples. The Mayaro Formation parasequences (5–15 m thick) are characterized by alternating fluid-mud intervals and sets of hummocky cross-stratified sandstones (HCS) passing upward into amalgamated swaley cross-stratified (SCS) sandstones. The fluid-mud intervals have flat or irregular tops occasionally overlain by amalgamated SCS sandstones with fluid-mud clasts.Very thick (1–1.5 m) fluid-mud intervals occur in places in both tide- and wave-dominated strata and these are probably large muddy bedforms similar to mud banks that migrate currently along the modern Amazon-Orinoco coast. The outcrop analysis strongly suggests that the fluid-mud banks, as they approached the Orinoco delta-front area, were handled differently depending on whether the delta-front lobes were wave- or tide-dominated. Tide-dominated delta lobes tended to trap the muds near the shoreline and on the subaqueous delta-front platform in water depth < 10 m with only minor volumes escaping offshore. In contrast, storm wave-dominated delta lobes had a more dynamic impact on the approaching mudbanks. Mud accumulated in the shallow water tend to be eroded and re-deposited into deeper water near the storm wave base (15–50 m water depth).The volumes of Pliocene Amazon mud transported along the innermost shelf and arriving on the Orinoco Delta were likely influenced by high-amplitude, Pliocene glacio-eustatic sea level fluctuations. During sea-level fall and lowstand periods, increased volumes of Amazon mud would have bypassed to the deep water and thus decreased mud volumes drifted and became incorporated in the Orinoco delta front. In contrast, sea-level rise and highstand periods would have promoted increased volumes of Amazon mud both on the shelf and onto the Orinoco, similar to the Holocene and modern muddy system.

IMPLEMENTING THE RULE OF LAW IN BRAZIL’S AMAZON FRONTIER

This piece traces the courageous and dedicated efforts of Brazilian judge Sueli Pereira Pini and her colleagues in Brazil’s northern state of Amapa to undertake an ambitious effort to deliver justice and other government services to the marginalized and disenfranchised inhabitants of Macapa municipality. That municipality serves as the capitol of Amapa state, and its residents include those residing in remote communities in the hinterlands accessible only via dirt roads and trails as well as those the Balique archipelago, part of the enormous Amazon River Delta, whose communities are only accessible by water-based transportation. Developing the justice-distribution network known as Justicia Itinerante for the land-based communities and Justicia Fluvial Itinerante for the communities in the archipelago involved acquiring and converting buses and Amazon riverboats to function as mobile courts and utilizing them to conduct proceedings in a diverse assortment of civil, criminal, family and commercial cases. It is an inspiring narrative demonstrating how passion and determination can combine to provide access to justice for those governments all too often ignore.

Anthropogenic disturbance of tropical forests threatens pollination services to açaí palm in the Amazon river delta

Abstract The açaí palm Euterpe oleracea Mart. in the Amazon river delta has seen rapid expansion to meet increased demand for its fruit. This has been achieved by transforming lowland forest habitats (floodplains) into simplified agroforests and intensive plantation in upland areas. As açaí palm makes an important contribution to the economy and food security of local communities, identifying management approaches that support biodiversity and ecosystem processes that underpin fruit production on açaí farms is essential. We compared flower‐visitor communities and açaí fruit production in floodplain forests and upland plantations, across gradients of local management intensity (i.e. açaí density per ha) and surrounding forest cover. The relative contribution of biotic pollination and degree of pollen limitation were assessed using insect exclusion and hand‐pollination experiments. We found that açaí flower visitors are highly diverse (c. 200 distinct taxa) and had variable responses to disturbance. Bee visitation was higher in floodplains and positively related to surrounding forest cover, but other flower visitors, including specialised curculionid beetles, were unresponsive to changes in surrounding forest cover. However, intensive management practices (i.e. high açaí palm densities) in floodplains and uplands had contrasting effects on flower‐visitor communities, with flower‐visitor richness being lower on intensively managed floodplain farms and ant densities being higher on intensive upland farms. Pollination experiments revealed açaí palm to be highly dependent on biotic pollination. Fruit set in open‐pollinated inflorescences was positively related to flower‐visitor richness and specialised curculionid beetle visitation, whereas the presence of ants on inflorescences had a negative effect. Synthesis and applications. Our study shows that pollinators are essential for açaí fruit production, but that intensive farming practices have eroded the relationship between surrounding forest cover and ecosystem function in floodplains (i.e. conversion of native forest into simplified agroforests) and increased the frequency of antagonistic interactions in uplands (e.g. high ant densities). These findings underline the value of extensive management practices, such as the maintenance of other tree species within farms and adjacent unmanaged forest patches, to ensure the long‐term sustainability of açaí fruit production in the Amazon river delta.

Dawestrema cycloancistrium (Monogenea) from the head pores of arapaimas.

Arapaima gigas is one of the main cultured fish species in South America, and monogenean parasites of this species cause large economic losses to fish farmers. During surveys of the parasites of cultured arapaimas from Mexiana Island in the Amazon River Delta, Rio Branco, in northwestern Brazilian Amazonia, and Yurimaguas, Peru, the monogenean Dawestrema cycloancistrium was found in the gills of A. gigas as well as in previously unreported sites, i.e. the head pores and chambers. The aim of this study was to investigate the transmission route of this parasite and its geographical distribution as well as to describe its morphology as observed by light and confocal imaging. Phalloidin labeling confirmed the presence of 2 prostatic reservoirs and showed muscular branches of fibers supporting haptoral sclerites. In arapaimas, the head connects to the gill chambers via 2 perforated scales located at the dorsolateral sides of the distal part of the head. The scales connect to thin channels and chambers situated in the proximal part of the head. These chambers are filled with cephalic mucus, which flows out to the environment through terminal pores. Adults and egg masses of monogeneans were found on the gills and inside the head pores and cavities of fish along with cephalic mucus. This indicates a specialized method of parasite transmission from adult fish to fingerlings during parental care (holding offspring in the mouth) or via head secretions, providing evidence of a new adapted mechanism of dispersion.

A conceptual framework for analyzing deltas as coupled social–ecological systems: an example from the Amazon River Delta

At the nexus of watersheds, land, coastal areas, oceans, and human settlements, river delta regions pose specific challenges to environmental governance and sustainability. Using the Amazon Estuary-Delta region (AD) as our focus, we reflect on the challenges created by the high degree of functional interdependencies shaping social–ecological dynamics of delta regions. The article introduces the initial design of a conceptual framework to analyze delta regions as coupled social–ecological systems (SES). The first part of the framework is used to define a delta SES according to a problem and/or collective action dilemma. Five components can be used to define a delta SES: social–economic systems, governance systems, ecosystems-resource systems, topographic-hydrological systems, and oceanic-climate systems. These components are used in association with six types of telecoupling conditions: socio-demographic, economic, governance, ecological, material, and climatic-hydrological. The second part of the framework presents a strategy for the analysis of collective action problems in delta regions, from sub-delta/local to delta to basin levels. This framework is intended to support both case studies and comparative analysis. The article provides illustrative applications of the framework to the AD. First, we apply the framework to define and characterize the AD as coupled SES. We then utilize the framework to diagnose an example of collective action problem related to the impacts of urban growth, and urban and industrial pollution on small-scale fishing resources. We argue that the functional interdependencies characteristic of delta regions require new approaches to understand, diagnose, and evaluate the current and future impacts of social–ecological changes and potential solutions to the sustainability dilemmas of delta regions.

Historical dynamics of Batrachochytrium dendrobatidis in Amazonia

The Amazon forest is known for its astonishing amphibian diversity, yet the potential distribution and underlying impacts of the most important amphibian pathogen is unknown for most of Amazonia. In this retrospective survey of preserved Leptodactylus frogs, collected over a 119 yr period, we used quantitative PCR to detect the fungal pathogen Batrachochytrium dendrobatidis (Bd) and performed spatial scan analyses to identify spatiotemporal clusters of Bd. We also quantified the potential effect of environmental factors on the likelihood of Bd occurrence and generated an updated suitability map for Bd in the Amazon that included our retrospective sampling. We detected Bd in lowland Amazon as early as 1935, in the state of Pará, Brazil, and we found low prevalence (∼ 3.8%) over time. We identified two statistically significant spatiotemporal clusters of Bd: a recent and narrow cluster in the Amazon River delta and a spatiotemporally broad cluster in the southern edge of Amazon and Brazilian savanna. Furthermore, we found an increase in Bd‐positive samples in the southwestern Amazon after the 1990s, coinciding with reported amphibian declines in neighboring high elevation sites on Andean slopes of Peru. Spatial regressions indicated that higher human interference, higher precipitation, and lower temperatures were significant predictors of Bd occurrence. Environmental niche modeling predicted some narrow areas of suitable climates along the Amazon's periphery and generally low climatic suitability for Bd in the central Amazon; although, we found clusters of Bd‐positive samples with unexpectedly high infection loads in areas of predicted low suitability. Our study indicates that accelerated human development may put Amazonian amphibians at risk from Bd introductions, and it highlights the potential need to monitor Bd dynamics near Amazonian port cities.

Asymmetrical deltas below wave base: Insights from the Fraser River Delta, Canada

AbstractThe Fraser River Delta exhibits distinct asymmetry in the sedimentological and neoichnological characteristics of the updrift (south) and downdrift (north) sides of the main distributary channel in water depths below storm‐wave base. The asymmetry is the result of net northward tidal flow. Tides erode sediments across the updrift delta front, whereas the downdrift delta front is an area of net deposition. A submarine channel prevents sand eroded from the updrift delta front from reaching the downdrift delta. The updrift delta front and updrift upper prodelta are composed of sand or heterolithic sand and mud that show a low density of burrowing (Bioturbation Index 0 to 3) and are dominated by simple traces. The downdrift delta front and prodelta, and the updrift lower prodelta are composed of homogeneous muds with significantly higher bioturbation intensities (Bioturbation Index 3 to 6), and a more diverse suite of traces akin to Cruziana Ichnofacies. Using the Fraser River Delta as an archetype and comparing the Fraser to the Amazon River Delta, a preliminary model for deep‐water (below storm‐wave base: ca 20 m) asymmetrical deltas is proposed. Firstly, deep‐water asymmetrical deltas are recognized from sediments deposited below storm‐wave base. At these depths, tidal and ocean currents are more likely to impact sediment transport, but wave processes are less effective as a sediment transport mechanism. Sediments deposited below storm‐wave base in deep‐water asymmetrical deltas will display the following: (i) the updrift delta front will be coarser‐grained (for example, sand‐dominated or heterolithic sand and mud), than the downdrift delta front (for example, mud‐dominated); and (ii) the updrift delta front should show low‐diversity suites of simple burrows. Depending on sedimentation rates, the downdrift delta front and prodelta may show either high diversity suites of traces that are dominated by both complex and simple burrows (low sedimentation rates) or low density and diversity suites akin to the updrift delta front (high sedimentation rates).

An assessment of cloud masking schemes for satellite ocean colour data of marine optical extremes

One of the most important steps in utilizing ocean colour remote-sensing data is subtracting the contribution of the atmosphere from the signal at the satellite to obtain marine water-leaving radiance. To be carried out accurately, this requires clear-sky conditions, i.e. all clouds need to be excluded or masked from the data prior to atmospheric correction. The standard cloud mask used routinely in the processing of NASA global ocean colour data is based on a simple threshold applied to the Rayleigh-corrected top-of-atmosphere (TOA) radiance. The threshold is kept purposefully low to ensure high-quality processing at a global scale. As a consequence, the standard scheme can sometimes inadvertently mask important extreme optical events such as intense blue–green algal (cyanobacteria) blooms or the outflow of sediment-rich waters from some of the world’s largest rivers. However, the importance of these extreme conditions, both for ecological and hydrological applications, requires that they should be appropriately monitored. Therefore, an assessment of existing cloud masking schemes that could provide valuable alternatives was carried out. A new hybrid cloud mask was also proposed and similarly tested. The selected schemes were systematically assessed over a full annual cycle of satellite ocean colour data on three example regions: the Baltic Sea, the Black and Azov Seas, and the Amazon River delta. The results indicate that the application of alternative cloud masking schemes produces a significant increase in clear-sky diagnostics that varies with the scheme and the region. Major occurrences of extreme optical conditions, such as cyanobacteria blooms, or river deltas formerly excluded from any processing may be recovered, but some schemes may underestimate the amount of thin clouds potentially detrimental to ocean colour atmospheric correction.

Distribuição da castanha-do-brasil (Bertholletia excelsa) através do tempo: desde a contração no refúgio glacial, sua expansão mediada pelos humanos, até a mudança climática antropogênica

Brazil nut (Bertholletia excelsa) is one of the most important non-timber forest producing tree species in the Amazon. One aspect related to the sustainability of Brazil nut that has so far received very limited attention in literature is how the species’ distribution has changed through time and will continue to do so in light of anthropogenic climate change. We modeled the potential distribution of Brazil nut during different past climates as well as during several future time periods. Of the past time periods, the Last Glacial Maximum (~21,000 BP) had the biggest impact on the present distribution of Brazil nut. The distribution of suitable habitat may have been restricted primarily to several potential refugia across southern Amazonia. On the other hand, the oldest Brazil nut remains found at the Pedra Pintada cave (~11,000 BP) were probably harvested by early humans from trees that reached the area after natural range expansion from one or more smaller refugia which may have been located close to the Amazon River delta. Future climate projections predict a positive future for Brazil nut. We conclude with a number of recommendations to improve the species’ conservation, use and management, both within and outside its current distribution area.