Amazonian Waters Research Articles

Water Typology in the Amazon: Close Correlation with the Hydrogeochemistry of River Basins

A study on the typology of Amazonian waters was developed in the North Geographic Region of Brazil, considering a set of historical data from 1995 to 2022. The objective was to discuss and point out which environmental parameters are considered preponderant within the classification criteria of Amazonian waters. Historical data on temperature, density, pH, conductivity, oxygen, transparency, light attenuation, turbidity, color, total and dissolved solids, hardness, alkalinity, CaCO3, BOD, COD, main cations and anions, iron, C, N and P fractions, silicate, trace elements (Al, Cu, Zn and Mn) and chlorophyll a were analyzed. The analysis comprised water samples from the National Hydrometeorological Network (Sub-Basins 10 to 19), with a total of 36 basins, including tributaries, lakes and adjacent streams. The historical series was statistically analyzed through the techniques of Cluster, Principal component analysis (PCA), Piper Diagram and image interpolation by the ordinary kriging method. The results indicated a strong seasonal trend, with an evident distinction between the flood and ebb periods. The typology of white, black and clear waters was also evidenced, this last group being an intermediate class to the others, due to the physical-chemical standards. The PCA highlighted the parameters conductivity, pH, calcium, bicarbonate and Dissolved inorganic carbon (DIC) (Factor 1), and turbidity and alkalinity (Factor 2) as preponderant in the water classification. The ionic balance demonstrated that the white waters stood out for the highest concentrations of calcium and magnesium. The results suggest a pattern of calcic waters oscillating towards sodic and carbonated waters, with a subgroup in the northern eastern region of seasonally sodic-chlorinated waters, due to the influence of ocean tides. Image interpolation suggested a predominance of white waters in the western southern zone (Western Amazon) and white waters transitioning to clear waters in the eastern zone (Eastern Amazon). The analysis also showed a predominant strip of black and clear waters in the northern zone, and a strip of white waters in the central Amazon.

Myxozoan Ceratomyxids Infecting the Gallbladder of Amazonian Ornamental Cichlid Fish: Description of Ellipsomyxa santarenensis n. sp. and Report of Ceratomyxa amazonensis in a New Host

Although most Myxozoa species of the genera Ceratomyxa and Ellipsomyxa have been described in marine hosts worldwide, an increasing diversity has been reported infecting South American freshwater fish, mainly in Amazonian waters. The present study deals with two species of myxozoan ceratomyxids parasitizing the gallbladder of Amazonian ornamental cichlids fish: Ceratomyxa amazonensis is identified from a new host—Geophagus altifrons; while Ellipsomyxa santarenensis n. sp. is described infecting Satanoperca jurupari. Morphological (light microscopy and transmission electron microscopy), molecular (small ribosomal subunit DNA—SSU-rDNA sequencing) and phylogenetic analyses were used to characterize both species. Ceratomyxa amazonensis showed a prevalence of 64.2%, with plasmodia showing a vermiform shape and motility. For E. santarenensis n. sp., the prevalence was 33.3%. Ultrastructural analysis revealed that the vermiform C. amazonensis plasmodia were composed of an outer cytoplasmic region and a large vacuole occupying the inner area. In E. santarenensis n. sp., cytoplasmic expansions were observed in pseudoplasmodia originating pseudopodia. SSU rDNA sequencing-based genetic distance analysis revealed a very small difference between C. amazonensis, parasite of G. altifrons, and C. amazonensis, parasite of S. discus—host of the original description, thus showing that they are the same species occurring in a new host. For Ellipsomyxa santarenensis n. sp., molecular data revealed a difference of 1.6% for Ellipsomyxa amazonensis and Ellipsomyxa paraensis. The phylogenetic analysis revealed the grouping of E. santarenensis n. sp. together with the other freshwater Ellipsomyxa species of the Amazonian region, and associated with the morphological data, it was possible to identify it as a new taxon within the genus Ellipsomyxa.

Challenges and alternatives for unmanned underwater vehicular research in the Amazon basin: Towards a more sustainable management of water resources and the environment

AbstractThe Amazon basin is one of the largest hydrographic systems in the world, possessing a great diversity of natural resources in need of more sustainable water and environmental management. However, as much of what lies beneath the surface of Amazonian waters is still unexplored, underwater exploration technologies are seen as a means of research and monitoring. The present work therefore aims to answer two research questions: What are the current technologies that could be implemented for unmanned underwater research in the Amazon waters? What are the main limitations and existing alternatives for using unmanned underwater vehicles in the rivers of this region to provide more sustainable water and environment management? Our results demonstrate that remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) are possible options in the short and long terms, respectively. The main challenges in implementing these technologies are related to the variations in hydraulic geometry, current velocities and turbidity of the rivers, as well as the preservation of the region's biodiversity. This research can be taken as a starting point for planners and decision makers seeking more sustainable underwater and environmental exploration of the Amazon river system.

Mapping the Amazon's fish under threat.

Ichthyologist Lucia Rapp Py-Daniel preserves and catalogues the fish of Amazonian waters as their numbers fall because of industrial development. Ichthyologist Lucia Rapp Py-Daniel preserves and catalogues the fish of Amazonian waters as their numbers fall because of industrial development.

Investigating the mechanisms of dissolved organic matter protection against copper toxicity in fish of Amazon's black waters

We investigated how natural dissolved organic matter (DOM) of the Rio Negro (Amazon) affects acute copper (Cu) toxicity to local fish: the cardinal tetra (Paracheirodon axelrodi) and the dwarf cichlid (Apistogramma agassizii). It is established that Cu2+ complexation with DOM decreases Cu bioavailability (and thus toxicity) to aquatic organisms, as conceptualized by the Biotic Ligand Model (BLM). However, we also know that Rio Negro's DOM can interact with fish gills and have a beneficial effect on Na+ homeostasis, the main target of acute Cu toxicity in freshwater animals. We aimed to tease apart these potential protective effects of DOM against Cu-induced Na+ imbalances in fish. In the laboratory, we acclimated fish to Rio Negro water (10 mg L−1 DOC) and to a low-DOM water (1.4 mg L−1 DOC) with similar ion composition and pH (5.9). We measured 3-h Cu uptake in gills and unidirectional and net Na+ physiological fluxes across a range of Cu concentrations in both waters. Various DOM pre-acclimation times (0, 1 and 5 days) were evaluated in experiments with P. axelrodi. Copper exposure led to similar levels of net Na+ loss in the two fish, but with distinct effects on Na+ influx and efflux rates reflecting their different ionoregulation strategies. Rio Negro DOM protected against Cu uptake and toxicity in the two fish species. Both Cu uptake in fish gills and Na+ regulation disturbances were relatively well predicted by the modelled aqueous free Cu2+ ion concentration. These findings suggest that protection by DOM occurs mainly from Cu complexation under the tested conditions. The prevalence of this geochemical-type protection over a physiological-type protection agrees with the BLM conceptual framework, supporting the use of the BLM to assess the risk of Cu in these Amazonian waters.

Flying Over Amazonian Waters: The Role of Rivers on the Distribution and Endemism Patterns of Neotropical Bats

The Amazon comprises many of the largest rivers in the planet and also houses some of the richest bat communities in the world. Rivers are important geographic barriers for the dispersal and distribution of different taxa worldwide and, particularly in the Amazon region, they form the conceptual and empirical bases for the recognition of the so-called Areas of Endemism of terrestrial vertebrates. Despite the vast literature on the role of rivers on vertebrate community structure in the Amazon Forest, this process has never been investigated using a comprehensive dataset of Neotropical bat communities in the region. In this study, we aimed at: (1) evaluating the patterns of bat endemism across the Amazon Forest; (2) testing for the relationship between the distribution of bat species in the Amazon and the interfluve Areas of Endemism as currently recognized, and; (3) analyzing the importance of major Amazonian rivers in bat beta-diversity (turnover and nestedness) in the Amazon. Our results indicate that rivers are not major barriers for the current distribution of most bat species, and bat community composition breaks were divided into two clusters separating the east and west regions, and a third cluster in northern Amazon. In addition, there was no significant overlap among species distribution limits and the interfluve Areas of Endemism. Interestingly, the geographic patterns that we found for bat communities composition breaks highly resembles the one recovered using bird communities, suggesting that similar ecological and historical drivers might be acting to determine the distribution of flying vertebrates in the Amazon. Moreover, Amazonian bat distribution and endemism patterns were likely shaped by factors other than rivers, such as species interactions and the current environmental conditions. In conclusion, our results highlight the importance of modern analytical approaches to investigate large scale ecological patterns in the Neotropical region, and also challenge the widely recognized role of rivers on the determination of community structure and endemism patterns in the Amazon Forest, at least for bats.

Hybrid Semi-Analytical Algorithm for Estimating Chlorophyll-A Concentration in Lower Amazon Floodplain Waters

The Amazon Basin is the largest on the planet, and its aquatic ecosystems affect and are affected by the Earth’s processes. Specifically, Amazon aquatic ecosystems have been subjected to severe anthropogenic impacts due to deforestation, mining, dam construction, and widespread agribusiness expansion. Therefore, the monitoring of these impacts has become crucial for conservation plans and environmental legislation enforcement. However, its continental dimensions, the high variability of Amazonian water mass constituents, and cloud cover frequency impose a challenge for developing accurate satellite algorithms for water quality retrieval such as chlorophyll-a concentration (Chl-a), which is a proxy for the trophic state. This study presents the first application of the hybrid semi-analytical algorithm (HSAA) for Chl-a retrieval using a Sentinel-3 OLCI sensor over five Amazonian floodplain lakes. Inherent and apparent optical properties (IOPs and AOPs), as well as limnological data, were collected at 94 sampling stations during four field campaigns along hydrological years spanning from 2015 to 2017 and used to parameterize the hybrid SAA to retrieve Chl-a in highly turbid Amazonian waters. We implemented a re-parametrizing approach, called the generalized stacked constraints model to the Amazonian waters (GSCMLAFW), and used it to decompose the total absorption αt(λ) into the absorption coefficients of detritus, CDOM, and phytoplankton (αphy(λ)). The estimated GSCMLAFWαphy(λ) achieved errors lower than 24% at the visible bands and 70% at NIR. The performance of HSAA-based Chl-a retrieval was validated with in situ measurements of Chl-a concentration, and then it was compared to literature Chl-a algorithms. The results showed a smaller mean absolute percentage error (MAPE) for HSAA Chl-a retrieval (36.93%) than empirical Rrs models (73.39%) using a 3-band algorithm, which confirms the better performance of the semi-analytical approach. Last, the calibrated HSAA model was used to estimate the Chl-a concentration in OLCI images acquired during 2017 and 2019 field campaigns, and the results demonstrated reasonable errors (MAPE = 57%) and indicated the potential of OLCI bands for Chl-a estimation. Therefore, the outcomes of this study support the advance of semi-analytical models in highly turbid waters and highlight the importance of re-parameterization with GSCM and the applicability of HSAA in Sentinel-3 OLCI data.

The farming and husbandry ofColossoma macropomum: From Amazonian waters to sustainable production

AbstractWithin the rich diversity of South American freshwater fish,Colossoma macropomum(Characiformes: Serrasalmidae), known as tambaqui, cachama or blackfin pacu, can reach 30 kg, is a traditional product in regional fish markets and has drawn the attention of fish farmers since the 1930s. Considerable progress achieved in different fields of aquaculture science has contributed to the growth of tambaqui production. Tambaqui has proven suitable for both monoculture and polyculture systems, and for both extensive and intensive production systems aimed at achieving sustainable, higher productivity with minimal environmental impact. Studies of the reproductive anatomy and physiology of the species proved fundamental to development of techniques to boost commercial production, contributing to development of protocols for hormonally induced spawning and artificial propagation in the 1970s. Newly hatched larvae must be fed with live foods until they can be weaned to artificial feeds at about 100 mg weight. Despite its importance for aquaculture, only a few studies have reported components of quantitative genetic variance and parameters for weight at age, morphometric traits and disease resistance. Genomic tools currently available can be applied to detect variation relevant to performance and to accelerate the process of genetic improvement. While the species’ feeding habit allows the use of diets containing 75%–85% plant protein, much more work needs to be done to optimize aquafeeds. Refinement of tambaqui production methods has the potential to significantly boost South American aquaculture. We recommend research on diets, genetic improvement and system optimization to spur further productivity and achieve sustainable tambaqui culture.

Physico-chemical assessment of waters used to irrigate agricultural lands of Amazon

The use of pesticides / fertilizers in plantations has become a problem in maintaining the quality of surface water. Thus, the objective of this study was to evaluate the water quality for irrigation purposes in the Rio Apéu microbasin – Para. The physico-chemical parameters evaluated were: pH, DO, SAR, TDS and EC measured in situ and the metals Al, Fe, Na, Ca, Mg determined in the laboratory Evandro Chagas Institute, according to the method of APHA. The average levels of pH (5.51), OD (5.04 mg L-1) are indications of normal condition in Amazonian waters. The results of Al (332 mg L-1) and Fe (5.74 mg L -1) imply the leaching of sediments from the geological formation of the region rich in these minerals, even though they present values above what is recommended by the legislation. The Richard classification allowed us to define that the waters of the study area have low salinity and sodicity, so they are not restricted to use. Thus, the results of the water quality analysis in the watershed can be concluded that it does not offer environmental problems in the use for irrigation activity

Biogeochemical water type influences community composition, species richness, and biomass in megadiverse Amazonian fish assemblages

Amazonian waters are classified into three biogeochemical categories by dissolved nutrient content, sediment type, transparency, and acidity—all important predictors of autochthonous and allochthonous primary production (PP): (1) nutrient-poor, low-sediment, high-transparency, humic-stained, acidic blackwaters; (2) nutrient-poor, low-sediment, high-transparency, neutral clearwaters; (3) nutrient-rich, low-transparency, alluvial sediment-laden, neutral whitewaters. The classification, first proposed by Alfred Russel Wallace in 1853, is well supported but its effects on fish are poorly understood. To investigate how Amazonian fish community composition and species richness are influenced by water type, we conducted quantitative year-round sampling of floodplain lake and river-margin habitats at a locality where all three water types co-occur. We sampled 22,398 fish from 310 species. Community composition was influenced more by water type than habitat. Whitewater communities were distinct from those of blackwaters and clearwaters, with community structure correlated strongly to conductivity and turbidity. Mean per-sampling event species richness and biomass were significantly higher in nutrient-rich whitewater floodplain lakes than in oligotrophic blackwater and clearwater river-floodplain systems and light-limited whitewater rivers. Our study provides novel insights into the influences of biogeochemical water type and ecosystem productivity on Earth’s most diverse aquatic vertebrate fauna and highlights the importance of including multiple water types in conservation planning.

Índice do Estado Trófico (IET) em águas amazônicas: baía do Marajó e baía do Guajará

O monitoramento da qualidade da água é de fundamental importância, pois através dela podemos diminuir os problemas relacionados à poluição e contaminação dos corpos hídricos. Pode-se citar como um dos problemas relacionados à qualidade da água a eutrofização, sendo esse um fenômeno que consiste na proliferação de algas em corpos d’água. Pesquisas que visam estudar os índices de qualidade da água são oportunas por ajudarem a evitar problemas maiores, relacionados à saúde pública, bem estar humano e até mesmo a potabilidade. Nesse sentido, este trabalho visou obter o Índice do Estado Trófico (IET) em águas amazônicas e comparar os resultados de fósforo total e/ou clorofila a de acordo com o CONAMA 357/2005. Os cálculos foram realizados de acordo com a metodologia de Lamparelli (2004), sendo uma adaptação para ambientes tropicais do índice adotado por Carlson (1977). Percebe- se que o lago Bolonha e a Baía do Guajará, obtiveram valores de “Supereutrófico” e variação de “Ultraliogotrófico” a “Supereutrófico” respectivamente para IET, sendo possível associar o uso e ocupação do solo próximo aos pontos de amostragens e a interferência urbana do recurso hídrico estudado. Já o rio Pará e o rio Maratauíra apresentaram baixo risco de eutrofização, com predominância do estado “ultraoligotrófico” indicando que as áreas de estudos apresentaram um baixo grau de trofia. Obteve-se valores de fósforo total acima do limite estabelecido pela Resolução CONAMA 357/2005 nos trabalhos realizados na baía do Guajará e no lago Bolonha para águas doces classe 2. Na área portuária de Barcarena e rio Maratauíra, apresentaram concentrações baixas de fósforo total.

Tambaqui (Colossoma macropomum) acclimated to different tropical waters from the Amazon basin shows specific acute-stress responses

Stress responses in teleosts include the release of hormones into the bloodstream. Their effects depend on the species and on the environmental conditions. The Amazon basin collects waters of diverse chemical composition, and some fish are able to inhabit several of them. However, the effects of these waters on the stress axis are still unknown. Here we show how acute air-exposure differently affects stress biomarkers in tambaqui (Colossoma macropomum), a tropical model species, when acclimated to two Amazonian waters (Rio Negro –RN- water rich in humic acids and poor in ions, and groundwater –IG- with no humic acids and higher concentration of ions). This study described primary and secondary stress responses after air exposure including plasma cortisol, energy metabolites, pH and ions, skin mucus energy metabolites, as well as gills and kidney Na+/K+-ATPase and Na+/H+-exchanger (NHE) activities. Several differences were described in these stress biomarkers due to the acclimation water. The most remarkable ones include increased mucus glucose only in RN-fish, and mucus lactate only in IG-fish after air exposure. Moreover, an inverse relationship between plasma cortisol and Na+ concentrations as well as a direct relationship between plasma ammonia and branchial NHE activity were observed only in RN-fish. Our results demonstrate how important is to study stress responses in fish acclimated to different environments, as physiological differences can be magnified during episodes of high energy expenditure. In addition to having a direct application in aquaculture, this study will improve the management of critical ecosystems such as the Amazon.

Gills versus kidney for ionoregulation in the obligate air-breathing Arapaima gigas, a fish with a kidney in its air-breathing organ.

In Arapaima gigas, an obligate air-breather endemic to ion-poor Amazonian waters, a large complex kidney runs through the air-breathing organ (ABO). Previous indirect evidence suggested that the kidney, relative to the small gills, may be exceptionally important in ionoregulation and nitrogen (N) waste excretion, with support of kidney function by direct O2 supply from the airspace. We tested these ideas by continuous urine collection and gill flux measurements in ∼700 g fish. ATPase activities were many-fold greater in kidney than gills. In normoxia, gill Na+ influx and efflux were in balance, with net losses of Cl- and K+ Urine flow rate (UFR, ∼11 ml kg-1h-1) and urinary ions (< 0.2 mmol l-1) were exceptional, with [urine]:[plasma] ratios of 0.02-0.002 for K+, Na+, and Cl-, indicating strong reabsorption with negligible urinary ion losses. Urinary [ammonia] was very high (10 mmol l-1, [urine]:[plasma] ∼17) indicating strong secretion. The kidney accounted for 21-24% of N excretion, with ammonia dominating (95%) over urea-N through both routes. High urinary [ammonia] was coupled to high urinary [HCO3-]. Aerial hypoxia (15.3 kPa) and aerial hyperoxia (>40.9 kPa) had no effects on UFR, but both inhibited branchial Na+ influx, revealing novel aspects of the osmorespiratory compromise. Aquatic hypoxia (4.1 kPa), but not aquatic hyperoxia (>40.9 kPa), inhibited gill Na+ influx, UFR and branchial and urinary ammonia excretion. We conclude that the kidney is more important than gills in ionoregulation, and is significant in N excretion. Although not definitive, our results do not indicate direct O2 supply from the ABO for kidney function.

The physiology of the Tambaqui (Colossoma macropomum) at pH 8.0.

The Tambaqui is a model neotropical teleost which is of great economic and cultural importance in artisanal fisheries and commercial aquaculture. It thrives in ion-poor, often acidic Amazonian waters and exhibits excellent regulation of physiology down to water pH 4.0. Curiously, however, it is reported to perform poorly in aquaculture at pH 8.0, an only slightly alkaline pH which would be benign for most freshwater fish. In initial experiments with Tambaqui of intermediate size (30-50g), we found that ammonia excretion rate was unchanged at pH 4, 5, 6, and 7, but elevated after 20-24h at pH 8, exactly opposite the pattern seen in most teleosts. Subsequent experiments with large Tambaqui (150-300g) demonstrated that only ammonia, and not urea excretion was increased at pH 8.0, and that the elevation was proportional to a general increase in MO2. There was an accompanying elevation in net acidic equivalent excretion and/or basic equivalent uptake which occurred mainly at the gills. Net Na+ balance was little affected while Cl- balance became negative, implicating a disturbance of Cl- versus base exchange rather than Na+ versus acid exchange. Arterial blood pH increased by 0.2 units at pH 8.0, reflecting combined metabolic and respiratory alkaloses. Most parameters recovered to control levels by 18-24h after return to pH 6.0. With respect to large Tambaqui, we conclude that a physiology adapted to acidic pH performs inappropriately at moderately alkaline pH. In small Tambaqui (4-15g), the responses were very different, with an initial inhibition of ammonia excretion rate at pH 8.0 followed by a subsequent restoration of control levels. Elevated ammonia excretion rate occurred only after return to pH 6.0. Furthermore, MO2, plasma cortisol, and branchial vH+ATPase activities all declined during pH 8.0 exposure in small Tambaqui, in contrast to the responses in larger fish. Overall, small Tambaqui appear to cope better at pH 8.0, a difference that may correlate with their natural history in the wild.

A Synoptic Assessment of the Amazon River-Ocean Continuum during Boreal Autumn: From Physics to Plankton Communities and Carbon Flux.

The Amazon generates the world's largest offshore river plume, which covers extensive areas of the tropical Atlantic. The data and samples in this study were obtained during the oceanographic cruise Camadas Finas III in October 2012 along the Amazon River-Ocean Continuum (AROC). The cruise occurred during boreal autumn, when the river plume reaches its maximum eastward extent. In this study, we examine the links between physics, biogeochemistry and plankton community structure along the AROC. Hydrographic results showed very different conditions, ranging from shallow well-mixed coastal waters to offshore areas, where low salinity Amazonian waters mix with open ocean waters. Nutrients, mainly and , were highly depleted in coastal regions, and the magnitude of primary production was greater than that of respiration (negative apparent oxygen utilization). In terms of phytoplankton groups, diatoms dominated the region from the river mouth to the edge of the area affected by the North Brazil Current (NBC) retroflection (with chlorophyll a concentrations ranging from 0.02 to 0.94 mg m−3). The North Equatorial Counter Current (NECC) region, east of retroflection, is fully oligotrophic and the most representative groups are Cyanobacteria and dinoflagellates. Additionally, in this region, blooms of cyanophyte species were associated with diatoms and Mesozooplankton (copepods). A total of 178 zooplankton taxa were observed in this area, with Copepoda being the most diverse and abundant group. Two different zooplankton communities were identified: a low-diversity, high-abundance coastal community and a high-diversity, low-abundance oceanic community offshore. The CO2 fugacity (fCO2sw), calculated from total alkalinity (1,450 < TA < 2,394 μmol kg−1) and dissolved inorganic carbon (1,303 < DIC < 2,062 μmol kg−1) measurements, confirms that the Amazon River plume is a sink of atmospheric CO2 in areas with salinities <35 psu, whereas, in regions with salinities >35 and higher-intensity winds, the CO2 flux is reversed. Lower fCO2sw values were observed in the NECC area. The ΔfCO2 in this region was less than 5 μatm (−0.3 mmol m−2 d−1), while the ΔfCO2 in the coastal region was approximately 50 μatm (+3.7 mmol m−2 d−1). During the cruise, heterotrophic and autotrophic processes were observed and are indicative of the influences of terrestrial material and biological activity, respectively.

Investigating copper toxicity in the tropical fish cardinal tetra (Paracheirodon axelrodi) in natural Amazonian waters: Measurements, modeling, and reality

Copper at high concentrations is an ionoregulatory toxicant in fish and its toxicity is known to be strongly modulated by the water chemistry. The toxicity of Cu to the tropical fish cardinal tetra (Paracheirodon axelrodi) was investigated in waters from two major rivers of the Amazon watershed: the Rio Negro (filtered <0.45μm, pH 5.6, DOC=8.4 mgL−1, Na=33μM, Ca=8μM) and the Rio Solimões (filtered <0.45μm, pH 6.7, DOC=2.8 mgL−1, Na=185μM, Ca=340μM), as well as in a natural “reference water” (groundwater) which was almost DOC-free (pH 6.0, DOC=0.34 mgL−1, Na=53μM, Ca=5μM). Acute 96-h mortality, Cu bioaccumulation and net flux rates of Na+, Cl−, K+ and total ammonia were determined in P. axelrodi exposed in each water. Copper speciation in each water was determined by two thermodynamic models and by potentiometry, and its toxicity was predicted based on the biotic ligand model (BLM) framework. Our results indicate that high Na+ loss is the main mode of toxic action of Cu in P. axelrodi, in accordance with general theory. Cardinal tetra showed a particularly high ability to tolerate Cu and to maintain Na+ balance, similar to the ability of this and other endemic Rio Negro species to tolerate low pH and ion-poor conditions. Cu toxicity was lower in Rio Negro than in the other two waters tested, and the free [Cu2+] at the LC50, as determined by any of the three speciation methods tested, was approximately 10-fold higher. This variation could not be captured by a realistic set of BLM parameters. At least in part, this observation may be due to gill physiological alterations induced by the abundant dissolved organic matter of the Rio Negro. The implication of this observation is that, for metals risk assessment in tropical waters, similar to the Rio Negro, care must be used in applying BLM models developed using temperate DOC and temperate species.

Adaptative processes, control measures, genetic background, and resilience of malaria vectors and environmental changes in the Amazon region

This study relates multiple parameters that are involved in the occurrence and control of malaria in the Amazon. Ebbs and floods, black and white waters, fishponds, and “repiquete” (Amazonian waters phenomenon) influence the density of Anopheles darlingi Root, 1926. The adaptive processes, genetic background, and resilience of Anopheles vectors change in response to climate and environmental changes. This study covers the diversity of anophelines, which increases due to anthropic activities. Regarding strategies for vector control, the following measures are important: (1) use mechanical barriers inside houses (screens and impregnated mosquito nets), (2) determine the level of anopheline resistance to insecticides, and (3) determine the effect of the physiological state of females on malaria transmission effectiveness. Bioinsecticides were found to be efficient in the control of immatures, and there was no alteration of the associated fauna. Data on genetic variability and vector populations demonstrated greater polymorphism in intradomicile subpopulations. Furthermore, knowledge on the structural genome and transcriptome of A. darlingi, associated with bio-ecology and evolution, may indicate an adaptive strategy of this species to the Amazon biome. There are anthropic activities and environmental and climatic changes that favor increased vector density, requiring specific control strategies to reduce populations of this species.

Are Amazonian fish more sensitive to ammonia? Toxicity of ammonia to eleven native species

Little is known about the tolerance of Amazonian fish to ammonia. However, elevated ammonia of anthropogenic origin may now occur. As Amazonian fish evolved in waters which are generally acidic (i.e., low NH3), we hypothesized that they would be more sensitive to ammonia than other freshwater fish. The acute (96-h) toxicity of NH4Cl was tested in native ion-poor soft water (pH 7.0, ~28 °C) using semi-static tests with 11 species. Species sensitivity distributions (SSDs) for LC5096 h and LC1096 h and calculations of the hazardous concentrations to the most sensitive 5% (HC5 values) were tabulated. Values of LC5096 h/LC1096 h (in mM total ammonia) ranged from 2.24/0.78 for Paracheirodon axelrodi (most sensitive) to 19.53/16.07 for Corydoras schwartzi (most tolerant). These results confirm our hypothesis that Amazonian fish are more sensitive to ammonia than other freshwater species. High levels of ammonia may be associated with hypoxia, especially during dry periods. Simultaneous hypoxia (15–20% saturation) exacerbated ammonia toxicity in the most sensitive species (P. axelrodi), but not in Astronotus ocellatus or Corydoras schwartzi, a facultative air-breather where prevention of air access doubled ammonia toxicity. The present data are useful in generating regulatory guidelines in Amazonian waters and indicate that further studies incorporating hypoxia and air access/denial are needed.

Hematological adjustments of the bony tongue Arapaima gigas under influence of amazonian waters

Arapaima gigas, populary known as pirarucu is largest freshwater fish in Amazon river, with great, economic and ecological, interest. Despite being an air breather its gill structure is quite close to water breathers, especially in early stages of development [1]. However, in animals above 100g the pillar cell system are embedded into the filament being the gill, an ion regulation active site. The effects of Amazonian rivers waters is well notices in fish [2], mainly by black water (BW), and white water (WW) where the ion fluxes can be meansured [3]. However information on the ionic regulation patters on this species are scarce as well implication by hematological adjustments. Such data could provide inferences on management conditions as well corroborate with what has been suggested by literature, which suggest this species as a panmitic population [4] able to deal with the hydrographic barrier formed by BW in the Amazon basin [5]. The present study aims was to analyzed A. gigas hematological parameters when exposed to BW and WW providing suitable hematological data concerning physiological responses in different types of water. Fish were acclimated seven days in three separated ponds containing BW, WW and well water (C), respectively. Control (C) fish were placed in the latter pond. Blood samples were taken from the caudal vessel at the end of acclimation period in order to perform measurement assays on levels of hemoglobin, hematocrit, mean corpuscular volume (MCV), mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, as well glucose, cholesterol and protein levels. Our findings corroborate the hypothesis stating that BW does interfere on fish adaptation specialy in small fish (~100g). These lack of adaptation should be due the gill morphology of small fish which is close to other water breather fish. However in large fish (~1000g) the findings cleary showed that neither WW or BW can interfere on plasma profile of analysed fish. The compromisse between gas exchange and ion regulation has been demonstrated previously. As hematological adjustment plays a role on such osmorespiratory compromise, the hematological parameters data presented by this study clearly demonstrate that changes in the hematological features play a crucial role in the water to air breathing transition behavior as well in the A. gigas gill ontogenetic changes. Despite black water systems being considered a barrier constraining the dispersion of several species; this seems not to be a problem for this species which has kept its ion-regulatory mechanisms even when immerse in black waters.

Time-series analysis of Landsat-MSS/TM/OLI images over Amazonian waters impacted by gold mining activities

Water siltation caused by artisanal gold mining has impacted the Tapajós River Basin in Brazil for the past 40years, however spatial-temporal information about changes in water quality and consequences to the aquatic environment is lacking. To address this, the Landsat satellite family sensors were used to retrieve total suspended solids (TSS) of the water of the Tapajós River from 1973 to 2013. An image processing approach that includes atmospheric correction, based on the 6S model, and glint removing, based on shortwave infrared correction, was applied and validated with in situ radiometric data. An optimization of the atmospheric correction having dark dense forest spectra as reference was applied and allowed a robust correction of MSS, TM and OLI signal to surface reflectance values. Sediment concentration was estimated based on a non-linear empirical regression between measured TSS and satellite surface reflectance at red band. The multi-temporal analysis of TSS showed that the sediment load in the Tapajós aquatic system is in synchrony with mining activities, and a constant seasonal variation of water siltation is observed throughout the time frame of this study. At the end of the rainy season, mining activities intensify and, coupled with low water flow, TSS increases. During the high water level, TSS concentrations were consistently lower because of high water dilution and low mining activity. In a decadal analysis, a peak of sediment concentration coincides with a peak of gold production in all sites analyzed during early 1990s. More recently, due to the currently gold rush, an increase in suspended solids has been observed mainly in the Novo and Tocantins rivers where industrial mining has been installed.