Can species guilds act as hubs for energy transfer in macrophyte meadows of Amazonian floodplain lakes?

Aquatic macrophytes are the main autochthonous component of primary production in the Amazon Basin. Floating meadows of these plants support habitats with highly diverse animal communities. Fishes inhabiting these habitats have been assumed to use a broad range of food items and compose a particular food web. We employed carbon (δ13C) and nitrogen (δ15N) stable isotope analysis to draw the trophic structure of these habitats and to trace the energy flow by its trophic levels. Fishes and other animals from 18 independent macrophyte meadows of a floodplain lake of the Solimões River (Amazonia, Brazil) were analyzed. The food web of macrophyte meadows consists of four trophic levels above autotrophic sources. In general, primary consumers exhibited a broader range of food sources than the upper trophic levels. Some fish species depended on a large number of food sources and at the same time are consumed by several predators. The energy transfer from one trophic level to the next was then mainly accomplished by these species concentrating a high-energy flux and acting as hubs in the food web. The broad range of δ13C values observed indicates that the organisms living in the macrophyte meadows utilize a great diversity of autotrophic sources.

Assessment of Human Health Risk of Metal(Loid) Content in Brazilian Sardine Along the Southwestern Atlantic.

The Brazilian sardine (Sardinella aurita) is an important food resource found in the subtropical Southwestern Atlantic Continental Shelf (CSSWA), but limited information about its metal(loid) concentrations is available, restricting effective risk assessment by its consumption. On this research, we hypothesized that S. aurita presents different metal(loid) concentrations within a latitudinal gradient in the CSSWA (northern and southern sectors). We also assessed the S. aurita consumption contamination risk in both sectors of the CSSWA. The results indicated that S. aurita might present different chemical and contamination profiles between the observed sectors, with highlights to As, Cr, and Fe at greater levels than the safety limits established by regulatory agencies. Such finds could be explained by urbanization, industrialization, continental and oceanographic processes along the CSSWA, corroborating our hypothesis for most observed metals(loid). On the other hand, our risk assessment analysis of metal(loid) concentrations did not indicate hazards for human consumption.

Bioconcentration and translocation of Cd and Hg in a tomato (Solanum lycopersicum) from cultivated soils in southeastern Brazil.

Food is the main source of toxic metals like mercury (Hg) and cadmium (Cd) to humans. This study evaluated the accumulation and translocation of Cd and Hg in a soil-plant system in four tomato plantations and assessed the risk associated with ingestion of these metals. Ten soil samples (rhizosphere) and 10 samples of plant tissues (leaf, ripe fruit, green fruit, and roots) were collected in each plantation. Spatial variation in Cd and Hg concentrations was negligible. The Cd level in rhizosphere was lower in comparison with that of plant tissues. Hg levels in rhizosphere were similar to roots and higher than the value observed in aerial parts of plants. The Cd bioconcentration factor was approximately five times higher compared to that of Hg. Approximately 93% and 48.6% of Cd and Hg accumulated in roots reached aerial parts, respectively. Our results indicate that tomato readily absorbs Cd accumulated in soil, translocating it to aerial parts. Comparatively, the absorption of Hg is not efficient. Levels of Cd in tomatoes were over 17 times higher than the maximum residual levels in 57.5% of ripe fruits and in 27.5% of green tomatoes.

Barium and its Importance as an Indicator of (Paleo)Productivity.

Barium (Ba) is a trace element which occurs predominantly as barite mineral (BaSO4) in the marine environment. Previous work suggests that barite concentrations are related to the organic carbon flux and marine biological debris in the water column suggesting a direct or indirect involvement in the marine biological cycling. In addition, barite has a high preservation rate (~30%) in sediments and it is less affected by early diagenesis than other proxies for productivity such as carbonates (~10%) and organic carbon (~1%), for example. Therefore, Ba is considered an excellent proxy for ocean (paleo)productivity. However, correlating barite to productivity involves some caveats. Specifically, the post-depositional formation of barite in oxic sediments can lead to Ba release into porewaters under anoxic conditions, which can form barite again under oxic conditions. This diagenetic formation is not correlated to export production as the seawater authigenic barite formed with decaying organic matter in the water column. Therefore, the main goal of this work is to briefly review the marine Ba cycle and highlight its importance for (paleo)productivity research.

Microbial and sponge loops modify fish production in phase-shifting coral reefs.

Shifts from coral to algae dominance of corals reefs have been correlated to fish biomass loss and increased microbial metabolism. Here we investigated reef benthic and planktonic primary production, benthic dissolved organic carbon (DOC) release and bacterial growth efficiency in the Abrolhos Bank, South Atlantic. Benthic DOC release rates are higher while water column bacterial growth efficiency is lower at impacted reefs. A trophic model based on the benthic and planktonic primary production was able to predict the observed relative fish biomass in healthy reefs. In contrast, in impacted reefs, the observed omnivorous fish biomass is higher, while that of the herbivorous/coralivorous fish is lower than predicted by the primary production-based model. Incorporating recycling of benthic-derived carbon in the model through microbial and sponge loops explains the difference and predicts the relative fish biomass in both reef types. Increased benthic carbon release rates and bacterial carbon metabolism, but decreased bacterial growth efficiency could lead to carbon losses through respiration and account for the uncoupling of benthic and fish production in phase-shifting reefs. Carbon recycling by microbial and sponge loops seems to promote an increase of small-bodied fish productivity in phase-shifting coral reefs.

Mercury and stable carbon and nitrogen isotopes in the natal Fur of two Antarctic pinniped species.

Southern elephant seal (SES) and Antarctic fur seal (AFS) are short Southern Ocean food web top predators and are spatial and temporal trend bioindicators of Antarctic Hg bioavailability. Hg, stable isotope composition (δ13C and δ15N) and trophic position (TP) regarding sex were determined using lanugo samples from Antarctic pinnipeds pups (SES n = 35 and AFS n = 11). Hg concentrations in over 50% of the SES pups (mean 5.9 ± 3.1 mg kg-1 dry wt.) are compatible with those found to cause neurologic damage to polar bears in the Arctic. No significant differences regarding sexes for SES or AFS are found based on mean Hg concentrations normalized by body weight. δ15N values and TPs are similar among both species, indicating that gestating SES and AFS mothers feed at the same trophic level. Significantly different δ13C values were found, indicating distinct feeding grounds for mothers belonging to both species when pup lanugo is formed in utero; while SES females like to feed in Antarctic waters, AFS females remain in sub-Antarctic waters. The differences in Hg and δ13C observed for both species reflect not only contrasting feeding habits and anthropogenic Hg inputs, but also maternal foraging strategies.

Metals and organic matter baselines in sediments in a cross-shelf gradient at Abrolhos Bank, SW Atlantic.

The present study performed geochemical fractioning of major and minor elements in a cross-shelf gradient of the Abrolhos Bank, where the largest and most diverse coral reefs in the South Atlantic are concentrated. The fractioning was performed using sequential extractions to determine the degree of availability and toxicity of the elements. The mobility pattern of the elements investigated were in the following order: Ca > Mn > Pb > Cr > Zn > Fe > V > Cu > Ba>Al > Ni > Ti. For elements, such as (Ti, Ni, Al, Ba, Cu, V, Fe, Zn, Cr, Pb), the highest concentrations were in the residual phase at some sampling sites. As established by Environment Canada (Threshold Effect Level - TEL and Probable Effect Level - PEL), Ba, Cr, and Ni produced values higher than the limits, associated with higher concentrations of other elements. In addition, significant proportions of these elements were found in mobile phases in the same sites. Thus, more rigorous measures are critical to avoid alarming levels of chronic environmental pollution inside and outside protected areas of the region. To enhance the sustainability of the region, more effective enforcement is crucial to prevent anthropic contamination that may threaten its biodiversity. The results provide the baseline for future studies regarding the potential impacts of the breach of the tailings dam in the region of Mariana, Minas Gerais.

Total Hg and methylmercury dynamics in a river-floodplain system in the Western Amazon: Influence of seasonality, organic matter and physical and chemical parameters.

Total mercury (Hg) and methylmercury (MeHg) circulation in a connected river-floodplain system composed of two black water (a small forest river, igarapé, and Cuniã Lake) and a white water body (Madeira River), located in the Madeira River Basin were evaluated during the rising-water, early and late falling-water periods. We assessed organic matter (C and N composition, (C:N)a; and δ13C isotopic signature), and physical and chemical influences (pH, dissolved O2, electric conductivity) in relationship to Hg and MeHg concentrations. Hg and MeHg concentrations in a sediment profile and three aquatic macrophytes (E. crassipes, E. azuera and Oryza sp.) were measured. Igarapé and Cuniã Lake showed higher Hg and MeHg concentrations (115-709; 10-25 ng g-1) in the suspended particulate matter compared (SPM) compared to the Madeira River (Hg: 5-16; MeHg: 0.2-0.3 ng g-1), partially independent of seasonality (p = 0.06). Total Hg had higher affinity for the SPM (1.75 times) than for dissolved organic matter. Organic matter characteristics correlated with MeHg concentrations (δ13C and (C:N)a; r2 = 0.79; p < 0.0001), as well as physical and chemical parameters of the water column (dissolved O2 and pH; r2 = 0.80; p < 0.0001), demonstrating that physical and chemical changes between the river-floodplain system affect MeHg circulation and production. The inverse correlation of MeHg and SO42- concentrations (r2 = 0.73; p < 0.0001) suggests the action of sulfate-reducing bacteria. Total Hg and MeHg concentrations as well as %MeHg were detected in the sediment profile (Hg: 24-51; MeHg: 0.6-3.2 ng g-1; %MeHg: 1.8-6.2) and aquatic macrophytes (Hg: 1-30; MeHg: 0.3-7.5 ng g-1; %MeHg: 1.6-33.7). We conclude that the highest Hg and MeHg concentrations in Cuniã Lake, compared to the Madeira River, are due to the physical and chemical differences between these environments.

Is there an indication of the origin of nutrient supply in different morphological structures of macrofauna at two different Brazilian southeastern sandy beaches? Comparison by C and N stable isotopes.

The goals of this study were to analyze if there is a difference in the stable isotopic ratio (δ13C and δ15N) of macrobenthic species sampled at two sandy beaches (one close to a river mouth and the other far from any freshwater input) and to identify differences in the stable isotopic ratio (δ13C and δ15N) in different body parts of three representative species of two Brazilian sandy beach macrofaunas: the polychaete Hemipodia californiensis, the mollusk bivalve Donax hanleyanus, and the crustacean decapod Emerita brasiliensis. No significant differences were detected in the δ13C stable isotopic ratio between the two sites analyzed; however, in the δ15N stable isotopic ratio, a significant difference was observed. Regarding the intraspecific response of stable isotopic ratio, D. hanleyanus showed a significant difference in carbon among different body part structures, while a trend for significance was observed for nitrogen isotopes. The differences were significant for both isotopes in E. brasiliensis, and no differences were observed among the body part structures in H. californiensis. There were significant differences in E. brasiliensis carapaces with regard to the δ15N stable isotopic ratio between the muscle and the whole body. Although the δ13C and δ15N stable isotopic ratio differs significantly in the digestive tract, muscles, and whole body of D. hanleyanus, such differences were not enough to determine changes in their trophic levels and food sources. Similar stable isotopic ratios were observed in the whole body, proboscis, and teeth of H. californiensis, highlighting this species as the top predator. In conclusion, stable isotopic analysis of benthic trophic structure can be employed as a tool in coastal management plans or environmental impact studies.

Methylmercury in environmental compartments of a hydroelectric reservoir in the Western Amazon, Brazil.

Damming rivers to generate electricity creates a lentic environment that favors methylmercury (MeHg) formation. Reservoirs in the Amazon are critical environments for MeHg formation, considering its old soils and the use of Hg in gold mining in the region. The objective of this study was to evaluate MeHg accumulation in three environmental compartments (aquatic macrophytes, suspended particulate matter (SPM) and sediment) of the Samuel reservoir (Western Amazon, Brazil), during the low water, ebb and high water hydrological periods, characterizing the dry season, the end of the rainy season and the rainy season, respectively. MeHg concentrations were determined through GC-AFS. The aquatic macrophytes presented higher %MeHg in their roots (up to 12%) compared to their other tissues. This ratio was 1.7 and 5.9 times higher than those observed for SPM and the sediment, but MeHg concentrations were the lowest (0.5-4.5 ng g-1) among the three environmental compartments. Contrary, the highest MeHg concentration was observed in SPM (104 ng g-1) during the low water period. The MeHg concentration in the sediment profile decreased with increasing depth (0.93-0.48 ng g-1) and with decreasing organic matter lability (increasing C:N ratio). In the SPM, on the other hand, MeHg concentration showed a positive association with increasing C:N ratio. We conclude that MeHg dynamics in the SPM are associated with the hydrological periods, with peaks during the low water period. The organic matter lability of the sediments is more limiting to the production of MeHg than the total Hg concentrations.

Insights on the freshwater microbiomes metabolic changes associated with the world's largest mining disaster.

To evaluate the impacts of the Fundão tailings dam failure (Minas Gerais, Brazil) on water quality of the Doce River, we analyzed metagenomics and physicochemical parameters during the month of the disaster and again 6 and 10 months after the disaster. To compare dam conditions before and after the failure, we performed a meta-analysis of physicochemical data from a public database. Immediately after the failure, suspended particulate matter (SPM) in the Doce River was 225-1877 mg L-1. Turbidity and dissolved aluminum and iron concentrations were extremely high, whereas dissolved oxygen was below Brazilian legislation norm (<5 mg L-1) in several locations. Six months later, physicochemical values were below thresholds set by Brazilian guidelines (e.g., SPM = 8-166 mg L-1). Short-term impacts on microbial communities included an increase in Actinobacteria and Bacteroidetes and gene sequences related to microbial virulence, motility, respiration, membrane transport, iron and nitrogen metabolism, suggesting changes in microbial metabolic profiles. The 11 recovered partial genomes from metagenomes (MAGs) had genes related to Fe cycle and metal resistance.

Remote sensing, isotopic composition and metagenomics analyses revealed Doce River ore plume reached the southern Abrolhos Bank Reefs.

On November 5th, 2015, the Fundão dam rupture released >50 million m3 of ore tailings into the Doce River, Minas Gerais State, Brazil. The huge volume of mud spread along the river and reached the sea, 17 days after the disaster, in Regência, Espírito Santo State (ES). In 2018, after three years of the disaster, the impacts of the ore tailings in the marine environment are still unclear. This study aims to investigate possible short-term impacts in marine biodiversity caused by the ore tailings' mud over the reef ecosystems that are closest to the disaster area: i.e. recently discovered reefs in the southern Abrolhos Bank. A remote sensing surveillance including winds, sea surface temperature, total suspended material and watercolor (MODIS Aqua data) indicated that the iron tailings plume reached the southern portion of Abrolhos Bank on June 16th, 2016. Subsequently, to obtain further evidence of the presence of the tailings in the coral reefs, water samples were collected in a gradient spanning from the river estuary to the reefs in southern Abrolhos Bank, we also analyzed the isotopic and microbial composition of the samples, as well as the reef benthic composition. Despite no clues of negative impact on benthic (coral) communities, isotopic analysis confirmed the presence of the plume over the reefs area. This study serves as a baseline for future long-term impact assessments of the health of coral reefs in the Abrolhos Bank.

Mercury, selenium and stable isotopes in four small cetaceans from the Southeastern Brazilian coast: Influence of feeding strategy.

Dolphins are good bioindicators of the contamination status of marine ecosystems, since their dietary and habitat plasticity in both coastal and offshore ecotypes provide information on the trace elements levels originated from natural and anthropogenic sources. In this context, this study aimed to investigate provides mercury (Hg), selenium (Se) levels, trophic ecology and feeding environments of four small cetaceans (Tursiops truncatus, Steno bredanensis, Sotalia guianensis and Pontoporia blainvillei) inhabiting the central-northern coast of Rio de Janeiro State, southeastern Brazil. For the latter, δ15N and δ13C stable isotopes were used as indicators in this regard. Stable isotope values indicate that the four studied species have distinctive foraging habitats, coastal and least coastal, and occupy different trophic positions. The significant relationship found between muscle Hg and δ15N suggests that individual foraging preference remains relatively constant for the studied dolphin species over extended periods. The individual prey size and species are probably responsible for the differences found in Hg and Se concentrations in muscle tissue among all dolphin species. The vulnerable small coastal cetacean, P. blainvillei, which feeds on small teleost fish and squid, presented the lowest muscular Hg concentrations (less than 3.5 µg g-1 dry wt.). Meanwhile, S. bredanensis is more likely to uptake large amounts of trace elements among the four dolphin species, due to its feeding habits mainly being large offshore fish that accumulate high amounts of trace elements in organs and tissues. Differences found between Hg concentrations in fetus-mother pairs were much higher in S. guianensis than in P. blainvillei, suggesting that maternal contribution of Hg via placenta was more significant for the former.

An extensive reef system at the Amazon River mouth.

Large rivers create major gaps in reef distribution along tropical shelves. The Amazon River represents 20% of the global riverine discharge to the ocean, generating up to a 1.3 × 10(6)-km(2) plume, and extensive muddy bottoms in the equatorial margin of South America. As a result, a wide area of the tropical North Atlantic is heavily affected in terms of salinity, pH, light penetration, and sedimentation. Such unfavorable conditions were thought to imprint a major gap in Western Atlantic reefs. We present an extensive carbonate system off the Amazon mouth, underneath the river plume. Significant carbonate sedimentation occurred during lowstand sea level, and still occurs in the outer shelf, resulting in complex hard-bottom topography. A permanent near-bottom wedge of ocean water, together with the seasonal nature of the plume's eastward retroflection, conditions the existence of this extensive (~9500 km(2)) hard-bottom mosaic. The Amazon reefs transition from accretive to erosional structures and encompass extensive rhodolith beds. Carbonate structures function as a connectivity corridor for wide depth-ranging reef-associated species, being heavily colonized by large sponges and other structure-forming filter feeders that dwell under low light and high levels of particulates. The oxycline between the plume and subplume is associated with chemoautotrophic and anaerobic microbial metabolisms. The system described here provides several insights about the responses of tropical reefs to suboptimal and marginal reef-building conditions, which are accelerating worldwide due to global changes.