Lake Batata Research Articles

Do vírus à floresta do igapó: uma revisão sistemática de 35 anos de monitoramento de um Lago Amazônico impactado por rejeitos de bauxita (Lago Batata)

Abstract: Aim Long-term ecological research often integrates many research groups and subjects in one or few sites sampled systematically along the time. In the Amazon, there is a tradition of long-term research in terrestrial habitats, but this has been less common in floodplain lakes. This study systematically reviews 35 years of research (1988-2022) in Batata Lake, a clear water flood plain lake impacted by bauxite mining tailings for ten years (1979-1989) and discuss some research opportunities and challenges for the future. Methods The review covered 99 scientific reports (78 papers and 21 book chapters) comprising a large spectrum of data from snapshot observations and experiments to enduring quarterly observational and hypothesis-testing studies. Soil, sediments, and the water column were consistently sampled in natural and impacted areas. Results Research topics were quite diverse and covered biological communities from aquatic virus to igapó flooded forests and provided an overview of ecological processes such as primary and secondary production. Ecological variables monitored along the project were constrained by a strong seasonality of the flood pulse and the effect of sampling areas (natural and impacted), which was performed by very connected research groups. Conclusions Despite the extensive information, long-term ecosystem function trends are still incomplete.

PHYTOPLANKTON BIOMASS INCREASES IN A SILT-IMPACTED AREA IN AN AMAZONIAN FLOOD-PLAIN LAKE OVER 15 YEARS

Tailings from bauxite mining in Porto Trombetas (Pará state, Central Amazonia, Brazil) was discharged (1979–1989) into Batata Lake affecting about 30% of its area. The lake belongs to a clear-water flood-plain system along the Trombetas River, a tributary of the Amazon River. Siltation is the main perceived factor impacting aquatic and flooded communities. Besides natural regeneration, a program to restore a section of igapó forest in the impacted area (IA) has been conducted since 1991. Decreased light is the main factor reducing total phytoplankton biomass (PhyBM) in IA. We hypothesized that PhyBM in IA increases over time because of the improvement of the underwater light conditions due to the natural regeneration and restoration. We sampled quarterly PhyBM and limnological variables (depth, transparency, temperature, pH, conductivity, dissolved oxygen, turbidity, suspended solids, total Kjeldahl nitrogen, and total phosphorus), over 15 years (2005–2019) at eight sampling sites in the two areas (N = 349). We also obtained daily climatic and hydrologic data. PhyBM was higher in NIA than in IA. The temporal trend in the annual mean of PhyBM increased significantly over time only in the IA, approximating the NIA values, confirming our general hypothesis. The increase of PhyBM in the IA was negatively related to the residual light attenuation caused by non-phytoplankton turbidity and to total phosphorus, and positively to air temperature and site depth (p < 0.05; Marginal r2 = 0.18; Conditional r2 = 0.29). Instead, in NIA, PhyBM was explained only by the increase in air temperature (p < 0.05; Marginal r2 = 0.15; Conditional r2 = 0.34). We concluded that the PhyBM in the IA positively responds to the synergy between increasing light availability, air temperature, and site depth, and decreasing total phosphorus concentrations, regardless of hydrologic phase.

Responses of Phytoplanktonic Chlorophyll-a Composition to Inorganic Turbidity Caused by Mine Tailings

Inorganic turbidity can limit light penetration in water and reduce phytoplankton photosynthesis. Anthropogenic activities such as mining can produce or augment the amount of suspended inorganic particles in water. Recent mining disasters in Brazil have released tons of mine tailings into aquatic ecosystems, with known and unknown negative consequences for aquatic life, biodiversity, and ecosystem services beyond the human and material losses. Here, we investigated the effects of inorganic turbidity on phytoplankton chlorophyll content and composition caused by sediments from two areas in Lake Batata, one natural and the other impacted by bauxite tailings. We experimentally compared the effects of different levels of turbidity (12, 50, and 300 NTU) caused by the addition of sediments from the two lake areas on a chlorophyll-a gradient (5, 15, and 25 μg/L). Inorganic turbidity did not consistently reduce chlorophyll-a concentrations. In treatments with high chlorophyll-a, high turbidity was associated with lower chlorophyll-a concentrations at the end of the experiment. On the other hand, in low-chlorophyll treatments, high turbidity was associated with higher chlorophyll-a concentrations. In treatments with sediments from the natural area, overall chlorophyll-a levels were higher than in treatments with sediments from the impacted area. Phagotrophic algae dominated both in treatments with sediments from the impacted area (Chrysophyceae 34%, Chlorophyceae 26%, and Cyanobacteria 22% of total density) and in treatments with sediment from the natural area (Euglenophyceae 26%, Chrysophyceae 23%, and Chlorophyceae 20%). We conclude that high turbidity does not lead to a reduction in chlorophyll-a concentrations and sediment from the natural area allowed higher chlorophyll-a levels, indicating that impacted area sediment affected more phytoplankton.

Zooplankton functional diversity as an indicator of a long‐term aquatic restoration in an Amazonian lake

Mining is an important economic activity that can have severe impacts on aquatic ecosystems. Plankton communities are commonly used as bioindicators of human‐related threats to freshwater environments due to their rapid response to environmental conditions changes. Here, we used zooplankton functional diversity to understand the recovery patterns of an Amazonian lake impacted by mining activity (input of bauxite tailings) after 30 years of natural attenuation and active restoration processes. Zooplankton species richness and functional diversity (Rao's quadratic entropy—FDQ and community‐level weighted means of trait values—CWM) were compared in impacted and reference areas during the flood period, in March 2015. We found a significant negative influence of turbidity on zooplankton FDQ, and similar FDQ and CWM values between the active restoration area and the reference area. These results suggest a positive effect of vegetation restoration efforts for the zooplankton community of Batata Lake. We demonstrated the utility of zooplankton functional diversity metrics as bioindicators of freshwater restoration, the response of the aquatic ecosystem to vegetation restoration and, consequently, water quality.

TWO-DECADE REMAINING EFFECTS OF BAUXITE TAILINGS ON THE FISH TAXONOMIC STRUCTURE OF A CLEAR-WATER FLOODPLAIN LAKE IN CENTRAL AMAZON (BATATA LAKE, PARÁ STATE, BRAZIL)

In recent decades, anthropic disturbances have led to major changes in biological communities. Batata Lake (Oriximina, Para State, Brazil) is located in the flood area of the right bank of Trombetas River and received effluents rich in mineral waste due to near mining activities in the 80's, which led to the siltation of 30% of its area and numerous local impacts. We monitored about to 20 years the ichthyofauna of Batata Lake and we assessed if there is still remaining effects of the siltation by bauxite tailings in the affected area. We sampled in Silted and Non-Silted areas in the filling period of 1991 to 2015, using a set of gillnets with mesh sizes between 15 to 70 mm. Differences in taxonomic structure (estimated richness, Simpson's dominance and Shannon's diversity) and in community composition among Silted and Non-Silted areas were evaluated with multivariate analysis, considering year as covariate. We sampled 10,435 individuals classified in 141 species. Only 41 species represented 90% of total abundance, which we considered the numerically dominant fishes in the lake. Among taxonomic indices, only estimated richness exhibited a significant trend through time; high estimated richnessin the Silted area during the first years of monitoring and posterior decreasing. This negative slope was highly affected by a single point in 1992, so we considered it a particular case in time and not a real temporal trend. Significant changes in community composition occurred among areas by differentiation in species abundance, and not by species loss. These results show that siltation effects in Batata Lake did not express itself as a loss of biodiversity, but in the reconfiguration of the community composition according to species niche.

Modelling methane formation in sediments of tropical lakes focusing on syntrophic acetate oxidation: Dynamic and static carbon isotope equations

A dynamic model including isotope variables has proved to be an effective tool for evaluating the relative importance of the processes that are taking place in parallel and compete for the same substrate. We present a mathematical description of cellulose conversion into methane and carbon dioxide in the anoxic sediments of three floodplain tropical lakes that were investigated before. Parallel processes of acetoclastic methanogenesis and syntrophic acetate oxidation competing for acetate and gaseous and dissolved H2, CO2, and CH4 are considered in dynamic equations for total and 13C carbon in CH4 and CO2. During cellulose microbial transformation, in accordance with experimental data and modelling, a greater volume of CH4 than CO2 is produced due to the higher CO2 solubility. Changes in the concentration of 13C contained in CH4 and CO2 allowed specifying the pathway of cellulose degradation. We have shown that neglection of syntrophic acetate oxidation results in unrealistically large fractionation factors for hydrogenotrophic methanogenesis, indicating that syntrophic acetate oxidation is of crucial importance in spite of its being fairly slow as compared to other processes. The model reveals that, in the absence of acetate oxidizers, the fraction of methane, fC, produced from H2/CO2 equals 0.33, while in the presence of acetate oxidizers, it is significantly higher (fC≈0.59 in Jatoba Lake and fC≈0.53 in Mussura Lake). In contrast to Jatoba and Mussura Lakes, in sediments of Batata Lake with much smaller initial microbial populations increasing during incubation, the acetoclastic methanogenesis dominates initially with a fC value of less than 0.1, but later the hydrogenotrophic methanogenesis becomes the dominant process, with a fC value of about 0.73 at the end of incubation. The high value of fC=0.641±0.133 is confirmed for 14 Brazilian lakes investigated before. Modelling has shown that the difference between the isotope signatures in methane and carbon dioxide is an informative index to indicate the contribution of syntrophic acetate oxidation for methane production from sediments. The Δ value increases when acetate oxidation becomes significant. The dynamics of carbon isotope signatures in methane and carbon dioxide improve the static isotope equations. In contrast to specific assessments ensuing from the static isotopic equations, the dynamic model enables taking changes in the whole set of experimental data and analyzing the overall system behavior at various model parameters.

The effects of mining tailings and flood pulse on zooplankton in an Amazonian floodplain environment (Batata Lake, Pará, Brazil)

The flood pulse, as well as anthropogenic impacts, may shape the patterns of zooplankton communities. We evaluated the influence of bauxite tailings and water levels on zooplankton at sampling times precisely defined according to the water level. Our study area was Batata Lake, an Amazonian floodplain lake impacted by bauxite tailings. Zooplankton was sampled for seven years, four times a year, at two stations, one natural and the other impacted by bauxite tailings. Zooplankton was identified to the lowest possible taxonomic level. Differences in richness and densities between periods and stations were evaluated with a two-way ANOVA. An indicator species analysis was performed to assign species to sampling stations. Community richness was lower at low water and higher at high water, whereas densities showed the opposite result. Only one species was identified as an indicator, highlighting that the zooplankton composition in natural and impacted areas was similar. Densities were also similar at these stations, except for cladocerans, which showed higher densities at the impacted station. The use of samples taken at precisely defined flood pulse periods yielded expected but refined results, as the samples were based on a precise relationship with water levels that previous studies did not include.

Virus-Bacterium Coupling Driven by both Turbidity and Hydrodynamics in an Amazonian Floodplain Lake

The importance of viruses in aquatic ecosystem functioning has been widely described. However, few studies have examined tropical aquatic ecosystems. Here, we evaluated for the first time viruses and their relationship with other planktonic communities in an Amazonian freshwater ecosystem. Coupling between viruses and bacteria was studied, focusing both on hydrologic dynamics and anthropogenic forced turbidity in the system (Lake Batata). Samples were taken during four hydrologic seasons at both natural and impacted sites to count virus-like particles (VLP) and bacteria. In parallel, virus-infected bacteria were identified and quantified by transmission electron microscopy (TEM). Viral abundance ranged from 0.5 × 10⁷ ± 0.2 × 10⁷ VLP ml⁻¹ (high-water season, impacted site) to 1.7 × 10⁷ ± 0.4 × 10⁷ VLP ml⁻¹ (low-water season, natural site). These data were strongly correlated with the bacterial abundance (r² = 0.84; P < 0.05), which ranged from 1.0 × 10⁶ ± 0.5 × 10⁶ cells ml⁻¹ (high water, impacted site) to 3.4 × 10⁶ ± 0.7 × 10⁶ cells ml⁻¹ (low water, natural site). Moreover, the viral abundance was weakly correlated with chlorophyll a, suggesting that most viruses were bacteriophages. TEM quantitative analyses revealed that the frequency of visibly infected cells was 20%, with 10 ± 3 phages per cell section. In general, we found a low virus-bacterium ratio (<7). Both the close coupling between the viral and bacterial abundances and the low virus-bacterium ratio suggest that viral abundance tends to be driven by the reduction of hosts for viral infection. Our results demonstrate that viruses are controlled by biological substrates, whereas in addition to grazing, bacteria are regulated by physical processes caused by turbidity, which affect underwater light distribution and dissolved organic carbon availability.

Methanogenic pathway, 13C isotope fractionation, and archaeal community composition in the sediment of two clear‐water lakes of Amazonia

We studied the methanogenic pathway and archaeal community composition in the sediment of two clearwater lakes, Lake Batata and Lake Mussura, in Amazonia. We measured CH4 production and δ13C of CO2, CH4, and acetate‐methyl in the presence and absence of CH3F, an inhibitor of acetotrophic methanogenesis. The fractionation factor of methanogenesis from CO2 was rather high in both lake sediments, which was consistent with the low concentrations of H2 and the small negative Gibbs free energy of hydrogenotrophic methanogenesis. The δ13C of acetate‐methyl was relatively low compared to that of organic matter and decreased further upon inhibition of acetate consumption by CH3F. Collectively, the data possibly suggest involvement of syntrophic acetate oxidation besides acetotrophic methanogenesis. The isotopic data were used to calculate the percent contribution of CO2 reduction to total methanogenesis, which was rather high (approximately 53–63%). Copy numbers of bacterial and archaeal 16S ribosomal ribonucleic acid (rRNA) genes were about 10‐fold higher in Lake Mussura than in Lake Batata, indicating that microbial numbers were not a limiting factor for production rates of CH4, which were similar in both lake sediments. The composition of the archaeal community was analyzed by cloning and sequencing of the genes coding for 16S rRNA and methyl coenzyme M reductase (mcrA), demonstrating the presence of acetotrophic Methanosaetaceae and different hydrogenotrophic methanogenic orders (Methanomicrobiales, Methanobacteriales, Methanocellales) in both lake sediments. Although methanogenic communities and pathways were principally comparable to those found in lake sediments of the midlatitudes, there were several particularities, e.g., the possible involvement of syntrophic acetate oxidation.

Interactive effects of environmental variability and human impacts on the long-term dynamics of an Amazonian floodplain lake and a South Atlantic coastal lagoon

Human activities are exposing freshwater ecosystems to a wide range of stressors, whose direct and indirect effects can be alleviated or exacerbated through interactive effects with dynamic environmental drivers. This study used long-term data from two Neotropical lacustrine freshwater systems (Batata Lake, an Amazonian floodplain lake and Imboassica lagoon, an Atlantic coastal lagoon) subjected to different kinds of environmental fluctuations (i.e., flood pulse and sandbar opening) and anthropogenic impacts (i.e., siltation and eutrophication). Our objective was to determine whether the effects of human perturbations are contingent on modifications of important biotic and abiotic characteristics through environmental variability. For both ecosystems, environmental variability consistently interacted with anthropogenic perturbations to alter most of the variables analyzed, such as nutrient dynamics, chlorophyll- a concentration, zooplankton and benthic invertebrate species richness, and temporal community stability, which indicates that interactive effects between environmental variability and anthropogenic perturbations may impact a myriad of ecosystem properties. Furthermore, the nature of these interactive effects was highly dependent on the variable considered and on the ecosystem analyzed. For example, at Imboassica lagoon, sandbar openings interacted synergistically with trophic state to increase the phosphorus concentration in the water column. At Batata Lake, flooding generally alleviated the negative effects of siltation on species richness by both diluting inorganic suspended material concentration and by promoting local recruitment from the regional species pool. Such results indicate that our ability to understand and predict the outcome of anthropogenic impacts on inland aquatic systems can be hampered if we consider human stressors as “static” phenomena disconnected from dynamic interactions with major local environmental drivers.

The role of Campsurus notatus (Ephemeroptera: Polymitarcytidae) bioturbation and sediment quality on potential gas fluxes in a tropical lake

About 30% of the total area of Lake Batata (Amazon) was impacted by the disposal of bauxite tailings originated from the process of washing bauxite. This effluent, composed by fine particles of clay and water, settled on top of the natural sediment, originating a new substratum with a different physical and chemical composition. This phenomenon created a new distinct habitat (impacted sediment) influencing the benthic community. The aim of this study was to evaluate the impact of bioturbation by Campsurus notatus (Ephemeroptera: Polymitarcytidae) on potential gas fluxes in the sediment of natural and impacted areas of the lake. The natural sediment had a significantly higher methane concentration when compared to the impacted one. In incubated sediment cores, the presence of C. notatus nymphs resulted in a significant increase in oxygen consumption and methane and carbon dioxide release to the water column. The effect of the presence of nymphs on methane was ambiguous. The C. notatus nymphs strongly decreased methane concentration in natural sediment samples, probably because of the enhancement of the oxic sediment area. However, this effect was not observed in impacted samples. Finally, the new substratum of Lake Batata decreased methane concentration in sediment and water column. C. notatus nymphs demonstrated to have a significant role on gas flux (methane and CO2) from sediment to water column as well as on oxygen consumption in Lake Batata, consequently influencing the carbon cycle in this lake.

Changes in the allocation of some chemical compounds in structures of Oryza glumaepatula (Steud) in an Amazonian lake subjected to an anthropic impact (Lake Batata, Porto Trombetas)

Changes in the allocation of some chemical compounds in structures of Oryza glumaepatula (Steud) in an Amazonian lake subjected to an anthropic impact (Lake Batata, Porto Trombetas)

Influence of Hydrological Pulse on Bacterial Growth and DOC Uptake in a Clear-Water Amazonian Lake

This study was conducted to evaluate: (1) the bacterial growth and the dissolved organic carbon (DOC) uptake in an Amazonian lake (Lake Batata) at high-water and low-water periods of the flood pulse; (2) the influence of nitrogen and phosphorus (NP) additions on bacterial growth and DOC uptake in Lake Batata at two flood pulse periods; and (3) the bioavailability of the main DOC sources in Lake Batata. Lake Batata is a typical clear-water Amazonian lake, located in the watershed of Trombetas River, Central Amazon, Brazil. Bacterial batch cultures were set up with 90% 0.2-microm filtered water and 10% inoculum from Lake Batata. N-NH(4)NO(3) and P-KH(2)PO(4), with final concentrations of 50 and 5 microM, respectively, were added to the cultures, except for controls. Extra sources of DOC (e.g., algal lysate, plant leachates) were added to constitute six distinct treatments. Bacterial response was measured by maximum bacterial abundance and rates of bacterial production, respiration, DOC uptake, and bacterial growth efficiency (BGE). Bacterial growth and DOC uptake were higher in NP treatments than in controls, indicating a consistent nutrient limitation in Lake Batata. The composition of DOC also seems to be an important regulating factor of bacterial growth in Lake Batata. Seasonally, bacterial growth and DOC bioavailability were higher at low-water period, when the phytoplankton is a significant extra source of DOC, than at high-water period, when the forest is the main source of DOC. DOC bioavailability was better estimated based on the diversity and the diagenetic stage of carbon compounds than on single classes of labile compounds. Changes in BGE were better related to CNP stoichiometry in the water, and the "excess" of organic substrates was oxidized in catabolism, despite the quality of these compounds for bacterial growth. Finally, we conclude that bacterial growth and DOC uptake vary throughout the flood pulse in clear-water Amazonian ecosystems as a result of changes in nutrient concentration and in DOC composition.

The Influence of Bauxite Tailings on the Growth and Development of Oryza glumaepatula in an Amazonian Lake

The influence of bauxite tailings on the growth and development of Oryza glumaepatula was studied in Lake Batata, a clear water lake of the Amazon. Lake Batata is an unusual lake because 30% of its total area was covered by bauxite tailings as the result of aluminum mining, influencing many communities and ecological processes. Changes in length, growth rates, total biomass production, density, culm diameter, net primary production and percentage of different plant organs of Oryza glumaepatula were studied for two consecutive flood pulses in natural and impacted areas of Lake Batata. The aim of this research was to test the hypothesis that the growth and development of this aquatic macrophyte is negatively affected in the areas impacted by bauxite tailings. This hypothesis was rejected because most studied parameters were higher in the impacted area, indicating that the growth and development of O. glumaepatula was not negatively affected by the presence of the bauxite tailings. The better development of O. glumaepatula in the impacted area was attributed to the less available space for germination than in the natural area. The lower density of individuals at the impacted area prevented future density dependent mortality that was observed in the natural areas and did not seem to occur in the impacted area.

Relationship between algae and bacteria in an Amazonian floodplain lake (Batata Lake, Pará, Brazil) — important CO2 pathways

"Relationship between algae and bacteria in an Amazonian floodplain lake (Batata Lake, Pará, Brazil) — important CO2 pathways." Internationale Vereinigung für theoretische und angewandte Limnologie: Verhandlungen, 29(2), pp. 601–602

Responses of the fish community to the flood pulse and siltation in a floodplain lake of the Trombetas River, Brazil

The distributions of the fish species were examined in relation to environmental variables, to evaluate the effects of environmental degradation on the fish community of Batata Lake, a typical Amazonian clearwater lake. From 1979 to 1989, tailings composed of water and clay, extracted from bauxite by water jets, were discharged into Batata Lake. The tailings spread into about 30% of the lake’s area, where the level of the lake bottom rose and turbidity increased. In the present study, multivariate analyses were performed on data for environmental parameters and fish density and biomass. Fish were collected with gillnets during the annual hydrological cycle (filling, flood, drawdown and dry periods), in the silted area, the partly silted area (intermediate) and the natural area. Values of the Shannon index, density and biomass were compared among areas and periods to evaluate the effects of the tailings on community structure. Sediment resuspension, which reduces transparency, is accentuated in shallow water, and was the main factor regulating differences in the community structure between the natural and silted areas. The decrease in transparency occurs mainly during the filling period in the silted area and during the low-water period in the silted and intermediate areas, when sediment resuspension increases concentrations of nutrients and chlorophyll-a. The strong influence of migratory and piscivore species in low-transparency waters is likely associated with the greater bacterioplankton productivity and turnover rate observed by other authors in the silted area, increasing the importance of the heterotrophic food chain in Batata Lake. Reduction of transparency in the silted area was a selective factor for fish species. The death of part of the flooded forest vegetation was decisive in lowering densities of the igapo-associated species in the silted area. The unconsolidated substrate, the death of part of the igapo forest and the negative effects of low transparency – inhibiting resident visually oriented species in the affected areas – are the main factors causing the low diversity in the silted area as a whole. The correlations between CPUEs, conductivity and nutrients and chlorophyll-a concentrations do not appear to reflect cause–effect relationships, indicating that these environmental parameters are poor predictors of fish density in Batata Lake.

Flood pulse influence and anthropic impact on the chemical composition and energy content of Oryza glumaepatula in an Amazonian lake

The aim of this research was to study the flood pulse influence and the anthropic impact caused by bauxite tailings on the chemical composition of O. glumaepatula in Batata lake (PA, Brazil). Sampling was carried out in stands of O. glumaepatula in the low-water, filling, high-water, and drawdown periods in impacted and natural areas of Batata lake. During the low-water and drawdown periods the stands of O. glumaepatula were exposed, and in the filling and high-water periods the water depth was respectively 1.4 and 3.8 m. The collected material was dried at 70 degrees C, ground, and concentrations of total phosphorus, total nitrogen, organic carbon, and energy content were determined. The results indicate that the biomass increase, caused by the rise in water level, has a dilution effect on nitrogen and phosphorus concentrations in O. glumaepatula. The energy contents did not present significant differences in any of the studied periods. The results suggest that from the low water to filling period, nitrogen becomes more limiting to O. glumaepatula in the impacted area, whereas phosphorus becomes more limiting in the natural area. The population of O. glumaepatula contributes to the recovery of the impacted area of Batata lake as the detritus from this species accumulates over the sediment. This accumulation impedes future re-suspension of the bauxite tailings and increases the organic matter and nutrient concentrations in the impacted sediment.

Influence of Campsurus notatus bioturbation on oxygen profile and uptake in sediments of an Amazonian lake impacted by bauxite tailings

Oxygen uptake rates and vertical profiles were determined in sediment taken from natural areas and areas impacted by bauxite tailings in Lake Batata, and in the U-shaped burrows constructed by the nymphs of the benthic ephemeropteran Campsurus notatus, under laboratory conditions. Sediment from impacted and natural areas containing different densities of nymphs of C. notatus (0 to 1,200 ind. m -2 ) were incubated in acrylic cores. In sediment from the natural area, O 2 was present only in the upper 3.5 mm. In the impacted area, the aerobic layer was deeper, with O 2 detected down to 6.5 mm depth. O 2 uptake was twice as high in sediment from the natural area (1.11 mmol O 2 m -2 h -1 ) as from the impacted area (0.61 mmol O 2 m -2 h -1 ). In cores containing nymphs of C. notatus, O 2 uptake was significantly higher than in sediments without C. notatus. The increase in the rates of O 2 uptake was positively correlated with the biomass of the nymphs (g DW m -2 ). The presence of C. notatus resulted in alteration of the O 2 profiles in the sediment of both areas, indicating the importance of these larvae in structuring O 2 profiles in the sediments of Lake Batata.

Length-weight relationships for five cladoceran species in an Amazonian lake

This work shows the length-weight regressions established for the five most frequent and abundant cladoceran species (Bosmina hagmanni, Bosminopsis deitersi, Ceriodaphnia cornuta, Diaphanosoma birgei, and Moina minuta) in two stations at Lake Batata. This lake has received for 10 years very fine bauxite processing tailings, which is responsible for the thick layer over the natural sediment still observed in its western section (impacted station). The individuals were separated into size classes, the dry weight values were determined for each class and were used for establishing weight-length equations. Bosminopsis deitersi and Ceriodaphnia cornuta were the species showing the smallest size in the two sampled areas (0.152 to 0.322 mm) and Diaphanosoma birgei was the largest (0.284 to 0.722 mm). In the natural station, Moina minuta and Bosminopsis deitersi were the lightest species (0.174 to 0.334 and 0.074 to 0.278 µg, respectively) and in the impacted station, Bosmina hagmanni and Moina minuta were the lightest (0.248 to 1.555 and 0.210 to 0.566 µg, respectively). In general, individuals from the impacted station exhibited smaller body sizes (0.152- 0.684 mm) and higher weight (0.208 - 1.983 mm), which can be explained by the ingestion of tailing particles. The equations established were shown to be adequate for weight estimates of the analyzed species since the differences found between the observed and estimated weights values were not statistically significant.

Effects of Inorganic Turbidity on the Phytoplankton of an Amazonian Lake Impacted by Bauxite Tailings

The dumping of bauxite tailings into Batata Lake, an Amazonian clear-water lake, generated high levels of turbidity and caused a serious decrease in phytoplankton densities, which could possibly be the result of a photosynthetic limitation due to light attenuation together with an increase in algal sinking due to the adhesion of clay particles. This study aimed to investigate the sinking process through the addition of different suspended clay concentrations in columns containing Batata lake water. Since no effect of the suspended clays on Batata Lake phytoplankton sinking was observed, it was then evaluated, under laboratory conditions, whether the low conductivity of the Batata Lake water could interfere with the algae-clay aggregation process. Cultures of two algal species known to be capable to aggregate to Batata Lake suspended clays in algal culture medium: Staurodesmus convergens and Phormidium amoenum, were added to both the low conductivity Batata Lake water (14 μS cm−1) and the high conductivity algal culture media (WC – 300 μS cm−1 and Z8 – 560 μS cm−1) together with Batata lake suspended clays. In both algal culture media and Batata lake water the two species had their sinking accelerated due to clay adhesion. It is thus suggested that the decrease in phytoplankton densities recorded in Batata Lake may not be related to an increase in phytoplankton loss rates due to algal-clay aggregation, but rather are a consequence of decreasing growth rates because of light attenuation.