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Saxitoxins are a class of toxins produced by at least two groups of evolutionarily distant organisms (cyanobacteria and dinoflagellates). While the toxicity of these toxins is relatively well characterized, to date little is known about their drivers and ecological functions, especially in lower latitude tropical and subtropical freshwater ecosystems. In the present study, we aimed to obtain a better understanding of the main drivers of saxitoxin concentrations in aquatic environments. We investigated the relationships among saxitoxin concentrations in a mesotrophic subtropical reservoir dominated by the cyanobacteria Cylindrospermopsis raciborskii with physical, chemical and biological water variables. The highest saxitoxin concentrations were 0.20 μg·L, which occurred in the samples with the highest densities of C. raciborskii (maximum of 4.3 × 10 org·mL) and the highest concentration of dissolved nutrients (nitrate from 0.2 to 0.8 μg·L, ortophosphate from 0.3 to 8.5 μg·L). These correlations were confirmed by statistical analyses. However, the highest saxitoxin relative concentrations (per trichome) were associated with lower C. raciborskii densities, suggesting that saxitoxin production or the selection of saxitoxin-producing strains was associated with the adaptation of this species to conditions of stress. Our results indicate that C. raciborskii toxin yields vary depending on the enrichment conditions having potential implications for reservoir management.

The implantation of wastewater treatment systems aims to minimize environmental impacts, but ultimately generates waste materials, such as sewage sludge, which must be properly discarded. Final disposal in landfills, and incineration are the most commonly used disposal methods, but both constitute a threat to the soil, water, air, and food chain. The most suitable alternative for the disposal of sewage sludge is its use as fertilizer, due to the nutrients in its composition, such as nitrogen, phosphorus, and organic carbon. However, the presence of potentially toxic metals is the main factor that limits such use. Many techniques have been employed in attempt to remove these toxic metals, including physical, chemical, and biological treatments, but the high cost of the physical and chemical treatments, as well as the risk of causing secondary pollution, makes this type of sewage sludge treatment an unsatisfactory option. Therefore, removing toxic metals through biological treatments has become an increasingly popular choice, as such treatments have been shown to be the most economically and environmentally beneficial methods. The aim of the present study was to provide a review of some of the most common alternative treatments for the incineration and disposal of sludge in landfills, emphasizing the physical, chemical, and biological processes that enable the removal of potentially toxic metals, for the purpose of obtaining a final product which can be used as fertilizers in farm soils.

The purpose of this work was to verify the benthic macroinvertebrates community responses through environmental factors along a headwater tropical reservoir. Samplings were taken with a Van-Veen grab along the reservoir in littoral and profundal regions and in the headwater, next to the dam and the middle of the reservoir. Samples were taken during both wet and dry seasons. Dissolved oxygen concentrations, electric conductivity, temperature and pH near the sediment have been performed in situ, at every sampling station by using a multiprobe and Secchi disc. Total water phosphorus and chlorophyll a concentrations were analyzed to determine the trophic state index. Sediment's organic matter, total phosphorus, nitrogen concentrations and granulometric composition were measured. In order to verify which environmental variables would have more influence over the benthic macroinvertebrates community, a canonical correspondence analysis (CCA) was performed. The total number of recorded taxa was 28. Among them, the family Chironomidae (Diptera) was the richest group (19 taxa). It can be proposed that the benthic macroinvertebrates community may be influenced by environmental conditions such as nutrient and organic matter availability, as well as dissolved oxygen concentration. Macroinvertebrates are adequate bioindicators of water quality due to their sensibility to environmental changes mentioned before. Chironomus sp, Limnodrilus hoffmeisteri and Branchiura sowerbyi comprises a group that can be considered bio-indicators of eutrophic conditions. A second group can be considered as indicator of mesotrophic conditions. The presence of two or more members from that group which comprises Tanytarsini spp, Fissimentum sp, Pelomus sp and Goeldichironomus sp, like predominant taxa, may indicates mesotrophic conditions.

We investigated the biomass, primary productivity, species diversity and their controlling factors in the deeper region of the Barra Bonita reservoir (22°29'S and 48°34'W) in the State of Sao Paulo, Brazil . To accomplish this, short term changes (days and month) were measured during two periods of the year, winter 1993 and summer 1994 . The response of the phytoplankton communities to the variability of the system, taking into account the Intermediate Disturbance Hypothesis (IDH), indicated that the frequency and intensity of the disturbances have a critical influence on the establishment of the communities . In Barra Bonita Reservoir the conditions for mixing in the winter were probably important for maintaining high diversity . On the other hand, in summer, the concentrations of suspended material, the high temperatures, and the greater stability of the water column, were probably responsible for permitting the establishment of Microcystis aeruginosa .

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Aim:The objective of the present study was to demonstrate the influences of the environment spatial heterogeneity on benthic macroinvertebrates considering transverse and longitudinal gradients as also seasonality. Methods: Four samplings were performed: two in the wet and two in the dry season in the riverine, transitional and lacustrine zones in the littoral and profundal regions of Itupararanga reservoir, SP, Brazil. Abiotic characterization of the water and of the sediment was performed. The biotic characterization was based on richness, dominance, diversity, and density of organisms, as well as on the relative abundance of predominant taxa. Two-way ANOSIM analyses were performed for both biotic and abiotic components, in order to test the significance of the differences in the longitudinal and transverse directions as well as of the differences between seasons. Results: Compartmentalization was present in both directions, longitudinal and transverse. In a general way, the littoral region presented higher diversity values when compared with the profundal region, and the riverine zone presented high densities and high percentage of taxons, which usually indicate organic pollution. The differentiation between the transitional and lacustrine zones was determined mainly by taxonomic composition. Seasonality was also observed and the transportation of small particles, the entrance of nutrients, and the presence of macrophytes were considered as determinants for differentiation. Conclusions: Together, these results demonstrate the responses of benthic macroinvertebrate communities considering distinct sources of variation: longitudinal heterogeneity, determined by the increasing distance from the forming rivers that leads to a gradient of physical and chemical conditions; transverse heterogeneity, determined by the proximity with the land environment and depth differences. Seasonal heterogeneity was recorded during the period of this research and it was determined by variations in water flow, in temperature, and in the carrying of matter, nutrients and organisms.Keywords: reservoir, diversity, neotropics, compartmentalization.Resumo: Objetivo: O objetivo do presente estudo foi demonstrar a influência da heterogeneidade espacial sobre os macroinvertebrados bentônicos considerando-se gradientes ambientais longitudinais e transversais bem como a sazonalidade. Métodos: Quatro coletas foram realizadas: duas durante a estação chuvosa e duas na estação seca compreendendo as zonas de rio, de transição e de lago bem como as regiões litorâneas e profundas do reservatório de Itupararanga, SP, Brasil. Foram realizadas as caracterizações abióticas da água e do sedimento. A caracterização biótica foi baseada na riqueza, dominância, diversidade e densidade de organismos, bem como na abundância relativa de táxons predominantes. Duas análises ANOSIM de entrada dupla foram realizadas considerando-se os componentes bióticos e abióticos, a fim de testar a heterogeneidade espacial longitudinal e transversal, bem como para te...