177 years of diatom studies in Brazil: knowledge, gaps, and perspectives.

The actual status of the progress and the main aspects of diatom studies in Brazil remain unknown. This paper describes a survey of published studies addressing material of Brazilian origin in non-marine aquatic environments. Our objectives are to (1) summarize and categorize diatom research topics, (2) to describe how related studies evolved and developed over time, as well as respective journals, (3) to identify the most studied regions and environments, and (4) to indicate the main institutions and works addressing diatom research and related interactions. We conducted a systematic review selecting 478 studies. Since the early studies, the approach on diatom floristic exclusively was the most frequent, even though, ecological studies have been increasing since the 2000s. However, these concentrate in the southern and southeastern. It was only in the last decades that other Brazilian regions became the setting of more extensive samplings, thus reflecting on the interactions between authors and institutions from the collection sites. However, the actual biodiversity scenario of diatoms in Brazil still seems to be underestimated, which may influence further conservation measures. Finally, we indicate some suggestions aimed at filling the sampling gaps presented/highlighted in this study.

Periphytic algal flora of the low Doce river, Espírito Santo State, Brazil, after ore tailings flow, 1: smooth cell walled Cosmarium Corda (Zygnematophyceae, Desmidiaceae / Ficoflórula perifítica do Baixo Rio Doce, Estado do Espírito Santo, Brasil, após passagem de rejeitos de minério, 1: Cosmarium Corda de parede lisa (Zygnematophyceae, Desmidiaceae

Study aimed at identifying and recording smooth or finely punctate cell walled Cosmarium Corda species of the low Doce river region, Espírito Santo State, Brazil. Periphytic material was collected monthly during the period October 2018 to February 2020, except for October 2019. We identified 22 taxa and analyzed the environmental conditions (trophic state, pH and total iron) in which each taxon occurred. Our study recorded 21 new records of smooth cell walled Cosmarium for Espírito Santo State and one (Cosmarium trilobulatum var. tumidum Willi Krieger & Gerloff) for Brazil.

Este estudo teve como objetivo identificar e registrar as espécies de Cosmarium Corda de parede lisa ou finamente pontuada na região do baixo rio Doce, no Estado do Espírito Santo, Brasil. O material perifítico foi coletado mensalmente durante o período outubro de 2018 a fevereiro de 2020, exceto no mês de outubro de 2019. Identificamos 22 táxons e analisamos as condições ambientais (estado trófico, pH e ferro total) nas quais cada táxon ocorreu. O estudo registrou 21 novos registros de Cosmarium de parede lisa para o Estado do Espírito Santo e um (Cosmarium trilobulatum var. tumidum Willi Krieger & Gerloff) para o Brasil.

Ecological thresholds of periphytic communities and ecosystems integrity in lower Doce River basin.

Freshwater biodiversity has been impacted by several stressors such as eutrophication, turbidity and metals. Besides these frequent impacts, large-scale accidents occasionally affect aquatic systems, input an intense load of contaminants to the water bodies, as in the case of the Fundão tailing dam collapse (Brazil), which launched millions of meters cubic of iron ore tailing in the Doce River Basin. Our aim in this study was to assess how much stress the environmental conditions of lentic and lotic environments in the lower region of this basin impact the periphytic community. In addition, we intend to verify whether the limits of changes of the periphytic communities agreed with Brazilian legislation for the protection of aquatic life. For that, monthly samplings were carried out in seven sampling stations in lentic environments and five in lotic environments, including the Doce River channel, between October/2018 and March/2021 (except in October/2019). Concentrations of metals (iron, aluminum, manganese and chromium), total nitrogen, total phosphorus, conductivity, and suspended particulate material were determined. The periphytic community was collected from natural substrates (macrophytes or pebbles) and quantified by the sedimentation chamber method. From these data, thresholds of concentrations of variables that caused changes in periphytic communities were determined by the Threshold Indicator Taxa ANalysis (TITAN). We concluded that evidence of chronic impact of iron ore tailing should be revealed and that the standards established by Brazilian legislation may be incompatible with the protection of aquatic life. Moreover, we found that the Doce River mouth and surrounding environments were the most stressful environments for the periphytic communities.

Homogenization of diatom assemblages is driven by eutrophication in tropical reservoirs.

Eutrophication is one of the most widespread causes of biotic homogenization in freshwater ecosystems. Biotic homogenization can be characterized as reductions in local diversity (alpha) and occupation of available niches by more generalist species. Beta diversity is expected to decrease in more homogeneous communities, however, there is no consensus on how it responds to eutrophication. We used a space-for-time approach to analyze the process of biotic homogenization on diatom assemblages in response to eutrophication in tropical reservoirs ranging from oligotrophic to hypereutrophic conditions. Diatom assemblages were analyzed in phytoplankton and surface sediment from 12 reservoirs with different trophic levels. We calculated total beta diversity and turnover and nestedness components and used regressions to analyze their relationships with productivity differences (without distance effects). Total beta diversity had a positive influence of the trophic gradient, whereas turnover was not related to eutrophication. However, we found that eutrophication and lower species richness (alpha diversity) led to increasing rates of the nestedness component. We also observed that the homogenization process was not characterized by invasion of new species, but, on the contrary, by filtering nutrient-rich tolerant species also present in oligo-mesotrophic reservoirs and able to occupy available niches in the eutrophic reservoirs. These findings (increase in nestedness, decrease in alpha diversity, and development of tolerant species) suggest that biotic homogenization is leading to a simplification of diatom assemblages in tropical reservoirs, making assemblages from eutrophic and hypereutrophic reservoirs a subset of assemblages from oligotrophic and mesotrophic ones.

Spatio-temporal changes in water quality in the Guarapiranga reservoir (São Paulo, Brazil): insights from a long-term monitoring data series.

The provision of drinking water in metropolises is a challenge that requires programs for continuous monitoring of water quality and processes that impact the land cover of the watershed. In this work, we investigated through multivariate statistical analysis the temporal and spatial trends of several variables, not yet explored in a data series that includes 42 years (1978-2020) of monitoring in the hydrographic basin of the Guarapiranga reservoir, in the São Paulo Metropolitan Region-SPMR (Brazil). This reservoir is the source of drinking water for 3.8 million people and plays a strategic role in the social, environmental, and economic structure at SPMR. Our results point to the continuous degradation of water quality in the reservoir, although with different causes and spatio-temporal aspects. Between the 1970s and 1980s, variables associated with erosion/silting played a more critical role. From the 1990s, the introduction of N and P intensified, and the concentration of thermotolerant coliforms increased. The loss of quality is mainly associated with the progressive advance of urban settlements without planning combined with the inefficient initiatives to control domestic sewage pollution. If there is no rapid and comprehensive intervention, there is a risk that the Guarapiranga reservoir may become unsuitable for drinking water supply and other types of use in the future. This scenario will represent a critical obstacle to regional development and the quality of life of the population.

Effects of land use and spatial processes in water and surface sediment of tropical reservoirs at local and regional scales.

The effects of land use and connectivity on the characteristics of aquatic ecosystems are thought to be scale-dependent. This study aimed to evaluate the relationships between land use and reservoir characteristics at two spatial scales, after controlling for spatial processes. Water and surface sediment samples were collected from 31 sites (7 reservoirs) in the Paiva Castro and Piracicaba River basins (Cantareira System, São Paulo State, Brazil), during austral summer and winter. The dataset included 15 water quality variables and 6 surface sediment variables. Land use variables (natural areas, pasture, agriculture and urban areas) were obtained at two spatial scales (buffer and watershed) in each reservoir. Spatial variables were calculated using Moran's Eigenvectors Maps and Asymmetric Eigenvector Maps. The strengths of the relationships between land use and sediment variables were stronger than those between land use and water quality variables. The strengths of some of the relationships were scale-dependent. Finally, spatial processes, mostly hydrological connectivity, play an important role in water-sediment quality and should be considered in landscape management programs.