Ecological preferences and distribution of Aulacoseira species in southeastern Brazilian reservoirs with varying trophic states were studied. One hundred and fourteen plankton samples (winter and summer) from 57 sites located in 16 reservoirs were analysed. Ten water quality parameters were measured. Ten Aulacoseira species were identified using light, scanning and transmission electron microscopy, and new information on their ecological preferences is provided here. Our results indicate that trophic gradient is the main driver of species distribution. Principal components analysis and calculation of weighted average nutrient optima revealed three indicator taxa, Aulacoseira tenella characteristic for oligotrophic waters and two varieties of Aulacoseira granulata (nominate and var. angustissima) typical for eutrophic reservoirs. This is the first ecological study of Aulacoseira in Brazil, adding information on the distribution of this genus in the tropics, and highlighting the need for species-level identification and regional studies to improve the use of diatoms in water quality assessment.
Two new diatom species, Fragilaria neotropica sp. nov. and F. spectra sp. nov., from six reservoirs with different trophic status in the Alto Tietê River Basin, São Paulo, Brazil, are described. Descriptions are based on light (LM) and scanning electron microscopy (SEM) data revealing that both taxa have distinctive features that separate them from each other and from other taxa currently in Fragilaria. Fragilaria neotropica has high stria density, broader (sometimes deformed) central area, and capitate (often deflected) apices. This species was found in high abundance as part of the phytoplankton, periphyton and surface sediments in mesotrophic reservoirs. On the other hand, F. spectra has indistinct striae (not clearly seen in LM), wide sternum, two rimoportulae per valve and lacks spines. This taxon was abundant in the phytoplankton and periphyton of oligotrophic to mesotrophic reservoirs. A discussion of morphological and ecological aspects in the light of available literature is presented, as well as a morphological comparison based on LM and SEM analysis of the original material of F. tenera.
Synedra rumpens var. fusa was originally described by Patrick, but there are only a few subsequent records of this variety in the literature. Analysis of samples from Brazilian reservoirs containing a morphologically similar taxon led us to the analysis of the type material of S. rumpens var. fusa, performed using light (LM) and scanning electron microscopy (SEM). In the present manuscript, an amendment to the description of the var. fusa is made and its transfer to the genus Fragilaria as F. fusa comb. et stat. nov. is proposed. Moreover, Fragilaria billingsii sp. nov. is described from a large multipurpose reservoir from the State of São Paulo, Brazil. Comparative discussions with morphologically related taxa found in the literature are presented. Regarding ecological preferences, the new species was found living in slightly acidic and meso-eutrophic waters.
-(Plankton and surface sediment diatoms in water supply reservoirs from the Metropolitan Region of São Paulo, São Paulo State, Southeastern Brazil). This study presents and compares the floristic diatom composition of plankton and surface sediments of the water supply reservoirs from the Alto Cotia System (Pedro Beicht and Cachoeira da Graça reservoirs), located in the Reserva Florestal do Morro Grande. Samplings were carried out in seven sites, during the dry and rainy seasons and in the sediment surface during the dry season. Physical and chemical water parameters were analyzed. Twenty-three taxa belonging to 11 genera were identified. Morphometric data, relevant comments, and spatial location of the species were provided. Richness was higher in sediments, with eight exclusive species. The cluster analysis indicates that diatom species composition varied more between the compartments (water and sediments) than between the reservoirs or seasons. Present work adds three new citations to Brazil, besides four other species to São Paulo State, contributing to pioneer information in reservoirs considered as a reference in water quality for the metropolitan region of São Paulo. Keywords: algae, Alto Cotia Water Supply System, Bacillariophyta, flora, Reseva Florestal do Morro Grande RESUMO -(Diatomáceas planctônicas e de sedimento superficial em represas de abastecimento da Região Metropolitana de São Paulo, SP, Sudeste do Brasil). Este estudo apresenta e compara a composição florística das diatomáceas planctônicas e de sedimentos superficiais das represas de abastecimento do Sistema Alto Cotia (represas Pedro Beicht e Cachoeira da Graça), inseridas na Reserva Florestal do Morro Grande. Foram realizadas coletas em sete estações nos períodos seco e chuvoso, e de sedimento superficial no período seco. As amostragens foram acompanhadas de análises físicas e químicas da água. Foram identificados 23 táxons distribuídos em 11 gêneros. São disponibilizados dados morfométricos, comentários relevantes e distribuição espacial das espécies. A riqueza foi mais elevada no sedimento, com oito espécies exclusivas. A análise de agrupamento indicou que a composição das diatomáceas variou mais entre compartimentos (água e sedimento) do que entre represas ou períodos climáticos. O trabalho acresce três novas ocorrências para o Brasil e, além dessas, quatro para o Estado de São Paulo, contribuindo com informações inéditas em represas de abastecimento consideradas como referência para a Região Metropolitana de São Paulo.
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