Association of periphytic diatom species of artificial substrate in lotic environments in the Arroio Sampaio Basin, RS, Brazil: relationships with abiotic variables

Navicula (Naviculaceae) no perifíton de riachos e novas ocorrências para o estado de Goiás

Resumo Este trabalho teve como objetivo inventariar e descrever as espécies de Navicula encontradas no perifíton em riachos do estado de Goiás, e contribuir com novos registros para o estado com a identificação de novas características taxonômicas. Amostras foram coletadas em nove ambientes lóticos, dos quais o material perifítico foi removido de gramíneas e seixos submersos. Foram preparadas lâminas permanentes com o material oxidado para observação, identificação e descrição dos espécimes. Como resultado, foram identificadas 10 espécies, das quais quatro são novos registros para o estado: Navicula leptostriata, Navicula symmetrica, Navicula neomundana e Navicula parablis. Os táxons mais frequentes foram Navicula leptostriata e Navicula parablis.

Development of the Trophic Water Quality Index (TWQI) for subtropical temperate Brazilian lotic systems

This research aimed at developing the Trophic Water Quality Index (TWQI) for subtropical temperate Brazilian lotic systems based on a review of the indicative values of diatom species obtained using multivariate analysis techniques and considering the environmental gradient defined by a series of measured physical, chemical, and microbiological variables. Sampling was conducted from 2005 to 2009 in the Pardo River Hydrographic Basin, Rio Grande do Sul (RS), Brazil, and in the Andreas Stream Hydrographic Basin, RS, from 2012 to 2013. A total of 140 biological samples and 211 abiotic samples were collected. Data were analyzed by cluster analysis based on the Ward method and canonical correspondence analysis (CCA). The results indicated that total phosphate, turbidity, ammonia nitrogen, electrical conductivity, dissolved oxygen, and thermotolerant coliforms showed a significant correlation with the sample ordination made by CCA, in relation to a gradient of eutrophication. Eutrophication was operationally defined in a broad sense, including the problem of organic pollution and eutrophication of the water. The determination of the different tolerance degrees to eutrophication of the diatom taxa was used to assign trophic values of 1, 2.5, and 4 to species, corresponding to levels of low, medium, and high tolerance, respectively. By using the trophic values obtained for each diatom species, the TWQI constituted a new technological tool for environmental monitoring studies and showed a consistent, robust, and objective database for water quality assessment in subtropical temperate Brazilian lotic systems.

Responses of periphytic diatoms to mechanical removal of Pistia stratiotes L. in a hypereutrophic subtropical reservoir: dynamics and tolerance

The Itaqui reservoir in Paraná state, southern Brazil, is dominated by the floating macrophyte Pistia stratiotes L. and is used for recreation and irrigation. The reservoir's excessive plant cover suggests an extreme trophic state and interferes with multiple uses. The aims of this study were to determine the trophic state of the reservoir water and to document the limnological conditions and the composition of the periphytic diatom community before and after the mechanical removal of macrophytes. As each diatom species has certain autoecological requirements in a given geographic area, another objective of the study was to identify diatoms that can be considered tolerant of the reservoir's trophic state in a substropical environment. Local water samples collected for physical and chemical analyses, including estimates of chlorophyll a, showed the hypereutrophic status of the reservoir before and after macrophyte removal. Environmental conditions exceeded acceptable values for fishing and irrigation, providing a clear example of how the inadequate management of water resources can directly reduce their usefulness. Trimestral sampling was carried out between May 2008 and February 2009. For quantitative analyses, biofilms were scrubbed off glass slides submerged for 30 days at a depth of approximately 40 cm. Diatom samples were cleaned with potassium permanganate and hydrochloric acid and mounted on permanent slides with Naphrax. All individuals found in random transects under three replicates were identified and counted up to a minimum of 600 valves. Thirteen species tolerant of eutrophication were selected. Four species mostly known from low-nutrient sites may be considered tolerant of eutrophic conditions. The composition of the diatom community was influenced by seasonal changes in temperature and rainfall. Canonical Correspondence Analyses confirmed a correlation between higher diatom densities and the increased photic zone following macrophyte removal.

Epipsammic diatoms in streams influenced by urban pollution, São Carlos, SP, Brazil

Epipsammic diatoms have important implications for ecosystem processes in lotic environments. Most of the studies on benthic diatoms concentrate on epilithic diatoms and very little is known about epipsammic diatoms. The objective of this study was to assess epipsammic diatom communities in streams in relation to environmental conditions. Epipsammic diatoms and water quality sampling was done at 7 sites during summer base flow period (2008). Forward stepwise multiple regression and canonical correspondence analysis (CCA) were used to determine environmental gradients along which species vary with physical and chemical variables. A total of 112 diatom species distributed among 44 genera were recorded. Altitude and the process of eutrophication played a significant role in structuring diatom communities in the study region.

O gênero Nitzschia (Bacillariaceae) em ambientes lacustres na Planície Costeira do Rio Grande do Sul, Brasil

Resumo O estudo taxonômico sobre o gênero Nitzschia Hassall, nas áreas da Lagoa do Casamento e do Butiazal de Tapes, localizados entre 30º40'-30º10'S e 50°30'-51º30'W, baseou-se em amostras de plâncton e metafíton, coletadas em 21 estações abrangendo diferentes ambientes (lagoas interligadas, lagoas isoladas, banhados e açude) no outono e primavera de 2003. Foram encontrados 35 táxons específicos e infra-específicos, destacando-se 11 novas ocorrências para o Estado e cinco para a Planície Costeira do Rio Grande do Sul. Quanto ao hábito, 91% dos táxons ocorreram no plâncton e metafíton e 9% restringiram-se ao metafíton. A área da Lagoa do Casamento apresentou maior riqueza (35 táxons) em relação à área do Butiazal de Tapes (13 táxons), provavelmente pela presença de ambientes em conexão com a laguna dos Patos, a qual detém uma flora rica de Nitzschia, associado às condições de alta condutividade e pH da água. São apresentadas descrições, ilustrações e comentários sobre as variações morfológicas e/ou métricas dos táxons.

Biological monitoring of lotic ecosystems: the role of diatoms

Increasing anthropogenic influence on lotic environments as a result of civilisation has captured public interest because of the consequent problems associated with deterioration of water quality. Various biological monitoring methods that provide a direct measure of ecological integrity by using the response of biota to environmental changes have been developed to monitor the ecological status of lotic environments. Diatoms have been used extensively in this regard and this review attempts to summarise the basic concepts associated with biological monitoring using benthic diatoms. Where possible, examples from work carried out in Brazil are used.

Gomphonema Ehrenberg e Gomphosphenia Lange-Bertalot (Bacillariophyceae) do Rio Maurício, Paraná, Brasil

Pouco se conhece sobre a biogeografia e variabilidade morfológica das espécies de Gomphonema e Gomphosphenia no Brasil. Gomphonema é um gênero bem representado em riqueza e abundância na flora algal perifítica, principalmente pela secreção de mucilagem pelo campo de poros, o que facilita a adesão das células aos substratos. As amostras analisadas foram removidas das porções vegetativas de Potamogeton polygonus Chamess. & Schltdl. e Egeria densa Planch., macrófitas coletadas no Rio Maurício, localizado no município de Fazenda Rio Grande, Paraná. A análise qualitativa do material resultou na determinação de 20 táxons. Onze espécies de Gomphonema e o gênero Gomphosphenia constituíram citações pioneiras para o Paraná. Os resultados de observações da ultra-estrutura de algumas espécies foi adicionado. A variabilidade do contorno valvar e os detalhes ultra-estruturais justificam futuras revisões taxonômicas de algumas espécies correlatas, como: G. gracile e Gomphonema sp.5, G. contraturris e G. salae, G. capitatum e G. laticollum.