Responses of periphytic diatoms to mechanical removal of Pistia stratiotes L. in a hypereutrophic subtropical reservoir: dynamics and tolerance (original) (raw)
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2013
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.
Diatoms are extremely diverse ubiquitous microalgae. This makes them good indicators of the quality of aquatic ecosystems, and they have been used for this purpose for the past 50 years. Since 2000, the European Water Framework Directive has required them to be used for assessing the ecological quality of watercourses. A typological framework has to be devised in order to compare rivers that are comparable, i.e. rivers with the same bioclimatic regions, that flow over the same geological substrate at similar altitudes. Various ecoregional classifications have been defined using these parameters. At a scale covering 4 European countries (Spain, France, Italy, and Switzerland) and at a regional scale (north-east France) we show that ecoregions and geology are determinant in explaining communities, and that pollution-related parameters are less important. Unlike some other authors, we did not observe any homogenization of communities as the level of pollution level increased. Moreover, we did not observe geographically restricted communities, which make it possible to pool data from geographically distinct ecoregions with the same physical characteristics. Diatoms display a very high degree of species diversity, which can be a problem for their routine use as assessment tools. We showed that when the precision of identification was increased from sub-division to species level, pollution assessment performances also increased, but to a much less marked extent than the number of taxa. Assessment performances at the genus and species levels are similar, whereas there are ten time more species than genera. We also showed that simplifying metrics (life-forms, ecological guilds) can be used to assess nutrient levels as effectively as diatom indices based on species. Furthermore, these metrics provide additional information about biofilm structure that is not available from species-based data. Finally, micropollutant pollution of rivers is of increasing concern to citizens. We hypothesize that diatoms could be good candidates for assessing herbicide pressure. Four experiments lasting 2 months were conducted in lotic mesocosms. We showed that diatoms surrounded by thick exopolysaccharide matrices were more resistant to dissolved pesticides. On the other hand, diatoms with a high cell surface in contact with the water were disadvantaged. This kind of metric could be used in situ at a larger scale. We conclude that these metrics could be useful for the purposes of diatom bioassessment. However, we also stress the importance of combining phylogeny and ecology to clarify which environmental pressures are forcing diatoms to adapt. Such studies will enhance diatom bioassessment.
Limnologica, 2019
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Acta Limnologica Brasiliensia, 2017
This study aimed to understand the seasonal variation of epilithic diatoms in the Gravataí River regarding their composition and density along the river, as well as the respective relationships with local limnological variables. Methods: The diatoms were sampled quarterly using a EDS sampler exposed for four weeks from September 2000 to August 2002. An area of 75 cm 2 was scraped off the upper surface of three submerged stones totalizing a composed sample. An aliquot of 1 ml of oxidized material was mounted on a slide for the quantitative and qualitative analysis. Results: A spacial organic contamination gradient was observed in the Gravataí river due the decrease of dissolved oxygen, and increase of BOD 5, total nitrogen and ortho-phosphate from the upper to the lower course and the predominance of eutrophic conditions during periods of higher temperature (spring and summer). The epilithic diatoms presented, in the upper stretch, a seasonal pattern in abundance with the highest densities during the fall and winter, the density enhance was associated to mild and low temperatures, lowest turbidity and nutrients availability. Bacillariaceae was dominant in the spring, Eunotiaceae and Bacillariaceae in the summer and fall and Gomphonemathaceae was strongly dominant followed by Eunotiaceae in winter. In the lower course Bacillariaceae was dominant in all seasons except on fall 2001. These changes were determined by the substitutions in the occurrence and relative abundance of some species as Achnanthidium minutissimum, Cocconeis placentula, Eunotia bilunaris, Frustulia saxonica, Gomphonema parvulum, Nitzchia palea and Sellaphora seminulum. Conclusions: The seasonality of the diatoms was well evidenced in upper stretch of the river, therefore in the lower course with greater anthropogenic impact, fewer changes occurs in the number of species present and/or of substitution of some species by others, showing that the seasonality of the diatoms can be affected by organic contamination and eutrophication.
Periphytic diatoms show a longitudinal gradient in a large subtropical shallow lake
Inland Waters, 2015
Some limnological differences among 3 areas in Mangueira Lake, Brazil, a large shallow oligo-mesotrophic system under continuous wind influence, were related to the wind action and influenced diatom community structure. Our goal was to investigate if wind and precipitation influence the attached communities, producing a heterogeneous diatom distribution along the lake. Sampling was performed in summers 2006 and 2008 at the North, Center, and South points of the lake. Biofilms were scraped from natural substrata for quantitative analyses; 17 species were considered abundant. The South is characterized by high transparency and high pH and is influenced by continuous wind perturbation (NE direction), both in frequency and intensity. The diatom community was characterized by low-profile guild and pioneer life-forms, which are resistant to physical disturbances. The North is shallow with high humic acids because of its proximity and interaction with the wetland, and it was characterized by high-profile and motile guilds. Interannual spatial variation was registered due the influence of continuous precipitation before the 2008 sampling date, which made the lake more homogeneous than it was in 2006. The Center acted as a transition point, which was more similar to the North in 2006 and more similar to the South in 2008. The longitudinal gradient was generated due to abiotic characteristics of the North and the South. The diatom community exhibited a longitudinal gradient N→S, and the diatom life-forms and ecological guilds were a useful tool for examining spatial heterogeneity.
Spatial Response of Epilithic Diatom Communities to Downstream Nutrient Increases
To monitor water quality and investigate relationships between downstream nutrient increases and diatom communities in the Pardo River Basin, Brazil, water and diatom samples were collected between 2005 and 2009. There were significant differences in diatom community composition among all river zones, with the greatest differences found between the upper and lower reaches. Significant changes were detected in relative abundances of diatom species and spatial structuring was evident. Dissolved oxygen, phosphates, turbidity, Eicherichia coli, and total dissolved solids were the most important variables shaping diatom communities, characterizing an organic pollution and eutrophication gradient. However, the hypothesis of sensitive species prevailing upstream and their gradual downstream replacement for more tolerant species was not confirmed because shifts in relative abundances of the same group of species in both the upper and lower reaches of the rivers were identified. Water Environ. Res., 87, 547 (2015).
"This work aims to analyse the response of epilithic diatom communities to environmental gradients in subtropical temperate southern Brazilian rivers to contribute to the development of a widely applicable methodology for water-quality monitoring. Samples for physical, chemical and biological determination were collected monthly, from December 2001 to November 2002 and from March 2003 to February 2004, at 9 stations along the rivers Pardo and Pardinho in the hydrographical basin of Rio Pardo, State of Rio Grande do Sul (RS), Brazil. Physical and chemical variables (water temperature, pH, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, nitrates, nitrites, phosphates and total dissolved solids) and biological variables (epilithic diatom communities) were used as parameters for water-quality assessment. The data matrix was examined by means of a multivariate ordination using Detrended Correspondence Analysis (DCA). In total, 270 taxa were identied to specic or infra-specic levels. The results showed that of all the physical and chemical variables used, the main gradient along the DCA rst axis was eutrophication, which was indicated by its signicant correlation with phosphates ( p < 0.001). Hence, the species’ scores on the DCA axis were used as an operational criterion for indicating their tolerance to eutrophication. From this analysis, the 10 taxa that were the most tolerant to eutrophication were: Cyclotella meneghiniana, Fallacia monoculata, Nitzschia acicularis, N. clausii, N. nana, N. palea, Nitzschia sp., Pinnularia sp., Sellaphora pupula sensu lato and Ulnaria acus. The present study showed that epilithic diatom assemblages reect anthropogenic changes in hydrographic basins in subtropical temperate streams, especially pollution by organic enrichment and eutrophication."
Anthropogenic eutrophication is a major form of perturbation in freshwaters, and several approaches aim to recognise its effects on lake ecosystems. We compared the responses of diatom species morphology , diversity indices and diatom indices to total phosphorus , total nitrogen and distance from a point stressor causing eutrophication in a large lake. We specifically examined the degree to which extent nutrients and distance to the stressor affect variation in the values of various biological indices and diatom valve size. In addition, special attention was given to the adequate repetition of diatom valve width measurements in the context of environmental assessment. Our results showed that diatom valve width was a better indicator of nutrient concentrations than any of the diatom and diversity indices examined. However, the results varied between the two study transects, suggesting that the diatom-based variables not only respond to nutrients but also to other environmental factors (e.g. shoreline morphology). We also found that when using the method based on diatom morphology, one should measure more valves than has been originally suggested to provide a more reliable picture of response to eutrophication. We argue that diatom morphology could be considered as an additional environmental assessment tool, because it may complement the information provided by the traditional diatom indices. Diatom valve width may also be more sensitive to early phases of the eutrophication process and its effects on freshwater ecosystems than various diatom indices that were developed in regional contexts with wide ranges in nutrient levels.