No abstract

No abstract

The purpose of this study was to explore the autecology of diatom species inhabiting the epipsammon and epiphyton in the freshwater-mixohaline zone of the Río de la Plata estuary. The diatoms are a conspicuous component of those communities. We discuss the optima and tolerance ranges of diatoms for the following environmental variables: conductivity, turbidity, pH, nutrients (phosphate, nitrate, nitrite, and ammonium), and dissolved oxygen levels as well as both the chemical and biological oxygen demand. The study was carried out on the Argentinean coastline between 34°27' S, 58°30' W and 35°23' S, 57°08' W. In total, 32 sampling sites influenced by different land uses were monitored along 168 km of shoreline. Epipsammic samples of the intertidal zone were taken at low tide during spring 2005, autumn and winter 2006, spring and summer 2007, and autumn 2008. Epiphytic samples were taken during summer, autumn, and spring 2000 and spring 2002. In total, 224 benthic species were identified in the 120 samples analyzed; 81 species had a frequency greater than 5% in the total sample dataset with more than 1% of relative abundance in at least 1 sample and were chosen for estimation of their optima and tolerances for selected water-quality characteristics. The physicochemical data analyzed indicated 2 gradients -increases in conductivity and turbidity along with decreases in the concentration of nutrients and organic matter -that generated different types of habitats for the species investigated.KEY WORDS: Diatoms · Optima · Tolerance range · Autecology · Epipsammon · Epiphyton · Coastal-plain estuary · Río de la Plata Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 418: [105][106][107][108][109][110][111][112][113][114][115][116][117] 2010 optima and tolerances for various aspects of water quality such as pH, salinity, temperature, nutrients, and light availability (i.e. turbidity;Cooper 1995). In a freshwater ecosystem, the dependence of benthic diatoms on nutrients has been so unequivocally clarified that microalgae have been classified according to trophic and saprobity classes and are thus used as sensitive indicators of water quality (Sláde

No abstract

No abstract

Chronic and pulse increments of salinity can cause different consequences on the aquatic communities, and its effects are related to factors such as the magnitude, frequency and ionic composition, as well as on the baseline salt concentrations in the water. The aim of this study was to explore the responses of the biofilms from a nutrient-rich stream to both pulse and chronic additions of salt, along with their recovery after the stressor had been removed. For this purpose, a microcosm study was conducted exposing biofilms to water enriched with sodium chloride in two treatments (press and pulse), and comparing the changes in the biofilm with control microcosms without salt additions. The experiment lasted 72h, and the variables measured included bacterial density, chlorophyll-a concentration, community composition, total carbohydrate content, oxygen consumption and the percentage of nuclear alterations in diatoms. Both treatments resulted in a decrease in the bacterial density of the biofilm and in oxygen consumption; the chronic treatment in particular also caused an increased percentage of nuclear abnormalities in the diatom assemblage. The biofilm recovered to control levels after the treatments had been discontinued for 72h. We concluded that the biofilms can be altered significantly under both chronic and pulse additions of salt even after a short-term exposure, and that the community can recover if the stressor is withdrawn.

No abstract

No abstract