Search Results (8)

A white encrustation of the Cotswold Weir wall in the lower reaches of the Condamine River, a tributary of the Murray–Darling River system in semi-arid Australia, was investigated following community concern that it indicated health risks from an unknown substance in the water resulting from mining and agricultural enterprises in the catchment. The vitreous white surface consisted of closely packed frustules of diatoms, observed by scanning electron microscopy, with an underlying layer of clay particles and dried filamentous green algae. Pennate diatoms identified in the white encrustation were the benthic species Nitzschia palea (predominant), Eolimna subminiscula, Craticula aff. cuspidata, Navicula viridula var. rostellata, and Luticola mutica. The centric diatom species Melosira varians was also present as filamentous chains of cylindrical frustules among the aggregated pennate diatom frustules. The encrustation was the remains of a periphyton (biofilm) of diatoms and green algae that had developed during protracted stream flow over the weir wall following record flooding. A dry period had resulted in the death of the diatoms and exposure of their aggregated siliceous frustules as a vitreous white coating. All diatom species identified are considered tolerant of eutrophic and mildly saline conditions. Chemical analyses of water from the Cotswold Weir, compared to long-term records, revealed higher salinity, with changes from March when the river was flowing to September when the white coating was noted, in electrical conductivity (299 to 461 µS/cm), and in sodium (26 to 43 mg/L) and chloride (26 to 75 mg/L) concentrations, respectively. Total nitrogen (0.82 to 1.6 mg/L) and total phosphorus (0.24 to 0.094 mg/L) were at mesotrophic and eutrophic concentrations, respectively, together with substantial dissolved silica concentrations (18 to 11 mg/L). Atomic ratios for total nitrogen/total phosphorus (7.6 to 37.6), nitrate-nitrogen/orthophosphate-phosphorus (2.3 to 274), and dissolved silica–silicon:orthophosphate-phosphorus (81.7 to 749) probably favoured diatoms over other photoautotrophs. While the diatomaceous encrustation indicated no health risks from the weir water, continued watch is required to avoid eutrophication and salinization of the river. Full article

Rivers are crucial hydrological cycle components, supporting ecosystems and human activities. Managing and protecting river water quality is essential. Diatoms, microscopic algae, are widespread and sensitive to changes in water quality, making them effective bioindicators. This study focused on the Kuils River in the Western Cape, South Africa, where diatom sampling was conducted at four sites. Their communities are affected by different physicochemical parameters, such as changes in pH, salinisation, eutrophication, and organic enrichment. A total of 98 diatom species were identified. The Omnidia software was used to calculate the Generic Diatom Index, Specific Pollution Index, and Trophic Diatom Index. Historical physicochemical data such as pH, chemical oxygen demand, and phosphorus were obtained from the Department of Water and Sanitation between 2019 and 2021 and were used to provide a reference for comparing diatoms. The results showed clear signs of pollution, as shifts in diatom species composition were observed. Pollution-tolerant species such as the Nitzschia palea (Kützing) W Smith 1856, Navicula viridula (Kützing) Ehrenberg 1838, Eunotia bilunaris (Ehrenberg) Schaarschmidt 1880, and Ulnaria ulna (Nitzsch) Compère 2001 dominated, while less pollution-tolerant species like Gomphonema parvulum f.saprophilum Lange-Bertalot and E. Reichardt 1993 and Stephanocylus meneghinianus (Kutzing) Kulikovskiy, Genkal, and Kociolek 2022 were less abundant. Both diatom indices and physicochemical data indicated poor water quality in the Kuils River. The study concludes that diatoms are a valuable tool for biomonitoring river water quality and recommends their use alongside traditional physicochemical methods for future assessments of river systems. Full article

In order to investigate non-cyanobacteria dominance succession from Microcystis blooms, particularly to diatom dominance, an experiment using varying colonial Microcystis biomasses expressed as bulk concentrations of 2.0, 4.0, 6.0, 8.0, 10.0, 12.0, 14.0, 16.0, 18.0, 20.0, 22.0, and 24.0 mL L⁻¹ was undertaken under continuous aeration mixing in a greenhouse during a hot summer where shading had reduced light level by 97%. The results showed that the algal shift process was affected by the initial biomass of the colonial Microcystis, and the algal community diversified. When the Microcystis bulk concentration was between 2.0 and 16.0 mL L⁻¹, the bloom became dominated by diatom Nitzschia palea, which aggregated on the mucilage sheathes of the Microcystis colonies. The diatom density at bulk concentration biomass of 2.0 mL L⁻¹ reached a maximum at 2.8 × 10⁵ cells mL⁻¹ on day 27. When the bulk concentration was at 18.0–24.0 mL L⁻¹, no diatom dominance appeared. The shift from a Microcystis bloom to diatom dominance was affected by the initial Microcystis biomass, and the most suitable bulk concentration biomass for colonial Microcystis was at 2–12 mL L⁻¹, in which the chlorophyll-a level was about from 285 to 1714 μg L⁻¹. The mechanism underlying this algal shift may be that the low light and nutrient levels in the Microcystis bloom promoted diatom aggregation growth on the mucilage sheaths of Microcystis colonies under continuous aeration mixing. Full article

Data about the ecotonic diatom communities of the Kamchatka Peninsula, a unique territory with strong volcanic activity, are very limited. We aimed to investigate diatom algae of the ecotones in the southeastern part of Kamchatka, including the Paratunka river valley, at the foot of the Vachkazhets volcano, and the bank of the Bystraya river. In total, 55 taxa were identified. The most diverse were the flora of the Paratunka river, with 31 taxa. Near the Bystraya river, 26 taxa were identified. Near the Vachkazhets volcano, 18 taxa were identified. Fragilariforma virescens, Planothidium lanceolatum, Pinnularia cf. subcapitata, Halamphora normanii, Nitzschia palea, and Eunotia exigua were the dominant species in the studied ecosystems, with the maximum abundance score. Pinnularia cf. subcapitata and Planothidium lanceolatum were found in all ecotones. In the studied habitats, small indifferent alkaliphilic cosmopolitan species prevailed. Our study revealed that the diatom species composition of the Kamchatka ecotones reflects their adaptability to survive in the extreme conditions of volcanic substrates. The results contribute to our knowledge of the ecology and biogeography of a number of diatom taxa. Full article

A floristic survey was performed on a temporary pond, “Laqui du Seignavoux”, situated in the Mont-Dore massif of the French Massif Central, between 2017 and 2019. Except in 2017, each year, we performed four sampling campaigns from April/May to December. Water samples and diatoms were collected. The temporary pond evolved from a poorly mineralized ecosystem due to snow, inducing oligotrophic and oligosaprobic water, well oxygenated in spring, to a more mineralized, less oxygenated, eutrophic–hypereutrophic, and polysaprobic environment in summer. This change in abiotic conditions was found to be linked to the presence of cattle, beginning in May, that trample and excrete in the pond, leading to higher ammonium and nitrate concentrations. During this period, the dominant species were Pinnularia sp., Nitzschia palea, and Nitzschia palea var. tenuirostris. In spring and winter, different species of Eunotia dominated the community such as Eunotia pseudogroenlandica. Finally, light microscopy (LM) and scanning electron microscopy (SEM) observations on a new species of the genus Pinnularia from the temporary pond are presented and the ecological preferences are discussed. Full article

Most of Korea’s rivers and lakes are subject to physico-chemical disturbances, such as increased water quantity and flow rates, and influx of nitrogen and phosphorus, due to intense rainfall concentrated in the Asian monsoon season. To examine the influence of rainfall on epilithic diatom communities, we measured the diatom distribution and river water quality at 29 sites along the main-stream and tributaries of the Hantangang River, Korea, in the period of 2012–2015. Water quality parameters in the polluted sites had improved following rainfall, but the response of dominant species varied with water quality; the dominant species Nitzschia fonticola decreased in abundance regardless of sampling sites, and the abundance of Achnanthidium minutissimum in the clean sites and Nitzschia palea in the polluted sites increased after rainfall, respectively. The community dynamic index (CDI) showed that the most obvious shift of epilithic diatom community occurred in the mid-polluted sites in 2013 with the highest rainfall. This suggest that the effect of rainfalls on the epilithic diatom community is dependent on various parameters, such as the magnitude of rainfall, water quality and its biotic compositions of diatom communities, but it also indicates that improving the water quality of rivers is important to promote the resilience of diatom communities to extremes of precipitation. Further investigation is needed to generalize the effects of monsoon rainfall on the epilithic diatom communities, considering rivers with different environmental characteristics. Full article

The relative tolerance of four diatoms (Nitzschia palea, Pinnularia mesolepta, Mayamaea atomus, and Gomphonema truncatum) to Cd was evaluated, including their proneness to deformities, and the severity of the abnormalities in relation to Cd concentration. The indirect effect of Cd on photosynthetic capacities was assessed during a short time exposure experiment using a dose-response approach to evaluate the relative tolerance of the four diatom species. The EC₂₅ were 9 (3, 23), 606 (348, 926), 1179 (1015, 1349) and 2394 (1890, 2896) µg/L for P. mesolepta, G. truncatum, N. palea, and M. atomus respectively. P. mesolepta was by far the most Cd sensitive species while M. atomus was the most tolerant. In addition, diatoms were exposed to a single concentration of Cd comparable to a heavily contaminated environment for a longer duration to evaluate the effect of Cd on growth kinetics and the deformities induced. N. palea, P. mesolepta, and M. atomus were able to grow when cultivated with Cd while G. truncatum was not. Cadmium strongly affected the effective quantum yield in G. truncatum (4.8 ± 5.9% of the control) and P. mesolepta cultures (29.2 ± 6.9% of the control). The effects were moderate for N. palea (88.3 ± 0.7% of the control) and no impact was observed for M. atomus. The results from the two approaches were in accordance since they identified N. palea and M. atomus as the two most tolerant species to Cd, while P. mesolepta and G. truncatum were the most sensitive. The microscopy analyses revealed that P. mesolepta was more impacted by Cd than N. palea and M. atomus considering both the quantity of abnormal cells and the severity of the deformities. Overall, this research shows that not all deformities can be considered equal for a water quality bio-assessment. The work highlights a need to take into account metal-tolerance/sensitivity of the species and the severity of the deformities. Full article

Benthic diatoms are an indispensable link of the water ecological system in terms of energy flow and material cycling, and they directly or indirectly reflect the status of the water environment. We sampled benthic diatoms and environmental factors from April to May of 2013 from 53 sites along the Ying River to study their application in local water trophic status assessment, with a focus on the dominant benthic diatom species, their composition and distribution pattern, and the relationship between benthic diatoms and environmental factors. A total of 370 species and varieties were identified, belonging to 56 genera and six orders. The dominant species were as follows: Nitzschia inconspicua Grunow, Achnanthidium minutissimum (Kützing) Czarnecki, Navicula aitchelbee L. L. Bahls, Nitzschia palea (Kützing) Smith, Cyclotella meneghiniana Kützing, Navicula submuralis Hustedt and Mayamaea atomus (Kützing) Lange-Bertalot. The Ying River was divided into five orders using the Strahler method and three regions according to total nitrogen, total phosphorus and ammonia nitrogen. In region Y-1, which had the lowest nutrient level, the dominant species was Achnanthidium minutissimum. In region Y-2, which had the highest nutrient level, Navicula aitchelbee, Nitzschia palea, and Cyclotella meneghiniana were dominant, while in region Y-3, which had moderate nutrient levels, Nitzschia inconspicua was dominant. Pearson’s correlation analysis and canonical correspondence analysis (CCA) revealed a significant correlation between the environmental factors with dominant species and diatom indices (especially the SPI). Our study indicates that dominant species and diatom indices can, to some extent, indicate the environment, especially nutrient distribution. Full article