Morphology, taxonomy and distribution of Stephanodiscus triporus (Bacillariophyceae) and related taxa

Stephanodiscus triporus was described in 1978, based on a study from the phytoplankton of Volgograd Reservoir that used transmission electron microscopy. This species is small, diameter 3.7–10.6 µm, with 14–30 striae and 30–60 areolae in 10 µm, and differs from other Stephanodiscus species by the presence of three satellite pores in the single central fultoportula. Later a new species similar in morphology to S. triporus, was described from Iowa, USA, namely S. vestibulis. A large population of S. vestibulis was found in Lake Balaton and the species also occurs in different Hungarian and French waters. Detailed comparison of S. triporus and S. vestibulis, based on our results and literature, showed they are very similar. Therefore we reinvestigated the type material of both and compared them with the Hungarian and French specimens. Conventional and geometric morphometric analyses were carried out, also including comparisons with the morphologically closest taxon, S. minutulus. There is a continuum of variation between S. triporus and S. vestibulis (in diameter, the number and morphology of the striae, the position of the valve face fultoportula with three satellite pores, the presence of a vestibulum having more or less the same shape). Hence we suggest that they are conspecific, with S. vestibulis a later synonym of S. triporus

Interesting diatoms from a special habitat

The epiphytic diatoms of the soda ponds of bomb craters were sampled in 2014. The small ponds (area: 7.1-86.5 m2, depth: 4 to 60 cm) are located in the northern part of the Kiskunság National Park (47°7.403 'N, 19°8.187'E), near the village of Apaj in Hungary. Their salinity ranges from fresh water to moderately saline levels (conductivity of 1.3 to 7.1 mS cm-1). This area has patchy surface salinization, because the flow pattern of groundwater results extensive surface salinization in those discharge areas where the infiltrating freshwater does not superimpose the upwelling saline water. The salts origin from the overpressured NaCl-type water of the Pre-Neogene basement and the NaHCO3-type water of the Neogene sediments. The ponds can be characterized by different areal extent, depth and salinity, various conductivity, hydroperiod (1–9 months, the deepest ones do not dry out in years with high amount of precipitation due to probably more or less continuous supply by groundwater), plant coverage and width of macrophyte belt. All of the ponds were sampled except for the ones with very short (shorter than one month) hydroperiod. A total of 80 diatom taxa, representing 33 genera, were identified in these ponds. The genus Nitzschia was represented by the largest number of species (16), followed by the genus Gomphonema with 9 taxa. IndVal analysis identified 15 species with significant indicator values for ponds. Some interesting, rare or new diatoms for Hungarian flora have also been recorded, including Gomphonema jadwigiae, Halamphora dominici, Navicula wiesneri, Nitzschia austriaca, N. vitrea, Surirella peisonis

Effect of Land Use on the Benthic Diatom Community of the Danube River in the Region of Budapest

(1) Urbanization significantly influences the ecosystems of rivers in various ways, including the so-called loading effect of wastewater production. Benthic diatoms are used in ecological status assessments of waters. Beside species composition, traits can be used as indicators. We aimed to evaluate how the loading of the large city of Budapest manifests in the physico-chemical variables of the River Danube and what species composition and trait response this loading results in for the benthic diatom communities. (2) Weekly samplings were performed at points upstream and downstream of Budapest on both riverbanks. Samples were compared, based on general physical-chemical variables and the concentration of thirty-four elements, as well as species composition and seven traits of species of diatom communities. Ecological status was assessed using the Specific Pollution Sensitivity Index (IPS). (3) Only a few measured environmental variables showed differences between the sampling points, suggesting that the nutrient loading has significantly decreased due to the installation of several efficiently working wastewater treatment plants since the introduction of the European Union Water Framework Directive. In contrast, the species composition and traits of species showed the effect of land use. Benthic diatoms indicate the environmental changes caused by land use in the longer-term, while chemical measurements reflect instantaneous status