Part of the geology in the Łódź province was formed during the Upper Permian period when rich Zechstein salt was deposited. Groundwater drains the deposits and flows out in the village of Pełczyska, creating a unique hydrogeological site in Central Poland. An inland, athalassic ecosystem can be a reference site for halophile microflora. The outflow with surrounding marshes has been an algological research site since 1964. The research reveals changes recorded in diatom assemblages from athalassic habitats, characterized by a wide range of salinity levels, and verifies the tolerance of taxa to salinity. The comparative analysis was based on the diatom material sampled in 1964-1965, 1992-1994 and on recently collected samples. The analysis revealed the temporal change in assemblages caused by a change in the chloride concentration, and the spatial change from one to another habitat type, characterized by varying salinity levels. The halophilic species in the studied habitats included e.g. Halamphora dominici, H. tenerrima, Navicula digitoconvergens, N. meulemansii, Staurophora salina. The analysis of changes allowed the verification of the species’ requirements and tolerance range to the salinity factor. Therefore, in the case of Fragilaria famelica and Halamphora sydowii, we propose a change in the halobion system classification.

The benthic diatoms collected during our recent research in athalassic habitats exemplify a high morphological variability within Chamaepinnularia krookiformis lange-Bertalot et krammer. The species has already been known from freshwater ecosystems as well as from brackish waters in different regions of Europe. This variability has been also confirmed by the analysis of the literature. However, this is the first time that the morphological variability of the species has been addressed. In order to revise C. krookiformis and describe a new species, which has been distinguished on the basis of our material, we compared it with the type material of Pinnularia krookiformis krammer 1992 from the periodic saline pool in Nordrhein-Westfalen (Germany). This study deals with a morphological analysis based on a large populations of C. krookiformis from Pełczyska (Central Poland). Selected morphological features were analysed, i.e.: valve length and width, number of striae in 10 µm, apices width, constrictions width, apices/constrictions width ratio, central-area length, and valve/central area length ratio. The results of light (LM) and scanning (SEM) microscopy, supported by multidimensional scaling (MDS), allowed for the distinction of three different morphotypes. Two of them match krammer concept of Pinnularia krookiformis from 1992, while the third, occurring in our samples in three sampling sites, is clearly different. Thus, we described a new species Chamaepinnularia plinskii sp. nov., by the following major features: the valves are linear, symmetric, with rounded, capitate apices, the axial area is narrow, expanding to a wide central area forming a fascia, distal raphe endings are hooked to the same side of the valve and striae slightly radiate in the middle and in the rounded apices, becoming parallel in constrictions, 20-26 in 10 µm. This species occurs in inland waters with a wide range of chloride concentration, from 1000 to 3500 mg.l-1 .

Post iron ore mining reservoirs in Łęczyca (Poland) can be considered extreme habitats because they are characterized by high pH, conductivity, and sulfate, sodium and potassium concentrations. We observed high abundances in these water bodies of several centric diatom species that are otherwise known from less extreme environments. These included Thalassiosira duostra, Cyclostephanos dubius, Stephanodiscus binatus, Stephanodiscus invisitatus, Stephanodiscus parvus, Stephanodiscus hantzschii, Lindavia aff. balatonis, Discostella woltereckii, Discostella pseudostelligera, and Cyclotella meneghiniana, revealing the eurytopic nature of these species. Morphological differences between populations from extreme habitats and their counterparts from less extreme environments may indicate phenotypic responses of eurytopic taxa to the differing environmental regimes, or the presence of distinct, more stenotopic taxa. In both cases, this could be relevant for biomonitoring. For this reason, we carefully observed the morphological variability of our target taxa in the Łęczyca reservoir samples compared with literature accounts from less extreme habitats, and in some cases, with type material of the species concerned. Specimens similar to Aulacoseira muzzanensis α-chains were observed. Following comparison with the type material of Melosira muzzanensis Meister (≡A. muzzanensis), we concluded that the Łęczyca populations are sufficiently different to be recognized as a separate species, here described as Aulacoseira pseudomuzzanensis sp. nov. The importance of identifying centric diatoms to species level for water management surveys is emphasized, even for those taxa that are difficult to identify using only LM.

The aim of the study was to compare the biological analyzes of the Linda River (Central Poland), which were based on three diatom indices: IO, GDI and IPS in order to select the best diatom index for the biological assessment of the lotic water quality. Additionally, the summary of the selected results of the biological and chemical analyzes was presented to show how precise the biological analyzes are as a basic tool in the assessment of the ecological status of the lotic waters. The results showed that each of the indices assessed the water in the Linda River to a specific but different quality class. The IO index showed class II of the water quality, while the IPS and GDI — class III. Statistical analysis conducted with the nonparametric Kruskal-Wallis test for independent samples (Kruskal, Wallis 1952) showed that differences in the values of individual indices at different sites were not statistically significant. It should be noticed that the IPS and GDI indices gave values that classify the water in the Linda River at least one class below. The obtained results confirmed that the biological methods are most reliable in the assessment of the water quality. These methods are less sensitive to a single impact of the environmental factors, therefore they permit accurate determination of the ecological status of the water ecosystems.

Contemporary assessment of the ecological status of aquatic ecosystems is based on various groups of organisms, including diatoms. Biological assessment, implemented by the Water Framework Directive, has been applied worldwide for more than 15 years. Currently, the most basic “tool” used in biomonitoring are diatom indices, which are routinely applied in Europe and other countries around the world. In Poland, the diatom indices have been used for over 5 years, which is a period of time allowing to summarize and evaluate the effectiveness of these methods in the assessment of aquatic ecosystems. The purpose of this work was to analyse the use of diatom indices in the biomonitoring of surface water by collecting data on the possibilities and limitations of using diatom indices for the objective assessment of water quality. Attention was paid to mistakes made in the course of biological assessment performed with the use of diatom phytobenthos, which have a significant impact on the obtained results. The paper also contains suggestions for introducing several important changes in biological monitoring, which will improve its quality and efficiency in assessing the ecological status of various aquatic ecosystems.