We studied diatoms from the fifteen springs selected in the Berchtesgaden National Park on behalf of the Bavarian State Ministry for the Environment to be sentinel environments of climate-change effects. For three of these springs, diatom data based on samples taken in 1997 were also available. A total of 162 species belonging to 49 genera were found sampling three microhabitat types (lithic materials, bryophytes, surface sediments). The cumulative percentage of all species included in a threat category including endangered species was 43%, confirming previous findings for comparable environments of the Alps. We could find a statistically significant positive association between the Meinzer variability index for discharge and the cumulative relative abundance of aerial diatom species. This study thus highlighted once again the relevance of discharge (and associated water-level) variability as an environmental determinant of diatom assemblages in spring ecosystems. Increased nitrate concentrations in some springs, likely due to diffuse airborne pollution and, locally, to impacts such as forest management, game, and cattle, led to a relevant occurrence of eutraphentic diatom species. Our results show a segregation of the older data in non-parametric diatom-based ordinations, suggesting a strong potential for the use of spring diatoms in studies aiming at tracking the effects of climate and environmental change.

Using light (LM, including plastid characterization on fresh material) and scanning electron microscopy (SEM), as well as a thorough morphological, physical, chemical, and biological characterization of the habitats, the present study aims at describing three species new to science. They belong to the genera Eunotia Ehrenb., Planothidium Round and L. Bukht., and Delicatophycus M.J. Wynne, and were found in two contrasting spring types in the northern Apennines. The three new species described differ morphologically from the most similar species by: less dense striae and areolae, and the absence of a ridge at the valve face-mantle transition (SEM feature) [Eunotia crassiminor Lange-Bert. et Cantonati sp. nov.; closest established species: Eunotia minor (Kütz.) Grunow]; narrower and shorter cells [Planothidium angustilanceolatum Lange-Bert. et Cantonati sp. nov.; most similar species: Planothidium lanceolatum (Bréb. ex Kütz.) Lange-Bert.]; barely-dorsiventral symmetry, set off ends, and lower density of the central dorsal striae [Delicatophycus crassiminutus Lange-Bert. et Cantonati sp. nov.; most similar species: Delicatophycus minutus M.J.Wynne]. Two of the three species we described are separated from the closest species by dimensions. Their description improved knowledge on two taxa (Eunotia minor s.l. and Planothidium lanceolatum s.l.) likely to be only partially resolved species complexes. We could also refine knowledge on the ecological profiles of the three newly-described species. Eunotia crassiminor sp. nov., as compared to Eunotia minor, appears to occur in colder inland waters with a circumneutral pH and a strict oligotrophy as well with respect to nitrogen. The typical habitat of Planothidium angustilanceolatum sp. nov. appears to be oligotrophic mountain flowing springs with low conductivity. Delicatophycus crassiminutus sp. nov. was observed only in limestone-precipitating springs, and is therefore likely to be restricted to hard water springs and comparable habitats where CO₂ degassing leads to carbonate precipitation. Springs are a unique but severely threatened wetland type. Therefore, the in-depth knowledge of the taxonomy and ecology of characteristic diatom species is important, because diatoms are excellent indicators of the quality and integrity of these peculiar ecosystems in the face of direct and indirect human impacts.

Given the limited understanding of species diversity and ecological preferences of diatoms of the genus Navicula in spring ecosystems, herein we present and describe as species new to science, Navicula aquaesuavis Lange-Bert., Levkov, Cid-Rodríguez, A.A.Saber and Cantonati sp. nov. This species was collected from a mountain spring located above the tree line at 1613 m a.s.l. in the Northern Apennines. The Fontana del Vescovo (Bishop’s spring), which is the locus classicus of the new species, has a low conductivity (60–70 µS cm⁻¹), temperature of ca. 5 °C, circumneutral pH (7.3–7.5), relatively low nitrate (ca. 1 mg L⁻¹), and also suffered from a discharge reduction from 1 to 0.1 L s⁻¹ from 2011 to 2023. The putative new species was confirmed by a second finding in Northern Macedonia, and we thoroughly document this second population as well. We seized the opportunity to describe this new Navicula and review the global literature on the diatom genus Navicula in spring ecosystems. Using the results of this review and our own databases on springs and wells in central Europe and Egypt, we discuss the main Navicula species and their environmental preferences in spring habitats.

Mires are significant C-sinks and important habitats for biodiversity conservation. Particularly in the Alpine peatlands, grazing and trampling cause mires to degrade, causing changes in plant communities that increase bulk density, peat erosion, and nutrient excesses. We took sixteen samples of epipelic and epiphytic diatoms from mire pools subjected to varying degrees of grazing in the Adamello-Brenta Nature Park (Trento, Italy). We identified >100 diatom species (ca. 70% included in Red List threat categories). We used nMDS to identify groups of diatom species. Their statistical significance was checked with an ANOSIM and, to identify the species that contributed most to the difference between the two groups, a BEST-SIMPER procedure was carried out. The multivariate analyses allowed us to identify significant differences among the most and least grazed sites, and to select the species that contributed most to this distinction. We confirmed that some species were more frequent and abundant in the most grazed sites and behaved as opportunists in the presence of a greater nutrient input, to the detriment of rare and sensitive species, which were more numerous and abundant in the less grazed sites. We provided useful information on grazing effects, underlining the importance of managing and protecting habitats of unique environmental value.

A new desmid microalga species, Cosmarium yassinii A.A. Saber, El-Sheekh, Kouwets et Cantonati sp. nov., was isolated from two hyper-arid mountain valleys, so-called “wadis”, in the Eastern Desert of Egypt. The distinctive morphological features of this new species were established using light and scanning electron microscopy observations, and also by documenting its life-cycle stages. Taxonomically, C. yassinii is characterized by a cell wall sculpture consisting of isolated granules or small warts arranged circularly in the swollen mid-region of each semicell, never forming parallel vertical ridges or costae as in morphologically similar species, and the interesting shape of the marginal granules appears as small emarginate “combs” or crenae, including its knobby zygospores. Similarities and differences with the morphologically most closely related species are discussed in detail. Ecologically, C. yassinii seems to prefer alkaline freshwater environments with lower nutrient concentrations and a NaCl/HCO₃ water type. The detailed assessment and documentation of the biodiversity of these peculiar freshwater ecosystems are a fundamental prerequisite to adequately inform their protection strategies.