Dataset of a flow intermittency study: Benthic communities of 13 alpine intermittent rivers.

In the last few decades, perennial mountain streams are becoming increasingly intermittent, due to global climate change and anthropogenic pressures. This phenomenon leads to negative effects on benthic communities' biodiversity and river ecosystems functionality. However, the impact of flow intermittency in previously perennial Alpine streams is still poorly investigated. This dataset consists of all the data collected during a spring sampling campaign performed in April-May 2017 along 13 mountain streams located in the SW Italian Alps. These watercourses have been selected because it was possible to identify two different sampling sites: one perennial, where water has always been flowing throughout the years, and one intermittent, which showed flowing water during the sampling campaign but, in the last decade, has experienced summer dry phases. All the sites have been characterized defining the microhabitats in which samples were retrieved, and physico-chemical data were collected at each site. Biological sampling included benthic macroinvertebrates and diatoms. Therefore, the present dataset offers various biological, ecological and physico-chemical information regarding Alpine streams which have recently become intermittent. Potentially, it could be used for comparisons with different benthic communities present in mountain rivers worldwide which are facing drying events too. The broad range of information present in this dataset offers the possibility to examine only the perennial sites themselves, as an example of good river functionality due to continuous flowing water, or only the intermittent ones, to better understand the effects of drying events on these peculiar ecosystems.

A diatom-based approach to refine nutrient concentrations compatible with the "good" status of Northern Italy rivers.

The identification of ecologically sound thresholds represents an important step toward improving the ecological status of rivers through appropriate measures to contain nutrient loads. The aim of the present study was to estimate phosphorus and nitrogen concentrations compatible with the achievement of the "good" ecological status of rivers from data collected in the Po River District, the largest hydrographic system in Italy. For this purpose, relationships between the diatom index used in Italy for the national assessment of the stream ecological status, the ICMi (Intercalibration Common Metric index), and total phosphorus and nitrate concentrations were analyzed using monitoring data collected between 2009 and 2019. The Po River Basin encompasses five distinct river types, from Alpine to Mediterranean to Lowlands, characterized by different anthropogenic pressures and water quality. Through regression analysis between the ICMi and nutrient concentrations, we estimated ranges of the latter values corresponding to a "good" ecological status for each river type. The resulting thresholds are far more stringent than the limits set by the Italian legislation for water quality classification. This is particularly true for total phosphorus, whose threshold value should be roughly halved for all river types. For nitrates, the results are more differentiated according to river type: the estimated thresholds are much more stringent than those currently in use for siliceous Alpine and Mediterranean rivers. Moreover, the availability of such a large database allowed also to assess the influence of one nutrient over the other on the diatom community and to highlight some critical issues in the formulation of ICMi for Mediterranean rivers.

Hydrological intermittency drives diversity decline and functional homogenization in benthic diatom communities.

Over the last decades, the combined effects of global climate changes and severe land use modifications have been exacerbating river hydrological alterations and habitat fragmentation in many Mediterranean rivers. This trend is predicted to intensify, with expected significant impacts on taxonomic and functional diversity of benthic communities in the next future. By comparing perennial and intermittent reaches, the present research aims at investigating the role of flow intermittency, driven by the combined effects of climatic variables and land use changes, on benthic diatom communities in Mediterranean streams (NW Italy), by analysing data collected over 11 years. In order to avoid potential confounding effects related to water quality, sites characterized by "poor" or "bad" water quality were excluded a priori. We observed significant differences between permanent and intermittent sections in terms of both climatic variables and land use: higher temperatures and lower precipitations, coupled with an extensive anthropic land use, intensify the natural flow intermittency in intermittent sites. This led to a significant decline in diatom species diversity, at both local and regional scales, and to changes to life history traits. In particular, communities of intermittent reaches were taxonomically and functionally different and less heterogeneous than assemblages characterizing perennial ones, showing higher percentages of small, mainly stalked and pioneer taxa belonging to the low profile guild. Conversely taxa colonizing permanent reaches were bigger, belonging to the high profile guild and able to produce colonies, thus indicating high environmental stability. Our results highlighted how hydrological alterations are profoundly threatening Mediterranean streams and the diatom communities inhabiting them, therefore representing an important benchmark in view of the improvement of biological indices for the assessment of intermittent rivers.

Functional Feeding Groups of Aquatic Insects Influence Trace Element Accumulation: Findings for Filterers, Scrapers and Predators from the Po Basin.

For this study, we measured the concentrations of 23 trace elements (Al, As, Ba, Bi, Cd, Cr, Co, Cu, Fe, Ga, Hg, In, Li, Mn, Mo, Ni, Pb, Se, Sr, Ti, Tl, V, and Zn) in the whole bodies of three functional feeding groups (FFG) (filterers-Hydropsychidae, scrapers-Heptageniidae, and predators-Odonata) of aquatic insects collected from two sites in the Po basin (Po Settimo and Malone Front, Northwest Italy) to determine: (a) how FFG influence trace element accumulations, (b) if scrapers accumulate higher elements compared to the other FFG, since they graze on periphyton, which represents one of the major sinks of metals, and (c) the potential use of macroinvertebrates to assess the bioavailability of trace elements in freshwater. The hierarchical clustering analysis generated three main groups based on trace element concentrations: the most abundant elements were Fe and Al, followed by Sr, In, Zn, V, Mo, and Cu. Tl was below the limit of detection (LOD) in all FFG. Ga was detected only in scrapers from both sites and Hg only in predators from Po Settimo. The principal component analysis showed that concentrations of Al, As, Bi, Cd, Co, Cr, Ga, Fe, In, Mn, Pb, Ni, and Sr were highest in scrapers, suggesting that trace elements accumulate from the ingestion of epilithic periphyton (biofilm). Odonata (predators) accumulate certain elements (Ba, Hg, Li, Se, V, Ti, and Zn) in higher concentrations by food ingestion composed of different aquatic organisms. Differently, Cu and Mo concentrations were the highest in filterers due to their bioavailability in the water column. Non-metric multidimensional scaling clearly differentiated the FFG based on their ability to accumulate trace elements. The findings from this study represent an important step toward the definition of an innovative approach based on trace element accumulation by macroinvertebrates.

Achnanthidium minutissimum (Bacillariophyta) valve deformities as indicators of metal enrichment in diverse widely-distributed freshwater habitats.

In the presence of different environmental stressors, diatoms can produce frustules presenting different types of deformities. Metals and trace elements are among the most common causes of these teratological forms. Metal enrichment in water bodies can be attributed to the geological setting of the area or to pollution. The widespread benthic diatom Achnanthidium minutissimum (ADMI) is one of the most metal-tolerant species. In the present study, ADMI teratologies were defined from samples taken from eight very diverse, widely-distributed inland-water habitats: streams affected by active and abandoned mining areas, a metal-contaminated stream, a spring in an old chalcopyrite mine, a mineral-water fountain, and a sediment core taken from a lake affected by metal contamination in the past. Deformed frustules of ADMI were characterised mainly by one (sometimes two) more or less bent off ending, conferring to the specimens a cymbelloid outline (cymbelliclinum-like teratology, CLT). Marked teratologies were distinguished from slight deformities. Hydrochemical analyses, including metals and trace elements, were carried out and enrichment factors (EF) relative to average crustal composition were calculated. To improve our knowledge on the potential of different metals and trace elements to trigger the occurrence of ADMI CLT, we carefully selected 15 springs out of 110 (CRENODAT dataset) where both ADMI and above-average metal or metalloid concentrations occurred, and re-analysed these samples. The results from the eight widely-distributed core sites as well as from the 15 selected CRENODAT springs led to the hypothesis that two metals (copper and zinc) and a metalloid (antimony) were the most likely triggers of ADMI CLT formation. From a quantitative point of view, it is worth noting that the lowest concentrations triggering ADMI CLT can be fairly low, particularly in the case of copper contamination. The antimony-rich site was characterised by a marked-teratology variant where both ends of ADMI were bent off.

NITZSCHIA ALICAE SP. NOV. AND N. PURIFORMIS SP. NOV., NEW DIATOMS FROM EUROPEAN RIVERS AND COMPARISON WITH THE TYPE MATERIAL OF N. SUBLINEARIS AND N. PURA(1).

Nitzschia sublinearis Hustedt and N. pura Hustedt are common oligosaprobic freshwater diatom species that frequently occur in diatom inventories, thus being important in water quality studies. Both are considered as species with overlapping diagnostic criteria in several floras, which is typical of the whole genus Nitzschia. The type material of Hustedt of N. sublinearis and N. pura was examined using LM and EM in order to document the range of variation within the type populations and to compare it with populations occurring in different European rivers. Detailed observations allowed recognition of two new freshwater diatom species: N. alicae sp. nov., occurring in mesotrophic up to eutrophic conditions, and N. puriformis sp. nov., mostly occurring in oligotrophic habitats, both in rivers and streams at middle and high altitudes. The most reliable taxonomic features that separate both new species from the most similar taxa are the density of fibulae and striae, valve shape, and valve width as well as the shape of areolae. Morphological examination of different populations indicates that N. puriformis is relatively common in European rivers and has been overlooked to date and confounded with N. pura by several researchers. By contrast, N. alicae has, to date, been collected only in Slovakia and Northern Italy, but with a high frequency of occurrence and sometimes in high abundance at sites.