Un nouvel Indice Diatomique Pratique pour l'évaluation de la qualité des eaux en réseau de surveillance

L'Indice de Polluosensibilité Spécifique (IPS) est considéré comme l'un des indices diatomiques les plus performants pour l'évaluation de la qualité des cours d'eau. Son utilisation en réseau de surveillance reste cependant limitée en raison de la nécessité de travailler au niveau spécifique voire infraspécifique et de la systématique en perpétuelle évolution. A l'opposé, l'Indice Diatomique Générique (IDG) est plus accessible dans sa mise en oeuvre mais ne permet pas d'obtenir des résultats très fiables. Un nouvel Indice Diatomique Pratique (IDP) a donc été mis au point sur un bassin versant expérimental à partir d'un jeu de 86 relevés. Dans un premier temps, les inventaires ont été classés en fonction des écarts observés entre IPS et IDG. Dans un second temps, ont été identifiées les espèces responsables de ces écarts en prenant en compte celles présentant une abondance relative supérieure à 5 % et une différence de polluosensibilité avec le genre correspondant supérieure ou égale à 0,4. Plusieurs IDP ont été mis au point et leurs performances, par rapport à l'IPS, étudiées. Il apparaît que la prise en compte des espèces responsables des écarts supérieurs ou égaux à 2 constitue le meilleur compromis entre fiabilité et applicabilité en réseau. Cette méthodologie a été appliquée aux 480 relevés effectués dans le bassin Artois - Picardie et aux 550 espèces inventoriées. Elle permet de proposer un indice diatomique pratique basé sur l'identification de 45 genres et 91 espèces.Macroinvertebrates constitute the main biological support for an evaluation of the quality of water courses and are, therefore, widely put to use in monitoring networks. However, for major water courses and canalized waterways the use of other methodologies is imperative. Diatoms and diatom indices are well adapted to the study of these environments. Among these, the Specific Polluosensitivity Index (SPI) established by CEMAGREF seems to be one of the better performing diatom indices. Calculation of this index relies on the Zelinka & Marvan formula derived from the saprobic system: SPI=[Epsilon]A[inf]j v[inf]j i[inf]j / [Epsilon] A[inf]j v[inf]j where A[inf]j is the relative abundance of the species j, v j is its indicative value ( 1 [smaller or equal] v[inf]j [smaller or equal] 3) and i[inf]j its pollution sensitivity (1 [smaller or equal] i[inf]j [smaller or equal] 5). The values initially falling in the range between 1 and 5 are transformed into values comprised between 1 and 20, in order to make comparisons between the various existing indices easier. Five categories of water quality can be distinguished according to the value of the index: SPI [Bigger or equal] 16: zero pollution or low eutrophication; 13.5 [smaller or equal] SPI < 16: moderate eutrophication; 11 [smaller or equal] SPI < 13.5: moderate pollution or heavy eutrophication; 7 [smaller or equal] SPI < 11: high pollution; SPI < 7 : very heavy pollution. However, the SPI index is rarely used because of two main obstacles: it requires data at a specific or even infraspecific level, and it is based on constantly changing systematics. Progress towards increased accessibility and, therefore, larger application was made with the elaboration of the Generic Diatomic Index (IDG) based on the same principle as the SPI. However, this GDI does not yield reliable results, in so far as certain genera, such as Navicula and Nitzschia, contain species with a widely differing ecologies. In order to provide a methodology that can be used as a matter of routine, a protocol for the elaboration of a Practical Diatomic Index (PDI) was established and tested on 86 inventories from the water basin of the river Aa (North of France). These were first classified into four categories according to the variations observed between SPI and GDI: category 1: |SPI-GDI| [bigger or equal] 3 ; category 2: 2 [smaller or equal] |SPI-GDI|; category 3: 1 [smaller or equal] |SPI-DGI| < 2 ; category 4: |SPI-DGI| < 1. For each of the first three categories, the species responsible for the variations were identified, taking into consideration those with a relative abundance of more than 5%, the pollution sensitivity of which showed, compared to the corresponding genus, a variation higher than or equal to 0.4. Thus, three indices corresponding respectively to category 1 (PDI1), 2 (PDI2), and 3 (PDI3) were proposed and tested against the SPI taken as reference index. The results of this comparative study can be summarized as follows:- GDI=0.57 SPI + 5.47 r=0.801 (242 species), - PDI1=0.86 SPI + 1.12 r=0.972 ( 27 species), - PDI2=0.95 SPI + 0.55 r=0.991 ( 39 species), - PDI3=0.96 SPI + 0.45 r=0.994 ( 42 species). To test the implications of replacing the presently used SPI by this practical index, a comparative study of the classification of inventories in four categories of hydrobiological quality was also carried out. This study shows that the mean, at - 1.76 ± 2.25 for the GDI, is reduced to 0.14 ± 0.94 for PDI1, to - 0.07 ± 0.51 for PDI2, and to - 0.07 ± 0.45 for PDI3. Given the variability of the index at one and the same site and in one sampling, PDI2 considered to be the best compromise between reliability and network applicability. The methodology corresponding to PDI2 was applied to the 480 samplings carried out in the Artois-Picardie basin and a new Practical Diatom Index is thus proposed for the monitoring of the 200 sites making up the monitoring network of the Artois-Picardie water basin. This PDI, built on a base of more than 550 species and varieties, rests on the joint determination of 45 genera and 91 species of which the pollution sensitivity coefficients and the indicative values are given

Digital university : a study of students’ experiences and expectations in the post-COVID era

In 2020, the education process at universities started to be redefined, parting with the traditional face-to-face form. The article presents the conclusions of exploratory study conducted at the Jagiellonian University in Kraków (Poland) on the students’ experiences of remote education as well as their expectations for the future. The study was conducted in the form of an online survey addressed to the entire population of science recipients at the Jagiellonian University, around 800 respondents completed the questionnaire. The obtained results show that most students rate remote education relatively high, although there are statistically significant differences in specific questions (e.g., theoretical classes are more suitable for online learning than practical classes). The authors paid special attention to the differences in the attitudes of students depending on their characteristics, the approach to remote education differs, in particular, depending on the gender and field of study. Students of social and humanist faculties view remote education most positively, and science students opinions are mostly negative. It has also been observed that some students are uncritically satisfied with most aspects of distance learning (the so-called "Tiggers"), while others are strong supporters of face-to-face education, reluctant to accept any changes (so-called "Eeyores"), so regardless of the scope of pro-quality activities undertaken, both criticism and praise of remote education can be expected. The obtained results open the field for further studies that would allow to confirm the covariance of multidimensional characteristics of students and their attitudes towards the digital university, and on the other hand would allow planning activities aimed at different and perhaps mutually contradictory expectations of the recipients of education

Autogenic versus environmental control during development of river biofilm

In the natural environment, microbial community structure of river biofilm is controlled by biotic and abiotic factors. This study explored the capacity to manipulate the structure of microbial communities by modifying environmental conditions during the course of biofilm development. River epilithic biofilm was cultivated in situ on artificial substrates placed parallel to river water flow. Substrates were incubated for 3 and 5.5 weeks in river to allow natural biofilm development, at two sites with contrasting physico-chemical characteristics. The first site (Aurade´ , Gers, France) was located in an agricultural watershed basin and the second site (Larroque, Haute-Garonne, France) was located in a forested watershed basin. After 3 weeks of biofilm development, a subset of substrates was collected from one site and transplanted to the second site where they remained for 2.5 further weeks. Epilithic bacterial community structure (at 3 weeks from each site and at 5.5 weeks from biofilms with and without transplantation) was assessed using PCR-DGGE of 16S rDNA fragment. Biofilm biomass was estimated using ash free dry mass (AFDM). After 3 weeks of development, biofilms from the two sites exhibited comparable AFDM values (average of 1.4¡0.2 g.mx2). A difference between the two sites was observed after 5.5 weeks of development: AFDM decreased for biofilms from the agricultural watershed basin (from 1.4 to 0.18 g.mx2) as a consequence of grazing pressure (Bithynia), and increased for biofilms from the forested agricultural watershed (from 1.4 to 2.6 g.mx2). Microbial community analyses revealed a differentiated community structure between biofilms from the different sites and exhibited a change of microbial community structure after 5.5 weeks of biofilm development. These observations confirm a process of ecological succession in microbial communities. Changing the incubation site during biofilm development modified the trajectory of these ecological successions, suggesting that site characteristics mainly conditioned the structure of these microbial communities

A new cell primo-culture method for freshwater benthic diatom communities

A new cell primo-culture method was developed for the benthic diatom community isolated from biofilm sampled in rivers. The approach comprised three steps: (1) scraping biofilm from river pebbles, (2) diatom isolation from biofilm, and (3) diatom community culture. With a view to designing a method able to stimulate the growth of diatoms, to limit the development of other microorganisms, and to maintain in culture a community similar to the original natural one, different factors were tested in step 3: cell culture medium (Chu No 10 vs Freshwater “WC” medium modified), cell culture vessel, and time of culture. The results showed that using Chu No 10 medium in an Erlenmeyer flask for cell culture was the optimal method, producing enough biomass for ecotoxicological tests as well as minimising development of other microorganisms. After 96 h of culture, communities differed from the original communities sampled in the two rivers studied. Species tolerant of eutrophic or saprobic conditions were favoured during culture. This method of diatom community culture affords the opportunity to assess, in vitro, the effects of different chemicals or effluents (water samples andindustrial effluents) on diatom communities, as well as on diatom cells, from a wide range of perspectives

Boosting DNA metabarcoding for biomonitoring with phylogenetic estimation of operational taxonomic units' ecological profiles

DNA metabarcoding has been introduced as a revolutionary way to identify organisms and monitor ecosystems. However, the potential of this approach for biomonitoring remains partially unfulfilled because a significant part of the sampled DNA cannot be affiliated to species due to incomplete reference libraries. Thus, biotic indices, which are based on the estimated abundances of species in a community and their ecological profiles, can be inaccurate. We propose to compute biotic indices using phylogenetic imputation of operational taxonomic units (OTUs') ecological profiles (OTU-PITI approach). First, OTUs sequences are inserted within a reference phylogeny. Second, OTUs' ecological profiles are estimated on the basis of their phylogenetic relationships with reference species whose ecology is known. Based on these ecological profiles, biotic indices can be computed using all available OTUs. Using freshwater diatoms as a case study, we show that short DNA barcodes can be placed accurately within a phylogeny and their ecological preferences estimated with a satisfactory level of precision. In the light of these results, we tested the approach with a data set of 139 environmental samples of benthic river diatoms for which the same biotic index (specific sensitivity index) was calculated using (a) traditional microscopy, (b) OTUs with taxonomic assignment approach, (c) OTUs with phylogenetic estimation of ecological profiles (OTU-PITI) and (d) OTU with taxonomic assignment completed by the phylogenetic approach (OTU-PITI) for unclassified OTUs. Using traditional microscopy as a reference, we found that the combination of the OTUs' taxonomic assignment completed by the phylogenetic method performed satisfactorily and substantially better than the other methods tested