Intérêts et signification écophysiologique de l'estimation de la biomasse et de l'activité photosynthétique de diverses fractions de taille phytoplanctonique en milieu lacustre eutrophe

L'évolution saisonnière de la biomasse phytoplanctonique (estimée par les biovolumes après dénombrements cellulaires et par le dosage de la chlorophylle a), de la production primaire et des coefficients d'activité (P/"BComptage" et P/"BChlorophylle") a été étudiée, par classes de taille, de mars à novembre 1985 dans un lac eutrophe (lac d'Aydat, Massif Central).Il apparaît que la fraction de taille 12-45 µm contribue pour environ 50 % à la biomasse phytoplanctonique totale quelque soit le descripteur de ta biomasse utilisé et pour 65 % à l'activité photosynthétique totale, l'importance quantitative de cette fraction de taille se traduit au niveau des phénomènes d'extinction de la lumière par une relation inverse et hautement significative entre concentrations en chlorophylle a associée à cette classe et les profondeurs de disparition du disque de Secchi (Zs).Si les corrélations linéaires établies entre la production primaire et les rapports surface/volume (S/V) sont significatives au sein de chaque classe, confirmant ainsi l'existence d'une relation directe entre ces 2 paramètres, les valeurs moyennes de P/B de la fraction de taille < 12 µm sont très différentes selon le mode d'expression de la biomasse. L'explication de cette divergence est à rattacher aux divers biais méthodologiques introduits dans les estimations de biomasse retenues dans notre étude. D'une part, la sous estimation de la fraction nanoplanctonique par la technique des dénombrements cellulaires entraîne par voie de conséquence une surestimation des valeurs de P/B"Comptage" attribuées à la fraction < 12 µm. D'autre part, il est reconnu que les teneurs en pigments sont, par unité de volume, supérieures pour la fraction nanoplanctonique que pour les cellules de grande taille. L'adoption d'un facteur unique de conversion entraîne donc une surestimation de ta biomasse de cette fraction.The seasonal distribution of phytoplanktonic biomass (estimated by biovolumes after cell counts and by chlorophyll a concentrations), primary production and primary production to biomass ratios (P/B"Counts" and P/B"Chlorophyll a") was studied by size fractionation in a eutrophic lake (lake Aydat, Massif Central).It appears that the 12-45 µm size fraction contributes about 50 % of the total phytoplanktonic biomass, regardless of what descriptor of the biomass is used and up to 65 % of the total photosynthetic activity. Clearly, the quantitative predominance of this fraction affects the water transparency (Zs) through the highly significant negative correlation obtained between Zs and the 12-45 µm chlorophyll a size fraction.The highly significant linear correlations obtained between the primary production of each fraction and surface to volume ratios (S/V) confirm the direct link between these two parameters. The mean values relative to the P/B of the < 12 µm fraction depend largely on the method used for the biomass estimates. First, the underestimation of the nanoplanktonic fraction by cell counts leads to an over-estimation of the < 12 µm P/B"Counts" fraction. Second, it is well known that chlorophyll a concentrations per unit volume are higher for nanoplankton than for larger cells. Thus, the use of the same biomass conversion factor for all the fractions, overestimates the nanoplankton biomass

Comparaison des peuplements chironomidiens du lac de l'Abbaye obtenus par différentes méthodes d'échantillonnage. Intérêts de la récolte des exuvies nymphales

Une étude des espèces chironomidiennes du lac de l'Abbaye a été effectuée au cours de l'année 1993. Le répertoire spécifique a été établi à partir de l'étude des peuplements imaginaux, nymphals et larvaires échantillonnés selon 5 méthodes: récolte des imagos au filet entomologique, récolte des exuvies nymphales, mise en élevage de stades pré-imaginaux, prélèvements de larves dans les sédiments et mise en place de substrats artificiels. Le peuplement chironomidien obtenu est constitué de 69 espèces. Une comparaison de la composition des peuplements obtenus par les différents modes d'échantillonnage permet de mettre en évidence les particularités de chaque méthode. La récolte des exuvies nymphales semble être la méthode la plus appropriée pour l'établissement d'un répertoire spécifique. Deux espèces dominantes du lac Chironomus anthracinus et Psilotanypus rufovittatus témoignent du caractère polyhumique et désoxygéné du lac. Cependant, la présence simultanée en forte proportion de Tanytarsus niger, Cladotanytarsus iucundus et C. atridorsum témoignent de la faible production pélagique et de la température froide du lac susceptible de minimiser les effets de la désoxygénation sur la communauté chironomidienne.A study of chironomid species was undertaken in Lake Abbaye during the year 1993. Lake Abbaye is located 910 m a.s.l., in a karstic area in the east of France near Switzerland (Figure 1). It covers 80 ha with a maximum depth of 19 m and a mean depth of 7.2 m. Profundal sediment has a high level of organic matter (30.2% dry weight) of mainly terrestrial origin. The accumulation of the organic matter resulted in hypoxic conditions at depth during the summer stratification. The lake is rather cold (maximum surface temperature: 23°C), holodimictic, and is ice-covered from late November to early April. The list of chironomid species obtained resulted from the use of 5 different sampling methods: (i) adults caught with an entomological net; (ii) pupal exuviae sampling at the sites where they were accumulated; (iii) rearing of larvae; (iv) sediment sampling and (v) sampling of larvae using artificial substrates. The sampling site locations are indicated in Figure 1. The present paper gives results and discussions about i) the taxonomic richness and composition of the total chironomid community, ii) the composition of the different communities collected and the characteristics of the five sampling methods, iii) a characterization of Lake Abbaye according to the dominating species.1. Total chironomid communityThe chironomid community of Lake Abbaye consisted of 69 species (Table 1). Compared to other European lakes, this community showed a rather high richness. In some great lakes, however, the number of chironomid species amounted to 140 or 168 species (Lake Innaren, Lake Constance). These particularly high richnesses probably resulted from the great number of substrata according to the great surface of the littoral zone of these lakes. The chironomid community of Lake Abbaye is specific to a mountain area as shown by the high proportion of species collected (82% of the total richness) found by SERRA-TOSIO and LAVILLE (1991) at altitudes exceeding 500 m. According to REISS and FITTKAU (1971), the presence of two particular species (Tanytarsus niger and T. miriforceps) reflects the glacial origin of the lake.2. Composition of the different chironomid communitiesSampling the pupal exuviae allowed us to collect more than 90% of the species with less than 5000 individuals whereas by catching adults this percentage did not exceed 79% with more than 28000 individuals collected and identified. By rearing larvae both the number of species (46 species, 66% of the total richness) and the number of emerging adults (1386 individuals) were low. The least efficient method appeared to be the sediment sampling, which allowed the identification of only 19 taxa (genera and species) compared to the 31 taxa collected by artificial substrates. This study clearly showed that pupal exuviae sampling was the most appropriate method to establish a list of species yielding the greatest ratio between species richness and the effectives.A comparison of the major contributed species among the different communities led to the conclusion that the sampling method strongly affects community composition. Whereas in adult population (Figure 2) the dominating species (relative density=10%) were Tanytarsus niger, Ablabesmyia monilis, A. longistyla and Polypedilum nubeculosum, the community of pupal exuviae (Figure 2) was dominated by Cladotanytarsus iucundus and that obtained by larvae rearing (Figure 2) showed two other (genera and species) dominating species (Psilotanypus rufovittatus and Einfeldia dissidens).The study of the chironomid community by catching adults presented two major difficulties. The first resulted from the sampling of adults that did not emerge from the lake itself. The second problem involved a better sampling of the bigger and/or the more accessible swarms. This method led to an overestimate of the species richness of the lake and modified the species proportions in the community. For example, the great proportion of two species, Ablabesmyia monilis and A. longistyla, in the adult community was observed in none of the other communities (Figure 2).In both larval populations (Figure 3), the genera Chironomus, Tanytarsus, Cladotanytarsus and Procladius dominated. The use of artificial substrates induced, however, a lot of modifications in some genera contributions. For example, the genus Einfeldia was collected at higher relative density in artificial substrates than in the sediment samples. Moreover, a lot of taxa (Glyptotendipes, Microtendipes, Paratendipes, Polypedilum, Cricotopus, Parakiefferiella) were exclusively collected, in larval communities, with the artificial substrates. Despite the well-known differences between the benthic communities collected in-situ and those sampled by artificial substrates (ROSENBERG et RESH, 1982), we think such a technique allows a correct study of the taxonomic richness. The use of identical substrates in different lakes should allow one to define a potential community also related solely to the water quality.3. Characterization of the Lake AbbayeThe study of the taxonomic composition of five different chironomid communities stresses the difficulty in characterizing the lake according to the dominating species. However, comparison between larval community (Figure 3) and imagos or exuviae populations (Figure 2) led to the conclusion that Lake Abbaye could be classified in the category of lakes with Tanytarsus (specially T. niger) and Cladotanytarsus (C. iucundus and C. atridorsum). The particularity of Lake Abbaye is that two groups of species dominated the community. The first, constituted by the aforementioned three species, is dominating in oligotrophic lakes (BRUNDIN, 1949). The second group, represented by Chironomus anthracinus and Psilotanypus rufovittatus, reflected the polyhumic and hypoxic characteristics of the lake. These results indicate that Lake Abbaye has low phytoplanktonic biomass but high organic matter content in its sediment, which originates from terrestrial or littoral inputs (VERNEAUX et al., 1987). The quite low temperature of the water probably minimizes both the degradation of the organic matter and the impact of hypoxic conditions on the chironomid community.4. ConclusionThe present paper clearly demonstrates the importance of the sampling method used to study chironomid communities. Sampling the pupal exuviae in the accumulation zones is the most appropriate method to study chironomids. In order to contribute to a better understanding of the relations between the chironomid species and the environmental conditions, our further research will concentrate on a study of the bathymetric distribution of these species. For this purpose, pupal exuviae will be sampled at different isobaths simultaneously with chemical and physical analyses of the water and sediments. The drift phenomenon of exuviae that could affect the bathymetric pattern of species seemed to be avoided when a criterion of minimum occurrence was taken into account (VERNEAUX, 1996)

Production primaire et activité bactérienne hétérotrophe potentielle au sein d'un lac eutrophe (lac d'Aydat, Puy-de-Dôme)

La production primaire phytoplanctenique et l'activité hétérotrophe bactérienne ont été étudiées parallèlement sur le lac d'AYDAT en 1985. L'activité photosynthétique, mesurée au alentours du midi solaire évolue entre 10 et 141 mg C m-2h-1, le maximum étant atteint en juillet. La vitesse maximale, V max, d'assimilation de glucose par les bactéries, (en présence de concentrations de traceur non limitantes) se situe entre 0,06 - 1,26 mg C m-2h-1. Le compartiment phytoplanctonique, de par sa production, semble être l'un des éléments régulateurs de l'activité hétérotrophe bactérienne en zone épilimnique.The seasonal distributions of phytoptanktonic primary production and bacterial heterotrophicpotentials (using respectivey 14C and 14Glucose incorporations) were studied in a eutrophic lake (Lake Aydat, Massif Central, France).Primary production and bacterial heterotrophic potentials vary respectively from 10 to 141 mg.C.m-2h-1 and from 0,06 to 1,26 mg.C.m-2h-1.The comparative evolution of these two activities in relation to the temperature shows that the general idea about "the temperature - bacterial development" model seems to be insufficient when the investigation takes place in a complex ecosystem such as Lake Aydat. Indeed, the phytoplanktonic compartment, apart from its production, seems to be one of the regulating elements of the heterotrophic bacterial activity whose variations cannot be explained by changes in temperature alone.In spite of the significant correlation obtained between bacterial activity and temperature, we should consider that the influence of this abiotic parameter on the bacterial development is an indirect one

Lagunage naturel de lixiviat de décharge

Dans le cadre d'un traitement par lagunage naturel des lixiviats d'une décharge d'ordures ménagères broyées, nous avons procédé au cours d'un cycle annuel (mai 1998 à mai 1999) à des analyses biologiques et physicochimiques des eaux à l'entrée (lixiviat brut), dans les quatre bassins successifs et à la sortie du dispositif (lixiviat traité) avant son rejet dans le milieu récepteur (ruisseau Mont Bonnet). L'évolution spatiotemporelle de la qualité des lixiviats a été approchée par le suivi des fluctuations saisonnières de divers paramètres (température, conductivité électrique, pH, oxygène dissous, potentiel redox, chlorures, fer, manganèse, nickel, zinc, azote total, phosphore total, ammonium, DBO, DCO et chlorophylle a). Les résultats montrent deux périodes de dysfonctionnement de la station durant l'année. Un dysfonctionnement estival marqué par une chute du rendement épuratoire du fer, du manganèse et de la DBO, sous l'effet d'une diminution du potentiel redox et du surplus de matières organiques autochtones. Le deuxième dysfonctionnement, observé en hiver et au début du printemps, est caractérisé par une chute des rendements épuratoires pour l'ensemble des éléments chimiques suivis. Cette chute des rendements épuratoires est vraisemblablement liée à la diminution importante des valeurs de pH durant cette période.The Etueffont municipal landfill waste (Northeast of Belfort, France) possesses a mode of exploitation by grinding wastes without compaction, to facilitate the aerobic degradation. This technique leads to a leachate production. The leachate was treated by natural lagoons consisting of 4 decantation basins then released in the brook (of Mont Bonnet). Efficiency of the epuration was estimated by calculation the net budget of elements (=Input-Output). The results showed that lagoons eliminated the quasi-totality of organic matters (about 80% of BOD) and dissolved substances (about 50 to 90%). Nevertheless, a decrease of epuration efficiency that has been observed in winter of all elements (temperature, electric conductivity, pH, dissolved oxygen, redox potential, chloride, iron, manganese, nickel, zink, total nitrogen, total phosphorus, ammonia, BOD, COD), was due to the decrease of pH (pH=4,5). However, in the begining of summer only Cu2+ and Fe2+ decreased. The collapse of BOD removel (- 8% observed in September 1998) was linked to the excedentary stock of organic matter products in the basins during the summer. The analysis of the monthly evolution of the efficiency epuration of NH4+, total nitrogen (TN) and total phosphorus (TP) indicate similary features. The net budget fluctuates between 50% in winter and 70% in summer. The weak values are noted in January 1999 (19% for NH4+ , 13% for TN and 14% for TP). This work showed that the natural lagooning is weakly efficient for this kind of landfill leachates

Étude préliminaire sur les échanges de phosphore à l'interface eau- sédiment au sein de la retenue d'Al Massira (Maroc)

Les échanges de phosphore à l'interface eau-sédiment ont été étudiés dans la retenue Al Massira. La campagne de prélèvements a été menée pendant la faible oxygénation des eaux profondes au mois d'octobre 1991. Les mesures des échanges de phosphore ont été réalisées in situ en chambre benthique.Les valeurs de pH sont élevées et reflètent clairement l'influence de la nature géologique du bassin versant sur la composition chimique des eaux. Ce bassin versant, formé essentiellement de roches sédimentaires calcaires, est vraisemblablement à l'origine des concentrations élevées en calcium mesurées dans les chambres benthiques.En période de faible oxygénation, on note une augmentation des teneurs en phosphore particulaire dans les eaux surnageantes en raison de la présence de complexes calcium-phosphore, fer-phosphore et manganèse-phosphore. En période d'anoxie, la réduction de ces complexes est accompagnée d'une aug- mentation des teneurs en phosphore.La densité bactérienne et la concentration en phosphore total et notamment en orthophosphates suivent une évolution temporelle comparable. Une fraction non négligeable du phosphore particulaire serait liée aux bactéries.Des mesures drastiques de déphosphatation du tributaire Oum Errbia doivent être prises pour éviter la dissociation des complexes Ca, Fe, Mn-Phosphore et le relargage de phosphore biodisponible.Phosphorus exchange at the sediment-water interface was studied in the Al Massira reservoir. This reservoir, located on the Oum Errbia river, is the most important freshwater resource in Morocco. It provides drinking water to the whole population of Casablanca and contributes to farming and to the functioning of several industrial plants. Our investigations were made in October 1991 and coincided with low oxygen concentrations in the deep layers. The measurements of phosphorus exchange have been made in sitn with a benthic chamber device.The results showed that these exchanges were regulated by a combination ofthe physical chemical variability of the environment and the geological composition of the catchment basin.The pH, which permanently exceeded 7 in Massira, suggests that calcium-bound phosphorus was primarily CaHFO4. Moreover, given the high phosphonrs inputs into the reservoir (570 tonnes. year-1), and despite the fact that, as soon as it reached the reservoir, a large fraction of this element was associated with to calcium, it's likely that the Massira reservoir is subject to eutrophication.In low oxygenated deep layers, we observed an increase in particulate phosphorus concentrations of the overlying water, due to the simultaneous presence of calcium-phosphorus, iron-phosphorus and manganese-phosphorus forms. Under anoxic conditions, the reduction ofthese complexes resulted in an increase of phosphorus concentrations.Bacterial cell numbers and total phosphorus concentratioru showed a comparable temporal behaviour. This would suggest that attached bacteria contributed at least partially to the total particulate phosphoms concentrations.We suggest that a drastic control of phosphorus inputs into the waters must be done through a program of dephosphorylation of tributaries to avoid the dissocation of calcium-, iron-, manganese-bound phosphorus with release upwards of bioavailable phosphorus

Time to establish an international vaccine candidate pool for potential highly infectious respiratory disease: a community's view.

In counteracting highly infectious and disruptive respiratory diseases such as COVID-19, vaccination remains the primary and safest way to prevent disease, reduce the severity of illness, and save lives. Unfortunately, vaccination is often not the first intervention deployed for a new pandemic, as it takes time to develop and test vaccines, and confirmation of safety requires a period of observation after vaccination to detect potential late-onset vaccine-associated adverse events. In the meantime, nonpharmacologic public health interventions such as mask-wearing and social distancing can provide some degree of protection. As climate change, with its environmental impacts on pathogen evolution and international mobility continue to rise, highly infectious respiratory diseases will likely emerge more frequently and their impact is expected to be substantial. How quickly a safe and efficacious vaccine can be deployed against rising infectious respiratory diseases may be the most important challenge that humanity will face in the near future. While some organizations are engaged in addressing the World Health Organization's "blueprint for priority diseases", the lack of worldwide preparedness, and the uncertainty around universal vaccine availability, remain major concerns. We therefore propose the establishment of an international candidate vaccine pool repository for potential respiratory diseases, supported by multiple stakeholders and countries that contribute facilities, technologies, and other medical and financial resources. The types and categories of candidate vaccines can be determined based on information from previous pandemics and epidemics. Each participant country or region can focus on developing one or a few vaccine types or categories, together covering most if not all possible potential infectious diseases. The safety of these vaccines can be tested using animal models. Information for effective candidates that can be potentially applied to humans will then be shared across all participants. When a new pandemic arises, these pre-selected and tested vaccines can be quickly tested in RCTs for human populations

Harnessing the NEON data revolution to advance open environmental science with a diverse and data-capable community

It is a critical time to reflect on the National Ecological Observatory Network (NEON) science to date as well as envision what research can be done right now with NEON (and other) data and what training is needed to enable a diverse user community. NEON became fully operational in May 2019 and has pivoted from planning and construction to operation and maintenance. In this overview, the history of and foundational thinking around NEON are discussed. A framework of open science is described with a discussion of how NEON can be situated as part of a larger data constellation—across existing networks and different suites of ecological measurements and sensors. Next, a synthesis of early NEON science, based on >100 existing publications, funded proposal efforts, and emergent science at the very first NEON Science Summit (hosted by Earth Lab at the University of Colorado Boulder in October 2019) is provided. Key questions that the ecology community will address with NEON data in the next 10 yr are outlined, from understanding drivers of biodiversity across spatial and temporal scales to defining complex feedback mechanisms in human–environmental systems. Last, the essential elements needed to engage and support a diverse and inclusive NEON user community are highlighted: training resources and tools that are openly available, funding for broad community engagement initiatives, and a mechanism to share and advertise those opportunities. NEON users require both the skills to work with NEON data and the ecological or environmental science domain knowledge to understand and interpret them. This paper synthesizes early directions in the community’s use of NEON data, and opportunities for the next 10 yr of NEON operations in emergent science themes, open science best practices, education and training, and community building

Variations spatiale et temporelle des abondances bactériennes dans quatre bassins de traitement du lixiviat de la décharge d'Étueffont (Belfort, France).

Le compartiment bactérien ainsi que différents paramètres physicochimiques ont été suivis mensuellement, de mai 1998 à mai 1999, dans le lixiviat brut et les quatre bassins de la station de traitement des ordures ménagères d'Étueffont (Territoire de Belfort, France). Les densités bactériennes varient de 0,04 x 106 à 0,35 x 106 bactéries ml-1 (m±sd=0,13x x 106± 0,12 106 bactéries ml-1) et diminuent du premier au dernier bassin. Ces abondances semblent très aléatoires et inférieures à celles rapportées dans la littérature pour des milieux de richesse comparable en matière organique. Ces faibles abondances sont vraisemblablement liées aux effets toxiques des lixiviats.info:eu-repo/semantics/publishe

Endogenous regulation of the growth-rate responses of a spring-dwelling strain of the freshwater alga, Chlorella minutissima, to light and temperature

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