Influence of hydraulic conductivity on communities of microorganisms and invertebrates in porous media: a case study in drinking water slow sand filters

Abstract.: The impact of reduced hydraulic conductivity on the abundance and diversity of microorganisms and invertebrates was examined in an artificial ecosystem consisting of a slow sand-filter. Sand-filters processed pre-treated lake water under high flow rates and acted as small ecosystems inhabited by a complex community. The first trophic level consisting of microorganisms serves as a food source for a dense community of protists, micro- and macro-invertebrates. The reduction of hydraulic conductivity due to the development of larger bacterial and fungal biomass induced a shift of the microbial community towards anaerobiosis that may increase clogging by carbonate precipitation. The presence of more bacterial prey seems to favour the development of higher trophic levels. Predation and bioturbation by eukaryotes were not able to counteract the reduction of hydraulic conductivity due to prokaryotic cloggin

Influence of nontrophic interactions between benthic invertebrates on river sediment processes: a microcosm study

The main objective of this study was to measure the impact of benthic invertebrate diversity on river sediment processes. We quantified the effects of interactions between three taxa (asellids, chironomid larvae, and tubificid worms). The impacts of different taxa richness treatments were measured on sediment reworking, O2 concentrations, bacterial abundances, and numbers of active bacteria in slow filtration sand–gravel columns. The coefficients of sediment reworking measured in multitaxa treatments were lower than those predicted from one-taxon treatments. The interactions among invertebrates also significantly reduced O2 concentrations in sediments. These results were probably due to interactions between the different sediment structures produced by each taxon (tubes, macropores, and fecal pellets) that modified water flow and associated microbial activities in the interstitial habitat. The stimulation of aerobic microbial processes with two- and three-taxa treatments, whereas one-taxon treatments could increase or decrease O2 consumption in columns, indicates that interactions among invertebrates limited the variability of the system functioning. We suggest that, beyond a small number of detritivorous taxa, a threshold effect on bioturbation process and microbial activities was produced by animals in the experimental system. Finally, the interactions between taxa played a significant role in microbial processes in the system studied

Water-sediment exchanges control microbial processes associated with leaf litter degradation in the hyporheic zone: a microcosm study

The present study aimed to experimentally quantify the influence of a reduction of surface sediment permeability on microbial characteristics and ecological processes (respiration and leaf litter decomposition) occurring in the hyporheic zone (i.e. the sedimentary interface between surface water and groundwater). The physical structure of the water-sediment interface was manipulated by adding a 2-cm layer of coarse sand (unclogged systems) or fine sand (clogged systems) at the sediment surface of slow filtration columns filled with a heterogeneous gravel/sand sedimentary matrix. The influence of clogging was quantified through measurements of hydraulic conductivity, water chemistry, microbial abundances and activities and associated processes (decomposition of alder leaf litter inserted at a depth of 9 cm in sediments, oxygen and nitrate consumption by microorganisms). Fine sand deposits drastically reduced hydraulic conductivity (by around 8-fold in comparison with unclogged systems topped by coarse sand) and associated water flow, leading to a sharp decrease in oxygen (reaching less than 1 mg L(-1) at 3 cm depth) and nitrate concentrations with depth in sediments. The shift from aerobic to anaerobic conditions in clogged systems favoured the establishment of denitrifying bacteria living on sediments. Analyses performed on buried leaf litter showed a reduction by 30% of organic matter decomposition in clogged systems in comparison with unclogged systems. This reduction was linked to a negative influence of clogging on the activities and abundances of leaf-associated microorganisms. Finally, our study clearly demonstrated that microbial processes involved in organic matter decomposition were dependent on hydraulic conductivity and oxygen availability in the hyporheic zone

Calibration and field application of an innovative passive sampler for monitoring groundwater quality

International audienc

L'infiltration des eaux pluviales en milieu urbain : conséquences sur l'écosystème aquatique souterrain

International audienceL'urbanisation induit une imperméabilisation des sols et une augmentation du ruissellement, réduisant ainsi la recharge de la nappe souterraine. La gestion des eaux de pluie consiste à les collecter et les infiltrer vers la nappe qui est protégée de la pollution par des processus auto-épurateurs localisés dans le sol et la zone insaturée. Les dynamiques de la matière organique et des micro-organismes ont été suivies dans les eaux de surface et les eaux souterraines en amont et en aval des trois systèmes d'infiltration (SI). Les teneurs en Carbone Organique dissous (COD) biodégradable et réfractaire ont été mesurées sur l'eau et la croissance des biofilms a été suivie à l'aide des substrats artificiels incubés dans le milieu. Le COD diminue fortement au cours de l'infiltration, mais sa fraction biodégradable demeure plus forte en aval de SI, tout comme les biofilms qui sont stimulés par les infiltrations en biomasse et en diversité. ABSTRACT Urbanization increases impervious surfaces and stormwater runoff reducing groundwater recharge. Stormwater management mainly consists in the collection of rain water and its infiltration to the aquifer, which is protected by the self-purification capacity of the soil and the unsaturated zone. The dynamics of organic matter and microorganisms were studied in surface water and in groundwater upstream and downstream of three stormwater infiltration systems (SIS). Dissolved Organic Carbon (DOC) concentrations were measured in surface and in ground waters, while biofilm dynamics were studied using artificial substrates incubated in the waters. DOC sharply decrease from surface water to the groundwater, but the biodegradable fraction of DOC was higher downstream than upstream of the SIS and the biofilms were stimulated by the infiltration for both biomass and bacterial diversity

Benzo(a)pyrene inhibits the role of the bioturbator Tubifex tubifex in river sediment biogeochemistry

International audienceThe interactions between invertebrates and micro-organisms living in streambed sediments often play key roles in the regulation of nutrient and organic matter fluxes in aquatic ecosystems. However, benthic sedi- ments also constitute a privileged compartment for the accumulation of persistent organic pollutants such as PAHs or PCBs that may affect the diversity, abundance and activity of benthic organisms. The objective of this study was to quantify the impact of sediment contamination with the PAH benzo(a)pyrene on the in- teraction between micro-organisms and the tubificid worm, Tubifex tubifex, which has been recognized as a major bioturbator in freshwater sediments. Sedimentary microcosms (slow filtration columns) contaminated or not with benzo(a)pyrene (3 tested concentrations: 0, 1 and 5 mg kg−1) at the sediment surface were in- cubated under laboratory conditions in the presence (100 individuals) or absence of T. tubifex. Although the surface sediment contaminations with 1 mg kg−1 and 5 mg kg−1 of benzo(a)pyrene did not affect tubificid worm survival, these contaminations significantly influenced the role played by T. tubifex in biogeochemical processes. Indeed, tubificid worms stimulated aerobic respiration, denitrification, dehydrogenase and hydrolytic activities of micro-organisms in uncontaminated sediments whereas such effects were inhibited in sediments polluted with benzo(a)pyrene. This inhibition was due to contaminant-induced changes in bioturbation (and especially bio-irrigation) activities of worms and their resulting effects on microbial processes. This study reveals the importance of sublethal concentrations of a contaminant on ecological processes in river sediments through affecting bioturbator-microbe interactions. Since they affect microbial processes involved in water purification processes, such impacts of sublethal concentrations of pollutants should be more often considered in ecosystem health assessment

Less effective selection leads to larger genomes

International audienceThe evolutionary origin of the striking genome size variations found in eukaryotes remains enigmatic. The effective size of populations, by controlling selection efficacy, is expected to be a key parameter underlying genome size evolution. However, this hypothesis has proved difficult to investigate using empirical datasets. Here, we tested this hypothesis using twenty-two de novo transcriptomes and low-coverage genomes of asellid isopods, which represent eleven independent habitat shifts from surface water to resource-poor groundwater. We show that these habitat shifts are associated with higher transcriptome-wide dN/dS. After ruling out the role of positive selection and pseudogenization, we show that these transcriptome-wide dN/dS increases are the consequence of a reduction in selection efficacy imposed by the smaller effective population size of subterranean species. This reduction is paralleled by an important increase in genome size (25% increase on average), an increase also confirmed in subterranean decapods and mollusks. We also control for an adaptive impact of genome size on life history traits but find no correlation between body size, or growth rate, and genome size. We show instead that the independent increases in genome size measured in subterranean isopods are the direct consequence of increasing invasion rates by repeated elements, which are less efficiently purged out by purifying selection. Contrary to selection efficacy, polymorphism is not correlated to genome size. We propose that recent demographic fluctuations and the difficulty to observe polymorphism variations in polymorphism-poor species can obfuscate the link between effective population size and genome size when polymorphism data is used alone

Gathering at the top? Environmental controls of microplastic uptake and biomagnification in freshwater food webs

Microplastics are ubiquitous in the environment, with high concentrations being detected now also in river corridors and sediments globally. Whilst there has been increasing field evidence of microplastics accumulation in the guts and tissues of freshwater and marine aquatic species, the uptake mechanisms of microplastics into freshwater food webs, and the physical and geological controls on pathway-specific exposures to microplastics, are not well understood. This knowledge gap is hampering the assessment of exposure risks, and potential ecotoxicological and public health impacts from microplastics. This review provides a comprehensive synthesis of key research challenges in analysing the environmental fate and transport of microplastics in freshwater ecosystems, including the identification of hydrological, sedimentological and particle property controls on microplastic accumulation in aquatic ecosystems. This mechanistic analysis outlines the dominant pathways for exposure to microplastics in freshwater ecosystems and identifies potentially critical uptake mechanisms and entry pathways for microplastics and associated contaminants into aquatic food webs as well as their risk to accumulate and biomagnify. We identify seven key research challenges that, if overcome, will permit the advancement beyond current conceptual limitations and provide the mechanistic process understanding required to assess microplastic exposure, uptake, hazard, and overall risk to aquatic systems and humans, and provide key insights into the priority impact pathways in freshwater ecosystems to support environmental management decision making

Rôle de la diversité des invertébrés à l'interface sédimentaire eau libre - eau interstitielle

Le but de cette étude était d'analyser l'action de la diversité des invertébrés sur le fonctionnement de l'interface sédimentaire eau libre - eau interstitielle. Dans une approche expérimentale 4 colonnes de sédiment traversées par un flux d'eau et fonctionnant en parallèle sont utilisées : une colonne témoin sans invertébrés et des triplicats ensemencés en invertébrés. Durant des expérimentations de 20 jours, des paramètres physico-chimiques et microbiens ont été mesurés à plusieurs horizons dans les colonnes. Les effets de trois taxons détritivores présentant des modes de vie distincts (oligochètes tubificidés, crustacés asellidés et diptères chironomidés) ont été étudiés. Les expériences ont abouti aux résultats suivants : L'approche expérimentale développée a permis de reconstituer un système d'interface présentant une forte hétérogénéité spatiale. Les deux genres d'oligochètes tubificidés testés sont fonctionellement redondants pour la majorité des processus étudiés (processus microbiens aérobies et anaérobies). Les trois groupes taxonomiques testés peuvent être classés dans trois groupes fonctionnels distincts car ils produisent des effets différents sur le fonctionnement de l'interface sédimentaire. Les interactions entre les taxons peuvent avoir un impact important sur le fonctionnement du système (transfert et transformation des nutriments). L'augmentation de 2 à 3 taxons détritivores par colonne n'a aucun effet significatif sur les fonctions mesurées (dénitrification, dégradation de la matière organique en anaérobiose, respiration aérobie). Ce résultat semble lié à une intensité de bioturbation "optimale" effectuée sur toute la surface de la colonne sédimentaire par 2 ou 3 taxons. En conclusion, les invertébrés et leur diversité ont un rôle important sur la régulation des flux d'énergie à l'interface eau libre - eau interstitielle. Cette diversité fonctionnelle doit être prise en compte dans l'étude des grands cycles biogéochimiques aux interfaces eau - sédimentLYON1-BU.Sciences (692662101) / SudocSudocFranceF