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

A Conceptual Framework for Understanding the Biogeochemistry of Dry Riverbeds Through the Lens of Soil Science

Intermittent rivers and ephemeral streams (IRES) encompass fluvial ecosystems that eventually stop flowing and run dry at some point in space and time. During the dry phase, channels of IRES consist mainly of dry riverbeds (DRBs), prevalent yet widely unexplored ecotones between dry and wet phases that can strongly influence the biogeochemistry of fluvial networks. DRBs are often overlooked because they do not strictly belong to either domain of soil or freshwater science. Due to this dual character of DRBs, we suggest that concepts and knowledge from soil science can be used to expand the understanding of IRES biogeochemistry. Based on this idea, we propose that DRBs can be conceptually understood as early stage soils exhibiting many similarities with soils through two main forces: i) time since last sediment transport event, and ii) the development status of stabilizing structures (e.g. soil crusts and/or vascular plants). Our analysis suggests that while DRBs and soils may differ in master physical attributes (e.g. soil horizons vs fluvial sedimentary facies), they become rapidly comparable in terms of microbial communities and biogeochemical processes. We further propose that drivers of DRBs biogeochemistry are similar to those of soils and, hence, concepts and methods used in soil science are transferable to DRBs research. Finally, our paper presents future research directions to advance the knowledge of DRBs and to understand their role in the biogeochemistry of intermittent fluvial networks

Simulating rewetting events in intermittent rivers and ephemeral streams: a global analysis of leached nutrients and organic matter

Climate change and human pressures are changing the global distribution and extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico‐chemical changes (preconditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale. We experimentally simulated, under standard laboratory conditions, rewetting of leaves, riverbed sediments, and epilithic biofilms collected during the dry phase across 205 IRES from five major climate zones. We determined the amounts and qualitative characteristics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds. In addition, we evaluated the variance in leachate characteristics in relation to selected environmental variables and substrate characteristics. We found that sediments, due to their large quantities within riverbeds, contribute most to the overall flux of dissolved substances during rewetting events (56‐98%), and that flux rates distinctly differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contributed most to the areal fluxes. The largest amounts of leached substances were found in the continental climate zone, coinciding with the lowest potential bioavailability of the leached organic matter. The opposite pattern was found in the arid zone. Environmental variables expected to be modified under climate change (i.e. potential evapotranspiration, aridity, dry period duration, land use) were correlated with the amount of leached substances, with the strongest relationship found for sediments. These results show that the role of IRES should be accounted for in global biogeochemical cycles, especially because prevalence of IRES will increase due to increasing severity of drying events

Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter

Climate change and human pressures are changing the global distribution and the ex‐ tent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico‐chemical changes (precon‐ ditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale. We experi‐ mentally simulated, under standard laboratory conditions, rewetting of leaves, river‐ bed sediments, and epilithic biofilms collected during the dry phase across 205 IRES from five major climate zones. We determined the amounts and qualitative character‐ istics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds. In addition, we evaluated the variance in leachate characteristics in relation to selected environmental variables and substrate characteristics. We found that sediments, due to their large quantities within riverbeds, contribute most to the overall flux of dis‐ solved substances during rewetting events (56%–98%), and that flux rates distinctly differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contrib‐ uted most to the areal fluxes. The largest amounts of leached substances were found in the continental climate zone, coinciding with the lowest potential bioavailability of the leached OM. The opposite pattern was found in the arid zone. Environmental vari‐ ables expected to be modified under climate change (i.e. potential evapotranspiration, aridity, dry period duration, land use) were correlated with the amount of leached sub‐ stances, with the strongest relationship found for sediments. These results show that the role of IRES should be accounted for in global biogeochemical cycles, especially because prevalence of IRES will increase due to increasing severity of drying event

Functional ecology in groundwater : linking organic matter flux and biological activity and diversity

Les réseaux trophiques jouent un rôle primordial dans la régulation des flux de matière et d’énergie au sein des écosystèmes. Dans le cadre des pratiques de recharge artificielle des aquifères, les biocénoses souterraines sont pleinement sollicitées et leur capacité à dégrader les flux de matière organique de surface conditionne le maintien de la qualité des eaux souterraines. L’objectif de ce travail est de déterminer l’influence d’une augmentation des flux de carbone organique dissous sur l’intensité des interactions trophiques entre les communautés microbiennes et les assemblages d’invertébrés au toit des nappes phréatiques rechargées artificiellement avec des eaux de ruissellement pluvial. A travers une approche expérimentale de terrain et de laboratoire, ce travail permet d’évaluer l’intensité des relations existant entre les flux de carbone organique dissous, les conditions environnementales, l’activité et la diversité de communautés microbiennes et l’abondance des communautés d’invertébrés.Food webs play a crucial role in regulating the fluxes of matter and energy within ecosystems. Artificial recharge of aquifers relies heavily on the ability of groundwater biocenoses to degrade organic matter fluxes that is a condition to maintain the quality of groundwater. The objective of this work is to determine the impact of increased dissolved organic carbon supply on the trophic interactions between the microbial communities and invertebrate assemblages at the upper layers of groundwater artificially recharged with stormwater. Through a combined field and laboratory experimental approach, this work allows ranking the strength of relationship between dissolved organic carbon fluxes, environmental conditions, activity and diversity of microbial communities and abundance of invertebrate assemblage

Écologie fonctionnelle dans les nappes phréatiques : liens entre flux de matière organique, activité et diversité biologiques

Food webs play a crucial role in regulating the fluxes of matter and energy within ecosystems. Artificial recharge of aquifers relies heavily on the ability of groundwater biocenoses to degrade organic matter fluxes that is a condition to maintain the quality of groundwater. The objective of this work is to determine the impact of increased dissolved organic carbon supply on the trophic interactions between the microbial communities and invertebrate assemblages at the upper layers of groundwater artificially recharged with stormwater. Through a combined field and laboratory experimental approach, this work allows ranking the strength of relationship between dissolved organic carbon fluxes, environmental conditions, activity and diversity of microbial communities and abundance of invertebrate assemblagesLes réseaux trophiques jouent un rôle primordial dans la régulation des flux de matière et d’énergie au sein des écosystèmes. Dans le cadre des pratiques de recharge artificielle des aquifères, les biocénoses souterraines sont pleinement sollicitées et leur capacité à dégrader les flux de matière organique de surface conditionne le maintien de la qualité des eaux souterraines. L’objectif de ce travail est de déterminer l’influence d’une augmentation des flux de carbone organique dissous sur l’intensité des interactions trophiques entre les communautés microbiennes et les assemblages d’invertébrés au toit des nappes phréatiques rechargées artificiellement avec des eaux de ruissellement pluvial. A travers une approche expérimentale de terrain et de laboratoire, ce travail permet d’évaluer l’intensité des relations existant entre les flux de carbone organique dissous, les conditions environnementales, l’activité et la diversité de communautés microbiennes et l’abondance des communautés d’invertébrés

La maternité en milieu carcéral (évolution historique au Centre Pénitentiaire de Rennes)

RENNES1-BU Santé (352382103) / SudocSudocFranceF

MODÉLISATION DES TRANSPORTS D'EAU, DE CHALEUR ET DE SOLUTÉ SOUS UN BASSIN DE D'INFILTRATION

International audienceL'urbanisation amène à imperméabiliser de façon massive la surface du sol, et donc à créer des bassins d'infiltration pour les eaux de pluie. Ces bassins provoquent des transports importants (hydriques, soluté, chaleur) qui peuvent perturber et polluer la nappe sous-jacente. Le milieu étant généralement très hétérogène, le calage entre expérimentation et modélisation est rarement satisfaisant à cause de la difficulté pour faire des mesures (accès au sous sol, faible densité et bruit). Nous proposons ici une étude numérique de l'influence de l'hétérogénéité du sol sur la répartition des champs de concentration en soluté et de température engendrés par un bassin d'infiltration. La modélisation confirme que l'évolution des concentrations en soluté est très bruitée par les hétérogénéités de perméabilité du sol. Le champ de température est beaucoup moins perturbé par les hétérogénéités, et donc plus facilement interprétable

Thermal influence of urban groundwater recharge from stormwater infiltration basins

International audienc

Plant Litter Decomposition in Intermittent Rivers and Ephemeral Streams

International audienceIntermittent rivers and ephemeral streams (hereafter IRES) are waterways that temporarily cease to flow and/or dry up. They represent half the length of the global river network and are expanding in time and space in response to global change. The hydrological regimes of IRES are characterized by alternating flowing, non-flowing and dry phases, which translate to varying importance of in-stream litter accumulation, processing and downstream transport. Decomposition agents, processes and rates dramatically change among these hydrological phases, leading to decomposition dynamics that differ markedly from perennial rivers and streams. As a result, IRES have a specific “biogeochemical heartbeat” characterized by high temporal and spatial variability of leaf decomposition, and so they can be idealized as pulsed bioreactors. The ecological effects of flow cessation and drying are sometimes visible far beyond rewetting, generating “legacy effects” that become apparent even during later flowing phases. Rewetting events can represent “hot moments” of litter decomposition due to the intense biological and physical activities, generating pulses of transport and decomposition. Upscaling the abundant reach-scale knowledge to larger river-network scales is probably one of the most challenging but timely paths for future research