Optimization of glass separating funnels to facilitate microplastic extraction from sediments.

Recent studies on the distribution of microplastics in aquatic sediments have deployed different methods and devices for density separation of microplastics from sediments. However, instrument specific limitations have been noted, including their high cost, difficulty in handling, or/and the potential for elevated contamination risk due to their plastic composition. This study improves existing sediment microplastic separation techniques by modifying the commonly used conical shape glass separating funnels. The modification consists in connecting a silicone tube at the base of the funnel, whose opening and closure was manually controlled by a Mohr clamp. This adjustment made to the funnels have effectively mitigated critical clogging problems frequently encountered in density separation units. An experiment was conducted using sand-based sediment spiked with polyamide fragments to validate this method modification. Following a complete extraction protocol with the modification of separating funnels, the microplastic extraction efficiency from sediments was high with a 90% recovery rate. Based on these promising results, future studies should consider naturally diverse substrates, as recovery efficiency may be sediment-dependent. Two key adjustments to the glass separation funnels:•Removal of stopcocks•Use of silicone tubes and Mohr clamps to control sediment release.

Warming drives feedback between plant phenotypes and ecosystem functioning in sub-Antarctic ponds.

Ample evidence indicates that warming affects individuals in plant communities, ultimately threatening biodiversity. Individual plants in communities are also exposed to plant-plant interaction that may affect their performance. However, trait responses to these two constraints have usually been studied separately, while they may influence processes at the ecosystem level. In turn, these ecological modifications may impact the phenotypes of plants through nutrient availability and uptake. We developed an experimental approach based on the macrophyte communities in the ponds of the sub-Antarctic Iles Kerguelen. Individuals of the species Limosella australis were grown under different temperature × plant-plant interaction treatments to assess their trait responses and create litters with different characteristics. The litters were then decomposed in the presence of individual plants at different temperatures to examine effects on ecosystem functioning and potential feedback affecting plant trait values. Leaf resource-acquisition- and -conservation-related traits were altered in the context of temperature × plant-plant interaction. At 13 °C, SLA and leaf C:N were higher under interspecific and intraspecific interactions than without interaction, whereas at 23 °C, these traits increased under intraspecific interaction only. These effects only slightly improved the individual performance, suggesting that plant-plant interaction is an additional selective pressure on individuals in the context of climate warming. The decay rate of litter increased with the Leaf Carbon Content at 13 °C and 18 °C, but decreased at 23 °C. The highest decay rate was recorded at 18 °C. Besides, we observed evidence of positive feedback of the decay rate alone, and in interaction with the temperature, respectively on the leaf C:N and Leaf Dry Matter Content, suggesting that variations in ecological processes affect plant phenotypes. Our findings demonstrate that warming can directly and indirectly affect the evolutionary and ecological processes occurring in aquatic ecosystems through plants.

Determination of groundwater origins and vulnerability based on multi-tracer investigations: New contributions from passive sampling and suspect screening approach.

Knowledge about groundwater origins and their interactions with surface water is fundamental to assess their vulnerability. In this context, hydrochemical and isotopic tracers are useful tools to investigate water origins and mixing. More recent studies examined the relevance of contaminants of emerging concern (CECs) as co-tracers to distinguish sources contributing to groundwater bodies. However, these studies focused on known and targeted CECs a priori selected regarding their origin and/or concentrations. This study aimed to improve these multi-tracer approaches using passive sampling and qualitative suspect screening by exploring a larger variety of historical and emerging concern contaminants in combination with hydrochemistry and water molecule isotopes. With this objective, an in-situ study was conducted in a drinking water catchment area located in an alluvial aquifer recharged by several water sources (both surface and groundwater sources). CECs determined by passive sampling and suspect screening allowed to provide in-depth chemical fingerprints of groundwater bodies by enabling the investigation of >2500 compounds with an increased analytical sensitivity. Obtained cocktails of CECs were discriminating enough to be used as chemical tracer in combination with hydrochemical and isotopic tracers. In addition, the occurrence and type of CECs contributed to a better understanding of groundwater-surface water interactions and highlighted short-time hydrological processes. Furthermore, the use of passive sampling with suspect screening analysis of CECs lead to a more realistic assessment and mapping of groundwater vulnerability.

Sediment reworking of intertidal sediments by the benthic foraminifera Haynesina germanica: the importance of motion behaviour and densities.

This study aimed to describe for the first time the vertical motion behaviour of the intertidal foraminifera Haynesina germanica and its contribution to bioturbation. Its infaunal behaviour leads to the creation of a one-end tube within the first centimetre of sediment. In addition, a vertical trail following behaviour was described for the first time in foraminifera, which may be linked to the sustainability of the biogenic sedimentary structures. As a consequence, H. germanica produces a vertical transport of both mud and fine sediment fractions similarly to the sediment reworking mode reported for gallery-diffusor benthic species. This finding allows us to refine the bioturbating mode of H. germanica, previously classified as surficial biodiffusor. Furthermore, sediment reworking intensity appeared to be dependent on the foraminiferal density. H. germanica would adapt its motion behaviour to deal with the intra-specific competition for food and space that may occur when density increases. Consequently, this behavioural modification would affect both the species and the individual contribution to sediment reworking processes. In fine, sediment reworking in H. germanica may further contribute to the bioirrigation of intertidal sediments, which has implications for oxygen availability in sediments and on aerobic microbial processes involved in carbon and nutrient cycling at the sediment-water interface.

Microplastics in Freshwater Sediments Impact the Role of a Main Bioturbator in Ecosystem Functioning.

While microplastic transport, fate, and effects have been a focus of studies globally, the consequences of their presence on ecosystem functioning have not received the same attention. With increasing evidence of the accumulation of microplastics at sediment-water interfaces there is a need to assess their impacts on ecosystem engineers, also known as bioturbators, which have direct and indirect effects on ecosystem health. This study investigated the impact of microplastics on the bioturbator Tubifex tubifex alongside any effects on the biogeochemical processes at the sediment-water interface. Bioturbators were exposed to four sediment microplastic concentrations: 0, 700, 7000, and 70000 particles kg-1 sediment dry weight. Though no mortality was present, a significant response to oxidative stress was detected in tubificid worms after exposure to medium microplastic concentration (7000 particles kg-1 sediment dry weight). This was accompanied by a reduction in worm bioturbation activities assessed by their ability to rework sediment and to stimulate exchange water fluxes at the sediment-water interface. Consequently, the contributions of tubificid worms on organic matter mineralization and nutrient fluxes were significantly reduced in the presence of microplastics. This study demonstrated that environmentally realistic microplastic concentrations had an impact on biogeochemical processes at the sediment-water interface by reducing the bioturbation activities of tubificid worms.

Aquifer recharge by stormwater infiltration basins: Hydrological and vadose zone characteristics control the impacts of basins on groundwater chemistry and microbiology.

Stormwater infiltration systems (SIS) are designed to collect and infiltrate urban stormwater runoff into the ground for flood risk mitigation and artificial aquifer recharge. Many studies have demonstrated that infiltration practices can impact groundwater chemistry and microbiology. However, quantitative assessments of the hydrogeological factors responsible of these changes remain scarce. Thus, the present study aimed to quantitatively test whether changes of groundwater chemistry and microbiology induced by SIS were linked to two factors associated with vadose zone properties (vadose zone thickness, water transit time from surface to groundwater) and one factor associated with groundwater recharge rate (assessed by groundwater table elevation during rain events). To evaluate changes in chemistry (NO3-, PO43- and dissolved organic carbon concentrations), groundwater samples were collected in wells located in SIS-impacted and non-SIS-impacted zones during experimental periods of 10 days. During the same periods, clay beads were incubated in the same wells to measure changes of groundwater microbial biofilms (microbial biomass, dehydrogenase and hydrolytic activities) induced by SIS. Results showed that changes in PO43- supplied to groundwater during stormwater infiltration was negatively correlated with vadose zone thickness. A short water transit time from surface to groundwater increased dissolved organic carbon concentrations in the aquifer which, in turn, increased biofilm biomasses in groundwater. The groundwater recharge rate during rain events (assessed by groundwater table elevation) diluted NO3- concentrations in the aquifer but also influenced the changes of biofilm activities induced by SIS. Groundwater recharge rate during rain events probably increased the fluxes of water and dissolved organic carbon in groundwater, stimulating the activity of microbial biofilms. Overall, the present study is the first to quantify conjointly several factors and processes (water transfer, dilution, solute fluxes) that could explain the impact of stormwater infiltration on chemistry and/or microbiology in groundwater.

Drivers of functional diversity in the hyporheic zone of a large river.

The effects of regional (hydrogeology and geomorphology) and local (sediment and hydrology) characteristics on hyporheic assemblages were studied along a 40-km reach of a large gravel-bed river. Hyporheic water and fauna were sampled at the upstream and downstream positions of 15 large gravel bars. The resulting 30 stations varied in their sediment grain size, stability and direction of river-aquifer exchanges. The study concludes that at the 40-km (sector) scale, the longitudinal distribution of hyporheic fauna was controlled by 1) the hydrogeology of the valley (i.e. gaining vs loosing sectors) that modifies abundance and taxonomic richness of stygobites 2) current channel morphometry of the river (i.e. shape and location of meanders), and 3) historical changes (i.e. river incision) which modify abundance and richness of assemblages. At the local scale, we found that surface grain size and stability of the sediment evaluated by visual observation were poor predictors of hyporheos composition. In contrast, the local hydrology (i.e. downwellings, upwellings, low vertical exchanges) explained a large part of the abundance, taxonomic richness and composition of the hyporheic assemblages. Stations with low vertical exchanges were found poorly colonized, while the upwelling zones were rich in stygobites and downwelling areas harbor abundant and species-rich temporary hyporheos. It was also observed that functional diversity was controlled by the same parameters, with high relative abundances of stygobites in upwelling zones and POM feeders in downwelling zones. The heterogeneity of hydrological patterns, with alternation of upwellings and downwellings may represent the optimal spatial structure for hyporheic biodiversity conservation and resilience in rivers.

Scale-dependent effects of vegetation on flow velocity and biogeochemical conditions in aquatic systems.

In rivers, scale-dependent feedbacks resulting from physical habitat modifications control the lateral expansion of submerged plant patches, while the mechanisms that limit patch expansion on a longitudinal dimension remain unknown. Our objective was to investigate the effects of patch length on physical habitat modification (i.e., flow velocity, sediment grain size distribution), the consequences for biogeochemical conditions (i.e., accumulation/depletion of nutrients, microbial respiration), and for individual plants (i.e., shoot length). We measured all of these parameters along natural patches of increasing length. These measurements were performed at two sites that differed in mean flow velocity, sediment grain size, and trophic level. The results showed a significant effect of patch length on organic matter content and nutrient concentrations in interstitial water. For the shortest patches sampled, all of these parameters had similar values to those measured at the upstream control position. For longer patches, organic matter content and orthophosphate and ammonium concentrations increased within the patch compared to the upstream bare sediment, whereas nitrate concentrations decreased, suggesting changes in vertical water exchanges and an increase in anaerobic microbial activities. Furthermore, plant height was related to patch length by a quadratic pattern, probably due reduced hydrodynamic stress occurring for increasing patch length, combined with conditions that are less favourable for plants over a threshold length, possibly due to the light limitation or to the high concentration of ammonium that in the concentration range we measured may be toxic for plants. The threshold lengths over which patches influence the nutrient concentrations were reduced for the site with higher nutrient levels. We demonstrated that the plant-induced modifications of the physical habitat exert important effects on biogeochemical conditions, with possible consequences for patch dynamics and ecosystem functioning.

Effects of bioturbation by tubificid worms on biogeochemical processes, bacterial community structure and diversity in heterotrophic wetland sediments.

Bioturbation activity of tubificid worms has been recognized as a key process influencing organic matter processing and nutrient cycling in benthic aquatic ecosystems. This activity is expected to modify benthic microbial communities by affecting the physical and chemical environment in sediments. Nevertheless, quantifications of bacterial community changes associated with bioturbation in freshwater ecosystems are still lacking. The present study aimed at evaluating the impact of tubificid worms on bacterial community structure using NGS approach (16S metabarcoding) and long (6 months) laboratory experiments on four heterotrophic wetland sediments. Worm bioturbation activity significantly stimulated biogeochemical processes at the water-sediment interface but only had a marginally significant effect on bacterial community structures. Yet, bacterial diversity was consistently reduced in presence of worms. Such decrease could be associated with the stimulation of organic matter mineralization by worms, leading to a reduction of the diversity of trophic niches available for bacterial species. The slight changes in bacterial community structures induced by bioturbation did not appear to control biogeochemical processes. Thus, the stimulation of biogeochemical processes by worm bioturbation was more associated with a stimulation of the initial bacterial community than with a drastic change in bacterial communities induced by worms.

Multiple stressors shape invertebrate assemblages and reduce their trophic niche: A case study in a regulated stream.

Few studies have addressed how the diversity of basal resources change with stream regulation and the potential consequences on river biota. We sampled invertebrates above and below a series of dams, over two years, at both downwelling and upwelling zones. In each zone, we recorded the daily temperature and flow variations, estimated the algal development, measured the available resources, and analysed carbon and nitrogen stable isotope compositions of the invertebrate community. The number of hydrological pulses were typically higher below the dams than above the dams especially during high-flow periods whereas the groundwater outlets had minor effects on invertebrate assemblages. Invertebrate abundance, richness and diversity tended to decrease below the dams. Co-inertia analysis showed that flow and temperature variations, and eutrophication explained most of the variance in the invertebrate assemblages, which comprised a higher number of resilient taxa below than above the dams. The proportions of pesticide-sensitive invertebrates were lower below the dams and ovoviviparous and more generalist taxa were prominent. We did not observe the expected CPOM decrease and FPOM increase downstream. Accordingly, the proportions of each functional feeding group were remarkably similar above and below the dams despite the long distance between the sectors (>100 kms). The diversity of basal resources used within assemblages progressively increased downstream above dams. In contrast, the diversity of resources used by organisms below the dams decreased from upstream to downstream suggesting a significant influence of flow regulation on aquatic food webs. Finally, the shorter trophic chains for the invertebrate assemblages below the dams suggests that the effects of stream regulation and eutrophication induced a simplification of food webs. To our knowledge, this study is the first to connect taxonomic and functional trait changes in response to multiple stressors with the associated modifications in isotopic niches within aquatic invertebrate assemblages. CONTEXT: Understanding how stream regulation and associated anthropogenic pressures act on aquatic assemblages and trophic niches is necessary to guide management actions. GOAL: We aimed to investigate the functional responses (traits and trophic niches) of aquatic invertebrate assemblages to stream regulation and eutrophication. METHODS: We used univariate and multivariate analyses to compare the invertebrate assemblages above and below the dams and to assess the contributions of hydrology (including groundwater supplies to the river), temperature and eutrophication to the variability in the composition of invertebrate assemblages. We also considered the relative utilization of a selected set of traits describing invertebrate resilience, resistance and specialization to address the potential functional effects of stream regulation on invertebrate assemblages. Finally, carbon and nitrogen isotope analyses allowed us to characterize the length and width of invertebrate assemblage food webs as related to the availability and diversity of basal resources. RESULTS: Invertebrate abundance and richness generally decreased below the dams, with the highest impacts on insect taxa. Co-inertia analysis showed that stream regulation and eutrophication were main drivers of the aquatic invertebrate assemblages. The analysis separated the sites above and below the dams according to flow and temperature variation, whereas eutrophication appeared as a secondary stressor that separated the sites within each sector. Furthermore, the series of dams resulted in (i) a higher proportion of resilient (e.g., multivoltine) and resistant (ovoviviparous) taxa and a majority of generalists in assemblages below dams, (ii) an impact on the classical dynamics of CPOM (decrease) and FPOM (increase) sources from upstream to downstream, and (iii) a reduction in the diversity of resource use and in the trophic chain length of invertebrate assemblages below dams. The cooler and less oxygenated upwelling zones had lower invertebrate abundance; however, contrary to our expectation, the variation in the groundwater supply did not affect the composition of epigean invertebrate assemblages. CONCLUSION: This study provides insights about the impacts of flow regime alteration and eutrophication on food webs that may have been caused by regulation of permanent streams. To our knowledge, this is the first to connect taxonomic and functional trait changes in response to multiple stressors with the associated modifications in energy fluxes in aquatic invertebrate assemblages. This study suggests that bed stability, which is associated with a reduction in channel mobility below the dams and with moderate eutrophication, may provide the shelter and resources that can locally favour invertebrate assemblage dynamics and lessen the effects of flow regulation. In addition, the study suggests that the biological trait-based approach and isotope analysis are complementary approaches for addressing ecosystem functioning. The relative utilization of traits indicates the functional potential of aquatic invertebrate assemblages to face multiple stressors whereas isotope analysis is an expression of the actual effect of the stressors on the trophic structure of aquatic invertebrate assemblages.

3D modelling of solute transport and mixing during managed aquifer recharge with an infiltration basin.

Artificial basins are used to recharge groundwater by many municipalities to improve the sustainability of storm water management. Despite its increasing operational implementation, artificial recharge still raises numerous questions related to its impact on groundwater quality. In this paper, a 3D numerical model of MAR basin/aquifer system was implemented in order to simulate the fate of water and pollutants. It was used to illustrate the complex distribution in time and space of a tracer contaminant injected in the basin. The model was based on a well instrumented storm water infiltration basin located in Chassieu (Lyon area, France). The well-known Richards model was used to simulate the water flow in the saturated and unsaturated zone of the study site. The transfer of solutes in the basin/aquifer system was modelled by the advection-dispersion-equation (ADE). The model was calibrated during a rain event using hydraulic head and electric conductivity data from a set of piezometers located around the basin. The flow model was validated on a one month period of basin operation presenting several rain events. The model was then used to simulate the fate of a solute pollutant considered as a tracer during a high intensity rain event. This simplified test case illustrated the mechanism of capillary trapping in the vadose zone and the effect of sampling point location on concentration measurements. Three main results were obtained: (1) capillary trapping promoted a retention of up to 20% of the injected tracer in the vadose zone, (2) 0 to 24% of the injected solute concentration could be recovered depending on the piezometer location, (3) the averaged concentration decreased by 50% if the measuring device is lowered by 5 m under the water table. These results were strongly site and event dependant but observed trends should be considered while discussing punctual water quality measurements used to monitor MAR systems. It also allowed to suggest some guidelines for sampling point positioning.

Influence of stormwater infiltration systems on the structure and the activities of groundwater biofilms: Are the effects restricted to rainy periods?

Stormwater infiltration systems (SIS) have been set up to collect and infiltrate urban stormwater runoff in order to reduce flooding and to artificially recharge aquifers. Such practices produce environmental changes in shallow groundwater ecosystems like an increase in organic matter concentrations that could drive changes in structure and functions of groundwater microbial communities. Previous works suggested that SIS influence groundwater physico-chemistry during either rainy and dry period but no study has examined the impact of SIS on groundwater microorganisms during both periods. This study aimed to fill this gap by assessing SIS impacts on groundwater quality parameters in three SIS with vadose zone thickness < 3 m during two contrasting meteorological conditions (rainy/dry periods). Physicochemical (dissolved organic carbon and nutrient concentrations) and microbial variables (biomass, dehydrogenase and hydrolytic activities, and bacterial community structure) were assessed on SIS-impacted and non-SIS-impacted zones of the aquifers for the three SIS. Using clay beads incubated in the aquifer to collect microbial biofilm, we show that SIS increased microbial activities, bacterial richness and diversity in groundwater biofilms during the rainy period but not during the dry period. In contrast, the significant differences in dissolved organic carbon and nutrient concentrations, biofilm biomass and bacterial community structures (Bray-Curtis distances, relative abundances of main bacterial orders) measured between SIS-impacted and non-SIS-impacted zones of the aquifer were comparable during the two periods. These results suggest that structural indicators of biofilm like biomass were probably controlled by long-term effects of SIS on concentrations of dissolved organic matter and nutrients whereas biofilm activities and bacterial richness were temporally stimulated by stormwater runoff infiltrations during the rainy period. This decoupling between the structural and functional responses of groundwater biofilms to stormwater infiltration practices suggests that biofilms functions were highly reactive to fluxes associated with aquifer recharge events.

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.

Emerging polar pollutants in groundwater: Potential impact of urban stormwater infiltration practices.

The quality of groundwater (GW) resources is decreasing partly due to chemical contaminations from a wide range of activities, such as industrial and agricultural enterprises and changes in land-use. In urban areas, one potential major pathway of GW contamination is associated with urban water management practices based on stormwater runoff infiltration systems (SIS). Data on the performance of the upper layer of soil and the unsaturated zone of infiltration basins to limit the contamination of GW by hydrophilic compounds are lacking. With this aim, the impact of infiltration practices on GW contamination was assessed for 12 pesticides and 4 pharmaceuticals selected according to their ecotoxicological relevance and their likelihood of being present in urban stormwater and GW. For this purpose, 3 campaigns were conducted at 4 SIS during storm events. For each campaign, passive samplers based on the use of Empore™ disk were deployed in GW wells upstream and downstream of SIS, as well as in the stormwater runoff entering the infiltration basins. Upstream and downstream GW contaminations were compared to evaluate the potential effect of SIS on GW contamination and possible relationships with stormwater runoff composition were examined. Our results showed two interesting opposite trends: (i) carbendazim, diuron, fluopyram, imidacloprid and lamotrigine had concentrations significantly increasing in GW impacted by infiltration, indicating a contribution of SIS to GW contamination, (ii) atrazine, simazine and 2 transformation products exhibited concentrations significantly decreasing with infiltration due to a probable dilution of historic GW contaminants with infiltrated stormwater runoff. The other 7 contaminants showed no general trend. This study demonstrates that passive samplers deployed in GW wells enabled the capture of emerging polar pollutants present at very low concentrations and allowed the assessment of infiltration practices on GW quality. New data on GW and urban stormwater are provided for poorly studied hazardous compounds.

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

This study describes the development of a novel Empore™ disk-based passive sampler specially adapted to groundwater monitoring. The sampler was calibrated in the laboratory using conditions that corresponded to groundwater (i.e. matrix medium, water temperature, flow rate and water flow across the disks). The retention and elution performance for sixteen semi-polar and polar pollutants on the Empore™ disk (47 mm diameter, SDB-XC) was evaluated. Recoveries were ~80% for the majority of compounds. Sampler uptake kinetics were measured over fourteen days at three concentrations (10, 100 and 500 ng L-1) and the sampling rate (RS) calculated for four compounds. There was no influence of concentration of the test analyte on the uptake profile; with mean RS varying between 0.018 ±â€¯0.007 L day-1 and 0.047 ±â€¯0.001 L day-1. Passive samplers were deployed in twelve characterized groundwater wells near Lyon (France). Atrazine, atrazine-desethyl and diuron were the main pollutants found with a maximum time-weighted concentration of 61 ±â€¯3, 62 ±â€¯24 and 127 ±â€¯49 ng L-1 respectively.

Ecological assessment of groundwater ecosystems disturbed by recharge systems using organic matter quality, biofilm characteristics, and bacterial diversity.

Recharge of aquifers by urban stormwater may trigger significant ecological changes that can be detrimental to the biodiversity and functioning of groundwater ecosystems. Here, the effects of aquifer recharge (AR) on three levels of parameters were investigated: dissolved organic carbon (DOC) quantity and quality, global biofilm characteristics, and diversity changes of bacterial communities. As DOC enrichment by AR can be mitigated by vadose zone (VZ) thickness, three AR sites with thin VZ (< 3 m) and three sites with thick VZ (> 10 m) were selected. For each AR site, clay beads were incubated over a 10-day-long rainy period through wells in recharged and non-recharged groundwaters. Total proteins, dehydrogenase, and hydrolytic activities were monitored from clay beads to assess biofilm development. Bacterial richness on beads was estimated by 16S rRNA-based metabarcoding. AR was found to significantly increase DOC and biodegradable DOC (BDOC) concentrations, biofilm development, and bacterial richness especially in sites with thin VZ. VZ thickness was inversely related to microbial growth indicators and bacterial richness in groundwater, through a control of DOC availability. The proportion of Bacteroidetes 16S rRNA gene reads was higher in recharged groundwater than in non-recharged groundwater, suggesting that this phylum could be used as an indicator of DOC enrichment associated with AR. Quantitative PCR assays for Bacteroides DNA confirmed these trends and showed an enrichment of this bacterial group in DOC-rich aquifer waters. The positive linear relationships between BDOC concentrations and biofilm variables highlighted a strong C-limitation of groundwater impacting bacterial species sorting and activity.

Use of passive sampling and high resolution mass spectrometry using a suspect screening approach to characterise emerging pollutants in contaminated groundwater and runoff.

Groundwater systems are being increasingly used to provide potable and other water supplies. Due to human activities, a range of organic pollutants is often detected in groundwater. One source of groundwater contamination is via stormwater infiltration basins, however, there is little information on the types of compounds present in these collection systems and their influence on the underlying groundwater. We developed an analytical strategy based on the use of passive sampling combined with liquid chromatography/high resolution quadrupole-time-of-flight mass spectrometry for screening for the presence of pesticide and pharmaceutical compounds in groundwater and stormwater runoff. Empore™ disk-based passive samplers (SDB-RPS and SDB-XC sorbents) were exposed, using for the first time a new specially designed deployment rig, for 10 days during a rainfall event in five different stormwater infiltration systems around Lyon, France. Stormwater runoff and groundwater (via a well, upstream and downstream of each basin) was sampled. Exposed Empore™ disks were solvent extracted (acetone and methanol) and the extracts analysed using a specific suspect compound screening workflow. High resolution mass spectrometry coupled with a suspect screening approach was found to be a useful tool as it allows a more comprehensive analysis than with targeted screening whilst being less time consuming than non-targeted screening. Using this analytical approach, 101 suspect compounds were tentatively identified, with 40 of this set being subsequently confirmed. The chemicals detected included fungicides, herbicides, insecticides, indicators of human activity, antibiotics, antiepileptics, antihypertensive and non-steroidal anti-inflammatory drugs as well as their metabolites. Polar pesticides were mainly detected in groundwater and pharmaceuticals were more frequently found in runoff. In terms of detection frequency of the pollutants, groundwater impacted by infiltration was found not to be significantly more contaminated than non-impacted groundwater.

Clay beads as artificial trapping matrices for monitoring bacterial distribution among urban stormwater infiltration systems and their connected aquifers.

Stormwater infiltration systems (SIS) have been developed to limit surface runoff and flooding in urban areas. The impacts of such practices on the ecological and biological quality of groundwater ecosystems remain poorly studied due to the lack of efficient methodologies to assess microbiological quality of aquifers. In the present study, a monitoring method based on the incubation of artificial matrices (clay beads) is presented to evaluate microbial biomass, microbial activities, and bacterial community structure. Four microbial variables (biomass, dehydrogenase and hydrolytic activities, bacterial community structures) were measured on clay beads incubated in three urban water types (stormwater surface runoffs, SIS-impacted and non-impacted groundwaters) for six SIS. Analyses based on next-generation sequencing (NGS) of partial rrs (16S rRNA) PCR products (V5-V6) were used to compare bacterial community structures of biofilms on clay beads after 10 days of incubation with those of waters collected from the same sampling points at three occasions. Biofilm biomass and activities on clay beads were indicative of nutrient transfers from surface to SIS-impacted groundwaters. Biofilms allowed impacts of SIS on groundwater bacterial community structures to be determined. Although bacterial communities on clay beads did not perfectly match those of waters, clay beads captured the most abundant bacterial taxa. They also captured bacterial taxa that were not detected in waters collected at three occasions during the incubation, demonstrating the integrative character of this approach. Monitoring biofilms on clay beads also allowed the tracking of bacterial genera containing species representing health concerns.

Aquifer recharge with stormwater runoff in urban areas: Influence of vadose zone thickness on nutrient and bacterial transfers from the surface of infiltration basins to groundwater.

Stormwater infiltration systems (SIS) have been built in urban areas to reduce the environmental impacts of stormwater runoff. Infiltration basins allow the transfer of stormwater runoff to aquifers but their abilities to retain contaminants depend on vadose zone properties. This study assessed the influence of vadose zone thickness (VZT) on the transfer of inorganic nutrients (PO43-, NO3-, NH4+), dissolved organic carbon (total -DOC- and biodegradable -BDOC-) and bacteria. A field experiment was conducted on three SIS with a thin vadose zone (<3 m) and three SIS with a thick vadose zone (>10 m). Water samples were collected at three times during a rainy period of 10 days in each infiltration basin (stormwater runoff), in the aquifer impacted by infiltration (impacted groundwater) and in the same aquifer but upstream of the infiltration area (non-impacted groundwater). Inorganic nutrients, organic matter, and dissolved oxygen (DO) were measured on all water samples. Bacterial community structures were investigated on water samples through a next-generation sequencing (NGS) scheme of 16S rRNA gene amplicons (V5-V6). The concentrations of DO and phosphate measured in SIS-impacted groundwaters were significantly influenced by VZT due to distinct biogeochemical processes occurring in the vadose zone. DOC and BDOC were efficiently retained in the vadose zone, regardless of its thickness. Bacterial transfers to the aquifer were overall low, but data obtained on day 10 indicated a significant bacterial transfer in SIS with a thin vadose zone. Water transit time and water saturation of the vadose zone were found important parameters for bacterial transfers. Most bacterial taxa (>60%) from impacted groundwaters were not detected in stormwater runoff and in non-impacted groundwaters, indicating that groundwater bacterial communities were significantly modified by processes associated with infiltration (remobilization of bacteria from vadose zone and/or species sorting).

Less effective selection leads to larger genomes.

The 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 data sets. Here, we tested this hypothesis using 22 de novo transcriptomes and low-coverage genomes of asellid isopods, which represent 11 independent habitat shifts from surface water to resource-poor groundwater. We show that these habitat shifts are associated with higher transcriptome-wide [Formula: see text] After ruling out the role of positive selection and pseudogenization, we show that these transcriptome-wide [Formula: see text] 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 repeat 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 of observing polymorphism variation in polymorphism-poor species can obfuscate the link between effective population size and genome size when polymorphism data are used alone.