A cost-effective method to quantify biological surface sediment reworking

We propose a simple and inexpensive method to determine the rate and pattern of surface sediment reworking by benthic organisms. Unlike many existing methods commonly used in bioturbation studies, which usually require sediment sampling, our approach is fully non-destructive and is well suited for investigating non-cohesive fine sediments in streams and rivers. Optical tracer (e.g., luminophores or coloured sand) disappearance or appearance is assessed through time based on optical quantification of surfaces occupied by tracers. Data are used to calculate surface sediment reworking (SSR) coefficients depicting bioturbation intensities. Using this method, we evaluated reworking activity of stream organisms (three benthic invertebrates and a fish) in laboratory microcosms mimicking pool habitats or directly in the field within arenas set in depositional zones. Our method was sensitive enough to measure SSR as low as 0.2 cm2.d-1, such as triggered by intermediate density (774 m-2) of Gammarus fossarum (Amphipoda) in microcosms. In contrast, complex invertebrate community in the field and a fish (Barbatula barabatula) in laboratory microcosms were found to yield to excessively high SSR (>60 cm2.d-1). Lastly, we suggest that images acquired during experiments can be used for qualitative evaluation of species-specific effects on sediment distribution

Fine sediment reduces vertical migrations of Gammarus pulex (Crustacea: Amphipoda) in response to surface water loss

Surface and subsurface sediments in river ecosystems are recognized as refuges that may promote invertebrate survival during disturbances such as floods and streambed drying. Refuge use is spatiotemporally variable, with environmental factors including substrate composition, in particular the proportion of fine sediment (FS), affecting the ability of organisms to move through interstitial spaces. We conducted a laboratory experiment to examine the effects of FS on the movement of Gammarus pulex Linnaeus (Crustacea: Amphipoda) into subsurface sediments in response to surface water loss. We hypothesized that increasing volumes of FS would impede and ultimately prevent individuals from migrating into the sediments. To test this hypothesis, the proportion of FS (1–2 mm diameter) present within an open gravel matrix (4–16 mm diameter) was varied from 10 to 20% by volume in 2.5% increments. Under control conditions (0% FS), 93% of individuals moved into subsurface sediments as the water level was reduced. The proportion of individuals moving into the subsurface decreased to 74% at 10% FS, and at 20% FS no individuals entered the sediments, supporting our hypothesis. These results demonstrate the importance of reducing FS inputs into river ecosystems and restoring FS-clogged riverbeds, to promote refuge use during increasingly common instream disturbances

Role of the hyporheic heterotrophic biofilm on transformation and toxicity of pesticides

The role of heterotrophic biofilm of water–sediment interface in detoxification processes was tested in abiotic and biotic conditions under laboratory conditions. Three toxicants, a herbicide (Diuron), a fungicide (Dimethomorph) and an insecticide (Chlorpyrifos-ethyl) have been tested in water percolating into columns reproducing hyporheic sediment. The detoxification processes were tested by comparing the water quality after 18 days of percolation with and without heterotrophic biofilm. Tested concentrations were 30 mg.Lx1 of Diuron diluted in 0.1% dimethyl sulfoxide (DMSO), 2 mg.Lx1 of Dimethomorph and 0.1 mg.Lx1 of Chlorpyrifos-ethyl. To characterise the detoxification efficiency of the system, we performed genotoxicity bioassays in amphibian larvae and rotifers and measured the respiration and denitrification of sediments. Although the presence of biofilm increased the production of N-(3,4 dichlorophenyl)-N-(methyl)-urea, a metabolite of diuron, the toxicity did not decrease irrespective of the bioassay. In the presence of biofilm, Dimethomorph concentrations decreased compared with abiotic conditions, from 2 mg.Lx1 to 0.4 mg.Lx1 after 18 days of percolation. For both Dimethomorph and Chlorpyrifos-ethyl additions, assessment of detoxification level by the biofilm depended on the test used: detoxification effect was found with amphibian larvae bioassay and no detoxification was observed with the rotifer test. Heterotrophic biofilm exerts a major influence in the biochemical transformation of contaminants such as pesticides, suggesting that the interface between running water and sediment plays a role in self-purification of stream reaches

Efficacy of treatments for demodex blepharitis: A systematic review and meta-analysis

Purpose We conducted a systematic review and meta-analysis to evaluate the efficacy of different treatment for Demodex blepharitis. Parameters studied were mites count, improvement of symptoms and mites’ eradication, stratified on type of treatments and mode of delivery of treatments (local or systemic). Method The PubMed, Cochrane Library, Embase, ClinicalTrials.gov, Google scholar and Science Direct databases were searched for studies reporting an efficacy of treatments for Demodex blepharitis. Results We included 19 studies (14 observational and 5 randomized clinical trials), for a total of 934 patients, 1741 eyes, and 13 different treatments. For mites count, eradication rate, and symptoms improvement, meta-analysis included fifteen, fourteen and thirteen studies, respectively. The overall effect sizes for efficiency of all treatments, globally, were 1.68 (95CI 1.25 to 2.12), 0.45 (0.26–0.64), and 0.76 (0.59–0.90), respectively. Except usual lid hygiene for mites count, Children's Hospital of Eastern Ontario ointment (CHEO) for both eradication rate and symptoms, and CHEO, 2% metronidazole ointment, and systemic metronidazole for eradication rate, all treatments were efficient. Stratified meta-analysis did not show significant differences between local and systemic treatments (1.22, 0.83 to 1.60 vs 2.24, 1.30 to 3.18 for mites count; 0.37, 0.21 to 0.54 vs 0.56, 0.06 to 0.99 for eradication rate; and 0.77, 0.58 to 0.92 vs 0.67, 0.25 to 0.98 for symptoms improvement). Conclusion We reported the efficiency of the different treatments of Demodex blepharitis. Because of less systemic side effects, local treatments seem promising molecules in the treatment of Demodex blepharitis

The role of organisms in hyporheic processes : gaps in current knowledge, needs for future research and applications

Fifty years after the hyporheic zone was first defined (Orghidan, 1959), there are still gaps in the knowledge regarding the role of biodiversity in hyporheic processes. First, some methodological questions remained unanswered regarding the interactions between biodiversity and physical processes, both for the study of habitat characteristics and interactions at different scales. Furthermore, many questions remain to be addressed to help inform our understanding of invertebrate community dynamics, especially regarding the trophic niches of organisms, the functional groups present within sediment, and their temporal changes. Understanding microbial community dynamics would require investigations about their relationship with the physical characteristics of the sediment, their diversity, their relationship with metabolic pathways, their inter- actions with invertebrates, and their response to environmental stress. Another fundamental research question is that of the importance of the hyporheic zone in the global metabolism of the river, which must be explored in relation to organic matter recycling, the effects of disturbances, and the degradation of contaminants. Finally, the application of this knowledge requires the development of methods for the estimation of hydro- logical exchanges, especially for the management of sediment clogging, the optimization of self-purification, and the integration of climate change in environmental policies. The development of descriptors of hyporheic zone health and of new metrology is also crucial to include specific targets in water policies for the long-term management of the system and a clear evaluation of restoration strategies

Direct observations of the effect of fine sediment deposition on the vertical movement of Gammarus pulex (Amphipoda: Gammaridae) during substratum drying

Benthic macroinvertebrates inhabit the streambed sediments of temporary streams during drying events. Fine sediment (< 2 mm in diameter) deposition and clogging of interstitial pathways reduces the connectivity between benthic and subsurface habitats, potentially inhibiting macroinvertebrate vertical movements. Direct observations within subsurface sediments are, however, inherently difficult. As a result, confirmation of macroinvertebrate vertical movement, and the effect of fine sediment, is limited. We used laboratory mesocosms containing transparent gravel sized particles (10–15 mm) to facilitate the direct observation and tracking of vertical movements by Gammarus pulex in response to water level reduction and sedimentation. Seven sediment treatments comprised two fine sediment fractions (small: 0.125–0.5 mm, coarse sand: 0.5–1 mm) deposited onto the surface of the substrate, and a control treatment where no fine sediment was applied. We found that G. pulex moved into the subsurface gravel sediments in response to drying, but their ability to remain submerged during water level reduction was impeded by fine sediment deposition. In particular deposition of the coarser sand fraction clogged the sediment surface, limiting vertical movements. Our results highlight the potential effect of sedimentation on G. pulex resistance to drying events in streams

Perceived discrimination based on the symptoms of covid-19, mental health, and emotional responses–the international online COVISTRESS survey

Background Despite the potential detrimental consequences for individuals’ health and discrimination from covid-19 symptoms, the outcomes have received little attention. This study examines the relationships between having personally experienced discrimination based on the symptoms of covid-19 (during the first wave of the pandemic), mental health, and emotional responses (anger and sadness). It was predicted that covid-19 discrimination would be positively related to poor mental health and that this relationship would be mediated by the emotions of anger and sadness. Methods The study was conducted using an online questionnaire from January to June 2020 (the Covistress network; including 44 countries). Participants were extracted from the COVISTRESS database (Ntotal = 280) with about a half declaring having been discriminated due to covid-19 symptoms (N = 135). Discriminated participants were compared to non-discriminated participants using ANOVA. A mediation analysis was conducted to examine the indirect effect of emotional responses and the relationships between perceived discrimination and self-reported mental health. Results The results indicated that individuals who experienced discrimination based on the symptoms of covid-19 had poorer mental health and experienced more anger and sadness. The relationship between covid-19 personal discrimination and mental health disappeared when the emotions of anger and sadness were statistically controlled for. The indirect effects for both anger and sadness were statistically significant. Discussion This study suggests that the covid-19 pandemic may have generated discriminatory behaviors toward those suspected of having symptoms and that this is related to poorer mental health via anger and sadness.publishedVersio