Identifying the impact of toxicity on stream macroinvertebrate communities in a multi-stressor context based on national ecological and ecotoxicological monitoring databases

In situ bioassays are used to measure the harmful effects induced by mixtures of toxic chemicals in watercourses. In France, national-scale biomonitoring data are available including invertebrate surveys and in-field chemical toxicity measures with caged gammarids to assess environmental toxicity of mixtures of chemicals. The main objective of our study is to present a proof-of-concept approach identifying possible links between in-field chemical toxicity, stressors and the ecological status. We used two active biomonitoring databases comprising lethal toxicity (222 in situ measures of gammarid mortality) and sublethal toxicity (101 in situ measures of feeding inhibition). We measured the ecological status of each active biomonitoring site using the I₂M₂ metric (macroinvertebrate-based multimetric index), accounted for known stressors of nutrients and organic matter, hydromorphology and chemical toxicity. We observed a negative relationship between stressors (hydromorphology, nutrients and organic matter, and chemical toxicity) and the good ecological status. This relationship was aggravated in watercourses where toxicity indicators were degraded. We validated this hypothesis for instance with nutrients and organic matter like nitrates or hydromorphological conditions like percentage of vegetation on banks. Future international assesments concerning the role of in-field toxic pollution on the ecological status in a multi-stressor context are now possible via the current methodology.

Quantification of multi-scale links of anthropogenic pressures with PAH and PCB bioavailable contamination in French freshwaters

Aquatic ecosystems are exposed to multiple environmental pressures including chemical contamination. Polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) known as preoccupying substances for the environment. Active biomonitoring (ABM) is a surveillance method for polluted aquatic ecosystems measuring bioavailable contamination. In this work, the aim was to quantify the total links between environmental pressures and bioavailable contamination (for PAHs and PCBs) at the French national scale. Based on 245 sites experimented by ABM from 2017 to 2019, environmental pressures (anthropogenic pressures and environmental parameters) were defined (point source landfill density, point source urban density, point source industry density, point source road density, nonpoint source industry density, nonpoint source road density, nonpoint source urban density, nutrients and organic matter, slope, dams, straightness, coarse sediment, summer precipitation, hydrographic network density and watershed size) and characterized by one or a combination of measures called stressor indicators. The links between environmental pressures and bioavailable POPs contamination (ABM measure) at a large spatial scale were defined and quantified via structural equation modeling. Point source urban density, nutrients and organic matter, summer precipitation, straightness and point source industry density are correlated positively with PAH bioavailable contamination. In contrast, nonpoint source urban density, nonpoint source industry density, nonpoint source road density and watershed size are positively correlated with PCB bioavailable contamination. The dominant pressures linked to PAHs and PCBs were different, respectively local and large-scale pressures were linked to PAH bioavailable contamination, and only large-scale pressures were linked to PCB bioavailable contamination.

Thermal signatures identify the influence of dams and ponds on stream temperature at the regional scale

Anthropogenic impoundments (e.g. large dams, small reservoirs, and ponds) are expanding in number globally, influencing downstream temperature regimes in a diversity of ways that depend on their structure and position along the river continuum. Because of the manifold downstream thermal responses, there has been a paucity of studies characterizing cumulative effect sizes at the catchment scale. Here, we introduce five thermal indicators based on the stream-air temperature relationship that together can identify the altered thermal signatures of dams and ponds. We used this thermal signature approach to evaluate a regional dataset of 330 daily stream temperature time series from stations throughout the Loire River basin, France, from 2008 to 2018. This basin (10⁵ km²) is one of the largest European catchments with contrasting natural and anthropogenic characteristics. The derived thermal signatures were cross-validated with several known catchment characteristics, which strongly supported separation into dam-like, pond-like and natural-like signatures. We characterize the thermal regime of each thermal signature and contextualize it using a set of ecologically relevant thermal metrics. Results indicate that large dams decreased summer stream temperature by 2 °C and delayed the annual stream temperature peak by 23 days relative to the natural regimes. In contrast, the cumulative effects of upstream ponds increased summer stream temperature by 2.3 °C and increased synchrony with air temperature regimes. These thermal signatures thus allow for identifying and quantifying downstream thermal and ecological influences of different types of anthropogenic infrastructures without prior information on the source of modification and upstream water temperature conditions.

How to quantify the links between bioavailable contamination in watercourses and pressures of anthropogenic land cover, contamination sources and hydromorphology at multiple scales?

Active biomonitoring permits the quantification of biological exposure to chemicals through measurements of bioavailable concentrations in biota and biological markers of toxicity in organisms. It enables respective comparison of the levels of contamination between sites and sampling campaigns. Caged gammarids are recently proposed as relevant probes for measuring bioavailable contamination in freshwater systems. The purpose of the present study was to develop a multi-pressure and multiscale approach, considering metallic contamination levels (from data based on active biomonitoring) as a response to pressures (combination of individual stressors). These pressures were anthropogenic land cover, industry density, wastewater treatment plant density, pressures on stream hydromorphological functioning, riverside vegetation and bioavailability factors. A dataset combining active biomonitoring and potentially related pressures was established at the French national scale, with 196 samplings from 2009 to 2016. The links between pressures and metallic contamination were defined and modelled via structural equation modeling (more specifically partial least squares - path modeling). The model enabled the understanding of the respective influences of pressures on metallic bioconcentration in caged sentinel organisms. Beyond validating the local influence of industries and wastewater treatment plants on metallic contamination, this model showed a complementary effect of driving forces of anthropogenic land cover (leading to human activities). It also quantified a significant influence of pressures on stream hydromorphological functioning, presence of vegetation and physico-chemical parameters on metal bioconcentration. This hierarchical multi-pressure approach could serve as a concept on how pressures and contamination (assessed by active biomonitoring) can be connected. Its future application will enable better understanding of environmental pressures leading to contamination in freshwater ecosystems.

A diagnosis-based approach to assess specific risks of river degradation in a multiple pressure context: Insights from fish communities

In the context of increasing pressure on water bodies, many fish-based indices have been developed to evaluate the ecological status of rivers. However, most of these indices suffer from several limitations, which hamper the capacity of water managers to select the most appropriate measures of restoration. Those limitations include: (i) being dependent on reference conditions, (ii) not satisfactorily handling complex and non-linear biological responses to pressure gradients, and (iii) being unable to identify specific risks of stream degradation in a multi-pressure context. To tackle those issues, we developed a diagnosis-based approach using Random Forest models to predict the impairment probabilities of river fish communities by 28 pressure categories (chemical, hydromorphological and biological). In addition, the database includes the abundances of 72 fish species collected from 1527 sites in France, sampled between 2005 and 2015; and fish taxonomic and biological information. Twenty random forest models provided at least good performances when evaluating impairment probabilities of fish communities by those pressures. The best performing models indicated that fish communities were impacted, on average, by 7.34 ± 0.03 abiotic pressure categories (mean ± SE), and that hydromorphological alterations (5.27 ± 0.02) were more often detected than chemical ones (2.06 ± 0.02). These models showed that alterations in longitudinal continuity, and contaminations by Polycyclic Aromatic Hydrocarbons were respectively the most frequent hydromorphological and chemical pressure categories in French rivers. This approach has also efficiently detected the functional impact of invasive alien species. Identifying and ranking the impacts of multiple anthropogenic pressures that trigger functional shifts in river biological communities is essential for managers to prioritize actions and to implement appropriate restoration programmes. Actually implemented in an R package, this approach has the capacity to detect a variety of impairments, resulting in an efficient assessment of ecological risks across various spatial and temporal scales.

Direct and indirect effects of multiple stressors on stream invertebrates across watershed, reach and site scales: A structural equation modelling better informing on hydromorphological impacts

The purpose of our approach was to take into account the nested spatial scales driving stream functioning in the description of pressures/ecological status links by analysing the results of a hierarchical model. The development of this model has allowed us to answer the following questions: Does the consideration of the indirect links between anthropogenic pressures and stream ecological status modify the hierarchy of pressure types impacting benthic invertebrates? Do the different nested scales play different roles in the anthropogenic pressures/ecological status relationship? Does this model lead to better understanding of the specific role of hydromorphology in the evaluation of stream ecological status? To achieve that goal, we used the Partial Least Square (PLS) path modelling method to develop a structural model linking variables describing (i) land use and hydromorphological alterations at the watershed scale, (ii) hydromorphological alterations at the reach scale, (iii) nutrients-organic matter contamination levels at the site scale, and (iv) substrate characteristics at the sampling site scale, to explain variation in values of a macroinvertebrate-based multimetric index: the French I₂M₂. We have highlighted the importance of land use effects exerted on both hydromorphological and chemical characteristics of streams observed at finer scales and their subsequent indirect impact on stream ecological status. Hydromorphological alterations have an effect on the substrate mosaic structure and on the concentrations of nutrients and organic matter at site scale. This result implies that stream hydromorphology can have a major indirect effect on macroinvertebrate assemblages and that the hierarchy of impacts of anthropogenic pressures on stream ecological status generally described in the literature - often determining strategic restoration priorities - has to be re-examined. Finally, the effects of nutrients and organic matter on macroinvertebrate assemblages are lower than expected when all the indirect effects of land use and hydromorphological alterations are taken into account.

Scale dependency in the hydromorphological control of a stream ecosystem functioning

Physical habitat degradation is prevalent in river ecosystems. Although still little is known about the ecological consequences of altered hydromorphology, understanding the factors at play can contribute to sustainable environmental management. In this study we aimed to identify the hydromorphological features controlling a key ecosystem function and the spatial scales where such linkages operate. As hydromorphological and chemical pressures often occur in parallel, we examined the relative importance of hydromorphological and chemical factors as determinants of leaf breakdown. Leaf breakdown assays were investigated at 82 sites of rivers throughout the French territory. Leaf breakdown data were then crossed with data on water quality and with a multi-scale hydromorphological assessment (i.e. upstream catchment, river segment, reach and habitat) when quantitative data were available. Microbial and total leaf breakdown rates exhibited differential responses to both hydromorphological and chemical alterations. Relationships between the chemical quality of the water and leaf breakdown were weak, while hydromorphological integrity explained independently up to 84.2% of leaf breakdown. Hydrological and morphological parameters were the main predictors of microbial leaf breakdown, whereas hydrological parameters had a major effect on total leaf breakdown, particularly at large scales, while morphological parameters were important at smaller scales. Microbial leaf breakdown were best predicted by hydromorphological features defined at the upstream catchment level whereas total leaf breakdown were best predicted by reach and habitat level geomorphic variables. This study demonstrates the use of leaf breakdown in a biomonitoring context and the importance of hydromorphological integrity for the functioning of running water. It provides new insights for environmental decision-makers to identify the management and restoration actions that have to be undertaken including the hydromorphogical features that should be kept in minimal maintenance to support leaf breakdown.

Unravelling river system impairments in stream networks with an integrated risk approach

Rivers are complex systems for which it is hard to make reliable assessments of causes and responses to impairments. We present a holistic risk-based framework for river ecosystem assessment integrating all potential intervening processes and functions. Risk approaches allow us to deal with uncertainty both in the construction of indicators for magnitude of stressors and in the inference of environmental processes and their impairment. Yet, here we go further than simply replacing uncertainty by a risk factor. We introduce a more accurate and rigorous notion of risk with a transcription of uncertainty in causal relationships in probability distributions for the magnitude of impairment and the weight of different descriptors, with an associated confidence in the diagnostic. We discuss how Bayesian belief networks and Bayesian hierarchical inference allow us to deal with this risk concept to predict impairments and potential recovery of river ecosystems. We developed a comprehensive approach for river ecosystem assessment, which offers an appealing tool to facilitate diagnosis of the likely causes of impairment and predict future conditions. The ability of the risk approaches to integrate multi-scale quantitative and qualitative descriptors in the identification of multiple stressor sources and pathways in the stream network, and their impairment of specific processes and structures is illustrated for the national-level risk analysis for hydromorphology and pesticide pollution. Not only does the risk-based framework provide a more complete picture of environmental impairments, but it also offers a comprehensive, user-friendly tool to instruct the decision process.

Composition and antibacterial activity of Pseudocytisus integrifolius (Salisb.) essential oil from Algeria

The essential oil composition of an endemic Algerian Cruciferae, Pseudocytisus integrifolius (Salisb.) Rehder, was analyzed by gas chromatography (GC) and GC-mass spectrometry (MS). Eighty-three components representing more than 96.5% of the oil were identified. The major components were dimethyl disulfide (33.4%), dimethyl trisulfide (24.2%), and an unsaturated nitrile (31.7%). Fractionation on a silica gel column led to the identification of trace-level compounds, in particular, polar compounds such as nitriles and aldehydes, and to the isolation of dimethyl disulfide, dimethyl trisulfide, and an unsaturated nitrile. Structural analysis using high-resolution mass spectrometry (HRMS) and 1H,13C NMR techniques enabled the identification of pent-4-enenitrile. Variation in essential oil composition and yields was studied according to harvesting time, drying, and parts of the plant. The essential oil of aerial parts was tested for its antibacterial activity using a paper disk method. The oil was effective on the inactivation of Escherichia coli and Pseudomonas aeruginosa and ineffective on the inactivation of Staphylococcus aureus.

Dietary polyunsaturated fatty acids modulate fatty acid composition and early activation steps of concanavalin A-stimulated rat thymocytes

The early biochemical responses to concanavalin A (Con A) of thymocytes from rats fed a saturated (coconut oil), (n-6) (sunflower oil) or (n-3) (fish oil) fatty acid-enriched diet for 3 wk were investigated. Fish oil feeding resulted in greater (n-3) polyunsaturated fatty acid level (PUFA) at the expense of (n-6) PUFA in total and individual thymocyte phospholipids. Such alterations of the fatty acid composition did not affect basal ornithine decarboxylase (ODC), cyclic nucleotide phosphodiesterase (PDE) or gamma-glutamyl transferase activities. However, the fish oil-enriched diet impaired some of the early thymocyte responses to Con A, such as the rapid induction (30 min) of soluble ODC and PDE activities. Synthesis of [3H]20:4(n-6) oxygenated metabolites was not different between the dietary groups; however, the uptake of [3H]20:4(n-6) into phospholipid classes was significantly lower in phosphatidylcholine and greater in phosphatidylethanolamine and phosphatidylinositol after fish oil feeding. Similarly, the Con A-induced remodeling of the [3H]20:4(n-6) esterification in phospholipids differed in sunflower oil- vs. fish oil-fed rats, suggesting a modulation of acyl CoA synthase and/or acyl CoA transferase activities. Thus, the modulation of Con A-induced ODC and PDE stimulation upon in vivo changes of membrane phospholipid fatty acid composition is not related to eicosanoid formation, but rather to the modification of the fatty acid acylation processes, altering phospholipid composition and signal transduction.

Early induction of ornithine decarboxylase occurs simultaneously with inositol phosphate accumulation in concanavalin A-stimulated rat thymocytes

Stimulation of rat thymocytes with the lectin ConA produced an early peak of ornithine decarboxylase (ODC) activity within 10 min. This ODC induction appeared as early as the well-known inositol phosphate accumulation following mitogenic stimulation, and may be part of the signal transduction mechanism. The distribution of counts among the inositol phosphates was constant during the overall time of Concanavalin A (ConA) stimulation. We conclude that early induction of pre-existing ODC may be independent of protein kinase C action.

Concanavalin A stimulates the Rolipram-sensitive isoforms of cyclic nucleotide phosphodiesterase in rat thymic lymphocytes

Pretreatment of rat thymic lymphocytes with Concanavalin A induced a very early (30 min) and substantial increase (+90%) of the soluble cAMP phosphodiesterase activity. The crude cytosolic phosphodiesterase activity of rat thymocytes could reproducively be resolved by Mono-Q ion exchange high performance liquid chromatography into four separate phosphodiesterase peaks: a cGMP-stimulated, two cAMP-specific Rolipram-sensitive and a cGMP-inhibited cardiotrope-sensitive peaks. Concanavalin A stimulated very specifically the activity of the two predominant cAMP-specific Rolipram sensitive peaks whereas it only slightly modified the cGMP-stimulated and the cGMP-inhibited forms. The present results strongly suggest that the Rolipram-sensitive cAMP PDE activity may play a key role in the control and regulation of mitogen-induced thymocyte proliferation.

Freeze-drying of brucella vaccine strain B 19

The B 19 brucellosis strain has been widely used in the production of live vaccine against Bovine Brucellosis in the field for the last 30 years. Many attempts have been made to stabilize this vaccine but it remains a problem for laboratories which prepare this vaccine. In order to improve our knowledge of the influence of residual moisture and the nature of the conditioning atomosphere, several batches of vaccine were prepared in the same freeze-drying apparatus, either with a different atmosphere, or with a different level of residual moisture. After freeze-drying, the percentage of live bacteria and the stability of the vaccine at 37 degrees and 4 degrees C were investigated. It is thus possible to determine under specific conditions the level of residual moisture which gives: a) the best stability and b) the correct percentage of live bacteria after freeze-drying. Furthermore, by using nitrogen, argon, or a vacuum in the freeze-drying procedure, it was possible to select the most favourable atmosphere for conditioning the vaccine.