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Streams located in vineyard areas are particularly exposed to mixtures of dissolved and particulate contaminants such as metals and organic pesticides. In this context, phototrophic biofilms are increasingly used as indicators of river water contaminations through pollution-induced community tolerance (PICT) assessments based on short-term toxicity tests with individual or mixtures of toxicants. We conducted a laboratory experiment to evaluate the relative influence of the dissolved and particulate fractions on the effects of metals and pesticides on phototrophic biofilms in a context of contamination from a vineyard watershed. Three sets of artificial channels were supplied with (i) unfiltered water from a stream reference site, (ii) unfiltered water from a stream contaminated site, and (iii) filtered water (0.45 μm) from the same contaminated site. Biofilm growth, diatom community structure, and dissolved toxicant concentrations differed slightly between channels supplied with unfiltered or filtered water from the contaminated site. However, PICT assessments with individual toxicants or mixtures of toxicants extracted from passive samplers suggested no significant difference in tolerance to metals and organic pesticides between phototrophic communities supplied with unfiltered or filtered contaminated water. Our results confirm the use of extracts from passive samplers as a promising approach in short-term toxicity tests to characterize impacts of contamination on aquatic communities.

Aquatic ecosystems are generally subjected to multiple perturbations due to simultaneous or successive combinations of various natural and anthropogenic environmental pressures. To better assess and predict the resulting ecological consequences, increasing attention should be given to the accumulation of stresses on freshwater ecosystems and its effects on the vulnerability of aquatic organisms, including microbial communities, which play crucial functional roles. Here we used a microcosm study to assess the influence of an experimental warming on the vulnerability of phototrophic and heterotrophic periphytic communities to acute and chronic copper (Cu) toxicity. Natural periphytic communities were submitted for 4 weeks to three different temperatures (18, 23, and 28°C) in microcosms contaminated (at about 15 μg L-1) or not with Cu. The vulnerability of both phototrophic and heterotrophic microbial communities to subsequent acute Cu stress was then assessed by measuring their levels of sensitivity to Cu from bioassays targeting phototrophic (photosynthetic activity) and heterotrophic (β-glucosidase and leucine aminopeptidase extracellular enzymatic activities) microbial functions. We postulated that both the increase in temperature and the chronic Cu exposure would modify microbial community structure, thus leading to changes in the capacity of phototrophic and heterotrophic communities to tolerate subsequent acute exposure to Cu. Our results demonstrated that the influence of temperature on the vulnerability of phototrophic and heterotrophic microbial communities to Cu toxicity can vary greatly according to function studied. These findings emphasize the importance of considering different functional compartments and different functional descriptors to better assess the vulnerability of periphyton to multiple stresses and predict the risks induced by multiple stressors for ecosystem balance and functioning. [ABSTRACT FROM AUTHOR]

Streams located in vineyard areas are highly prone to metal pollution. In a context of global change, aquatic systems are generally subjected to multi-stress conditions due to multiple chemical and/or physical pressures. Among various environmental factors that modulate the ecological effects of toxicants, special attention should be paid to climate change, which is driving an increase in extreme climate events such as sharp temperature rises. In lotic ecosystems, periphyton ensures key ecological functions such as primary production and nutrient cycling. However, although the effects of metals on microbial communities are relatively well known, there is scant data on possible interactions between temperature increase and metal pollution. Here we led a study to evaluate the influence of temperature on the response of phototrophic periphyton to copper (Cu) exposure. Winter communities, collected in a 8 °C river water, were subjected for six weeks to four thermal conditions in microcosms in presence or not of Cu (nominal concentration of 15 μg L −1 ). At the initial river temperature (8 °C), our results confirmed the chronic impact of Cu on periphyton, both in terms of structure (biomass, distribution of algal groups, diatomic composition) and function (photosynthetic efficiency). At higher temperatures (13, 18 and 23 °C), Cu effects were modulated. Indeed, temperature increase reduced Cu effects on algal biomass, algal class proportions, diatom assemblage composition and photosynthetic efficiency. This reduction of Cu effects on periphyton may be related to lower bioaccumulation of Cu and/or to selection of more Cu-tolerant species at higher temperatures. [ABSTRACT FROM AUTHOR]

Pollution-induced community tolerance (PICT) approaches involve comparing tolerance levels of natural communities to a particular contaminant or a contaminant mixture using short-term toxicity tests performed under controlled conditions. However, results from toxicity tests can be modulated by various environmental and experimental conditions, raising questions about their reproducibility and comparability. In this context, the present study aimed to determine the influence of exposure duration, periphyton suspension concentration, and periphyton maturation stage on the measurement of short-term effects of copper on phototrophic periphyton communities. Our results showed the very weak influence of exposure duration in the tested range (2-6 h) on toxicity level, whereas periphyton biomass in the tested suspension (in terms of both chlorophyll a concentrations and dry weight), proved a crucial determinant in toxicity assessment. Results also highlighted the potential tolerance increase with the periphyton maturation stage. This parameter conditioned the positive linear relationship between tolerance level and periphyton suspension concentration, leading to an increase in the linear regression slope with the maturation stage. This suggests that such a relationship is probably highly periphyton-dependent. Consequently, to enable data toxicity comparisons, an a priori normalization of the periphyton suspension biomass is necessary, and PICT approaches require the use, as much of possible, of periphyton with similar maturation stage. Finally, the present study clearly shows that a better standardization of PICT approaches could help to improve reproducibility. It could thus facilitate the comparison of tolerance levels measured in the same study (e.g., spatial and/or temporal and/or inter-treatment comparison) as well as the comparison obtained from different experimental and in situ research. [ABSTRACT FROM AUTHOR]

Abstract: The European water legislation highlights the necessity of developing ecological criteria for assessing the quality of aquatic ecosystem. While a multitude of ecological indicators has been proposed and validated for streams, rivers and lakes, these indicators are not available for groundwater ecosystems. In the present study, we developed a method based on the measurements of the growth and activity of microorganisms developed on artificial substrates (glass beads) incubated in wells to characterize the trophic status of groundwater. Incubation sites were selected in an urban aquifer where previous works showed contrasting trophic conditions in groundwater due to artificial groundwater recharge practices. Total proteins, total carbohydrates, dehydrogenase and hydrolytic activities were measured on glass beads incubated in wells for two periods of 2 months (October–December 2010 and April–June 2011). Biofilm measured on glass beads was significantly more developed and active in wells where groundwater was enriched with dissolved organic matter due to artificial groundwater recharge. Indeed, most microbial variables (total proteins and dehydrogenase activities for the two incubation periods and hydrolytic activities for the second incubation period) were significantly and positively correlated with the concentrations of dissolved organic carbon (DOC) in groundwater. The availability of phosphorus also tended to influence biofilm growth (assessed by total carbohydrates) when PO4 3− concentrations were lower than 50μg/l. Overall, our study clearly demonstrated that artificial substrates acting as colonisable area for microorganisms could be used to efficiently monitor nutrient enrichment in aquifers. [Copyright &y& Elsevier]

Purpose: Best management practices encompass diverse artificial groundwater recharge (AGR) systems that heavily rely upon the capacity of the soil and vadose zone to retain large quantities of organic matter generated during stormwater runoff on urban catchments. However, the supply of stormwater-derived dissolved organic carbon (DOC) at the water-table region of aquifers can enhance the rate of biogeochemical processes by fueling heterotrophic microbial metabolism. This study examined changes in the abundance and activity of sediment biofilm in response to increased DOC supply at the water table of an urban aquifer intentionally recharged with stormwater. Changes in microbial abundance and activity under field conditions were compared with those measured in laboratory slow filtration columns supplied with an easily biodegradable source of DOC. Materials and methods: Biomass and activities of attached bacteria were measured on aquifer sediment samples collected at multiple depths below the groundwater table. The same microbial variables were measured on aquifer sediments introduced in slow filtration columns supplied with three distinct concentrations of biodegradable dissolved organic carbon (0.5, 1.5, and 2.5 mg l of C-acetate). Results and discussion: Biofilm was significantly more abundant and active beneath AGR sites than at control sites not intentionally recharged with stormwater. Individual cells also exhibited higher specific dehydrogenase and hydrolytic activities, and the protein content of biofilm was significantly increased by AGR with stormwater. The stimulation of the microbial community was all the more pronounced when the flux of DOC reaching the groundwater table was high. However, the increase in microbial biomass and activity at AGR sites was 7.5 times lower than that measured in slow filtration columns in which aquifer sediments were supplied with an easily biodegradable source of DOC. Conclusions: Our results indicated that the soil and vadose zone at AGR sites efficiently retained the more labile fraction of DOC, thereby enabling the infiltration of large quantities of stormwater without excessively stimulating the growth of microbial biofilm in groundwater. However, our results showed that groundwater bacterial activity was stimulated by enhanced DOC fluxes. As microorganisms experience severe organic carbon limitation in most pristine aquifers, we suggest that groundwater biofilms could be used as sensitive indicators for assessing the DOC fluxes reaching aquifers. [ABSTRACT FROM AUTHOR]

Changes in agricultural practices related to environmental policies such as the European Water Framework Directive should lead to a decrease in pesticide contamination levels in rivers draining agricultural areas. However, there is still a need for biological tools to evaluate resulting ecological changes, namely to evaluate ecological recovery following the improvement of surface water chemical quality. Accordingly, the main purpose of this study was to assess the relevance of a pollution-induced community tolerance (PICT) approach in natural phototrophic biofilms to estimate microbial community recovery following a decrease in diuron contamination due to the ban of the use of this herbicide on vineyards. To this end, we performed a 3-year field study (2009–2011) in the Morcille River (France), located in the French Beaujolais wine region. This river was frequently contaminated by diuron (among other organic and inorganic pesticides), with increasing concentrations downstream. Following the ban on diuron, imposed in December 2008, a progressive decrease in diuron concentrations was observed in the Morcille River. While the mean annual tolerance levels measured at the low contaminated station remained relatively constant over years, a clear and significant decreasing trend was observed at the medium and high contaminated stations during the survey. This temporal evolution revealed a direct link between a change in agricultural practice due to the ban of diuron and an increase in the sensitivity of phototrophic biofilms to this herbicide. This finding brings further new evidence that PICT has great potential to detect microbial community recovery following chemical restoration due to changes in the agricultural use of pesticides. [ABSTRACT FROM AUTHOR]