Hydrodynamics Alter the Tolerance of Autotrophic Biofilm Communities Toward Herbicides

Multiple stressors pose potential risk to aquatic ecosystems and are the main reasons for failing ecological quality standards. However, mechanisms how multiple stressors act on aquatic community structure and functioning are poorly understood. This is especially true for two important stressors types, hydrodynamic alterations and toxicants. Here we perform a mesocosm experiment in hydraulic flumes connected as a bypass to a natural stream to test the interactive effects of both factors on natural (inoculated from streams water) biofilms. Biofilms, i.e., the community of autotrophic and heterotrophic microorganisms and their extracellular polymeric substances (EPS) in association with substratum, are key players in stream functioning. We hypothesized (i) that the tolerance of biofilms toward toxicants (the herbicide Prometryn) decreases with increasing hydraulic stress. As EPS is known as an absorber of chemicals, we hypothesize (ii) that the EPS to cell ratio correlates with both hydraulic stress and herbicide tolerance. Tolerance values were derived from concentration-response assays. Both, the herbicide tolerance and the biovolume of the EPS significantly correlated with the turbulent kinetic energy (TKE), while the diversity of diatoms (the dominant group within the stream biofilms) increased with flow velocity. This indicates that the positive effect of TKE on community tolerance was mediated by turbulence-induced changes in the EPS biovolume. This conclusion was supported by a second experiment, showing decreasing effects of the herbicide to a diatom biofilm (Nitzschia palea) with increasing content of artificial EPS. We conclude that increasing hydrodynamic forces in streams result in an increasing tolerance of microbial communities toward chemical pollution by changes in EPS-mediated bioavailability of toxicants

Exposure pathways matter: Aquatic phototrophic communities respond differently to agricultural run-off exposed via sediment or water

1. Small shallow ponds are widespread but understudied water bodies in agricultural landscapes. Agricultural run-off (ARO) transports pesticides and nutrients into adjacent aquatic ecosystems where they occur dissolved in the water column or are bound to sediments. Consequently, aquatic communities are affected by ARO via different exposure pathways. We hypothesize that sediment-bound ARO mainly affects submerged rooted macrophytes, while phytoplankton and periphyton are more prone to ARO in water. These primary producers compete for resources resulting in a regime shift between alternative stable states of macrophyte or phytoplankton dominance. We hypothesize that warming increases nutrient release from sediments and thereby facilitates the occurrence of phytoplankton dominance. 2. Using a full-factorial microcosm design, we exposed aquatic primary producers to either sediment or water application of a mixture of common pesticides (terbuthylazine, pirimicarb, tebuconazole and copper) and nitrate at two concentrations and two temperatures (22°C and 26°C) for 4 weeks. Initial and final concentrations of pesticides and nitrate, final biomass of macrophytes, periphyton and phytoplankton, pesticide accumulation in macrophytes and changes in carbon, nitrogen and phosphorus content and selected exoenzyme activities in the sediment were measured. 3. We found lower final macrophyte biomass for both ARO treatments compared to controls, indicating a prevalence of negative effects by herbicides and competition for light with other phototrophs. In contrast, phytoplankton and periphyton biomass increased, but only when exposed to ARO via the water column, indicating a prevalence of positive effects by nutrient supply. Microbial carbon and nutrient cycling in sediments was not affected by ARO. Higher temperature mitigated ARO-related effects on macrophytes under sediment exposure. 4. Synthesis and application. ARO poses a strong risk of submerged macrophyte loss and establishment of turbid conditions with phytoplankton dominance in aquatic ecosystems. In conclusion, exposure pathways as well as indirect and interacting effects of multiple stressors need to be considered when designing appropriate mitigation measures. Under climate change, we suggest to prioritize local measures as buffer strips a reduced use of pesticides and fertilizers, and sediment removal as appropriate measures to protect these vulnerable but widespread aquatic systems, which are highly relevant for biodiversity in agricultural landscapes

Assessment of biomarkers in macrophytes exposed to individual and combined pollutants of agricultural run-off and climate change

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Impact of agricultural run-off and climate warming on shallow aquatic ecosystems – possible effects on a regime shift between aquatic primary producers

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Regime shifts in freshwater ecosystems exposed to multiple stressors by increasing temperature, fertilizers and pesticides (CLIMSHIFT)

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Impact combiné du ruissellement agricole et du réchauffement climatique sur les producteurs et consommateurs primaires dans les cours d'eau agricoles

International audienceLes masses d'eau peu profondes des zones agricoles sont affectées par le réchauffement climatique et les ruissellements contenant nitrate et pesticides. Ces facteurs de stress multiples sont au centre du projet ANR PRCI CLIMSHIFT (climshift.eu; [1-3]). L'étude présentée ici a été réalisée à l'aide des rivières artificielles de la plateforme expérimentale"LIECOSCOPE" du LIEC (Metz,France).Plusieurs hypothèses ont été émises :1-le Ruissellement Agricole (RA)composé d'un herbicide, un insecticide, un fongicide, du cuivre et du nitrate, va favoriser les algues filamenteuses par rapport aux macrophytes dans les cours d'eau agricoles,2-le RA va affecter négativement les consommateurs primaires, et 3-le réchauffement va impacter les macroinvertébrés sensibles à l'oxygénation de l'eau.Nous avons déployé un plan factoriel complet (réchauffement, RA dans 16 rivières artificielles (4 conditions x 4 réplicas) contenant des macrophytes émergés et submergés, du périphyton, de la litière d'aulne et différents macroinvertébrés (gammares, moules, escargots). Dans les premières semaines, le RA a induit un très grand développement des algues vertes filamenteusescouvranteset du périphyton ce qui a probablement contribué à la diminution rapide de la forte dose de nitrate introduite initialement. En fin d'expérience (semaine 6 à 7), les algues filamenteuses se sont effondrées, le phytoplancton a augmenté, probablement du fait d'une libération massive de phosphore provenant des algues filamenteuses en décomposition. Le réchauffement n'a eu que des effets mineurs sur les algues. Les macrophytes se sont développés tardivement avec une dominance de Potamogeton perfoliatus, profitant le plus du réchauffement. Le RA a affecté négativement son développement à un stade plus tardif, suggérant des effets indirects causés par la compétition avec les algues filamenteuses. Par ailleurs, le RA a eu un effet négatif important sur la reproduction des gammares et des escargots, probablement causé par les pesticides et conduisant à un contrôle réduit du périphyton. Le RA et le réchauffement ont fortement augmenté la mortalité des moules. Nos résultats reflètent les observations souvent faites au début du printemps dans beaucoup des cours d'eau naturels des zones agricoles, qui présentent d'abord des densités élevées d'algues filamenteuses, puis le développement du phytoplancton, entravant ainsi le développement des macrophytes immergés

A question of complexity: Investigating regime shifts caused by agricultural run-off and climate warming between aquatic plants and microalgae in micro- and mesocosms

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Biotic interactions shape the effect of combined stressors on shallow lake ecosystems: insight from microcosms experiments.

International audienceOrganisms living in aquatic ecosystems such as shallow lakes are generally affected by multiple anthropogenic stressors such as pesticides and nitrate input from agricultural runoff or increase in temperature due to global warming. While organisms are affected directly by the stressors, they are also affected indirectly through biotic interactions. The aim of our study was to determine the implication of biotic interactions in the effect of multiple stressors on shallow lake ecosystems. We performed a set of microcosm experiments in which organisms were exposed to a cocktail of organic pesticides, copper and nitrate to simulate agricultural runoff. Different scenario of pollutant input, as one or several pulses, were used. A 4°C warming was also used to simulate the impact of global warming. Two separate experiments were performed to determine the direct effect of on a primary producer community (submerged macrophytes, periphyton and phytoplankton) and on a primary consumer, the benthivorous snail Lymnaea stagnalis. In a third experiment, primary producers and three different primary consumers (Daphnia, mussel, snail) were exposed together to allow trophic interactions. When primary producers and consumers were exposed separately, agricultural runoff had a direct positive effect on phytoplankton and a strong negative effect on L. stagnalis. When exposed together, phytoplankton showed in contrast a significant decrease. Using structural equation modelling, we determined that this effect on phytoplankton was not a direct effect of the agricultural runoff but an indirect effect. Indeed, inhibition of L. stagnalis grazing on periphyton induced a positive effect of agricultural runoff on periphyton, while periphyton reduced the development of phytoplankton through competitive interactions. This demonstrates the importance of taking into account biotic interactions to understand the effect of multiples stressors on shallow lake ecosystems