Feeding preferences of two detritivores related to size and metal content of leaves: the crustaceans Atyaephyra desmarestii (Millet) and Echinogammarus meridionalis (Pinkster)

Impacts of low concentrations of nanoplastics on leaf litter decomposition and food quality for detritivores in streams

In forested streams, leaf litter decomposition is a vital ecosystem process, governed primarily by aquatic hyphomycetes. These fungi are crucial mediators of nutrients and energy to invertebrates and higher trophic levels. Very little information is available on the impact of low concentrations of different sizes of nanoplastic particles (NPPs) on leaf litter decomposition and aquatic hyphomycetes communities. Besides, NPPs impact on leaf litter nutritional quality and invertebrate feeding behaviour is unknown. We conducted a microcosm assay with varying concentrations (0-25 μg L^-1) of small (100 nm; SNPPs) and large (1000 nm; LNPPs) plastic particles to assess their impact on leaf litter decomposition, sporulation rates and community structure of aquatic hyphomycetes. Furthermore, leaf litter was retrieved and fed to invertebrates to assess feeding rates. Our results indicated that leaf litter decomposition, fungal sporulation and abundance were significantly affected by NPPs concentrations and sizes. By contrast, leaf litter nutritional quality was impacted only by sizes. The NPPs, particularly SNPPs, augmented leaf litter polyunsaturated fatty acids (18-31%), consequently improving food quality; however, invertebrates' feeding rates were not impacted. Overall, our study provides novel insights on the risks posed by NPPs with pronounced impact at the basal trophic level.

Importance of exposure route in determining nanosilver impacts on a stream detrital processing chain

The commercial use and spread of silver nanoparticles (AgNPs) in freshwaters have greatly increased over the last decade. Both AgNPs and ionic silver (Ag⁺) released from nanoparticles are toxic to organisms and compromise ecosystem processes such as leaf litter decomposition. Yet little is known about how AgNPs affect multitrophic systems of interacting species. Furthermore, past work has focused on waterborne exposure with scarce attention given to effects mediated by the consumption of contaminated food. We assessed the importance of direct (via water) and indirect (via diet) AgNP exposure to a processing chain comprising leaf litter, fungi, a shredder (Gammarus pulex) and a collector (Habroleptoides confusa) in microcosms. Direct exposure to contaminated water for 15 days impaired microbial leaf decomposition by ∼50% and leaf-associated fungal biomass by ∼10%. Leaf consumption was reduced by ∼20% but only when G. pulex was exposed to silver via contaminated leaves. There was no effect on FPOM production. Ag ⁺ could impose oxidative stress on the shredders and collectors independent of exposure route, as indicated by increased catalase and glutathione S-transferase activities and decreased superoxide dismutase activity. The activity of a neuronal enzyme (cholinesterase) in collectors, but not shredders, also decreased by almost 50% when the animals were indirectly exposed to AgNP. Our results show that AgNPs and Ag⁺ may disrupt detrital processing chains through direct and indirect exposure routes, even at low concentrations. This highlights the importance of AgNP exposure pathways to interconnected stream biota and ecosystem processes for realistic assessments of risks to freshwater ecosystems.

Combined effect of copper sulfate and water temperature on key freshwater trophic levels - Approaching potential climatic change scenarios

This work relied on the use microcosms to evaluate the individual and the combined effects of different levels of copper sulfate (0.0, 0.013, 0.064 and 0.318mg Cu L^-1) - a fungicide commonly exceeding allowable thresholds in agricultural areas - and a range of water temperature increase scenarios (15, 20 and 25°C) on freshwater species belonging to different functional groups. Hence, the growth inhibition of primary producers (the microalgae Raphidocelis subcapitata and the macrophyte Lemna minor), as well as the survival and feeding behavior of a shredder species (the Trichoptera Schizopelex sp.) were evaluated. The results revealed that copper was toxic to primary producers growth, as well as shredders growth and survival, being the growth of L. minor particularly affected. Higher water temperatures had generally enhanced the growth of primary producers under non-contaminated (microalgae and macrophytes) or low-contaminated (macrophytes) conditions. Despite the tendency for a more pronounced toxicity of copper under increasing water temperatures, a significant interaction between the two factors was only observed for microalgae. Since the test organisms represent relevant functional groups for sustaining freshwater systems functions, the present results may raise some concerns on the impacts caused by possible future climate change scenarios in aquatic habitats chronically exposed to the frequent or intensive use of the fungicide copper sulfate.