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Streams generally are affected by multiple stressors acting at different timescales. Periphyton, often the most important primary producer in these ecosystems, may respond to short-term impacts as well as to different long-term environmental conditions with potentially various changes in community structure. Here, we experimentally investigated the effects of sudden flow pulses on periphyton communities as a way to mimic extreme precipitation events in lowland streams that are predicted to occur more often with climate change in some regions. Using outdoor flumes, we allowed periphyton to colonise nutrient-diffusion substrates under two light conditions (50% shade and fully open) and nutrient availabilities (control, with access only to stream nutrients, and N–P-enriched) along a gradient in baseflows (0.43 to 2.17 L/s). After one month, we exposed the communities to a flow pulse (two-fold peak flow increase to simulate conditions of a potentially high disturbance) and analysed the responses of biomass and taxonomic composition. Flow pulse promoted periphyton growth in the lowest range of the baseflow but led to biomass reduction in the highest range. Light was the second major driver of biomass accrual, whereas nutrient enrichment had a strong effect on community composition both before and after the pulse (i.e., diatom dominance vs. green algae dominance in scenarios without and with enrichment, respectively). In all treatments, the flow pulse promoted a higher taxonomic richness, suggesting a partial reset of the succession of the periphyton communities. However, independent of flow and resources, periphyton communities showed low ecological resistance against the pulse with changes in chlorophyll a, biovolume and taxonomic richness to the pulse. We demonstrated that the effects of pulses on periphyton are similar in terms of biomass but varied strongly regarding composition depending on their initial structure, which is in turn mediated by the baseflow normally experienced by the systems, and on light and nutrient availability. Our results highlight the importance of testing multiple stressors, such as an increase in extreme events, under a wide range of environmental conditions (i.e., flow regime, trophic state, light availability). This approach allows us to detect potential interaction effects and non-linear responses, and highlights that the environmental settings ultimately determine the net effects of flow pulses on community structure and probably also on several important ecosystem processes.

Ponds occupy a large share of standing water worldwide and play an important role in providing various ecosystem services. There are concerted efforts of the European Union either to create new ponds, or to restore and preserve existing ponds as nature-based solutions to provide benefits to ecosystem and human well-being. As part of the EU PONDERFUL project, selected pondscapes (i.e. landscapes of ponds) in eight different countries – hereafter “demo-sites”, are studied to comprehensively understand their characteristics and their efficiency to provide ecosystem services. In addition, the needs and knowledge of stakeholders who own, work, research, or benefit from the pondscapes are also important, because of their capabilities to create, manage and develop the pondscapes. Therefore, we established connection with stakeholders to study their preferences and visions on the pondscapes. Using the analytic hierarchy process, this study shows that in general stakeholders in the European and Turkish demo-sites prefer environmental benefits to economic benefits, while stakeholders in the Uruguayan demo-sites rank the economic benefits higher. More specifically, in the European and Turkish demo-sites, the biodiversity benefits, i.e. life-cycle maintenance, habitat and gene pool protection, receive the highest ranking among all groups. On the other hand, stakeholders at the Uruguayan demo-sites rank provisioning benefits as the most important, because many ponds in Uruguayan demo-sites are being used for agricultural purposes. Understanding those preferences helps policy makers to address the needs of stakeholders more correctly, when considering any action or policy for the pondscapes.

To investigate the potential long-term consequences of environmental warming in subtropical systems, we compare the trophic structure of shallow lakes in tropical and subtropical regions. In total, 25 meso-eutrophic lakes with piscivorous fish were sampled during summer along a latitudinal gradient in South America. The fish catch per unit of effort and the omnivorous fish to zooplankton biomass ratios were significantly lower in the tropical lakes. Despite the lower fish biomass, no significant difference was found in zooplankton or phytoplankton communities or in the zooplankton to phytoplankton biomass ratio between the two sets of lakes. Nevertheless, regression models based on the combined dataset show higher cyanobacteria and total phytoplankton biomass at lower zooplankton to phytoplankton biomass ratio and higher omnivorous fish to zooplankton biomass ratio. Cyanobacteria biomass was dominated by non bloom-forming taxa and was inversely related to the biomass of calanoid copepods suggesting that these herbivores may play an important role in controlling edible cyanobacteria in warm shallow lakes. Overall, our results, however, suggest that warming will have relatively minor impacts on the pelagic trophic structure of shallow subtropical lakes supporting the idea of weaker trophic cascades in warm (sub)tropical lakes in comparison to temperate ones.

Body size plays a key role in the functioning of communities and ecosystems. However, this ecological trait is commonly under strong selection pressure by environmental drivers, such as temperature, nutrients, predation, and food quality. Understanding how environmental factors interact to shape the body size structure of communities is, therefore, of fundamental and applied interest. Using a unique database from 12 Neotropical lakes, we quantified the community-weighted mean trait (CWM) of zooplankton body size. We investigated how temperature, total phosphorus, abundance of predators (planktivorous fish) and food availability (abundance of edible and inedible algae) affect CWM of zooplankton body size. We also analyzed the interactions among these environmental predictors, and their cascading effects on zooplankton body size. We found that planktivorous fish, inedible algae, and edible algae had strong direct impacts on CWM of zooplankton body size. In particular, planktivorous fish and inedible algae decreased the CWM of body size, whereas edible algae increased it. Temperature and total phosphorus indirectly affected CWM of body size by increasing the abundance of planktivorous fish and inedible algae, and decreasing the abundance of edible algae. Our findings illustrate that environmental factors act in combination and affect zooplankton body size through multiple pathways. Therefore, focusing on the interaction between environmental predictors rather than just their isolated effects may provide a more mechanistic understanding of how environmental changes drive the body size structure of biotic communities.

Climate-induced changes in precipitation and land-use intensification affect the discharge of streams worldwide, which, together with eutrophication and loss of riparian canopy, can affect periphyton biomass and composition, and therefore, ultimately the stream functioning. We investigated the responses of periphyton biomass and life-forms (i.e., high profile, low profile and motile) to these changes applying an experimental approach by modulating nutrients (nutrient diffusion substrates enriched with 0.5 M NH4NO3 + 0.031 M KH2PO4 and without nutrient enrichment) and light availability (50% shade and full light) along a gradient in discharge ranging from 0.46 to 3.89 L/s (0.7 to 6.5 cm/s) in twelve large-sized (12- m long) outdoor flumes resembling lowland streams. We also analysed the potential effects of other environmental variables including macroinvertebrates on the responses of periphyton to discharge, nutrients, and light. Light and nutrient availability drastically affected periphyton biomass and composition responses to discharge. Periphyton biomass decreased with increasing discharge when shaded but this did not happen when exposed to full light. Under full light conditions, nutrient enrichment mediated an increase in the periphyton biomass with increasing discharge, possibly reflecting an increased metabolism, but this did not happen under non-enriched conditions. Enrichment further affected the compositional responses of periphyton to discharge, with an increase in the biomass of motile, fast growing, small-sized flagellated at low discharge conditions, and mitigating a loss of high profile periphyton under higher discharges. Light did not affect periphyton composition, and the abundance or feeding-group composition of the macroinvertebrates did not affect biomass or composition of the periphyton either. Our results suggest that nutrient enrichment and light play an important synergistic role in the responses of the periphyton biomass and composition to discharge and emphasize the relevance of riparian canopy conservation and eutrophication control to avoid periphyton growth under increased discharge scenarios in small lowland streams. (C) 2021 Published by Elsevier B.V.