Variacions en el procés de la retenció de nutrients associades al desenvolupament algal en el riu de Perles (vall d'Alinyà, Alt Urgell)

La capacitat d?autodepuració s?ha estudiat en tres trams del riu de Perles (vall d?Alinyà, Alt Urgell), un riu d?ordre quart que drena una conca calcària on hi ha una aportació de nutrients d?origen antropogènic a la part alta de la conca i una disminució progressiva en la concentració de nutrients al llarg del riu. Els trams estudiats eren similars quant a hidrologia i geomorfologia, però diferents quant a concentracions de nutrients i comunitats biològiques. L?objectiu d?aquest treball ha estat contrastar la capacitat d?autodepuració segons les diferències en la composició de la comunitat biològica. Els resultats indiquen que comunitats amb major abundància d?algues filamentoses pròpies de trams amb concentracions moderades de nutrients tenen un poder autodepuratiu major que comunitats amb menor abundància d?algues filamentoses pròpies de trams pobres en nutrients.Self-depuration capacity was studied in three reaches of Perles river (Alinyà Valley, Alt Urgell), a fourth order stream that drains a calcareous watershed where there is a focussal nutrient input of antropic origin in the headwaters and a progressive decrease in nutrient concentration downstream. The studied reaches were similar in hidrology and geomorphology but showing differences in nutrient concentration and biologic communities. The objective of this study was to contrast the self-depuration capacity in relation to biologycal community differences. Results showed that communities with higher recovery values of filamentous algaes from reaches with a moderate nutrient concentration, had a higher self-depuration capacity than communities with smaller recovery values of filamentous algaes from poor nutrient reaches.La capacidad de autodepuración se ha estudiado en 3 tramos del río de Perles, (Valle de Alinyà, Alt Urgell), un río de cuarto orden que drena una cuenca calcárea en la que hay una aportación de nutrientes de origen antropogénico en la parte alta de la cuenca y una progresiva disminución en la concentración de nutrientes a lo largo del río. Los tramos estudiados eran similares en cuando a hidrología y geomorfología pero distintos en cuanto a concentración de nutrientes y comunidad biológica. El objetivo de este trabajo ha sido contrastar la capacidad de autodepuración en función de las diferencias en la composición de la comunidad biológica. Los resultados indican que comunidades con mayor abundancia de algas filamentosas propias de tramos con concentraciones moderadas de nutrientes tienen un poder de autodepuración mayor que comunidades con menor abundancia de algas filamentosas propias de tramos pobres en nutrientes

Thermal Heterogeneity in River Floodplains

River floodplains are composed of a shifting mosaic of aquatic and terrestrial habitats. Each habitat type exhibits distinct environmental and ecological properties. Temperature is a key property driving ecological processes and controlling the composition and distribution of biota. However, given the size and complexity of floodplains, ground surveys based on point measurements are spatially limited. In this study, we applied thermal infrared (IR) imagery to quantify surface temperature patterns at 12-15min intervals over 24h cycles in two near-natural Alpine river floodplains (Roseg, Tagliamento). Furthermore, vertical temperature distribution was measured at 3-5min intervals in unsaturated gravel sediment deposits (at 1cm distances; 0-29cm depth). Each habitat type exhibited a distinct thermal signature creating a complex thermal mosaic. The diel temperature pulse and maximum daily temperature were the main thermal components that differentiated habitat types. In both floodplains, exposed gravel sediments exhibited the highest diel pulse (up to 23°C), whereas in aquatic habitats the pulse was as low as 11°C (main channel in the Roseg floodplain). In the unsaturated gravel sediment deposits, the maximum diel kinetic temperature pulse ranged from 40.4°C (sediment surface) to 2.7°C (29cm sediment depth). Vertically, the spatiotemporal variation of temperature was about as high as horizontally across the entire floodplain surface. This study emphasized that remotely sensed thermal IR imagery provides a powerful non-invasive method to quantitatively assess thermal heterogeneity of complex aquatic and terrestrial ecosystems at a resolution required to understand ecosystem processes and the distribution of biot

Duration and frequency of non‐flow periods affect the abundance and diversity of stream meiofauna

Majdi N, Colls M, Weiss L, Acuña V, Sabater S, Traunspurger W. Duration and frequency of non‐flow periods affect the abundance and diversity of stream meiofauna. Freshwater Biology. 2020;65(11):1906-1922.Abstract Intermittent streams (IS) comprise a large proportion of the drainage network in many parts of the world. The non‐flow period of IS are known to impact stream biota because aquatic habitats dry out. However, less well understood are the relative effects of the temporal component of these drying events including their duration and frequency. Here, we characterised effects of temporal component of drying events on abundant and species‐rich meiofauna. The effects were assessed in 22 streams in the north‐eastern Iberian Peninsula. The duration and frequency of non‐flow events was characterized over a period of 250 days prior to sampling the sediment‐dwelling meiofauna in riffle zones that completely dried out. Overall, meiofauna abundances were amongst the highest ever reported for streambeds. Most meiofaunal taxa correlated positively with the frequency of drying events and correlated positively with the length of dry periods recorded shortly before sampling, suggesting that the community was able to recover quickly. Tardigrades were the only group to correlate positively with the longest dry periods, suggesting that they had the best resilience capabilities in streams that had experienced the longest droughts. On average, nematodes made up half of the meiofauna. We identified a total of 113 different nematode species. The nematode community was more taxonomically diverse in IS, with a smaller proportion of bacterivores and a higher proportion of fungivore species such as Filenchus vulgaris. Thereby resembling the trophic structure commonly observed in soil ecosystems. Our results show that most meiofauna were positively influenced by drying disturbance, that is being able to quickly recover after them. This suggests outstanding resilience capabilities, and points out meiofaunal organisms as key players for kick‐starting stream food webs and functions once flow returns

El Nino southern oscillation and seasonal drought drive riparian input dynamics in a Mediterranean stream

Inland waters substantially contribute to global carbon fluxes, and within them, low-order forested streams are important processors of allochthonous organic matter (OM) inputs. Leaf litter quantity and quality are expected to change in response to global change (e.g., climate change, land use change) but few long-term studies exist to better understand these shifts. The goal of this study was to assess the quantity and quality of OM sources to determine which global and local environmental factors control the dynamics of OM at the reach scale. The study was performed on a Mediterranean stream edged by a deciduous riparian forest over a 10-yr-time period. Riparian inputs, benthic and transported OM, and its carbon and nitrogen content were determined. The quantity of riparian inputs (912 +/- 56 g dry mass m(-2) yr(-1)) was comparable to temperate regions with deciduous riparian forests, but the Mediterranean climate determined the different dynamics of these inputs. El Nino Southern Oscillation was strongly related to the interannual variability in riparian inputs through changes in precipitation. The annual amount of inputs depended on previous cumulated nonflow periods, with successive nonflow periods causing a progressive decrease in riparian inputs. The distribution of inputs throughout the year followed either a unimodal or bimodal pattern according to the absence or presence of a nonflow period in summer. In addition, drought caused lower quality (higher carbon : nitrogen molar ratio) riparian inputs. Changes in the quantity and quality of OM were explained by both present and past local and global factors

Immediate and Legacy Effects of Urban Pollution on River Ecosystem Functioning: a Mesocosm Experiment

Effluents from urban wastewater treatment plants (WWTP) consist of complex mixtures of substances that can affect processes in the receiving ecosystems. Some of these substances (toxic contaminants) stress biological activity at all concentrations, while others (e.g., nutrients) subsidize it at low concentrations and stress it above a threshold, causing subsidy-stress responses. Thus, the overall effects of WWTP effluents depend mostly on their composition and the dilution capacity of the receiving water bodies. We assessed the immediate and legacy effects of WWTP effluents in artificial streams, where we measured the uptake of soluble reactive phosphorus (SRP) by the biofilm, biomass accrual, benthic metabolism and organic matter decomposition (OMD). In a first phase (32 d), the channels were subjected to a gradient of effluent contribution, from pure stream water to pure effluent. WWTP effluent affected the ecosystem processes we measured, although we found no clear subsidy-stress patterns except for biofilm biomass accrual. Instead, most of the processes were subsidized, although they showed complex and process-specific patterns. Benthic metabolism and OMD were subsidized without saturation, as they peaked at medium and high levels of pollution, respectively, but they never fell below control levels. SRP uptake was the only process that decreased with increasing effluent concentration. In a second phase of the experiment (23 d), all channels were kept on pure stream water to analyse the legacy effects of the effluent. For most of the processes, there were clear legacy effects, which followed either subsidy, stress, or subsidy-stress patterns. SRP uptake capacity was stressed with increasing pollution legacy, whereas algal accrual and benthic metabolism continued being subsidized. Conversely, biofilm biomass accrual and OMD showed no legacy effects. Overall, the WWTP effluent caused complex and process-specific responses in our experiment, mainly driven by the mixed contribution of subsidizers and stressors. These results help improving our understanding of the effects of urban pollution on stream ecosystem functioning. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.This research was supported by the European Union 7th Framework Programme (GLOBAQUA; 603629-ENV-2013-6.2.1). Authors also acknowledge the financial support from the University of the Basque Country (pre-doctoral fellowship to O. Pereda), the Basque Government (Consolidated Research Group: Stream Ecology 7-CA-18/10), and the Economy and Knowledge Department of the Catalan Government (Consolidated Research Group: ICRA-ENV 2017 SGR 1124). Authors are also especially grateful to Maria Casellas, Carme Font, Carmen Gutiérrez, Ferran Romero and Laia Sabater-Liesa for their assistance during the laboratory experiments

Impact and mitigation of global change on freshwater-related ecosystem services in Southern Europe

Global change is severely impacting the biosphere that, through ecosystem services, sustains human well-being. Such impacts are expected to increase unless mitigation management actions are implemented. Despite the call from the scientific and political arenas for their implementation, few studies assess the effectiveness of actions on freshwater-related services. Here, by modeling water provisioning, water purification and erosion control under current and future conditions, we assess future trends of service provision with and without mitigation policies. In particular, two different storylines combine multiple climate, land use/land cover and agricultural management scenarios, and represent a pro-efficiency business as usual (myopic storyline) and a future that considers social and environmental sustainability (sustainable storyline). The mentioned services are modeled for the horizon 2050 and in three South European river basins: Ebro, Adige and Sava, which encompass the wide socio-environmental diversity of the region. Our results indicate that Mediterranean basins (Ebro) are extremely vulnerable to global change respect Alpine (Adige) or Continental (Sava) basins, as the Ebro might experience a decrease in water availability up to 40%, whereas the decrease is of only 2–4% in the Adige or negligible in the Sava. However, Mediterranean basins are also more sensitive to the implementation of mitigation actions, which would compensate the drop in water provisioning. Results also indicate that the regulating services of water purification and erosion control will gain more relevance in the future, as both services increased between 4 and 20% in both global change scenarios as a result of the expansion of agricultural and urban areas. Overall, the impact of global change is diverse among services and across river basins in Southern Europe, with the Mediterranean basins as the most vulnerable and the Continental as the least. The implementation of mitigation actions can compensate the impact and therefore deserves full political attention

Effects Of Human-Driven Water Stress on River Ecosystems: a Meta-Analysis

Human appropriation of water resources may induce water stress in freshwater ecosystems when ecosystem needs are not met. Intensive abstraction and regulation cause river ecosystems to shift towards non-natural flow regimes, which might have implications for their water quality, biological structure and functioning. We performed a meta-analysis of published studies to assess the potential effects of water stress on nutrients, microcontaminants, biological communities (bacteria, algae, invertebrates and fish), and ecosystem functions (organic matter breakdown, gross primary production and respiration). Despite the different nature of the flow regime changes, our meta-analysis showed significant effects of human-driven water stress, such as significant increases in algal biomass and metabolism and reduced invertebrate richness, abundance and density and organic matter decomposition. Water stress also significantly decreased phosphate concentration and increased the concentration of pharmaceutical compounds. The magnitude of significant effects was dependent on climate, rainfall regime, period of the year, river size and type of water stress. Among the different causes of water stress, flow regulation by dams produced the strongest effects, followed by water abstraction and channelization.This project was funded by the European Commission under the grant No. 603629 - project GLOBAQUA. VF acknowledges financial support from the Portuguese Foundation for Science and Technology (FCT) through UID/MAR/04292/2013 and IF/00129/2014. The authors acknowledge the support from the Economy and Knowledge Department of the Catalan Government through the Consolidated Research Group (ICRA-ENV 2017 SGR 1124)

Flow regulation increases food-chain length through omnivory mechanisms in a Mediterranean river network

[EN] Dams fragment river systems worldwide, and Mediterranean-climate rivers, characterised by highly seasonal hydrographs and adapted biotas, are particularly impacted by flow regulation. Whereas the effects of flow regulation on hydrology, sediment transport and biodiversity have long been examined, responses at the food-web level remain understudied. Environmental variation is a key control of food-web structure. Thus, we predicted that flow regulation would impact food-chain length (FCL) via changes in the flow variation regime, and we tested this prediction in a set of flow unregulated to completely regulated reaches in a Mediterranean river basin. In each reach, we characterised flow variation, together with two other putative controls of FCL (productivity and habitat size). We combined community data with carbon and nitrogen stable isotopes to estimate food-chain length, and Bayesian mixing models allowed estimates of dietary proportions of consumers. Flow variation was paramount in controlling FCL in the studied river network, and this same control largely explained the degree of omnivory among top predators. Thus, omnivory mechanisms were the main proximate structural mechanism allowing shifts in food-web structure and linking disturbance regimes to FCL. Our results suggest that flow regulation in Mediterranean rivers may impact food-web structure even when no significant changes in community composition are observed. If highly variable Mediterranean streams become increasingly affected by flow regulation, the resulting more stable conditions could enhance intraguild predation and thus lengthen riverine food chains.We thank Roberto Merciai, Jose Andres Lopez and Joan Font for their help in the field, Lina Ramirez-Solano and Emili Garcia-Berthou for their help with analyses and Marc Montenegro for the illustrations in Fig. 1. The Sabo Lab at Arizona State University and anonymous reviewers provided suggestions that improved the quality of the article. This study was funded by the Spanish Ministry of Economy and Competitiveness through the SCARCE project (CSD2009-00065). Authors acknowledge the support from the Catalan Government through the Consolidated Research Groups 'Fluvial Dynamics Research Group (2014 SGR 645)' and the 'Catalan Institute for Water Research (2014 SGR 291)'.Ruhí, A.; Muñoz, I.; Tornés, E.; Batalla, R.; Vericat, D.; Ponsati, L.; Acuña, V.... (2016). Flow regulation increases food-chain length through omnivory mechanisms in a Mediterranean river network. Freshwater Biology. 61(9):1536-1549. https://doi.org/10.1111/fwb.12794S1536154961

Aquatic macroinvertebrates under stress: bioaccumulation of emerging contaminants and metabolomics implications

The current knowledge on bioaccumulation of emerging contaminants (ECs) in aquatic invertebrates exposed to the realistic environmental concentrations is limited. Even less is known about the effects of chemical pollution exposure on the metabolome of aquatic invertebrates. We conducted an in situ translocation experiment with passive filter-feeding caddisfly larvae (Hydropsyche sp.) in an effluent-influenced river in order to i) unravel the bioaccumulation (and recovery) dynamics of ECs in aquatic invertebrates, and ii) test whether exposure to environmentally realistic concentrations of ECs will translate into metabolic profile changes in the insects. The experiment was carried out at two sites, upstream and downstream of the discharge of an urban wastewater treatment plant effluent. The translocated animals were collected at 2-week intervals for 46 days. Both pharmaceuticals and endocrine disrupting compounds (EDCs) were detected in water (62 and 7 compounds, respectively), whereas in Hydropsyche tissues 5 EDCs accumulated. Overall, specimens from the upstream site translocated to the impacted site reached higher ECs concentrations in their tissues, as a reflection of the contaminants’ water concentrations. However, bioaccumulation was a temporary process susceptible to change under lower contaminant concentrations. Non-targeted metabolite profiling detected fine metabolic changes in translocated Hydropsyche larvae. Both translocations equally induced stress, but it was higher in animals translocated to the impacted site

Does the severity of non-flow period influence ecosystem structure and function of temporary streams? A mesocosm study

Global change is dramatically altering flow regimes worldwide. Among the most important consequences are the transition of many permanent waterways to temporary waterways, the increase in duration and frequency of non‐flow periods of temporary streams, and the increase in the severity (i.e. irradiance, temperature and humidity) of the non‐flow period. Nowadays, there is a lack of knowledge on how changes in duration, frequency and severity of the non‐flow period will reflect on biodiversity and biogeochemical changes in temporary streams. We designed a manipulative experiment using artificial streams to evaluate the effects of severity of the non‐flow period on stream biofilms. Sixteen artificial streams were assigned to four treatments: continuous flow, continuous intermittency and intermittency with and without rain events. Effects were assessed on selected features of stream biofilm structure (i.e. bacterial density and basal fluorescence) and function (photosynthetic efficiency and enzymatic activities), as well as CO2 emissions and dissolved organic matter quantity and quality from water column and sediments. The occurrence of rain events during the non‐flow period enhanced organic carbon processing and CO2 emissions to the atmosphere, reducing the sediment reservoir of exportable organic carbon and therefore reducing the dissolved organic carbon exports from streambeds at flow resumption. Given the ongoing reducing trends in the frequency of rain events in semi‐arid and arid regions, we expect temporary streams to process and emit less and to export more carbon to downstream systems