The effect of sieve mesh size on the description of macroinvertebrate communities

Considerable time and effort is required to estimate the abundance and biomass of benthic macroinvertebrates, and often variable mesh size sieves are used to clean collected samples. We test whether the use of a mesh with a 1 mm pore size is adequate to obtain a valid description of a benthic macroinvertebrate community. Stream benthic surber samples were collected from 24 headwater streams. The densities, biotic indices and biological traits ofmacroinvertebrates retained in al mm mesh ('> 1 mm' fraction) were compared to the same descriptors for the of macroinvertebrates retained in a 0.5 mm mesh sieve ('total'). We found that, if only the large fraction (> 1 rnm) is examined, the cornmunity descriptors are affected. Nevertheless, the observed changes were proportional and predictable for all of the variables describing invertebrate communities. Statistical differenti­ation of the tested metrics between sites was similar for both mesh sizes. Depending on the aim of the study (e.g., environmental impact assessments), the use of a 1 mm mesh sieve would be sufficient in describing macroinvertebrate communities.Para las estimas de abundancia y biomasa, el procesado de las muestras en laboratorio de invertebrados bentónicos requiere un tiempo y esfuerzo considerable y generalmente implica el uso de tamices de diferente luz de malla para lavar la muestra. Nuestro trabajo trata de comprobar si es suficiente para una descripción válida de la comunidad el uso de un tamiz de malla de 1 mm de poro en el procesado de muestras. Con tal propósito se recogieron muestras bentónicas de río en 24 tramos de cabecera y se compararon densidades, índices bióticos y rasgos biológicos de los invertebrados que eran retenidos en un tamiz de luz de malla de 1 mm (fracción '>1 mm') con los obtenidos usando una de 0.5 mm ('total'). Nuestro estudio revela que el análisis exclusivo de la malla gruesa afecta a los descriptores de la comunidad. Sin embargo, los cambios observados son proporcionales para todas las variables y se pueden predecir bien con ecuaciones lineales. Por otro lado, la diferenciación estadística entre estaciones es similar usando ambos tipos de malla, lo que en definitiva sugiere que, dependiendo del objetivo del estudio (por ejemplo, evaluación de impacto ambiental), el examen de la fauna retenida en un tamiz de 1 mm de poro puede ser suficiente para la descripción de las comunidades de macroinvertebrados

Resource preference of two stream detritivores in the laboratory largely differs from the supply of detritus below eucalypt plantations

Detritivores are pivotal in forest streams as they process detritus and promote secondary production. Many studies have addressed the preference of freshwater detritivores towards materials of differing quality. Nevertheless, few studies compare the resource preferences in the laboratory with the availability in the field. In the present study, feeding preferences of two stream detritivores (the caddisfly Sericostoma pyrenaicum and the amphipod Echinogammarus tarragonensis), over three native leaf species (alder, chestnut and oak) and an exotic species (eucalypt) were quantified in the laboratory. Preference for eucalypt leaves conditioned for 1, 2 and 3 weeks was also described. We then contrasted the preference patterns in the laboratory feeding experiments with a 15-month-long benthic standing stock time series of a stream below a native deciduous forest and another below a eucalypt plantation. Both detritivores preferred consuming alder leaves and more conditioned eucalypt leaves, although the amphipod was more selective than the caddisfly. The consumption preference in the laboratory was unmatched by the availability in the field, especially under eucalypt plantations and for the amphipod. Our results show that the strength of the preference for high-quality resources can differ among different taxa, which can modulate their response to land use changes.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This study was funded by the Spanish Dirección General de Enseñanza Superior e Investigación Científica (Project DGESIC PB98-0151) and finanacial support in terms of a predoctoral Grant to A. Otermin from Basque Government

Short-term effects of a large dam decommissioning on biofilm structure and functioning

Aging dams and the rising efforts to restore stream ecosystems are increasing the number of dam decommissioning programs. Although dam decommissioning aims at improving in-stream habitat, biodiversity, and ecosystem functioning in the long term, it might also cause ecological impacts in the short term due to the mobilization of the sediment accumulated in the reservoir. Benthic biofilm in particular can be impaired by episodes of high turbidity and scouring. We conducted a multiple before-after/control-impact experiment to assess the effects of the drawdown of a large dam (42 m tall), a first step to its decommissioning, on biofilm structure (biomass and chlorophyll-a) and functioning (metabolism, nutrient uptake, and organic matter breakdown). Our results show that the reservoir drawdown reduced the autotrophic biofilm biomass (chlorophyll-a) downstream from the dam, which in turn lowered metabolism. However, nitrogen and phosphorus uptake by the biofilm was not affected. Organic matter breakdown was slower below the dam than in nearby undammed reaches before and during drawdown. All drawdown effects quickly disappeared and reaches downstream from the dam approached values found in nearby undammed reaches. Thus, our results indicate that the effects of reservoir drawdown on stream biofilms exist but may be small and disappear rapidly.This research was supported by the Fundación BBVA (064-17). The authors also acknowledge the financial support from the Basque Government (Consolidated Research Group: Stream Ecology 7-CA-18/10) predoctoral fellowships from the University of the Basque Country UPV/EHU (M.A.). The authors are especially grateful to the municipality of Donostia-San Sebastian and the staff of Artikutza for their continuous support during the experiment

Sea lamprey nests promote the diversity of benthic macroinvertebrate assemblages

The habitat heterogeneity hypothesis states that increased habitat heterogeneity promotes species diversity through increased availability of ecological niches. We aimed at describing the local-scale (i.e. nest and adjacent substrate) effects of nests of the sea lamprey (Petro- myzon marinus L.) as ecosystem engineer on macroinvertebrate assemblages. We hypoth- esized that increased streambed physical heterogeneity caused by sea lamprey spawning would modify invertebrate assemblages and specific biologic traits and promote reach-scale diversity. We sampled thirty lamprey nests of the Nive River, a river of the south western France with a length of 79.3 km and tributary of the Adour River, in three zones: the unmodi- fied riverbed (upstream) and zones corresponding to the nest: the area excavated (pit) and the downstream accumulation of pebbles and cobbles (mound). The increased habitat het- erogeneity created by lamprey was accompanied by biological heterogeneity with a reduced density of invertebrates (3777 ± 1332 individuals per m2 in upstream, 2649 ± 1386 individu- als per m2 in pit and 3833 ± 1052 individuals per m2 in mound) and number of taxa (23.5 ± 3.9 taxa for upstream, 18.6 ± 3.9 taxa in pit and 21.2 ± 4.5 taxa for mound) in the pit com- pared to other zones. However the overall taxa diversity in nest increased with 82 ± 14 taxa compared to the 69 ± 8 taxa estimated in upstream zone. Diversity indices were consistent with the previous results indicating a loss of α diversity in pit but a higher β diversity between a pit and a mound than between two upstream zones, especially considering Morisita index accounting for taxa abundance. Trait analysis showed high functional diversity within zones with a reduced proportion of collectors, scrapers, shredders, litter/mud preference and small invertebrates in mound, while the proportion of “slabs, blocks, stones and pebbles” prefer- ence and largest invertebrates increased. Pit presented the opposite trend, while upstream had globally intermediate trait proportions. Our results highlight important effects on species and functional diversity due to habitat heterogeneity created by a nest-building species, what can ultimately influence food webs and nutrient processes in river ecosystemsFunctioning was financed by Pole Gestion des Migrateurs Amphihalins dans leur Environnement (https://www6.rennes.inrae.fr/u3e/PRESENTATION/Organisation/Pole-MIAME).M.D.PhDs was financed by University of Pau and Pays de l'Adour (https://www.univ-pau.fr/fr/index.html) and UPV/EHU (https://www.ehu.eus/es/home).Field work used resources from the IE ECP Experimental Facility of the UMR Ecobiop (https://www6.bordeaux-aquitaine.inrae.fr/ie-ecp-ecobiop).The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Grant no. IT1471-22 from the Basque Government funded this study

Land use drives detritivore size structure and decomposition through shifts in resource quality and quantity

Land use change and nutrient pollution are two pervasive stressors that can modify carbon cycling, as they influence the inputs and the transformation of detritus. Understanding their impact on stream food webs and on diversity is particularly pressing, as streams are largely fuelled by detrital material received from the adjacent riparian environment. Here we assess how a switch from native deciduous forest to Eucalyptus plantations and nutrient enrichment alter the size distribution of stream detritivore communities and decomposition rates of detritus. As expected, more detritus resulted in higher size-independent, or overall, abundance (i.e. higher intercept of size spectra). This change in overall abundance was mainly driven by a change of the relative contribution of large taxa (Amphipoda and Trichoptera), which changed from an average relative abundance of 55.5 to 77.2 % between the sites compared for resource quantity differences in our study. In contrast, detritus quality modified the relative abundance of large vs small individuals (i.e. size spectra slopes), with shallow slopes of size spectra (proportionately more large individuals) associated with sites with nutrient-richer waters and steeper slopes (proportionately fewer large individuals) associated with sites draining Eucalyptus plantations. Decomposition rates of alder leaves due to macroinvertebrates increased from 0.0003 to 0.0142 when relative contribution of large organisms increased (modelled slopes of size spectra: −1.00 and − 0.33, respectively), highlighting the importance of large sized individuals for ecosystem functioning. Our study reveals that land use change and nutrient pollution can greatly impair the transfer of energy through the detrital or ‘brown’ food web by means of intra- and inter-specific responses to quality and quantity of the detritus. These responses enable linking land use change and nutrient pollution to ecosystem productivity and carbon cycling.This work was carried out with financial support from the EU Commission within the RivFunction project (contract EVK1-CT-2001-00088). AL acknowledges the financial support by the mobility program Ikermugikortasuna-2019 of the Basque Government

Tertiary wastewater treatment combined with high dilution rates fails to eliminate impacts on receiving stream invertebrate assemblages

he amount of wastewater processed in treatment plants is increasing following more strict environmental regulations. Treatment facilities are implementing upgrades to abate the concentrations of nutrients and contaminants and, thus, reduce their effects on receiving systems. Although many studies characterized the chemical composition and ecotoxicological effects of treated wastewater, its environmental effects are still poorly known, as receiving water bodies are often subjected to other stressors. We performed a field manipulative experiment to measure the response of invertebrate assemblages to one year of tertiary-treated wastewater discharges. We poured treated wastewater from an urban wastewater treatment plant into the lower-most 100-m of a previously unpolluted stream (3.6 % daily flow on average) while using another upstream reach as control. The positive correlation between effect sizes of abundance changes and IBMWP scores suggested assemblage modifications were following taxa tolerance to ecological impairment. The treatment increased the temporal variability of SPEARorganic, EPT relative abundance, and invertebrate functional redundancy. Our results show that even in this best-case scenario of tertiary-treated and highly diluted wastewater, the abundance of the most sensitive taxa in the aquatic assemblages is reduced. Further improvements in wastewater treatments seem necessary to ensure these effluents do not modify receiving water ecosystems.We greatly appreciate the kind and continuous support provided by all the Apraitz WWTP operators before and during fieldwork. We also thank many volunteers from the University of the Basque Country (UPV/EHU) and the University Rey Juan Carlos for their assistance with fieldwork and laboratory analyses. This research was part of the 603629-ENV-2013-6.2.1 (GLOBAQUA) project funded by the European Community's Seventh Framework Programme. We also acknowledge the financial support from the Basque Government (Consolidated Research Group: Stream Ecology 7-CA-18/10). Ioar de Guzmán was supported by a pre-doctoral fellowship from the Basque Government

Interactive effects of discharge reduction and fine sediments on stream biofilm metabolism

Discharge reduction, as caused by water diversion for hydropower, and fine sediments deposition, are prevalent stressors that may affect multiple ecosystem functions in streams. Periphytic biofilms play a key role in stream ecosystem functioning and are potentially affected by these stressors and their interaction. We experimentally assessed the interactive effects of discharge and fine sediments on biofilm metabolism in artificial indoor channels using a factorial split-plot design with two explanatory variables: water discharge (20, 39, 62, 141 and 174 cm3 s-1) and fine sediments (no sediment or 1100 mg L-1 of sediments). We incubated artificial tiles for 25 days in an unpolluted stream to allow biofilm colonization, and then placed them into the indoor channels for acclimation for 18 days. Subsequently, we manipulated water discharge and fine sediments and, after 17 days, we measured biofilm chlorophyll-a concentration and metabolism. Water velocity (range, 0.5 to 3.0 cm s-1) and sediment deposition (range, 6.1 to 16.6 mg cm-2) increased with discharge, the latter showing that the effect of increased inputs prevailed over sloughing. In the no-sediment treatments, discharge did not affect biofilm metabolism, but reduced chlorophyll-a. Sediments, probably as a consequence of nutrients released, promoted metabolism of biofilm and chlorophyll-a, which became independent of water discharge. Our results indicate that pulses of fine sediments can promote biofilm algal biomass and metabolism, but show interactive effects with discharge. Although discharge reduction can affect the abundance of basal resources for food webs, its complex interactions with fine sediments make it difficult to forecast the extent and direction of the changes.This research was funded by the Spanish Department of Economy, Industry and Competitiveness through the project GL2016-77487-R(DIVERSION),the European Social Fund, the Basque Government (Consolidated Research Group IT951-16) and the Biscay Province Council (61/2015). AVPC carried out this workt hanksto a pre-doctoral grant by the Spanish Department of Economy, Industry and Competitiveness (BES-2017-081959). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Temperature Sensitivity of Microbial Litter Decomposition in Freshwaters: Role of Leaf Litter Quality and Environmental Characteristics

Ongoing global warming is expected to alter temperature-dependent processes. Nevertheless, how co-occurring local drivers will influence temperature sensitivity of plant litter decomposition in lotic ecosystems remains uncertain. Here, we examined the temperature sensitivity of microbial-mediated decomposition, microbial respiration, fungal biomass and leaf nutrients of two plant species varying in litter quality. We also assessed whether the type of microbial community and stream water characteristics influence such responses to temperature. We incubated alder (Alnus glutinosa) and eucalypt (Eucalyptus globulus) litter discs in three streams differing in autumn–winter water temperature (range 4.6–8.9 °C). Simultaneously, in laboratory microcosms, litter discs microbially conditioned in these streams were incubated at 5, 10 and 15 °C with water from the conditioning stream and with a water control from an additional stream. Both in the field and in the laboratory, higher temperatures enhanced litter decomposition rates, except for eucalypt in the field. Leaf quality modified the response of decomposition to temperature in the field, with eucalypt leaf litter showing a lower increase, whereas it did not in the laboratory. The origin of microbial community only affected the decomposition rates in the laboratory, but it did not modify the response to temperature. Water quality only defined the phosphorus content of the leaf litter or the fungal biomass, but it did not modify the response to temperature. Our results suggest that the acceleration in decomposition by global warming will be shaped by local factors, mainly by leaf litter quality, in headwater streams.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This research was financed by the Ministry of Science and Innovation of the Spanish Government (CGL2010-22129-C04-01). S. Monroy was supported by a predoctoral grant by the Spanish Ministry of Economy and Competitiveness (BES-2012–060743) and a postdoctoral grant from the University of the Basque Country (DOKBERRI 2018 I)

Testing Wastewater Treatment Plant Effluent Effects on Microbial and Detritivore Performance: a Combined Field and Laboratory Experiment

The amount of pollutants and nutrients entering rivers via point sources is increasing along with human population and activity. Although wastewater treatment plants (WWTPs) greatly reduce pollutant loads into the environment, excess nutrient loading is a problem in many streams. Using a Community and Ecosystem Function (CEF) approach, we quantified the effects of WWTP effluent on the performance of microbes and detritivores associated to organic matter decomposition, a key ecosystem process. We measured organic matter breakdown rates, respiration rates and exo-enzymatic activities of aquatic microbes. We also measured food consumption and growth rates and RNA to body-mass ratios (RNA:BM) of a dominant amphipod Echinogammarus berilloni. We predicted responses to follow a subsidy-stress pattern and differences between treatments to increase over time. To examine temporal effects of effluent, we performed a laboratory microcosm experiment under a range of effluent concentrations (0, 20, 40, 60, 80 and 100%), taking samples over time (days 8, 15 and 30; 4 and 10 replicates to assess microbe and detritivore performance respectively, per treatment and day). This experiment was combined with a field in situ Before-After Control-Impact Paired (BACIP) experiment whereby we added WWTP effluent poured (10 L s(-1) during 20-40 min every 2 h) into a stream and collected microbial and detritivore samples at days 8 and 15 (5 and 15 replicates to assess the microbe and detritivore performance respectively, per period, reach and sampling day). Responses were clearer in the laboratory experiment, where the effluent caused a general subsidy response. Field measures did not show any significant response, probably because of the high dilution of the effluent in stream water (average of 1.6%). None of the measured variables in any of the experiments followed the predicted subsidy-stress response. Microbial breakdown, respiration rates, exo-enzymatic activities and invertebrate RNA:BM increased with effluent concentrations. Differences in microbial respiration and exo-enzymatic activities among effluent treatments increased with incubation time, whereas microbial breakdown rates and RNA:BM were consistent over time. At the end of the laboratory experiment, microbial respiration rates increased 156% and RN:BM 115% at 100% effluent concentration. Detritivore consumption and growth rates increased asymptotically, and both responses increased with by incubation time. Our results indicate that WWTP effluent stimulates microbial activities and alters detritivore performance, and stream water dilution may mitigate these effects.This work has been supported by the EU7th Framework Programme Funding under Grant agreement no. 603629-ENV-2013-6.2.1-Globaqua. We also acknowledge financial support in terms of pre doctoral grants from the University of the Basque Country UPV/EHU (L. Solagaistua) and the Basque Government (I. de Guzman, L. Mijangos). The manuscript benefited greatly from the valuable comments of John Kominoski and two anonymous referees. Also SGIker technical and human support (UPV/EHU, MICINN, GV/EJ, ESF) is gratefully acknowledged

Water diversion and pollution interactively shape freshwater food webs through bottom-up mechanisms

[EN] Water diversion and pollution are two pervasive stressors in river ecosystems that often co-occur. Individual effects of both stressors on basal resources available to stream communities have been described, with diversion reducing detritus standing stocks and pollution increasing biomass of primary producers. However, interactive effects of both stressors on the structure and trophic basis of food webs remain unknown. We hypothesized that the interaction between both stressors increases the contribution of the green pathway in stream food webs. Given the key role of the high-quality, but less abundant, primary producers, we also hypothesized an increase in food web complexity with larger trophic diversity in the presence of water diversion and pollution. To test these hypotheses, we selected four rivers in a range of pollution subject to similar water diversion schemes, and we compared food webs upstream and downstream of the diversion. We characterized food webs by means of stable isotope analysis. Both stressors directly changed the availability of basal resources, with water diversion affecting the brown food web by decreasing detritus stocks, and pollution enhancing the green food web by promoting biofilm production. The propagation of the effects at the base of the food web to higher trophic levels differed between stressors. Water diversion had little effect on the structure of food webs, but pollution increased food chain length and trophic diversity, and reduced trophic redundancy. The effects at higher trophic levels were exacerbated when combining both stressors, as the relative contribution of biofilm to the stock of basal resources increased even further. Overall, we conclude that moderate pollution increases food web complexity and that the interaction with water abstraction seems to amplify this effect. Our study shows the importance of assessing the interaction between stressors to create predictive tools for a proper management of ecosystems.Ministerio de Economia, Industria y Competitividad, Gobierno de Espana, Grant/Award Number: GL2016-77487-R; European Social Fund; Diputacion Foral de Bizkaia; Serra Hunter Fellow; Labex, Grant/Award Number: ANR-10-LABX-41; H2020 European Research Council; Eusko Jaurlaritza; Consejo Nacional de Investigaciones Cientificas y Tecnicas; FRAGCLIM Consolidator, Grant/Award Number: 72617