Non-lethal sampling for stable isotope analysis of pike Esox lucius: how mucus, scale and fin tissue compare to muscle.

Stable isotope analysis (SIA) was used to examine the isotopic relationships between dorsal muscle and fin, scale and epidermal mucus in pike Esox lucius. δ13 C and δ15 N varied predictably within each tissue pairing, with conversion factors calculated for the surrogate tissues, enabling their application to the non-lethal sampling of E. lucius for SIA. This article is protected by copyright. All rights reserved

Carbon dioxide fluxes increase from day to night across European streams

Globally, inland waters emit over 2 Pg of carbon per year as carbon dioxide, of which the majority originates from streams and rivers. Despite the global significance of fluvial carbon dioxide emissions, little is known about their diel dynamics. Here we present a large-scale assessment of day- and night-time carbon dioxide fluxes at the water-air interface across 34 European streams. We directly measured fluxes four times between October 2016 and July 2017 using drifting chambers. Median fluxes are 1.4 and 2.1 mmol m−2 h−1 at midday and midnight, respectively, with night fluxes exceeding those during the day by 39%. We attribute diel carbon dioxide flux variability mainly to changes in the water partial pressure of carbon dioxide. However, no consistent drivers could be identified across sites. Our findings highlight widespread day-night changes in fluvial carbon dioxide fluxes and suggest that the time of day greatly influences measured carbon dioxide fluxes across European streams

Effective monitoring of freshwater fish

Freshwater ecosystems constitute only a small fraction of the planet’s water resources, yet support much of its diversity, with freshwater fish accounting for more species than birds, mammals, amphibians, or reptiles. Fresh waters are, however, particularly vulnerable to anthropogenic impacts, including habitat loss, climate and land use change, nutrient enrichment, and biological invasions. This environmental degradation, combined with unprecedented rates of biodiversity change, highlights the importance of robust and replicable programmes to monitor freshwater fish assemblages. Such monitoring programmes can have diverse aims, including confirming the presence of a single species (e.g. early detection of alien species), tracking changes in the abundance of threatened species, or documenting long-term temporal changes in entire communities. Irrespective of their motivation, monitoring programmes are only fit for purpose if they have clearly articulated aims and collect data that can meet those aims. This review, therefore, highlights the importance of identifying the key aims in monitoring programmes, and outlines the different methods of sampling freshwater fish that can be used to meet these aims. We emphasise that investigators must address issues around sampling design, statistical power, species’ detectability, taxonomy, and ethics in their monitoring programmes. Additionally, programmes must ensure that high-quality monitoring data are properly curated and deposited in repositories that will endure. Through fostering improved practice in freshwater fish monitoring, this review aims to help programmes improve understanding of the processes that shape the Earth's freshwater ecosystems, and help protect these systems in face of rapid environmental change

Les mesures nocturnes pour évaluer les flux de CO2 dans les cours d'eau : une étude internationale

International audienceGlobally, streams represent major CO2 emitters, accounting for approximately 70% of the total flux from inland waters. Hence, a proper understanding of carbon dioxide (CO2) uptake and emissions from streams is crucial for accurately estimating aquatic global carbon emissions. However, diurnal dynamics of these fluxes are still not comprehensively quantified, contributing to a high uncertainty in regional and global carbon budgets. Within the EuroRun project, the 1st Collaborative European Freshwater Science Project for Young Researchers, we aimed to assess spatial and seasonal variability of day- and night-time CO2 fluxes of 34 streams across 11 European countries. CO2 fluxes were measured with drifting flux chambers once per season at midday and midnight. The median CO2 fluxes during the day amounted to 1.4 µmol m-2 h-1 (IQR 0.5 to 3.1) and during the night to 2.1 µmol m-2 h-1 (IQR 0.95 to 3.75). The CO2 fluxes during night exceeded those during day by up to eight times. Interestingly, these differences occurred throughout all seasons and showed no latitudinal patterns. Our results highlight the importance of night-time fluxes to accurately assess CO2 fluxes from streams. As most studies are performed during the day, our survey indicates that global carbon budgets are currently underestimating the amount of CO2 released by streams