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Intermittent rivers and ephemeral streams (IRES) may represent over half the global stream network, but their contribution to respiration and carbon dioxide (CO2) emissions is largely undetermined. In particular, little is known about the variability and drivers of respiration in IRES sediments upon rewetting, which could result in large pulses of CO2. We present a global study examining sediments from 200 dry IRES reaches spanning multiple biomes. Results from standardized assays show that mean respiration increased 32‐fold to 66‐fold upon sediment rewetting. Structural equation modeling indicates that this response was driven by sediment texture and organic matter quantity and quality, which, in turn, were influenced by climate, land use, and riparian plant cover. Our estimates suggest that respiration pulses resulting from rewetting of IRES sediments could contribute significantly to annual CO2emissions from the global stream network, with a single respiration pulse potentially increasing emission by 0.2–0.7%. As the spatial and temporal extent of IRES increases globally, our results highlight the importance of recognizing the influence of wetting‐drying cycles on respiration and CO2emissions in stream networks. Sediment respiration in intermittent rivers and ephemeral streams increases substantially in response to rewettingRespiration pulses are driven by sediment properties, which, in turn, are influenced by climate and catchment characteristicsEffects of wetting‐drying cycles on respiration and CO2emissions in stream networks need consideration in upscaling and modeling efforts

Perennial rivers and streams make a disproportionate contribution to global carbon (C) cycling. However, the contribution of intermittent rivers and ephemeral streams (IRES), which sometimes cease to flow and can dry completely, is largely ignored although they represent over half the global river network. Substantial amounts of terrestrial plant litter (TPL) accumulate in dry riverbeds and, upon rewetting, this material can undergo rapid microbial processing. We present the results of a global research collaboration that collected and analysed TPL from 212 dry riverbeds across major environmental gradients and climate zones. We assessed litter decomposability by quantifying the litter carbon-to-nitrogen ratio and oxygen (O2) consumption in standardized assays and estimated the potential short-term CO2emissions during rewetting events. Aridity, cover of riparian vegetation, channel width and dry-phase duration explained most variability in the quantity and decomposability of plant litter in IRES. Our estimates indicate that a single pulse of CO2emission upon litter rewetting contributes up to 10% of the daily CO2emission from perennial rivers and stream, particularly in temperate climates. This indicates that the contributions of IRES should be included in global C-cycling assessments. Rewetting of plant litter accumulated in dry riverbeds releases pulses of CO2, reveals a global analysis of intermittent rivers and ephemeral streams.

Bergmann’s rule predicts increasing body sizes at higher elevations. The elevational Rapoport’s rule predicts an increase of elevational range size with higher elevations. Both rules have often been related to effects of temperature. Larger bodies allow more efficient heat preservation at lower temperature, explaining Bergmann’s rule. Higher temperature variability may select for adaptations that allow increased range sizes, explaining Rapoport’s rule. The generality of both rules has been challenged and evidence towards explanatory mechanisms has been equivocal. We investigated temperature and its variability as explanations for Bergmann’s and Rapoport’s rule in moths along an elevation gradient in Switzerland. In particular, we tested for relationships between elevation, temperature and body size across almost 300 species of Macrolepidoptera along a gradient from 600 to 2400 m a.s.l. The gradient was resampled throughout the vegetation season, which allowed assessing temperature effects independently from elevation. We controlled analyses for covariate traits of moths and their phylogeny. We found a positive relationship between body size and elevation, but no link with temperature. Furthermore, there was no positive link between average elevation and elevational range, but there was between temperature variability and elevational range. We conclude that mechanisms other than temperature can lead to increasing body sizes with elevation (supporting Bergmann’s pattern, but not the mechanism). Contrary to that, data support the mechanism for Rapoport’s rule: high temperature variability is associated with large ranges. However, because temperature variability is not necessarily increasing with elevation, it may not always lead to the geographic pattern predicted.

Bergmann’s rule predicts increasing body sizes at higher elevations. The elevational Rapoport’s rule predicts an increase of elevational range size with higher elevations. Both rules have often been related to effects of temperature. Larger bodies allow more efficient heat preservation at lower temperature, explaining Bergmann’s rule. Higher temperature variability may select for adaptations that allow increased range sizes, explaining Rapoport’s rule. The generality of both rules has been challenged and evidence towards explanatory mechanisms has been equivocal. We investigated temperature and its variability as explanations for Bergmann’s and Rapoport’s rule in moths along an elevation gradient in Switzerland. In particular, we tested for relationships between elevation, temperature and body size across almost 300 species of Macrolepidoptera along a gradient from 600 to 2400 m a.s.l. The gradient was resampled throughout the vegetation season, which allowed assessing temperature effects independently from elevation. We controlled analyses for covariate traits of moths and their phylogeny. We found a positive relationship between body size and elevation, but no link with temperature. Furthermore, there was no positive link between average elevation and elevational range, but there was between temperature variability and elevational range. We conclude that mechanisms other than temperature can lead to increasing body sizes with elevation (supporting Bergmann’s pattern, but not the mechanism). Contrary to that, data support the mechanism for Rapoport’s rule: high temperature variability is associated with large ranges. However, because temperature variability is not necessarily increasing with elevation, it may not always lead to the geographic pattern predicted.

Se realizó una encuesta sobre el perfil de utilización y las limitaciones de la práctica de la anestesia regional en Chile.

In the version of this Article originally published, the affiliation for M. I. Arce was incorrect; it should have been: 5Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany. This has now been corrected in the online versions of the Article.

Background. In obese patients, reduced functional residual capacity exacerbated by supine position might decrease the effectiveness of pre-oxygenation and the tolerance to apnoea. The aim of this study was to compare the effect of body posture during pre-oxygenation, sitting or supine, on its effectiveness in obese patients. Methods. Forty obese patients (BMI ≥35 kg m−2) undergoing surgery with general anaesthesia were randomly assigned to one of two groups: Group 1 (sitting, n=20) or Group 2 (supine, n=20). In the predetermined body position, pre-oxygenation was achieved with eight deep breaths within 60 s and an oxygen flow of 10 litre min−1. After rapid sequence induction of anaesthesia in decubitus position, the trachea was intubated and the patient was left apneic and disconnected from the anaesthesia circuit until Spo2 decreased to 90%. The time taken for desaturation to 90% from the end of induction of anaesthesia was recorded. Arterial blood oxygen tension was measured before (baseline) and after pre-oxygenation. Values were compared with two-way anova and unpaired Student's t-test. Results. Oxygen and carbon dioxide tensions were similar between groups, both at baseline and after pre-oxygenation. However, the mean time to desaturation to 90% was significantly longer in the sitting group compared with the supine group [mean (sd): 214 (28) vs 162 (38) s, P<0.05]. Conclusions. Pre-oxygenation in sitting position significantly extends the tolerance to apnoea in obese patients when compared with the supine position.