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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.

Depuis 1986, le réservoir du Mirgenbach, mis en eau en 1985 reçoit les eaux échauffées issues de la centrale électronucléaire de Cattenom. Les conditions physicochimiques et la biomasse chlorophyllienne sont étudiées depuis cette date, les poissons étant échantillonnés selon un protocole standardisé depuis le couplage de la dernière tranche, en 1991. L'évolution thermique est décrite puis comparée à d'autres systèmes naturels ou échauffés. Dans le Mirgenbach, l'isolement des populations de poissons et le brassage de l'eau facilitent l'observation d'une incidence des rejets sur l'évolution du peuplement, l'abondance des populations et les traits biologiques individuels. Le seuil élevé de la température hivernale et son augmentation précoce déclenchent une reproduction et un développement individuels rapides. Le plan d'eau connaît un déclin régulier de la biomasse (chlorophylle et poissons) tandis que la contamination cuprique augmente. La diminution progressive pour plusieurs espèces, des effectifs, de la longévité, des longueurs maximales, de l'âge et de la taille à maturité sexuelle contribuent au déclin de la masse globale ou individuelle maximale. L'effet de ces contraintes s'observa d'abord sur les perches et gardons avant de s'étendre aux espèces thermophiles (brèmes communes et bordelières, perche soleil). D'après l'examen de la littérature, ces observations résulteraient de l'altération du développement sexuel et du défaut croissant en ressource trophique.

Radiative recombination (RR) into the K shell and L subshells of U92+ ions interacting with cooling electrons has been studied in an x-ray RR experiment at the electron cooler of the Experimental Storage Ring at GSI. The measured radiative recombination rate coefficients for electron-ion relative energies in the range 0-1000 meV demonstrate the importance of relativistic effects. The observed asymmetry of the measured À'-RR x-ray emission with respect to the cooling energy, i.e., zero average relative velocity ({vK\) = 0), are explained by fully relativistic RR calculations. With our new approach, we show that the study of the angular distribution of RR photons for different relative energies opens new perspectives for detailed understanding of the RR of ions with cooling electrons in cold magnetized plasma. [ABSTRACT FROM AUTHOR]

A detailed investigation of the Lα 1,2 (L3→ M4,5) and Lβ1 (L2→M4) x-ray satellite and hypersatellite structures in zirconium, molybdenum, and palladium atoms multiply ionized by impact with 278.6-MeV oxygen ions is reported. The x-ray spectra were measured with a high-resolution von Hamos bent crystal spectrometer. For the interpretation of the complex spectral features, relativistic multiconfiguration Dirac-Fock calculations were performed for all multivacancy configurations expected to contribute to the observed spectra. The data analysis clearly demonstrates that the spectra are dominated by structures originating from (L-1M-m N-1) satellite and (L-2M-m N-1) hypersatellite transitions corresponding to the radiative decay of the excited multivacancy configurations. The ionization probabilities of the L and M shell were determined from the data and compared with theoretical predictions from the geometrical model and the semiclassical approximation, using in the latter case both relativistic hydrogenlike and self-consistent Dirac-Hartree-Fock wave functions. The results support the independent electron picture of the multiple ionization. They also show the importance of using relativistic and self-consistent electronic wave functions for the L and M shells [ABSTRACT FROM AUTHOR]

The Mirgenbach reservoir was filled in 1985 and received since 1986 the overheated cooling waters of the electronuclear power plant of Cattenom. Physicochemical conditions and chlorophyll biomass were studied from that time. Fishes were sampled according to a standardized protocol since the coupling of the last unit in 1991. The thermal evolution was described then compared with the other natural or overheated systems. In the Mirgenbach, the isolation of fish populations with well mixed waters, facilitated the observation of incidence of the discharges on community evolution, abundance of populations and individual biological traits. The high threshold of the wintry temperature and its early rise set off the reproduction and causes a fast individual development. The reservoir knew a regular decline of the biomass (chlorophyll and fishes) whereas copper contamination increased. The progressive decrease for several species, of population size, longevity, maximal lengths, size and age of sexual maturity, contributed to the decline of the global or individual maximal mass. These constraints pressed at first on perch and roach and then on thermophilic species (bream and silver bream, pumpkinseed fish). According to literature, these constraints may be explained by a sexual developmental impairment and the increasing shortage of trophic resource. Depuis 1986, le r?servoir du Mirgenbach, mis en eau en 1985 re?oit les eaux ?chauff?es issues de la centrale ?lectronucl?aire de Cattenom. Les conditions physicochimiques et la biomasse chlorophyllienne sont ?tudi?es depuis cette date, les poissons ?tant ?chantillonn?s selon un protocole standardis? depuis le couplage de la derni?re tranche, en 1991. L'?volution thermique est d?crite puis compar?e ? d'autres syst?mes naturels ou ?chauff?s. Dans le Mirgenbach, l'isolement des populations de poissons et le brassage de l'eau facilitent l'observation d'une incidence des rejets sur l'?volution du peuplement, l'abondance des populations et les traits biologiques individuels. Le seuil ?lev? de la temp?rature hivernale et son augmentation pr?coce d?clenchent une reproduction et un d?veloppement individuels rapides. Le plan d'eau conna?t un d?clin r?gulier de la biomasse (chlorophylle et poissons) tandis que la contamination cuprique augmente. La diminution progressive pour plusieurs esp?ces, des effectifs, de la long?vit?, des longueurs maximales, de l'?ge et de la taille ? maturit? sexuelle contribuent au d?clin de la masse globale ou individuelle maximale. L'effet de ces contraintes s'observa d'abord sur les perches et gardons avant de s'?tendre aux esp?ces thermophiles (br?mes communes et bordeli?res, perche soleil). D'apr?s l'examen de la litt?rature, ces observations r?sulteraient de l'alt?ration du d?veloppement sexuel et du d?faut croissant en ressource trophique.

A new type of sediment trap, which overcomes a methodological gap in the study of sedimentation fluxes in shallow lentic systems, is described. The sedimentation rates measured in the field with these new traps were compared with those from other plate and cylindrical traps. As do other plate traps, the new traps allow the resuspension of deposited particles observed on bottom sediments. Furthermore, the new traps do not disturb particle sedimentation on the collecting area and allow to collect the net sedimentation rates in lentic systems.

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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.