Recognition of elevated concentrations of aciniform soot in Cretaceous-Paleogene (K-P) boundary sediments worldwide led to the hypothesis that global-scale forest wildfi res could have been generated by the K-P boundary bolide impact and might have contributed directly to the extinction event. The wildfi res are estimated to have injected 10 13 t of CO 2 into the atmosphere, resulting in an interval of greenhouse warming. Yet minimal amounts of charred plant remains and abundant noncharred material occur in various K-P boundary locations across North America. This refutes the inference that wildfi res occurred on a global scale, and requires an alternative explanation for the aciniform soot. Here we describe signifi cant concentrations of carbon cenospheres in K-P boundary sediments from New Zealand, Denmark, and Canada. Carbon cenospheres are thought to derive solely from incomplete combustion of pulverized coal or fuel-oil droplets, which suggests that the impact may have combusted organic-rich target crust. The Chicxulub impact crater is located adjacent to the Cantarell oil reservoir, one of the most productive oil fi elds on Earth. This indicates that abundance of organic carbon in the Chicxulub target crust was likely to have been above global mean values. But even if we discount Chicxulub's organic-rich locality, the global mean crustal abundance for fossil organic matter is more than adequate to account for observed concentrations of both carbon cenospheres and aciniform soot, therefore making the global wildfi re hypothesis unnecessary.

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Many prey fishes rely on damage-released chemical alarm cues to detect and avoid predators. The ability to use these cues has been shown to confer considerable survival benefits to individuals. While several laboratory studies and a single field study have demonstrated that an ambient pH of 6.0 impairs fishes in their ability to detect these alarm cues, no study had yet compared the response to alarm cue exposures across populations residing in multiple streams of a different acidity level. In our study, we conducted live behavioural observations in five nursery streams, ranging in pH from 5.71 to 7.49 on two age classes (young of the year and parr) of wild juvenile Atlantic salmon (Salmo salar). We aimed to assess if the detection of these chemical alarm cues was constantly dependant on the ambient pH or if variations in the detection occurred among populations of the different streams regardless of the ambient acidity level. Our results demonstrated that salmon present in any acidic stream did not respond to alarm cues, while those in neutral streams exhibited typical alarm responses.Résumé : Plusieurs poissons proies utilisent les signaux d'alerte chimiques libérés par les blessures pour détecter et éviter les prédateurs. Il a été démontré que la capacité d'utiliser ces signaux procure aux individus des bénéfices significatifs de survie. Bien que plusieurs études de laboratoire et une seule étude de terrain aient prouvé qu'un pH ambiant de 6,0 compromet la capacité des poissons à percevoir ces signaux d'alerte, aucune recherche n'a encore comparé les réactions à la présence des signaux d'alerte dans une gamme de populations habitant des cours d'eau avec des niveaux différents d'acidité. Dans notre travail, nous avons mené des observations comportementales en nature dans cinq cours d'eau d'élevage dont les pH variaient de 5,71 à 7,49 chez deux classes d'âge (jeunes de l'année et tacons) de jeunes saumons atlantiques (Salmo salar) sauvages. Nous tentons de déterminer si la perception de ces signaux chimiques d'alerte dépend à tout coup du pH ambiant ou s'il existe des variations entre les populations des différents cours d'eau indépendantes des niveaux ambiants d'acidité. Nos résultats démontrent que tous les saumons qui habitent les cours d'eau acides ne réagissent pas aux signaux d'alerte, alors que ceux des cours d'eau neutres montrent des réactions typiques d'alerte.[Traduit par la Rédaction] Leduc et al. 2363

Large-scale wetland restoration often focuses on repairing the hydrologic connections degraded by anthropogenic modifications. Of these hydrologic connections, groundwater discharge is an important target, as these surface water ecosystem control points are important for thermal stability, among other ecosystem services. However, evaluating the effectiveness of the restoration activities on establishing groundwater discharge connection is often difficult over large areas and inaccessible terrain. Unoccupied aircraft systems (UAS) are now routinely used for collecting aerial imagery and creating digital surface models (DSM). Lightweight thermal infrared (TIR) sensors provide another payload option for generation of sub-meter-resolution aerial TIR orthophotos. This technology allows for the rapid and safe survey of groundwater discharge areas. Aerial TIR water-surface data were collected in March 2019 at Tidmarsh Farms, a former commercial cranberry peatland located in coastal Massachusetts, USA (41 • 54 17" N 70 • 34 17" W), where stream and wetland restoration actions were completed in 2016. Here, we present a 0.4 km 2 georeferenced, temperature-calibrated TIR orthophoto of the area. The image represents a mosaic of nearly 900 TIR images captured by UAS in a single morning with a total flight time of 36 min and is supported by a DSM derived from UAS-visible imagery. The survey was conducted in winter to maximize temperature contrast between relatively warm groundwater and colder ambient surface environment; lower-density groundwater rises above cool surface waters and thus can be imaged by a UAS. The resulting TIR orthomosaic shows fine detail of seepage distribution and downstream influence along the several restored channel forms, which was an objective of the ecological restoration design. The restored stream channel has increased connectivity to peatland groundwater discharge, reducing the ecosystem thermal stressors. Such aerial techniques can be used to guide ecological restoration design and assess post-restoration outcomes, especially in settings where ecosystem structure and function is governed by groundwater and surface water interaction.(DSM) of surface water-related features [2][3][4]. Lightweight TIR sensors provide another remotely sensed data type that can be used to generate high-resolution (<1 m) TIR orthophotos (e.g., [5]). However, the use of TIR-equipped UAS is relatively novel, only recently finding environmental and hydrological applications [1,[5][6][7][8][9][10]. Examples include environmental monitoring of natural geothermal systems [5] and distinguishing sewer and stormflow discharges from groundwater based on characteristic temperatures [9]. In engineered peatlands, UAS TIR was used to guide water isotopic sampling for a similar goal of parsing groundwater discharge endmembers [10].Recently, there has been a movement to better incorporate ecological services and functions into stream and wetland restoration projects [11]. Hydrological process-based wetland restoration requires understa...

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Recent studies with cyprinid and characin (superorder Ostariophysi) fishes suggest that purine-N-oxides function as chemical alarm cues (alarm pheromones) and that the nitrogen oxide functional group acts as the chief molecular trigger. To further test the hypothesis that the nitrogen-oxide functional group is evolutionarily conserved as an active component of the Ostariophysan alarm pheromone system, we exposed juvenile channel catfish (Ictalurus punctatus, Siluriformes) to conspecific skin extract, hypoxanthine-3-N-oxide (the putative alarm pheromone) and a suite of structurally and functionally similar compounds. Conspecific skin extract and hypoxanthine-3-N-oxide elicited significant increases in species typical antipredator behaviors. A structurally dissimilar compound possessing a nitrogen oxide functional group (pyridine-N-oxide) elicited a significant, but less intense alarm response. Compounds lacking a nitrogen oxide functional group were not significantly different from control stimuli. In addition, two non-Ostariophysan species known to possess chemical alarm cues (convict cichlids, Acrchocentrus nigrofasciatus, Cichlidae, Acanthopterygii and rainbow trout, Oncorhynchus mykiss, Salmonidae, Protacanthopterygii) did not show any increase in antipredator behavior in response to hypoxanthine-3-N-oxide. These data demonstrate the conservation of chemical alarm cues within at least three orders of the superorder Ostariophysi.

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