Geometry and topology of estuary and braided river channel networks automatically extracted from topographic data

Automatic extraction of channel networks from topography in systems with multiple interconnected channels, like braided rivers and estuaries, remains a major challenge in hydrology and geomorphology. Representing channelized systems as networks provides a mathematical framework for analyzing transport and geomorphology. In this paper, we introduce a mathematically rigorous methodology and software for extracting channel network topology and geometry from digital elevation models (DEMs) and analyze such channel networks in estuaries and braided rivers. Channels are represented as network links, while channel confluences and bifurcations are represented as network nodes. We analyze and compare DEMs from the field and those generated by numerical modeling. We use a metric called the volume parameter that characterizes the volume of deposited material separating channels to quantify the volume of reworkable sediment deposited between links, which is a measure for the spatial scale associated with each network link. Scale asymmetry is observed in most links downstream of bifurcations, indicating geometric asymmetry and bifurcation stability. The length of links relative to system size scales with volume parameter value to the power of 0.24–0.35, while the number of links decreases and does not exhibit power law behavior. Link depth distributions indicate that the estuaries studied tend to organize around a deep main channel that exists at the largest scale while braided rivers have channel depths that are more evenly distributed across scales. The methods and results presented establish a benchmark for quantifying the topology and geometry of multichannel networks from DEMs with a new automatic extraction tool

Adjustment of metabolite composition in the haemolymph to seasonal variations in the land snail Helix pomatia.

International audienceIn temperate regions, land snails are subjected to subzero temperatures in winter and hot temperatures often associated to drought in summer. The response to these environmental factors is usually a state of inactivity, hibernation and aestivation, respectively, in a temperature and humidity buffered refuge, accompanied by physiological adjustments to resist cold or heat stress. We investigated how environmental factors in the microhabitat and body condition influence the metabolite composition of haemolymph of the endangered species Helix pomatia. We used UPLC and GC-MS techniques and analyzed annual biochemical variations in a multivariate model. Hibernation and activity months differed in metabolite composition. Snails used photoperiod as cue for seasonal climatic variations to initiate a physiological state and were also highly sensitive to temperature variations, therefore constantly adjusting their physiological processes. Galactose levels gave evidence for the persistence of metabolic activity with energy expenditure during hibernation and for high reproductive activity in June. Triglycerides accumulated prior to hibernation might act as cryoprotectants or energy reserves. During the last month of hibernation snails activated physiological processes related to arousal. During activity, protein metabolism was reflected by high amino acid level. An exceptional aestivation period was observed in April giving evidence for heat stress responses, like the protection of cells from dehydration by polyols and saccharides, the membrane stabilization by cholesterol and enhanced metabolism using the anaerobic succinic acid pathway to sustain costly stress responses. In conclusion, physiological adjustments to environmental variations in Helix pomatia involve water loss regulation, cryoprotectant or heatprotectant accumulation

Oxygen dependence of metabolism and cellular adaptation in vertebrate muscles: a review

The key roles the cardiovascular system play in the complex distribution of blood, and consequently oxygen, have been extensively studied in vertebrates. Numerous studies have also revealed the complex and varied ways in which tissues cope with compromised oxygen supply. The links between these two processes are the subject of much current research. This article aims to review how blood supply influences tissue oxygenation and affects metabolism, and how this might have played a role in the evolution of the complex muscle arrangements which characterise vertebrates. Muscle tissue is the greatest proportion of body mass in most vertebrates and undergoes dramatic alterations in metabolism and associated oxygen flux. Special attention is given to the myotome of fishes, in which the partitioning of the fibre types contrasts with the mosaic arrangement of tetrapods. This gives us the opportunity to study pure whole vascularised muscle blocks, rather than single fibres, and further explore the interrelationship between oxygen supply and tissue energetics.<br /