Hydrologische Eigenschaften typischer Waldhumusformen unter Gemeiner Kiefer im Nordostsächsischen Tiefland: Wasserspeicherung - Hydrophobie - Versickerung

Labor- und Felduntersuchungen zum Infiltrationsverhalten des Auflagehumus eines bestockungstypischen Reinbestandes aus Gemeiner Kiefer erlauben eine nähere Kennzeichnung seiner hydrologischen Funktionen. Während in der Vegetationsperiode 2014 eine mehrmalige Wiederbefeuchtung des Auflagehumus und Zwischenspeicherung auftritt, bleibt dieser im niederschlagsreicheren Folgejahr fast über die gesamte Vegetationsperiode trocken. Hier verzögert eine im Frühsommer induzierte Hydrophobie die Wiederbefeuchtung. Selbst nach Starkniederschlägen findet bis in den Winter keine nennenswerte Wasserspeicherung mehr statt. Gleichwohl wird die Humusauflage wegen ihres sehr hohen Gesamtporenvolumens ungehindert durchsickert, was zur wiederholten Aufsättigung des oberen Mineralbodens in der Vegetationszeit führt

Shark Imaging

of fishes is currently a field of intense, multidisciplinary research. Of special interest are certain species of fish like tuna and several types of sharks (thunniform swimmers), that have developped an especially effective way of swimming and can reach velocities up to 70 km/h with only little movement of the body. To understand the swimming mechanics of these fishes, a threedimensional model of the muscle structure is required. While histologic techniques are extremely time-consuming for the examination of these large structures, MRI could reveal the inner muscle structures fast and without damaging the sample. Subjects and Methods: To investigate on the possibilities of examining the muscle structure of sharks with MRI, a formalin-fixated zebra shark with a length of 50 cm, and excised muscle tissue from a thresher shark were examined in a human 3T scanner. The fish was positioned prone on the spine coil. Since the goal was to differentiate between muscle and connective tissue, which has a thickness in the order of 0.1 mm, highly resolved 3D-images with a resolution of (0.4 mm)3 and a high SNR were acquired. Best contrast and sufficient SNR was achieved with a 3D FLASH sequence with a TR of 15 ms and an echo time of 5.59 ms. 22 averages were taken with a matrix size of 1024×256×256 within 6 hours. Results: The following figure shows a coronal slice through the entire shark. Throughout the whole body, the connective tissue can clearly be identified as dark lines in the brighter muscle tissue

Whether depositing fat or losing weight, fish maintain a balance

In fish, the relative amount of tissues of different densities changes significantly over short periods throughout the year, depending on the availability of food, nutrition and their developmental status, such as sexual maturation. If a land-living animal accumulates fat it influences not only its general state of health, but also markedly increases its energy expenditure for locomotion owing to the force of gravity. On a body submerged in water, this force, which acts on the centre of gravity (COG), is counterbalanced by a lifting force that is negligible in air and which acts on the centre of buoyancy (COB). Any difference in the longitudinal positions of the two centres will therefore result in pitching moments that must be counteracted by body or fin movements. The displacement of the COG away from the COB is a result of tissues of different density (e.g. bones and fat) not being distributed homogeneously along the body axis. Moreover, the proportions of tissues of different densities change significantly with feeding status. It is still unknown whether these changes produce a displacement of the COG and thus affect the hydrostatic stability of fish. Analysis of computed tomography and magnetic resonance imaging images of Atlantic herring, Atlantic salmon and Atlantic mackerel reveals that the COG is fairly constant in each species, although we recorded major interspecies differences in the relative amount of fat, muscle and bone. We conclude that the distribution of different tissues along the body axis is very closely adjusted to the swimming mode of the fish by keeping the COG constant, independent of the body fat status, and that fish can cope with large variations in energy intake without jeopardizing their COG and thus their swimming performance