Geoökologie der Frostböden auf Island und ihre Bedeutung für die Bodennutzung

• Main Author: Schunke, Ekkehard
• Format: Text
• Language: German
• Published: Goltze 1977
• Subjects: Brunsvicensien der Universitätsbibliothek Braunschweig; Abhandlungen der BWG; 577; 550; Boden; Ice; Iceland; palsas; permafrost
• Online Access: https://dx.doi.org/10.24355/dbbs.084-201306271102-0; https://publikationsserver.tu-braunschweig.de/receive/dbbs_mods_00052132

Mangels anderer terrestrischer Ressourcen ist für Island das natürliche und kultivierte Grasland die wichtigste Grundlage der Landnutzung (Viehzucht). Dieses Nutzungspotential wird durch frostdynamische Vorgänge nachhaltig beeinträchtigt, insbesondere durch Thufur-Bildung, Rasenschälen sowie durch Permafrostbodendegradation und -aggradation. Im folgenden Artikel werden die Prozesse und Faktoren dieser agrarisch relevanten Frostbodenformen zusammenfassend behandelt. Seit den 60er Jahren dieses Jahrhunderts ist eine Intensivierung der frostdynamischen Vorgänge im Boden zu verzeichnen. Diese hat ihre Ursache in einer Verschärfung des Frostregimes in der bodennahen Luftschicht: Während der Periode 1965-1975 hat sich die jährliche Kältesumme gegenüber der besonders warmen Periode 1924-1934 um rund 25-30 % erhöht. Vor allem die Verschärfung des Frostregimes im Vorwinter erlangt große kryopedogene Wirksamkeit, da dem Boden zu diesem Zeitpunkt noch keine geschlossene, thermisch-isolierende Schneedecke von größerer Mächtigkeit aufliegt. Die Intensivierung der frostbedingten Morphodynamik induziert eine Labilisierung des Landschaftshaushaltes. Somit führen anthropogene Eingriffe, etwa in Form der Überweidung, besonders leicht zu einer Störung des geoökologischen Gleichgewichtes und lösen eine drastische Minderung des Landnutzungspotentials aus. : Lacking other resources the output of the natural and cultivated grassland (in the widest sense) is the most important basis of land use (cattle-breeding) in Iceland. This available potential is persistently impaired by cryogenic processes, especially by the formation of earth hummocks, turf exfoliation and by the degradation and aggradation of permafrost. In the present paper the processes and factors of these agriculturally relevant periglacial forms are summarized. The results are based on cryopedological field studies carried out in different regions of Iceland during the years 1970-1972 and 1975-1976. The formation of earth hummocks (thufurs) is the most common cryopedological phenomenon in the Icelandic grass-covered areas. It results from a cryodynamically induced subsurface soil movement. The immense frequency and the pronounced forms of the thufurs in Iceland originate from a coincidence of a favourable frost climatic milieu and the widespread occurrence of a highly frost susceptible fine-grained soil, the loess-like material of móhella. The turf exfoliation, one of the most important environmental problems in Iceland at present, is predominantly caused by gelideflation. It is favoured by the strong frost action in the uppermost layers of the soil by way of frost heaving and the formation of needle ice as well as by the poor cohesion of the fine-grained soils in Iceland which ensues from the small portion of organic and clayey matter. In addition, the destruction of the vegetation cover by trampling of the grazing cattle is an essentially inducing factor. The actual condition of the Icelandic (sporadic) permafrost is characterized by simultaneous degradation and aggradation, whereby aggradation prevails. The actual permafrost aggradation is conspicuously witnessed by the formation of new palsas: As a whole more than 1200 recent palsas at about 30 different localities have been registered. The actual intensification of the cryogenic processes in the soil is caused by a recent aggravation of the freezing regime: During the period 1965-1975 the average sum of negative degree days during the frost period (freezing index) has increased by about 25-30 per cent as compared to the exceptionally warm period 1924-1934. This aggravation of the frost climate especially during the pre-winter period (Oct.-Nov.) are particularly effective because, at this time, the soil has no continuous thermic-isolating snow cover of greater thickness. The intensification of the cryogenic morphodynamic, ensuing from the aggravation of the frost climate, causes an instableness of the geo-ecological budget. Therefore anthropogenic interference, e.g. by way of overgrazing, easily leads to a disturbance of the geo-ecological balance in the course of which the basis of land utilization is severly reduced.