A chronosequence of soils near the Franz Josef Glacier

Abstract

One method of studying the effects of Time as a Soil Forming Factor is the recognition and investigation of a Chronosequence, wherein four of the five Soil Forming Factors are kept constant or ineffectively varying. Thus, observed differences between soils of different ages forming a sequence are deemed to be the result of the lapse of varying intervals of Time since the initiation of soil formation. It is helpful to assign accurate ages to the soils of such a Chronosequence, allowing the derivation of Chronofunctlons, rate equations of soil formation. In many parts of the world, intermittent alteration of the Earth's surface by mudflows, volcanism or processes of glaciation has provided areas of terrain whose relative and absolute ages can be determined by the techniques of the botanist and geomorphologist with some degree of confidence. Such an area occurs in the vicinity of the Franz Josef Glacier, which has at various known times deposited morainic and alluvial debris in defined places. A succession of plants has colonised these ground-surfaces, and on them a Chronosequence of soils has developed concomitantly, Deposition of organic matter in and upon the parent material initiates depth-gradients of many soil characteristics such as reaction, bulk-density, and contents of organic carbon, nitrogen and various fractions of phosphorus. Under the influence of a warm and extremely humid climate the processes of weathering and leaching within the soil profile are responsible for striking gains, losses, transformations and redistributions of many organic and inorganic constituents, Some of these changes have been studied during the past four years, following an earlier investigation by the present author of the most youthful soils of the Chronosequence in 1962 and 1963. This initial work traced the development of six ecosystems 0, 6, 12, 25, 45 and 55 years of age. Spectacular accretion of nitrogen, especially, showed no indications of having reached any apparent steady-state in the oldest ecosystem, despite the impending elimination from the botanical succession of Carmichaelia grandiflora, a native legume, Clearly, it was important to determine nitrogen contents and the point of steady-state of nitrogen in soils older than 55 years, which lack any plants known to be capable of nitrogen fixation. In addition, the recognition of older soils, whose position on an orderly continuum of soil development could be assumed with some degree of confidence, would provide considerable information about rates of change of many other aspects of soil morphology, mineralogy and physical and chemical characteristics.