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Abstract "Heft 5"


Freiburger Bodenkundliche Abhandlungen

Schriftenreihe des
Institut für Bodenkunde und Waldernährungslehre
der Albert-Ludwigs-Universität Freiburg i.Br.
Schriftleitung: F. Hädrich


Heft 5


Awad Said Ghanem


Altersstellung und anthropogene Beeinflussung
von Parabraunerden in der Emmendinger Vorbergzone

Freiburg im Breisgau 1976

ISSN 0344-2691

Summary:

In these study the occurence, genesis and age of Parabraunerde formed on loess in the Emmendinger foothill zone (in the southern part of the 'Upper-Rhine Plain' near Freiburg in Breisgau) was investigated.
In order to examine the influence of different soil forming    factors on soil development, the following sites in the Emmendinger foothill zone have been selected for investigation (the influence on the for ming of Parabraunerde in the Sudbaden area):
1)    The relic forest at Langleid near Malterdingen, and those at Hurst and Erdenhart near Heimbach. These have been studied to investigate anthropogenic influences because they have old terraces of approximately 500 to 600 years in age which were afforested again some 250 years ago according to records in local archives.
2)    The Vierdorferwald, chosen to allow comparison of the development of Parabraunerde formed under natural forest vegetation in comparison to 1)
3)    The Teninger area, a flat region which is relatively dryer than the other sites and has been used intensively for agriculture since the 3rd century or earlier.
Research areas are those which are near to natural conditions. There Parabraunerde still exists, whereas due to agricultural use especially at slopes only Pararendzina is spread.
The soil types of importance for the studies' problem were mapped out and marked off. Parabraunerde and Pararendzina, as well as intermediate types between them having different degrees of decarbonatization and different clay content, were thereby identified. The remains of fossilized buried soils and the loess layers between them down to the underlying triassic limestone were mapped out in the selected areas, classified according to their age, and a stratigraphic identification was attempted. One strongly developed fossilized Parabraunerde formation (I) was found on loess relatively poor in dolomite and two less fossilized soil formations were found within the lighter colored loess (II, III, IV) which has higher content in dolomite.
From the collective findings of the region and the results of the survey, the following points are especially worth noting:
1)    The Parabraunerde is the most wide-spread distributed soil type in all of the investigated areas.
2)    In the cultivated forest free areas the Pararendzina is distributed in its cultivated climax form whereas Parabraunerde is seldom to be found.
3)    Through anthropogenic influences the Parabraunerde in Langleid, Hurst and Erdenhart is mostly truncated so that there is no strongly developed (thick) Al layer to be found which relates to the thickness of the Btlayer.
4)    After the destruction of Parabraunerde by terrassing, Pararendzina was formed on the terraces. After cultivation and the subsequent 250 years of forestation Parabraunerde did not develop again.
5)    Fossil soil formations which form part of the present ground surface occured in the relic forest on those terraces which had anthropogenic influence. These formations were termed Relic-Parabraunerde.
The occurence and distribution of Parabraunerde in Vierdorferwald, under natural woodland vegetation without clearing (as stated in archives) as well as in the Teninger area which is a flat area (recent loess deposits over the lower terrace) relatively dryer than the other areas and which is intensively cultivated, supports the idea of holocenic development on these lowland regions. Therefore the holocenic development of Parabraunerde in the relic forest regions of Langleid, Hurst and Erdenhart can be assumed, particularly because the occurence of the intermediate types confirms it. Therefore the occurence of Parabraunerde in this area already identified by HADRICH (1962) can be regarded as holocenic development.
Furthermore this investigation showed that the development of Pararendzina is primarily related to steep slopes, to relatively dry situations (see HADRICH, 1966, p. 24), and especially in areas where thick layers of loess occur, and not only in areas where anthropogenic disturbance has taken place. The analysis of field observation and description permitted correlation of the thickness of loess layers, slope situation, type of soil, anthropogenic influence, land use, and the intensity of weathering:
a)    Loess layers on the south or southwest slopes are mainly thicker than those on north and northwest slopes.
b)    On the thick loess layers on the south or southwest slopes there is mainly Pararendzina development and on the thin loess layers on the north and northwest slopes there is mainly Parabraunerde.
c)    Everywhere in thick loess deposit man has built the terraces for vineyards or agricultural use.
c) Thin loess layers which are possibly more slowly sedimented are comparatively more weatherbeaten than the thicker macromorpholo-gical disjointed loess layers.
In the laboratory a total of 211 samples from 28 profiles were analysed for grain size, pH, carbonate content, oxalate soluble Fe (Feo), Mn (Mno), and Al (A1o), dithlonite soluble Fe (Fed), Mn (Mnd), and Al (Ald), as well as total content in Ca, Mg, K, Na, Fe, Mn and Al after desintegration by HF-HClO4. N and C were measured on selected samples.
Laboratory results were processed by computer to calculate averages, standard deviation, and several quotients. This was done in order to enable a parallel to be drawn between loesses and soils of different ages. The most important laboratory results were as follows:
1)    The varying courses of the respective depth function of the mineral fractions for oxalate and dithionite soluble Fe, Mn, and Al, as well as their clay content have characterized soil dynamic processes, especially a loss in the Al, -horizon and the enrichment in the Bt-horizon of the examined Parabraunerde profile.
2)    The depth function typical for Parabraunerde were well developed in the Vierdorferwald and in the Teningen area. In comparison are those in the three relic forest areas of Langleid, Erdenhart, and Hurst in some profiles, according to the degree of anthropogenic influence less clearly defined.
3)    Through the higher Feo percentage of Fed one can distinguish easily the respective holocenic and relic Parabraunerde formation (~ 23 %) from the fossil soils (~ 9 %). On the other hand there exists no statistically certain differences between the fossil soil formations of different ages, at least not between fossil soil formations I and II.
4)    The loess I is easily distinguished from the overlying lighter dolomite-rich loess because of its dolomite content, lime concretions and its color and structure.
5)    The homogeneity of the loess was uncertain in particular places because of the various admixtures of lime concretions of different forms, snail relics, and Fe and Mn concretions. This applied especially to highly weathered thin loess layers.
5)    Alo  and Ald contribute only a small part of the total context of Al, approximately 3.5 % in the loess' and in the Bt material. In comparison, Fed constitutes approximately 30 - 32 % of the total iron in the loess and 36 - 47 % in the Bt material.
6)    The course of Ald  is similar to that of Alt, except in the holocenic Parabraunerden where a weak or no correlation is present.
7)    Clay content increases with increasing age, as do Fet and Alt (in soils free of carbonates). This connection lies in that the clay content in the Bt-horizons of the fossil soil formations
I > fossil soil formations II> fossil soil formations III and that the clay particles are more enriched with Fe and Al than the larger particles.
9)    Micromorphological investigation confirmed the most important field and laboratory results, as follows:
A - The holocenic Parabraunerde is characterized by thin undisturbed clay coatings.
B - In the Vierdorferwald the textural differentiation was
further confirmed by the presence of an Al-horizon which is rich in silt, but poor in clay (no clay coatins) and a Bt-horizon enriched with clay coatings.
C - The relic soil formation is characterized by the presence of recent, thin clay coatings and old, relatively thick, disturbed clay coatings which are found within the aggregates and occur even in the top Ah-horizon.
D - The intermediate types of differently decarbonated Pararend-zina to Parabraunerde are characterized by filling of the old pores of the Ah-horizon with silty material and by the formation of new pores within the old pores, filled with thinner and more recent clay coatings.
Thus, in all of the investigated Parabraunerde profiles and intermediate types lessivation processes were found to have taken place and are still evident today.


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