Roger Langohr

Small scale secondary CaCO3 accumulations in selected sections of the European loess belt. Morphological forms and potential for paleoenvironmental reconstruction

Eighteen important Quaternary loess paleosoil sites have been studied across the European loess belt. They included approximately 50 buried soils, the over and/or underlying loess and the present-day surface soils (where possible). From the numerous types of secondary CaCO3 accumulations recognized, only the small scale accumulations are discussed in this paper, including calcified root cells, CaCO3 hypocoatings, needle-fiber calcite, powdery calcite coatings, earthworm biospheroliths, and calcite pseudomorphs on gypsum. Most of the features studied are found in the rhizosphere microecosystem. Each of these features showed a unique relationship with organic matter, micro-organism and plant distribution, moisture and leaching processes. For example, the exceptional abundance of calcified root cells is an indicator of a long stability of soil surface during favorable climatic conditions. Needle-fiber calcite is related to biomineralization of saprophytes in soils with sufficient moisture and decomposing organic matter. The presence of powdery calcite coatings covering clay and Mn coatings in non-calcareous soils indicates a change from leaching to non-leaching soil moisture regimes. Earthworm biospheroids provide arguments for a relative stability of the soil surface, without rapid burial processes or drastic, prolonged water stress. Finally, gypsum pseudomorphs are indicators of changes in local climatic parameters. In addition to a discussion of the genesis and the dynamics of the various accumulations, several examples are given to show how these accumulations can be used as indicators of a changing environment, such as renewed loess deposition, the extent of drought or varying intensity of leaching during the year. To conclude, various forms of small scale secondary CaCO3 accumulations are common in the loess paleosoils and each type has the potential to contribute to a better understanding of the evolution of the paleoenvironment. Therefore, it is proposed that their individual presence or absence throughout the pedostratigraphical levels and throughout the (paleo)topography should be recorded at all scales of observation.

Micromorphological study of construction materials and living floors in the medieval motte of Werken (West Flanders, Belgium)

The “Hoge Andjoen,” an early medieval motte (860–960 A.D.) is an artificial hill made up of at least eight man-made “ground raising/leveling” layers. Each layer is associated with a stabilization level and a well-preserved occupation surface with evidence such as living floors, traces of cultivation, and goat/sheep trampling. The presence of this hill generated a local rise in the original groundwater table present in the natural, buried soil of the site. In some parts of the hill, and with little relation to the sedimentary boundaries, this process generated permanent water stagnation with pronounced anaerobic conditions and locally strong gradients of oxidoreduction. These gradients created a series of particular migrations and accumulations of iron, manganese, and phosphorus components. All organic artifacts, such as oak posts, wooden floors, leather, and seeds remained well preserved in the strongly reduced parts of the hill; they are completely decayed in the aerated zones of the hill. The soil moisture regime within the motte further influenced a series of postdepositional migrations/accumulations of clay and organic matter. The micromorphological study of this archaeological site allows verification of hypotheses developed during field surveying. These hypotheses relate mainly to the origin and mode of dumping of the various types of earthy material, the human activities related to the nine successive living floors, and the traces of numerous postdepo-sitional processes observed throughout this archaeological structure.

European Humus Forms Reference Base

In Europe an abundance of humus taxonomies exists starting with early approaches in the late 19th century. Frequently used in an international context, they do not cover all site conditions in the European area. Although having basic concepts and general lines, the European (and North American, Canadian) classification systems differ in important parameters used for the description and classification of humus forms. These discrepancies result in incongruities, so require adjustments when exchanging partially compatible soil data, even between nearby countries. In 2003, 26 European specialists in humus forms met in Trento (Italy) and decided to formulate rules of classification based on morphogenetic descriptions and diagnostic horizons, adapted to European ecological conditions. Taking into account old and new European and North American systems of humus forms classification, six main references (Anmoor, Mull, Moder, Mor, Amphi and Tangel) were defined, each of them further dividing into detailed categories. This inventory assigned a strong discriminatory power to the action of the pedofauna. Both semiterrestrial (anoxic) and terrestrial (aerated) topsoils were classified. The descriptors of the diagnostic horizons were conceived in accordance with the spirit of recent international soil classifications. Assigning an “ecological value” to each main humus form along a gradient dividing those characterized by accumulation of poorly transformed organic matter, from very biologically active forms degrading and incorporating all organic remains, this European system of classification avoids a hierarchical structure and allows an elastic approach open to additional ecological contributions and renditions.

The use of a comparative particle size distribution index for the numerical classification of soil parent materials: application to mollisols of the Argentinian pampa.

Abstract A method to estimate the magnitude of discontinuities or similarities in parent materials having equivalent mineralogical composition is proposed. It is based on a particle size distribution index which compares for two samples the weight percentages of all fractions taken between selected size limits. The indexes form a matrix and are used to construct a dendrogram which illustrates the clustering into groups. The calculations are carried out by computer using a Fortran programme. The technique was applied to a set of soil samples of Mollisols in the humid undulating pampa in Argentina and good agreement with field observations was obtained.

Distribution and dynamics of shrub roots in recent coastal dune valley ecosystems of Belgium

Abstract A chronosequence, up to 60 years old, was investigated in the Westhoek Nature Reserve. Root growth of the shrubs in dune valleys was found to be restricted to the surface Albi and Bbi horizons which often did not exceed 25 cm. The thickness of these horizons and the amount of litter and humus could be explained by the position along secondary topo-hydrosequences within the chronosequence. The mostly stratified sands underlying the Albi and Bbi horizons had a higher bulk density. In these relatively dense Cd horizons root growth of new colonizing shrubs seems to be possible only along old root or stem channels of the previous vegetation of dune building plants such as Ammophila and Salix which grew in pace with the accumulating dune. It is concluded that root growth in these sandy soils is restricted by the high penetration resistance of the closely packed sands in the subsurface horizons. The root penetration problem in these sandy soils explains the uniform vegetation physiognomy better than other climatic or edaphic factors.

Morphological characterisation of humus forms in recent coastal dune ecosystems in Belgium and northern France

Abstract The morphology of humus profiles, developed on recent sandy coastal dune ecosystems, is studied on macro- and microscale. Humus and soil profiles were described, sampled and analysed. Undisturbed, oriented samples were taken from the surface horizons for micromorphological study. The soils are situated in the National Biological Reserve of the Opal Coast, Merlimont, France and near De Haan, Belgium. On both sites, the parent material consists of aeolian calcareous sand. Surface horizons, however, are decarbonated due to leaching processes. In Merlimont, the sequence consists of two profiles, one under Pinus nigra ssp. laricio and one under Populus nigra ssp. nigra , characterised by a Resimor 1 /Dysmoder 2 and Rhizomull 1 /Mesomull 2 humus type, respectively. At the De Haan site, three profiles under Quercus robur , Populus ssp. and P. nigra var. austriaca are investigated. The humus types are respectively Mullmoder 1 to Mull/Dysmull 2 , Mull 1 / Oligomull 2 , Mormoder 1 /Dysmoder 2 . Differences among the humus profiles are related to presence/absence among the L-, F-, H- and A-horizons, structure, rooting, presence of hyphae, sclerotia and excrements. Macromorphologically, the difference between humus profiles under coniferous and deciduous forest/grassland is evident by thicker L-, F and/or H-horizons under coniferous trees. The microstructure of the L- and F-horizons shows a loose packing of subhorizontally oriented needles. The microstructure of the H-horizons varies from intergrain microaggregate to locally weak crumb. The microstructure of the surface mineral horizon of all profiles is mainly intergrain microaggregate, sometimes single grain and exceptionally bridged grain. Intimate mixing and complexation of organic matter to the mineral fraction into aggregates is very limited in the A-horizons. All A-horizons, irrespective of the humus type, are to some degree characterised by a “pepper and salt” appearance. The horizon symbol “H+E” is introduced to label this morphology. The Mull humus forms under deciduous trees are indicative of rather intense mesofauna activities. The absence of a crumb structure in the A-horizon of these soils could be due to the fast disintegration of earthworm casts in these sandy soils with no clay or silt fraction.

The Conservation and Degradation of Archaeological Soil Features in Flanders and Brussels: The example of Watermaal-Bosvoorde

Ten years ago, an extensive literature study on the conservation and degradation of soil features in Flanders was conducted. The outcome was a report discussing the state of preservation. The present contribution intends to synthesize the chief outcomes of that research and to present a case study where the theoretical knowledge and recommendations then put forward have been applied.