Peter Felix-Henningsen

Soil microstructure as an under-explored feature of biological soil crust hydrological properties: case study from the NW Negev Desert

Biological soil crusts (BSCs) can play an important role in hydrological cycles, especially in dryland ecosystems where the availability of water is limited. Many factors influence the hydrological behavior of BSCs, one of which is the microstructure. In order to describe the influence of the soil microstructure of BSCs on water redistribution, we investigated the change of the pore system of three different successional stages of BSCs, as well as their respective subcrusts in the NW Negev desert, Israel, using 2-dimensional thin sections, as well as non-invasive X-ray 3D computed microtomography (XCMT) and mercury intrusion porosimetry. Our results show that the pore system undergoes significant changes during crust succession. Both the total porosity, as well as the pore sizes significantly increased from cyano- to lichen- to mosscrust and the pore geometry changed from tortuous to straight pore shapes. We introduce two new mechanisms that contribute to the hydrological properties of the BSCs in the NW Negev that impede infiltration: (i) vesicular pores and (ii) a discontinuous pore system with capillary barrier effects, caused by a rapid change of grain sizes due to sand burial. Since both of these mechanisms are present mostly in early stage cyanobacterial crusts and their abundance decreases strongly with succession, it is very likely that they influence BSC hydrology to different extents in the various crust types and that they are partly responsible for differences in runoff in the NW Negev.

The status and dynamics of some trace elements in a savanna soil under long-term cultivation

A recent study in the savanna suggested that the surface soils might be contaminated with Ti, V, U and Th because of increasing phosphate fertilizer applications. In this study, we determined the dynamics of Ga, V, U, Nb, Y, La, Ce and Nd in a savanna soil that has received NPK fertilizers, farmyard manure (FYM) and FYM + NPK for 50 years using an adjacent uncultivated or native site as a reference. The concentrations of the elements in the soils were determined by X-ray fluorescence. Mass balance calculations indicated that Nb, U, Y, La, Ce and Nd increased by between 8 and 61% in the cultivated soil compared with the uncultivated natural site. Long-term application of FYM increased the masses of Nb (16%), Th (40%), La (26%), Ce (44%) and Nd (54%). There were no discernible changes in the masses of the trace elements that could be unambiguously associated with phosphate fertilizer applications. It was, thus, concluded that physical accumulation as leaching losses and crop removal depleted soluble ions, stabilization by organo-mineral complexes and aeolian deposition are the probable soil enrichment mechanisms of these trace elements during cultivation.

Paleosols on Pleistocene dunes as indicators of paleo-monsoon events in the Sahara of East Niger

Abstract In a SW–NE traverse across the Tenere desert and the southern Tchigai mountainous region, only one generation of ancient dunes was found, overlain by recent, active eolian sand sheets and dunes. Paleosols on these dunes display red-brown to yellow-brown Bw horizons up to 100 cm thick and are classified as Chromi-Cambic Arenosols and Cambic Arenosols, respectively. The structure of the soil horizons is stabilized by pedogenic cementation and often shows effects of bioturbation. Near the shores of previously more extensive paleolakes, these paleosols change into Gleyic Arenosols. The former shore lines are frequently marked by seams of goethite rhizoconcretions (“bog iron ores”). Within the paleolake depressions, ancient dune sediments bleached by gleying are covered by silt-rich lacustrine sediments. Neolithic artifacts on the lacustrine sediments indicate that during an arid climatic period, the paleolakes contracted in size and did not reach their fullest original extent during the late Neolithic humid period. This suggests the existence of earlier periods with enhanced humidity. Because of a decrease in humidity from SW to NE, the degree of rubefication and several physical, chemical and mineralogical properties of the paleosols are related to their position along the traverse. A gradient of decreasing weathering intensity from SW to NE is paralleled by local variations in mineralogical properties of the parent materials and in rates of dust deposition. Consequently, the two effects on soil properties are difficult to separate.

Mesozoic-Tertiary weathering and soil formation on slates of the Rhenish Massif, Germany

Abstract Weathering of Paleozoic slates and sandstones of the Rhenish Massif in western Germany, which occurred during the Upper Mesozoic and Tertiary under warm, humid tropical to subtropical climatic conditions, led to the formation of a regolith up to 150 metres thick. In flat upland areas of the Hunsru¨ck and Eifel, where the tectonic uplift was relatively weak, remnants of this weathering mantle, more or less truncated by Upper Tertiary and Pleistocene erosion, are still preserved. On overlapping sections and drill cores of an autochthonous paleosoil and the saprolite underneath, the morphological, geochemical and mineralogical zonation of a complete profile of the weathering mantle has been reconstructed. A fossil pre-Oligocene Plinthitic Acrisol, covered by Oligocene fluvial sediments, displays characteristics formed under a high groundwater table. On the other hand the underlying saprolite can be subdivided into a lower reduction horizon and an upper oxidation horizon, each of them more than 40 meters thick. This indicates a polygenesis of the weathering mantle during the Tertiary, due to descending groundwater tables caused by the beginning tectonic uplift of the Rhenish Massif and drier climatic periods during the Middle Tertiary. During the Upper Oligocene the deposition of kaolinitic clays derived from removed horizons of the kaolinitic soils started in fault-block depressions. Periglacial processes during the Pleistocene led to a further removal of the weathering mantle and to the deposition of superficial layers on top of the autochthonous remnants of the saprolite. Presently the kaolinitic sediments as well as the saprolite are exploited as kaolin deposits.

Heavy metals in soils from Tirana (Albania)

This study was aimed to establish background and reference values of total heavy metals in soils from a representative area of Albania (Tirana). Thirty-eight soil samples collected from genetic horizons of major soil types of Tirana were analyzed for important physicochemical properties by standard methods and for total contents of Cd, Cr, Ni, Pb, Zn, and Cu by atomic absorption spectrometer, after extraction with aqua regia. The results showed that the total contents of Cd, Cr, Ni, Pb, Zn, and Cu in surface horizons varied widely with respective mean values of 0.3 (±0.6), 174.2 (±63.7), 305.9 (±133.0), 19.7 (±12.4), 95.5 (±26.3), and 42.7 (±6.8) mg/kg. The highest metal contents were found in two soils developed in limestone. The depth distribution of metals showed a tendency for accumulation of Cd and Pb in the surface horizons of three soils, suggesting that these metals partially come from anthropogenic inputs. Correlation analysis indicated that the metal contents of soils were controlled by soil properties, including pH, CaCO3, clay, organic matter, cation exchange capacity, and Fe oxides. The background values (given as the 90th percentile) were much higher than those reported in the literature, showing that the levels of respective metals were naturally higher. The total metal contents of some soils were above background levels, suggesting metal pollution. The reference values for all the analyzed metals were quite consistent with those of the Dutch system. The proposed background and reference values can be used to evaluate the soil pollution with these elements.

Geology, soils and saprolites of the Swaziland Middleveld

Abstract Quartz-diorite, diorite and granodiorite of Archaic ages are the most common rock types in the Swaziland Middleveld. The composition of the regolith cover is dominated by soil-saprolite complexes. The genetic and mineralogical gradient within the soil-saprolite complexes and the grade and spatial distribution of denudation of the land surface are important characteristics for evaluating the vulnerability to erosion and the site properties of eroded areas in land use planning. The saprolites were formed by intensive chemical weathering under warm and humid climatic conditions dating from Lower Cretaceous times. The saprolitisation process can be considered polygenetic, subdividing the saprolites into a near-surface oxidation zone and an underlying reduction zone caused by the geochemical environment. Assuming isovolumetric weathering, the mass losses of the upper saprolite zones, obtained as pore volume, amount to between 41.1 and 54.0%, depending on the mineral composition of the parent rock. Even in the lower saprolite zones plagioclases were transformed into white pseudomorphs of kaolinite. The weathering of feldspars, micas and amphiboles and the amount of Fe-oxides increase towards the surface. The clay fraction of the saprolites is dominated by kaolinite, with small amounts of illite and smectite. The latter reaches a maximum in the middle saprolite zones which coincidentally show a distinctly lower amphibole content. Therefore, smectite is formed as an intermediate phase and is not stable at higher weathering intensities in the upper saprolite zones which are characterized by desilification and removal of bases. Typical soils of the Middleveld are Ferralsols associated with Cambisols and Acrisols. Most of the recent soils have developed from colluvial sediments characterized by a multi-layer structure often marked by embedded stone lines. A strict genetic dependence between the parent rocks and the overlying soils has not been established. The different sediments which form the allochthonous part lead to compound horizons. The micromorphological investigations indicate a former Luvisol-Acrisol phase with deep-penetrating illuviation during the polygenetic soil formation. The mineral composition of the soils is dominated by quartz and kaolinite accompanied by small amounts of illite. Gibbsite is present in the uppermost soil horizons and can be interpreted as indicative of the recent phase of ferrallitization.

Soil erosion in Swaziland: a synthesis

Abstract The main conclusions of the research project on soil erosion and sedimentation in Swaziland are as follows. (1) Soil erosion has worsened over the last 20 years. The proportion of an 1800 km 2 study area in the Middleveld classified as ‘high erosion class’ has increased from 6.7 to 13.6% between 1972 and 1990. (2) Gully erosion is the main process and is concentrated within the Manzini, Jabuleni, Lobamba and Chibidze land systems, all characterised by soil-saprolite complexes. (3) Overgrazing and compaction along paths and tracks lower the infiltration rate of the clay-rich ferralitic soils, promoting surface runoff and the formation of rills. (4) Once the rill deepens and cuts through the soil on to the underlying saprolite, gullies develop rapidly because of the low shear strength of the material. (5) Soil erosion problems are compounded by the existing system of land tenure and increasing pressure of livestock and population on the land. (6) In some instances, population pressure can lead to improvements in land management and better soil protection. Recommendations for controlling soil erosion and for further research are presented.

Genese und Stratigraphie periglazialer Deckschichten auf der Hochfläche des Ost-Hunsrücks (Rheinisches Schiefergebirge)

Aus den unterdevonischen Schiefern und Sandsteinen des Osthunsrucks bildete sich unter warm-humiden Klimabedingungen des ausgehenden Mesozoikum und Tertiar eine kaolinitische Verwitterungsdecke mit einem bis zu 150 m machtigen Saprolit. In den Kaltzeiten des Pleistozans war das Rheinische Schiefergebirge Periglazialgebiet. Als Folge der tektonischen Hebung fuhrte die von den grosen Flussen Rhein und Mosel ausgehende ruckschreitende Erosion zur Zerschneidung der Rumpfflache durch Kerbtaler und zu ihrer randlichen Auflosung in Riedel. Kryoklastik, Solifluktion und fluviale Abspulung fuhrten auch in den Plateaulagen zu einer Abtragung der oberen Abschnitte der prapleistozanen Verwitterungsdecke. Uber dem mesozoisch-tertiaren Saprolit wurden periglaziale Deckschichten abgelagert. In den Plateaulagen und masig geneigten Hanglagen der quartaren Taler sind drei Schichtkomplexe ausgebildet, die sich schwermineralogisch, petrographisch und morphologisch untergliedern lassen. Die weichen bis murben Saprolitgesteine gingen durch Frostsprengung und Solifluktion in eine strukturlose lehmige Basisfolge uber, die noch frei von losburtigen Schwermineralen ist. Ihr Mineralbestand und der Skelettanteil werden von dem Verwitterungsgrad des unterlagernden Saprolits bestimmt. Uber der Basisfolge lagert, mit deutlicher Schichtgrenze abgesetzt, eine Mittelfolge aus loslehmhaltigen Solifluktionsdecken. Ihre mikromorphologischen Merkmale eines reliktischen, periglazial uberpragten Bt-Horizonts, der zu einer interglazialen Parabraunerde gehorte, lassen den Schlus zu, das ein Teil der Lossedimentation und damit auch die Genese der Basis- und Mittelfolge mindestens in das Risglazial zu stellen ist. Wahrend des Wurms war die flachenhafte Abtragung der Landoberflache somit nur relativ schwach. Abermals wurde die Mittelfolge durch periglaziale Umlagerungsprozesse und weitere Losbeimengung uberpragt. Den Abschlus der Deckschichtenfolge bildet ein aolisches Decksediment der Jungeren Tundrenzeit aus Loslehm mit einem hohen Anteil an Laacher-Bims-Aschen. Auch dieses Substrat wurde in den Hochlagen des Mittelgebirges noch solifluidal verlagert. In den Erosionslagen im Bereich der Talsohle der quartaren Taler fehlt die mesozoisch-tertiare Verwitterungsdecke vollstandig. Aus dem freigelegten frischen Schiefer entstand durch Kryoklastik ein grober Frostschutt, der kaum noch solifluidal verfrachtet wurde. Die Feinsubstanz der Schuttdecke resultiert im wesentlichen aus der Einspulung von bimshaltigem Staub im Allerod und der Jungeren Tundrenzeit.

Paleoclimatic interpretation of a thick intra-saalian paleosol the “bleached loam” on the drenthe moraines of Northern Germany

Summary In the Red Cliff of the Isle of Sylt (55°N) the exposed Drenthe till is weathered to depths generally exceeding 10 m and contains a bleached paleosol (“bleached loam”) at locations with plane relief. A light greyish bleached horizon, some 2–4 m thick and extremely poor in free Fe and Mn oxides, overlies a thick, reddish brown oxide-enrichment horizon which displays the same textural and structural characteristics. The “bleached loam” is overlain by a younger, brownish coloured “upper moraine” with an Eemian lessive soil on top which after formation underwent periglacial reworking. This stratigraphic superposition makes it possible to deduce the existence of a weathering period within the Saalian glaciation complex. The mobilization of the oxides in the bleached horizon under primarily reducing conditions, their vertical translocation following a redox gradient and finally the formation of lepidocrocite in the enrichment horizon might indicate a pedogenesis under markedly humid climatic conditions lacking permafrost. Results of pollen analyses from samples of the “bleached loam” corroborate the paleopedological interpretation. The predominance of ERICACEAE and GRAMINEAE as well as the lack of arboreal vegetation indicates cool humid conditions during soil formation.

Dynamics of copper fractions and solubility in a savanna soil under continuous cultivation

An understanding of the influence of soil management practices on the distribution, form and solubility of trace metals in soils is required to formulate appropriate guidelines for the applications of organic manures and inorganic fertilizers for sustainable soil fertility and environmental protection. The distribution, forms and solubility of Cu were investigated in a savanna soil under long-term cultivation and varying management practices which included fertilization with NPK, farmyard manure (FYM), NPK+FYM and a control which received neither NPK nor FYM for 50 years. Total Cu varied between 5 and 13 mg kg−1. Long-term application of FYM and FYM+NPK significantly increased DTPA extractable Cu in the surface horizon, and in the subsurface horizon in FYM fertilized fields. Averaged across the sampling depths, cultivation and management history did not affect the concentration of DTPA extractable Cu, water-soluble Cu, organically complexed Cu and residual Cu. But fertilization with FYM and FYM+NPK significantly increased organically complexed Cu in the surface layer as compared to NPK fertilization. Solubility equilibria studies indicated that Cu2+ activities in soil solution approached an apparent equilibrium with cupric ferrite (CuFe2O4), suggesting that the control on Cu2+ solubility was either a CuFe2O4 or a Cu solid with solubility similar to cupric ferrite. The soil management practices involving combined application of inorganic fertilizers and farmyard manure did not seem to pose any risk of inducing Cu deficiency, but sole application of inorganic NPK poses such a risk.