Stefano Carnicelli

The Ziway–Shala lake basin (main Ethiopian rift, Ethiopia): a revision of basin evolution with special reference to the Late Quaternary

Abstract The Ziway–Shala basin, in the Main Ethiopian Rift (MER), is a reference site for regional to global paleoclimatic reconstructions. We undertook and interpreted a stratigraphical, pedological and geomorphological study, including a new geological map scale 1:250,000, to provide a Late Quaternary-centred revised geological history of the basin. 1 We mapped several Late Quaternary sedimentary units and arranged them in four major unconformity-bounded stratigraphic units (synthems), recording equivalent phases of geomorphic change. A new, extensive, soil survey allowed us to establish a pedostratigraphic unit, the T’ora geosol, as a distinctive marker of landscape stability and instability in the area during the Holocene. Climate change was a major control on geo-morphologic evolution of this area during the intense climate fluctuations of the last 100,000 years. Extensive lake systems developed during relatively humid Last Glacial interstadials and in the early-mid Holocene; this last was characterized by short, but high-amplitude, regressions during arid pulses. Major lakes’ lowering occurred in the terminal Pleistocene and in the last 5000 years. Evidences for high or very high terminal Pleistocene lake levels suggest possible non-climatic controls on changes in lakes’ extension and volumes between Late Pleistocene and Holocene. We suggest that modifications of hydrological thresholds, due to activity of structures parallel and transversal to the MER, established new lakes’ boundaries between terminal Pleistocene and early Holocene, setting the maximum level of Holocene lake systems at about 1670 m a.s.l. The integrated analysis of lacustrine, fluvial, slope and soil systems provided a basis for a general interpretation of relations between climatic changes and geomorphic processes at a basin scale.

Weathering of chlorite to a low-charge expandable mineral in a spodosol on the Apennine Mountains, Italy

The clay fraction of a Spodosol and its parent rock in the Apennine mountains of central Italy were studied by powder X-raydiffraction (XRD) and infrared (IR) spectroscopy, to evaluate the possibility of transformation of chlorite into low-charge expandable minerals. Results indicated that the main phyl-losilicate in the rock was a slightly weathered trioctahedral chlorite, rich in both Mg and Fe, together with dioctahedral mica and minor amounts of kaolinite. In the BC horizon, chlorite has undergone partial transformation into 2 vermiculitic components, in 1 of which the interlayer could be removed by hot Na-citrate treatment; the presence of a regular interstratified mineral (high-charge corrensite) was also observed. Further changes in the structure of chlorite were detected in the Bsl horizon, becoming more evident towards the soil surface. The first stage of weathering of chlorite involved Fe oxidation and partial expulsion of Mg from the hydroxide sheet, followed by deposition of Al in the interlayer space. Iron is also removed from the interlayer sheet, possibly remaining, in the oxidized state, in the 2:1 octahedral sheet, and so contributing to the lowering of layer charge and transformation to a dioctahedral structure. When approaching the surface, Al removal from the interlayers is enhanced by complexing agents, and further charge reduction leads to the formation of 2:1 minerals with a smectite nature. Illite, because of its low content in the soil clay fraction, contributes marginally to this weathering sequence, forming the high charged expandable component observed in the Bhs horizon. At the soil surface, arandomly interstratified vermiculite/illite was detected, which probably originated from K fixation by the higher-charged expandable minerals. This study of weathering in a natural soil strongly supports the hypothesis, previously ascertained by laboratory experiments, that chlorite can transform into a low-charge expandable mineral.

Use of aerial photographs, Landsat TM imagery and multidisciplinary field survey for land-cover change analysis in the lakes region (Ethiopia)

Early multidisciplinary surveys in the Lakes region of central/south Ethiopia show a highly variable land cover pattern characterised by complex interactions between environmental parameters and socio-economic dynamics. From an ecological point of view the area is highly sensitive and both food security and soil conservation are becoming serious problems for the rapidly growing population. The intensive land cover changes observed in this area during the last few decades beg accurate analysis. Land-cover change analysis over a long time-span was performed. Interpretation (API) of aerial photographs dated 1972 and classification of a 1994 Landsat TM image were used. Problems due to the heterogeneous nature of the data were overcome with a method for quantifying land cover on aerial photographs, thus producing data comparable to TM classification results. As land cover is linked, through land use, to social dynamics, in ground control use was made of the results of parallel socio-economic investigations. From the analysis, a general trend of increase in cultivated surfaces was noted. Unique strategies of land allocation according to physical settings were observed. A trend in the evolution of badlands was identified: rapid reactivation of previous erosion in newly cropped areas occurred; within a few decades this erosion reached quasi-equilibrium. The methods adopted showed some accuracy limitations, but allowed land-cover change analysis over a 22-year time-span, providing important insight into recent phenomena and present trends.

Effects of gypsum on hydrological, mechanical and porosity properties of a kaolinitic crusting soil

Numerous papers have shown the effectiveness of gypsum addition in reducing crust formation on sodic or generally non-acid soils, while the effect on acid soils has been less frequently studied and is less known. The present paper reports the results of a series of field rainfall simulations on an acid red soil (Rhodic Kandiustalf) in Northeast Zimbabwe. In these experiments, gypsum effect on hydrological behaviour in subsequent rainstorms was verified, and the mechanical properties of the crusts so formed were assessed by a modified hand penetrometer. The results showed the ability of gypsum to improve overall infiltration, mostly by reducing the rate of infiltration decay in the non-steady portion of a Horton-type infiltration curve; such rate of infiltration decay was shown to be not constant in subsequent rainstorms, with a well defined increasing trend, that was, however, less marked for gypsum-treated plots. Effect on final infiltration rate was much less significant. Surface crusts formed on gypsum-treated plots were shown to be significantly harder than those formed on untreated plots. Both results could be explained by the observation that a substantial loss of clay from the soil surface took place in untreated plots, while this process was significantly reduced by gypsum treatment. This lesser clay depletion would be effective in slowing structural collapse during wetting, and was also observed to allow the regeneration of a better developed soil structure on drying, so further slowing soil response in subsequent rainstorms. The greater clay content in the surface layer could also induce a higher degree of cohesion, so explaining the greater surface crust strength induced by gypsum treatment.

Microbial dynamics in Mediterranean Moder humus

There is a growing interest in the links between humus forms and soil biota, and little is known about these links in Mediterranean ecosystems. Culture-independent techniques, such as DNA extraction followed by DGGE and enzyme activities, allowed us to compare microbial communities in two horizons of a forest soil in different seasonal conditions. Direct in situ lysis was applied for extraction of DNA from soil; intracellular DNA was separated from extracellular and used to represent the composition of microflora. The aims were to describe how biochemical and microbiological parameters correlate with topsoil properties in typical Mediterranean Moder humus. Changes in bacterial and fungal community composition were evident from DGGE profiles. Degrees of similarity and clustering correlation coefficients showed that the seasonal conditions may affect the composition and activity of bacterial and fungal communities in the OH horizon, while in the E horizon the two communities were hardly modified. In the same season, OH and E horizons showed a different composition of bacterial and fungal communities and different enzyme activities, suggesting similar behaviour of eubacteria and fungi relatively to all the variables analysed. Evidently, different organic carbon content in soil horizons influenced microflora composition and microbial activities involved in the P and N cycles.

Influence of parent material on clay minerals formation in Podzols of Trentino, Italy

Abstract The formation of clay minerals was investigated in Spodosols developed in the subalpine belt, with similar exposure, climate and age, but deriving from different parent materials. All the soils were classified as Haplic Podzols and showed the characteristic eluviation and illuviation features of Fe, Al and organic carbon. However, varying parent material lithology led to different clay mineral assemblages in the soil. Smectite could be found in the E horizons of soils developed from granodiorite and tonalite materials. Its formation was strongly dependent on the presence of chlorite in the parent material. If nearly no other 2:1 mineral components, such as chlorite, are present in the lower soil horizons, then a residual micaceous mineral becomes the dominant clay mineral. The latter derives from a mica-vermiculite interstratified mineral.

Iron oxide mineralogy in red and brown soils developed on calcareous rocks in central Italy

Abstract Samples of 9 red and brown closely associated soils developed from highly calcareous materials in central Tuscany, Italy, were analyzed to determine: the mineralogical properties of the iron oxides, the relationship between redness and hematite content, and the relationship between parent material and iron oxide mineralogy. Goethite and hematite were the only crystalline iron oxides detected in the A, E and B horizons studied. X-ray data indicated that they were either poorly crystalline or of small particle size. A high proportion (67 to 95%) of the total iron was extracted by dithionite, and oxalate-extractable Fe was less than 10% of Fed in most of the samples. The extent of Al substitution in goethite was positively correlated (R2=0.68) to crystal dimension along the 110 direction. This finding is consistent with those for aluminous goethites synthesized at 25°C but at odds with some published data for natural goethites. Redness rating of dry crushed samples, as determined with Munsell colour charts, was positively correlated (R2=0.79) with hematite content. Redness rating, however, would provide only a crude estimate of hematite content. The soils with the lowest content of total iron had by far the lowest hematite content; nearly all of the crystalline iron oxide was goethite. This lends support to the hypothesis that parent material influences the development of iron oxides in soils.

Biological and physico-chemical processes influence cutin and suberin biomarker distribution in two Mediterranean forest soil profiles

Recent investigations have shown macromolecules, such as cutins, and suberins as effective markers for above and belowground plant tissues. These biopolyesters contain structural units specific for different litter components and for root biomass. The aim of this work was to understand the fate of plant organic matter (OM) in Mediterranean forest soils by evaluating the incorporation of cutin and suberin by measuring specific biomarkers. Soil and plant tissue (leaves, woods and roots) samples were collected in two mixed Mediterranean forests of Quercus ilex (holm oak) in costal stands in Tuscany (central Italy), which have different ecological and edaphic features. Ester-bound lipids of mineral and organic horizons and the overlying vegetation were analysed using the saponification method in order to depolymerise cutins and suberins and release their specific structural units. Cutin and suberin specific aliphatic monomers were identified and quantified by gas chromatographic techniques. The distribution of cutin and suberin specific monomers in plant tissue suggested that mid-chain hydroxy acids can be used as leaf-specific markers and α,ω-alkanedioic acids and ωC18:1 as root-specific markers. Differences in the distributions of biomarkers specific for above and belowground plant-derived OM was observed in the two types of soils, suggesting contrasted degradation, stabilisation and transport mechanisms that may be related to soil physico-chemical properties. The acidic and dry soil appeared to inhibit microbial activity, favouring stabilization of leaf-derived compounds, while, in the more fertile soil, protection within aggregates appeared to better preserve root-derived compounds.

Effect of gypsum on seedling emergence in a kaolinitic crusting soil

Abstract The emergence capability of maize seeds in a kaolinitic red tropical soil from Zimbabwe, subjected to rainfall simulation, was investigated under three kinds of treatment: untreated, 2.5 T·ha−1 and 5 T·ha−1 of phosphogypsum. Samples treated with gypsum exhibited a strong increase of crust strength and a decrease of the percentage of the cracked areas; they also showed a lower bulk density and a higher residual moisture content in air-dry condition. Gypsum translocation was limited to the first millimeters of the soil. A possible explanation advanced is the loss of brittle behaviour in treated samples, due to greater retention of clay in the surface soil layer; non-brittle behaviour by the treated soil would hamper soil cracking by emerging seeds and their emergence through cracks.

Pore space degradation in Zimbabwean crusting soils

Abstract Carnicelli, S., Ferrari, G.A. and Pagliai, M., 1994. Pore space degradation in Zimbabwean crusting soils. In: A.J. Ringrose-Voase and G.S. Humphreys (Editors), Soil Micromorphology: Studies in Management and Genesis. Proc. IX Int. Working Meeting on Soil Micromorphology, Townsville, Australia, July 1992. Developments in Soil Science 22, Elsevier, Amsterdam, pp. 677–686.