We investigated the effect of organic matter and weathering on the lability and solid phase speci... more We investigated the effect of organic matter and weathering on the lability and solid phase speciation of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) in two contrasting subalpine regions in the Italian Alps. Cr, Ni and Cu could be linked to weathering. This was not the case for Pb. Since organic matter (OM) influences the solid phase speciation of heavy metals, the total organic C and N content, the C and N content of different density fractions of OM and also of the labile (oxidised by H(2)O(2)) and stable (H(2)O(2)-resistant) fractions were determined. Soil OM stocks were high and soils on north-facing slopes had more OM than the south-facing sites to which they were paired. Density measurements and the H(2)O(2) fractionation indicated that the higher OM content on north-facing sites was due to an accumulation of weakly degraded organic material. Due to higher weathering intensity on north-facing sites, the abundance of the EDTA-extractable heavy metals was higher than on south-facing sites. All EDTA-extractable heavy metals showed a good correlation to the water-soluble phenolic concentrations which indicates that the metals were probably translocated as metal-organic complexes. Pb and Cu correlate not only to the light (density < 1 g/cm(3)) and labile, organic fraction but also to the heavy (density > 2 g/cm(3)) and stable fraction. High-mountain ecosystems like the Alps are sensitive to changing environmental conditions such as global warming. A warmer climate and the more favourable conditions it brings for biological activity, especially at cooler sites, will probably lead in the short- to mid-term to an increased loss of accumulated, weakly degraded OM. As the Pb and Cu content is significantly related to the labile organic matter pools, the risk exists that an increase in OM mineralisation could affect the storage capacity and mobility of these metals in soils.
We investigated the effect of organic matter and weathering on the lability and solid phase speci... more We investigated the effect of organic matter and weathering on the lability and solid phase speciation of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) in two contrasting subalpine regions in the Italian Alps. Cr, Ni and Cu could be linked to weathering. This was not the case for Pb. Since organic matter (OM) influences the solid phase speciation of heavy metals, the total organic C and N content, the C and N content of different density fractions of OM and also of the labile (oxidised by H(2)O(2)) and stable (H(2)O(2)-resistant) fractions were determined. Soil OM stocks were high and soils on north-facing slopes had more OM than the south-facing sites to which they were paired. Density measurements and the H(2)O(2) fractionation indicated that the higher OM content on north-facing sites was due to an accumulation of weakly degraded organic material. Due to higher weathering intensity on north-facing sites, the abundance of the EDTA-extractable heavy metals was higher than on south-facing sites. All EDTA-extractable heavy metals showed a good correlation to the water-soluble phenolic concentrations which indicates that the metals were probably translocated as metal-organic complexes. Pb and Cu correlate not only to the light (density < 1 g/cm(3)) and labile, organic fraction but also to the heavy (density > 2 g/cm(3)) and stable fraction. High-mountain ecosystems like the Alps are sensitive to changing environmental conditions such as global warming. A warmer climate and the more favourable conditions it brings for biological activity, especially at cooler sites, will probably lead in the short- to mid-term to an increased loss of accumulated, weakly degraded OM. As the Pb and Cu content is significantly related to the labile organic matter pools, the risk exists that an increase in OM mineralisation could affect the storage capacity and mobility of these metals in soils.
The function of human geophagy has long been questioned. We sought to test hypotheses concerning ... more The function of human geophagy has long been questioned. We sought to test hypotheses concerning its potential physiological effects through analysis of soils and patterns in geophagy behavior. Eleven samples of geophagic soils consumed by pregnant women on Pemba Island, Zanzibar, Tanzania, were characterized according to their color, texture, major element chemistry, trace element chemistry, bulk mineralogy, and clay mineralogy. An epidemiological study (N=2367) and ethnographic interviews (N=57) on Pemba yielded information about geophagic behaviors and sociodemographic and biological characteristics of those who consumed earth. The soils varied widely in color, ranging from light red to white through various shades of brown and yellow, and texture ranged from clay to sand. Major element chemistry of the soils also varied greatly; most were low in Fe and Ca. Trace elements, whether of biological or non-biological significance, were uniformly low when compared with normal ranges of mineral soils. The sole commonality among the samples is that all clay fractions were dominated by a kaolin mineral: kaolinite, halloysite, or a mixture of both. Geophagy behavior also varied greatly, with one major exception: a greater proportion of pregnant women (7.1%) and young children (4.5%) consumed earth than non-pregnant women (0.2%) or men (0%). The presence of kaolin mineral in all samples, its palliative and detoxifying properties, and the highest prevalence of geophagy among those most biologically vulnerable suggest that geophagy may be a protective behavior.
The present work focuses on the subalpine range of the Italian Alps to determine the influence of... more The present work focuses on the subalpine range of the Italian Alps to determine the influence of aspect and consequently climate on soil humus properties and chemistry. This was done by comparing soils developing in north- and south-facing sites on siliceous parent material. The soils were investigated with respect to the total organic C and N content, C and N contents of organic matter (OM) density fractions and of labile (oxidised by H2O2) and stable (H2O2-resistant) fractions. Further characterisation of OM and the different fractions was performed with Diffuse Reflection Infrared Fourier Transform (DRIFT), Scanning Electron Microscopy/Electron Diffuse Scattering (SEM/EDS) and radiocarbon dating. The soils at north-facing slopes had a higher OM content. Density measurements and the H2O2 fractionation proved that this higher content was primarily due to a more pronounced accumulation of weakly degraded, labile organic materials when compared to the south-facing slopes. Independent of the sites, a large part of OM (around 50% of OM) was fixed in the densest fraction (>2 g/cm3) which correlated well with the abundance of the H2O2-resistant fraction. The 14C ages of the latter were up to 17,000 years, reflecting the presence of stable, refractory OM and the effectiveness of organo-mineral interactions in protecting OM from decay. Podzolisation has been more intense at north-facing sites. Due to the accumulation of weakly degraded OM, eluviation of Fe and Al is strongly enhanced. High-mountain ecosystems like the Alps are very sensitive to changing environmental conditions such as global warming. Especially at cooler sites, the obtained results suggest that a warmer climate, and thus more favourable conditions for biological activity, will lead in the short- to mid-term to an increased loss of accumulated, weakly degraded OM.
Mount Amiata is a volcano that has been extinct for 200 ka. It is located in southern Tuscany, ce... more Mount Amiata is a volcano that has been extinct for 200 ka. It is located in southern Tuscany, central Italy, and is composed largely of trachydacitic rocks. The soils of Mt. Amiata show a dark, carbon-rich A horizon that overlies a slightly structured Bw horizon or, directly, a very thick saprolite, which at a depth of about 3 m still maintains some ellipsoidal cores of coherent material. Mineral weathering in two of these soils, one under beech and the other under chestnut, was studied in detail. The mineralogy of the parent rock consists predominantly of volcanic glass with phenocrysts of feldspar (principally K-feldspar), biotite and pyroxene. The main weathering products are an embryonic form of halloysite and gibbsite, while allophane is usually absent or occurs in minor amounts. SEM evidence indicates that the clay minerals form directly from the weathering of volcanic glass in an environment where Si is preferentially depleted in relation to Al. In the saprolite an anomalous situation is observed where optically fresh ferromagnesian minerals are thickly coated by clay particles whereas the surfaces of the glass and feldspar grains are relatively much cleaner. However, the ferromagnesian minerals are also much more heavily colonised by fungal hyphae and it is proposed that this results in the preferential deposition or flocculation of colloidal suspensions which translocate from higher positions in the weathering profile. D
By integrating the results of recent studies on the concentration and flux of Si in European fore... more By integrating the results of recent studies on the concentration and flux of Si in European forest soils (podzols and acid brown soils) with published evidence on the amounts of Si cycled through forest vegetation, we conclude that phytoliths must be the principal immediate source and sink of silica in soil solution, although mineral weathering is the ultimate source. During the growing season, forest vegetation takes up most of the Si made available by weathering of soil minerals and by phytolith dissolution, and converts it into phytoliths. Phytoliths will be the principal source of Si leached from the soil during winter rains and spring snowmelt.
Soil organic matter (SOM) may give precious information about the age of soil landscapes and, thu... more Soil organic matter (SOM) may give precious information about the age of soil landscapes and, thus, can contribute to decipher geomorphic surface dynamics. We tested five methods of isolating the oldest possible stable organic matter of 2 soil profiles developed on a Pleistocene morainic paragneiss substratum in an Alpine environment in northern Italy. Before and after the individual treatments, the organic fraction was dated with 14 C. The first two methods consist of the oxidation of organic matter with 10% hypochlorite (NaOCl), followed by dissolution of minerals with 10% hydrofluoric acid (HF) or 1 M aqua regia. Methods 3 and 4 were similar to the first two but with a changed order of the treatments (chemical oxidation as the last step). Method 5 consisted only of a treatment with hydrogen peroxide (H 2 O 2 ) for 7 days. Methods 1-4 enabled, in theory, the separation of labile, mineral-protected and recalcitrant SOM fractions. With method 5 only two different fractions can be discerned, i.e. a labile one and a stable one. The lowest ages for each soil were obtained with methods 1-3 (5176 and 8835 cal BP). Higher ages were obtained with method 4 (aqua regia and NaOCl). In general, methods 1-4 showed increasing ages with increasing soil depth. The H 2 O 2 treatment, however, left behind an organic fraction with the highest ages of up to 17,000 cal BP in the topsoil and decreasing ages with soil depth. In general, the 14 C ages of the treatment-resistant fraction increased in the order: untreated samples b method 3 (HF + NaOCl) ≤ method 1 (NaOCl + HF) ≈ method 2 (NaOCl + aqua regia) b method 4 (aqua regia + NaOCl) b method 5 (H 2 O 2 ). Before and after the individual treatments, the fractions were analysed for their C and N content, functional groups were measured with FT-IR and complementary information was obtained with SEM-EDS. The changes in functional groups before and after the treatment with methods 1 and 3 were not very distinct. NaOCl was a too weak reagent to oxidise all labile organic matter in soils. It seems to work more or less properly only in soils with a low OC content. The use of HF produced artefacts such as the precipitation of cryolite. This could also influence organic matter (coprecipitation) and finally its age. HF treatment destroyed kaolinite and attacked quartz but did not have a great deal of effect on other phyllosilicates like mica. The subdivision of OM into a labile, mineral-protected and recalcitrant fraction using NaOCl and HF was consequently far from being precise. Consequently, these methods might be considered questionable. About 90% of organic C was oxidised with H 2 O 2 (method 5) but only 60% of N removed. The remaining organic matter was enriched in nitrogen with a C/N ratio between 3 and 10, aliphatic, aromatic and amide compounds. H 2 O 2 isolated the oldest and most stable OM pool. Our results indicate that the isolated organic matter after the H 2 O 2 treatment can probably be used to estimate the age of the earliest formation of Holocene/Pleistocene-aged Alpine soils. The obtained ages corresponded well with the maximum age of charcoal fragments and the geomorphologic settingsin particular the end of the Egesen-equivalent glacial state and the oldest Dryas.
Twenty one samples of relatively pure tubular halloysites (HNTs) from localities in Australia, Ch... more Twenty one samples of relatively pure tubular halloysites (HNTs) from localities in Australia, China, New Zealand, Scotland, Turkey, and the USA have been investigated by X-ray diffraction (XRD), infrared spectroscopy (IR) and electron microscopy. The halloysites occur as cylindrical tubular forms with circular or elliptical cross sections and curved layers and also as prismatic tubular forms with polygonal cross sections and flat faces. Measurements of particle size indicate a range from 40 to 12700 nm for tube lengths and from 20 to 600 nm for diameters. Size distributions are positively skewed with means lengths ranging from 170 to 950 nm and mean diameters from 50 to 160 nm. Cylindrical tubes are systematically smaller than prismatic ones. Features related to order/disorder in XRD patterns e.g. as measured by a 'cylindrical/prismatic' (CP) index and IR spectra as measured by an 'OH stretching band ratio' are related to the proportions of cylindrical versus prismatic tubes and correlated with other physical measurements such as specific surface area and cation exchange capacity. The relationships of size to geometric form, along with evidence for the existence of the prismatic form in the hydrated state and the same 2M 1 stacking sequence irrespective of hydration state (i.e. 10 vs 7 Å) or form, suggests that prismatic halloysites are the result of continued growth of cylindrical forms.
We investigated the effect of organic matter and weathering on the lability and solid phase speci... more We investigated the effect of organic matter and weathering on the lability and solid phase speciation of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) in two contrasting subalpine regions in the Italian Alps. Cr, Ni and Cu could be linked to weathering. This was not the case for Pb. Since organic matter (OM) influences the solid phase speciation of heavy metals, the total organic C and N content, the C and N content of different density fractions of OM and also of the labile (oxidised by H(2)O(2)) and stable (H(2)O(2)-resistant) fractions were determined. Soil OM stocks were high and soils on north-facing slopes had more OM than the south-facing sites to which they were paired. Density measurements and the H(2)O(2) fractionation indicated that the higher OM content on north-facing sites was due to an accumulation of weakly degraded organic material. Due to higher weathering intensity on north-facing sites, the abundance of the EDTA-extractable heavy metals was higher than on south-facing sites. All EDTA-extractable heavy metals showed a good correlation to the water-soluble phenolic concentrations which indicates that the metals were probably translocated as metal-organic complexes. Pb and Cu correlate not only to the light (density < 1 g/cm(3)) and labile, organic fraction but also to the heavy (density > 2 g/cm(3)) and stable fraction. High-mountain ecosystems like the Alps are sensitive to changing environmental conditions such as global warming. A warmer climate and the more favourable conditions it brings for biological activity, especially at cooler sites, will probably lead in the short- to mid-term to an increased loss of accumulated, weakly degraded OM. As the Pb and Cu content is significantly related to the labile organic matter pools, the risk exists that an increase in OM mineralisation could affect the storage capacity and mobility of these metals in soils.
We investigated the effect of organic matter and weathering on the lability and solid phase speci... more We investigated the effect of organic matter and weathering on the lability and solid phase speciation of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) in two contrasting subalpine regions in the Italian Alps. Cr, Ni and Cu could be linked to weathering. This was not the case for Pb. Since organic matter (OM) influences the solid phase speciation of heavy metals, the total organic C and N content, the C and N content of different density fractions of OM and also of the labile (oxidised by H(2)O(2)) and stable (H(2)O(2)-resistant) fractions were determined. Soil OM stocks were high and soils on north-facing slopes had more OM than the south-facing sites to which they were paired. Density measurements and the H(2)O(2) fractionation indicated that the higher OM content on north-facing sites was due to an accumulation of weakly degraded organic material. Due to higher weathering intensity on north-facing sites, the abundance of the EDTA-extractable heavy metals was higher than on south-facing sites. All EDTA-extractable heavy metals showed a good correlation to the water-soluble phenolic concentrations which indicates that the metals were probably translocated as metal-organic complexes. Pb and Cu correlate not only to the light (density < 1 g/cm(3)) and labile, organic fraction but also to the heavy (density > 2 g/cm(3)) and stable fraction. High-mountain ecosystems like the Alps are sensitive to changing environmental conditions such as global warming. A warmer climate and the more favourable conditions it brings for biological activity, especially at cooler sites, will probably lead in the short- to mid-term to an increased loss of accumulated, weakly degraded OM. As the Pb and Cu content is significantly related to the labile organic matter pools, the risk exists that an increase in OM mineralisation could affect the storage capacity and mobility of these metals in soils.
The function of human geophagy has long been questioned. We sought to test hypotheses concerning ... more The function of human geophagy has long been questioned. We sought to test hypotheses concerning its potential physiological effects through analysis of soils and patterns in geophagy behavior. Eleven samples of geophagic soils consumed by pregnant women on Pemba Island, Zanzibar, Tanzania, were characterized according to their color, texture, major element chemistry, trace element chemistry, bulk mineralogy, and clay mineralogy. An epidemiological study (N=2367) and ethnographic interviews (N=57) on Pemba yielded information about geophagic behaviors and sociodemographic and biological characteristics of those who consumed earth. The soils varied widely in color, ranging from light red to white through various shades of brown and yellow, and texture ranged from clay to sand. Major element chemistry of the soils also varied greatly; most were low in Fe and Ca. Trace elements, whether of biological or non-biological significance, were uniformly low when compared with normal ranges of mineral soils. The sole commonality among the samples is that all clay fractions were dominated by a kaolin mineral: kaolinite, halloysite, or a mixture of both. Geophagy behavior also varied greatly, with one major exception: a greater proportion of pregnant women (7.1%) and young children (4.5%) consumed earth than non-pregnant women (0.2%) or men (0%). The presence of kaolin mineral in all samples, its palliative and detoxifying properties, and the highest prevalence of geophagy among those most biologically vulnerable suggest that geophagy may be a protective behavior.
The present work focuses on the subalpine range of the Italian Alps to determine the influence of... more The present work focuses on the subalpine range of the Italian Alps to determine the influence of aspect and consequently climate on soil humus properties and chemistry. This was done by comparing soils developing in north- and south-facing sites on siliceous parent material. The soils were investigated with respect to the total organic C and N content, C and N contents of organic matter (OM) density fractions and of labile (oxidised by H2O2) and stable (H2O2-resistant) fractions. Further characterisation of OM and the different fractions was performed with Diffuse Reflection Infrared Fourier Transform (DRIFT), Scanning Electron Microscopy/Electron Diffuse Scattering (SEM/EDS) and radiocarbon dating. The soils at north-facing slopes had a higher OM content. Density measurements and the H2O2 fractionation proved that this higher content was primarily due to a more pronounced accumulation of weakly degraded, labile organic materials when compared to the south-facing slopes. Independent of the sites, a large part of OM (around 50% of OM) was fixed in the densest fraction (>2 g/cm3) which correlated well with the abundance of the H2O2-resistant fraction. The 14C ages of the latter were up to 17,000 years, reflecting the presence of stable, refractory OM and the effectiveness of organo-mineral interactions in protecting OM from decay. Podzolisation has been more intense at north-facing sites. Due to the accumulation of weakly degraded OM, eluviation of Fe and Al is strongly enhanced. High-mountain ecosystems like the Alps are very sensitive to changing environmental conditions such as global warming. Especially at cooler sites, the obtained results suggest that a warmer climate, and thus more favourable conditions for biological activity, will lead in the short- to mid-term to an increased loss of accumulated, weakly degraded OM.
Mount Amiata is a volcano that has been extinct for 200 ka. It is located in southern Tuscany, ce... more Mount Amiata is a volcano that has been extinct for 200 ka. It is located in southern Tuscany, central Italy, and is composed largely of trachydacitic rocks. The soils of Mt. Amiata show a dark, carbon-rich A horizon that overlies a slightly structured Bw horizon or, directly, a very thick saprolite, which at a depth of about 3 m still maintains some ellipsoidal cores of coherent material. Mineral weathering in two of these soils, one under beech and the other under chestnut, was studied in detail. The mineralogy of the parent rock consists predominantly of volcanic glass with phenocrysts of feldspar (principally K-feldspar), biotite and pyroxene. The main weathering products are an embryonic form of halloysite and gibbsite, while allophane is usually absent or occurs in minor amounts. SEM evidence indicates that the clay minerals form directly from the weathering of volcanic glass in an environment where Si is preferentially depleted in relation to Al. In the saprolite an anomalous situation is observed where optically fresh ferromagnesian minerals are thickly coated by clay particles whereas the surfaces of the glass and feldspar grains are relatively much cleaner. However, the ferromagnesian minerals are also much more heavily colonised by fungal hyphae and it is proposed that this results in the preferential deposition or flocculation of colloidal suspensions which translocate from higher positions in the weathering profile. D
By integrating the results of recent studies on the concentration and flux of Si in European fore... more By integrating the results of recent studies on the concentration and flux of Si in European forest soils (podzols and acid brown soils) with published evidence on the amounts of Si cycled through forest vegetation, we conclude that phytoliths must be the principal immediate source and sink of silica in soil solution, although mineral weathering is the ultimate source. During the growing season, forest vegetation takes up most of the Si made available by weathering of soil minerals and by phytolith dissolution, and converts it into phytoliths. Phytoliths will be the principal source of Si leached from the soil during winter rains and spring snowmelt.
Soil organic matter (SOM) may give precious information about the age of soil landscapes and, thu... more Soil organic matter (SOM) may give precious information about the age of soil landscapes and, thus, can contribute to decipher geomorphic surface dynamics. We tested five methods of isolating the oldest possible stable organic matter of 2 soil profiles developed on a Pleistocene morainic paragneiss substratum in an Alpine environment in northern Italy. Before and after the individual treatments, the organic fraction was dated with 14 C. The first two methods consist of the oxidation of organic matter with 10% hypochlorite (NaOCl), followed by dissolution of minerals with 10% hydrofluoric acid (HF) or 1 M aqua regia. Methods 3 and 4 were similar to the first two but with a changed order of the treatments (chemical oxidation as the last step). Method 5 consisted only of a treatment with hydrogen peroxide (H 2 O 2 ) for 7 days. Methods 1-4 enabled, in theory, the separation of labile, mineral-protected and recalcitrant SOM fractions. With method 5 only two different fractions can be discerned, i.e. a labile one and a stable one. The lowest ages for each soil were obtained with methods 1-3 (5176 and 8835 cal BP). Higher ages were obtained with method 4 (aqua regia and NaOCl). In general, methods 1-4 showed increasing ages with increasing soil depth. The H 2 O 2 treatment, however, left behind an organic fraction with the highest ages of up to 17,000 cal BP in the topsoil and decreasing ages with soil depth. In general, the 14 C ages of the treatment-resistant fraction increased in the order: untreated samples b method 3 (HF + NaOCl) ≤ method 1 (NaOCl + HF) ≈ method 2 (NaOCl + aqua regia) b method 4 (aqua regia + NaOCl) b method 5 (H 2 O 2 ). Before and after the individual treatments, the fractions were analysed for their C and N content, functional groups were measured with FT-IR and complementary information was obtained with SEM-EDS. The changes in functional groups before and after the treatment with methods 1 and 3 were not very distinct. NaOCl was a too weak reagent to oxidise all labile organic matter in soils. It seems to work more or less properly only in soils with a low OC content. The use of HF produced artefacts such as the precipitation of cryolite. This could also influence organic matter (coprecipitation) and finally its age. HF treatment destroyed kaolinite and attacked quartz but did not have a great deal of effect on other phyllosilicates like mica. The subdivision of OM into a labile, mineral-protected and recalcitrant fraction using NaOCl and HF was consequently far from being precise. Consequently, these methods might be considered questionable. About 90% of organic C was oxidised with H 2 O 2 (method 5) but only 60% of N removed. The remaining organic matter was enriched in nitrogen with a C/N ratio between 3 and 10, aliphatic, aromatic and amide compounds. H 2 O 2 isolated the oldest and most stable OM pool. Our results indicate that the isolated organic matter after the H 2 O 2 treatment can probably be used to estimate the age of the earliest formation of Holocene/Pleistocene-aged Alpine soils. The obtained ages corresponded well with the maximum age of charcoal fragments and the geomorphologic settingsin particular the end of the Egesen-equivalent glacial state and the oldest Dryas.
Twenty one samples of relatively pure tubular halloysites (HNTs) from localities in Australia, Ch... more Twenty one samples of relatively pure tubular halloysites (HNTs) from localities in Australia, China, New Zealand, Scotland, Turkey, and the USA have been investigated by X-ray diffraction (XRD), infrared spectroscopy (IR) and electron microscopy. The halloysites occur as cylindrical tubular forms with circular or elliptical cross sections and curved layers and also as prismatic tubular forms with polygonal cross sections and flat faces. Measurements of particle size indicate a range from 40 to 12700 nm for tube lengths and from 20 to 600 nm for diameters. Size distributions are positively skewed with means lengths ranging from 170 to 950 nm and mean diameters from 50 to 160 nm. Cylindrical tubes are systematically smaller than prismatic ones. Features related to order/disorder in XRD patterns e.g. as measured by a 'cylindrical/prismatic' (CP) index and IR spectra as measured by an 'OH stretching band ratio' are related to the proportions of cylindrical versus prismatic tubes and correlated with other physical measurements such as specific surface area and cation exchange capacity. The relationships of size to geometric form, along with evidence for the existence of the prismatic form in the hydrated state and the same 2M 1 stacking sequence irrespective of hydration state (i.e. 10 vs 7 Å) or form, suggests that prismatic halloysites are the result of continued growth of cylindrical forms.
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