Markus Egli

Weathering and evolution of soils formed on granitic, glacial deposits: results from chronosequences of Swiss alpine environments

Abstract Two soil chronosequences of mountainous ecosystems in Switzerland served as the basis to calculate the accumulation of soil organic matter, transformation of pedogenic Fe and Al and net losses of the main elements (Ca, Mg, K, Na, Fe, Al, Mn and Si) by means of mass-balance calculations. Elemental losses due to deglaciation and exposure to the weathering environment were calculated. These mass balance calculations indicate that extensive mineral weathering resulted in significant leaching losses of Si, major base cations, and Al (particularly from the upper horizons). The losses are especially pronounced in the early stages of soil formation. In most cases, the exponential decay model incorporating an asymptotic or logarithmic regression model seems to provide a good description of weathering. The greatest changes in the soil chemistry of these alpine soils on granitic host material occurred within the first 3000–4000 years of soil development. Later, the weathering rates decreased rapidly and the overall depletion of elements nearly reached an asymptote. We also found that the mean ratio of [Al t Fe d ]/[Al d Fe t ] of the fine earth of the A, E and B horizons is closely linked to the duration of soil development. A very rapid decrease of this ratio also occurred at the beginning of soil evolution in order to reach asymptotic values after about 3000 years. Consequently, this ratio could be a good indicator of the age of alpine soils. Furthermore, there is a close relationship between the mass of organic C or N in the whole profile and the soil age: the older the soil the higher the corresponding mass per unit area. The chronofunctions presented give a first attempt of the chemical soil evolution in the Alps. However, only little data has been available up until now regarding alpine soils, and this fact inhibits a more detailed observation of the changes that have occurred over a period of 2000–8000 years of soil formation under similar climatic conditions.

Germination, Genetics, and Growth of an Ancient Date Seed

An ancient date seed (Phoenix dactylifera L.) excavated from Masada and radiocarbon-dated to the first century Common Era was germinated. Climatic conditions at the Dead Sea may have contributed to the longevity of this oldest, directly dated, viable seed. Growth and development of the seedling over 26 months was compatible with normal date seedlings propagated from modern seeds. Preliminary molecular characterization demonstrated high levels of genetic variation in comparison to modern, elite date cultivars currently growing in Israel. As a representative of an extinct date palm population, this seedling can provide insights into the historic date culture of the Dead Sea region. It also has importance for seed banking and conservation and may be of relevance to modern date palm cultivation.

Weathering rates as a function of climate: results from a climosequence of the Val Genova (Trentino, Italian Alps)

A soil sequence in northern Italy along an elevational gradient ranging from moderate (950 m a.s.l.) to high alpine (2440 m a.s.l.) climate zones was investigated with respect to element losses (Ca, Mg, K, Na, Fe, Al, Si, Mn) and the development of clay minerals. Element losses were derived from mass balance calculations that are based on enrichment/depletion factors using immobile element contents (Ti). Mass balance calculations indicated that extensive mineral weathering resulted in significant leaching losses of major base cations (with losses up to >80% of the initial content in the parent material), Al (particularly, from upper horizons) and Si. Element denudation was greatest in subalpine forests near the timberline. Weathering rates decreased with both higher and lower altitudes. The pattern of smectite distribution along the climosequence has strong similarities to the Al, Si, Na and K losses, while an inverse trend could be detected for clay minerals with a high amount of interlayered Al. Highest smectite contents with up to 30% of the clay fraction and also highest weathering rates were found at sites in subalpine forest near the timberline. Higher precipitation rates and the production of chelating compounds in the soil are believed to promote the appearance of smectites. Weathering rates of Na and K were additionally modelled as a function of precipitation and temperature. The relationship between climate and element weathering is strongly nonlinear and is thought to be overshadowed by the pronounced podzolisation effect near the timberline.

Clay mineral formation in soils of two different chronosequences in the Swiss Alps

Two chronosequences of soils developed from postglacial tills, at two different sites in the Swiss Alps, were studied with respect to their soil mineralogy and chemistry. The age of these soils ranged between 0 and 11,500 years. The parent material for both chronosequences was similar, but differences were found in the clay fraction. Within the considered time span, podzols developed at both sites, however at one site already after about 3000 years and at the other a few years later. Especially trioctahedral minerals were strongly weathered within the time span of about 11,000 years. Smectite and regularly interstratified dioctahedral mica/smectite could be found in the most weathered horizons at one site. The origin of smectite could be traced back to both chlorite and trioctahedral mica which supports the fact that smectite is the end product of chlorite alteration and regularly interstratified mica/smectite (or even smectite) the end product of mica weathering in strongly leached and acidified horizons. At the other site, smectite was already present in the parent material, most presumably due to hydrothermal formation. During the first 500 years of soil formation, a kind of retrograde podzolisation was observed leading to the elimination of this smectite. Within the same time, increased amounts of dioctahedral minerals were formed and after 11,000 years, a small proportion of pedogenic smectite was discernible, again. Main clay mineral transformations occurred at both sites within the first 3000 years of soil development. Weathering and transformation reactions were most advanced in the E horizon being almost complete after 3000 years at one site. The presence of significant amounts of chlorite and/or a minimal content of mica of ca. 5% seems, however, to be compulsory in order to detect low charge expandable minerals already after a 3000-year duration of soil formation in the Alps, otherwise smectite formation is retarded.

Formation rates of smectites derived from two Holocene chronosequences in the Swiss Alps

The formation rate of smectitic components in alpine soils is derived from two chronosequences in the Swiss Alps covering a time span of 11 500 years. The soils developed on granitic parent material. The lithologies between the two chronosequences (investigation areas), however, showed some distinct differences with respect to the main mineralogy and, to a lower extent, to the chemistry. The chronofunctions of smectitic phase formation (g/kgclay/year) were fitted to data using an exponential formation model. Extensive mineral weathering resulted in significant losses of chlorite and mica and the corresponding formation of smectite and regularly and irregularly interstratified mica–smectite. This formation is especially pronounced in the early stages of soil formation. Our investigations reveal that the greatest changes in soil clay mineralogy of alpine soils on granitic or gneiss host material occur within the first 1000–3000 years of soil development. At both investigation sites, the annual formation rates are in a similar order of magnitude with 0.1 g/kg/year or even higher at the start of soil formation and with values <0.01 g/kg/year after about 7000 years. The pedogenetic smectites from the E or Bs horizons included several populations with various interlayer charges. This heterogeneity seems to be related to the nature of their precursors.

Melting Glaciers and Soil Development in the Proglacial Area Morteratsch (Swiss Alps): I. Soil Type Chronosequence

ABSTRACT Proglacial areas in the Alps usually cover a time span of deglaciation of about 150 years (time since the end of the “Little Ice Age” in the 1850s). In these proglacial areas soils have started to develop. In view of the foreseeable climate change, the time factor is of growing interest with respect to the landscape and consequently the soil development. We investigated soil changes (primarily on the basis of soil types) in the proglacial area Morteratsch (Swiss Alps) to derive time trends that can be used as a basis for spatial modeling. Differences in the soil development could be primarily interpreted in view of the time scale and topography (landscape shape, slope, aspect). Data was managed with GIS and regression analyses. Input data sets were the digital soil map, the glacial states, and the digital elevation model. The calculations were done raster based (GRID, 20 m resolution). After about 20 years the first signs of soil development could be found. Around 25% of the area of the valley floor is covered with weakly developed Skeletic/Lithic Leptosol after about 30 years of deglaciation. One hundred years of soil development led to a strong decrease of the Skeletic/Lithic Leptosol in favor of the Humi-Skeletic Leptosol and Ranker. Fluvisols and Cambisols play a subordinate role also after 100–150 years. Undisturbed and fast soil evolution was measured in flat positions and on slopes up to about 14°. In general, the various landforms also correlated well with soil evolution. One of the most surprising facts was that the weathering between south- and north-facing sites differed distinctly, with the north-facing sites having the higher weathering rates. Soil moisture seems to be a decisive factor in weathering. Thicker snow packs probably inhibit or reduce soil frost and allow larger fluxes of snowmelt water to infiltrate into already moist profiles. Slope, exposure and to a lesser extent also the landform determined the soil development: these influences could be quantified using regression analyses. These analyses serve as a basis for further spatio-temporal modeling.

Are humus forms, mesofauna and microflora in subalpine forest soils sensitive to thermal conditions?

This study focuses on the biological and morphological development of humus profiles in forested Italian Alpine soils as a function of climate. Humus form description, systematic investigation of microannelid communities and polyphasic biochemical fingerprinting of soil microbial communities (denaturing gradient gel electrophoresis (DGGE) and phospholipid fatty acid analysis (PLFA)) were performed to compare sites differing in mean annual temperature due to different altitude and exposure. Although the soil biota showed complex responses, several differences in soil biological properties seem to be due to thermal differences. Although soil acidity also determines biological properties, it is not a state factor but rather influenced by them. The thickness of the organic layer and the acidification of the subjacent mineral horizon increased under cooler conditions (north-exposure; higher altitude), whereas the thickness of the A horizon inversely decreased. Species richness of microannelid assemblages was higher under warmer conditions (south-exposure; lower altitude) and the vertical distribution of microannelids shifted along the gradient to lower temperatures from predominant occurrence in the mineral soil to exclusive occurrence in the organic layer. Microbial biomass (total PLFA) was higher at the cooler sites; the prevalence of Gram-negative bacteria could be ascribed to their better adaptation to lower temperature, pH and nutrient contents. The δ13C signatures of the PLFA markers suggested a lower decomposition rate at the cooler sites, resulting in a lower respiratory loss and an accumulation of weakly decomposed organic material. DGGE data supported the PLFA results. Both parameters reflected the expected thermal sequence. This multidisciplinary case study provided indications of an association of climate, mesofauna and microbiota using the humus form as an overall link. More data are however needed and further investigations are encouraged.

WEATHERING OF SOILS IN ALPINE AREAS AS INFLUENCED BY CLIMATE AND PARENT MATERIAL

Two soil sequences in northern Italy (Val di Fiemme and Val Genova) along an elevational gradient ranging from moderate (950 m a.s.l.) to high alpine (2440 m a.s.l.) climate zones were investigated with respect to element losses (Ca, Mg, K, Na, Fe, Al, Si, Mn) and development of clay minerals. Soils formed on paleo-rhyolitic parent material in Val di Fiemme and on tonalitic-granodioritic morainic material in Val Genova. All the soils have a similar age (∼12,000 y) and have been classified as Podzols. The soils are very acid and the pH values tend to increase with decreasing altitude. Podzolization processes were most intense in the range of the subalpine forest up to the timberline (1400–1900 m above sea-level (a.s.l.)). Element leaching was greatest in this range and weathering rates decrease with both higher and lower altitudes. Due to the different lithologies and precipitations between the two valleys, the total amount of chemical weathering was slightly different, although the same trends with altitude could be observed. Imogolite-type materials (ITM) are generally of minor importance. Greater concentrations of ITM were observed in the Bhs or Bs horizons of the Episkeleti-Entic Podzols at the lower altitudes. Iron eluviation was similar in all Podzols while larger amounts of eluviated Al were detected in Val Genova. The pattern of smectite distribution along the climosequences had similarities to the trend of cation losses. The largest amount of low-charge expandable minerals seems to exist in the range of the subalpine forest up to the timberline. The development of clay minerals with a smaller layer charge was more advanced in Podzols on rhyolitic material where smectite could be detected in the Bhs and Bs horizon. Parent material influenced chemical weathering in the soils along the two climosequences and essentially determined the degree of weathering and the formation of clay minerals.

Quantitative aspects of carbonate leaching of soils with differing ages and climates

Abstract Carbonate leaching rates in several soils in Switzerland and in the Lake Constance region were calculated and related to landscape development. The leached depth of the soil, the carbonate content and the soil density profile are sensitive to soil age. A first database of carbonate leaching and its relationship to soil age is presented. A simple relationship between the amount of precipitation and carbonate losses was found. Water draining from calcareous soils from subarctic to temperate areas was usually close to equilibrium with calcite and dolomite. Thus, the annual amount of rainfall and consequently the percolation are the most important factors in carbonate leaching. The influence of temperature is comparatively low. Carbonate dissolution rates amounted to approximately 1.7–3.0 mol m−2 year−1 if they are referred (normalised) to 1000 mm soil water fluxes. Soils on coarse parent material may have slightly lower carbonate dissolution rates in the order of approximately 1.7–2.2 mol m−2 year−1 (normalised to a 1000 mm output), while other sites with smaller grain sizes had slightly higher dissolution rates (2.2–3.0 mol m−2 year−1).

Charcoal fragments of Alpine soils as an indicator of landscape evolution during the Holocene in Val di Sole (Trentino, Italy)

Subalpine and Alpine soils in Val di Sole (Trentino, Italy) have been investigated in order to reconstruct vegetation changes and human impact during the Holocene period. Archaeological findings have demonstrated that Alpine sites have been populated since pre-historical times. Humans have had a great impact on the natural landscape evolution. One of the most-used tools has been fire. The use of fire has enabled the landscape to be cleared to provide new pastures for grazing and also to allow it to be used for agricultural purposes. The 14C dating of charcoal fragments found in subalpine and Alpine soils provide information about the type of vegetation, fires, human impact and soil formation throughout the Holocene. The degree of podzolisation indicates weathering effects and provides information about the stability of the surfaces. According to our results, a quick forest expansion establishment phase must have occurred shortly after the Lateglacial around 10 500 cal. BP. Pinus sylvestris, Pinus mugo as well as Larix decidua established in the investigation area in that period. Picea abies had not yet migrated into this region at the transition to the Boreal (around 9000 cal. BP). The vegetation of the investigated area has not substantially changed during the last 10 000 years. Pinus mugo was more widespread in some areas during the Older Atlanticum, and the treeline was about 150 m higher at the end of the Younger Dryas than today. Some other sites were most probably used as pasture during the Bronze Age and later abandoned, leading to a natural reforestation. In the investigated area 13 fire events in the past 10 700 years have been recognised, and seven of them can reasonably be attributed to human origin.