Dan H. Yaalon

Down to earth

Nature” and “social life” tended to be separated by Enlightenment thinkers, setting the stage for a long-standing tension between geology and social-cultural theory. Such a division suppressed the liveliness that humans have often attributed to material things. Several scholars and artists, many of whom would advocate new materialisms, have attempted to recapture this liveliness. Drawing upon these developments, we use the notion of “geosocialities” (the commingling of the geologic and the social and the sensibilities involved) to facilitate appreciation of the mineral and the alignment between geology and social-cultural theory. While geosocialities overlap with nature-cultures and “biosocialities,” they are “harder” in the sense of drawing attention to geology and its relation to social life. Such a move seems timely, keeping in mind the popular claim that in the Anthropocene, humans have become a geologic force. At the same time, it opens up a down-to-earth form of geopolitics that exceeds classic notions of the term, attending to different geologic scales; to living bodies, human and nonhuman; to solid rock; and to the planet. We develop our argument through engagement with two sites. One concerns the inscription of human activities in volcanic rock, the second the embodiment of isotopes in living beings. These examples raise questions about the multiple scales of geosociality, which intertwine biography and Earth “itself.”Why soil — and soil science — matters.

Soils in the Mediterranean region: what makes them different?

Mediterranean climates are characterized by winter rains — with some months of excess rainfall over evatranspiration, warm and dry summer months with moisutre deficits — drying out soils and their annual vegetation (xeric moisture regime). They are found on western parts of all continents, between the cooler temperature zone and the hot dry desert zone. The largest Mediterranean region, surrounding the Mediterranean Sea extends over 4,300,000 km2 and exhibits a wide variety of soils and geo-ecosystems. Characteristics landscape attributes are the high proportion of mountains with sleep slopes, significant additions of Saharan desert dust to practically all soils of the region, and a large proportion of limestone and other calcareous rocks as soil parent materials. Characteristics soil behavior features are moderate weathering with pervection (leaching, lessivage) of mostly 2:1 clays into B horizons (Xeralfs:Luvisols), hematite-induced reddening of the clays due to summer dehydration of free iron oxyhydroxides, carbonate dissolution and reprecipitation with prevalence of calcic horizons (Xerolls; Calcisols) in semiarid regions, and development of Vertisols, mostly in lowlands, where deep layers of swelling/cracking clays have sedimented. Shallows soils on nearly bare slopes, mostly a result of erosion subsequent to deforestation, are frequent (Leptosols, Cambiosols; Inceptisols, Entisols). Red (or Brown) Mediterranean soils are no longer used as a separate classification group in modern, well defined, soil property-controlled taxonomies (Soil Taxonomy; FAO system), but were partially replaced by Duchaufours term Fersiallitic soils in some classification systems. Terra Rossa continues to be used in some classification for hard limestone derived red soils, mostly shallow. The effects of mans past and current interference with the lanscape are pervasive in most regions, and predictions for possible future effects on the soils and ecosystems, due to greenhouse gas induced warming and rainfall change, are partly negative, partly still too uncertain.

Conceptual models in pedogenesis: Can soil-forming functions be solved?

Abstract Quantitative solutions of the univariant soil-forming functions are reviewed. Lithofunctions are essentially of a comparative nature. Numerical solutions are possible if a coding of the parent material or its properties is made. The number of solutions of topofunctions and climofunctions is already considerable, though too few generally valid equations have been derived. These are required for the further development of the general solutions. Numerical solutions of true biotic functions are likely to remain exceptional and the biotic attributes are best considered as a dependent variable and property of the soil-ecosystem, like any of the soil properties. Several chronofunctions have been obtained for the initial stages of soil formation, and good graphical summaries for long-term soil development functions have been constructed, but strict numerical chronofunctions are rare because the difficulties in isolating and dating properly controlled sites. Runges energy model uses incongruous terms whilst it essentially follows the tenets of the factorial system, but neglects the parent material (capacity) factor. Chesworths weathering trend line does not disprove the absence of the steady state and his inference from this and his criticism of the state factor equation are essentially invalid. Because the number of degrees of freedom in the solution of the general soil formation function is rather large, the best way for advancing the solution of the state equation is by increasing the solutions of the univariant functions. It is suggested that the next step should be the preparation of a family of topofunctions, graphically or numerically, showing their change with time and on different parent materials or under different macroclimates. Computerized simulation models of such multivariate functions can then be prepared and compared with real data for further refinement and for pinpointing univariant functions or equations which are needed for the improvement of the solutions already obtained. Whereas the relevance of the univariant and multivariant functions of the state factors is in deriving the significant or major causal relationships, and thus explain or predict the distribution of soils in space and time, the computer simulation strategy can advance the quantification of the process-oriented models of soil dynamics.

Effect of matrix composition on carbonate nodule crystallization

The mechanism of carbonate nodule formation in three soil profiles of different texture was elucidated by the application of several methods: petrographic microscopy, electron microprobe, and scanning electron microscope analysis. The profiles chosen for detailed investigation included: a loessial Serozem overlying a buried soil developed on calcareous sand in the semiarid climate of the northern Negev, Israel (EH); a polygenetic Husmas soil with secondary carbonate enrichment in a leached red mediterranean sandy clay loam from the southern Pleshet, Israel (GA); a brown Grumusol with carbonate nodules in the lower horizon from the Zebulon valley, Israel (GR). Three kinds of carbonate nodules were distinguished according to their morphology and origin: (1) orthic nodules, which have skeleton grains similar to the surrounding soil and a gradual transition to the soil matrix — these are formed in situ; (2) disorthic nodules, which on the basis of their sharp boundaries can be judged as having been subjected to some pedoturbation but have a fabric resembling the surrounding matrix; and (3) allothic nodules, which have a fabric that differs in composition from the soil in which they are incorporated and are thus judged to have been transported into the soil. This study indicates that the orthic nodules in the loessial Serozem and in the buried soil have been formed by gradual precipitation of carbonate in the microvoids of the matrix resulting in greater density and a partial expulsion of the non-carbonate clay to the fringes. X-ray spectroscopy traverses and cathode-ray distributions of the Al, Mg and Fe by microprobe indicate the presence of clay in the nodule and its gradual increase towards the still active fringes. In disorthic nodules no such increase toward the fringes was observed. Observations with the scanning electron microscope (SEM) indicate a diameter of 1.5–4 μ for the microcalcite in the Serozem and 4–7 μ for that in the buried sandy soil. Both are layered and built up from oval subhedral crystals 0.2–0.6 μ in size, a morphological type which has not been reported previously. From a detailed study of these profiles and from comparisons with some other soils, the authors conclude that the size and growth of the calcite crystals in the nodule is determined by the matrix composition, in particular by the presence of clay minerals. In a coarse-grained sandy matrix, microsparite and sparite precipitate, thus filling the voids. Similarly the vughs between the carbonate-free stable and compact peds of the Grumusol serve as good sites for the crystallization of a sparite fabric. On the other hand, the presence of dispersed clay minerals in the calcareous Serozem soil offers a large number of nucleation points for the formation of a micritic fabric, which then occludes part of the clay minerals. The presence of the clay retards and possibly even prevents a subsequent growth and recrystallization of the calcite crystallites.

Two causes for runoff initiation on microbiotic crusts: Hydrophobicity and pore clogging

Hydrophobicity and pore clogging are suggested as two mechanisms responsible for generating runoff over microbiotic crusts overlying dune sand. Although natural microbiotic crusts in the Hallamish dune field (Negev Desert, Israel) did not show any hydrophobicity, that was not the case with natural crusts subjected to long periods of continuous wetness in the lab. Monoalgal crusts, grown in the lab, also showed high hydrophobicity when dry. The hydrophobicity vanished, however, once the surface was wetted. Runoff on monoalgal lab-grown crusts was obtained when (i) the dry crust exhibited hydrophobic properties and (ii) the wetted crust no longer showed water repellence. Although runoff generation caused by hydrophobicity is expected, it is suggested that runoff initiation when the crusts do not exhibit any hydrophobicity stems from the high water absorption and swelling of the exopolysaccharide cyanobacterial sheaths causing pore clogging. The multi-layered structure of the crust and filament migration to the surface may enhance pore clogging. The experiments and their interpretation are supported by reinterpretation of published data.

Micromorphological fabrics and developmental stages of carbonate nodular forms related to soil characteristics

Abstract Carbonate nodules often constitute the first stage of calcrete formation. Micromorphological analysis of carbonate nodules and nodular fabrics in different soil materials shows that their development is a function of several factors: nature of the host matrix (texture, porosity), carbonate and non-carbonate clay distribution, bulk density and the interactions among them. Different micromorphological stages, therefore, exist in different soil materials. In calcareous, medium-textured soil materials, the stages of nodule formation are related to the increase of the density of the nodule caused by the accumulation of microcalcites. In such a soil material the following stages occur: (1) microcalcites within the low-to-moderate density matrix; (2) microcalcites of moderate to high density and moderately dense, diffuse nodules; parallel calcans may occur; (3) microcalcites of high density with dense microcalcitic nodules. During these stages the amount of non-carbonate clay decreases but is homogeneously dispersed and disseminated with the microcalcites. In general, the size of microcalcites, 1–8 μm, is inversely related to the clay content. In non-calcareous, medium-to-fine textured soil materials, secondary carbonate precipitates in intrapedal and/or interpedal voids as large sparry crystals. Due to pedoturbation processes, the nodules thus formed are subjected to recrystallization, resulting in a microsparry pattern. The development stages are: (1) few calcans and crystal chambers; (2) crystic nodules mainly of sparry crystals and an increase of calcans and crystic chambers; (3) recrystallized nodules composed mainly of microspars. In coarse-grained materials, secondary carbonates precipitate directly in voids as sparry crystals and the resulting nodules are of the crystic type. The large crystals are often subjected to recrystallization. In partly calcareous, coarse-grained materials with additions of calcareous dust, particular micromorphological carbonate forms occur. In the C horizon, cutanic calciasepic fabric forms besides zones of crystic fabric which gradually become calciasepic in the B horizon and include the typical nodular forms of the calcareous medium-textured soil material, together with appreciable amounts of glaebular halos. The processes leading to the formation of these stages occur essentially without a significant biogenic influence. Where carbonate segregation occurs as rhizomorphs surrounding active roots, the fabric is always micritic even in coarse textural soil material.

Evolution of reg soils in Southern Israel and Sinai

Abstract Reg soils (mostly Camborthids and Gypsiorthids) cover some 15% of the Negev and Sinai deserts. Analytical data of seven profiles on depositional surfaces of increasing age in the Negev show clear relationships between ages of surfaces and soil profile features, exemplified in the development of the cambic, salic and gypsic horizons. The youngest soil, a Coarse Desert Alluvium soil (Typic Torriorthent) of dry wadi beds, up to a few thousand years old, has little profile differentiation and is generally non-saline or slightly saline. On the higher terraces connected with the Lisan Formation (about 70 000–12 000 years B.P.) clear profile differentiation and the beginning of development of cambic horizons can be discerned, evident in their colour-textural p differences. The soils are already saline and somewhat gypsiferous. Both soils are not yet defined as Regs because of their negligible or restricted profile differentiation. Reg soils on the older and higher geomorphic surfaces in the Arava Rift Valley, several hundred thousand years old, have well-differentiated profiles, with cambic, salic and gypsic horizons. Below their stony desert pavements, typical Reg soils have light coloured vesicular horizons, over mellow, very pale brown loam, frequently with laminar structure, almost completely stone-free layers. The reddish brown loamy to clay loam B horizons are very saline and show intensive salt weathering of gravels. Gypsic and petrogypsic horizons occur at depth. Such Reg soils represent the stable surfaces and soils of deserts and were developed over a long period of desert weathering.

Saharan dust and desert loess: effect on surrounding soils

Abstract Only specific desert environments are significant suppliers of the millions of tons of dust blown out annually from the Sahara to its fringes and across the seas. The major dustsource is weathered debris detrained by fluvial transport and redeposited on alluvial fans, in wadis and terminal basins. Rocky gravel and wet sebha surfaces are the only effective dust traps in the desert. Thick loess mantles accumulate on the fringes of the desert after medium or long distance transport where the rate of accretion exceeds 50 g m −2 per year over long a period. At lower deposition rates the dust becomes incorporated and assimilated by the local ground soil (or ocean sediment). Such additions have affected distant areas in southern Europe and Africa and have contributed to their fertility. More desert loess-derived or affected soils are likely to be recognized in the future.

Calcium carbonate nodules in soils: 13O/16O and 13C/12C ratios and 14C contents

Abstract δ 18 O values, δ 13 C values and 14 C ages were determined in ten CaCO 3 , nodule populations collected from soil and paleosols in the Israeli coastal plain. The selected soils were carbonate-free when formed and the nodules in them represent either reprecipitation of carbonate illuviated from overlying horizons (descending mode) or precipitated from a raised brackish water table (ascending mode). The 14 C ages represent the times of migration (illuviation) or eustatic movement (both climate-related) and the stable isotopic conditions reflect the environmental conditions at such times. The δ 13 C values of most populations were found to have a wide range and cannot be used to reconstruct former climates. This wide range is attributed to microvariations of pCO 2 in the soil. Because the δ 18 O ranges in the same samples are usually comparable to analytical uncertainties and because the δ 18 O mean values follow an age-correlated pattern, they permit us to place the soils in one of three categories. In two cases where nodules were soft both turned out to be young (∼ 1000 years) and to have wide ranges in δ 18 O values; the latter are apparently due to continual re-equilibration with new soil solutions. In three cases of the descending mode of nodule formation, 12,000–14,000 year-old hard nodules had very narrow δ 18 O whose means reflect the rainfall value at that time. The period between 12,000–14,000 years B.P. is independently known to be one of higher precipitation/evaporation ratio and of more intensive soil formation. These ascending-mode populations of hard nodules had narrow ranges in δ 18 O (reflecting a mixture of sea water and rainfall) and all turned out to be 3,000–4,000 years old. At this period the sea reached its highest elevation, resulting in raising the nearcoast water table.

Catenary soil relationships in Israel, 1. the netanya cate na on coastal dunes of the sharon

Abstract A typical catena of red mediterranean soils in the Sharon area was investigated, consisting of nazazic hamra on the upland, sandy clay loam hamra on the moderate slope, nazaz (= pseudogley) at the footslope and hydromorphic grumusol in the swampy toeslope positions. The pedomorphic surface originated on sandy parent material which became enriched with fine aeolian sediments. Redeposition of this material which accumulated on leaves and other plant residues took place on the footslope and marshy basins. The relative accumulation of the air-borne deposits determined the texture of the soil and in turn also illuviation and turbation processes, clay mineral weathering and leaching intensity. Textural differentiation in well drained profiles on the upper and crest slope is pronounced, indicating a high intensity of leaching and clay mobility. The degree of leaching is also evident in the pH values, clay mineral composition and the population of the exchange complex. Soils of the bottomland and its fringes are poorly drained and show the effect of gleying processes. Clay pans have developed on the footslope. The soils may be considered mature the whole catena is in a dynamic equilibrium with the present environment. The big differences in properties of the various soils in this catena are thus mainly due to processes governed by the relief factor.