Serpentinite soil

Gasser, U. G., and Dahlgren, R. A. (1994). Sohd-phase speciation and surface association of metals in serpentinitic soils. Soil Sci. 158, 409—420. 

Fig. 2.19 (a)-(c) A serpentinite soil site in France (Massif Central) and the site-typical vegetation ferns (2.19b), including extremely metallotolerant species. Ferns, specialized flowers and some scrubs (2.19c) take over while woodified plants are absent. September 2006, all photographs by the author... 

The readiness with which plants adapt to changing metal spectra in their environment (which is most important in their ability to set root on extreme sites such as serpentinite soils) in the above way is suggesting that, as a rule, metal misallocation can be tolerated within limited ranges only, proving reserves to be small in most cases, in full accord with the assumption that many trace (Ni) and ultratrace (Mo) metals do not execute much more than the minimum number of functions in plants (3) required by SNA reasoning. 

A higher content of magnesium is characteristic of basic and ultrabasic magmatic and metamorphic rocks (e.g., basalt and serpen-tinite) and their weathering products. Mg-rich rock-forming minerals are biotite and other dark-colored silicate minerals, as well as serpentine. In the case of the serpentinite soils, a Mg-adapted natural vegetation has developed. In the case of sediments, dolomite is a Mg-rich limestone young sediments deposited from seawater are also Mg-rich, as can be seen in marsh soils. 

In chernozems formed on serpentinite diluvium, Co content is in the range of 10-30 mg/kg, while in chestnut and chestnut vertic soils, Co concentrations vary from 3-15 and 15-45 mg/kg, respectively. Soils on basalt, andesite and gabbro contain 15-68 mg/kg total Cu. Total Mn in chernozems is in the range of 520-850 mg/kg. Chestnut soils have 42-106 mg/kg Zn content. Total Zn in saline alkali soils is in the range of 40-60 mg/kg Zn. Bioavailable Zn (ammonium acetate-extractable Zn) in chernozems, chestnut soils and saline alkali soils of the steppe zones varies from trace amounts to 3.8 mg/kg (1-8.3% of total Zn). In chernozems of Northern Bulgaria, total B is in the range of 25-53 mg/kg. Boron increases in saline soils and saline alkali soils. 

In the Ural-Sakmara basin, total Cu is 60-70 mg/kg in chernozems on secondary sediments. Chestnut soils on weathered basic rocks in the Or-Kumak basin contain higher Cu (88-96 mg/kg). The average Pb concentrations are 11-25 mg/kg in chernozems derived from serpentinite and secondary/tertiary sediments of the Ural-Sakmara basin. Soils in the Ural-Sakmara basin on serpentinite contain 133 mg/kg total Ni. 

In addition to anthropogenic pollution, some serpentine soils derived from Fe and Mg-rich ultramafic rocks are enriched in Ni, Cr and Co. In North America, ultramafic rocks form two discontinuous bands along the east and west side of the continent. The largest area of ultramafic terrain is in the Klamath Mountains province of northern California and southern Oregon (Lee et al., 2001). Serpentinite is a metamorphic rock formed from low... 

Lee B.D., Graham R.C., Laurent T.E., Amrhein C., Creasy R.M. Spatial distributions of soil chemical conditions in a serpentinitic wetland and surrounding landscape. Soil Sic Soc Am J 2001 65 1183-1196. 

Cobalt toxicity is occasionally found in high-Co soils formed from serpentinite and other ultrabasic rocks. Deficiency is most likely in coarse-textured, acid-leached soils alkaline or calcareous soils and humus-rich soils. Extractability by strong acids can range from very little (< 1%) to a large fraction (>30%) of the total Co, depending on the forms of Co in the soil. 

Chromium is rated as an immobile element, most of which is difficult to extract from soils even by aggressive chemical agents. Toxicity of Cr to plants is occasionally seen in unusually Cr-rich soils formed from the parent rock, serpentinite, or under high pH conditions favorable to Cr oxidation. 

Cu and Zn in concentrations up to three times those of granites. Mg-rich silicate rocks, such as peridotites and. serpentinites, typically enrich. soils, plants and waters with very high amounts of Mg, Fe, Cr, Co, Ni and V, but other trace elements remain very low. Al-rich silicate rocks, such as shales and micaschists, are often rich in sulfur and metal traces such as Zn, Pb, and Cd. In contra.st, carbonate dominated rocks, such as lime.stones or sulfate bearing dolomites, typically contribute to enrich their environment with Mn, F, S, Cl, Ba, Sr, As, Cd and radon. In conclusion, in.sujficient knowledge of this natural contribution can lead to misinterpretations of contaminated sites, e.specially for elements such as Ni, Cr, Zn, V, Cd and As. 

In the parent rock, only Co, Zn, V and particularly Cr and Ni are important trace elements (up to several thousand ppm for the latter two). The other trace elements are below the detection limit of most instruments (bottom of Fig. lOD, Appendix A.3). The soil profile described on Fig. lOD is only 10-cm-thick and lies on peridotites. The soil is acid (pH between 5.7 and 5.9), but the soil percolation and spring waters are alkaline (pH 1.6-1.9). This is a general tendency in soils developed on peridotitic rocks. In a comparable situation on serpentinites, but in a colder climate, Juchler (1988) describes percolation waters whose pH increased from 6.1 in the 0-horizon to 7.2 in the BC-horizon and 8.1 in local springs. Such alkaline waters, buffered by various hydrous Mg-carbonates are typical for ground waters from Mg-rich rocks all over the world (Pfeifer, 1977). 

Apart from the metal rich zones in the neighborhood of ore deposits and other rocks especially rich in particular trace elements such as peridotites and serpentinites, from central Europe, little data exist yet on the dependence of trace element behavior in common rocks. For several elements, such as Ni and As, upper limits of the trace uptake of plants seem to exist. As soil and plant concentrations are concerned, the uptake is normally dependant on the available concentrations determined with extraction methods such as 0.1 N NaN03. Whereas data on higher plants are relatively abundant, more data on naturally Influenced trace elements in mosses and lichens would certainly be useful. 

Lateric surface formations are found in hot and wet tropical areas, seated in the equatorial regions of the world. Laterite soil is usually infertile. Examples of finding places are Brazil, Nigeria, Malaysia and Hawaii (Price, 1986). Lateric covers have mostly a thickness of a few metres but they can, occasionally, be much thicker. Laterite covers are often found on top of acidic rock (i.e. granites, granitic gneiss but also many sediments such as clays and sandstones), whereas the softer lateric soils are formed on rocks that are free of quartz (i.e. basalt, serpentinite and such) (Schellmann, 2007). 

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