Heavy Metals As Indicators of Serpentinitic Soils.

Abstract: Serpentinitic soils are characterized by low calcium to magnesium ratio, high heavy metal contents, and relatively low concentrations of plant macronutrients. An evaluation of a toposequence in the South Hills Open Spaces in San Luis Obispo, CA, was performed, in order to better understand the chemical properties indicative of soils derived from serpentinitic parent materials. US EPA Method 3050a was used to determine “total” concentrations of cobalt, chromium, manganese, nickel, and zinc for each horizon of six slope positions. Calcium increased with soil depth in more developed soils of the catena. Concentrations of Ni and Cr also increased with depth, while amounts of Co, Mn, and Zn generally decreased with depth at most slope positions. Subsurface soil horizons contained higher clay percentages and were more enriched in metal concentrations than surface horizons. Heavy metal concentrations decreased in Cr horizons relative to the solum and all soils had extremely low Ca to Mg ratios (<0.5). This latter chemical property was most diagnostic of soils derived from serpentinitic parent material in our study, and will influence the vegetation of these soils. A comprehensive knowledge of serpentinite properties is necessary to ensure proper land management and coordinate future agricultural applications in the numerous regions worldwide where serpentinitic parent materials occur.