Reassessment of Polynov's Ion Mobility Series

Abstract

AbstractPolynov (1937) calculated the relative mobilities of important elements in landscapes: Cl > SO4 > Ca > Na > Mg > K > Si > Fe > Al. This series depicts a general weathering sequence that is essential to understanding many aspects of soil genesis and soil geography. It is argued on tbeoretical grounds that Ca and Na are out of proper sequence in Polynov's series. Polynov estimated ion mobilities by comparing the average content of elements in igneous rock to the average content of the same elements in river waters. However, an estimated 80% of the rocks at the earth's surface, which supply most of the leachate to rivers, are sedimentary. Accordingly, Polynov's mobility series was recalculated after adjusting rock chemical composition for the dominance of sedimentary rock types at the earth's surface. By using the elemental composition of igneous rocks in his calculations, Polynov greatly overestimated the amount of Na relative to Ca in rocks providing leachate to rivers. As a result, he significantly underestimated the mobility of Na relative to Ca. It is recommended that Polynov's ion mobility series be modified to the following: Cl > SO4 > Na > Ca > Mg > K > Si > Fe > Al. This study showed that Na is much more mobile (relative mobility 18.0) than Ca (8.1), Mg (5.4), or K (3.5). Therefore, it is recommended that Na be placed in a distinct mobility phase (II) second in relative mobility to Cl and SO4 (I).