Rates of weathering and chemical depletion in soils across a chronosequence of Lake Michigan sand dunes

Accumulation of soil organic matter and depletion of base cations and trace metals were measured in surface soils (i.e., O horizon and upper 15 cm of mineral soil) across a similar to 4150-year soil chronosequence of dune-capped beach ridges bordering northern Lake Michigan. Within 400 years of beach-ridge formation, coniferous forest develops, soil C and N accumulate to steady-state levels of similar to 40 and similar to 1.3 Mg ha(-1), respectively, and the pH of the upper mineral soil decreases from 8.5 to 4.3 as carbonate minerals dissolve. After substantial proportions of Ca and Mg have been removed, an incipient spodic horizon can be observed, the upper surface of which progressively deepens with increasing soil age. Analysis of soil strain of the upper mineral soil showed gradual dilation reaching 121% after several centuries of soil development. After accounting for soil dilation, quantities of Ca, Mg, P, Zn, Mn, Fe, and V in the upper 15 cm of mineral soil decreased exponentially to low asymptotic levels representing quantities contained in weathering-resistant minerals. Mass balance modeling indicated weathering and elemental losses in the order of decreasing decay constant as: Ca > Mg > Mn > Zn = P > V > Fe > Al > K > Na, Ti. This sequence is consistent with weathering of carbonates, then ferromagnesian minerals, then feldspars. P levels are tightly coupled with Ca losses in soils older than 200 years, suggesting that Ca, rather than Fe or Al, stabilizes P. High concentrations of heavy metals in the organic horizon relative to the upper mineral soil indicate atmospheric inputs of industrial pollutants. (C) 1998 Elsevier Science B.V. All rights reserved.