Chemical weathering and chemical denudation dynamics through ecosystem development and disturbance

Abstract

Mineral weathering and chemical denudation of terrestrial environments are understood by both geochemists, and ecologists to be affected by rooted plant growth. We used unique 20-year "sandbox" experiments to test the predictions of both disciplines regarding the influence of tree growth and harvest on chemical weathering and denudation of Ca2+, Mg2+ and K+. Results showed 3 temporal phases: 1) weathering-dominated rapid uptake of mineral nutrients with retention in trees and soil, and low denudation; 2) biocycling-dominated nutrient uptake with slower tree growth, and chemical fluxes reduced to near zero; and 3) denudation-dominated loss of nutrient reserves after harvest by disruption of biotic regulation. Overall, a red pine sandbox used and retained its resources more effectively than a reference non-vascular system. The results suggest that disturbance may be an important factor controlling chemical denudation rates. Temporal variations of the fluxes highlight difficulties of extrapolating weathering and denudation rates over long timescales. Copyright 2008 by the American Geophysical Union.