Mineral Dissolution Rates in Plot-Scale Field and Laboratory Experiments

摘要

In recent years, much research has been focused on the mechanisms by which aciddeposition from the atmosphere is neutralized as it passes through soil. Although there are several short-term mechanisms of acid buffering, the dominant long-term mechanism is mineral weathering. Understanding the rates at which minerals weather in the soil is thus essential for predicting the long-term effects of acid deposition on surface-water chemistry. Mineral dissolution rates were measured on identical mineral material in field and laboratory experiments. Field dissolution rates were measured in 6 small (2 sq m) plots on a spodosol in eastern Maine, USA. The plots were irrigated with HCl at pH's 2, 2.5 and 3; soil solutions were collected by tension lysimeters at 25-cm depth. The composition of the soil solutions, together with the grain-size distribution and mineralogy of the soil, were used to calculate mineral dissolution rates. Laboratory dissolution experiments were performed on the 75-150 micrometer size fraction of soil from the site in flow-through reactors at pH-values corresponding to the pH of the bulk soil solution. The use of small plots and 'untreated' minerals from the same plots eliminates many of the uncertainties encountered in previous field-laboratory comparisons.