Resolving the Scale-Dependence of Mineral Weathering Rates

Comparison between mineral weathering rates determined in the laboratory and in the field commonly reveals large discrepancies, with order(s)-of-magnitude lower rates in the field. Such unresolved scale-dependence seriously limits our ability to extrapolate laboratory results to other scales and conditions. This extrapolation is necessary for quantifying environmental impacts, for instance from acid mine drainage, acid deposition, soil acidification, geological disposal of hazardous waste, and weathering feedback to climate change. We use the well-characterized deposits of mining waste rock at the Aitik site in northern Sweden, for which weathering rates have been previously published, as a model system for investigating this apparent scale-dependence of these rates. We show that the scale-dependence exhibited by the Aitik data is to a large degree predictable by quantification of the effects of a few critical and readily available, bulk-averaged physico chemical characteristics. The fact that this scale-dependence exhibited by the Aitik data is consistent with other laboratory and watershed studies suggests that at least some of the quantified effects are of general applicability and importance when extrapolating weathering rates from the laboratory to the field.