Resolving the scale-dependence of mineral weathering rates

Comparison between mineral weathering rates determined in the laboratory an d in the field commonly reveals large discrepancies, with order(s)-of-magni tude lower rates in the field. Such unresolved scale-dependence seriously l imits our ability to extrapolate laboratory results to other scales and con ditions. This extrapolation is necessary for quantifying environmental impa cts, for instance from acid mine drainage, acid deposition, soil acidificat ion, geological disposal of hazardous waste, and weathering feedback to cli mate change. We use the well-characterized deposits of mining waste rock at the Aitik site in northern Sweden, for which weathering rates have been pr eviously 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 ef fects of a few critical and readily available, bulk-averaged physicochemica l characteristics. The fact that this scale-dependence exhibited by the Ait ik data is consistent with other laboratory and watershed studies suggests that at least some of the quantified effects are of general applicability a nd importance when extrapolating weathering rates from the laboratory to th e field.