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Pyrite Oxidation Drives Exceptionally High Weathering Rates and Geologic CO 2 Release in Mountaintop‐Mined Landscapes
Author(s) -
Ross Matthew R. V.,
Nippgen Fabian,
Hassett Brooke A.,
McGlynn Brian L.,
Bernhardt Emily S.
Publication year - 2018
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2017gb005798
Subject(s) - weathering , pyrite , carbonate , bedrock , sulfate , geology , coal , soil production function , sulfuric acid , acid mine drainage , geochemistry , environmental chemistry , chemistry , soil science , soil water , geomorphology , pedogenesis , inorganic chemistry , organic chemistry
Weathering is the ultimate source of solutes for ecosystems, controls chemical denudation of landscapes, and drives the geologic carbon cycle. Mining and other land‐moving operations enhance physical weathering by bringing large volumes of shattered bedrock to the surface. Yet, the relative influence of these activities on chemical weathering remains poorly constrained. Here we show that catchments impacted by mountaintop removal coal mining have among the highest rates of chemical weathering ever reported. Mined catchments deliver more than 7,600 kg·ha −1 ·year −1 of dissolved solids downstream. The chemical signatures of these exceptionally high weathering rates reflect the product of sulfuric acid weathering of carbonate‐bearing rock, driven by the oxidation of pyritic materials. As this strong acid rapidly weathers surrounding carbonate materials, H + ions are consumed and Ca 2+ , Mg 2+ , and HCO 3 − ions are exported to balance the elevated SO 4 2− exports, generating alkaline mine drainage. The sulfate exports from pyrite oxidation in mountaintop‐mined catchments account for ~5–7% of global sulfate derived from pyrite, despite occupying less than 0.006% of total land area. Further, the suite of weathering reactions liberate 100–450 kg of rock‐derived C·ha −1 ·year −1 as CO 2 , with an additional 90–150 kg C·ha −1 ·year −1 of C released when HCO 3 − reaches the ocean. This rock C release contributes to the high carbon costs of coal combustion.