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Title: Predicting sedimentary bedrock subsurface weathering fronts and weathering rates

Abstract

Although bedrock weathering strongly influences water quality and global carbon and nitrogen budgets, the weathering depths and rates within subsurface are not well understood nor predictable. Determination of both porewater chemistry and subsurface water flow are needed in order to develop more complete understanding and obtain weathering rates. In a long-term field study, we applied a multiphase approach along a mountainous watershed hillslope transect underlain by marine shale. Here we report three findings. First, the deepest extent of the water table determines the weathering front, and the range of annually water table oscillations determines the thickness of the weathering zone. Below the lowest water table, permanently water-saturated bedrock remains reducing, preventing deeper pyrite oxidation. Secondly, carbonate minerals and potentially rock organic matter share the same weathering front depth with pyrite, contrary to models where weathering fronts are stratified. Thirdly, the measurements-based weathering rates from subsurface shale are high, amounting to base cation exports of about 70 kmol c ha -1 y -1, yet consistent with weathering of marine shale. Finally, by integrating geochemical and hydrological data we present a new conceptual model that can be applied in other settings to predict weathering and water quality responses to climate change.

Authors:
 [1];  [1];  [1];  [1];  [2];  [2];  [2];  [1]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Rocky Mountain Biological Lab., Crested Butte, CO (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1581391
Grant/Contract Number:  
[AC02-05CH11231]
Resource Type:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
[ Journal Volume: 9; Journal Issue: 1]; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; element cycles; hydrology

Citation Formats

Wan, Jiamin, Tokunaga, Tetsu K., Williams, Kenneth H., Dong, Wenming, Brown, Wendy, Henderson, Amanda N., Newman, Alexander W., and Hubbard, Susan S. Predicting sedimentary bedrock subsurface weathering fronts and weathering rates. United States: N. p., 2019. Web. doi:10.1038/s41598-019-53205-2.
Wan, Jiamin, Tokunaga, Tetsu K., Williams, Kenneth H., Dong, Wenming, Brown, Wendy, Henderson, Amanda N., Newman, Alexander W., & Hubbard, Susan S. Predicting sedimentary bedrock subsurface weathering fronts and weathering rates. United States. doi:10.1038/s41598-019-53205-2.
Wan, Jiamin, Tokunaga, Tetsu K., Williams, Kenneth H., Dong, Wenming, Brown, Wendy, Henderson, Amanda N., Newman, Alexander W., and Hubbard, Susan S. Wed . "Predicting sedimentary bedrock subsurface weathering fronts and weathering rates". United States. doi:10.1038/s41598-019-53205-2. https://www.osti.gov/servlets/purl/1581391.
@article{osti_1581391,
title = {Predicting sedimentary bedrock subsurface weathering fronts and weathering rates},
author = {Wan, Jiamin and Tokunaga, Tetsu K. and Williams, Kenneth H. and Dong, Wenming and Brown, Wendy and Henderson, Amanda N. and Newman, Alexander W. and Hubbard, Susan S.},
abstractNote = {Although bedrock weathering strongly influences water quality and global carbon and nitrogen budgets, the weathering depths and rates within subsurface are not well understood nor predictable. Determination of both porewater chemistry and subsurface water flow are needed in order to develop more complete understanding and obtain weathering rates. In a long-term field study, we applied a multiphase approach along a mountainous watershed hillslope transect underlain by marine shale. Here we report three findings. First, the deepest extent of the water table determines the weathering front, and the range of annually water table oscillations determines the thickness of the weathering zone. Below the lowest water table, permanently water-saturated bedrock remains reducing, preventing deeper pyrite oxidation. Secondly, carbonate minerals and potentially rock organic matter share the same weathering front depth with pyrite, contrary to models where weathering fronts are stratified. Thirdly, the measurements-based weathering rates from subsurface shale are high, amounting to base cation exports of about 70 kmolc ha-1 y-1, yet consistent with weathering of marine shale. Finally, by integrating geochemical and hydrological data we present a new conceptual model that can be applied in other settings to predict weathering and water quality responses to climate change.},
doi = {10.1038/s41598-019-53205-2},
journal = {Scientific Reports},
number = [1],
volume = [9],
place = {United States},
year = {2019},
month = {11}
}

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