Predicting sedimentary bedrock subsurface weathering fronts and weathering rates
Predicting sedimentary bedrock subsurface weathering fronts and weathering rates
复制标题
预测沉积基岩地下风化锋和风化速率
作者：
J. Wan;T. Tokunaga;K. Williams;W. Dong;Wendy S Brown;A. Henderson;A. Newman;S. Hubbard
尽管基岩风化强烈影响水质和全球碳、氮收支，但地下岩层的风化深度和风化速率尚未得到很好的了解和预测。为了更全面地了解和获得风化速率，需要测定孔隙水化学和地下水流量。在长期的野外研究中，我们沿着海相页岩下的山区分水岭山坡样带应用了多阶段方法。在这里，我们报告了三个发现。首先，地下水位的最深程度决定了风化锋，而年地下水位波动的范围决定了风化带的厚度。在最低水位以下，永久饱和水的基岩仍在减少，防止了更深层次的黄铁矿氧化。其次，碳酸盐矿物和潜在的岩石有机质与黄铁矿具有相同的风化前缘深度，与风化前缘分层的模式相反。第三，基于测量的地下页岩风化速率很高，盐基阳离子输出量约为70kmolc ha−1 y−1，但与海相页岩的风化一致。最后，通过综合地球化学和水文数据，我们提出了一个新的概念模型，该模型可以应用于其他环境，以预测风化和水质对气候变化的响应。
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：
10.1073/pnas.1404763111
发表时间：
2014-04
期刊：
Proceedings of the National Academy of Sciences
影响因子：
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作者：
D. Rempe;W. Dietrich
通讯作者：
D. Rempe;W. Dietrich