A coupled geomorphic and geochemical model for testing the dominant controls on chemical weathering rates in eroding landscapes

关于化学风化速率的主要驱动因素，出现了激烈的辩论。一种假说认为，由于风化反应是由孔隙水化学驱动的，气候，特别是降雨，控制着化学风化速率。相反，另一种假设认为化学风化是由风化带中“新鲜”矿物的供应驱动的，而化学风化的主要驱动力是物理侵蚀。评估这两个假设的相对重要性的研究取得了有限的成功。一方面，侧重于孔隙水化学的详细地球化学研究没有考虑物理剥蚀和侧向沉积物搬运等地貌过程。这些研究无法深入了解侵蚀景观导致化学风化速率增加的机制。这是因为化学风化速率在空间上是不均匀的（正如世纪的土壤科学所证明的那样），侵蚀物质以不同的化学风化速率不断横向移动通过景观的各个部分。另一方面，对侵蚀驱动的风化速率的研究主要是基于盆地范围内风化速率的经验研究，没有考虑风化反应。为了真正研究气候和物理侵蚀对化学风化速率的相对重要性，必须考虑风化反应和沉积物的产生和运输。在这项研究中，PI首次提出将最先进的地球化学模型与详细的地貌模型联合收割机相结合。提出的模型将能够预测耦合的地球化学和地貌演变的山坡土壤使用两个端元化学风化假说。为了测试该模型，以及化学风化的两个驱动因素的相对重要性，已确定了一个现场的两个端元假设预测对比的化学风化的空间分布。该现场具有独特的综合地貌和地球化学测量系列：现场测量可独立校准模型，并将模型结果与长期化学风化速率和固态化学进行比较。因此，通过结合使用最先进的数值模拟和详尽的地球化学和地貌数据集，该项目将测试气候（通过降雨和孔隙水化学）或物理侵蚀率是否在控制侵蚀景观的化学风化率方面占主导地位。

A vigorous debate has emerged over the primary driver of chemical weathering rates. One hypothesis states that because weathering reactions are driven by pore water chemistry, climate, specifically rainfall, controls chemical weathering rates. In contrast, another hypothesis states that chemical weathering is driven by the supply of 'fresh' minerals to the weathering zone, and the dominant driver of chemical weathering is physical erosion. Studies evaluating the relative importance of these two hypotheses have had limited success. On the one hand, detailed geochemical studies that focus on pore water chemistry make no provision for geomorphic processes such as physical denudation and lateral sediment transport. Such studies cannot yield insights into the mechanisms that drive increased chemical weathering rates from eroding landscapes. This is because chemical weathering rates are spatially heterogeneous (as a century of soil science can attest) and eroding materials continuously move laterally through parts of the landscape with varying chemical weathering rates. On the other hand, studies focusing on weathering rates driven by erosion are largely based on empirical studies of basin wide weathering rates and make no provision for weathering reactions. To truly examine the relative importance of climate and physical erosion on chemical weathering rates, one must account for both weathering reactions and the generation and transport of sediment. In this study the PI proposes, for the first time, to combine a state of the art geochemical model with a detailed geomorphic model. The proposed model will be capable of predicting the coupled geochemical and geomorphic evolution of hillslope soils using both end member chemical weathering hypotheses. To test the model, and the relative importance of the two drivers of chemical weathering, a field site has been identified where the two end member hypothesis predict contrasting spatial distributions of chemical weathering. This field site has a uniquely comprehensive series of both geomorphic and geochemical measurements: at the site measurements exist to independently calibrate the model and compare model results with long term chemical weathering rates and solid state chemistry. Thus, by using a combination of state of the art numerical modelling and an exhaustive geochemical and geomorphic dataset, this project will test if climate (via rainfall and pore water chemistry) or physical erosion rates are dominant in controlling chemical weathering rates in an eroding landscape.