Capturing the complexity of soil evolution: Heterogeneities in rock cover and chemical weathering in Montana's Rocky Mountains
Capturing the complexity of soil evolution: Heterogeneities in rock cover and chemical weathering in Montana's Rocky Mountains
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DOI：
10.1016/j.geomorph.2022.108186
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发表时间：
2022-03
期刊：
影响因子：
3.9
通讯作者：
S. S. Benjaram-S.;J. Dixon;A. Wilcox
中科院分区：
文献类型：
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作者：
S. S. Benjaram-S.;J. Dixon;A. Wilcox
我们研究了美国蒙大拿州西部落基山脉北部两座邻近山脉的化学风化、土壤覆盖持久性和地形之间的关系。我们通过调整未风化的岩石碎片、巨石和基岩暴露对局部和景观尺度的贡献，增强了测量化学风化的现有工具。调整后的风化强度认识到，量化山区系统中的风化应该考虑岩石暴露，而不是仅仅关注细粒土幔。我们的研究系统独特的形态是由其独特的气候历史塑造的。以前被冰川覆盖的比特鲁特山脉由陡峭的山坡和丰富的岩石覆盖组成，而邻近的未冰川覆盖的蓝宝石山脉则呈现出凸出的、覆盖着土壤的山坡。超过 380 次土壤厚度测量、118 次土壤和岩石地球化学分析以及数字地形分析表明，富含基岩的系统中的斑块土壤厚度大约是连续土壤覆盖景观中的斑块土壤厚度的一半，并且风化程度减少了约 45%，尽管潮湿的条件预计会增强风化作用。当考虑研究流域土壤和基岩覆盖层中的粗岩石碎片时，这些差异会增加。与富含基岩的 Bitterroot 系统相比，接近连续覆盖的 Sapphire 系统在流域范围内经历的风化强度约为 1.5 倍。山区研究系统中的岩石暴露随着坡度的增加而增加。然而，我们没有发现土壤丰度或风化强度下降的明确阈值，而且即使在最陡的山坡上（占坡度 >30° 的景观面积的约 60%），土壤也具有惊人的弹性。我们的新数据量化了当地和景观尺度的土壤丰度和化学风化强度。这项工作强调了如何将土壤和岩石覆盖的测量纳入量化化学风化的研究中，因为传统方法可能会严重高估和错误描述山区环境中的风化状况。
We investigate the relationship between chemical weathering, persistence of soil cover, and topography in two neighboring mountain ranges in the northern Rockies of western Montana, USA. We augment existing tools for measuring chemical weathering with adjustments for both local and landscape-scale contributions from unweathered rock fragments, boulders, and bedrock exposure. Adjusted weathering intensities recognize that quantifying weathering in mountainous systems should account for rock exposure, rather than focusing solely on fine-grained soil mantles. Our study systems' distinct morphologies are shaped by their unique climate histories. The previously glaciated Bitterroot Mountains consist of steep hillslopes with abundant rock cover, while the neighboring unglaciated Sapphire Mountains display convex, soil-mantled hillslopes. Over 380 soil thickness measurements, 118 analyses of soil and rock geochemistry, and digital terrain analysis reveal that patchy soils in the bedrock-rich system are roughly half as thick as those in the continuously-soil-mantled landscape, and ~45% less weathered, despite wetter conditions that would be expected to enhance weathering. These disparities increase when accounting for coarse rock fragments in soils and bedrock cover across the study catchments. The near continuously soil-mantled Sapphire system experiences ~1.5 times greater weathering intensity at a catchment scale compared to the bedrock-rich Bitterroot system. Rock exposure across the mountainous study system increases with increasing slope gradient. However, we find no clear threshold at which soils decrease in abundance or weathering intensity, and soils are surprisingly resilient even at the steepest hillslopes (comprising ~60% of the landscape area at slopes >30°). Our new data quantify soil abundance and chemical weathering intensity at both local and landscape scales. This work highlights how measurements of soil and rock cover need to be incorporated into studies quantifying chemical weathering, as traditional approaches may significantly overestimate and mischaracterize weathering regimes in mountain environments.