Hydrology of a Semiarid Loess‐Paleosol Sequence, and Implications for Buried Soil Connection to the Modern Climate, Plant‐Available Moisture, and Loess Tableland Persistence
Hydrology of a Semiarid Loess‐Paleosol Sequence, and Implications for Buried Soil Connection to the Modern Climate, Plant‐Available Moisture, and Loess Tableland Persistence
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半干旱黄土-古土壤序列的水文特征，以及埋藏土与现代气候、植物有效水分和黄土塬区持久性的联系
DOI：
10.1029/2022jf006800
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发表时间：
2022-12
期刊：
影响因子：
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通讯作者：
T. McDowell;J. Mason;T. Vo;E. Marín-Spiotta
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文献类型：
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作者：
T. McDowell;J. Mason;T. Vo;E. Marín-Spiotta
土壤水文学为了解地貌过程中埋藏的有机碳（OC）的命运以及径流、渗透和植物根系吸收对长期侵蚀和景观演变的影响提供了重要背景。我们使用Hydrus 1D模拟了美国中部大平原侵蚀台地上4.5 m黄土-古土壤序列的水文学，Hydrus 1D是一种数值非饱和流模型，通过高分辨率测量土壤持水率和导水率曲线进行参数化，这对于黄土和古土壤是不同的。我们假设：（a）古土壤与现代气候的联系取决于它们的埋藏深度;（B）根区的古土壤比未风化的黄土具有更宽的孔隙尺寸分布;（c）这种更宽的孔隙尺寸分布增加了根系吸水，使植被对干旱更具适应力，增加了黄土高原的稳定性，尽管土壤具有高侵蚀性和高局部起伏。四年不同的年总降水量进行了模拟观测的配置文件和两个假设的配置文件，一个没有古土壤，另一个浅，强烈发展的古土壤。在这些模拟中，浅古土壤中的土壤水分迅速响应降水，而深埋的古土壤在很大程度上与现代气候脱节，有助于埋藏的OC保存。与我们的预期相反，古土壤的存在并没有增加根吸收相对于未风化的黄土在潮湿或干燥的年份。我们所研究的未风化的粗黄土可能具有最佳的孔隙分布，以便于根系吸收，这为为什么高度易蚀的黄土塬地持续存在提供了另一种假设。
Soil hydrology provides important background for understanding the fate of organic carbon (OC) buried by geomorphic processes as well as the influence of runoff, infiltration, and plant root uptake on long‐term erosion and landscape evolution. We modeled the hydrology of a 4.5‐m loess‐paleosol sequence on an eroding tableland in the U.S. central Great Plains using Hydrus 1D, a numerical unsaturated flow model, parameterized with high resolution measurements of the soil water retention and hydraulic conductivity curves, which were distinct for the loess and paleosols. We hypothesized that (a) the connection of paleosols to modern climate depends on their burial depth, (b) paleosols in the root zone would have broader pore‐size distributions than unweathered loess, and (c) this broader pore‐size distribution increased root water uptake and made vegetation more resilient to drought, increasing the stability of loess tablelands despite high erodibility and high local relief. Four years with varying total annual precipitation were simulated for the observed profile and two hypothetical profiles, one without paleosols and another with a shallow, strongly developed paleosol. In these simulations, soil moisture in shallow paleosols responds quickly to precipitation while a deeply buried paleosol is largely disconnected from the modern climate, contributing to buried OC preservation. Contrary to our expectation, the presence of paleosols did not increase root uptake relative to unweathered loess in either wet or dry years. The unweathered coarse loess we studied may have an optimal pore‐size distribution for root uptake, providing an alternative hypothesis for why highly erodible loess tablelands persist.