ABSTRACT

This 20-month study of a prairie hillslope seep system builds upon and extends the soil moisture record from a previous study conducted during the most extreme drought ever recorded in Texas. We seek to improve understanding of how prolonged drought impacts seep-headwater hydrology, and to determine how well dominant vegetation reflects changes in volumetric soil moisture (θv). Results show the entire hillslope saturates after storm events, but due to severe drought, no surface runoff or channel flow was recorded. We documented changes in soil moisture, with the highest θv occurring along the deeper footslope soils. We hypothesize hyperseasonal environments, or seasonal waterlogging/desiccation of upland vegetation in poorly drained soils, exist in the study area and are the first to quantify hyperseasonality, or % change in magnitude of θv throughout a hydrologic year. The seep and riparian plots aligned with lower hyperseasonality, indicating seasonal hypoxia, but not complete desiccation. High hyperseasonality occurred along the midslope barrens, indicative of a true hyperseasonal environment. We suggest a ≥ 90% threshold would likely indicate true hyperseasonal cyclicity of anaerobic and xeric regimes. Our results provide insight to how extreme drought impacts seep-headwater systems, and how predicted hotter, drier conditions may alter their hydrologic regime.

摘要

这项为期 20 个月的草原山坡渗水系统研究建立在并扩展了先前在德克萨斯州有史以来最极端干旱期间进行的研究的土壤湿度记录。我们寻求加深对长期干旱如何影响渗水源水文的理解，并确定主要植被如何很好地反映体积土壤水分 (θv) 的变化。结果显示，风暴事件后整个山坡饱和，但由于严重干旱，没有记录到地表径流或河道流量。我们记录了土壤水分的变化，最高的 θv 发生在更深的山坡土壤中。我们假设研究区域存在超季节性环境，或高地植被在排水不良的土壤中的季节性内涝/干燥，并且是第一个量化超季节性的，或 整个水文年 θv 幅度的百分比变化。渗水和河岸地块与较低的超季节性一致，表明季节性缺氧，但不完全干燥。沿中坡贫瘠之地发生高度超季节性，表明存在真正的超季节性环境。我们建议 ≥ 90% 的阈值可能表明厌氧和干旱状态的真正超季节性循环。我们的结果提供了关于极端干旱如何影响渗水源系统以及预测的更热、更干燥的条件如何改变其水文状况的见解。我们建议 ≥ 90% 的阈值可能表明厌氧和干旱状态的真正超季节性循环。我们的结果提供了关于极端干旱如何影响渗水源系统以及预测的更热、更干燥的条件如何改变其水文状况的见解。我们建议 ≥ 90% 的阈值可能表明厌氧和干旱状态的真正超季节性循环。我们的结果提供了关于极端干旱如何影响渗水源系统以及预测的更热、更干燥的条件如何改变其水文状况的见解。