Parameterization of river incision models requires accounting for environmental heterogeneity: insights from the tropical Andes
Parameterization of river incision models requires accounting for environmental heterogeneity: insights from the tropical Andes
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DOI：
10.5194/esurf-8-447-2020
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发表时间：
2020-06-03
影响因子：
3.4
通讯作者：
Govers, Gerard
中科院分区：
文献类型：
--
作者：
Campforts, Benjamin;Vanacker, Veerle;Govers, Gerard
景观演化模型可用于评估千年时间尺度上降雨变率对基岩河流下切的影响。然而，在自然环境中分离降雨变率的作用仍然困难，部分原因是对河流下切的环境控制因素（如岩性异质性）的约束较差。在这项研究中，我们使用三种不同的河流功率模型探讨了厄瓜多尔安第斯山脉基岩河流下切速率的空间差异。由于地形降水导致的显著降雨梯度以及高度的岩性异质性使我们能够探究这些控制因素的相对作用。首先，我们使用基于面积的河流功率模型仔细研究岩性异质性在河流下切速率中的作用。我们表明岩性异质性是预测下切速率空间模式的关键。考虑岩性异质性揭示了河流坡度（河流下切的一个指标）与宇宙成因放射性核素（CRNs）得出的剥蚀速率之间的非线性关系。其次，我们使用基于径流和随机阈值的河流功率模型，并结合一个水文数据集，来计算时空径流变率，从而探究这种非线性关系。统计建模表明，河流坡度与剥蚀速率之间的非线性关系可归因于空间径流梯度和下切阈值。我们的研究结果对宇宙成因放射性核素得出的剥蚀速率的整体解释以及河流下切模型的使用有两个主要启示：（i）只有在考虑岩性等环境因素的混杂作用时，应用复杂的河流功率模型来解释景观尺度上的剥蚀速率才是相关的；（ii）地形降水导致的径流空间模式与下切阈值相结合，解释了河流坡度与宇宙成因放射性核素得出的剥蚀速率之间的部分非线性关系。我们的方法可作为一个框架，用于研究区域到大陆尺度上河流下切、岩性异质性和气候之间的耦合关系。
Landscape evolution models can be used to assess the impact of rainfall variability on bedrock river incision over millennial timescales. However, isolating the role of rainfall variability remains difficult in natural environments, in part because environmental controls on river incision such as lithological heterogeneity are poorly constrained. In this study, we explore spatial differences in the rate of bedrock river incision in the Ecuadorian Andes using three different stream power models. A pronounced rainfall gradient due to orographic precipitation and high lithological heterogeneity enable us to explore the relative roles of these controls. First, we use an area-based stream power model to scrutinize the role of lithological heterogeneity in river incision rates. We show that lithological heterogeneity is key to predicting the spatial patterns of incision rates. Accounting for lithological heterogeneity reveals a nonlinear relationship between river steepness, a proxy for river incision, and denudation rates derived from cosmogenic radionuclide (CRNs). Second, we explore this nonlinearity using runoff-based and stochastic-threshold stream power models, combined with a hydrological dataset, to calculate spatial and temporal runoff variability. Statistical modeling suggests that the nonlinear relationship between river steepness and denudation rates can be attributed to a spatial runoff gradient and incision thresholds. Our findings have two main implications for the overall interpretation of CRN-derived denudation rates and the use of river incision models: (i) applying sophisticated stream power models to explain denudation rates at the landscape scale is only relevant when accounting for the confounding role of environmental factors such as lithology, and (ii) spatial patterns in runoff due to orographic precipitation in combination with incision thresholds explain part of the nonlinearity between river steepness and CRN-derived denudation rates. Our methodology can be used as a framework to study the coupling between river incision, lithological heterogeneity and climate at regional to continental scales.