Sediments stored in reservoirs provide useful information about landscape erosion rates that are needed for understanding the geomorphologic evolution of sites and also for engineering purposes. In arid and semi-arid landscapes, the differentiation of sedimentation pulses is required since landscape erosion usually occurs in short periods and involves the mobilization of large volume of sediments. We analyzed the sediments stored at the El Molinito dam, that was built in 1991, which is located in the lower course of the Sonora river, NW Mexico. The river basin of the study area is dominated by arid to semi-arid conditions, where human activities are characterized by the extensive grazing for cattle and open-pit mining. The physical properties of sediments were analyzed using OSL, fall-out Cs-137, K-40 and magnetic susceptibility (MS) from four sediment cores. We found that the IRSL/BLSL and MS reveal how the density of grains settled at different parts of the reservoir changed prior and after the dam construction. The K-40 data exhibit a similar result as the IRSL/BLSL and MS values. The activity of Cs-137 has a similar pattern prior and after the dam construction, what indicates that this tracer is unaffected by the dam construction. We found that the Cs-137 is a reliable indicator of how rainfall relates to erosion within the river basin. We conclude that the IRSL/BLSL and MS analysis can aid the interpretation of how sediment is mobilized prior to their deposition and transport in arid to semi-arid landscapes where erosion is episodic and seasonal. Moreover, the approach used in this research can be used for engineering studies to accurately identify the depth at which the sedimentation of reservoir initiates and to estimate the different sedimentation rates. We also found that the analysis of Cs-137 in the sediments stored in the dam also yield useful information of the dominant landscape dynamics. This information is valuable using climate data since they allow the understanding of the main mechanisms related to the sediment routing from source-to-sink in dams built around the 1950s.

储存在水库中的沉积物提供了有关景观侵蚀率的有用信息，这些信息对于了解场地的地貌演变和工程目的都是必不可少的。在干旱和半干旱景观中，由于景观侵蚀通常发生在短时间内并且涉及大量沉积物的流动，因此需要区分沉积脉冲。我们分析了 El Molinito 大坝储存的沉积物，该大坝建于 1991 年，位于墨西哥西北部索诺拉河下游。研究区流域以干旱至半干旱条件为主，人类活动以放牧放牧和露天采矿为特征。沉积物的物理性质使用 OSL、Fall-out Cs-137、来自四个沉积物岩心的 K-40 和磁化率 (MS)。我们发现 IRSL/BLSL 和 MS 揭示了在大坝建造前后沉积在水库不同部位的颗粒密度如何变化。K-40 数据表现出与 IRSL/BLSL 和 MS 值相似的结果。Cs-137 的活性在大坝建设前后具有相似的模式，这表明该示踪剂不受大坝建设的影响。我们发现 Cs-137 是降雨与流域内侵蚀关系的可靠指标。我们得出结论，IRSL/BLSL 和 MS 分析可以帮助解释沉积物在沉积和运输之前如何在干旱到半干旱景观中流动，其中侵蚀是偶发性和季节性的。而且，本研究中使用的方法可用于工程研究，以准确识别水库开始沉积的深度并估计不同的沉积速率。我们还发现，对储存在大坝中的沉积物中 Cs-137 的分析也产生了有关主要景观动态的有用信息。这些信息对于使用气候数据很有价值，因为它们有助于了解与 1950 年代左右建造的大坝中从源到汇的沉积物路径相关的主要机制。