Completion of Glen Canyon Dam in 1963 resulted in complete elimination of sediment delivery from the upstream Colorado River basin to Grand Canyon and nearly complete control of spring snowmelt floods responsible for creating channel and bar morphology. Management of the river ecosystem in Grand Canyon National Park now relies on dam-release floods to redistribute tributary-derived sediment accumulated on the channel bed to higher-elevation sandbars. Here, we used multivariate mixing analysis of sediment elemental compositions to evaluate the extent to which flood deposits derive from tributary-supplied sand compared to reworked, relict predam sediment. The concentrations of seven major and trace elements (Fe, Ca, K, Ti, Rb, Sr, and Zr) were measured in very fine–, fine-, and medium-grained sand from flood deposits using X-ray fluorescence and interpreted using a Bayesian mixing model to characterize the proportion of sand originating from the Paria River, the only major tributary within the study reach. Flood deposits from the 2013 and 2014 controlled floods contained 69% ± 16% and 84% ± 20% Paria River–derived material, respectively, with substantial variation among sites. Based on a sand mass balance, we calculated that under decreasing storage conditions since 1963, ∼77%–83% of the annual Paria River sand flux needs to be retained within the mass of active sand stored in Marble Canyon each year to reach the observed concentration of Paria River sand at sample locations. This finding suggests that the use of controlled floods may continue to be effective for sandbar maintenance, provided sand inputs from the Paria River do not decline.

中文翻译：

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使用亚利桑那州亚利桑那州大峡谷国家公园的元素示踪剂估算支流沙输入对受控沙床修复用洪水沉积的贡献

格伦峡谷大坝于1963年竣工，从而彻​​底消除了从上游科罗拉多河流域到大峡谷的沉积物输送，并几乎完全控制了造成通道和条形形态的春季融雪洪水。现在，大峡谷国家公园的河流生态系统管理依靠大坝泄洪，将河床堆积的支流沉积物重新分配给高海拔沙洲。在这里，我们使用了沉积物元素组成的多元混合分析来评估从支流补给的沙土中获得的洪水沉积物与经过改造的，遗留的坝前沉积物相比的泛滥程度。分别以极细，极细，高，低，高，低的浓度测量了七个主要和微量元素（Fe，Ca，K，Ti，Rb，Sr和Zr）的浓度。用X射线荧光分析洪水沉积物中的中粒沙子，并使用贝叶斯混合模型进行解释，以表征源自帕里亚河（研究范围内唯一的主要支流）的沙子所占的比例。2013年和2014年受控洪水的洪水沉积物分别含有帕里亚河衍生的69％±16％和84％±20％的物质，各站点之间差异很大。根据砂的质量平衡，我们计算出自1963年以来在不断减少的存储条件下，每年需要将每年约有77％–83％的帕里亚河砂通量保留在大理石峡谷中存储的活性砂中样品位置的帕里亚河砂浓度。这一发现表明，受控洪水的使用可能会继续有效地维护沙洲，