Purpose

Suspended particulate matter (SPM) transport through rivers is a major vector of nutrients and pollutants to continental shelf areas. To develop efficient sediment management strategies, there is a need to obtain quantitative information on SPM sources. For many years, the geochemical properties of SPM have been commonly used as tracers to identify sediment sources. In large watersheds, with numerous sources, the expected alteration of tracers during their transport requires that their reactivity be taken into account.

Materials and methods

To overcome this issue, we tested the use of major and trace element signatures in the residual fraction of SPM, using two different extraction methods. This original fingerprinting approach was applied to the Upper Rhône River basin (~20,000 km²) in order to assess the respective SPM contributions of its main five tributaries (Arve, Ain, Fier, Guiers, and Bourbre Rivers) for contrasted hydrological conditions (base flow periods, flood events and dam flushing). By incorporating element concentrations previously corrected from particle size distribution in a mixing model coupled to Monte Carlo simulations, we estimated the associated uncertainties of the SPM contributions from each tributary. The relative SPM contributions obtained using this fingerprinting approach were compared with those calculated with a 1-D hydro-sedimentary model.

Results and discussion

The use of element concentrations, such as Zn, P, Cu, Pb, Mn, or Sr, in the total fraction of SPM as conservative fingerprinting properties was not suitable, since they are mainly bound (> 50%) to reactive carrier phases. By using Ba, Ni, Fe, Mg, Cu, Sr, and V concentrations in the SPM residual fraction, the apportionment modeling of SPM sources was successfully assessed. The fingerprinting approach showed that, in base flow conditions, SPM originated mainly from the Arve River. During dam flushing event, the fingerprinting approach consistently estimated that re-suspended sediments came from the Arve River, while the 1-D hydro-sedimentary model estimated a proportion of re-suspended sediment originating within the Rhône River.

Conclusions

This original fingerprinting approach highlighted the relevance of using geochemical properties in the non-reactive fraction of SPM in order to obtain reliable information on spatial sources of SPM in a large river basin. This methodology opens up promising perspectives to better track SPM sources in highly reactive environments such as estuaries/delta or in historical sediment archives.

中文翻译：

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颗粒物元素浓度的反应性：法国罗纳河上游悬浮颗粒物来源的分配评估

目的

河流中的悬浮颗粒物（SPM）是向大陆架地区输送养分和污染物的主要媒介。为了制定有效的沉积物管理策略，需要获得有关SPM来源的定量信息。多年来，SPM的地球化学特性通常被用作示踪剂以识别沉积物来源。在有众多来源的大型流域中，示踪剂在运输过程中的预期变化需要考虑其反应性。

材料和方法

为了克服这个问题，我们使用两种不同的提取方法测试了SPM残留部分中主要元素和痕量元素签名的使用。这种原始的指纹识别方法已应用于罗纳河上游流域（〜20,000 km ²），以评估其主要五个支流（Arve，Ain，Fier，Guier和Bourbre河流）在不同水文条件（基准流量时段，洪水事件和大坝冲刷）下的SPM贡献。通过将先前根据粒度分布校正的元素浓度纳入与蒙特卡洛模拟耦合的混合模型中，我们估算了各支流SPM贡献的相关不确定性。将使用这种指纹方法获得的相对SPM贡献与使用一维水沉降模型计算的相对SPM贡献进行比较。

结果与讨论

在SPM的总分数中使用诸如Zn，P，Cu，Pb，Mn或Sr之类的元素浓度作为保守指纹特征是不合适的，因为它们主要结合（> 50％）与反应性载流相。通过在SPM残留分数中使用Ba，Ni，Fe，Mg，Cu，Sr和V浓度，成功评估了SPM源的分配模型。指纹图谱方法显示，在基本水流条件下，SPM主要来源于阿尔维河。在大坝冲洗事件期间，指纹识别方法一致地估计出重新悬浮的沉积物来自阿尔维河，而一维水沉积模型估算出一定比例的重新悬浮的沉积物源自罗纳河。

结论

这种原始的指纹识别方法突显了在SPM的非反应部分中使用地球化学特性的相关性，以便获得有关大流域SPM空间来源的可靠信息。这种方法学开辟了前景广阔的前景，以便在高反应性环境（例如河口/三角洲）或历史沉积物档案中更好地跟踪SPM来源。