Reactivity of particulate element concentrations: apportionment assessment of suspended particulate matter sources in the Upper Rhône River, France

Abstract

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 km 2 ) 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 discussionThe 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.

Tributary contributions to sediment deposited in the Jacuí Delta, Southern Brazil

“…Unfortunately, there are few alternative methods to take this process into account. When high local anthropogenic pollution levels are found (which is not the case in the current research, otherwise it would have been outlined by the range test), alternative analysis techniques targeting the residual metal fraction were shown to provide an alternative, which may be recommended in study areas characterized by high local anthropogenic pollution levels (Dabrin et al, 2021).…”

Using particle size distributions to fingerprint suspended sediment sources—Evaluation at laboratory and catchment scales

“…The independent validation of sediment source fingerprinting estimates has been rarely undertaken (e.g., Batista et al, 2022; Gaspar et al, 2019). To validate estimated source proportions using PSDs as a fingerprint herein, we used sediment budget estimates generated using conventional water sampling; this has, to date, been used in few sediment fingerprinting studies (e.g., Collins et al, 1998; Dabrin et al, 2021; Tiecher et al, 2022), mainly due to the extra costs associated with the installation of equipment and sampling (Collins et al, 2020, 2017; Collins & Walling, 2004).…”

Improving the design and implementation of sediment fingerprinting studies: summary and outcomes of the TRACING 2021 Scientific School

“…Besides supporting the design of fingerprinting studies, complementary information can also be collected using other geomorphological methods. This includes topographic surveys, the analysis of aerial photographs or satellite images (Foucher et al 2021b ), sediment facies surveys (Minella et al 2008 ; Navratil et al 2010 ; Vandromme et al 2017 ), hydro-sedimentary monitoring (Navratil et al 2012b ; Gateuille et al 2019 ), the calculation of connectivity indices (Borselli et al 2008 ; Chartin et al 2017 ), hydro-sedimentary modelling (Launay et al 2019 ; Dabrin et al 2021 ), and soil erosion modelling (Palazón et al 2016 ). Recent methodological developments relying on cutting-edge devices may enable a more flexible approach in collecting complementary information, such as the deployment of uncrewed aerial vehicles to map sediment connectivity patterns with a high spatial and/or temporal resolution (Heckmann et al 2018 ) across hillslopes and catchments (Estrany et al 2019 ; Hooke et al 2021 ).…”