Quantification of tributaries contributions using a confluence-based sediment fingerprinting approach in the Canche river watershed (France)

Sediment source fingerprints of natural processes and anthropogenic pressures: A contribution to manage the Paraopeba River basin impacted by the B1 tailings dam collapse

Understanding the origins of sediment transport in river systems is crucial for effective watershed management, especially after catastrophic events. This information is essential for the development of integrated strategies that guarantee water security in river basins. The present study aimed to investigate the rupture of the B1 tailings dam of the Córrego do Feijão mine, which drastically affected the Brumadinho region (Minas Gerais, Brazil). To address this issue, a confluence-based sediment fingerprinting approach was developed through the SedSAT model. Uncertainty was assessed through Monte Carlo simulations and Mean Absolute Error (MAE). Estimates of the overall average contributions of each tributary were quantified for each station and annually during the period 2019-2021. It was observed that the sampling point PT-09, closest to the dam breach, contributed to almost 80% of the Paraopeba River in 2019. Despite the dredging efforts, this percentage increased to 90% in 2020 due to the need to restore the highly degraded area. Additionally, the main tributaries contributing to sediment increase in the river are Manso River "TT-03" (almost 36%), associated with an area with a high percentage of urban land use, and Cedro stream "TT-07" (almost 71%), whose geology promotes erosion, leading to higher sediment concentration. Uncertainties arise from the limited number of available tracers, variations caused by dredging activities, and reduced data in 2020 due to the pandemic. Parameters such as land use, riparian vegetation degradation, downstream basin geology, and increased precipitation are key factors for successfully assessing tributary contributions to the Paraopeba River. The obtained results are promising for a preliminary analysis, allowing the quantification of key areas due to higher erosion and studying how this disaster affected the watershed. This information is crucial for improving decision-making, environmental governance, and the development of mitigating measures to ensure water security. This study is pioneering in evaluating this methodology in watersheds affected by environmental disasters, where restoration efforts are ongoing.

Accumulation and transport of nutrient and pollutant elements in riparian soils, sediments, and river waters across the Thames River Watershed, Connecticut, USA

Understanding drivers of nutrient and pollutant elements (NPEs) in soils, sediments, and river water is important for protecting water resources and aquatic ecosystems. The objectives of this study were to quantify accumulation and transport of NPEs (P, As, Cd, Cu, Ni, Pb, and Zn) in riparian soils, sediments, river water, and watershed-scale exports within seven post-industrial subwatersheds of the Thames River, Connecticut, USA. Suspended sediments and river water samples were collected from February 2019 to January 2020. Arsenic concentrations in soil (6 to 18 mg kg-1) and sediments (8 to 85 mg kg-1) generally exceeded state and federal EPA quality targets but not river water. Elevated Pb 'hot spots' occurred in some riparian soils (>2000 mg kg-1) and sediments (>200 mg kg-1), but the other NPEs concentrations were below toxic thresholds. Riparian soil concentrations and watershed land cover were generally weak predictors for NPE concentrations in bottom sediments, suspended sediments, and river water. DOC, Mn, and Fe concentrations were important predictors for area-normalized dissolved and sediment-bound export of NPEs across the seven watersheds. Dissolved export was greater than sediment export for Mn, P, As, Cd, Cu, and Ni but not for Fe, Pb, and Zn. Watersheds with higher farmland had higher P river water concentrations, but the larger, more urbanized watershed had the highest total and area-normalized P export. An estuarine sediment core that captures sediment from the whole watershed and spans pre-industrial conditions through present shows that export of most NPEs has decreased since its peak, but all remain above baseline throughout the Thames River watershed. Future constraints on surface soil-river exchange and erosion inputs are needed to investigate rates of NPE sourcing to the watersheds.

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

PURPOSE

Identifying best practices for sediment fingerprinting or tracing is important to allow the quantification of sediment contributions from catchment sources. Although sediment fingerprinting has been applied with reasonable success, the deployment of this method remains associated with many issues and limitations.

METHODS

Seminars and debates were organised during a 4-day Thematic School in October 2021 to come up with concrete suggestions to improve the design and implementation of tracing methods.

RESULTS

First, we suggest a better use of geomorphological information to improve study design. Researchers are invited to scrutinise all the knowledge available on the catchment of interest, and to obtain multiple lines of evidence regarding sediment source contributions. Second, we think that scientific knowledge could be improved with local knowledge and we propose a scale of participation describing different levels of involvement of locals in research. Third, we recommend the use of state-of-the-art sediment tracing protocols to conduct sampling, deal with particle size, and examine data before modelling and accounting for the hydro-meteorological context under investigation. Fourth, we promote best practices in modelling, including the importance of running multiple models, selecting appropriate tracers, and reporting on model errors and uncertainty. Fifth, we suggest best practices to share tracing data and samples, which will increase the visibility of the fingerprinting technique in geoscience. Sixth, we suggest that a better formulation of hypotheses could improve our knowledge about erosion and sediment transport processes in a more unified way.

CONCLUSION

With the suggested improvements, sediment fingerprinting, which is interdisciplinary in nature, could play a major role to meet the current and future challenges associated with global change.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11368-022-03203-1.

Fingerprinting sub-basin spatial suspended sediment sources by combining geochemical tracers and weathering indices

Transport and deposition of fine-grained sediment, a pervasive nonpoint source pollutant, cause deleterious off-site impacts for water quality and aquatic ecosystems. Sediment fingerprinting provides one means of identifying the spatial sources of mobilised sediment delivered to fluvial systems in order to help target sediment control strategies and uptake of such source tracing procedures has been steadily increasing. Nonetheless, there remains a need to continue testing and comparing different composite signatures for source discrimination including the incorporation of physically grounded information relevant to erosion patterns. Accordingly, the objective of this study was to compare the discrimination and apportionment of sub-basin spatial suspended sediment sources in a mountainous basin in northern Tehran, Iran, using composite signatures comprising conventional geochemical tracers combined with lithological weathering indices or only the former. The list of conventional geochemical properties comprised Al, Ca, Cu, Fe, K, Mg, Mn, Na, Ni, Sr, Ti, and Zn whilst three weathering indices were included: the chemical index of alteration (CIA), the weathering index of Parker (WIP), and the indicator of recycling (IR) which were all calculated based on elemental oxides. Using a composite signature combining conventional geochemical tracers and one weathering index (IR), the relative contributions from the sub-basin spatial sources were estimated at 1 (Imamzadeh Davood; 1.4%), 2 (Taloon; 13.4%), 3 (Soleghan; 35.9%), and 4 (Keshar; 48.4%) compared with corresponding respective estimates of 0.7%, 45.5%, 40.2%, and 13.3% using conventional geochemical tracers alone. Wald-Wolfowitz Runs test pairwise comparisons of the posterior distributions of predicted source proportions generated using the two different composite signatures confirmed statistically significant differences. These differing proportions demonstrated the sensitivity of predicted source apportionment to the inclusion or exclusion of a weathering index providing information reflecting the relative coverage of more erodible lithological formations in each of the sub-basins (32.7% sub-basin 1, 53.6% sub-basin 2, 58.5% sub-basin 3, and 63.2% sub-basin 4). The outputs of this study will be used to target sediment mitigation strategies.

Transfer Pathways and Fluxes of Water-Soluble Pesticides in Various Compartments of the Agricultural Catchment of the Canche River (Northern France)

Five frequently used water-soluble pesticides (atrazine, diflufenican, metolachlor, pendimethalin, and ethofumesate) were monitored in surface water and groundwater of an agricultural catchment (Canche River) in Northern France for examining the edge-of-field pathways of substances and their characteristic time of transport. The study of surface water contamination was conducted in 2016 through two time scales: continuously over one year at a single location of the catchment and punctually during four seasons at 15 sampling locations along a longitudinal river profile. In addition, groundwater in winter and summer shows a generally low and relatively constant contamination level. Nevertheless, the outflow of pesticides from groundwater results in a background contamination of surface water. In addition to this, a contamination peak above the baseline level is observed in surface water subsequently to the period of substance application on the fields. Our results show that pesticides were essentially transported into the surface water by fast flow components (runoff water). Loss of pesticides during the contamination peak period and long-term monitoring were compared showing that the transport of substances within weeks after pesticides spreading dominates the annual flux of pesticides, except for atrazine which shows a constant background contamination pattern. Low frequency monitoring schemes provide only a partial picture of the contamination state and do not enable to evaluate the true contamination state of such rivers with regard to the fact that 3/4 of the annual load of pesticides are transported in the stream during only 2–3 months.

Assessing temporal variability and controlling factors of the sediment budget of a small agricultural catchment in Northern France (the Pommeroye)

A high-frequency monitoring station was implemented at the outlet of the small catchment of the Pommeroye (0.54 km²) in Northern France to study erosion by runoff and hydro-sedimentological responses to heavy rainfall events in the context of Quaternary loess deposits. The aim of this experimental work is to assess the temporal variability of sediment yield and to identify the factors controlling the hydro-sedimentary response. To achieve this goal, statistical and hydro-sedimentary dynamic analyses were performed. During two years of monitoring (April 2016–April 2018), 48 flood events were recorded. The specific sediment yield (SSY) is highly variable and was evaluated to 29.4–70 t km^-2 yr⁻¹ which is conventional for the study region. Most of the sediment yield was produced in winter (55%) and autumn (42%). Only 3% of SSY were produced during spring and summer periods. According to our results, only 6% of the erosive events are responsible for the transport of more than 40% of the sediment flux recorded at the outlet. This underlines the temporal variability of the hydro-sedimentary production in small agricultural catchments for which most of the hydro-sedimentary flux is produced during a limited number of events. The results of statistical analyses show that the total amount of rainfall and the duration of a rainfall episode are the main controlling factors on the hydro-sedimentary response. Our results also suggest that the rainfall kinetic energy better reflects the sediment detachment, and that the 48 h-antecedent rainfall is not linked to the hydro-sedimentary response.