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Purpose: Over the last 60 years, intensification of soil cultivation led to an acceleration of soil erosion and sediment delivery to river systems. In Martinique, this acceleration has led to the remobilization of a toxic insecticide (i.e. chlordecone) used in the 1970s-1990s to control banana weevil. A previous study attributed this accelerated remobilization to the application of glyphosate in plantations from the 1990s onwards. To further unambiguously confirm this link, the identification of soil erosion sources supplied to coastal sediment is essential. Methods: Accordingly, sediment fingerprinting tools were adapted and applied to a coastal sediment core collected in the Galion Bay. Potential source samples (n=37) were collected across the drainage area. Along with the coastal sediment core layers, these samples were analysed for potential tracing properties. The optimal suite of tracers was then selected and introduced into an un-mixing model to quantify their contributions to coastal sediment. Results: Results showed that subsoil (i.e. soil layer < 30 cm depth) and banana plantation soil surface supply the major sources of sediment (49-78% and 12-36%, respectively) to the Galion Bay and that their contributions increased since 2000, in line with chlordecone and glyphosate fluxes. Conclusion: This evolution may be attributed to the higher sensitivity of banana plantations to erosion that may have been enhanced by the glyphosate application leaving the soil uncovered with vegetation and to the contamination of both topsoil and deep soil layers ( < 30 cm) layers with chlordecone due to its vertical transfer along the soil profile and its redistribution across hillslopes. [ABSTRACT FROM AUTHOR]

Purpose: Fine sediment deposition is an important component of the catchment sediment budget and affects river morphology, biology, and contaminant transfer. However, the driving factors of fine sediment deposition remain poorly understood at the catchment scale, limiting our ability to model this process. Methods: Fine sediment deposition and river reach characteristics were collected over the entire river network of three medium-sized (200–2200 km2) temperate catchments, corresponding to 11,302 river reaches. This unique database was analyzed and used to develop and evaluate a random forest model. The model was used to predict sediment deposition and analyze its driving factors. Results: Fine sediment deposition displayed a high spatial variability and a weak but significant relationship with the Strahler order and river reach width (Pearson coefficient r = −0.4 and 0.4, respectively), indicating the likely nonlinear influence of river reach characteristics. The random forest model predicted fine sediment deposition intensity with an accuracy of 81%, depending on the availability of training data. Bed substrate granularity, flow condition, reach depth and width, and the proportion of cropland and forest were the six most influential variables on fine sediment deposition intensity, suggesting the importance of both hillslope and within-river channel processes in controlling fine sediment deposition. Conclusion: This study presented and analyzed a unique dataset. It also demonstrated the potential of random forest approaches to predict fine sediment deposition at the catchment scale. The proposed approach is complementary to measurements and process-based models. It may be useful for improving the understanding of sediment connectivity in catchments, the design of future measurement campaigns, and help prioritize areas to implement mitigation strategies. [ABSTRACT FROM AUTHOR]

Purpose: Spectrocolourimetric measurements provide a relatively inexpensive, quick and non-destructive alternative to the analysis of geochemical and organic matter properties. When used in the analysis of sediments and their potential sources, these colour parameters may provide important information on the dominant processes (i.e. erosion) occurring in the Critical Zone. Here, they are used to investigate whether eroded sediment is derived from forest (i.e. natural), cultivated (i.e. anthropogenic) or subsoil sources in order to assess their potential to monitor the effect of decontamination in regions impacted by fallout from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Materials and methods: Fifteen spectrocolourimetric properties (L*, a*, b*, C*, h, x, y, z, L, a, b, u*, v*, u', v') were measured in potential source (n = 37) and sediment (n = 400) samples collected during 13 campaigns from 2011 to 2017 after major flood events in two catchments (total surface area of 450 km2) draining the main FDNPP radioactive pollution plume. Potential sources included topsoil from forest and cultivated sources along with subsoil material originating from landslides, channel banks and the decontamination of cultivated areas. The optimum set of parameters used in the mixed linear model to calculate the sediment source contributions was obtained through the use of a range test, the Kruskal–Wallis H test and a linear discriminant analysis. Results and discussion: Nine selected colour parameters correctly classified 100% of the source samples (i.e. forest, subsoil and cultivated sources). The results illustrate that cultivated landscapes were the main source of sediment to these river systems (mean 56%, SD 34%) followed by subsoil (mean 26%, SD 16%) and forest sources (mean 21%, SD 24%). However, these contributions varied strongly over time, with a peak of subsoil contributions (mean 57%, SD 17%) in Fall 2015, coinciding with the occurrence of a typhoon after the remediation works. These results were consistent with monitoring studies conducted in the same area that showed the major impact of typhoon Etau in September 2015 on sediment and radiocaesium fluxes. Conclusions: These original results demonstrate that spectrocolourimetric measurements may contribute to the routine monitoring of the effectiveness of remediation works in this post-accidental context. Owing to the inexpensive, rapid and non-destructive analyses, spectrocolourimetric-based tracing methods have significant potential to provide information on the dominant erosion processes occurring in the Critical Zone. [ABSTRACT FROM AUTHOR]

Highlights: [•] We test and validate an improved discharge-concentration rating curve. [•] Sediment fluxes may be calculated from infrequent and degraded concentration data. [•] The number of concentration data matters more than the sampling frequency. [•] We provide an application for some of the major French rivers. [ABSTRACT FROM AUTHOR]

The definition of the Anthropocene boundary is being discussed across various disciplines. In this study, we have focused our research on the sedimentary responses of landscape to human activity, as a response to agricultural changes over the 20th century in Europe.In the absence of long-term records of sediment transported by river systems, sediment deposited in lakes may represent a powerful archive for reconstructing the evolution of sediment yields in response to global changes. Accordingly, sedimentary fluxes were reconstructed in 10 ponds located at the outlet of small agricultural headwater catchments distributed across the Loire Basin, in Western France. These study sites were selected in order to represent a large variety of land cover/land use changes, landscape morphologies and agriculture dynamics. The objective was to investigate whether a common evolution of sediment yields was observed.The results obtained show the occurrence of a general transition in the sediment production during the second half of the 20th century (between 1945 and 1960), with two contrasting trajectories. On the one hand, sediment delivery decreased in catchments witnessing a decline of agriculture, with a 70% decrease of sediment delivery. On the other hand, in lowland areas affected by intensification of land management after WWII (land consolidation, stream redesign, edge removal or agricultural drainage implementation), sediment deposits record a sharp acceleration, by one order of magnitude. The recent sediment dynamics therefore emphasizes a significant change associated to the post-1950 period, with a sharp positive or negative trend. These local observations are in agreement with data compiled from other countries across the Northern Hemisphere (Europe, USA, Japan). In contrast, there is a lack of similar data from catchments located in the Southern Hemisphere (e.g. in South America, developing countries). [ABSTRACT FROM AUTHOR]

Spectrocolorimetric properties provide a quick, low-cost and non-destructive alternative to the measurement of geochemical and organic matter parameters. Their potential to discriminate between forest, cultivated and subsoil sources was tested in soils and sediment collected in coastal catchments draining the main radioactive pollution plume of Fukushima Prefecture, Japan.Fifteen spectrocolorimetric properties were determined in potential source (n=37) and sediment (n=400) samples collected during 13 campaigns from 2011–2017 in two catchments (covering a total surface area of 450 km²) draining the main radioactive pollution plume. Potential sources included topsoil from forest and cropland sources along with subsoil material originating from landslides, channel banks and the decontamination of cultivated areas. The optimum set of parameters used in the mixed linear model to calculate the sediment source contributions was obtained through the use of a range test, the Kruskal-Wallis H-test, and a linear discriminant analysis. Nine colour parameters correctly classified 100% of the source samples (forest, subsoil and cultivated sources). The results illustrate that cultivated landscapes were the main source of sediment to these river systems (mean 56%, SD 34%) followed by subsoil (mean 26%, SD 16%) and forest sources (mean 21%, SD 24%). However, these contributions strongly varied over time, with a peak of subsoil contributions (mean 57%, SD 17%) in Fall 2015, coinciding with the occurrence of a typhoon after the remediation works. These original results demonstrate that spectrocolorimetric measurements provide a powerful tool for the monitoring of the effectiveness of remediation works in this post-accidental context. [ABSTRACT FROM AUTHOR]