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New Caledonia is an island located in the south-west of the Pacific Ocean, containing large nickel resources. It is currently the world's sixth largest nickel producer. Although the mining sector has contributed to the economic growth in New Caledonia since the 1870s, it is considered to be the main driver of environmental degradation. Indeed, the excessive sediment input generated by soil erosion from open-cast mining areas has strongly modified the morphology of rivers (hyper-sedimentation) and impacted the island's ecosystems (flooding, lagoon siltation, water pollution).Nevertheless, the past and ongoing contributions of suspended sediment sources have not yet been quantified. The objective of the current research is to characterize the evolution of sediment source contributions over the last 40 years to identify the mining activities impacts (showing a peak in the 1970s) and the sediment pollution.To this end, a pilot sediment tracing study has been conducted in one of the first areas exploited for nickel mining, the 400-km² Thio River catchment. Mining (ie. overburden, bare mining soil and access road erosion) and no-mining sources (ie. landslides, bushfires) were identified with an approach combining radionuclide and geochemical measurements. In addition, a 1.60 m long sediment core was collected in the Thio river deltaic floodplain in April 2016. Sediment dating was carried out on the chronology of flooding based on a rainfall-discharge statistical analysis in the Thio region. A distribution modelling approach was used to reconstruct sediment source contribution temporal variability in the successive sediment layers.Results demonstrate that the contribution of mining sources largely dominated with a mean contribution of 65 % over the entire profile. The fifteen flooding events identified by the statistical analysis generated the deposition of around 1 m of sediment in the floodplain at that location over the last forty years. An increase in the mining source contribution was observed along the sediment profile and particularly at 1-m depth, i.e. a depth corresponding to the 1970s nickel production peak. In the future, similar studies should be carried out in other catchments draining mines in New Caledonia to investigate whether the temporal changes in the mining source contribution were similar to those observed in the Thio river catchment in order to guide the implementation of control measures. [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]