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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]

An important step in the sediment source fingerprinting approach is the selection of the appropriate tracing parameters to maximise source discrimination. In order to reduce uncertainties and increase discrimination between sources it may be necessary to use multiple tracing parameters. Accordingly, this study investigates the discrimination and apportionment of sediment sources in a rural agricultural catchment obtained by combining colour, magnetic, and geochemical fingerprinting approaches. The Conceição River catchment (804 km²) has predominantly deep and highly weathered Ferralsols with land-use consisting of croplands (73%), pastures (18%), forests (8%) and other uses (1%). A total of 189 samples were taken from the main sediment sources, including: Croplands (CR, n=78), pastures (P, n=24), unpaved roads (UR, n=38), gullies (G, n=15) and stream bank (SB, n=34). Sediment samples were taken from the surface bed (n=10) of the river and with time integrated samplers (n=4). Twenty-two geochemical tracers, 6 magnetic properties and 24 colour parameters were analyzed. Tracers were selected following a three step procedure, including: (i) a conservative range test (95% confident interval), (ii) a Kruskal–Wallis H test, and (iii) discriminant function analysis (DFA). The DFA was performed using four different sets of variables: (i) geochemical variables only (G); (ii) geochemical+magnetic+colour (GMC); (iii) geochemical+colour (GC); (iv) geochemical+magnetic (GM). The selected tracers were introduced into a modified version of the classical Solver-based mixing model that in order to determine the relative contribution of different sources to in-stream sediment through simultaneously minimizing mixing model difference. The G and GC DFAs both resulted 69% of samples correct classified (SCC) as no colour parameters were selected by the DFA. The GMC and GM approaches improved the discrimination, both resulting in 76% of SCC. For the G and GC approaches, the average source contribution for the 12 sediment samples were P 47%, SB 29%, CR 19%, UR 5% and G 0%. For the GMC and GM approaches, the contribution of each source was P 41%, SB 37%, CR 14%, UR 8% and G 0%. These results are counterintuitive to field observations where cropland is anticipated to contribute more sediment than pastures. Future research should use artificial mixtures to validate these results. Both magnetic and colour parameters hold potential to improve discrimination between sources, particularly magnetic parameters in catchments with high weathered soils. [ABSTRACT FROM AUTHOR]

The hydrological dynamics of a small rural river catchment in southern Brazil have been used to understand the impact of agricultural activity on soil and water resource degradation. The monitoring and modeling strategies employed to better understand the integrated phenomena focus on surface flow dynamics and the associated processes, such as erosion, sediment yield (SY), and chemical element transfer. In this context, monitoring and modeling techniques are combined in order to include the main hydrological processes involved in soil and water resource degradation. The project began in 2002 and over 500 rainfall-runoff-sediment events and suspended sediment concentration make up the hydrological database under different land use and soil management conditions. The 1.2 km2 catchment of the study is characterized by the presence of shallow soils, high slope, intense agricultural activity, and high SY (~150 t.km-2.y-1). Techniques that enable the identification of the origin and redistribution of sediments (e.g fingerprinting approach and Cs137) and hydrograph analysis are being used to further understand the dynamics of SY in the catchment. The comprehension of the factors involved in the SY dynamics has allowed the improvement and application of different mathematical models (e.g., LISEM and WATERSHED) to simulate surface flow and SY. These models are used to represent the influence of soil and water conservation practices while considering the interaction between the different landscape components (crops, roads, drainage network, etc.). From this set of data and tools, the capacity of the agricultural production system, drainage network, wetlands and riparian forests in accelerating or retarding water flow, sediment, and chemical elements in the landscape are evaluated. All of these studies have been used to improve soil and water conservation practices at catchment scale, meeting the expectations of farmers in erosion control and water storage as well as of the society interested in maintaining the hydrological functions of soils in catchment scale. [ABSTRACT FROM AUTHOR]

A major challenge in geomorphology is reconciling the disparity between runoff coefficients and erosion rates from the field to the catchment scale. In the European loess belt, a decrease of runoff coefficients and erosion rates occurs with increasing spatial scales. Indeed, it is important to understand the scale dependency of run-off and erosion to manage the off-site impacts of accelerated soil erosion. Accordingly, a continuous simulation of the scale dependency of runoff and erosion, from the field scale to the catchment scale (100 – 1000 km²) was conducted with the Water and Sediment (WaterSed) model for two catchments (Andelle-756 km², and Austreberthe-214 km²) over 12 years (>1000 events). Scale effects were evident with a 100-fold decrease in runoff coefficients and sediment delivery ratios between the field scale and the catchment scale. In spite of a low variability of the annual rainfall (19%), the inter-annual variability of the runoff volume (37%) and erosion rates (92%) at catchment outlets were high. The inter-annual variability of runoff and erosion was closely linked to the number of extreme events per year and their distribution through the year, in particular during periods with highly crusted soil surface states. For these high magnitude events, a complex distributed modelling approach was not necessary as the ability of the soil surface and of the landscape to retain overland flows are largely exceeded. The seasonality of soil surface characteristics also affected the scale dependency of runoff and erosion, from the field scale to the catchment scale. However, this is only observed up to a certain spatial extent, i.e. where hillslope erosion processes are governed by hortonian overland flow. When saturation flows are generated, topography and soil depth become the dominant factors. Understanding runoff and sediment response at different scales should focus on the location and amount of runoff and sediment production within the catchment and the capacity of the downstream flow path to retain or transfer overland flow and sediment. Furthermore, this study demonstrates the need to implement model that represent both hortonian and saturation flows when simulating erosion events at the catchment scale. [ABSTRACT FROM AUTHOR]