Abstract Opencast mining has exacerbated land degradation in New Caledonia, a French archipelago located in the south-west Pacific Ocean. Developed since the 1880s, mining has become the major economic activity in some catchments, which strongly disrupted sediment dynamics. Reconstructing the temporal changes of sediment source contributions is essential to understand the driving factors of soil erosion in response to i) the occurrence of cyclones, ii) the changes in mining practices during the last several decades, and iii) other soil degradation processes such as extensive soil erosion induced by fires, overgrazing and trampling of invasive species, and landslides. Accordingly, a multi-parameter analysis including gamma spectrometry, color and X-ray fluorescence measurements was conducted on a sediment core collected in a deltaic floodplain at the outlet of one of the first areas exploited for nickel mining, the Thio River catchment (397-km2). One geochemical tracer (i.e. K) has been used to quantify changes in sediment sources in the successive sediment layers deposited since the beginning of mining activity. The results showed that the contribution of mining tributaries largely dominated, with a mean contribution of 74% (SD 13%) of material sampled in the sediment core. This contribution notably increased after the mechanization of mining activities (i.e. from 1950s; increase of 18%). The occurrence of Cyclone Alison in 1975 triggered the progressive transfer of mining waste accumulated on the foothills over 25 years into the river system. This tipping point could be identified in the sediment sequence, which demonstrates that over the last 41 years (i.e. 1975–2016), a ~84-cm deep sediment deposit has accumulated in the alluvial floodplain of the Thio River catchment (mean annual deposition rate of 2 cm yr−1). Currently, the progressive release and downstream transfer of this mining waste is still ongoing ~45 years after Cyclone Alison. Although environmental legislation was introduced in 1975, mining tributary contributions to sediment still dominate (80%, SD 5%). Overall, this multi-proxy approach to examining the cumulative effects of mining activities on downstream sediment dynamics could be implemented in other mining catchments of New Caledonia and around the world to compare the respective mining source contributions to sediment and their evolution throughout time in these contrasted areas.

中文翻译：

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重建镍采矿活动对南太平洋岛屿河流和泻湖沉积物供应的影响：从 Thio 早期采矿场（新喀里多尼亚）吸取的经验教训

摘要 露天采矿加剧了位于西南太平洋的法国群岛新喀里多尼亚的土地退化。自 1880 年代以来，采矿业已成为一些流域的主要经济活动，这严重扰乱了沉积物动态。重建沉积物来源贡献的时间变化对于理解土壤侵蚀的驱动因素是必不可少的，因为 i) 气旋的发生，ii) 过去几十年采矿实践的变化，以及 iii) 其他土壤退化过程，例如由火灾、过度放牧和践踏入侵物种以及山体滑坡引起的大面积土壤侵蚀。因此，包括伽马光谱法在内的多参数分析，颜色和 X 射线荧光测量是对收集在三角洲漫滩中的沉积岩芯进行的，该沉积岩位于最早用于镍矿开采的地区之一，Thio 河集水区（397 平方公里）的出口处。一种地球化学示踪剂（即 K）已被用于量化自采矿活动开始以来沉积的连续沉积层中沉积物来源的变化。结果表明，采矿支流的贡献在很大程度上占主导地位，沉积岩芯中采样的材料的平均贡献为 74% (SD 13%)。在采矿活动机械化之后，这一贡献显着增加（即从 1950 年代开始；增加了 18%）。1975 年发生的飓风艾莉森引发了 25 年来积累在山脚下的采矿废物逐渐转移到河流系统中。这个临界点可以在沉积物序列中确定，这表明在过去 41 年（即 1975-2016 年）中，约 84 厘米深的沉积物沉积在 Thio 河流域的冲积平原（平均年沉积率） 2 cm yr−1)。目前，在飓风艾莉森之后大约 45 年，这种采矿废物的逐步释放和下游转移仍在进行中。尽管 1975 年引入了环境立法，但采矿支流对沉积物的贡献仍然占主导地位（80%，SD 5%）。全面的，