Long-term (21–30 years) erosional responses of rainforest terrain in the Upper Segama catchment, Sabah, to selective logging are assessed at slope, small and large catchment scales. In the 0.44 km2 Baru catchment, slope erosion measurements over 1990–2010 and sediment fingerprinting indicate that sediment sources 21 years after logging in 1989 are mainly road-linked, including fresh landslips and gullying of scars and toe deposits of 1994–1996 landslides. Analysis and modelling of 5–15 min stream-suspended sediment and discharge data demonstrate a reduction in storm-sediment response between 1996 and 2009, but not yet to pre-logging levels. An unmixing model using bed-sediment geochemical data indicates that 49 per cent of the 216 t km−2 a−1 2009 sediment yield comes from 10 per cent of its area affected by road-linked landslides. Fallout 210Pb and 137Cs values from a lateral bench core indicate that sedimentation rates in the 721 km2 Upper Segama catchment less than doubled with initially highly selective, low-slope logging in the 1980s, but rose 7–13 times when steep terrain was logged in 1992–1993 and 1999–2000. The need to keep steeplands under forest is emphasized if landsliding associated with current and predicted rises in extreme rainstorm magnitude-frequency is to be reduced in scale.
展开▼
机译:在坡度,小规模和大规模流域尺度上,评估了沙巴上塞加玛上游流域雨林地形对选择性伐木的长期侵蚀响应(21-30年)。在巴鲁流域的0.44 km 2 sup>中,1990-2010年的坡度侵蚀测量和泥沙指纹显示,1989年采伐21年后的泥沙源主要是道路相关的,包括新鲜的山崩以及疤痕和脚趾的沟壑。 1994-1996年滑坡沉积物。对5–15分钟的水流悬浮沉积物和流量数据的分析和建模表明,1996年至2009年期间,风暴沉积物的响应有所减少,但尚未达到测井前的水平。使用沉积物地球化学数据的分解模型表明,2009年216 t km -2 sup> a -1 sup>的沉积物中49%来自其受影响区域的10%与公路有关的滑坡。侧向岩心的沉降 210 sup> Pb和 137 sup> Cs值表明,塞古玛河上游721 km 2 sup>流域的沉积速率最初不超过两倍。在1980年代是高度选择性的低坡度测井,但在1992-1993年和1999-2000年记录陡峭地形时,则上升了7-13倍。如果要减小与当前和预计的极端暴雨幅度频率相关的滑坡,则需要在森林下保持陡峭的土地。
展开▼