Carroll Erin M, Miller Wally W, Johnson Dale W, Saito Laurel, Qualls Robert G, Walker Roger F
Department of Natural Resources and Environmental Science, College of Agriculture, Biotechnology, and Natural Resources, University of Nevada-Reno, Reno, NV 89512, USA.
J Environ Qual. 2007 May 25;36(4):1105-11. doi: 10.2134/jeq2006.0466. Print 2007 Jul-Aug.
High intensity wildfire due to long-term fire suppression and heavy fuels buildup can render watersheds highly susceptible to wind and water erosion. The 2002 "Gondola" wildfire, located just southeast of Lake Tahoe, NV-CA, was followed 2 wk later by a severe hail and rainfall event that deposited 7.6 to 15.2 mm of precipitation over a 3 to 5 h time period. This resulted in a substantive upland ash and sediment flow with subsequent down-gradient riparian zone deposition. Point measurements and ESRI ArcView were applied to spatially assess source area contributions and the extent of ash and sediment flow deposition in the riparian zone. A deposition mass of 380 Mg of ash and sediment over 0.82 ha and pre-wildfire surface bulk density measurements were used in conjunction with two source area assessments to generate an estimation of 10.1 mm as the average depth of surface material eroded from the upland source area. Compared to previous measurements of erosion during rainfall simulation studies, the erosion of 1800 to 6700 g m(-2) mm(-1) determined from this study was as much as four orders of magnitude larger. Wildfire, followed by the single event documented in this investigation, enhanced soil water repellency and contributed 17 to 67% of the reported 15 to 60 mm ky(-1) of non-glacial, baseline erosion rates occurring in mountainous, granitic terrain sites in the Sierra Nevada. High fuel loads now common to the Lake Tahoe Basin increase the risk that similar erosion events will become more commonplace, potentially contributing to the accelerated degradation of Lake Tahoe's water clarity.
由于长期的火灾抑制和大量燃料堆积导致的高强度野火，会使流域极易受到风和水的侵蚀。2002年发生在内华达州-加利福尼亚州太浩湖东南部的“贡多拉”野火，两周后遭遇了一场严重的冰雹和降雨事件，在3至5小时内降水量达7.6至15.2毫米。这导致了大量山地灰烬和泥沙流，并随后在下游河岸带沉积。采用点位测量和ESRI ArcView软件对河岸带灰烬和泥沙流沉积的源区贡献及范围进行空间评估。结合0.82公顷范围内380吨的灰烬和泥沙沉积量以及野火前的地表容重测量数据，通过两次源区评估得出，高地源区被侵蚀的地表物质平均深度估计为10.1毫米。与之前降雨模拟研究中的侵蚀测量结果相比，本研究确定的1800至6700克·米⁻²·毫米⁻¹的侵蚀量高出多达四个数量级。野火之后，加上本次调查记录的单一事件，增强了土壤斥水性，并且在内华达山脉山区花岗岩地形站点报告的15至60毫米·千年⁻¹的非冰川基线侵蚀率中，此类事件贡献了17%至67%。目前太浩湖流域常见的高燃料负荷增加了类似侵蚀事件变得更加普遍的风险，这可能会加速太浩湖湖水清澈度的下降。
