Sediment storage by instream wood in forested mountain streams mediates sediment movement from hillslopes through the channel network and can alter channel morphology at multiple spatial scales. Mixed bedrock-alluvial channels are prevalent in mountain stream networks, yet the distribution and geomorphic impact of large wood within these streams are poorly understood. To estimate how the distribution of large wood in a mixed bedrock-alluvial stream relates to sediment storage, we measured and characterized large wood, and we surveyed the volume of associated sediment within a stream in the Bitterroot Mountains, Montana. The upstream portion of the study reach is predominantly alluvial and the downstream portion has significant bedrock exposure along the channel bed and banks. Wood volume and sediment storage in the mixed bedrock-alluvial subreach are 50% and 15%, respectively, of those measured in the alluvial subreach. Most wood is organized into jams, and two channel-spanning jams within the upstream subreach account for 50% and 80% of the reach-averaged wood and sediment volume, respectively. The volume of sediment stored by wood in the full reach is the same order of magnitude as the estimated annual bedload export. Our study highlights the interactions among channel form and the fluxes and storage of wood and sediment. Wood that forms channel-spanning jams, which store a disproportionate amount of wood and sediment in the study reach, may accentuate differences between alluvial and bedrock-dominated subreaches in mountain stream networks, by promoting sediment deposition and storage upstream and by reducing sediment supply to downstream reaches.

在森林深处的山间溪流中，流入木材的沉积物介导了从山坡通过渠道网络的沉积物运动，并且可以在多个空间尺度上改变渠道的形态。混合的基岩冲积河道在山区河流网络中很普遍，但是人们对这些河流中大木材的分布和地貌影响知之甚少。为了估算混合基岩冲积流中大木材的分布与沉积物的储藏之间的关系，我们测量并表征了大木材，并调查了蒙大拿州Bitterroot山中一条小溪中相关沉积物的体积。研究范围的上游部分主要是冲积物，下游部分沿河床和河床有大量的基岩暴露。混合基岩冲积分区的木材体积和沉积物储量分别是冲积分区的木材体积和沉积物的15％。大多数木材被组织成堵塞物，上游次延伸区域内的两个跨通道堵塞物分别占作用域平均木材和沉积物量的50％和80％。木材在整个范围内存储的沉积物量与估计的年度床位出口量相同数量级。我们的研究强调了河道形式与木材和沉积物通量和存储之间的相互作用。形成跨河阻塞的木材，在研究范围内存储了不成比例的木材和沉积物，可能会加剧山区河流网络中冲积层和基岩支配的子区域之间的差异，