The relative stability of salmon redds and unspawned streambeds
The relative stability of salmon redds and unspawned streambeds
复制标题
鲑鱼红河和未产卵河床的相对稳定性
DOI：
--
复制
发表时间：
2015
期刊：
影响因子：
--
通讯作者：
A. Fremier
中科院分区：
文献类型：
--
作者：
T. H. Buxton;J. Buffington;E. Yager;Marwan A. Hassan;A. Fremier
在雌鲑鱼筑巢的地方，河床物质被混合，细小的沉积物被筛掉，河床物质被移动到类似沙丘形状的尾流丘中。完成的redd表面比未产生的床更粗糙，分选更好，这被认为增加了redd的稳定性，因为较大的颗粒更重，更难移动，分选增加了流动性的摩擦角。然而，产卵也会使沉积物松动，并形成加速流动的地形，这可以增加颗粒的流动性。我们解决这些因素控制的相对稳定性的redds和unspawned床在水槽实验中，redds构建了一个动态的技术，模仿雌性鲑鱼的筑巢行为。虽然红层表面相对粗糙，但测量的夹带力表明，与未产卵床相比，产卵降低的颗粒运动阻力平均降低了12-37%。此外，对于相同的排放量，边界剪应力是13-41%，由于流动收敛的尾部溢出的redd高。颗粒夹带的视觉测量进一步表明redd不稳定性，因为床平均剪切应力在初始运动时低22%，在释放时低29%，从而动员了redd上的所有粒度。总体而言，结果表明，redds是不稳定的相比，unspawned床，这增加了冲刷埋蛋的风险，但可能有利于细沉积物冲刷和提高产卵砾石的质量为后代的产卵。因此，管理鲑鱼返回增加河床扰动可能是一个有效的工具，减少沉积对鲑鱼繁殖的影响。
Where female salmon build nests (“redds”), streambed material is mixed, fine sediment is winnowed, and bed material is moved into a tailspill mound resembling the shape of a dune. Completed redd surfaces are coarser and better sorted than unspawned beds, which is thought to increase redd stability because larger grains are heavier and harder to move, and sorting increases friction angles for mobility. However, spawning also loosens sediment and creates topography that accelerates flow, which can increase particle mobility. We address these factors controlling the relative stability of redds and unspawned beds in flume experiments where redds were constructed with a dynamic technique that mimics the nesting behavior of female salmon. Although redds exhibited relatively coarse surfaces, measured entrainment forces indicate particle loosening by spawning lowered grain resistance to motion by 12–37% on average compared to unspawned beds. In addition, for the same discharges, boundary shear stress was 13–41% higher on a redd due to flow convergence on the tailspill. Visual measurements of particle entrainment further indicated redd instability, as bed‐average shear stress was 22% lower at incipient motion and 29% lower at the discharge that mobilized all grain sizes on a redd. Overall, results demonstrate that redds are unstable compared to unspawned beds, which increases the risk of scour for buried eggs but may facilitate fine sediment flushing and improve the quality of spawning gravels for future generations of spawners. Therefore, managing salmon returns to increase streambed disturbance may be an effective tool for reducing sedimentation impacts on salmon reproduction.