Department of Civil and Environmental Engineering, Ehime University, Bunkyo-cho 3, Matsuyama, Ehime, 790-8577, Japan.
Department of Civil and Environmental Engineering, University of Yamanashi, 4-3-11 Takeda, Kofu, Yamanashi, 400-851, Japan.
Sci Rep. 2018 Jul 5;8(1):10185. doi: 10.1038/s41598-018-28624-2.
Sediment bypass tunnels (SBTs) are guiding structures used to reduce sediment accumulation in reservoirs during high flows by transporting sediments to downstream reaches during operation. Previous studies monitoring the ecological effects of SBT operations on downstream reaches suggest a positive influence of SBTs on riverbed sediment conditions and macroinvertebrate communities based on traditional morphology-based surveys. Morphology-based macroinvertebrate assessments are costly and time-consuming, and the large number of morphologically cryptic, small-sized and undescribed species usually results in coarse taxonomic identification. Here, we used DNA metabarcoding analysis to assess the influence of SBT operations on macroinvertebrates downstream of SBT outlets by estimating species diversity and pairwise community dissimilarity between upstream and downstream locations in dam-fragmented rivers with operational SBTs in comparison to dam-fragmented (i.e., no SBTs) and free-flowing rivers (i.e., no dam). We found that macroinvertebrate community dissimilarity decreases with increasing operation time and frequency of SBTs. These factors of SBT operation influence changes in riverbed features, e.g. sediment relations, that subsequently effect the recovery of downstream macroinvertebrate communities to their respective upstream communities. Macroinvertebrate abundance using morphologically-identified specimens was positively correlated to read abundance using metabarcoding. This supports and reinforces the use of quantitative estimates for diversity analysis with metabarcoding data.
泥沙绕流隧道 (SBT) 是一种引导结构，用于在高水流期间通过在运行期间将泥沙输送到下游河段来减少水库中的泥沙淤积。以前的研究监测了 SBT 运行对下游河段的生态影响，表明 SBT 对河床泥沙条件和大型无脊椎动物群落有积极影响，这是基于传统基于形态的调查。基于形态的大型无脊椎动物评估既昂贵又耗时，并且由于形态上的隐蔽性、小尺寸和未描述的物种数量众多，通常导致分类识别粗糙。在这里，我们使用 DNA 宏条形码分析来评估 SBT 操作对 SBT 出口下游大型无脊椎动物的影响，方法是通过比较操作 SBT 的大坝破碎河流与大坝破碎（即无 SBT）和自由流动河流（即无大坝）的上游和下游位置之间的物种多样性和成对群落差异来估计物种多样性。我们发现，大型无脊椎动物群落的差异随着 SBT 操作时间和频率的增加而减小。SBT 操作的这些因素影响河床特征的变化，例如泥沙关系，随后影响下游大型无脊椎动物群落对各自上游群落的恢复。使用形态鉴定标本的大型无脊椎动物丰度与使用宏条形码的读取丰度呈正相关。这支持并加强了使用宏条形码数据进行多样性分析的定量估计。
