Understanding the relationship between a dam's size and its ecological effects is important for prioritization of river restoration efforts based on dam removal. Although much is known about the effects of large storage dams, this information may not be applicable to small dams, which represent the vast majority of dams being considered for removal. To better understand how dam effects vary with size, we conducted a multidisciplinary study of the downstream effect of dams on a range of ecological characteristics including geomorphology, water chemistry, periphyton, riparian vegetation, benthic macroinvertebrates, and fish. We related dam size variables to the downstream–upstream fractional difference in measured ecological characteristics for 16 dams in the mid‐Atlantic region ranging from 0.9 to 57 m high, with hydraulic residence times (HRTs) ranging from 30 min to 1.5 years. For a range of physical attributes, larger dams had larger effects. For example, the water surface width below dams was greater below large dams. By contrast, there was no effect of dam size on sediment grain size, though the fraction of fine‐grained bed material was lower below dams independently of dam size. Larger dams tended to reduce water quality more, with decreased downstream dissolved oxygen and increased temperature. Larger dams decreased inorganic nutrients (N, P, Si), but increased particulate nutrients (N, P) in downstream reaches. Aquatic organisms tended to have greater dissimilarity in species composition below larger dams (for fish and periphyton), lower taxonomic diversity (for macroinvertebrates), and greater pollution tolerance (for periphyton and macroinvertebrates). Plants responded differently below large and small dams, with fewer invasive species below large dams, but more below small dams. Overall, these results demonstrate that larger dams have much greater impact on the ecosystem components we measured, and hence their removal has the greatest potential for restoring river ecosystems.

中文翻译：

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水坝对河流生态系统的尺寸依赖性影响以及对水坝拆除结果的影响


了解水坝规模与其生态影响之间的关系对于确定基于水坝拆除的河流恢复工作的优先顺序非常重要。尽管人们对大型蓄水坝的影响了解很多，但这些信息可能不适用于小型水坝，因为小型水坝代表了正在考虑拆除的绝大多数水坝。为了更好地了解水坝影响如何随规模而变化，我们对水坝下游对一系列生态特征的影响进行了多学科研究，包括地貌、水化学、附生生物、河岸植被、底栖大型无脊椎动物和鱼类。我们将大西洋中部地区 16 个水坝的水坝尺寸变量与测量的生态特征的下游-上游分数差异相关联，水坝高度从 0.9 到 57 m，水力停留时间 (HRT) 范围从 30 分钟到 1.5 年。对于一系列物理属性，较大的水坝具有更大的影响。例如，大坝下方的水面宽度更大。相比之下，尽管细粒床物质的比例低于大坝，但与大坝尺寸无关，大坝尺寸对沉积物粒度没有影响。较大的水坝往往会更多地降低水质，导致下游溶解氧减少和温度升高。较大的水坝减少了下游河段的无机养分（N、P、Si），但增加了颗粒养分（N、P）。较大水坝以下的水生生物在物种组成上往往具有更大的差异（对于鱼类和附生生物），较低的分类多样性（对于大型无脊椎动物）和较高的污染耐受性（对于附生生物和大型无脊椎动物）。 大坝和小坝下方的植物反应不同，大坝下方的入侵物种较少，但小坝下方的入侵物种较多。总体而言，这些结果表明，较大的水坝对我们测量的生态系统组成部分的影响要大得多，因此拆除它们对于恢复河流生态系统具有最大的潜力。