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Estimating the timescale of fluvial response to anthropogenic disturbance using two generations of dams on the South River, Massachusetts, USA
Earth Surface Processes and Landforms ( IF 2.8 ) Pub Date : 2020-06-18 , DOI: 10.1002/esp.4886 Samantha Dow 1, 2 , Noah P. Snyder 1 , William B. Ouimet 2 , Anna M. Martini 3 , Brian Yellen 4 , Jonathan D. Woodruff 4 , Robert M. Newton 5 , Dorothy J. Merritts 6 , Robert C. Walter 6
Earth Surface Processes and Landforms ( IF 2.8 ) Pub Date : 2020-06-18 , DOI: 10.1002/esp.4886 Samantha Dow 1, 2 , Noah P. Snyder 1 , William B. Ouimet 2 , Anna M. Martini 3 , Brian Yellen 4 , Jonathan D. Woodruff 4 , Robert M. Newton 5 , Dorothy J. Merritts 6 , Robert C. Walter 6
Affiliation
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Centuries‐long intensive land‐use change in the north‐eastern United States provides the opportunity to study the timescale of geomorphic response to anthropogenic disturbances. In this region, forest‐clearing and agricultural practices following EuroAmerican settlement led to deposition of legacy sediment along valley bottoms, including behind mill dams. The South River in western Massachusetts experienced two generations of damming, beginning with mill dams up to 6‐m high in the eighteenth–nineteenth century, and followed by construction of the Conway Electric Dam (CED), a 17‐m‐tall hydroelectric dam near the watershed outlet in 1906. We use the mercury (Hg) concentration in upstream deposits along the South River to constrain the magnitude, source, and timing of inputs to the CED impoundment. Based on cesium‐137 (137Cs) chronology and results from a sediment mixing model, remobilized legacy sediment comprised 
% of the sediment load in the South River prior to 1954; thereafter, from 1954 to 1980s, erosion from glacial deposits likely dominated (63 ± 14%), but with legacy sediments still a substantial source (37 ± 14%). We also use the CED reservoir deposits to estimate sediment yield through time, and find it decreased after 1952. These results are consistent with high rates of mobilization of legacy sediment as historic dams breached in the early twentieth century, and suggest rapid initial response to channel incision, followed by a long decay in the second half of the century, that is likely dependent on large flood events to access legacy sediment stored in banks. Identifying sources of sediment in a watershed and quantifying erosion rates can help to guide river restoration practices. Our findings suggest a short fluvial recovery time from the eighteenth–nineteenth century to perturbation during the first half of the twentieth century, with subsequent return to a dominant long‐term signal from erosion of glacial deposits, with anthropogenic sediment persisting as a secondary source. © 2020 John Wiley & Sons, Ltd.
中文翻译：
使用美国马萨诸塞州南河上的两代水坝估算河流对人为干扰的反应时间尺度
美国东北部长达数世纪的密集土地利用变化为研究人为干扰的地貌反应的时间尺度提供了机会。在该地区，欧裔美国人定居后的森林砍伐和农业活动导致沿谷底（包括碾压水坝后）的传统沉积物沉积。马萨诸塞州西部的南河经历了两代筑坝，始于18世纪至19世纪高至6 m高的碾磨水坝，其后建造了一座17米高的水坝大坝Conway Electric Dam（CED）。 1906年，在流域出口附近。我们使用南河沿岸上游沉积物中的汞（Hg）浓度来约束CED蓄水装置的投入量，来源和时间安排。基于铯137（137CS）年表和沉积物混合模型的结果，包括固定的遗留沉积物1954年之前南河中的沉积物负荷百分比；此后，从1954年到1980年代，冰川沉积物的侵蚀很可能占主导地位（63±14％），但传统沉积物仍是主要的沉积物来源（37±14％）。我们还使用CED水库沉积物来估算随时间推移的沉积物产量，并发现其在1952年后有所下降。这些结果与二十世纪初历史性大坝被冲破而对旧沉积物的高动员率相一致，并建议对河道的快速初始响应切割，然后在本世纪下半叶经过长时间的腐烂，这很可能取决于大洪水事件来获取存储在河岸中的遗留沉积物。识别流域中的沉积物来源并量化侵蚀速率可以帮助指导河流恢复实践。我们的发现表明，从18世纪到19世纪，河床恢复时间很短，在20世纪上半叶出现扰动，随后又恢复了长期的主要信号，即冰川沉积物的侵蚀，而人为沉积物仍是次要来源。分级为4 +©2020 John Wiley＆Sons，Ltd.
更新日期：2020-06-18
% of the sediment load in the South River prior to 1954; thereafter, from 1954 to 1980s, erosion from glacial deposits likely dominated (63 ± 14%), but with legacy sediments still a substantial source (37 ± 14%). We also use the CED reservoir deposits to estimate sediment yield through time, and find it decreased after 1952. These results are consistent with high rates of mobilization of legacy sediment as historic dams breached in the early twentieth century, and suggest rapid initial response to channel incision, followed by a long decay in the second half of the century, that is likely dependent on large flood events to access legacy sediment stored in banks. Identifying sources of sediment in a watershed and quantifying erosion rates can help to guide river restoration practices. Our findings suggest a short fluvial recovery time from the eighteenth–nineteenth century to perturbation during the first half of the twentieth century, with subsequent return to a dominant long‐term signal from erosion of glacial deposits, with anthropogenic sediment persisting as a secondary source. © 2020 John Wiley & Sons, Ltd.
中文翻译：
使用美国马萨诸塞州南河上的两代水坝估算河流对人为干扰的反应时间尺度
美国东北部长达数世纪的密集土地利用变化为研究人为干扰的地貌反应的时间尺度提供了机会。在该地区，欧裔美国人定居后的森林砍伐和农业活动导致沿谷底（包括碾压水坝后）的传统沉积物沉积。马萨诸塞州西部的南河经历了两代筑坝，始于18世纪至19世纪高至6 m高的碾磨水坝，其后建造了一座17米高的水坝大坝Conway Electric Dam（CED）。 1906年，在流域出口附近。我们使用南河沿岸上游沉积物中的汞（Hg）浓度来约束CED蓄水装置的投入量，来源和时间安排。基于铯137（137CS）年表和沉积物混合模型的结果，包括固定的遗留沉积物
1954年之前南河中的沉积物负荷百分比；此后，从1954年到1980年代，冰川沉积物的侵蚀很可能占主导地位（63±14％），但传统沉积物仍是主要的沉积物来源（37±14％）。我们还使用CED水库沉积物来估算随时间推移的沉积物产量，并发现其在1952年后有所下降。这些结果与二十世纪初历史性大坝被冲破而对旧沉积物的高动员率相一致，并建议对河道的快速初始响应切割，然后在本世纪下半叶经过长时间的腐烂，这很可能取决于大洪水事件来获取存储在河岸中的遗留沉积物。识别流域中的沉积物来源并量化侵蚀速率可以帮助指导河流恢复实践。我们的发现表明，从18世纪到19世纪，河床恢复时间很短，在20世纪上半叶出现扰动，随后又恢复了长期的主要信号，即冰川沉积物的侵蚀，而人为沉积物仍是次要来源。分级为4 +©2020 John Wiley＆Sons，Ltd.
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