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Small, surface-release dams can impair natural stream connectivity by disrupting the flow of water, sediment, nutrients, and biota. Many dams built during the 19th and 20th centuries have exceeded their functional lifespan, and as a result, dam removal has become an increasingly prevalent stream restoration method. However, many streams have not been consistently monitored before and after dam removal, and there is a paucity of information regarding how dam removals affect stream ecosystems across different dam, stream, and landscape characteristics. Therefore, this study aimed to quantify the effects of dams and dam removals on a critical water quality parameter (dissolved oxygen) across 16 Massachusetts streams with completed (10 sites) or upcoming dam removals. We collected continuous dissolved oxygen data for 1-3 years prior to removal and up to 3 years following removal in upstream, downstream, and impounded or formerly impounded reaches. Prior to dam removal, we found lower DO within impoundments compared to upstream reaches but did not find a consistent downstream effect on DO. Within one year following dam removal, DO in impoundments generally recovered to upstream reference conditions. These data suggest that reduced DO caused by small dams may be quickly ameliorated by dam removal, but the extent of recovery may be related to the magnitude of impact prior to removal. An understanding of the factors influencing recovery of stream ecosystems following dam removal may inform our understanding of biotic responses and help set expectations for restoration.

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Name	Format	Description	Link
	55	Landing page for access to the data	https://doi.org/10.5066/P9L2ATHV
	55	The metadata original format	https://data.usgs.gov/datacatalog/metadata/USGS.632b0c98d34e71c6d67bc071.xml

Effects of Small Dams and Dam Removals on Stream Dissolved Oxygen in Massachusetts, USA

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