Dam removal as a tool to increase ecological resilience through water quality improvements

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Katherine. M Abbott, Allison H. Roy, Peter A. Zaidel, Kristopher M. Houle, Keith H. Nislow

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Small, obsolete dams create abrupt discontinuities in stream thermal regimes, flow regimes, and biotic assemblages, and impair systems’ ability to respond to additional anthropogenic stressors, including climate change. Improved water quality following dam removal may increase the ecological resilience of streams to climate-driven warming, yet the extent and timescale of water quality recovery following removal is not well understood. We collected extensive pre- and post-removal temperature and dissolved oxygen (DO) data at 16 dam removal sites (9 have been removed to date) across Massachusetts to quantify water quality responses to removal and capture dam-specific and landscape-scale differences driving responses. Prior to removal, most sites experienced downstream warming, although the magnitude and spatial extent of dam impacts on temperature varied across sites, as well as seasons. 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, and downstream warming was reduced or eliminated at some, but not all sites. These data suggest that reduced DO caused by small dams may be quickly ameliorated by dam removal, but thermal recovery may vary depending on dam (e.g., dam and impoundment size), stream (e.g., upstream temperatures), and watershed characteristics (e.g., impervious/forest cover). An understanding of water quality shifts following dam removal may inform our understanding of biotic responses, particularly for thermally-sensitive taxa that are most vulnerable to climate change.

Resource Type:
Conference Presentation, SER2021

Pre-approved for CECs under SER's CERP program