Moore, E.R., M.M. Rahman, M. Sena, J.G. Galella, B. Joshi, A.Yaculak, M. Peipoch, J. Kan, and S. Inamdar. 2026. Earth’s Future 14(9): e2025EF006892.
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Abstract
Dams and their legacies have substantially altered riparian ecosystems worldwide and these effects could persist for decades or centuries into the future. However, how biogeochemical characteristics of riparian sediments evolve with depth and time post dam removal is poorly understood.
We studied 12 riparian sites across three Mid-Atlantic watersheds in the United States over a chronosequence of 0–234 years since dam removal/breach. Sediments were sampled every 0.3 m to a maximum depth of 4 m upstream of dams. Sediment physico-chemical characteristics evolved asynchronously and at different rates with depth and time post dam breach. Gravimetric water content, ammonium nitrogen, ripening index and bioavailable and amorphous forms of iron were elevated in wet and reducing sediment conditions but low in drained and oxic sediments. Bulk density increased while total organic carbon and nitrogen decreased slowly following drainage after dam removal.
We attributed these changes to complex interactions of changes in groundwater levels, vertical variation in sediment texture, amount and forms of iron oxides, and organic matter content in post-dam sediments and buried pre-dam soil horizons. Given the ubiquity of existing and removed dams globally, understanding and quantifying these changes are important for advancing new paradigms for anthropogenic alteration of riparian ecosystems, assessing effectiveness of riparian buffers for pollution mitigation, and guiding restoration and management options post dam removal.
