Beavers affect nitrate storage and transformation at the sediment–water interface

Abstract Rewilding is a restoration strategy aimed at re-establishing ecosystem processes and functions. This study focuses on the reintroduction of Eurasian beavers ( Castor fibre ) at a rewilding site at Knepp Estate, Sussex, UK, and their impact on nitrate (NO 3 − ) fluxes at the sediment–water interface during Autumn 2024. In-stream water quality, temperature, and field measurements of patch-scale NO 3 − fluxes were measured at sites upstream, downstream, from the margins of the beaver pond and two control sites. To complement field analyses, controlled laboratory measurements of NO 3 − fluxes on fresh (non-sterilized) and sterile sediments from each site were conducted to establish the microbial processes involved in sediment NO 3 − fluxes. Significantly higher in-stream NO 3 − concentrations were recorded within the beaver pond compared to the other sites, but this level was below the UK Environmental Quality Standards. NO 3 − removal from the sediment–water interface was significantly higher downstream and within the beaver pond relative to upstream and catchment control sites. Results show that stream reaching downstream of beaver activity contain sediments that have a greater ability to facilitate biological removal of NO 3 − in a low-nutrient rewilded system.