Coastal managers in Delaware examined whether biochar input from prescribed burns restores ecosystem services after removal of Phragmites australis, an invasive grass species.

The Project Phragmites australis is an invasive grass species that affects many marshes along the U.S east coast, often displacing native grasses. Removing Phragmites has been a decades-long management goal as managers seek to restore native high marsh habitat and ecosystem functions and services. Phragmites removal and restoration efforts have proven beneficial for habitat and biodiversity. However, its removal has potentially negative impacts on water quality and carbon storage, as Phragmites stores nitrogen and phosphorus and accumulates organic carbon more effectively than native marsh vegetation. Tidal wetland managers are left with uncertainties about these tradeoffs of Phragmites removal and their implications for achieving marsh restoration goals. A potential approach for managing tradeoffs associated with Phragmites removal is to use prescribed fire. While prescribed fire is a common method for vegetation removal, there has been limited research on the biogeochemical benefits provided by burned biomass or "biochar". Biochar may increase soil nitrogen removal and carbon and phosphorus storage, which can help to counteract losses in ecosystem services due to Phragmites removal.

Collaborating with regional coastal managers, this project team compared salt marshes with and without a history of prescribed burns at Delaware National Estuarine Research Reserve and area marshes to better quantify how fire impacts marshes and their ecosystem services. The team collected and analyzed salt marsh sediment cores at multiple sites and found that the marshes that were more frequently burned had enhanced carbon storage. They also used biochar amendments to learn more about other biogeochemical metrics, like denitrification potential and phosphorus storage, and found that biochar's impact on these metrics were limited.

The project convened an Advisory Committee that held productive discussions on current and potential Phragmites management practices, prescribed burn practices, and climate-adaptive decision-making procedures, in the context of the project's findings. These conversations helped inform a comprehensive report on the impacts of prescribed burns on tidal marsh ecosystem services. This report will allow for easier transfer of knowledge among the project's partners, including Delaware NERR, Delaware Natural Resources and Environmental Control, U.S. Fish and Wildlife Service, Center for the Inland Bays, Partnership for the Delaware Estuary, and Delaware Wild Lands.