Coastal wetlands, when impounded and artificially freshened, can emit excessive methane. This study assesses coastal methane reduction opportunities in the contiguous US by integrating publicly available map layers, reevaluating greenhouse gas emissions datasets, and employing scenarios informed by GIS and surveys of coastal managers. The study reveals that coastal impoundments are under-mapped nationally by approximately 50%. Restoring freshwater-impounded wetlands to brackish or saline conditions offers the most significant climate benefit, although such restorations are less frequent than other potential conversions. Nationally, the estimated potential emissions reduction is 0.91 Teragrams of carbon dioxide equivalents per year, a more conservative assessment than prior estimates. The study provides a map of 1,796 parcels with potential for tidal reconnection.

James R. Holmquist, Meagan Eagle, Rebecca Lee Molinari, Sydney K. Nick, Liana C. Stachowicz, Kevin D. Kroeger