Salt marsh climate change adaptation: Using runnels to adapt to accelerating sea level rise within a drowning New England salt marsh

Sea level rise within New England is accelerating at a rate faster than the global average, leaving salt marshes particularly susceptible to degradation. Hydrological alteration is a type of climate change adaptation technique that can be used to combat the effects of sea level rise within salt marshes. Runnels (shallow channels) are a type of climate adaptation strategy used to enhance drainage in drowning marshes. In this study, we investigated the impacts of runnel installations, 3-5 years post-implementation, on soil properties, vegetation composition, and greenhouse gas fluxes. We studied two runnel treatments (Low Elevation Runnel and High Elevation Runnel) and found that in the Low Elevation Runnel areas Spartina alterniflora stem density significantly increased in the three growing seasons after runnels were installed, and the high marsh plant, Spartina patens, persisted in the High Elevation Runnel areas. There was a significant difference in carbon dioxide uptake rates among treatments, with the unmanipulated (Reference) areas having the highest uptake rates and an increase in CO2 uptake over time seen in the Low Elevation Runnel treatment. These findings highlight the potential use of a climate change adaptation strategy to combat sea level rise impacts and provide insights for future adaptation efforts.