BOHA SET Brief: Boston Harbor’s Salt Marshes: Keeping Pace or Falling Behind?

Sharron, Edmund

Coastal wetlands exist within a narrow range of elevation which is influenced by local hydrologic conditions. As sea level rises, coastal wetland systems must build elevation at a rate equal to or greater than the rate of sea-level rise to maintain favorable hydrologic conditions for their survival. With global rates of sea-level rise predicted to increase over the coming decades (Church et al. 2010), many more coastal wetlands may become vulnerable to increased inundation. Additionally, certain areas of the coast, such as the mid-Atlantic region, can undergo even greater sea-level rise due to changes in coastal ocean circulation and spatial variation in rates of glacio-isostatic adjustment and Holocene sediment compaction (Engelhart et al. 2009, Miller et al. 2013, Sallenger et al. 2012). The Northeast Coastal & Barrier Inventory and Monitoring Network (NCBN) uses the SET technique (surface elevation table) to monitor elevation change as a vital sign of salt marsh health at Boston Harbor Islands National Recreation Area. The SET technique has been widely used for documenting and interpreting trends in surface elevation dynamics over time and assessing wetland vulnerability to sea-level rise (Cahoon et al. 2006, Jankowski et al. 2017, McKee 2011, Saintilan et al. 2022, Sasmito et al. 2016, Webb et al. 2013). In this report, we use these data to answer the following questions: 1. What are the elevation dynamics of coastal wetlands at Boston Harbor Islands National Recreation Area? 2. How do local hydrology and tidal datums relate to marsh surface elevations? 3. Is elevation gain sufficient to keep pace with current and predicted future sea level rise?