Understanding the Fate of Jug Bay Tidal Freshwater Marshes Under Current Relative Sea Level Rise Conditions

Tidal freshwater marshes (TFMs), found in the upper tidal reaches of river estuaries, are characterized by high diversity and productivity. These ecosystems are threatened by climate change, but unlike other coastal wetlands, there is a lack of information about the impact and their response to this threat. To understand the resilience of Jug Bay TFMs to sea level rise (SLR), surface elevation change was measured in low and mid-high marsh areas along primary and secondary channels. Elevation change exhibited significant temporal and spatial variability. A marked seasonality showed higher elevation during the growing season, and episodic storms altered elevation trajectories. Spatially, elevation change was significantly affected by channel category and marsh zone. Low marsh along primary channels lost elevation (-11.57 mm year-1), while the mid-high marsh gained elevation (+2.65 mm year-1). In secondary channels, both low (+11.29 mm year-1) and mid-high marshes (+5.43 mm year-1) gained elevation. A shoreline change analysis for the Patuxent and Western Branch rivers (2007-2018) showed change rates between -0.35 and -0.90 m year-1. A 2019 upland migration study indicated that most TFMs studied are not able to migrate due to steep slopes. Overall, marsh in more protected areas, along secondary channels, are more resilient, while low marsh in primary channels the most vulnerable to SLR. With low upland migration potential, studied marshes have to rely mainly on vertical elevation gain to keep up with SLR. If restoration is considered in this system, it should focus on the vulnerable low marsh zones along primary channels.