Using System Dynamics Modeling to Understand how Environmental Changes Impact a Combined Human and Natural Salt Marsh System

Abstract:

The salt marshes of the Plum Island Estuary (PIE), Massachusetts are experiencing two major biophysical alterations that affect the species and people who depend on these marshes for their well-being. Climate change is enabling the burrowing marsh fiddler crab, Uca pugnax (a known ecosystem engineer), to expand its range in PIE marshes. Additionally, increased sea level rise (SLR) is altering marsh structure and function through changes in marsh plant zonation and marsh shrinkage. These environmental shifts could lead to a cascade of changes affecting both the survival of resident species and the emotional burden of people living near PIE via shifts in ecosystem functioning and services, respectively. To determine whether the synergistic effects of these two stressors will impact this complex Coupled Human and Natural System (CHANS), we asked the following questions: 1) how will sea level rise and burrowing crabs influence PIE ecosystem functioning and services through time; and 2) how will these changes impact the well-being of species and local residents through time? We used System Dynamics Modeling (SDM), which incorporates both quantitative and qualitative data, to better understand feedbacks, non-linearities, and alterations in this system at different time horizons. Our models predominately show a decline in total marsh area as a function of increased rates of erosion. This cascades to decreased area available for feeding and reproduction for species throughout the marsh. In addition, this limits the ability of PIE marshes to provide critical aesthetic ecosystem services to residents living in close proximity to this habitat (e.g., emotional well-being, areas of refuge and inspiration, etc.). Our study provides compelling insight for managers in PIE, and offers a framework applicable to various ecosystems worldwide.