SALT MARSH MANAGEMENT: MONITORING THREATS AND IMPLEMENTING CLIMATE ADAPTATION INITIATIVES

Abstract

Salt marshes serve as important coastal resources both economically and environmentally and are particularly susceptible to the negative implications of climate change. As climate change impacts become more prevalent, it is important to understand how salt marshes will respond. Two climate change impacts on salt marshes are macroalgae inundation and accelerated relative sea-level rise (hereafter referred to as SLR). Due to warming temperatures and sea level rise, salt marshes can be inundated by macroalgae through tidal movement, and the impacts of this excess macroalgal accumulation are poorly understood. Sea level rise also has negative implications on salt marsh by leading to vegetation die-back and ultimately salt marsh loss. Coastal managers within Rhode Island have successfully collaborated to implement climate change adaptation projects through strategic planning and communication. This dissertation highlights the important steps of salt marsh management: 1) Identifying the impacts of potential salt marsh threats (Chapter 1), 2) Monitoring salt marsh response to climate change adaptation projects (Chapter 2), and 3) Describing the important steps to plan and implement climate change adaptation projects (Chapter 3). Chapter 1 focuses on the impacts of macroalgal densities within Rhode Island on salt marsh environments. In this study, we investigated how current, relatively low density ephemeral (Ulva spp.) and perennial (Fucus spp.) algal wrack coverage impacts Spartina alterniflora (low marsh plant) survival and associated greenhouse gas fluxes. We created mesocosms with S. alterniflora-vegetated soil cores using a 2 X 2 factorial design with Fucus and Ulva present or absent to test the effects of macroalgal inundation. We found that S. alterniflora was resilient to these densities of macroalgal coverage, and this coverage did not significantly impact greenhouse gas fluxes. In Chapter 2, we investigated the impacts of two climate change adaptation projects, hydrological restoration (dredged runnels) and sediment enhancement, that have been implemented in Rhode Island to combat the effects of sea level rise within salt marshes. Here, we investigated the impacts of these adaptation techniques on soil properties, vegetation composition, and greenhouse gas fluxes (methane and carbon dioxide). We found that plant density in certain runnel areas increased after runnels were installed and runnels assisted in maintaining Spartina patens (high marsh plant) coverage. Carbon dioxide uptake increased in a runnel treatment and control as vegetation increased over time. Sediment enhancement treatment did not lead to vegetation or belowground biomass recolonization and produced insignificant greenhouse gas fluxes. Chapter 3 focuses on the incorporation