Coastal wetlands sequester carbon, attenuate waves and storm surge, filter out nutrients and pollutants, and act as nursery habitat for important fisheries. The value of these ecosystems is underscored by their vulnerability to climate change, especially sea level rise. To persist under the threat of rising sea level, coastal wetlands must build elevation vertically. Delivery of sediment to the marsh during tidal flooding is a key component in the ecogeomorphic feedbacks that lead to elevation gain. Despite the importance of suspended sediment to assessing coastal wetland vulnerability, many questions remain unanswered. This dissertation addresses the impact of suspended sediment concentration on wetland geomorphology from fine-scale processes to global patterns and from thriving systems to those experiencing significant environmental change. In Chapter I, I explore alterations to sediment transport and geomorphology caused by an acute vegetation disturbance in a Georgia saltmarsh. My results showed that the loss of vegetation was reversed the trajectory of the site from a prograding marsh to an eroding marsh. In Chapter II, I investigate how suspended sediment travels across the marsh platform using high frequency, long-term measurements in the Plum Island Estuary, Massachusetts. In contrast to the current paradigm, I found that sediment supply in the marsh interior is largely decoupled from channel sediment supply. Chapter III focuses on the role of sediment transport in mangrove encroachment into salt marshes in Australia. My work suggests that mangroves do not inhibit the ability of salt marsh to accrete vertically and that the removal of mangroves to preserve salt marsh would be ineffective. In Chapter IV, I analyze the relationship between suspended sediment concentration, tidal range, and accretion in salt marshes from around the world. My work emphasizes the importance of mineral accretion and marsh elevation when making predictions about marsh response to sea level rise. These results help bridge the gap between numerical models which predict marshes are capable of surviving high rates of relative sea level rise and field studies which suggest drowning at much lower rates. As a whole, my dissertation demonstrates that physical processes and the ways in which biology mediate these processes are critical to the ability of coastal wetlands to persist. As the rate of sea level rise continues to accelerate, it is increasingly important to understand the controls on vertical elevation growth in coastal wetlands at the scale of several meters to thousands of kilometers and in pristine systems to degraded environments
