Water Salinity Impacts Aggregation, Settling, and Deposition of Fluvial Sediment.

Global wetlands have declined by 21-35% since the 18th century, losing approximately 1.3 million square miles. Infrastructure development, specifically, river channelization via levee construction, is a driver of this decline. In response, large-scale river diversion projects have been proposed to enhance sediment deposition and stabilize coastal wetlands. However, the role of aquatic chemistry in controlling the fluvial sediment deposition remains elusive. Here, we demonstrate that land formation by fluvial sediment deposition is intrinsically linked to wetland water salinity, which influences the sediment aggregation and settling kinetics. In laboratory experiments, Mississippi River sediments were exposed to a range of salinities that mimic the conditions in Louisiana wetlands. Our results show that higher ionic strength accelerates sediment aggregation and settling due to electrical double-layer compression while also reducing the packing density of deposited sediments, potentially impacting land stability. These findings point to the importance of incorporating salinity effects to optimize sediment diversion strategies.