Water-Level Rise and Nonmonotonic Salinity Change Across Louisiana Coastal Wetlands Over Fifteen Years

Abstract Long-term monitoring is vital to understanding how coastal wetlands respond to environmental changes. Using 15 years (2008–2022) of hourly water-level and salinity data from over 300 Coastwide Reference Monitoring System (CRMS) stations in Louisiana, USA, this study quantifies annual and decadal trends in water levels and salinity across nine basins and five vegetation types. The variations and trends were evaluated using a 12-month moving average method. Water levels increased statewide at 13.9 mm yr -1 , leading to an increase in inundation depth of 5.9 mm yr -1 . The influence of local climatic drivers (sea surface temperature, river flow, precipitation, and wind) varies with local hydrogeomorphic settings. In marine-influenced saline and brackish marshes, water levels covaried more strongly with surface temperature in the Gulf of Mexico. Concurrently, elevated river flows and local precipitation further increased water levels in freshwater marshes and swamps. Salinity levels showed high sensitivity to freshwater inputs and steadily decreased from 2011 to 2020, consistent with increased freshwater inputs. These results indicate that salinity responses in deltaic wetlands are possibly non-monotonic and strongly modulated by freshwater variability, even under ongoing sea-level rise. This comprehensive study on one of the most vulnerable coastal wetland systems provides insights into future coastal wetland responses and resilience broadly. Also, the automated, data-driven workflow provides transferable inputs to process-based modeling, enabling scenario evaluation and resilience planning in dynamic coastal wetlands.