USACE Jacksonville District Submerged Aquatic Vegetation and Freshwater Wetlands Monitoring

GLE conducted Year 7 (2024/2025) submerged aquatic vegetation (SAV) and tidal freshwater wetlands monitoring for the Jacksonville Harbor Deepening Project. Year 7 monitoring included quarterly SAV and biannual freshwater wetlands monitoring events spanning the period of October 2024 through August 2025.

The Jacksonville Harbor federal navigation channel extends ~20 miles up the Lower St. Johns River (LSJR) from the Atlantic Ocean to the Port of Jacksonville (JAXPORT) Talleyrand Marine Terminal in Jacksonville, FL. The Water Resources Reform Development Act of 2014 authorized deepening of the lower 13-mile channel reach from -40 ft MLLW to -47 ft MLLW to accommodate larger deep draft cargo vessels at the JAXPORT Blount Island and Dames Point terminals. Deepening of the lower 11-mile channel reach through the Blount Island Marine Terminal was initiated in 2018 and completed in 2022. The Jacksonville District used hydrodynamic and ecological models to evaluate the effects of the deepening project on salinity and biological resources in the LSJR. The model-projected effects of the project include minor salinity increases in the LSJR above the deepened channel and associated minor secondary effects on SAV and freshwater wetlands in the form of increased salinity stress. Biological monitoring protocols to quantify potential project-induced salinity effects on SAV and freshwater wetlands were incorporated as conditions of a Florida Department of Environmental Protection Environmental Resource Permit.  Monitoring was conducted prior to and during project construction (2017-2022) and will continue for at least 10 years post-construction (2032).

The primary objective of the Year 7 SAV and freshwater wetlands monitoring project was to detect and quantify vegetation changes in the LSJR over time. Monitoring results will ultimately be used to quantify the effects of the deepening project and determine if there are any project-induced effects on SAV and freshwater wetlands that exceed those predicted by the hydrodynamic and ecological models. Future analyses will incorporate salinity monitoring data and additional modeling to confirm cause and effect relationships and distinguish the impacts of channel deepening from the effects of other factors such as drought and sea level rise.