Storm Surge Effects On The Vertical Distribution Of Salinity and Extractable Ammonium In Freshwater Soils and Deltaic Sediments.

Coastal wetland systems experience both short- and long-term changes in salinity as a result of tropical storm surge, sea level rise, cold fronts, and tidal forces.  The short-term changes in salinity resulting from storm surge can potentially affect soil porewater salinities in coastal freshwater wetlands, but the spatial and temporal extent is unknown.  Researchers have investigated effects of salinity on biogeochemical processes, but none have determined how quickly and to what depth the salt could penetrate down into a freshwater tidal wetland soil. Intact cores were collected from an island (non-vegetated) and marsh (vegetated) site in the Wax Lake Delta, located at the mouth of the Atchafalaya River in coastal Louisiana.  Soils were exposed to surface water at 35 ppt for 1, 2, or 4 weeks.  Salinity levels increased significantly in the soil columns of both vegetated and non-vegetated treatments over time and extended down to ~ 12 cm in depth after 1 week. Initially, extractable ammonium decreased by an average of 92% and 75% in the top 10 cm of the non-vegetated and vegetated cores, respectively. However, the ammonium levels began to recover with time in the vegetated cores, likely linked to nitrogen mineralization of the soil organic matter. These results demonstrate that short-term salinity fluctuations can dramatically alter the porewater salinity throughout a significant portion of the macrophyte rhizosphere influencing nutrient availability and potentially affecting plant recovery after storms.