Assessing Greenhouse Gas Structural and Functional Resilience of Freshwater Coastal Wetlands Subject to Persistent Saltwater Intrusion Events
Authors
Diana Taj*, Jorge Villa (jorge.villa@louisiana.edu)
Institutions
University of Louisiana–Lafayette, LA
Abstract
Acute saltwater intrusion (SWI) events, often triggered by storm surges during high-intensity hurricanes, significantly impact the dynamics of freshwater wetlands. This study focuses on patches dominated by Typha domingensis and Panicum hemitomon, two prevalent wetland species in freshwater wetlands of the northern Gulf of Mexico, and investigates their physiological and functional response to acute SWI events in different durations of 1-, 3-, and 5- days with an approximate 2 practical salinity unit (PSU) concentration in an experimental wetland ecosystem complex following a before-after impact control experimental design. Measurements of methane (CH4) fluxes, carbon dioxide (CO2) fluxes, and soil porewater concentrations (5-, 10-, 20-cm depths), and spectral indices [normalized difference vegetation index (NDVI), photochemical reflectance index (PRI), plant senescence reflectance index (PSRI)] had diverging responses from two ecohydrological patches. In the T. domingensis patches, fluxes were not affected by the three SWI events. Porewater concentrations remain unaffected as well, regardless of the SWI duration except for CH4 concentrations at 20 cm soil depth, which increased after the 5-day SWI.
NDVIs decreased only in the 3-day SWI, but PRI and PSRI were similar before and after the SWI events. In the P. hemitomon patch, CO2 fluxes (i.e., emissions) decreased after the 3-day treatment, whereas CH4 fluxes did not change. The team also observed a decrease in the CO2 porewater concentration at the 20-cm depth, but no changes for CH4 concentrations. Again, the PSRI and PRI remained unchanged after SWI events, but surprisingly, the NDVI increased during the 1-day SWI event. These results support the resiliency of T. domingensis and susceptibility of P. hemitomon. Increasing the salinity may challenge the resiliency to low disturbances and give insight on further adaptational physiological and functional responses. The next steps in this research include analyzing data from a similar three-level duration experimentation for five PSU-simulated SWI events: a new field campaign to evaluate variable responses to longer inundation periods.