Degree

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

Document Type

Dissertation

Abstract

Coastal wetlands in Louisiana have experienced unprecedented wetland loss. These changes are expected to accelerate under rapid environmental changes. Fruits of rapid environmental changes are increasing water elevation, hydroperiod and salinity, frequent major hurricanes, early transition from intertidal to subtidal zone, and changes in species distribution. One aspect of coastal resilience refers to the ability of wetlands to maintain elevation relative to sea level while sustaining ecological function under changing environmental conditions. Achieving such understanding requires integrating hydrologic forcing, biogeochemical processes, vegetation dynamics, and geomorphic change within a unified framework that captures both gradual trends and short-term variability. This study aims to develop a modeling framework to determine relative influence of riverine vs coastal forcings in active and inactive coastal deltaic basins to predict relative changes to each boundary condition to wetland area stability in the future given scenarios of climate change. This involved developing a modeling framework that includes a spatiotemporal regression salinity model, time-series analysis of river discharge and forecast, use the statistical tools to forecast salinity till 2125, investigate the cellulose persistence in deeper soil, incorporate interannual variability, state-dependent parameter forcing, and hurricane sediment pulse in the ecogeomorphic model. East of Houma Navigation Canal (HNC) showed persistently elevated salinity than the west in Atchafalaya and Terrebonne basin. Incorporation of sea-level and discharge in the salinity model provided plausible accuracy in prediction (predictive-R2 was 0.96 in the west and 0.77 in the east of HNC) in test period. East zone is marine dominated while west is mostly river controlled. Time-series discharge analysis had moderate pointwise agreement (Predictive-R2 ~0.3) in test and train period considering inherent variability and complexity. However, distribution fidelity was high (corr2 > 0.90). Model forecast reveals that east may experience 4~4.3 times higher zone-level salinity change rate than west, while the change in middle portion of each zone seems higher than the ends. Cellulose persistence investigation in active basin’s fresh (CRMS 479), brackish (CRMS 0399), saline (CRMS 0322), and inactive basin’s brackish (CRMS 0396), saline (CRMS 0421) sites reveal cellulose existence in the deeper soil (50-100 cm), and it covaries with lignin across depths and sites. Modified NUMAR versions successfully captured the interannual variability and state-dependent parameter forcing. Study suggests that active basin’s brackish and saline, and inactive brackish sites may turn into subtidal from intertidal by ~2050 due to subsidence and sea-level rise (SSP2-4.5). Episodic inorganic sediment incorporation in the model didn’t produce enough buffers to offset the effect of sea-level rise and subsidence significantly in the brackish sites to slow the transition. Sequential development in this study has strengthened the ecogeomorphic model and opened new avenue for further research that can provide instrumental insights for wetland management decisions under climate change scenarios.

Date

5-3-2026

Committee Chair

Twilley, Robert R.

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

Download

Available for download on Wednesday, May 02, 2029

Share

COinS