Wetland Gain and Loss in the Mississippi River Bird-Foot Delta

Abstract

The Mississippi River Bird-foot Delta (MRBD) has long been at risk of deterioration due to Relative Sea Level Rise (RSLR), yet information on historical spatial distribution in wetland gain and loss remains limited. Using a Random Forest algorithm in Google Earth Engine, we extract wetland area from multiple Landsat images spanning 1990–2022. Data are integrated with sediment load, wave dynamics, sea level, and surface elevation to analyze drivers of wetland gain and loss. Results indicate a minor net change of only 1.21 km², with a total gain of 160.83 km² and a total loss of 159.62 km². Overall stability of wetland area masks significant regional variability, with notable wetland expansion in the interior and substantial losses along eastern and southeastern margins. Sediment diversion toward the interior of the delta lead to distributaries narrowing (Main Pass and Pass a Loutre) that further hindered sediment-laden water transport into deltaic margins. Wetland dynamics along the edges were closely linked to wave action, with large-scale retreat in northern (4.0 ± 9.9 m/yr), eastern (58.0 ± 48.2 m/yr), and southeastern (38.6 ± 15.8 m/yr) regions, while progradation in the southern (13.6 ± 10.1 m/yr) and western areas (7.4 ± 19.4 m/yr). Fluvial sediments significantly impact wetland growth with 1-year lag. Vertical accretion of wetlands exceeds RSLR, indicating equilibrium along vertical dimension but are affected by lateral dynamics driven by wave and fluvial sediment inputs. In conclusion, the MRBD is abandoning the distal parts to wave erosion, while focusing on building wetlands in the interior to create a more compact delta.