Evaluating Spatio-temporal Dynamics of Water Quality in the Atchafalaya Basin Using Landsat 8 & 9 Surface Reflectance Imagery

Abstract. The Atchafalaya Basin, a critical ecological and hydrological region in Louisiana, faces growing water quality challenges driven by anthropogenic modifications and fragmentation. While conventional in situ water quality monitoring provides accurate measurements, its limited spatial and temporal coverage makes it inadequate for assessing pollution dynamics across such a vast and complex watershed. This study therefore employs the use Landsat 8 & 9 Collection 2, Level 2 to evaluate the spatio-temporal dynamics of water quality in the Atchafalaya Basin from 2010 to 2024. By leveraging the high spatial (10–20 m) and temporal (5-day) resolution of Landsat 8 & 9 imagery, the research examines key indicators of water quality, including chlorophyll-a, turbidity, and secchi depth variations in the basin. Chlorophyll-a results showed predominantly low to moderate concentrations in 2015 (0-25 μg/L), indicating largely oligotrophic to mesotrophic conditions, but by 2024 chlorophyll-a concentrations exceeded 25 μg/L across most parts of the basin, especially in the southern region signifying a shift toward eutrophic conditions. Water clarity and turbidity exhibited similar patterns, with Secchi depth declining from a maximum of 4.2 m to 3.7 m (reduced water clarity) and widespread values near 0.2 m in 2024, while turbidity ranged from 3.4 to 180 NTU, showing broader spatial distribution of elevated turbidity in 2024. To address the declining condition of the basin, restoration efforts focus on adaptive water management, sediment control, and habitat improvement, while remote sensing effectively retrieves surface water reflectance values to monitor restoration progress and water quality changes in the Atchafalaya Basin.