EXAMINING THE INFLUENCE OF SALTWATER INTRUSION ON MANGROVE BIOMASS IN THE CAN GIO BIOSPHERE RESERVE (1993–2023): INSIGHTS FROM SUN-GLINT CORRECTED SATELLITE IMAGERY

Abstract

Salinity serves as a pivotal determinant in the growth and progression of mangrove forests. This study aims to investigate the impact of saline intrusion on the aboveground biomass (AGB) of the Can Gio mangrove forest from 1993 to 2023. Notably, the AGB has experienced a decline primarily due to escalating saline water intrusion. However, the coastal area is always subject to waves and wind, which create an uneven sea surface and result in sun glint. Sun glint alters the reflectance spectrum values and often occurs in high-resolution satellite images, leading to significant distortions. To enhance the accuracy of satellite imagery results, this research innovatively utilized satellite image data that has been corrected for sun glint, addressing the adverse effects of solar radiation. Based on the urgency of the project in the current context, this study employed the SVM-XGBoost-1 and SVM-XGBoost-2 (Support Vector Machine-Extreme Gradient Boosting) hybrid models to estimate the AGB and salinity of the Can Gio mangrove forest, thus establishing a correlation between these two variables. The hybrid models exhibited superior performance compared to non-optimized models, with Coefficient of Determination (R2) value exceeding 0.83 and a reduction in Root Mean Square Error (RMSE) to 4.982 and 3.026, respectively. The computed results showcase an inverse proportional relationship, wherein an increase in salinity results in a decrease in the AGB of the Can Gio mangrove forest. The fringe region, where saltwater and freshwater merge and interact with human disturbances, along with areas possessing biomass reserves of 150 or more, are notably affected. This underscores the substantial impact of saline intrusion on the reduction of AGB over the past three decades. The findings from this study provide valuable insights for managers, equipping them with the necessary information to implement effective conservation measures for the Can Gio mangrove biosphere reserve.