Monitoring mangrove degradation caused by oil spills using spaceborne multispectral and SAR imagery

Mangroves are important coastal ecosystems that provide essential ecological services. However, they are highly susceptible to human-induced disturbances, such as oil spills. In that respect, developing scalable monitoring solutions to evaluate the impact of such disturbances on mangroves has become crucial. To that aim, this study evaluates the capability of combined spaceborne multispectral and SAR imagery to assess rapid oil spill cleaning efforts and the potential impacts of persistent oil contamination on mangrove vegetation. The proposed approach involves mapping the distribution of dominant mangrove tree species and their response to oil pollution based on optical vegetation indices. Our approach was first tested in two historical spilled regions: the Bertioga channel (São Paulo, Brazil) and the Barataria Bay (Louisiana, USA). Then, it was applied to areas exposed to the 2019 oil spill in northeastern Brazil, which has had an impact on mangroves that remains so far unknown. Our approach demonstrates that optical and SAR imagery effectively detects changes in mangrove tree health and species distribution over time following oil spills. It also allows tracking symptoms of defoliation and other indicators of plant stress in mangrove areas historically affected by large oil spills. The study reveals that no or minor alterations in mangrove health occurred during the four-year period following the 2019 oil spill in northeastern Brazil, suggesting that extensive clean-up efforts, meteorological, and coastal conditions may have prevented major impacts of the oil spill on these ecosystems.