Changes in soil organic matter content and quality in Amazonian mangrove forests converted to shrimp farms

Mangroves are highly efficient carbon sinks, yet they are increasingly threatened by aquaculture expansion. Moreover, the long-term impacts of shrimp farming on soil organic matter (SOM) quality and carbon sequestration in Amazonian mangroves remain poorly understood, particularly regarding changes in SOM composition and their consequences for ecosystem resilience. This study compares soil organic matter (SOM) in pristine mangroves, mangroves converted to shrimp ponds, and mangroves adjacent to shrimp ponds in the Brazilian Amazon. We showed that pristine mangroves soils had higher soil organic carbon (SOC) ranging from 25 to 32 g.kg - ¹, higher C/N ratio (15.6–20.9), and stable δ¹³C (-27.5 to -27.0 ‰) and δ 15 N (3.6 to 3.3 ‰), with SOM rich in lignin, carbohydrates, and polyaromatic compounds. In contrast, mangroves converted to shrimp ponds had lower SOC (