Cadmium and rising tides: Amplified greenhouse gas emissions from mangrove sediment

Abstract

Mangrove ecosystems, renowned for their carbon sequestration capabilities, also contribute to the emission of greenhouse gases from their sediments. They are under stress from human activities and global changes, such as heavy metal pollution and rising sea levels, which can affect carbon stability and greenhouse gas emissions. However, the combined impact of these factors is not fully understood to date. This study assessed the impact of cadmium contamination at varying levels of inundation depths on the emission of CO₂, N₂O, and CH₄ from mangrove sediments. The findings indicated that increased inundation depth intensifies the effect of low cadmium concentrations on CO₂ emissions, with sediment CO₂ flux doubling from 3430 μmol m⁻² h⁻¹ to 6720 μmol m⁻² h⁻¹. In contrast, deeper water levels reduced N₂O emissions in the presence of high cadmium concentrations, lowering sediment N₂O flux from 14.10 μmol m⁻² h⁻¹ to 10.13 μmol m⁻² h⁻¹. These results highlight that the combined effects of rising inundation depth and cadmium pollution can enhance greenhouse gas emissions from mangrove sediments. It is crucial to consider the synergistic effects of pollution and rising sea levels on the stability of sediment carbon and gas emission rates in the conservation and management of mangroves. Such assessments will bolster efforts to protect blue carbon and achieve carbon neutrality in the future.