Integrated effects of bioturbation, warming and sea-level rise on mobility of sulfide and metalloids in sediment porewater of mangrove wetlands

Global warming and sea-level rise exert profound impacts on coastal mangrove ecosystems, where widespread benthic crabs change sediment properties and regulate material cycles. How crab bioturbation perturbs the mobilities of bioavailable arsenic (As), antimony (Sb) and sulfide in sediment-water systems and their variability in response to temperature and sea-level rise is still unknown. By combining field monitoring and laboratory experiments, we found that As was mobilized under sulfidic conditions while Sb was mobilized under oxic conditions in mangrove sediments. Crab burrowing greatly enhanced oxidizing conditions, resulting in enhanced Sb mobilization and release but As sequestration by iron/manganese oxides. In control experiments with non-bioturbation, the more sulfidic conditions triggered the contrasting situation of As remobilization and release but Sb precipitation and burial. Moreover, the bioturbated sediments were highly heterogeneous for spatial distributions of labile sulfide, As and Sb as presented by 2-D high-resolution imaging and Moran's Index (patchy at the <1 cm scale). Warming stimulated stronger burrowing activities, which led to more oxic conditions and further Sb mobilization and As sequestration, whilst sea-level rise did the opposite via suppressing crab bur-rowing activity. This work highlights that global climate changes have the potential to significantly alter element cycles in coastal mangrove wetlands by regulating benthic bioturbation and redox chemistry.

Automated summary

Global warming and sea-level rise have significant effects on coastal mangrove ecosystems, particularly on the behavior of benthic crabs and their impact on sediment properties and material cycles. This study explores how crab bioturbation affects the movement of bioavailable arsenic (As), antimony (Sb), and sulfide in sediment-water systems, and how these processes are influenced by temperature and sea-level rise. The results indicate that crab burrowing enhances oxidizing conditions, leading to increased mobilization and release of Sb but sequestration of As by iron/manganese oxides. The study also highlights the spatial heterogeneity of labile sulfide, As, and Sb in bioturbated sediments, and the contrasting effects of warming and sea-level rise on benthic bioturbation and redox chemistry.