Aquaculture types drive variability in mangrove soil carbon-nitrogen stocks and OC sources via dredging wastewater

Wastewater discharge from coastal aquaculture into mangroves constitutes a globally widespread environmental challenge. The ecological impact of aquaculture wastewater discharge on mangroves remains to be elucidated. This study investigated the effects of dredging wastewater discharged from different aquaculture ponds, including shrimp ponds, fish-crab ponds, and razor clam ponds, on carbon and nitrogen storage in mangrove soils. To this end, we collected soil core samples and analysed soil properties. Dredging wastewater significantly increased the soil total nitrogen (TN) content; however, it showed varying effects on the organic carbon (OC) content based on aquaculture species and soil depth. Wastewater discharge from shrimp ponds significantly affected mangrove soil pH, water content, and bulk density and increased mangrove soil OC stocks (20.78 %). In contrast, wastewater discharge from razor clam ponds decreased the soil OC stocks. Dredging wastewater increased the soil TN stocks (22.59 %-93.91 %), with the lowest increase resulting from fish-crab pond wastewater. Using shrimp and fish-crab farming to enhance mangrove soil carbon sequestration could offset the negative impacts of razor clam ponds, optimizing both ecological benefits (blue carbon storage) and economic outputs (aquaculture productivity). The Bayesian stable isotope mixing model indicated that dredging wastewater was the primary source (41.58-69.33 %) of mangrove soil OC in the aquaculture pond discharge area. The findings of this study will aid in assessing the blue carbon function of mangrove ecosystems in the context of anthropogenic disturbances and facilitating scientific planning of coastal aquaculture types.