Temporal dynamics of lateral carbon export from an onshore aquaculture farm

Many coastal areas are hotspots of aquaculture expansion, where the overuse of artificial feeds results in the accumulation of organic carbon in nearshore aquaculture ponds. In rural areas, wastewater from the aquaculture ponds is discharged to the nearshore waters through artificial ditches causing lateral carbon export from the land to the ocean. Such flux may be meaningful in coastal carbon budgets since aquaculture is the hotspot of carbon sequestration and storage. To quantify the magnitude and temporal dynamics of lateral carbon export from aquaculture ponds, we used high-frequency in-situ monitoring of turbidity, fluorescent dissolved organic matter, etc. across different temporal scales. We measured water levels and velocity profiles in a ditch cross-section to obtain year-round water exchange. Carbon export was integrated from water fluxes and organic carbon concentrations. Our results suggested that aquaculture ponds were a source of particular organic carbon (POC) and dissolved organic carbon (DOC). The net lateral flux of POC and DOC was 148 & PLUSMN; 38 kg yr-1 and 296 & PLUSMN; 18 kg yr-1. Temporally, the export of POC and DOC is influenced by both tides and wastewater discharge. Under the disturbance with aquaculture wastewater discharge, the mean DOC export in the ditch increased by 497 kg, which was 1.5 times that of the undisturbed; the mean POC export increased by 190 kg, which was 1.8 times that of the undisturbed. Thus, aquaculture activities can considerably disturb the coastal carbon balance by facilitating carbon-rich fluid exchange from onshore farms to nearshore estuaries. As

Automated summary

Many coastal areas with aquaculture expansion experience the accumulation of organic carbon in nearshore aquaculture ponds due to the overuse of artificial feeds. Wastewater from these ponds is discharged into the ocean through artificial ditches, resulting in lateral carbon export from land to water. The study found that aquaculture ponds are a source of particular organic carbon (POC) and dissolved organic carbon (DOC), and the net lateral flux of POC and DOC is influenced by tides and wastewater discharge. Aquaculture activities can greatly disturb the coastal carbon balance by facilitating the exchange of carbon-rich fluids from onshore farms to nearshore estuaries.