Assessment of effluent water quality according to aquaculture activities using absorption and fluorescence spectroscopy

This study investigated organic pollution dynamics in a land-based olive flounder (Paralichthys olivaceus) aquafarm on Jeju Island, Korea, comparing water quality during regular feeding and fasting periods. Two 24-h (hour) monitoring campaigns were conducted to assess changes in chromophoric (CDOM) and fluorescent dissolved organic matter (FDOM), alongside conventional parameters such as chemical oxygen demand (COD), dissolved organic carbon (DOC), and total dissolved nitrogen (TDN). Feed elution experiments explored the relationship between feed quantity and eluted organic matter composition. Significant differences (p < 0.01) in influent and effluent water quality were observed during feeding, exhibiting significant increases in DOC, TDN, and FDOM. Feeding and excretion rapidly altered water quality, followed by gradual increases 7-8 h post-feeding. Strong correlations between DOC and CDOM and FDOM in both influent and effluent highlight the potential of optical properties as indicators of aquaculture-derived organic wastewater. Notably, we identified a unique fluorescence peak, which does not correspond to previously reported FDOM peaks. Lower humification index values (< 4), coupled with elevated fluorescence and biological indices in effluent compared to influent, suggest biological activity within the aquafarm enhances DOM concentration and modifies its optical characteristics. These findings demonstrate the utility of optical analysis for rapid and robust monitoring of aquaculture effluents, providing insights for improved water quality management strategies.