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

 Aquaculture plays a crucial role in sustainable food production, but excessive organic matter discharge can lead to environmental issues such as eutrophication and algal blooms. This study investigated the dynamics of organic pollution in a land-based olive flounder (Paralichthys olivaceus) aquafarm on Jeju Island, Korea, comparing water quality during feeding and fasting periods. Two 24-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 were conducted to examine temporal changes in dissolved organic matter following feed addition. Significant differences (p<0.01) were observed between influent and effluent during feeding, with DOC, TDN, and FDOM increasing by 10–200% within one hour. When the peak excretion rate occurred 8–9 hours after feeding, all water quality parameters except specific ultraviolet absorbance (SUVA₂₅₄) showed increasing trends. A gradual increase was observed 7–8 hours post-feeding for all water quality parameters except SUVA₂₅₄, and feed elution experiments also showed a similar trend over time, suggesting the influence of excretion and unconsumed feed. Robust correlations between DOC and optical parameters were observed in both influent and effluent (r² = 0.56–0.91, P<0.001), suggesting that CDOM and FDOM can be used as indicators of aquaculture-derived organic wastewater. A unique fluorescence peak, previously unreported and observed in both effluent and feed elution samples, may serve as a tracer for aquaculture feed. These findings demonstrate that optical analysis is effective for rapid monitoring and can aid in tracing organic pollutants, informing water quality management strategies to support sustainable aquaculture while minimizing environmental impacts.