Impact of aquaculture on distribution of dissolved organic matter in coastal Jeju Island, Korea, based on absorption and fluorescence spectroscopy

Abstract

In Jeju Island, multiple land-based aquafarms were fully operational along most coastal region. However, the effect of effluent on distribution and behaviours of dissolved organic matter (DOM) in the coastal water are still unknown. To decipher characteristics of organic pollution, we compared physicochemical parameters with spectral optical properties near the coastal aquafarms in Jeju Island. Absorption spectra were measured to calculate the absorption coefficient, spectral slope coefficient, and specific UV absorbance. Fluorescent DOM was analysed using fluorescence spectroscopy coupled with parallel factor analysis. Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) were measured using high-temperature catalytic oxidation. The DOC concentration near the discharge outlet was twice higher than that in natural groundwater, and the TDN concentration exponentially increased close to the outlet. These distribution patterns indicate that aquafarms are a significant source of DOM. Herein, principal component analysis was applied to categorise the DOM origins. There were two distinct groups, namely, aquaculture activity for TDN with humic-like and high molecular weights DOM (PC1: 48.1%) and natural biological activity in the coastal water for DOC enrichment and protein-like DOM (PC2: 18.8%). We conclude that the aquafarms significantly discharge organic nitrogen pollutants and provoke in situ production of organic carbon. Furthermore, these findings indicate the potential of optical techniques for the efficient monitoring of anthropogenic organic pollutants from aquafarms worldwide.

Chromophoric Dissolved Organic Matter and Dissolved Organic Carbon in Lakes Across an Elevational Gradient From the Mountains to the Sea

“…Components similar to component 1 in this study have been attributed to terrestrial humic‐like material (Du et al., 2016; Kothawala et al., 2012; Stedmon et al., 2003; Tank et al., 2011; Xiao et al., 2019). Components similar to component 2 in our study have been attributed to microbially‐derived humic material or phytoplankton degradation products (Kim et al., 2022; Zhang et al., 2010; Zhang, Yin, Liu, et al., 2011). We attribute component 2 to terrestrial humic material that has undergone microbial processing, as identified in Zhou et al.…”

Factors controlling the distribution of dissolved organic carbon and nitrogen in the coastal waters off Jeju Island

“…Additionally, the TDN concentration (0.13 ± 0.03 mg/L) in the study area, which can act as a marker of aquaculture activity, was lower than that recorded from drainage samples (0.74 ± 0.46 mg/L) directly obtained at the discharge outlet in the aquafarm region and in the coastal water near the aquafarm outlet (0.25 ± 0.26 mg/L). However, it was similar to the TDN concentration observed at a control site (0.12 ± 0.05 mg/L) located more than 5 km away from the aquafarms (Kim et al, 2022). Furthermore, in contrast to the findings reported by Oh et al (2021) for areas influenced by fresh/saline groundwater and landbased fish farm wastewater within 0.5 km of the coast, we observed that the DIN concentration did not follow the expected pattern of a decrease with an increase in salinity (Table S2), exhibiting an increase instead (Spearman's r = 0.290, p < 0.01).…”

Environmental impact on marginal coastal benthic communities within the Jeju Island, South Korea temperate transition zone

“…Indeed, nutrient availability in Jeju's coastal waters is strongly related to land-based, anthropogenic activities, such as land-operated fish farms which are present in the vicinity of SH. Wastewater from land-operated fish farms accounts for up to 95% of the seawater ammonium (Kwon et al, 2022), increasing coastal DIN and DIP concentrations (Choi et al, 2021), and generally contributes significantly to the nitrogen budget in the coastal waters of Jeju (Koh et al, 2013;Kim et al, 2022b). Sea water enriched in ammonium is preferred by coralline algae, which dominate SH (Nguyen et al, 2020;Kwon et al, 2022).…”