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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. [ABSTRACT FROM AUTHOR]

In this study, we investigated the influence of fish-farm activities on the inventory of trace elements (Mn, Fe, Co, Ni, and Cu) in the coastal waters off the fish-farm plants on Jeju Island, Korea. NH 4 + and rare earth elements (REEs) were used as tracers to examine the production and removal processes. Relatively higher concentrations of trace elements were observed in the coastal waters and significantly correlated with NH 4 +. Our results suggest that the excess dissolved trace elements in the coastal waters could be mainly produced inside fish farms, together with the production of NH 4 + and light-REEs (La to Nd). Although dissolved trace elements were found to be partially scavenged onto particles in the fish-farm rearing waters, indicated by the significant removal of particle-reactive Ce, these particles would be eventually discharged into the coastal ocean and release the dissolved trace elements back into the water columns. • Trace elements were greatly enriched in the coastal waters off the fish farms. • Trace elements were produced inside farm waters, together with LREEs and NH 4 +. • REEs and NH 4 + can trace the production and removal processes in fish-farm waters. [ABSTRACT FROM AUTHOR]

To determine the driving mechanisms between submarine groundwater discharge (SGD) and massive blooms of the green alga Ulva , we examined the magnitude of SGD and SGD-derived nutrient fluxes from November 2019 to July 2020 in Ihotewoo (north) and Bangdu (east) bays, Jeju Island, Korea. The variability of SGD flux at both the sites, where the hydraulic gradient is low, closely followed the daily variability of the tidal range, indicating that SGD flux is primarily driven by tidal pumping. Although the average annual SGD-driven nutrient fluxes were 24–37 % lower in Bangdu Bay than in Ihotewoo Bay, massive Ulva blooms only occurred in Bangdu Bay. A longer residence time (poor water exchange) and continuous SGD input with high dissolved inorganic nitrogen play a significant role in the growth and extentsion of Ulva blooms. • Submarine groundwater discharge (SGD) flux is primarily driven by tidal pumping. • SGD-driven nutrient fluxes are relatively lower in Bangdu Bay than in Ihotewoo Bay. • Poor water exchange and SGD-driven DIN load are important for green tide blooms. [ABSTRACT FROM AUTHOR]

Abstract: We observed the origin, behavior, and flux of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), colored dissolved organic matter (CDOM), and dissolved inorganic nitrogen (DIN) in the subterranean estuary of a volcanic island, Jeju, Korea. The sampling of surface seawater and coastal groundwater was conducted in Hwasun Bay, Jeju, in three sampling campaigns (October 2010, January 2011, and June 2011). We observed conservative mixing of these components in this subterranean environment for a salinity range from 0 to 32. The fresh groundwater was characterized by relatively high DON, DIN, and CDOM, while the marine groundwater showed relatively high DOC. The DON and DIN fluxes through submarine groundwater discharge (SGD) in the groundwater of Hwasun Bay were estimated to be 1.3×105 and 2.9×105 mold−1, respectively. In the seawater of Hwasun Bay, the groundwater-origin DON was almost conservative while about 91% of the groundwater-origin DIN was removed perhaps due to biological production. The DON flux from the entire Jeju was estimated to be 7.9×108 molyr−1, which is comparable to some of the world''s large rivers. Thus, our study highlights that DON flux through SGD is potentially important for delivery of organic nitrogen to further offshore while DIN is readily utilized by marine plankton in near-shore waters under N-limited conditions. [Copyright &y& Elsevier]

Abstract We investigated spatiotemporal distributions of dissolved inorganic nutrients and organic carbon (DOC) and nitrogen (DON) in coastal waters and land-based fish farm wastewater to determine effects of wastewater on seawater of Jeju Island, Korea. The nutrient concentrations in seawater were lower than in wastewater with negative correlations against salinity, indicating a terrestrial source. Wastewater-derived DOC and DON were transported offshore while wastewater-derived inorganic nutrients were effectively removed, likely via biological production, and this was closely linked to decline in N:P ratios. The correlations between DOC, DON, and colored dissolved organic matter suggest that organic matters likely originate from the fish farm wastewater. Quantitatively, the estimated wastewater-derived DOC flux was equivalent to that through submarine groundwater, which is a significant water source on the island. Our results will be able to trace contaminant sources and support assessments of seawater quality for appropriate regulation of fish farm wastewater discharge into coastal zones. • Dissolved nutrients were measured to determine effect of fish–farm wastewater. • CDOM was used as a tracer to identify the origins of DOM in seawater. • Fish–farm wastewater can result in organic matter pollution in coastal waters. [ABSTRACT FROM AUTHOR]

We measured the concentrations of dissolved inorganic nutrients and the dual isotopic composition of nitrate (δ15N-NO 3 − and δ18O-NO 3 −) in coastal waters off Jeju, a volcanic island in Korea, to trace its main sources. Sampling of seawater and fresh groundwater was conducted in four different coastal areas of Jeju Island: Haengwon (HW), Pyoseon (PS), Ilgwa (IG), and Sagye (SG) in May 2020 and 2021. The significant negative correlations between NO 3 − and salinity in the four areas indicate that the main source of NO 3 − is fresh submarine groundwater discharge (FSGD), with the extrapolated fresh groundwater endmember values ranging from 170 to 300 μM (δ15N-NO 3 −: 4.1–10.8 and δ18O-NO 3 −: 1.7–6.4). The actual sources of SGD-driven NO 3 − in these coastal waters were determined using a bi-plot diagram (δ15N-NO 3 − vs. δ18O-NO 3 −) and a Bayesian stable isotope mixing model (MixSIAR). The results showed that, besides the background contribution from open-ocean waters, the main sources of NO 3 − in HW were fertilizer (69 ± 5%) and manure and sewage (24 ± 7%) and those in PS, IG, and SG were manure and sewage (PS: 53 ± 11%, IG: 57 ± 12%, SG: 63 ± 13%) and fertilizer (PS: 27 ± 8%, IG: 24 ± 5%, SG: 22 ± 5%). Our extrapolation approach for NO 3 − dual isotopes provides a better way to evaluate the main sources of NO 3 − in coastal waters off volcanic islands where SGD-driven NO 3 − is significant, but its actual source groundwater cannot be located. [Display omitted] • Fresh groundwater is the dominant source of NO 3 − in coastal waters off Jeju Island. • Dual NO 3 − isotopes revealed different NO 3 − sources in groundwater and coastal water. • A Bayesian stable isotope mixing model distinguished the source of NO 3 − in SGD. • In the northern Jeju, fertilizer was the main source of NO 3 − (69%). • In the southern Jeju, manure and sewage were the main sources of NO 3 − (53–63%). [ABSTRACT FROM AUTHOR]

The concentrations of nutrients and dissolved organic matter (DOM) in the coastal waters off Jeju Island, Korea, are known to be influenced mainly by submarine groundwater discharge (SGD) and fish-farm effluents, in addition to the background open-ocean seawater from the Tsushima Current. However, the differentiation of the effect of fish-farm effluents from SGD is very challenging since most of the farms in this island utilize groundwater as a rearing water. Thus, in this study, we measured the concentrations of nutrients and fluorescent DOM (FDOM) in seawater, fresh groundwater (FGW), and farm water in two coastal areas off Jeju Island, in May and August 2021, in order to determine the effect of SGD versus fish-farm effluents. The results showed that humic-like FDOM (FDOM H) and NH 4 + concentrations were greatly enriched owing to organic matter decomposition in the farm waters. We used FDOM H , as a tracer for the farm effluent. The end-member mixing model for FDOM H and salinity showed that FGW contributed about 73% of NO 3 − (avg. 17 ± 20 μM), whereas the farm effluent contributed about 95% of NH 4 + (avg. 5.6 ± 4.1 μM) and 71% of FDOM H (avg. 0.86 ± 0.49 R.U.) in the coastal waters. Thus, our result shows that fish-farm effluents can be an important source of anthropogenic DOM and nutrients in coastal waters, where farms are being operated intensively. • Fresh groundwater is a dominant source of NO 3 − in coastal waters off Jeju • Humic-like FDOM and NH 4 + concentrations were greatly enhanced in fish-farm waters • Humic-like FDOM can trace fish-farm effluent sources in the coastal waters [ABSTRACT FROM AUTHOR]

Large-scale Sargassum blooms have been increasingly observed in coastal zones in recent years. Sargassum horneri (Turner) C. Agardh blooms (pelagic) have been observed in Jeju Island (Korea) and the southwest of the Korean Peninsula, causing serious problems for seaweed and abalone farms as well as for fisheries, tourism and recreational industries. The present study explored the physiological responses of attached and pelagic S. horneri populations cultivated under different nutrient concentrations (HN: 50 μM of nitrogen and 5 μM of phosphorus; LN: 5 μM of nitrogen and 0.5 μM of phosphorus) and photosynthetically active radiation (PAR) (H-PAR: 250; M-PAR: 150; L-PAR: 50 μmol photons m−2 s−1) for 25 days. Relative growth rates (RGR) were significantly lower in the pelagic population than that in the attached population. All thalli from the pelagic population died within 20 days. Chlorophyll a and c , and carotenoids were significantly higher at HN than at LN, and decreased as PAR increased for both populations. For the attached population, photosynthetic rate, tissue nitrogen, and carbon and nitrogen removal were also significantly higher at HN than at LN. These results suggest that high nutrient and lower PAR increased the biomass accumulation of attached populations in coastal areas. Nutrient limitation and high PAR may accelerate senescence of the pelagic populations while traveling on the sea surface from their point of origin. • Attached population of Sargassum horneri (Turner) C. Agardh grew faster than pelagic population. • High nutrients increased growth rate in both populations. • In the attached population photosynthesis and tissue nitrogen increased with increasing levels of nutrients. • High PAR decreased pigment content in both populations. • High-PAR decreased growth rate but did not affect growth and photosynthesis of attached population. [ABSTRACT FROM AUTHOR]