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

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.

Nonlinear internal wave spirals in the northern East China Sea.

Oceanic internal waves are known to be important to the understanding of underwater acoustics, marine biogeochemistry, submarine navigation and engineering, and the Earth's climate. In spite of the importance and increased knowledge of their ubiquity, the wave generation is still poorly understood in most parts of the world's oceans. Here, we use satellite synthetic aperture radar images, in-situ observations, and numerical models to (1) show that wave energy (having relatively high amplitude) radiates from a shallow sill in the East China Sea in all directions, but with a significant time lag dependent on background conditions, (2) reveal that wave fronts are locally formed with often favorable conditions for re-initiation, and (3) demonstrate the resulting variety of wave patterns. These findings would be the case for any broad shelf having shallow sills with time-varying conditions, and therefore have significant implications on the redistribution of energy and materials in the global as well as regional ocean.