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The spatiotemporal distributions of nutrients in coastal waters surrounding eight wastewater treatment plants
(WWTPs) in four seasons were investigated to determine the effects of WWTP effluents on seawater off Jeju
Island, Korea. The highest concentrations of nutrients were observed in the outlets of WWTPs with relatively high
ammonium concentrations among dissolved inorganic nitrogen (DIN). The reduced DIN (NO2? and NH4+)/total
DIN ratios are used as a potential short-term index for marine environmental conditions. In seawater surrounding
the WWTPs, relatively low nutrient concentrations were observed in spring and fall, due to enhanced biological
production, which is closely linked to decreased N/P ratios. Because the highest WWTP effluent fluxes of
ammonium in this study were similar to the fluxes of nutrients from submarine groundwater discharge, diffusion
from bottom sediments, and discharge from land-based fish farm wastewater, WWTP effluent-derived nutrients
are potentially important in oligotrophic environments and can be readily utilized by phytoplankton.
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