제주도 담지하수 유출량 변화에 따른 영양염류와 용존유기물질 플럭스 특성 연구

Abstract

To investigate the impact of Submarine Groundwater Discharge (SGD) on Hwasun Bay, surveys were conducted 13 times in total in Hwasun Bay, Jeju Island from January through December 2019. Throughout the entire period, collecting submarine fresh groundwater, submarine saline groundwater, bay water, and open water, the water temperature, salinity, and the concentrations of Dissolved Inorganic Nitrogen (DIN), Dissolved Inorganic Phosphate (DIP), Dissolved Silicate (DSi), and Dissolved Organic Carbon (DOC) were measured. Nutrients showed significant negative correlations (DIN: r2 = 0.82, DIP: r2 = 0.63 DSi: r2 = 0.82) in all the surveys, and there was an impact of Submarine Fresh Groundwater Discharge (SFGD) in this bay. DOC showed a significant positive correlation (r2 = 0.69) in all the surveys and tended to increase to the open sea, so it is judged that there was an increase in concentration due to biological activity, rather than depending on SFGD. The residence time was calculated based on the tidal prism, and through the calculated result, SFGD was estimated, using the DSi-mass balance model, and as a result, it was 1.210106 m3 d-1. As a result of the estimation of the flux by multiplying the concentration of nutrients in the groundwater and SFGD, DIN, DIP, and DSi were respectively 6.7 ± 4.8, 0.004 ± 0.003, 4.0 ± 4.210105 mol yr-1. Also, as a result of the calculation of the nutrients-mass balance model, of the total flux of nutritive salts supplied to Hwasun Bay, DIN, DIP, and DSi, supplied by SFGD were respectively approximately 96, 25, and 80 %, and of them, about 49, 84, and 41 % were removed by biological production, and 51, 16, and 59 % were mixed with the open sea water and leaked. As compared to the previous studies conducted in Hwasun Bay, in this study, as the groundwater runoff decreased, and nutrient flux increased, it is judged that the groundwater is depleted, and the contamination progresses. Currently, on Jeju Island, the contamination of the groundwater is in progress, which must seriously be recognized. Thus, to understand the behavior of SGD, it is necessary to trace the origins of substances, using various radioactive isotopes, to conduct an extensive study of the spatial and temporal scales, including wider areas and natural phenomena like typhoons, simultaneously and to continue to monitor them.