Distributions of Dissolved Trace Metals in the Nakdong River Estuary: Influence of an Estuarine Barrage on Their Geochemical Behaviors

초록

Estuaries are locations where river water meets seawater and act as complex biogeochemical reactors that modify the fluxes and chemical composition of water. To manage the water supply and prevent saltwater intrusion, estuarine barrages have been constructed, which obstruct water flow and affect biogeochemical processes in estuarine environments. To investigate the influence of the estuarine barrage on the geochemical behavior of dissolved trace metals (Fe, Co, Ni, Mo, and Cd), water samples were collected along the Nakdong River Estuary, where an estuarine barrage is present. The distributions of dissolved trace metals varied by element. Dissolved Mo and Cd showed the lowest concentrations upstream of the Nakdong River Estuarine Barrage (NREB) and increased gradually toward the sea, exhibiting strong positive correlations with salinity (r(2) >= 0.97; p < 0.001), suggesting that the presence of the estuarine barrage does not seem to affect their distributions. In contrast, dissolved Ni and Fe showed the highest concentrations upstream and negative correlations with salinity (r(2) >= 0.73; p < 0.001). At sites downstream of the NREB, where freshwater overflow occurs through floodgates, dissolved Ni concentrations slightly increased, possibly as a result of desorption from suspended particles, while dissolved Fe was notably depleted, likely due to salt-induced coagulation of river-borne colloids. Dissolved Mn and Co showed the most pronounced spatial contrasts, with significant upstream depletion and abrupt downstream increases, indicating strong influence of the estuarine barrage on their distributions. Overall, our results demonstrate that the presence of an estuarine barrage significantly alter the spatial distributions and geochemical behaviors of certain dissolved trace metals in estuarine environments.

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