A Study on Chemical Oxygen Demand (COD) Concentration Distribution and Its Hydrodynamic Mechanisms in Liaodong Bay, China

Abstract

In order to reveal the impact of hydrodynamic conditions on the transport and diffusion of pollutants in Liaodong Bay in China, this article uses MIKE21 to establish a numerical model to simulate the hydrodynamic mechanisms of tidal currents and residual currents in Liaodong Bay. The model has been calibrated using observation data from 10 stations, and the simulation results of the tidal currents, Euler residual currents, Lagrangian residual currents, and particle tracking in Liaodong Bay have been calculated. Subsequently, a comparative analysis is conducted based on the abovementioned data and measured data, exploring the impact of hydrodynamic conditions on the transport and diffusion of COD in Liaodong Bay. The research results in this article indicate that high concentration COD areas are mainly concentrated in the coastal areas around the estuary of the Liao River and the Daliao River, and river input is the main source of COD in Liaodong Bay. The Euler residual circulation can form COD enrichment in some areas, which is significantly higher than the background concentration, and the large-scale transportation of COD after entering Liaodong Bay is determined by the Lagrangian residual current. The particle tracking results in the estuarine area can effectively characterize the actual transportation of pollutants. The results of the Lagrangian residual flow and particle tracking in the bay indicate that river pollutants are mainly transported to the west bank after entering Liaodong Bay. The distribution of a COD concentration of 1.5 mg/L confirms this finding. The research findings presented in this paper offer valuable insights into the spatial distribution and transportation mechanisms of pollutants. These results hold significant implications for pollution prevention and mitigation strategies in comparable bay environments.